abstract
stringlengths 3
192k
| title
stringlengths 4
857
|
|---|---|
we present new models for low-mass stars down to the hydrogen-burning limit that consistently couple atmosphere and interior structures, thereby superseding the widely used bcah98 models. the new models include updated molecular linelists and solar abundances, as well as atmospheric convection parameters calibrated on 2d/3d radiative hydrodynamics simulations. comparison of these models with observations in various colour-magnitude diagrams for various ages shows significant improvement over previous generations of models. the new models can solve flaws that are present in the previous ones, such as the prediction of optical colours that are too blue compared to m dwarf observations. they can also reproduce the four components of the young quadruple system lkca 3 in a colour-magnitude diagram with one single isochrone, in contrast to any presently existing model. in this paper we also highlight the need for consistency when comparing models and observations, with the necessity of using evolutionary models and colours based on the same atmospheric structures. | new evolutionary models for pre-main sequence and main sequence low-mass stars down to the hydrogen-burning limit |
in the present letter, we consider a class of extended scalar-tensor-gauss-bonnet (estgb) theories for which the scalar degree of freedom is excited only in the extreme curvature regime. we show that in the mentioned class of estgb theories there exist new black-hole solutions that are formed by spontaneous scalarization of the schwarzschild black holes in the extreme curvature regime. in this regime, below certain mass, the schwarzschild solution becomes unstable and a new branch of solutions with a nontrivial scalar field bifurcates from the schwarzschild one. as a matter of fact, more than one branch with a nontrivial scalar field can bifurcate at different masses, but only the first one is supposed to be stable. this effect is quite similar to the spontaneous scalarization of neutron stars. in contrast to the standard spontaneous scalarization of neutron stars, which is induced by the presence of matter, in our case, the scalarization is induced by the curvature of the spacetime. | new gauss-bonnet black holes with curvature-induced scalarization in extended scalar-tensor theories |
context. measuring how the physical properties of galaxies change across cosmic times is essential to understand galaxy formation and evolution. with the advent of numerous ground-based and space-borne instruments launched over the past few decades we now have exquisite multi-wavelength observations of galaxies from the far-ultraviolet (fuv) to the radio domain. to tap into this mine of data and obtain new insight into the formation and evolution of galaxies, it is essential that we are able to extract information from their spectral energy distribution (sed).aims: we present a completely new implementation of code investigating galaxy emission (cigale). written in python, its main aims are to easily and efficiently model the fuv to radio spectrum of galaxies and estimate their physical properties such as star formation rate, attenuation, dust luminosity, stellar mass, and many other physical quantities.methods: to compute the spectral models, cigale builds composite stellar populations from simple stellar populations combined with highly flexible star formation histories, calculates the emission from gas ionised by massive stars, and attenuates both the stars and the ionised gas with a highly flexible attenuation curve. based on an energy balance principle, the absorbed energy is then re-emitted by the dust in the mid- and far-infrared domains while thermal and non-thermal components are also included, extending the spectrum far into the radio range. a large grid of models is then fitted to the data and the physical properties are estimated through the analysis of the likelihood distribution.results: cigale is a versatile and easy-to-use tool that makes full use of the architecture of multi-core computers, building grids of millions of models and analysing samples of thousands of galaxies, both at high speed. beyond fitting the seds of galaxies and parameter estimations, it can also be used as a model-generation tool or serve as a library to build new applications. a copy of the code is only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/622/a103 | cigale: a python code investigating galaxy emission |
vienna atomic line database (vald) is a collection of critically evaluated laboratory parameters for individual atomic transitions, complemented by theoretical calculations. vald is actively used by astronomers for stellar spectroscopic studies—model atmosphere calculations, atmospheric parameter determinations, abundance analysis etc. the two first vald releases contained parameters for atomic transitions only. in a major upgrade of vald—vald3, publically available from spring 2014, atomic data was complemented with parameters of molecular lines. the diatomic molecules c2, ch, cn, co, oh, mgh, sih, tio are now included. for each transition vald provides species name, wavelength, energy, quantum number j and landé-factor of the lower and upper levels, radiative, stark and van der waals damping factors and a full description of electronic configurarion and term information of both levels. compared to the previous versions we have revised and verify all of the existing data and added new measurements and calculations for transitions in the range between 20 å and 200 microns. all transitions were complemented with term designations in a consistent way and electron configurations when available. all data were checked for consistency: listed wavelength versus ritz, selection rules etc. a new bibliographic system keeps track of literature references for each parameter in a given transition throughout the merging process so that every selected data entry can be traced to the original source. the query language and the extraction tools can now handle various units, vacuum and air wavelengths. in the upgrade process we had an intensive interaction with data producers, which was very helpful for improving the quality of the vald content. | a major upgrade of the vald database |
the all-sky automated survey for supernovae (asas-sn) is working toward imaging the entire visible sky every night to a depth of v∼ 17 mag. the present data covers the sky and spans ∼2-5 years with ∼100-400 epochs of observation. the data should contain some ∼1 million variable sources, and the ultimate goal is to have a database of these observations publicly accessible. we describe here a first step, a simple but unprecedented web interface https://asas-sn.osu.edu/ that provides an up to date aperture photometry light curve for any user-selected sky coordinate. the v band photometry is obtained using a two-pixel (16.″0) radius aperture and is calibrated against the apass catalog. because the light curves are produced in real time, this web tool is relatively slow and can only be used for small samples of objects. however, it also imposes no selection bias on the part of the asas-sn team, allowing the user to obtain a light curve for any point on the celestial sphere. we present the tool, describe its capabilities, limitations, and known issues, and provide a few illustrative examples. | the all-sky automated survey for supernovae (asas-sn) light curve server v1.0 |
quantum monte carlo methods have proved valuable to study the structure and reactions of light nuclei and nucleonic matter starting from realistic nuclear interactions and currents. these ab initio calculations reproduce many low-lying states, moments, and transitions in light nuclei, and simultaneously predict many properties of light nuclei and neutron matter over a rather wide range of energy and momenta. the nuclear interactions and currents are reviewed along with a description of the continuum quantum monte carlo methods used in nuclear physics. these methods are similar to those used in condensed matter and electronic structure but naturally include spin-isospin, tensor, spin-orbit, and three-body interactions. a variety of results are presented, including the low-lying spectra of light nuclei, nuclear form factors, and transition matrix elements. low-energy scattering techniques, studies of the electroweak response of nuclei relevant in electron and neutrino scattering, and the properties of dense nucleonic matter as found in neutron stars are also described. a coherent picture of nuclear structure and dynamics emerges based upon rather simple but realistic interactions and currents. | quantum monte carlo methods for nuclear physics |
the zwicky transient facility (ztf) is a new robotic time-domain survey currently in progress using the palomar 48-inch schmidt telescope. ztf uses a 47 square degree field with a 600 megapixel camera to scan the entire northern visible sky at rates of ∼3760 square degrees/hour to median depths of g ∼ 20.8 and r ∼ 20.6 mag (ab, 5σ in 30 sec). we describe the science data system that is housed at ipac, caltech. this comprises the data-processing pipelines, alert production system, data archive, and user interfaces for accessing and analyzing the products. the real-time pipeline employs a novel image-differencing algorithm, optimized for the detection of point-source transient events. these events are vetted for reliability using a machine-learned classifier and combined with contextual information to generate data-rich alert packets. the packets become available for distribution typically within 13 minutes (95th percentile) of observation. detected events are also linked to generate candidate moving-object tracks using a novel algorithm. objects that move fast enough to streak in the individual exposures are also extracted and vetted. we present some preliminary results of the calibration performance delivered by the real-time pipeline. the reconstructed astrometric accuracy per science image with respect to gaia dr1 is typically 45 to 85 milliarcsec. this is the rms per-axis on the sky for sources extracted with photometric s/n ≥ 10 and hence corresponds to the typical astrometric uncertainty down to this limit. the derived photometric precision (repeatability) at bright unsaturated fluxes varies between 8 and 25 millimag. the high end of these ranges corresponds to an airmass approaching ∼2—the limit of the public survey. photometric calibration accuracy with respect to pan-starrs1 is generally better than 2%. the products support a broad range of scientific applications: fast and young supernovae; rare flux transients; variable stars; eclipsing binaries; variability from active galactic nuclei; counterparts to gravitational wave sources; a more complete census of type ia supernovae; and solar-system objects. | the zwicky transient facility: data processing, products, and archive |
the ligo and virgo detectors have directly observed gravitational waves from mergers of pairs of stellar-mass black holes, along with a smaller number of mergers involving neutron stars. these observations raise the hope that compact object mergers could be used as a probe of stellar and binary evolution, and perhaps of stellar dynamics. this colloquium-style article summarises the existing observations, describes theoretical predictions for formation channels of merging stellar-mass black-hole binaries along with their rates and observable properties, and presents some prospects for gravitational-wave astronomy. | merging stellar-mass binary black holes |
we present an overview of a new integral field spectroscopic survey called manga (mapping nearby galaxies at apache point observatory), one of three core programs in the fourth-generation sloan digital sky survey (sdss-iv) that began on 2014 july 1. manga will investigate the internal kinematic structure and composition of gas and stars in an unprecedented sample of 10,000 nearby galaxies. we summarize essential characteristics of the instrument and survey design in the context of manga's key science goals and present prototype observations to demonstrate manga's scientific potential. manga employs dithered observations with 17 fiber-bundle integral field units that vary in diameter from 12'' (19 fibers) to 32'' (127 fibers). two dual-channel spectrographs provide simultaneous wavelength coverage over 3600-10300 å at r ~ 2000. with a typical integration time of 3 hr, manga reaches a target r-band signal-to-noise ratio of 4-8 (å-1 per 2'' fiber) at 23 ab mag arcsec-2, which is typical for the outskirts of manga galaxies. targets are selected with m * >~ 109 m ⊙ using sdss-i redshifts and i-band luminosity to achieve uniform radial coverage in terms of the effective radius, an approximately flat distribution in stellar mass, and a sample spanning a wide range of environments. analysis of our prototype observations demonstrates manga's ability to probe gas ionization, shed light on recent star formation and quenching, enable dynamical modeling, decompose constituent components, and map the composition of stellar populations. manga's spatially resolved spectra will enable an unprecedented study of the astrophysics of nearby galaxies in the coming 6 yr. | overview of the sdss-iv manga survey: mapping nearby galaxies at apache point observatory |
the ensemble of chemical element abundance measurements for stars, along with precision distances and orbit properties, provides high-dimensional data to study the evolution of the milky way. with this third data release of the galactic archaeology with hermes (galah) survey, we publish 678 423 spectra for 588 571 mostly nearby stars (81.2 per cent of stars are within <2 kpc), observed with the hermes spectrograph at the anglo-australian telescope. this release (hereafter galah+ dr3) includes all observations from galah phase 1 (bright, main, and faint survey, 70 per cent), k2-hermes (17 per cent), tess-hermes (5 per cent), and a subset of ancillary observations (8 per cent) including the bulge and >75 stellar clusters. we derive stellar parameters teff, log g, [fe/h], vmic, vbroad, and vrad using our modified version of the spectrum synthesis code spectroscopy made easy (sme) and 1d marcs model atmospheres. we break spectroscopic degeneracies in our spectrum analysis with astrometry from gaia dr2 and photometry from 2mass. we report abundance ratios [x/fe] for 30 different elements (11 of which are based on non-lte computations) covering five nucleosynthetic pathways. we describe validations for accuracy and precision, flagging of peculiar stars/measurements and recommendations for using our results. our catalogue comprises 65 per cent dwarfs, 34 per cent giants, and 1 per cent other/unclassified stars. based on unflagged chemical composition and age, we find 62 per cent young low-$\alpha$, 9 per cent young high-$\alpha$, 27 per cent old high-$\alpha$, and 2 per cent stars with [fe/h] ≤ -1. based on kinematics, 4 per cent are halo stars. several value-added-catalogues, including stellar ages and dynamics, updated after gaia edr3, accompany this release and allow chrono-chemodynamic analyses, as we showcase. | the galah+ survey: third data release |
finding and characterizing the first galaxies that illuminated the early universe at cosmic dawn is pivotal to understand the physical conditions and the processes that led to the formation of the first stars. in the first few months of operations, imaging from the james webb space telescope (jwst) has been used to identify tens of candidates of galaxies at redshift (z) greater than 10, less than 450 million years after the big bang. however, none of such candidates has yet been confirmed spectroscopically, leaving open the possibility that they are actually low-redshift interlopers. here we present spectroscopic confirmation and analysis of four galaxies unambiguously detected at redshift 10.3 ≤ z ≤ 13.2, previously selected from jwst near infrared camera imaging. the spectra reveal that these primeval galaxies are metal poor, have masses on the order of about 107-108 solar masses and young ages. the damping wings that shape the continuum close to the lyman edge provide constraints on the neutral hydrogen fraction of the intergalactic medium from normal star-forming galaxies. these findings demonstrate the rapid emergence of the first generations of galaxies at cosmic dawn. | spectroscopic confirmation of four metal-poor galaxies at z = 10.3-13.2 |
we reduce and analyse the available jwst ero and ers nircam imaging (smacs0723, glass, ceers) in combination with the latest deep ground-based near-infrared imaging in the cosmos field (provided by ultravista dr5) to produce a new measurement of the evolving galaxy uv luminosity function (lf) over the redshift range z = 8 - 15. this yields a new estimate of the evolution of uv luminosity density (ρuv), and hence cosmic star formation rate density (ρsfr) out to within <300 myr of the big bang. our results confirm that the high-redshift lf is best described by a double power law (rather than a schechter) function up to z ~ 10, and that the lf and the resulting derived ρuv (and thus ρsfr), continues to decline gradually and steadily up to z ~ 15 (as anticipated from previous studies which analysed the pre-existing data in a consistent manner to this study). we provide details of the 61 high-redshift galaxy candidates, 47 of which are new, that have enabled this new analysis. our sample contains 6 galaxies at z ≥ 12, one of which appears to set a new redshift record as an apparently robust galaxy candidate at z ≃ 16.4, the properties of which we therefore consider in detail. the advances presented here emphasize the importance of achieving high dynamic range in studies of early galaxy evolution, and re-affirm the enormous potential of forthcoming larger jwst programmes to transform our understanding of the young universe. | the evolution of the galaxy uv luminosity function at redshifts z ≃ 8 - 15 from deep jwst and ground-based near-infrared imaging |
$jwst$'s first glimpse of the $z>10$ universe has yielded a surprising abundance of luminous galaxy candidates. here we present the most extreme of these systems: ceers-1749. based on $0.6-5\mu$m photometry, this strikingly luminous ($\approx$26 mag) galaxy appears to lie at $z\approx17$. this would make it an $m_{\rm{uv}}\approx-22$, $m_{\rm{\star}}\approx5\times10^{9}m_{\rm{\odot}}$ system that formed a mere $\sim220$ myrs after the big bang. the implied number density of this galaxy and its analogues challenges virtually every early galaxy evolution model that assumes $\lambda$cdm cosmology. however, there is strong environmental evidence supporting a secondary redshift solution of $z\approx5$: all three of the galaxy's nearest neighbors at $<2.5$" have photometric redshifts of $z\approx5$. further, we show that ceers-1749 may lie in a $z\approx5$ protocluster that is $\gtrsim5\times$ overdense compared to the field. intense line emission at $z\approx5$ from a quiescent galaxy harboring ionized gas, or from a dusty starburst, may provide satisfactory explanations for ceers-1749's photometry. the emission lines at $z\approx5$ conspire to boost the $>2\mu$m photometry, producing an apparent blue slope as well as a strong break in the sed. such a perfectly disguised contaminant is possible only in a narrow redshift window ($\delta z\lesssim0.1$), implying that the permitted volume for such interlopers may not be a major concern for $z>10$ searches, particularly when medium-bands are deployed. if ceers-1749 is confirmed to lie at $z\approx5$, it will be the highest-redshift quiescent galaxy, or one of the lowest mass dusty galaxies of the early universe detected to-date. both redshift solutions of this intriguing galaxy hold the potential to challenge existing models of early galaxy evolution, making spectroscopic follow-up of this source critical. | schrodinger's galaxy candidate: puzzlingly luminous at $z\\approx17$, or dusty/quenched at $z\\approx5$? |
the gravitational-wave signal gw190521 is consistent with a binary black hole (bbh) merger source at redshift 0.8 with unusually high component masses, ${85}_{-14}^{+21}$ m⊙ and ${66}_{-18}^{+17}$ m⊙, compared to previously reported events, and shows mild evidence for spin-induced orbital precession. the primary falls in the mass gap predicted by (pulsational) pair-instability supernova theory, in the approximate range 65-120 m⊙. the probability that at least one of the black holes in gw190521 is in that range is 99.0%. the final mass of the merger ( ${142}_{-16}^{+28}$ m⊙) classifies it as an intermediate-mass black hole. under the assumption of a quasi-circular bbh coalescence, we detail the physical properties of gw190521's source binary and its post-merger remnant, including component masses and spin vectors. three different waveform models, as well as direct comparison to numerical solutions of general relativity, yield consistent estimates of these properties. tests of strong-field general relativity targeting the merger-ringdown stages of the coalescence indicate consistency of the observed signal with theoretical predictions. we estimate the merger rate of similar systems to be ${0.13}_{-0.11}^{+0.30}\,{{\rm{gpc}}}^{-3}\,{{\rm{yr}}}^{-1}$ . we discuss the astrophysical implications of gw190521 for stellar collapse and for the possible formation of black holes in the pair-instability mass gap through various channels: via (multiple) stellar coalescences, or via hierarchical mergers of lower-mass black holes in star clusters or in active galactic nuclei. we find it to be unlikely that gw190521 is a strongly lensed signal of a lower-mass black hole binary merger. we also discuss more exotic possible sources for gw190521, including a highly eccentric black hole binary, or a primordial black hole binary. | properties and astrophysical implications of the 150 m⊙ binary black hole merger gw190521 |
magnetospheric multiscale (mms), a nasa four-spacecraft constellation mission launched on march 12, 2015, will investigate magnetic reconnection in the boundary regions of the earth's magnetosphere, particularly along its dayside boundary with the solar wind and the neutral sheet in the magnetic tail. the most important goal of mms is to conduct a definitive experiment to determine what causes magnetic field lines to reconnect in a collisionless plasma. the significance of the mms results will extend far beyond the earth's magnetosphere because reconnection is known to occur in interplanetary space and in the solar corona where it is responsible for solar flares and the disconnection events known as coronal mass ejections. active research is also being conducted on reconnection in the laboratory and specifically in magnetic-confinement fusion devices in which it is a limiting factor in achieving and maintaining electron temperatures high enough to initiate fusion. finally, reconnection is proposed as the cause of numerous phenomena throughout the universe such as comet-tail disconnection events, magnetar flares, supernova ejections, and dynamics of neutron-star accretion disks. the mms mission design is focused on answering specific questions about reconnection at the earth's magnetosphere. the prime focus of the mission is on determining the kinetic processes occurring in the electron diffusion region that are responsible for reconnection and that determine how it is initiated; but the mission will also place that physics into the context of the broad spectrum of physical processes associated with reconnection. connections to other disciplines such as solar physics, astrophysics, and laboratory plasma physics are expected to be made through theory and modeling as informed by the mms results. | magnetospheric multiscale overview and science objectives |
we present atacama large millimeter/submillimeter array (alma) observations from the 2014 long baseline campaign in dust continuum and spectral line emission from the hl tau region. the continuum images at wavelengths of 2.9, 1.3, and 0.87 mm have unprecedented angular resolutions of 0.″ 075 (10 au) to 0.″ 025 (3.5 au), revealing an astonishing level of detail in the circumstellar disk surrounding the young solar analog hl tau, with a pattern of bright and dark rings observed at all wavelengths. by fitting ellipses to the most distinct rings, we measure precise values for the disk inclination (46\buildrel{\circ}\over{.} 72+/- 0\buildrel{\circ}\over{.} 05) and position angle (+138\buildrel{\circ}\over{.} 02+/- 0\buildrel{\circ}\over{.} 07). we obtain a high-fidelity image of the 1.0 mm spectral index (α), which ranges from α ∼ 2.0 in the optically thick central peak and two brightest rings, increasing to 2.3-3.0 in the dark rings. the dark rings are not devoid of emission, and we estimate a grain emissivity index of 0.8 for the innermost dark ring and lower for subsequent dark rings, consistent with some degree of grain growth and evolution. additional clues that the rings arise from planet formation include an increase in their central offsets with radius and the presence of numerous orbital resonances. at a resolution of 35 au, we resolve the molecular component of the disk in hco+ (1-0) which exhibits a pattern over lsr velocities from 2-12 km s-1 consistent with keplerian motion around a ∼1.3 {m}⊙star, although complicated by absorption at low blueshifted velocities. we also serendipitously detect and resolve the nearby protostars xz tau (a/b) and lkhα358 at 2.9 mm. . | the 2014 alma long baseline campaign: first results from high angular resolution observations toward the hl tau region |
we present the new tng50 cosmological, magnetohydrodynamical simulation - the third and final volume of the illustristng project. this simulation occupies a unique combination of large volume and high resolution, with a 50 mpc box sampled by 21603 gas cells (baryon mass of 8 × 104 m⊙). the median spatial resolution of star-forming interstellar medium gas is ∼100-140 pc. this resolution approaches or exceeds that of modern `zoom' simulations of individual massive galaxies, while the volume contains ∼20 000 resolved galaxies with m_\star ≳ 10^7 m⊙. herein we show first results from tng50, focusing on galactic outflows driven by supernovae as well as supermassive black hole feedback. we find that the outflow mass loading is a non-monotonic function of galaxy stellar mass, turning over and rising rapidly above 1010.5 m⊙ due to the action of the central black hole (bh). the outflow velocity increases with stellar mass, and at fixed mass it is faster at higher redshift. the tng model can produce high-velocity, multiphase outflows that include cool, dense components. these outflows reach speeds in excess of 3000 km s-1 out to 20 kpc with an ejective, bh-driven origin. critically, we show how the relative simplicity of model inputs (and scalings) at the injection scale produces complex behaviour at galactic and halo scales. for example, despite isotropic wind launching, outflows exhibit natural collimation and an emergent bipolarity. furthermore, galaxies above the star-forming main sequence drive faster outflows, although this correlation inverts at high mass with the onset of quenching, whereby low-luminosity, slowly accreting, massive bhs drive the strongest outflows. | first results from the tng50 simulation: galactic outflows driven by supernovae and black hole feedback |
we present the third data release from the parkes pulsar timing array (ppta) project. the release contains observations of 32 pulsars obtained using the 64-m parkes `murriyang' radio telescope. the data span is up to 18 yr with a typical cadence of 3 weeks. this data release is formed by combining an updated version of our second data release with $∼$ 3 yr of more recent data primarily obtained using an ultra-wide-bandwidth receiver system that operates between 704 and 4032 mhz. we provide calibrated pulse profiles, flux density dynamic spectra, pulse times of arrival, and initial pulsar timing models. we describe methods for processing such wide-bandwidth observations and compare this data release with our previous release. | the parkes pulsar timing array third data release |
one century after its formulation, einstein's general relativity (gr) has made remarkable predictions and turned out to be compatible with all experimental tests. most of these tests probe the theory in the weak-field regime, and there are theoretical and experimental reasons to believe that gr should be modified when gravitational fields are strong and spacetime curvature is large. the best astrophysical laboratories to probe strong-field gravity are black holes and neutron stars, whether isolated or in binary systems. we review the motivations to consider extensions of gr. we present a (necessarily incomplete) catalog of modified theories of gravity for which strong-field predictions have been computed and contrasted to einstein's theory, and we summarize our current understanding of the structure and dynamics of compact objects in these theories. we discuss current bounds on modified gravity from binary pulsar and cosmological observations, and we highlight the potential of future gravitational wave measurements to inform us on the behavior of gravity in the strong-field regime. | testing general relativity with present and future astrophysical observations |
we summarize our current knowledge of neutron-star masses and radii. recent instrumentation and computational advances have resulted in a rapid increase in the discovery rate and precise timing of radio pulsars in binaries in the past few years, leading to a large number of mass measurements. these discoveries show that the neutron-star mass distribution is much wider than previously thought, with three known pulsars now firmly in the 1.9-2.0-m⊙ mass range. for radii, large, high-quality data sets from x-ray satellites as well as significant progress in theoretical modeling led to considerable progress in the measurements, placing them in the 10-11.5-km range and shrinking their uncertainties, owing to a better understanding of the sources of systematic errors. the combination of the massive-neutron-star discoveries, the tighter radius measurements, and improved laboratory constraints of the properties of dense matter has already made a substantial impact on our understanding of the composition and bulk properties of cold nuclear matter at densities higher than that of the atomic nucleus, a major unsolved problem in modern physics. | masses, radii, and the equation of state of neutron stars |
we introduce the simba simulations, the next generation of the mufasa cosmological galaxy formation simulations run with gizmo's meshless finite mass hydrodynamics. simba includes updates to mufasa's sub-resolution star formation and feedback prescriptions, and introduces black hole growth via the torque-limited accretion model of anglés-alcázar et al. from cold gas and bondi accretion from hot gas, along with black hole feedback via kinetic bipolar outflows and x-ray energy. ejection velocities are taken to be {∼ } 10^3 km s^{-1} at high eddington ratios, increasing to {∼ } 8000 km s^{-1} at eddington ratios below 2 per cent, with a constant momentum input of 20l/c. simba further includes an on-the-fly dust production, growth, and destruction model. our simba run with (100h^{-1} mpc)^3 and 10243 gas elements reproduces numerous observables, including galaxy stellar mass functions at z = 0-6, the stellar mass-star formation rate main sequence, h i and h2 fractions, the mass-metallicity relation at z ≈ 0, 2, star-forming galaxy sizes, hot gas fractions in massive haloes, and z = 0 galaxy dust properties. however, simba also yields an insufficiently sharp truncation of the z = 0 mass function, and too-large sizes for low-mass quenched galaxies. we show that simba's jet feedback is primarily responsible for quenching massive galaxies. | simba: cosmological simulations with black hole growth and feedback |
measurement of the distances to nearby galaxies has improved rapidly in recent decades. the ever-present challenge is to reduce systematic effects, especially as greater distances are probed and the uncertainties become larger. in this paper, we combine several recent calibrations of the tip of the red giant branch (trgb) method. these calibrations are internally self-consistent at the 1% level. new gaia early data release 3 data provide an additional consistency check at a (lower) 5% level of accuracy, a result of the well-documented gaia angular covariance bias. the updated trgb calibration applied to a sample of type ia supernovae from the carnegie supernova project results in a value of the hubble constant of h0 = 69.8 ± 0.6 (stat) ± 1.6 (sys) km s-1 mpc-1. no statistically significant difference is found between the value of h0 based on the trgb and that determined from the cosmic microwave background. the trgb results are also consistent to within 2σ with the shoes and spitzer plus hubble space telescope (hst) key project cepheid calibrations. the trgb results alone do not demand additional new physics beyond the standard (λcdm) cosmological model. they have the advantage of simplicity of the underlying physics (the core he flash) and small systematic uncertainties (from extinction, metallicity, and crowding). finally, the strengths and weaknesses of both the trgb and cepheids are reviewed, and prospects for addressing the current discrepancy with future gaia, hst, and james webb space telescope observations are discussed. resolving this discrepancy is essential for ascertaining if the claimed tension in h0 between the locally measured and cmb-inferred values is physically motivated. * based on observations made with the nasa/esa hubble space telescope, obtained at the space telescope science institute, which is operated by the association of universities for research in astronomy, inc., under nasa contract nas 5-26555. these observations are associated with program nos. 13472, 13691, 9477, and 10399. | measurements of the hubble constant: tensions in perspective |
galaxies with stellar masses as high as roughly 1011 solar masses have been identified1-3 out to redshifts z of roughly 6, around 1 billion years after the big bang. it has been difficult to find massive galaxies at even earlier times, as the balmer break region, which is needed for accurate mass estimates, is redshifted to wavelengths beyond 2.5 μm. here we make use of the 1-5 μm coverage of the james webb space telescope early release observations to search for intrinsically red galaxies in the first roughly 750 million years of cosmic history. in the survey area, we find six candidate massive galaxies (stellar mass more than 1010 solar masses) at 7.4 ≤ z ≤ 9.1, 500-700 myr after the big bang, including one galaxy with a possible stellar mass of roughly 1011 solar masses. if verified with spectroscopy, the stellar mass density in massive galaxies would be much higher than anticipated from previous studies on the basis of rest-frame ultraviolet-selected samples. | a population of red candidate massive galaxies600 myr after the big bang |
we present our current best estimate of the plausible observing scenarios for the advanced ligo, advanced virgo and kagra gravitational-wave detectors over the next several years, with the intention of providing information to facilitate planning for multi-messenger astronomy with gravitational waves. we estimate the sensitivity of the network to transient gravitational-wave signals for the third (o3), fourth (o4) and fifth observing (o5) runs, including the planned upgrades of the advanced ligo and advanced virgo detectors. we study the capability of the network to determine the sky location of the source for gravitational-wave signals from the inspiral of binary systems of compact objects, that is binary neutron star, neutron star-black hole, and binary black hole systems. the ability to localize the sources is given as a sky-area probability, luminosity distance, and comoving volume. the median sky localization area (90% credible region) is expected to be a few hundreds of square degrees for all types of binary systems during o3 with the advanced ligo and virgo (hlv) network. the median sky localization area will improve to a few tens of square degrees during o4 with the advanced ligo, virgo, and kagra (hlvk) network. during o3, the median localization volume (90% credible region) is expected to be on the order of 105,106,107mpc3 for binary neutron star, neutron star-black hole, and binary black hole systems, respectively. the localization volume in o4 is expected to be about a factor two smaller than in o3. we predict a detection count of 1-1+12(10-10+52) for binary neutron star mergers, of 0-0+19(1-1+91) for neutron star-black hole mergers, and 17-11+22(79-44+89) for binary black hole mergers in a one-calendar-year observing run of the hlv network during o3 (hlvk network during o4). we evaluate sensitivity and localization expectations for unmodeled signal searches, including the search for intermediate mass black hole binary mergers. | prospects for observing and localizing gravitational-wave transients with advanced ligo, advanced virgo and kagra |
we present results from 13 cosmological simulations that explore the parameter space of the `evolution and assembly of galaxies and their environments' (eagle) simulation project. four of the simulations follow the evolution of a periodic cube l = 50 cmpc on a side, and each employs a different subgrid model of the energetic feedback associated with star formation. the relevant parameters were adjusted so that the simulations each reproduce the observed galaxy stellar mass function at z = 0.1. three of the simulations fail to form disc galaxies as extended as observed, and we show analytically that this is a consequence of numerical radiative losses that reduce the efficiency of stellar feedback in high-density gas. such losses are greatly reduced in the fourth simulation - the eagle reference model - by injecting more energy in higher density gas. this model produces galaxies with the observed size distribution, and also reproduces many galaxy scaling relations. in the remaining nine simulations, a single parameter or process of the reference model was varied at a time. we find that the properties of galaxies with stellar mass ≲ m⋆ (the `knee' of the galaxy stellar mass function) are largely governed by feedback associated with star formation, while those of more massive galaxies are also controlled by feedback from accretion on to their central black holes. both processes must be efficient in order to reproduce the observed galaxy population. in general, simulations that have been calibrated to reproduce the low-redshift galaxy stellar mass function will still not form realistic galaxies, but the additional requirement that galaxy sizes be acceptable leads to agreement with a large range of observables. | the eagle simulations of galaxy formation: calibration of subgrid physics and model variations |
the james webb space telescope (jwst) is revolutionizing our knowledge of $z>5$ galaxies and their actively accreting black holes. using the jwst cycle 1 treasury program ultradeep nirspec and nircam observations before the epoch of reionization (uncover) in the lensing field abell 2744, we report the identification of a sample of little red dots at $3 < z_{\rm{phot}} < 7$ that likely contain highly-reddened accreting supermassive black holes. using a nircam-only selection to f444w$<27.7$ mag, we find 26 sources over the $\sim45$ arcmin$^{2}$ field that are blue in f115w$-$f200w$\sim0$ (or $\beta_{\rm uv}\sim-2.0$ for $f_{\lambda} \propto \lambda^\beta$), red in f200w$-$f444w = $1-4$ ($\beta_{\rm opt} \sim +2.0$), and are dominated by a point-source like central component. of the 20 sources with deep alma 1.2-mm coverage, none are detected individually or in a stack. for the majority of the sample, sed fits to the jwst+alma observations prefer models with hot dust rather than obscured star-formation to reproduce the red nircam colors and alma 1.2-mm non-detections. while compact dusty star formation can not be ruled out, the combination of extremely small sizes ($\langle r_e \rangle\approx50$ pc after correction for magnification), red rest-frame optical slopes, and hot dust can by explained by reddened broad-line active galactic nuclei (agns). our targets have faint $m_{\rm 1450} \approx -14\ \, {\rm to} -18$ mag but inferred bolometric luminosities of $l_{\rm bol} = 10^{43}-10^{46}$ erg/s, reflecting their obscured nature. if the candidates are confirmed as agns with upcoming uncover spectroscopy, then we have found an abundant population of reddened luminous agn that are at least ten times more numerous than uv-luminous agn at the same intrinsic bolometric luminosity. | uncover: candidate red active galactic nuclei at 3<z<7 with jwst and alma |
we report the discovery of a candidate galaxy with a photo-z of z ~ 12 in the first epoch of the james webb space telescope (jwst) cosmic evolution early release science survey. following conservative selection criteria, we identify a source with a robust z phot = ${11.8}_{-0.2}^{+0.3}$ (1σ uncertainty) with m f200w = 27.3 and ≳7σ detections in five filters. the source is not detected at λ < 1.4 μm in deep imaging from both hubble space telescope (hst) and jwst and has faint ~3σ detections in jwst f150w and hst f160w, which signal a lyα break near the red edge of both filters, implying z ~ 12. this object (maisie's galaxy) exhibits f115w - f200w > 1.9 mag (2σ lower limit) with a blue continuum slope, resulting in 99.6% of the photo-z probability distribution function favoring z > 11. all data-quality images show no artifacts at the candidate's position, and independent analyses consistently find a strong preference for z > 11. its colors are inconsistent with galactic stars, and it is resolved (rh= 340 ± 14 pc). maisie's galaxy has log m */m ⊙ ~ 8.5 and is highly star-forming (log ssfr ~ -8.2 yr-1), with a blue rest-uv color (β ~ -2.5) indicating little dust, though not extremely low metallicity. while the presence of this source is in tension with most predictions, it agrees with empirical extrapolations assuming uv luminosity functions that smoothly decline with increasing redshift. should follow-up spectroscopy validate this redshift, our universe was already aglow with galaxies less than 400 myr after the big bang. | a long time ago in a galaxy far, far away: a candidate z ∼ 12 galaxy in early jwst ceers imaging |
bayesian parameter estimation is fast becoming the language of gravitational-wave astronomy. it is the method by which gravitational-wave data is used to infer the sources’ astrophysical properties. we introduce a user-friendly bayesian inference library for gravitational-wave astronomy, bilby. this python code provides expert-level parameter estimation infrastructure with straightforward syntax and tools that facilitate use by beginners. it allows users to perform accurate and reliable gravitational-wave parameter estimation on both real, freely available data from ligo/virgo and simulated data. we provide a suite of examples for the analysis of compact binary mergers and other types of signal models, including supernovae and the remnants of binary neutron star mergers. these examples illustrate how to change the signal model, implement new likelihood functions, and add new detectors. bilby has additional functionality to do population studies using hierarchical bayesian modeling. we provide an example in which we infer the shape of the black hole mass distribution from an ensemble of observations of binary black hole mergers. | bilby: a user-friendly bayesian inference library for gravitational-wave astronomy |
i start by providing an updated summary of the penalized pixel-fitting (ppxf) method that is used to extract the stellar and gas kinematics, as well as the stellar population of galaxies, via full spectrum fitting. i then focus on the problem of extracting the kinematics when the velocity dispersion σ is smaller than the velocity sampling δv that is generally, by design, close to the instrumental dispersion σinst. the standard approach consists of convolving templates with a discretized kernel, while fitting for its parameters. this is obviously very inaccurate when σ ≲ δv/2, due to undersampling. oversampling can prevent this, but it has drawbacks. here i present a more accurate and efficient alternative. it avoids the evaluation of the undersampled kernel and instead directly computes its well-sampled analytic fourier transform, for use with the convolution theorem. a simple analytic transform exists when the kernel is described by the popular gauss-hermite parametrization (which includes the gaussian as special case) for the line-of-sight velocity distribution. i describe how this idea was implemented in a significant upgrade to the publicly available ppxf software. the key advantage of the new approach is that it provides accurate velocities regardless of σ. this is important e.g. for spectroscopic surveys targeting galaxies with σ ≪ σinst, for galaxy redshift determinations or for measuring line-of-sight velocities of individual stars. the proposed method could also be used to fix gaussian convolution algorithms used in today's popular software packages. | improving the full spectrum fitting method: accurate convolution with gauss-hermite functions |
context. gaia data release 2 provides high-precision astrometry and three-band photometry for about 1.3 billion sources over the full sky. the precision, accuracy, and homogeneity of both astrometry and photometry are unprecedented.aims: we highlight the power of the gaia dr2 in studying many fine structures of the hertzsprung-russell diagram (hrd). gaia allows us to present many different hrds, depending in particular on stellar population selections. we do not aim here for completeness in terms of types of stars or stellar evolutionary aspects. instead, we have chosen several illustrative examples.methods: we describe some of the selections that can be made in gaia dr2 to highlight the main structures of the gaia hrds. we select both field and cluster (open and globular) stars, compare the observations with previous classifications and with stellar evolutionary tracks, and we present variations of the gaia hrd with age, metallicity, and kinematics. late stages of stellar evolution such as hot subdwarfs, post-agb stars, planetary nebulae, and white dwarfs are also analysed, as well as low-mass brown dwarf objects.results: the gaia hrds are unprecedented in both precision and coverage of the various milky way stellar populations and stellar evolutionary phases. many fine structures of the hrds are presented. the clear split of the white dwarf sequence into hydrogen and helium white dwarfs is presented for the first time in an hrd. the relation between kinematics and the hrd is nicely illustrated. two different populations in a classical kinematic selection of the halo are unambiguously identified in the hrd. membership and mean parameters for a selected list of open clusters are provided. they allow drawing very detailed cluster sequences, highlighting fine structures, and providing extremely precise empirical isochrones that will lead to more insight in stellar physics.conclusions: gaia dr2 demonstrates the potential of combining precise astrometry and photometry for large samples for studies in stellar evolution and stellar population and opens an entire new area for hrd-based studies. the full table a.1 is only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/616/a10 | gaia data release 2. observational hertzsprung-russell diagrams |
the cosmic origin of elements heavier than iron has long been uncertain. theoretical modelling shows that the matter that is expelled in the violent merger of two neutron stars can assemble into heavy elements such as gold and platinum in a process known as rapid neutron capture (r-process) nucleosynthesis. the radioactive decay of isotopes of the heavy elements is predicted to power a distinctive thermal glow (a ‘kilonova’). the discovery of an electromagnetic counterpart to the gravitational-wave source gw170817 represents the first opportunity to detect and scrutinize a sample of freshly synthesized r-process elements. here we report models that predict the electromagnetic emission of kilonovae in detail and enable the mass, velocity and composition of ejecta to be derived from observations. we compare the models to the optical and infrared radiation associated with the gw170817 event to argue that the observed source is a kilonova. we infer the presence of two distinct components of ejecta, one composed primarily of light (atomic mass number less than 140) and one of heavy (atomic mass number greater than 140) r-process elements. the ejected mass and a merger rate inferred from gw170817 imply that such mergers are a dominant mode of r-process production in the universe. | origin of the heavy elements in binary neutron-star mergers from a gravitational-wave event |
the detection of gravitational waves originating from a neutron-star merger, gw170817, by the ligo and virgo collaborations has recently provided new stringent limits on the tidal deformabilities of the stars involved in the collision. combining this measurement with the existence of two-solar-mass stars, we generate a generic family of neutron-star-matter equations of state (eoss) that interpolate between state-of-the-art theoretical results at low and high baryon density. comparing the results to ones obtained without the tidal-deformability constraint, we witness a dramatic reduction in the family of allowed eoss. based on our analysis, we conclude that the maximal radius of a 1.4-solar-mass neutron star is 13.6 km, and that the smallest allowed tidal deformability of a similar-mass star is λ (1.4 m⊙)=120 . | gravitational-wave constraints on the neutron-star-matter equation of state |
the production of about half of the heavy elements found in nature is assigned to a specific astrophysical nucleosynthesis process: the rapid neutron-capture process (r process). although this idea was postulated more than six decades ago, the full understanding faces two types of uncertainties or open questions: (a) the nucleosynthesis path in the nuclear chart runs close to the neutron-drip line, where presently only limited experimental information is available, and one has to rely strongly on theoretical predictions for nuclear properties. (b) while for many years the occurrence of the r process has been associated with supernovae, where the innermost ejecta close to the central neutron star were supposed to be neutron rich, more recent studies have cast substantial doubts on this environment. possibly only a weak r process, with no or negligible production of the third r -process peak, can be accounted for, while much more neutron-rich conditions, including an r -process path with fission cycling, are likely responsible for the majority of the heavy r -process elements. such conditions could result during the ejection of initially highly neutron-rich matter, as found in neutron stars, or during the fast ejection of matter that has previously experienced strong electron captures at high densities. possible scenarios are the mergers of neutron stars, neutron-star-black hole mergers, but also include rare classes of supernovae as well as hypernovae or collapsars with polar jet ejecta, and possibly also accretion disk outflows related to the collapse of fast rotating massive stars. the composition of the ejecta from each event determines the temporal evolution of the r -process abundances during the "chemical" evolution of the galaxy. stellar r -process abundance observations have provided insight into and constraints on the frequency of and conditions in the responsible stellar production sites. one of them, neutron-star mergers, was just identified thanks to the observation of the r -process kilonova electromagnetic transient following the gravitational wave event gw170817. these observations, which are becoming increasingly precise due to improved experimental atomic data and high-resolution observations, have been particularly important in defining the heavy element abundance patterns of the old halo stars, and thus in determining the extent and nature of the earliest nucleosynthesis in the galaxy. combining new results and important breakthroughs in the related nuclear, atomic, and astronomical fields of science, this review attempts to answer the question "how were the elements from iron to uranium made?" | origin of the heaviest elements: the rapid neutron-capture process |
modeling galaxy formation in a cosmological context presents one of the greatest challenges in astrophysics today due to the vast range of scales and numerous physical processes involved. here we review the current status of models that employ two leading techniques to simulate the physics of galaxy formation: semianalytic models and numerical hydrodynamic simulations. we focus on a set of observational targets that describe the evolution of the global and structural properties of galaxies from roughly cosmic high noon (z â¼ 2-3) to the present. although minor discrepancies remain, overall, models show remarkable convergence among different methods and make predictions that are in qualitative agreement with observations. modelers have converged on a core set of physical processes that are critical for shaping galaxy properties. this core set includes cosmological accretion, strong stellar-driven winds that are more efficient at low masses, black hole feedback that preferentially suppresses star formation at high masses, and structural and morphological evolution through merging and environmental processes. however, all cosmological models currently adopt phenomenological implementations of many of these core processes, which must be tuned to observations. many details of how these diverse processes interact within a hierarchical structure formation setting remain poorly understood. emerging multiscale simulations are helping to bridge the gap between stellar and cosmological scales, placing models on a firmer, more physically grounded footing. concurrently, upcoming telescope facilities will provide new challenges and constraints for models, particularly by directly constraining inflows and outflows through observations of gas in and around galaxies. | physical models of galaxy formation in a cosmological framework |
we analyse the gas-phase metallicity properties of a sample of low stellar mass (log m*/m_sun <= 9) galaxies at 3 < z < 10, observed with jwst/nirspec as part of the jades programme in its deep goods-s tier. by combining this sample with more massive galaxies at similar redshifts from other programmes, we study the scaling relations between stellar mass, oxygen abundance (o/h), and star-formation rate (sfr) for 146 galaxies, spanning across three orders of magnitude in stellar mass and out to the epoch of early galaxy assembly. we find evidence for a shallower slope at the low-mass-end of the mass-metallicity relation (mzr), with 12 + log(o/h) = (7.72+-0.02) + (0.17+-0.03) log(m* / 10^8 m_sun), in good agreement with the mzr probed by local analogues of high-redshift systems like 'green pea' and 'blueberry' galaxies. the inferred slope is well matched by models including 'momentum-driven' sne winds, suggesting that feedback mechanisms in dwarf galaxies (and at high-z) might be different from those in place at higher masses. the evolution in the normalisation is observed to be relatively mild compared to previous determinations of the mzr at z~3 (~ 0.1 - 0.2 dex across the explored mass regime). we observe a deviation from the local fundamental metallicity relation (fmr) for our sample at high redshift, especially at z > 6, with galaxies significantly less enriched (with a median offset in log(o/h) of ~ 0.5 dex, significant at ~ 5 sigma) than predicted given their m* and sfr. these observations are consistent with an enhanced stochasticity in the star-formation history, and/or with an increased efficiency in metal removals by outflows, prompting us to reconsider the nature of the relationship between m*, o/h, and sfr in the early universe. | jades: insights on the low-mass end of the mass--metallicity--star-formation rate relation at $3 < z < 10$ from deep jwst/nirspec spectroscopy |
galaxy formation is at the heart of our understanding of cosmic evolution. although there is a consensus that galaxies emerged from the expanding matter background by gravitational instability of primordial fluctuations, a number of additional physical processes must be understood and implemented in theoretical models before these can be reliably used to interpret observations. in parallel, the astonishing recent progresses made in detecting galaxies that formed only a few hundreds of million years after the big bang is pushing the quest for more sophisticated and detailed studies of early structures. in this review, we combine the information gleaned from different theoretical models/studies to build a coherent picture of the universe in its early stages which includes the physics of galaxy formation along with the impact that early structures had on large-scale processes as cosmic reionization and metal enrichment of the intergalactic medium. | early galaxy formation and its large-scale effects |
we report the discovery of an accreting supermassive black hole at z = 8.679. this galaxy, denoted here as ceers_1019, was previously discovered as a lyα-break galaxy by hubble with a lyα redshift from keck. as part of the cosmic evolution early release science (ceers) survey, we have observed this source with jwst/nirspec, miri, nircam, and nircam/wfss and uncovered a plethora of emission lines. the hβ line is best fit by a narrow plus a broad component, where the latter is measured at 2.5σ with an fwhm ~1200 km s-1. we conclude this originates in the broadline region of an active galactic nucleus (agn). this is supported by the presence of weak high-ionization lines (n v, n iv], and c iii]), as well as a spatial point-source component. the implied mass of the black hole (bh) is log (m bh/m ⊙) = 6.95 ± 0.37, and we estimate that it is accreting at 1.2 ± 0.5 times the eddington limit. the 1-8 μm photometric spectral energy distribution shows a continuum dominated by starlight and constrains the host galaxy to be massive (log m/m⊙ ~9.5) and highly star-forming (star formation rate, or sfr ~ 30 m⊙ yr-1; log ssfr ~ - 7.9 yr-1). the line ratios show that the gas is metal-poor (z/z ⊙ ~ 0.1), dense (ne~ 103 cm-3), and highly ionized (log u ~ - 2.1). we use this present highest-redshift agn discovery to place constraints on bh seeding models and find that a combination of either super-eddington accretion from stellar seeds or eddington accretion from very massive bh seeds is required to form this object. | a ceers discovery of an accreting supermassive black hole 570 myr after the big bang: identifying a progenitor of massive z > 6 quasars |
we compile observations of early-type binaries identified via spectroscopy, eclipses, long-baseline interferometry, adaptive optics, common proper motion, etc. each observational technique is sensitive to companions across a narrow parameter space of orbital periods p and mass ratios q = {m}{comp}/m 1. after combining the samples from the various surveys and correcting for their respective selection effects, we find that the properties of companions to o-type and b-type main-sequence (ms) stars differ among three regimes. first, at short orbital periods p ≲ 20 days (separations a ≲ 0.4 au), the binaries have small eccentricities e ≲ 0.4, favor modest mass ratios < q> ≈ 0.5, and exhibit a small excess of twins q > 0.95. second, the companion frequency peaks at intermediate periods log p (days) ≈ 3.5 (a ≈ 10 au), where the binaries have mass ratios weighted toward small values q ≈ 0.2-0.3 and follow a maxwellian “thermal” eccentricity distribution. finally, companions with long orbital periods log p (days) ≈ 5.5-7.5 (a ≈ 200-5000 au) are outer tertiary components in hierarchical triples and have a mass ratio distribution across q ≈ 0.1-1.0 that is nearly consistent with random pairings drawn from the initial mass function. we discuss these companion distributions and properties in the context of binary-star formation and evolution. we also reanalyze the binary statistics of solar-type ms primaries, taking into account that 30% ± 10% of single-lined spectroscopic binaries likely contain white dwarf companions instead of low-mass stellar secondaries. the mean frequency of stellar companions with q > 0.1 and log p (days) < 8.0 per primary increases from 0.50 ± 0.04 for solar-type ms primaries to 2.1 ± 0.3 for o-type ms primaries. we fit joint probability density functions f({m}1,q,p,e)\ne f({m}1)f(q)f(p)f(e) to the corrected distributions, which can be incorporated into binary population synthesis studies. | mind your ps and qs: the interrelation between period (p) and mass-ratio (q) distributions of binary stars |
multimessenger gravitational-wave (gw) astronomy has commenced with the detection of the binary neutron star merger gw170817 and its associated electromagnetic counterparts. the almost coincident observation of both signals places an exquisite bound on the gw speed |cg/c -1 |≤5 ×10-16 . we use this result to probe the nature of dark energy (de), showing that a large class of scalar-tensor theories and de models are highly disfavored. as an example we consider the covariant galileon, a cosmologically viable, well motivated gravity theory which predicts a variable gw speed at low redshift. our results eliminate any late-universe application of these models, as well as their horndeski and most of their beyond horndeski generalizations. three alternatives (and their combinations) emerge as the only possible scalar-tensor de models: (1) restricting horndeski's action to its simplest terms, (2) applying a conformal transformation which preserves the causal structure, and (3) compensating the different terms that modify the gw speed (to be robust, the compensation has to be independent on the background on which gws propagate). our conclusions extend to any other gravity theory predicting varying cg such as einstein-aether, hořava gravity, generalized proca, tensor-vector-scalar gravity (teves), and other mond-like gravities. | dark energy after gw170817: dead ends and the road ahead |
the laser interferometer space antenna (lisa) will be a transformative experiment for gravitational wave astronomy, and, as such, it will offer unique opportunities to address many key astrophysical questions in a completely novel way. the synergy with ground-based and space-born instruments in the electromagnetic domain, by enabling multi-messenger observations, will add further to the discovery potential of lisa. the next decade is crucial to prepare the astrophysical community for lisa's first observations. this review outlines the extensive landscape of astrophysical theory, numerical simulations, and astronomical observations that are instrumental for modeling and interpreting the upcoming lisa datastream. to this aim, the current knowledge in three main source classes for lisa is reviewed; ultra-compact stellar-mass binaries, massive black hole binaries, and extreme or interme-diate mass ratio inspirals. the relevant astrophysical processes and the established modeling techniques are summarized. likewise, open issues and gaps in our understanding of these sources are highlighted, along with an indication of how lisa could help making progress in the different areas. new research avenues that lisa itself, or its joint exploitation with upcoming studies in the electromagnetic domain, will enable, are also illustrated. improvements in modeling and analysis approaches, such as the combination of numerical simulations and modern data science techniques, are discussed. this review is intended to be a starting point for using lisa as a new discovery tool for understanding our universe. | astrophysics with the laser interferometer space antenna |
we present a new cosmological, magnetohydrodynamical simulation for galaxy formation: tng50, the third and final instalment of the illustristng project. tng50 evolves 2 × 21603 dark matter particles and gas cells in a volume 50 comoving mpc across. it hence reaches a numerical resolution typical of zoom-in simulations, with a baryonic element mass of 8.5× 10^4 m_{\odot } and an average cell size of 70-140 pc in the star-forming regions of galaxies. simultaneously, tng50 samples ∼700 (6500) galaxies with stellar masses above 10^{10} (10^8) m_{\odot } at z = 1. here we investigate the structural and kinematical evolution of star-forming galaxies across cosmic time (0 ≲ z ≲ 6). we quantify their sizes, disc heights, 3d shapes, and degree of rotational versus dispersion-supported motions as traced by rest-frame v-band light (i.e. roughly stellar mass) and by h α light (i.e. star-forming and dense gas). the unprecedented resolution of tng50 enables us to model galaxies with sub-kpc half-light radii and with ≲300-pc disc heights. coupled with the large-volume statistics, we characterize a diverse, redshift- and mass-dependent structural and kinematical morphological mix of galaxies all the way to early epochs. our model predicts that for star-forming galaxies the fraction of disc-like morphologies, based on 3d stellar shapes, increases with both cosmic time and galaxy stellar mass. gas kinematics reveal that the vast majority of 10^{9-11.5} m_{\odot } star-forming galaxies are rotationally supported discs for most cosmic epochs (vrot/σ > 2-3, z ≲ 5), being dynamically hotter at earlier epochs (z ≳ 1.5). despite large velocity dispersion at high redshift, cold and dense gas in galaxies predominantly arranges in disky or elongated shapes at all times and masses; these gaseous components exhibit rotationally dominated motions far exceeding the collisionless stellar bodies. | first results from the tng50 simulation: the evolution of stellar and gaseous discs across cosmic time |
for over 100 years, the group-theoretic characterization of crystalline solids has provided the foundational language for diverse problems in physics and chemistry. however, the group theory of crystals with commensurate magnetic order has remained incomplete for the past 70 years, due to the complicated symmetries of magnetic crystals. in this work, we complete the 100-year-old problem of crystalline group theory by deriving the small corepresentations, momentum stars, compatibility relations, and magnetic elementary band corepresentations of the 1,421 magnetic space groups (msgs), which we have made freely accessible through tools on the bilbao crystallographic server. we extend topological quantum chemistry to the msgs to form a complete, real-space theory of band topology in magnetic and nonmagnetic crystalline solids - magnetic topological quantum chemistry (mtqc). using mtqc, we derive the complete set of symmetry-based indicators of electronic band topology, for which we identify symmetry-respecting bulk and anomalous surface and hinge states. | magnetic topological quantum chemistry |
the cologne database for molecular spectroscopy, cdms, was founded 1998 to provide in its catalog section line lists of mostly molecular species which are or may be observed in various astronomical sources (usually) by radio astronomical means. the line lists contain transition frequencies with qualified accuracies, intensities, quantum numbers, as well as further auxiliary information. they have been generated from critically evaluated experimental line lists, mostly from laboratory experiments, employing established hamiltonian models. separate entries exist for different isotopic species and usually also for different vibrational states. as of december 2015, the number of entries is 792. they are available online as ascii tables with additional files documenting information on the entries. the virtual atomic and molecular data centre, vamdc, was founded more than 5 years ago as a common platform for atomic and molecular data. this platform facilitates exchange not only between spectroscopic databases related to astrophysics or astrochemistry, but also with collisional and kinetic databases. a dedicated infrastructure was developed to provide a common data format in the various databases enabling queries to a large variety of databases on atomic and molecular data at once. for cdms, the incorporation in vamdc was combined with several modifications on the generation of cdms catalog entries. here we introduce related changes to the data structure and the data content in the cdms. the new data scheme allows us to incorporate all previous data entries but in addition allows us also to include entries based on new theoretical descriptions. moreover, the cdms entries have been transferred into a mysql database format. these developments within the vamdc framework have in part been driven by the needs of the astronomical community to be able to deal efficiently with large data sets obtained with the herschel space telescope or, more recently, with the atacama large millimeter array. | the cologne database for molecular spectroscopy, cdms, in the virtual atomic and molecular data centre, vamdc |
a range of quantum field theoretical phenomena driven by external magnetic fields and their applications in relativistic systems and quasirelativistic condensed matter ones, such as graphene and dirac/weyl semimetals, are reviewed. we start by introducing the underlying physics of the magnetic catalysis. the dimensional reduction of the low-energy dynamics of relativistic fermions in an external magnetic field is explained and its role in catalyzing spontaneous symmetry breaking is emphasized. the general theoretical consideration is supplemented by the analysis of the magnetic catalysis in quantum electrodynamics, chromodynamics and quasirelativistic models relevant for condensed matter physics. by generalizing the ideas of the magnetic catalysis to the case of nonzero density and temperature, we argue that other interesting phenomena take place. the chiral magnetic and chiral separation effects are perhaps the most interesting among them. in addition to the general discussion of the physics underlying chiral magnetic and separation effects, we also review their possible phenomenological implications in heavy-ion collisions and compact stars. we also discuss the application of the magnetic catalysis ideas for the description of the quantum hall effect in monolayer and bilayer graphene, and conclude that the generalized magnetic catalysis, including both the magnetic catalysis condensates and the quantum hall ferromagnetic ones, lies at the basis of this phenomenon. we also consider how an external magnetic field affects the underlying physics in a class of three-dimensional quasirelativistic condensed matter systems, dirac semimetals. while at sufficiently low temperatures and zero density of charge carriers, such semimetals are expected to reveal the regime of the magnetic catalysis, the regime of weyl semimetals with chiral asymmetry is realized at nonzero density. finally, we discuss the interplay between relativistic quantum field theories (including quantum electrodynamics and quantum chromodynamics) in a magnetic field and noncommutative field theories, which leads to a new type of the latter, nonlocal noncommutative field theories. | quantum field theory in a magnetic field: from quantum chromodynamics to graphene and dirac semimetals |
the bigcode project is an open-scientific collaboration working on the responsible development of large language models for code. this tech report describes the progress of the collaboration until december 2022, outlining the current state of the personally identifiable information (pii) redaction pipeline, the experiments conducted to de-risk the model architecture, and the experiments investigating better preprocessing methods for the training data. we train 1.1b parameter models on the java, javascript, and python subsets of the stack and evaluate them on the multipl-e text-to-code benchmark. we find that more aggressive filtering of near-duplicates can further boost performance and, surprisingly, that selecting files from repositories with 5+ github stars deteriorates performance significantly. our best model outperforms previous open-source multilingual code generation models (incoder-6.7b and codegen-multi-2.7b) in both left-to-right generation and infilling on the java, javascript, and python portions of multipl-e, despite being a substantially smaller model. all models are released under an openrail license at https://hf.co/bigcode. | santacoder: don't reach for the stars! |
the highly elliptical, 16-year-period orbit of the star s2 around the massive black hole candidate sgr a* is a sensitive probe of the gravitational field in the galactic centre. near pericentre at 120 au ≈ 1400 schwarzschild radii, the star has an orbital speed of ≈7650 km s-1, such that the first-order effects of special and general relativity have now become detectable with current capabilities. over the past 26 years, we have monitored the radial velocity and motion on the sky of s2, mainly with the sinfoni and naco adaptive optics instruments on the eso very large telescope, and since 2016 and leading up to the pericentre approach in may 2018, with the four-telescope interferometric beam-combiner instrument gravity. from data up to and including pericentre, we robustly detect the combined gravitational redshift and relativistic transverse doppler effect for s2 of z = δλ / λ ≈ 200 km s-1/c with different statistical analysis methods. when parameterising the post-newtonian contribution from these effects by a factor f , with f = 0 and f = 1 corresponding to the newtonian and general relativistic limits, respectively, we find from posterior fitting with different weighting schemes f = 0.90 ± 0.09|stat ± 0.15|sys. the s2 data are inconsistent with pure newtonian dynamics. this paper is dedicated to tal alexander, who passed away about a week before the pericentre approach of s2. | detection of the gravitational redshift in the orbit of the star s2 near the galactic centre massive black hole |
using a large sample of main sequence stars with 7d measurements supplied by gaia and sdss, we study the kinematic properties of the local (within ∼10 kpc from the sun) stellar halo. we demonstrate that the halo's velocity ellipsoid evolves strongly with metallicity. at the low-[fe/h] end, the orbital anisotropy (the amount of motion in the radial direction compared with the tangential one) is mildly radial, with 0.2 <β< 0.4. for stars with [fe/h] > -1.7, however, we measure extreme values of β∼ 0.9. across the metallicity range considered, namely-3 < [fe/h] < -1, the stellar halo's spin is minimal, at the level of 20< \bar{v}_{θ }(kms^{-1}) < 30. using a suite of cosmological zoom-in simulations of halo formation, we deduce that the observed acute anisotropy is inconsistent with the continuous accretion of dwarf satellites. instead, we argue, the stellar debris in the inner halo was deposited in a major accretion event by a satellite with mvir > 1010m⊙ around the epoch of the galactic disc formation, between 8 and 11 gyr ago. the radical halo anisotropy is the result of the dramatic radialization of the massive progenitor's orbit, amplified by the action of the growing disc. | co-formation of the disc and the stellar halo |
in this paper we provide a first physical interpretation for the event horizon telescope's (eht) 2017 observations of sgr a*. our main approach is to compare resolved eht data at 230 ghz and unresolved non-eht observations from radio to x-ray wavelengths to predictions from a library of models based on time-dependent general relativistic magnetohydrodynamics simulations, including aligned, tilted, and stellar-wind-fed simulations; radiative transfer is performed assuming both thermal and nonthermal electron distribution functions. we test the models against 11 constraints drawn from eht 230 ghz data and observations at 86 ghz, 2.2 μm, and in the x-ray. all models fail at least one constraint. light-curve variability provides a particularly severe constraint, failing nearly all strongly magnetized (magnetically arrested disk (mad)) models and a large fraction of weakly magnetized models. a number of models fail only the variability constraints. we identify a promising cluster of these models, which are mad and have inclination i ≤ 30°. they have accretion rate (5.2-9.5) × 10-9 m ⊙ yr-1, bolometric luminosity (6.8-9.2) × 1035 erg s-1, and outflow power (1.3-4.8) × 1038 erg s-1. we also find that all models with i ≥ 70° fail at least two constraints, as do all models with equal ion and electron temperature; exploratory, nonthermal model sets tend to have higher 2.2 μm flux density; and the population of cold electrons is limited by x-ray constraints due to the risk of bremsstrahlung overproduction. finally, we discuss physical and numerical limitations of the models, highlighting the possible importance of kinetic effects and duration of the simulations. | first sagittarius a* event horizon telescope results. v. testing astrophysical models of the galactic center black hole |
the inefficiency of star formation in massive elliptical galaxies is widely believed to be caused by the interactions of an active galactic nucleus (agn) with the surrounding gas. achieving a sufficiently rapid reddening of moderately massive galaxies without expelling too many baryons has however proven difficult for hydrodynamical simulations of galaxy formation, prompting us to explore a new model for the accretion and feedback effects of supermassive black holes. for high-accretion rates relative to the eddington limit, we assume that a fraction of the accreted rest mass energy heats the surrounding gas thermally, similar to the 'quasar mode' in previous work. for low-accretion rates, we invoke a new, pure kinetic feedback model that imparts momentum to the surrounding gas in a stochastic manner. these two modes of feedback are motivated both by theoretical conjectures for the existence of different types of accretion flows as well as recent observational evidence for the importance of kinetic agn winds in quenching galaxies. we find that a large fraction of the injected kinetic energy in this mode thermalizes via shocks in the surrounding gas, thereby providing a distributed heating channel. in cosmological simulations, the resulting model produces red, non-star-forming massive elliptical galaxies, and achieves realistic gas fractions, black hole growth histories and thermodynamic profiles in large haloes. | simulating galaxy formation with black hole driven thermal and kinetic feedback |
inference of the physical properties of stellar populations from observed photometry and spectroscopy is a key goal in the study of galaxy evolution. in recent years, the quality and quantity of the available data have increased, and there have been corresponding efforts to increase the realism of the stellar population models used to interpret these observations. describing the observed galaxy spectral energy distributions in detail now requires physical models with a large number of highly correlated parameters. these models do not fit easily on grids and necessitate a full exploration of the available parameter space. we present prospector, a flexible code for inferring stellar population parameters from photometry and spectroscopy spanning uv through ir wavelengths. this code is based on forward modeling the data and monte carlo sampling the posterior parameter distribution, enabling complex models and exploration of moderate dimensional parameter spaces. we describe the key ingredients of the code and discuss the general philosophy driving the design of these ingredients. we demonstrate some capabilities of the code on several data sets, including mock and real data. | stellar population inference with prospector |
laboratory experiments sensitive to the equation of state of neutron rich matter in the vicinity of nuclear saturation density provide the first rung in a "density ladder" that connects terrestrial experiments to astronomical observations. in this context, the neutron skin thickness of 208pb (rskin208) provides a stringent laboratory constraint on the density dependence of the symmetry energy. in turn, an improved value of rskin208 has been reported recently by the prex collaboration. exploiting the strong correlation between rskin208 and the slope of the symmetry energy l within a specific class of relativistic energy density functionals, we report a value of l =(106 ±37 ) mev —which systematically overestimates current limits based on both theoretical approaches and experimental measurements. the impact of such a stiff symmetry energy on some critical neutron-star observables is also examined. | implications of prex-2 on the equation of state of neutron-rich matter |
solar probe plus (spp) will be the first spacecraft to fly into the low solar corona. spp's main science goal is to determine the structure and dynamics of the sun's coronal magnetic field, understand how the solar corona and wind are heated and accelerated, and determine what processes accelerate energetic particles. understanding these fundamental phenomena has been a top-priority science goal for over five decades, dating back to the 1958 simpson committee report. the scale and concept of such a mission has been revised at intervals since that time, yet the core has always been a close encounter with the sun. the mission design and the technology and engineering developments enable spp to meet its science objectives to: (1) trace the flow of energy that heats and accelerates the solar corona and solar wind; (2) determine the structure and dynamics of the plasma and magnetic fields at the sources of the solar wind; and (3) explore mechanisms that accelerate and transport energetic particles. the spp mission was confirmed in march 2014 and is under development as a part of nasa's living with a star (lws) program. spp is scheduled for launch in mid-2018, and will perform 24 orbits over a 7-year nominal mission duration. seven venus gravity assists gradually reduce spp's perihelion from 35 solar radii (rs) for the first orbit to {<}10 rs for the final three orbits. in this paper we present the science, mission concept and the baseline vehicle for spp, and examine how the mission will address the key science questions | the solar probe plus mission: humanity's first visit to our star |
we introduce a new framework for quantifying correlated uncertainties of the infinite-matter equation of state derived from chiral effective field theory (χ eft ). bayesian machine learning via gaussian processes with physics-based hyperparameters allows us to efficiently quantify and propagate theoretical uncertainties of the equation of state, such as χ eft truncation errors, to derived quantities. we apply this framework to state-of-the-art many-body perturbation theory calculations with nucleon-nucleon and three-nucleon interactions up to fourth order in the χ eft expansion. this produces the first statistically robust uncertainty estimates for key quantities of neutron stars. we give results up to twice nuclear saturation density for the energy per particle, pressure, and speed of sound of neutron matter, as well as for the nuclear symmetry energy and its derivative. at nuclear saturation density, the predicted symmetry energy and its slope are consistent with experimental constraints. | how well do we know the neutron-matter equation of state at the densities inside neutron stars? a bayesian approach with correlated uncertainties |
we present a 0.16% precise and 0.27% accurate determination of r0, the distance to the galactic center. our measurement uses the star s2 on its 16-year orbit around the massive black hole sgr a* that we followed astrometrically and spectroscopically for 27 years. since 2017, we added near-infrared interferometry with the vlti beam combiner gravity, yielding a direct measurement of the separation vector between s2 and sgr a* with an accuracy as good as 20 μas in the best cases. s2 passed the pericenter of its highly eccentric orbit in may 2018, and we followed the passage with dense sampling throughout the year. together with our spectroscopy, in the best cases with an error of 7 km s-1, this yields a geometric distance estimate of r0 = 8178 ± 13stat. ± 22sys. pc. this work updates our previous publication, in which we reported the first detection of the gravitational redshift in the s2 data. the redshift term is now detected with a significance level of 20σ with fredshift = 1.04 ± 0.05. gravity has been developed by a collaboration of the max planck institute for extraterrestrial physics, lesia of paris observatory/cnrs/upmc/univ. paris diderot and ipag of université grenoble alpes/cnrs, the max planck institute for astronomy, the university of cologne, the centro de astrofísica e gravitaçâo, and the european southern observatory. | a geometric distance measurement to the galactic center black hole with 0.3% uncertainty |
we describe keck-telescope spectrophotometry and imaging of the companion of the "black widow" pulsar psr j0952-0607, the fastest known spinning neutron star (ns) in the disk of the milky way. the companion is very faint at minimum brightness, presenting observational challenges, but we have measured multicolor light curves and obtained radial velocities over the illuminated "day" half of the orbit. the model fits indicate system inclination i = 59.°8 ± 1.°9 and a pulsar mass m ns = 2.35 ± 0.17 m ⊙, the largest well-measured mass found to date. modeling uncertainties are small, since the heating is not extreme; the companion lies well within its roche lobe and a simple direct-heating model provides the best fit. if the ns started at a typical pulsar birth mass, nearly 1 m ⊙ has been accreted; this may be connected with the especially low intrinsic dipole surface field, estimated at 6 × 107 g. joined with reanalysis of other black widow and redback pulsars, we find that the minimum value for the maximum ns mass is ${m}_{\max }\gt 2.19\,{m}_{\odot }$ (2.09 m ⊙) at 1σ (3σ) confidence. this is ~ 0.15 m ⊙ heavier than the lower limit on ${m}_{\max }$ implied by the white dwarf-pulsar binaries measured via radio shapiro-delay techniques. | psr j0952-0607: the fastest and heaviest known galactic neutron star |
technology has advanced to the point that it is possible to image the entire sky every night and process the data in real time. the sky is hardly static: many interesting phenomena occur, including variable stationary objects such as stars or qsos, transient stationary objects such as supernovae or m dwarf flares, and moving objects such as asteroids and the stars themselves. funded by nasa, we have designed and built a sky survey system for the purpose of finding dangerous near-earth asteroids (neas). this system, the “asteroid terrestrial-impact last alert system” (atlas), has been optimized to produce the best survey capability per unit cost, and therefore is an efficient and competitive system for finding potentially hazardous asteroids (phas) but also for tracking variables and finding transients. while carrying out its nasa mission, atlas now discovers more bright (m < 19) supernovae candidates than any ground based survey, frequently detecting very young explosions due to its 2 day cadence. atlas discovered the afterglow of a gamma-ray burst independent of the high energy trigger and has released a variable star catalog of 5 × 106 sources. this is the first of a series of articles describing atlas, devoted to the design and performance of the atlas system. subsequent articles will describe in more detail the software, the survey strategy, atlas-derived nea population statistics, transient detections, and the first data release of variable stars and transient light curves. | atlas: a high-cadence all-sky survey system |
the observation of electromagnetic radiation from radio to γ-ray wavelengths has provided a wealth of information about the universe. however, at pev (1015 ev) energies and above, most of the universe is impenetrable to photons. new messengers, namely cosmic neutrinos, are needed to explore the most extreme environments of the universe where black holes, neutron stars, and stellar explosions transform gravitational energy into non-thermal cosmic rays. these energetic particles have millions of times higher energies than those produced in the most powerful particle accelerators on earth. as neutrinos can escape from regions otherwise opaque to radiation, they allow an unique view deep into exploding stars and the vicinity of the event horizons of black holes. the discovery of cosmic neutrinos with icecube has opened this new window on the universe. icecube has been successful in finding first evidence for cosmic particle acceleration in the jet of an active galactic nucleus. yet, ultimately, its sensitivity is too limited to detect even the brightest neutrino sources with high significance, or to detect populations of less luminous sources. in this white paper, we present an overview of a next-generation instrument, icecube-gen2, which will sharpen our understanding of the processes and environments that govern the universe at the highest energies. icecube-gen2 is designed to: | icecube-gen2: the window to the extreme universe |
we present the cosmos201524 catalog, which contains precise photometric redshifts and stellar masses for more than half a million objects over the 2deg2 cosmos field. including new {{yjhk}}{{s}} images from the ultravista-dr2 survey, y-band images from subaru/hyper-suprime-cam, and infrared data from the spitzer large area survey with the hyper-suprime-cam spitzer legacy program, this near-infrared-selected catalog is highly optimized for the study of galaxy evolution and environments in the early universe. to maximize catalog completeness for bluer objects and at higher redshifts, objects have been detected on a χ 2 sum of the {{yjhk}}{{s}} and z ++ images. the catalog contains ∼ 6× {10}5 objects in the 1.5 deg2 ultravista-dr2 region and ∼ 1.5× {10}5 objects are detected in the “ultra-deep stripes” (0.62 deg2) at {k}{{s}}≤slant 24.7 (3σ, 3″, ab magnitude). through a comparison with the zcosmos-bright spectroscopic redshifts, we measure a photometric redshift precision of {σ }{{δ }z/(1+{z}s)} = 0.007 and a catastrophic failure fraction of η = 0.5%. at 3\lt z\lt 6, using the unique database of spectroscopic redshifts in cosmos, we find {σ }{{δ }z/(1+{z}s)} = 0.021 and η = 13.2 % . the deepest regions reach a 90% completeness limit of {10}10{m}⊙to z = 4. detailed comparisons of the color distributions, number counts, and clustering show excellent agreement with the literature in the same mass ranges. cosmos2015 represents a unique, publicly available, valuable resource with which to investigate the evolution of galaxies within their environment back to the earliest stages of the history of the universe. the cosmos2015 catalog is distributed via anonymous ftp and through the usual astronomical archive systems (cds, eso phase 3, irsa). | the cosmos2015 catalog: exploring the 1 < z < 6 universe with half a million galaxies |
i describe the design, implementation, and usage of galpy, a python package for galactic-dynamics calculations. at its core, galpy consists of a general framework for representing galactic potentials both in python and in c (for accelerated computations); galpy functions, objects, and methods can generally take arbitrary combinations of these as arguments. numerical orbit integration is supported with a variety of runge-kutta-type and symplectic integrators. for planar orbits, integration of the phase-space volume is also possible. galpy supports the calculation of action-angle coordinates and orbital frequencies for a given phase-space point for general spherical potentials, using state-of-the-art numerical approximations for axisymmetric potentials, and making use of a recent general approximation for any static potential. a number of different distribution functions (dfs) are also included in the current release; currently, these consist of two-dimensional axisymmetric and non-axisymmetric disk dfs, a three-dimensional disk df, and a df framework for tidal streams. i provide several examples to illustrate the use of the code. i present a simple model for the milky way's gravitational potential consistent with the latest observations. i also numerically calculate the oort functions for different tracer populations of stars and compare them to a new analytical approximation. additionally, i characterize the response of a kinematically warm disk to an elliptical m = 2 perturbation in detail. overall, galpy consists of about 54,000 lines, including 23,000 lines of code in the module, 11,000 lines of test code, and about 20,000 lines of documentation. the test suite covers 99.6% of the code. galpy is available at http://github.com/jobovy/galpy with extensive documentation available at http://galpy.readthedocs.org/en/latest. | galpy: a python library for galactic dynamics |
recent developments in the theory of pure neutron matter and experiments concerning the symmetry energy of nuclear matter, coupled with recent measurements of high-mass neutron stars, now allow for relatively tight constraints on the equation of state of dense matter. we review how these constraints are formulated and describe the implications they have for neutron stars and core-collapse supernovae. we also examine thermal properties of dense matter, which are important for supernovae and neutron star mergers, but which cannot be nearly as well constrained at this time by experiment. in addition, we consider the role of the equation of state in medium-energy heavy-ion collisions. | the equation of state of hot, dense matter and neutron stars |
sdss-v will be an all-sky, multi-epoch spectroscopic survey of over six million objects. it is designed to decode the history of the milky way, trace the emergence of the chemical elements, reveal the inner workings of stars, and investigate the origin of planets. it will also create an integral-field spectroscopic map of the gas in the galaxy and the local group that is 1,000x larger than the current state of the art and at high enough spatial resolution to reveal the self-regulation mechanisms of galactic ecosystems. sdss-v will pioneer systematic, spectroscopic monitoring across the whole sky, revealing changes on timescales from 20 minutes to 20 years. the survey will thus track the flickers, flares, and radical transformations of the most luminous persistent objects in the universe: massive black holes growing at the centers of galaxies. the scope and flexibility of sdss-v will be unique among extant and future spectroscopic surveys: it is all-sky, with matched survey infrastructures in both hemispheres; it provides near-ir and optical multi-object fiber spectroscopy that is rapidly reconfigurable to serve high target densities, targets of opportunity, and time-domain monitoring; and it provides optical, ultra-wide-field integral field spectroscopy. sdss-v, with its programs anticipated to start in 2020, will be well-timed to multiply the scientific output from major space missions (e.g., tess, gaia, erosita) and ground-based projects. sdss-v builds on the 25-year heritage of sdss's advances in data analysis, collaboration infrastructure, and product deliverables. the project is now refining its science scope, optimizing the survey strategies, and developing new hardware that builds on the sdss-iv infrastructure. we present here an overview of the current state of these developments as we seek to build our worldwide consortium of institutional and individual members. | sdss-v: pioneering panoptic spectroscopy |
the theory governing the strong nuclear force—quantum chromodynamics—predicts that at sufficiently high energy densities, hadronic nuclear matter undergoes a deconfinement transition to a new phase of quarks and gluons1. although this has been observed in ultrarelativistic heavy-ion collisions2,3, it is currently an open question whether quark matter exists inside neutron stars4. by combining astrophysical observations and theoretical ab initio calculations in a model-independent way, we find that the inferred properties of matter in the cores of neutron stars with mass corresponding to 1.4 solar masses (m⊙) are compatible with nuclear model calculations. however, the matter in the interior of maximally massive stable neutron stars exhibits characteristics of the deconfined phase, which we interpret as evidence for the presence of quark-matter cores. for the heaviest reliably observed neutron stars5,6 with mass m ≈ 2m⊙, the presence of quark matter is found to be linked to the behaviour of the speed of sound cs in strongly interacting matter. if the conformal bound cs2≤1 /3 ? (ref. 7) is not strongly violated, massive neutron stars are predicted to have sizable quark-matter cores. this finding has important implications for the phenomenology of neutron stars and affects the dynamics of neutron star mergers with at least one sufficiently massive participant. | evidence for quark-matter cores in massive neutron stars |
a review is given of various theoretical approaches for the equation of state (eos) of dense matter, relevant for the description of core-collapse supernovae, compact stars, and compact star mergers. the emphasis is put on models that are applicable to all of these scenarios. such eos models have to cover large ranges in baryon number density, temperature, and isospin asymmetry. the characteristics of matter change dramatically within these ranges, from a mixture of nucleons, nuclei, and electrons to uniform, strongly interacting matter containing nucleons, and possibly other particles such as hyperons or quarks. as the development of an eos requires joint efforts from many directions, different theoretical approaches are considered and relevant experimental and observational constraints which provide insights for future research are discussed. finally, results from applications of the discussed eos models are summarized. | equations of state for supernovae and compact stars |
we present a catalog of 717 candidate galaxies at $z > 8$ selected from 125 square arcminutes of nircam imaging as part of the jwst advanced deep extragalactic survey (jades). we combine the full jades imaging dataset with data from the jems and fresco jwst surveys along with extremely deep existing observations from hst/acs for a final filter set that includes fifteen jwst/nircam filters and five hst/acs filters. the high-redshift galaxy candidates were selected from their estimated photometric redshifts calculated using a template fitting approach, followed by visual inspection from seven independent reviewers. we explore these candidates in detail, highlighting interesting resolved or extended sources, sources with very red long-wavelength slopes, and our highest redshift candidates, which extend to $z_{phot} = 18$. we also investigate potential contamination by stellar objects, and do not find strong evidence from sed fitting that these faint high-redshift galaxy candidates are low-mass stars. over 93\% of the sources are newly identified from our deep jades imaging, including 31 new galaxy candidates at $z_{phot} > 12$. using 42 sources in our sample with measured spectroscopic redshifts from nirspec and fresco, we find excellent agreement to our photometric redshift estimates, with no catastrophic outliers and an average difference of $\langle \delta z = z_{phot}- z_{spec} \rangle= 0.26$. these sources comprise one of the most robust samples for probing the early buildup of galaxies within the first few hundred million years of the universe's history. | the cosmos in its infancy: jades galaxy candidates at z > 8 in goods-s and goods-n |
we combine electromagnetic (em) and gravitational-wave (gw) information on the binary neutron star (ns) merger gw170817 in order to constrain the radii {r}{ns} and maximum mass {m}\maxof nss. gw170817 was followed by a range of em counterparts, including a weak gamma-ray burst (grb), kilonova (kn) emission from the radioactive decay of the merger ejecta, and x-ray/radio emission consistent with being the synchrotron afterglow of a more powerful off-axis jet. the type of compact remnant produced in the immediate merger aftermath, and its predicted em signal, depend sensitively on the high-density ns equation of state (eos). for a soft eos that supports a low {m}\max , the merger undergoes a prompt collapse accompanied by a small quantity of shock-heated or disk-wind ejecta, inconsistent with the large quantity ≳ {10}-2 {m}⊙of lanthanide-free ejecta inferred from the kn. on the other hand, if {m}\maxis sufficiently large, then the merger product is a rapidly rotating supramassive ns (smns), which must spin down before collapsing into a black hole. a fraction of the enormous rotational energy necessarily released by the smns during this process is transferred to the ejecta, either into the grb jet (energy {e}{grb}) or the kn ejecta (energy {e}{ej}), also inconsistent with observations. by combining the total binary mass of gw170817 inferred from the gw signal with conservative upper limits on {e}{grb} and {e}{ej} from em observations, we constrain the likelihood probability of a wide range of previously allowed eoss. these two constraints delineate an allowed region of the {m}\max {--}{r}{ns} parameter space, which, once marginalized over ns radius, places an upper limit of {m}\max ≲ 2.17 {m}⊙(90%), which is tighter or arguably less model-dependent than other current constraints. | constraining the maximum mass of neutron stars from multi-messenger observations of gw170817 |
we present uv, optical, and near-infrared (nir) photometry of the first electromagnetic counterpart to a gravitational wave source from advanced laser interferometer gravitational-wave observatory (ligo)/virgo, the binary neutron star merger gw170817. our data set extends from the discovery of the optical counterpart at 0.47-18.5 days post-merger, and includes observations with the dark energy camera (decam), gemini-south/flamingos-2 (gs/f2), and the hubble space telescope (hst). the spectral energy distribution (sed) inferred from this photometry at 0.6 days is well described by a blackbody model with t≈ 8300 k, a radius of r≈ 4.5× {10}14 cm (corresponding to an expansion velocity of v≈ 0.3c), and a bolometric luminosity of {l}{bol}≈ 5× {10}41 erg s-1. at 1.5 days we find a multi-component sed across the optical and nir, and subsequently we observe rapid fading in the uv and blue optical bands and significant reddening of the optical/nir colors. modeling the entire data set, we find that models with heating from radioactive decay of 56ni, or those with only a single component of opacity from r-process elements, fail to capture the rapid optical decline and red optical/nir colors. instead, models with two components consistent with lanthanide-poor and lanthanide-rich ejecta provide a good fit to the data; the resulting “blue” component has {m}{ej}{blue}≈ 0.01 {m}⊙and {v}{ej}{blue}≈ 0.3 {{c}}, and the “red” component has {m}{ej}{red}≈ 0.04 {m}⊙and {v}{ej}{red}≈ 0.1 {{c}}. these ejecta masses are broadly consistent with the estimated r-process production rate required to explain the milky way r-process abundances, providing the first evidence that binary neutron star (bns) mergers can be a dominant site of r-process enrichment. | the electromagnetic counterpart of the binary neutron star merger ligo/virgo gw170817. ii. uv, optical, and near-infrared light curves and comparison to kilonova models |
the mergers of binary compact objects such as neutron stars and black holes are of central interest to several areas of astrophysics, including as the progenitors of gamma-ray bursts (grbs), sources of high-frequency gravitational waves and likely production sites for heavy element nucleosynthesis via rapid neutron capture (the r-process). these heavy elements include some of great geophysical, biological and cultural importance, such as thorium, iodine and gold. here we present observations of the exceptionally bright gamma-ray burst grb 230307a. we show that grb 230307a belongs to the class of long-duration gamma-ray bursts associated with compact object mergers, and contains a kilonova similar to at2017gfo, associated with the gravitational-wave merger gw170817. we obtained james webb space telescope mid-infrared (mid-ir) imaging and spectroscopy 29 and 61 days after the burst. the spectroscopy shows an emission line at 2.15 microns which we interpret as tellurium (atomic mass a=130), and a very red source, emitting most of its light in the mid-ir due to the production of lanthanides. these observations demonstrate that nucleosynthesis in grbs can create r-process elements across a broad atomic mass range and play a central role in heavy element nucleosynthesis across the universe. | jwst detection of heavy neutron capture elements in a compact object merger |
we report on the discovery of two low-luminosity, broad-line active galactic nuclei (agns) at z > 5 identified using jwst nirspec spectroscopy from the cosmic evolution early release science (ceers) survey. we detect broad hα emission in the spectra of both sources, with fwhm of 2060 ± 290 km s-1 and 1800 ± 200 km s-1, resulting in virial black hole (bh) masses that are 1-2 dex below those of existing samples of luminous quasars at z > 5. the first source, ceers 2782 at z = 5.242, is 2-3 dex fainter than known quasars at similar redshifts and was previously identified as a candidate low-luminosity agn based on its morphology and rest-frame optical spectral energy distribution (sed). we measure a bh mass of m bh = (1.3 ± 0.4) × 107 m ⊙, confirming that this agn is powered by the least massive bh known in the universe at the end of cosmic reionization. the second source, ceers 746 at z = 5.624, is inferred to be a heavily obscured, broad-line agn caught in a transition phase between a dust-obscured starburst and an unobscured quasar. we estimate its bh mass to be in the range of m bh ≃ (0.9-4.7) × 107 m ⊙, depending on the level of dust obscuration assumed. we perform sed fitting to derive host stellar masses, m ⋆, allowing us to place constraints on the bh-galaxy mass relationship in the lowest mass range yet probed in the early universe. the m bh/m ⋆ ratio for ceers 2782, in particular, is consistent with or higher than the empirical relationship seen in massive galaxies at z = 0. we examine the narrow emission line ratios of both sources and find that their location on the bpt and ohno diagrams is consistent with model predictions for moderately low metallicity agns with z/z ⊙ ≃ 0.2-0.4. the spectroscopic identification of low-luminosity, broad-line agns at z > 5 with m bh ≃ 107 m ⊙ demonstrates the capability of jwst to push bh masses closer to the range predicted for the bh seed population and provides a unique opportunity to study the early stages of bh-galaxy assembly. | hidden little monsters: spectroscopic identification of low-mass, broad-line agns at z > 5 with ceers |
we present the first statistical sample of faint type 1 agns at z > 4 identified by jwst/nirspec deep spectroscopy. among the 185 galaxies at z spec = 3.8-8.9 confirmed with nirspec, our systematic search for broad-line emission reveals 10 type 1 agns at z = 4.015-6.936 whose broad component is only seen in the permitted hα line and not in the forbidden [o iii]λ5007 line that is detected with greater significance than hα. the broad hα line widths of fwhm ≃ 1000-6000 km s-1 suggest that the agns have low-mass black holes with m bh ~ 106-108 m ⊙, remarkably lower than those of low-luminosity quasars previously identified at z > 4 with ground-based telescopes. jwst and hubble space telescope high-resolution images reveal that the majority of them show extended morphologies indicating significant contribution to the total lights from their host galaxies, except for three compact objects two of which show red spectral energy distributions, probably in a transition phase from faint agns to low luminosity quasars. careful agn-host decomposition analyses show that their host's stellar masses are systematically lower than the local relation between the black hole mass and the stellar mass, implying a fast black hole growth consistent with predictions from theoretical simulations. a high fraction of the broad-line agns (~5%), higher than z ~ 0, indicates that the number density of such faint agns is higher than an extrapolation of the quasar luminosity function, implying a large population of agns in the early universe. such faint agns contribute to cosmic reionization, while the total contribution is not large, up to ~50% at z ~ 6, because of their faint nature. | a jwst/nirspec first census of broad-line agns at z = 4-7: detection of 10 faint agns with m bh 106-108 m ⊙ and their host galaxy properties |
context. the second gaia data release (gaia dr2) provides precise five-parameter astrometric data (positions, proper motions, and parallaxes) for an unprecedented number of sources (more than 1.3 billion, mostly stars). this new wealth of data will enable the undertaking of statistical analysis of many astrophysical problems that were previously infeasible for lack of reliable astrometry, and in particular because of the lack of parallaxes. however, the use of this wealth of astrometric data comes with a specific challenge: how can the astrophysical parameters of interest be properly inferred from these data?aims: the main focus of this paper, but not the only focus, is the issue of the estimation of distances from parallaxes, possibly combined with other information. we start with a critical review of the methods traditionally used to obtain distances from parallaxes and their shortcomings. then we provide guidelines on how to use parallaxes more efficiently to estimate distances by using bayesian methods. in particular we also show that negative parallaxes, or parallaxes with relatively large uncertainties still contain valuable information. finally, we provide examples that show more generally how to use astrometric data for parameter estimation, including the combination of proper motions and parallaxes and the handling of covariances in the uncertainties.methods: the paper contains examples based on simulated gaia data to illustrate the problems and the solutions proposed. furthermore, the developments and methods proposed in the paper are linked to a set of tutorials included in the gaia archive documentation that provide practical examples and a good starting point for the application of the recommendations to actual problems. in all cases the source code for the analysis methods is provided.results: our main recommendation is to always treat the derivation of (astro-)physical parameters from astrometric data, in particular when parallaxes are involved, as an inference problem which should preferably be handled with a full bayesian approach.conclusions: gaia will provide fundamental data for many fields of astronomy. further data releases will provide more data, and more precise data. nevertheless, to fully use the potential it will always be necessary to pay careful attention to the statistical treatment of parallaxes and proper motions. the purpose of this paper is to help astronomers find the correct approach. | gaia data release 2. using gaia parallaxes |
the zwicky transient facility (ztf), a public-private enterprise, is a new time-domain survey employing a dedicated camera on the palomar 48-inch schmidt telescope with a 47 deg2 field of view and an 8 second readout time. it is well positioned in the development of time-domain astronomy, offering operations at 10% of the scale and style of the large synoptic survey telescope (lsst) with a single 1-m class survey telescope. the public surveys will cover the observable northern sky every three nights in g and r filters and the visible galactic plane every night in g and r. alerts generated by these surveys are sent in real time to brokers. a consortium of universities that provided funding (“partnership”) are undertaking several boutique surveys. the combination of these surveys producing one million alerts per night allows for exploration of transient and variable astrophysical phenomena brighter than r ∼ 20.5 on timescales of minutes to years. we describe the primary science objectives driving ztf, including the physics of supernovae and relativistic explosions, multi-messenger astrophysics, supernova cosmology, active galactic nuclei, and tidal disruption events, stellar variability, and solar system objects. | the zwicky transient facility: science objectives |
neutrinos play a crucial role in the collapse and explosion of massive stars, governing the infall dynamics of the stellar core, triggering and fueling the explosion and driving the cooling and deleptonization of the newly formed neutron star. due to their role neutrinos carry information from the heart of the explosion and, due to their weakly interacting nature, offer the only direct probe of the dynamics and thermodynamics at the center of a supernova. in this paper, we review the present status of modelling the neutrino physics and signal formation in collapsing and exploding stars. we assess the capability of current and planned large underground neutrino detectors to yield faithful information of the time and flavor-dependent neutrino signal from a future galactic supernova. we show how the observable neutrino burst would provide a benchmark for fundamental supernova physics with unprecedented richness of detail. exploiting the treasure of the measured neutrino events requires a careful discrimination of source-generated properties from signal features that originate on the way to the detector. as for the latter, we discuss self-induced flavor conversions associated with neutrino-neutrino interactions that occur in the deepest stellar regions; matter effects that modify the pattern of flavor conversions in the dynamical stellar envelope; neutrino-oscillation signatures that result from structural features associated with the shock-wave propagation as well as turbulent mass motions in post-shock layers. finally, we highlight our current understanding of the formation of the diffuse supernova neutrino background and we analyse the perspectives for a detection of this relic signal that integrates the contributions from all past core-collapse supernovae in the universe. | supernova neutrinos: production, oscillations and detection |
we present a reduction and analysis of the james webb space telescope (jwst) smacs 0723 field using new post-launch calibrations to conduct a search for ultra-high-redshift galaxies (z > 9) present within the epoch of reionization. we conduct this search by modelling photometric redshifts in several ways for all sources and by applying conservative magnitude cuts (mf200w < 28) to identify strong lyman breaks greater than 1 mag. we find four z > 9 candidate galaxies which have not previously been identified, with one object at z = 11.5, and another which is possibly a close pair of galaxies. we measure redshifts for candidate galaxies from other studies and find the recovery rate to be only 23 per cent, with many being assigned lower redshift, dusty solutions in our work. most of our z > 9 sample show evidence for balmer-breaks, or extreme emission lines from h β and [o iii], demonstrating that the stellar populations could be advanced in age or very young depending on the cause of the f444w excess. we discuss the resolved structures of these early galaxies and find that the sérsic indices reveal a mixture of light concentration levels, but that the sizes of all our systems are exceptionally small (<0.5 kpc). these systems have stellar masses m* ~ 109.0 m⊙, with our z ~ 11.5 candidate a dwarf galaxy with a stellar mass m* ~ 107.8-108.2 m⊙. these candidate ultra high-redshift galaxies are excellent targets for future nirspec observations aimed to better understand their physical nature. | discovery and properties of ultra-high redshift galaxies (9 < z < 12) in the jwst ero smacs 0723 field |
the gas surrounding galaxies outside their disks or interstellar medium and inside their virial radii is known as the circumgalactic medium (cgm). in recent years this component of galaxies has assumed an important role in our understanding of galaxy evolution owing to rapid advances in observational access to this diffuse, nearly invisible material. observations and simulations of this component of galaxies suggest that it is a multiphase medium characterized by rich dynamics and complex ionization states. the cgm is a source for a galaxy's star-forming fuel, the venue for galactic feedback and recycling, and perhaps the key regulator of the galactic gas supply. we review our evolving knowledge of the cgm with emphasis on its mass, dynamical state, and coevolution with galaxies. observations from all redshifts and from across the electromagnetic spectrum indicate that cgm gas has a key role in galaxy evolution. we summarize the state of this field and pose unanswered questions for future research. | the circumgalactic medium |
the detection of an electromagnetic counterpart (grb 170817a) to the gravitational-wave signal (gw170817) from the merger of two neutron stars opens a completely new arena for testing theories of gravity. we show that this measurement allows us to place stringent constraints on general scalar-tensor and vector-tensor theories, while allowing us to place an independent bound on the graviton mass in bimetric theories of gravity. these constraints severely reduce the viable range of cosmological models that have been proposed as alternatives to general relativistic cosmology. | strong constraints on cosmological gravity from gw170817 and grb 170817a |
the merger of two neutron stars is predicted to give rise to three major detectable phenomena: a short burst of γ-rays, a gravitational-wave signal, and a transient optical-near-infrared source powered by the synthesis of large amounts of very heavy elements via rapid neutron capture (the r-process). such transients, named ‘macronovae’ or ‘kilonovae’, are believed to be centres of production of rare elements such as gold and platinum. the most compelling evidence so far for a kilonova was a very faint near-infrared rebrightening in the afterglow of a short γ-ray burst at redshift z = 0.356, although findings indicating bluer events have been reported. here we report the spectral identification and describe the physical properties of a bright kilonova associated with the gravitational-wave source gw170817 and γ-ray burst grb 170817a associated with a galaxy at a distance of 40 megaparsecs from earth. using a series of spectra from ground-based observatories covering the wavelength range from the ultraviolet to the near-infrared, we find that the kilonova is characterized by rapidly expanding ejecta with spectral features similar to those predicted by current models. the ejecta is optically thick early on, with a velocity of about 0.2 times light speed, and reaches a radius of about 50 astronomical units in only 1.5 days. as the ejecta expands, broad absorption-like lines appear on the spectral continuum, indicating atomic species produced by nucleosynthesis that occurs in the post-merger fast-moving dynamical ejecta and in two slower (0.05 times light speed) wind regions. comparison with spectral models suggests that the merger ejected 0.03 to 0.05 solar masses of material, including high-opacity lanthanides. | spectroscopic identification of r-process nucleosynthesis in a double neutron-star merger |
we report the international gamma-ray astrophysics laboratory (integral) detection of the short gamma-ray burst grb 170817a (discovered by fermi-gbm) with a signal-to-noise ratio of 4.6, and, for the first time, its association with the gravitational waves (gws) from binary neutron star (bns) merging event gw170817 detected by the ligo and virgo observatories. the significance of association between the gamma-ray burst observed by integral and gw170817 is 3.2σ, while the association between the fermi-gbm and integral detections is 4.2σ. grb 170817a was detected by the spi-acs instrument about 2 s after the end of the gw event. we measure a fluence of (1.4 ± 0.4 ± 0.6) × 10-7 erg cm-2 (75-2000 kev), where, respectively, the statistical error is given at the 1σ confidence level, and the systematic error corresponds to the uncertainty in the spectral model and instrument response. we also report on the pointed follow-up observations carried out by integral, starting 19.5 hr after the event, and lasting for 5.4 days. we provide a stringent upper limit on any electromagnetic signal in a very broad energy range, from 3 kev to 8 mev, constraining the soft gamma-ray afterglow flux to <7.1 × 10-11 erg cm-2 s-1 (80-300 kev). exploiting the unique capabilities of integral, we constrained the gamma-ray line emission from radioactive decays that are expected to be the principal source of the energy behind a kilonova event following a bns coalescence. finally, we put a stringent upper limit on any delayed bursting activity, for example, from a newly formed magnetar. | integral detection of the first prompt gamma-ray signal coincident with the gravitational-wave event gw170817 |
in our modern understanding of galaxy formation, every galaxy forms within a dark matter halo. the formation and growth of galaxies over time is connected to the growth of the halos in which they form. the advent of large galaxy surveys as well as high-resolution cosmological simulations has provided a new window into the statistical relationship between galaxies and halos and its evolution. here, we define this galaxy-halo connection as the multivariate distribution of galaxy and halo properties that can be derived from observations and simulations. this galaxy-halo connection provides a key test of physical galaxy-formation models; it also plays an essential role in constraints of cosmological models using galaxy surveys and in elucidating the properties of dark matter using galaxies. we review techniques for inferring the galaxy-halo connection and the insights that have arisen from these approaches. some things we have learned are that galaxy-formation efficiency is a strong function of halo mass; at its peak in halos around a pivot halo mass of 1012m⊙, less than 20% of the available baryons have turned into stars by the present day; the intrinsic scatter in galaxy stellar mass is small, less than 0.2 dex at a given halo mass above this pivot mass; below this pivot mass galaxy stellar mass is a strong function of halo mass; the majority of stars over cosmic time were formed in a narrow region around this pivot mass. we also highlight key open questions about how galaxies and halos are connected, including understanding the correlations with secondary properties and the connection of these properties to galaxy clustering. | the connection between galaxies and their dark matter halos |
to reach a deeper understanding of the origin of elements in the periodic table, we construct galactic chemical evolution (gce) models for all stable elements from c (a = 12) to u (a = 238) from first principles, i.e., using theoretical nucleosynthesis yields and event rates of all chemical enrichment sources. this enables us to predict the origin of elements as a function of time and environment. in the solar neighborhood, we find that stars with initial masses of m > 30m⊙ can become failed supernovae if there is a significant contribution from hypernovae (hne) at m ∼ 20-50m⊙. the contribution to gce from super-asymptotic giant branch (agb) stars (with m ∼ 8-10m⊙ at solar metallicity) is negligible, unless hybrid white dwarfs from low-mass super-agb stars explode as so-called type iax supernovae, or high-mass super-agb stars explode as electron-capture supernovae (ecsne). among neutron-capture elements, the observed abundances of the second (ba) and third (pb) peak elements are well reproduced with our updated yields of the slow neutron-capture process (s-process) from agb stars. the first peak elements (sr, y, zr) are sufficiently produced by ecsne together with agb stars. neutron star mergers can produce rapid neutron-capture process (r-process) elements up to th and u, but the timescales are too long to explain observations at low metallicities. the observed evolutionary trends, such as for eu, can well be explained if ∼3% of 25-50m⊙ hne are magneto-rotational supernovae producing r-process elements. along with the solar neighborhood, we also predict the evolutionary trends in the halo, bulge, and thick disk for future comparison with galactic archeology surveys. | the origin of elements from carbon to uranium |
context. the chemical composition of the sun is a fundamental yardstick in astronomy, relative to which essentially all cosmic objects are referenced. as such, having accurate knowledge of the solar elemental abundances is crucial for an extremely broad range of topics.aims: we reassess the solar abundances of all 83 long-lived elements, using highly realistic solar modelling and state-of-the-art spectroscopic analysis techniques coupled with the best available atomic data and observations.methods: the basis for our solar spectroscopic analysis is a three-dimensional (3d) radiative-hydrodynamical model of the solar surface convection and atmosphere, which reproduces the full arsenal of key observational diagnostics. new complete and comprehensive 3d spectral line formation calculations taking into account of departures from local thermodynamic equilibrium (non-lte) are presented for na, mg, k, ca, and fe using comprehensive model atoms with reliable radiative and collisional data. our newly derived abundances for c, n, and o are based on a 3d non-lte analysis of permitted and forbidden atomic lines as well as 3d lte calculations for a total of 879 molecular transitions of ch, c2, co, nh, cn, and oh. previous 3d-based calculations for another 50 elements are re-evaluated based on updated atomic data, a stringent selection of lines, improved consideration of blends, and new non-lte calculations available in the literature. for elements where spectroscopic determinations of the quiet sun are not possible, the recommended solar abundances are revisited based on complementary methods, including helioseismology (he), solar wind data from the genesis sample return mission (noble gases), sunspot observations (four elements), and measurements of the most primitive meteorites (15 elements).results: our new improved analysis confirms the relatively low solar abundances of c, n, and o obtained in our previous 3d-based studies: log ϵc = 8.46 ± 0.04, log ϵn = 7.83 ± 0.07, and log ϵo = 8.69 ± 0.04. excellent agreement between all available atomic and molecular indicators is achieved for c and o, but for n the atomic lines imply a lower abundance than for the molecular transitions for unknown reasons. the revised solar abundances for the other elements also typically agree well with our previously recommended values, with only li, f, ne, mg, cl, kr, rb, rh, ba, w, ir, and pb differing by more than 0.05 dex. the here-advocated present-day photospheric metal mass fraction is only slightly higher than our previous value, mainly due to the revised ne abundance from genesis solar wind measurements: xsurface = 0.7438 ± 0.0054, ysurface = 0.2423 ± 0.0054, zsurface = 0.0139 ± 0.0006, and zsurface/xsurface = 0.0187 ± 0.0009. overall, the solar abundances agree well with those of ci chondritic meteorites, but we identify a correlation with condensation temperature such that moderately volatile elements are enhanced by ≈0.04 dex in the ci chondrites and refractory elements possibly depleted by ≈0.02 dex, conflicting with conventional wisdom of the past half-century. instead, the solar chemical composition more closely resembles that of the fine-grained matrix of cm chondrites with the expected exception of the highly volatile elements.conclusions: updated present-day solar photospheric and proto-solar abundances are presented for 83 elements, including for all long-lived isotopes. the so-called solar modelling problem - a persistent discrepancy between helioseismology and solar interior models constructed with a low solar metallicity similar to that advocated here - remains intact with our revised solar abundances, suggesting shortcomings with the computed opacities and/or treatment of mixing below the convection zone in existing standard solar models. the uncovered trend between the solar and ci chondritic abundances with condensation temperature is not yet understood but is likely imprinted by planet formation, especially since a similar trend of opposite sign is observed between the sun and solar twins. | the chemical make-up of the sun: a 2020 vision |
nucleosynthesis, light curves, explosion energies, and remnant masses are calculated for a grid of supernovae (sne) resulting from massive stars with solar metallicity and masses from 9.0 to 120 {m}⊙ . the full evolution is followed using an adaptive reaction network of up to 2000 nuclei. a novel aspect of the survey is the use of a one-dimensional neutrino transport model for the explosion. this explosion model has been calibrated to give the observed energy for sn 1987a, using five standard progenitors, and for the crab sn using a 9.6 {m}⊙progenitor. as a result of using a calibrated central engine, the final kinetic energy of the sn is variable and sensitive to the structure of each pre-sn star. many progenitors with extended core structures do not explode, but become black holes (bhs), and the masses of exploding stars do not form a simply connected set. the resulting nucleosynthesis agrees reasonably well with the sun provided that a reasonable contribution from sne ia is also allowed, but with a deficiency of light s-process isotopes. the resulting neutron star initial mass function has a mean gravitational mass near 1.4 {m}⊙ . the average bh mass is about 9 {m}⊙if only the helium core implodes, and 14 {m}⊙if the entire pre-sn star collapses. only ∼10% of sne come from stars over 20 {m}⊙ , and some of these are type ib or ic. some useful systematics of type iip light curves are explored. | core-collapse supernovae from 9 to 120 solar masses based on neutrino-powered explosions |
we present a new model for the distribution of free electrons in the galaxy, the magellanic clouds, and the intergalactic medium (igm) that can be used to estimate distances to real or simulated pulsars and fast radio bursts (frbs) based on their dispersion measure (dm). the galactic model has an extended thick disk representing the so-called warm interstellar medium, a thin disk representing the galactic molecular ring, spiral arms based on a recent fit to galactic h ii regions, a galactic center disk, and seven local features including the gum nebula, galactic loop i, and the local bubble. an offset of the sun from the galactic plane and a warp of the outer galactic disk are included in the model. parameters of the galactic model are determined by fitting to 189 pulsars with independently determined distances and dms. simple models are used for the magellanic clouds and the igm. galactic model distances are within the uncertainty range for 86 of the 189 independently determined distances and within 20% of the nearest limit for a further 38 pulsars. we estimate that 95% of predicted galactic pulsar distances will have a relative error of less than a factor of 0.9. the predictions of ymw16 are compared to those of the tc93 and ne2001 models showing that ymw16 performs significantly better on all measures. timescales for pulse broadening due to interstellar scattering are estimated for (real or simulated) galactic and magellanic cloud pulsars and frbs. | a new electron-density model for estimation of pulsar and frb distances |
surveys with the james webb space telescope (jwst) have discovered candidate galaxies in the first 400 myr of cosmic time. preliminary indications have suggested these candidate galaxies may be more massive and abundant than previously thought. however, without confirmed distances, their inferred properties remain uncertain. here we identify four galaxies located in the jwst advanced deep extragalactic survey near-infrared camera imaging with photometric redshifts z of roughly 10-13. these galaxies include the first redshift z > 12 systems discovered with distances spectroscopically confirmed by jwst in a companion paper. using stellar population modelling, we find the galaxies typically contain 100 million solar masses in stars, in stellar populations that are less than 100 million years old. the moderate star-formation rates and compact sizes suggest elevated star-formation rate surface densities, a key indicator of their formation pathways. taken together, these measurements show that the first galaxies contributing to cosmic reionization formed rapidly and with intense internal radiation fields. | identification and properties of intense star-forming galaxies at redshifts z > 10 |
we describe the first public data release of the dark energy survey, des dr1, consisting of reduced single-epoch images, co-added images, co-added source catalogs, and associated products and services assembled over the first 3 yr of des science operations. des dr1 is based on optical/near-infrared imaging from 345 distinct nights (2013 august to 2016 february) by the dark energy camera mounted on the 4 m blanco telescope at the cerro tololo inter-american observatory in chile. we release data from the des wide-area survey covering ∼5000 deg2 of the southern galactic cap in five broad photometric bands, grizy. des dr1 has a median delivered point-spread function of g=1.12, r = 0.96, i = 0.88, z = 0.84, and y = 0.″90 fwhm, a photometric precision of <1% in all bands, and an astrometric precision of 151 {mas}. the median co-added catalog depth for a 1.″95 diameter aperture at signal-to-noise ratio (s/n) = 10 is g = 24.33, r = 24.08, i = 23.44, z = 22.69, and y = 21.44 {mag} . des dr1 includes nearly 400 million distinct astronomical objects detected in ∼10,000 co-add tiles of size 0.534 deg2 produced from ∼39,000 individual exposures. benchmark galaxy and stellar samples contain ∼310 million and ∼80 million objects, respectively, following a basic object quality selection. these data are accessible through a range of interfaces, including query web clients, image cutout servers, jupyter notebooks, and an interactive co-add image visualization tool. des dr1 constitutes the largest photometric data set to date at the achieved depth and photometric precision. | the dark energy survey: data release 1 |
we introduce a new generation of parsec-colibri stellar isochrones that includes a detailed treatment of the thermally pulsing asymptotic giant branch (tp-agb) phase, covering a wide range of initial metallicities (0.0001 < zi < 0.06). compared to previous releases, the main novelties and improvements are use of new tp-agb tracks and related atmosphere models and spectra for m and c-type stars; inclusion of the surface h+he+cno abundances in the isochrone tables, accounting for the effects of diffusion, dredge-up episodes and hot-bottom burning; inclusion of complete thermal pulse cycles, with a complete description of the in-cycle changes in the stellar parameters; new pulsation models to describe the long-period variability in the fundamental and first-overtone modes; and new dust models that follow the growth of the grains during the agb evolution, in combination with radiative transfer calculations for the reprocessing of the photospheric emission. overall, these improvements are expected to lead to a more consistent and detailed description of properties of tp-agb stars expected in resolved stellar populations, especially in regard to their mean photometric properties from optical to mid-infrared wavelengths. we illustrate the expected numbers of tp-agb stars of different types in stellar populations covering a wide range of ages and initial metallicities, providing further details on the “c-star island” that appears at intermediate values of age and metallicity, and about the agb-boosting effect that occurs at ages close to 1.6-gyr for populations of all metallicities. the isochrones are available through a new dedicated web server. | a new generation of parsec-colibri stellar isochrones including the tp-agb phase |
the binary population and spectral synthesis suite of binary stellar evolution models and synthetic stellar populations provides a framework for the physically motivated analysis of both the integrated light from distant stellar populations and the detailed properties of those nearby. we present a new version 2.1 data release of these models, detailing the methodology by which binary population and spectral synthesis incorporates binary mass transfer and its effect on stellar evolution pathways, as well as the construction of simple stellar populations. we demonstrate key tests of the latest binary population and spectral synthesis model suite demonstrating its ability to reproduce the colours and derived properties of resolved stellar populations, including well-constrained eclipsing binaries. we consider observational constraints on the ratio of massive star types and the distribution of stellar remnant masses. we describe the identification of supernova progenitors in our models, and demonstrate a good agreement to the properties of observed progenitors. we also test our models against photometric and spectroscopic observations of unresolved stellar populations, both in the local and distant universe, finding that binary models provide a self-consistent explanation for observed galaxy properties across a broad redshift range. finally, we carefully describe the limitations of our models, and areas where we expect to see significant improvement in future versions. | binary population and spectral synthesis version 2.1: construction, observational verification, and new results |
we present the first event horizon telescope (eht) observations of sagittarius a* (sgr a$^*$), the galactic center source associated with a supermassive black hole. these observations were conducted in 2017 using a global interferometric array of eight telescopes operating at a wavelength of $\lambda=1.3\,{\rm mm}$. the eht data resolve a compact emission region with intrahour variability. a variety of imaging and modeling analyses all support an image that is dominated by a bright, thick ring with a diameter of $51.8 \pm 2.3$\,\uas (68\% credible interval). the ring has modest azimuthal brightness asymmetry and a comparatively dim interior. using a large suite of numerical simulations, we demonstrate that the eht images of sgr a$^*$ are consistent with the expected appearance of a kerr black hole with mass ${\sim}4 \times 10^6\,{\rm m}_\odot$, which is inferred to exist at this location based on previous infrared observations of individual stellar orbits as well as maser proper motion studies. our model comparisons disfavor scenarios where the black hole is viewed at high inclination ($i > 50^\circ$), as well as non-spinning black holes and those with retrograde accretion disks. our results provide direct evidence for the presence of a supermassive black hole at the center of the milky way galaxy, and for the first time we connect the predictions from dynamical measurements of stellar orbits on scales of $10^3-10^5$ gravitational radii to event horizon-scale images and variability. furthermore, a comparison with the eht results for the supermassive black hole m87$^*$ shows consistency with the predictions of general relativity spanning over three orders of magnitude in central mass. | first sagittarius a* event horizon telescope results. i. the shadow of the supermassive black hole in the center of the milky way |
a long-standing paradigm in astrophysics is that collisions—or mergers—of two neutron stars form highly relativistic and collimated outflows (jets) that power γ-ray bursts of short (less than two seconds) duration. the observational support for this model, however, is only indirect. a hitherto outstanding prediction is that gravitational-wave events from such mergers should be associated with γ-ray bursts, and that a majority of these bursts should be seen off-axis, that is, they should point away from earth. here we report the discovery observations of the x-ray counterpart associated with the gravitational-wave event gw170817. although the electromagnetic counterpart at optical and infrared frequencies is dominated by the radioactive glow (known as a ‘kilonova’) from freshly synthesized rapid neutron capture (r-process) material in the merger ejecta, observations at x-ray and, later, radio frequencies are consistent with a short γ-ray burst viewed off-axis. our detection of x-ray emission at a location coincident with the kilonova transient provides the missing observational link between short γ-ray bursts and gravitational waves from neutron-star mergers, and gives independent confirmation of the collimated nature of the γ-ray-burst emission. | the x-ray counterpart to the gravitational-wave event gw170817 |
context. open clusters are convenient probes of the structure and history of the galactic disk. they are also fundamental to stellar evolution studies. the second gaia data release contains precise astrometry at the submilliarcsecond level and homogeneous photometry at the mmag level, that can be used to characterise a large number of clusters over the entire sky.aims: in this study we aim to establish a list of members and derive mean parameters, in particular distances, for as many clusters as possible, making use of gaia data alone.methods: we compiled a list of thousands of known or putative clusters from the literature. we then applied an unsupervised membership assignment code, upmask, to the gaia dr2 data contained within the fields of those clusters.results: we obtained a list of members and cluster parameters for 1229 clusters. as expected, the youngest clusters are seen to be tightly distributed near the galactic plane and to trace the spiral arms of the milky way, while older objects are more uniformly distributed, deviate further from the plane, and tend to be located at larger galactocentric distances. thanks to the quality of gaia dr2 astrometry, the fully homogeneous parameters derived in this study are the most precise to date. furthermore, we report on the serendipitous discovery of 60 new open clusters in the fields analysed during this study. full table 1 is only available in electronic form at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?j/a+a/618/a93 | a gaia dr2 view of the open cluster population in the milky way |
the recent discovery by advanced ligo and advanced virgo of a gravitational wave signal from a binary neutron star inspiral has enabled tests of general relativity (gr) with this new type of source. this source, for the first time, permits tests of strong-field dynamics of compact binaries in the presence of matter. in this letter, we place constraints on the dipole radiation and possible deviations from gr in the post-newtonian coefficients that govern the inspiral regime. bounds on modified dispersion of gravitational waves are obtained; in combination with information from the observed electromagnetic counterpart we can also constrain effects due to large extra dimensions. finally, the polarization content of the gravitational wave signal is studied. the results of all tests performed here show good agreement with gr. | tests of general relativity with gw170817 |
we review applications of string theory to cosmology, from primordial times to the present-day accelerated expansion. starting with a brief overview of cosmology and string compactifications, we discuss in detail moduli stabilisation, inflation in string theory, the impact of string theory on post-inflationary dynamics (reheating, moduli domination, kination), dark energy (the cosmological constant from a string landscape and models of quintessence) and various alternative scenarios (string/brane gases, the pre big-bang scenario, rolling tachyons, ekpyrotic/cyclic cosmologies, bubbles of nothing, s-brane and holographic cosmologies). the state of the art in string constructions is described in each topic and, where relevant, connections to swampland conjectures are made. the possibilities for novel particles and excitations (axions, moduli, cosmic strings, branes, solitons, oscillons and boson stars) are emphasised. implications for the physics of the cmb, gravitational waves, dark matter and dark radiation are discussed along with potential observational signatures. | string cosmology: from the early universe to today |
neutrino-neutrino refraction dominates the flavor evolution in core-collapse supernovae, neutron star mergers, and the early universe. ordinary neutrino flavor conversions develop on timescales determined by the vacuum oscillation frequency. however, when the neutrino density is large enough, collective flavor conversions may arise because of pairwise neutrino scattering. pairwise conversions are deemed fast because they are expected to occur on timescales that depend on the neutrino-neutrino interaction energy (i.e., on the neutrino number density) and are regulated by the angular distributions of electron neutrinos and antineutrinos. the enigmatic phenomenon of fast pairwise conversions has been overlooked for a long time. however, because of the fast conversion rate, pairwise conversions could occur in the proximity of the neutrino decoupling region with yet-to-be-understood implications for the hydrodynamics of astrophysical sources and the synthesis of the heavy elements. we review the physics of this fascinating phenomenon and its implications for neutrino-dense sources. | new developments in flavor evolution of a dense neutrino gas |
we present hubble space telescope (hst) photometry of a selected sample of 50 long-period, low-extinction milky way cepheids measured on the same wfc3 f555w-, f814w-, and f160w-band photometric system as extragalactic cepheids in type ia supernova host galaxies. these bright cepheids were observed with the wfc3 spatial scanning mode in the optical and near-infrared to mitigate saturation and reduce pixel-to-pixel calibration errors to reach a mean photometric error of 5 mmag per observation. we use the new gaia dr2 parallaxes and hst photometry to simultaneously constrain the cosmic distance scale and to measure the dr2 parallax zeropoint offset appropriate for cepheids. we find the latter to be -46 ± 13 μas or ±6 μas for a fixed distance scale, higher than found from quasars, as expected for these brighter and redder sources. the precision of the distance scale from dr2 has been reduced by a factor of 2.5 because of the need to independently determine the parallax offset. the best-fit distance scale is 1.006 ± 0.033, relative to the scale from riess et al. with h 0 = 73.24 km s-1 mpc-1 used to predict the parallaxes photometrically, and is inconsistent with the scale needed to match the planck 2016 cosmic microwave background data combined with λcdm at the 2.9σ confidence level (99.6%). at 96.5% confidence we find that the formal dr2 errors may be underestimated as indicated. we identify additional errors associated with the use of augmented cepheid samples utilizing ground-based photometry and discuss their likely origins. including the dr2 parallaxes with all prior distance-ladder data raises the current tension between the late and early universe route to the hubble constant to 3.8σ (99.99%). with the final expected precision from gaia, the sample of 50 cepheids with hst photometry will limit to 0.5% the contribution of the first rung of the distance ladder to the uncertainty in h 0. | milky way cepheid standards for measuring cosmic distances and application to gaia dr2: implications for the hubble constant |
we compile and analyze approximately 200 trigonometric parallaxes and proper motions of molecular masers associated with very young high-mass stars. most of the measurements come from the bessel survey using the vlba and the japanese vera project. these measurements strongly suggest that the milky way is a four-arm spiral, with some extra arm segments and spurs. fitting log-periodic spirals to the locations of the masers, allowing for “kinks” in the spirals and using well-established arm tangencies in the fourth galactic quadrant, allows us to significantly expand our view of the structure of the milky way. we present an updated model for its spiral structure and incorporate it into our previously published parallax-based distance-estimation program for sources associated with spiral arms. modeling the three-dimensional space motions yields estimates of the distance to the galactic center, {r}0=8.15+/- 0.15 {kpc}, the circular rotation speed at the sun's position, {{{\theta }}}0=236+/- 7 km s-1, and the nature of the rotation curve. our data strongly constrain the full circular velocity of the sun, {{{\theta }}}0+{v}⊙ =247+/- 4 km s-1, and its angular velocity, ({{{\theta }}}0+{v}⊙ )/{r}0=30.32+/- 0.27 km s-1 kpc-1. transforming the measured space motions to a galactocentric frame which rotates with the galaxy, we find non-circular velocity components typically ≲10 km s-1. however, near the galactic bar and in a portion of the perseus arm we find significantly larger non-circular motions. young high-mass stars within 7 kpc of the galactic center have a scale height of only 19 pc, and thus are well suited to define the galactic plane. we find that the orientation of the plane is consistent with the iau-defined plane to within ±0.°1, and that the sun is offset toward the north galactic pole by {z}⊙ =5.5+/- 5.8 pc. accounting for this offset places the central supermassive black hole, sgr a*, in the midplane of the galaxy. the measured motions perpendicular to the plane of the galaxy limit precession of the plane to ≲4 km s-1 at the radius of the sun. using our improved galactic parameters, we predict the hulse-taylor binary pulsar to be at a distance of 6.54 ± 0.24 kpc, assuming its orbital decay from gravitational radiation follows general relativity. | trigonometric parallaxes of high-mass star-forming regions: our view of the milky way |
reionization is thought to be driven by faint star-forming galaxies, but characterizing this population in detail has long remained very challenging. here we utilize deep nine-band nircam imaging from jades to study the star-forming and ionizing properties of 756 $z\sim6-9$ galaxies, including hundreds of very uv-faint objects ($m_\mathrm{uv}>-18$). the faintest ($m\sim30$) galaxies in our sample typically have stellar masses of $m_\ast\sim(1-3)\times10^7$ $m_\odot$ and young light-weighted ages ($\sim$50 myr), though some show strong balmer breaks implying much older ages ($\sim$500 myr). we find no evidence for extremely massive galaxies ($>3\times10^{10}$ $m_\odot$) in our sample. we infer a strong (factor $>$2) decline in the typical [oiii]$+$h$\beta$ ews towards very faint $z\sim6-9$ galaxies, yet a weak uv luminosity dependence on the h$\alpha$ ews at $z\sim6$. we demonstrate that these ew trends can be explained if fainter galaxies have systematically lower metallicities as well as more recently-declining star formation histories relative to the most uv-luminous galaxies in our sample. our data provide evidence that the brightest galaxies are frequently experiencing a recent strong upturn in sfr. we also discuss how the ew trends may be influenced by a strong correlation between $m_\mathrm{uv}$ and lyman continuum escape fraction. this alternative explanation has dramatically different implications for the contribution of galaxies along the luminosity function to cosmic reionization, highlighting the need for deep spectroscopic follow-up. finally, we quantify the photometric overdensities around two $z>7$ strong ly$\alpha$ emitters in the jades footprint. one ly$\alpha$ emitter lies close to a strong photometric overdensity while the other shows no significant nearby overdensity, perhaps implying that not all strong $z>7$ ly$\alpha$ emitters reside in large ionized bubbles. | the star-forming and ionizing properties of dwarf z~6-9 galaxies in jades: insights on bursty star formation and ionized bubble growth |
gravitational waves were discovered with the detection of binary black-hole mergers and they should also be detectable from lower-mass neutron-star mergers. these are predicted to eject material rich in heavy radioactive isotopes that can power an electromagnetic signal. this signal is luminous at optical and infrared wavelengths and is called a kilonova. the gravitational-wave source gw170817 arose from a binary neutron-star merger in the nearby universe with a relatively well confined sky position and distance estimate. here we report observations and physical modelling of a rapidly fading electromagnetic transient in the galaxy ngc 4993, which is spatially coincident with gw170817 and with a weak, short γ-ray burst. the transient has physical parameters that broadly match the theoretical predictions of blue kilonovae from neutron-star mergers. the emitted electromagnetic radiation can be explained with an ejected mass of 0.04 ± 0.01 solar masses, with an opacity of less than 0.5 square centimetres per gram, at a velocity of 0.2 ± 0.1 times light speed. the power source is constrained to have a power-law slope of -1.2 ± 0.3, consistent with radioactive powering from r-process nuclides. (the r-process is a series of neutron capture reactions that synthesise many of the elements heavier than iron.) we identify line features in the spectra that are consistent with light r-process elements (atomic masses of 90-140). as it fades, the transient rapidly becomes red, and a higher-opacity, lanthanide-rich ejecta component may contribute to the emission. this indicates that neutron-star mergers produce gravitational waves and radioactively powered kilonovae, and are a nucleosynthetic source of the r-process elements. | a kilonova as the electromagnetic counterpart to a gravitational-wave source |
we study a new population of extremely red objects (eros) recently discovered by jwst based on their nircam colors f277w$-$f444w $>1.5$ mag. we find 37 eros in the ceers field with f444w $<28$ mag and photometric redshifts between $5<z<7$, with median $z=6.9^{+1.0}_{-1.6}$. surprisingly, despite their red long-wavelength colors, these eros have blue short-wavelength colors (f150w$-$f200w$\sim$0 mag) indicative of bimodal seds with a red, steep slope in the rest-frame optical, and a blue, flat slope in the rest-frame uv. moreover, all these eros are unresolved, point-like sources in all nircam bands. we analyze the spectral energy distributions of 8 of them with miri and nirspec observations using stellar population models and agn templates. we find that a dusty galaxy or an obscured agn provide similarly good sed fits but different stellar properties: massive and dusty, log m/m_sun$\sim$10 and a$_{\rm v}\gtrsim3$ mag, or low mass and obscuration, log m/m_sun$\sim$7.5 and a$_{\rm v}\sim0$ mag, hosting an obscured qso. sed modeling does not favor either scenario, but their unresolved sizes are more suggestive of an agn. if any eros are confirmed to have log m/m_sun$\gtrsim10.5$, it would increase pre-jwst number densities at $z>7$ by up to a factor $\sim$60. similarly, if they are osos with luminosities in the l$_{\rm bol}>10^{46-47}$ erg s$^{-1}$ range, their number would exceed that of bright blue qsos by more than two orders of magnitude. additional photometry at mid-ir wavelengths will reveal the true nature of the red continuum emission in these eros and will place this puzzling population in the right context of galaxy evolution. | extremely red galaxies at $z=5-9$ with miri and nirspec: dusty galaxies or obscured agns? |
magnetars are young and highly magnetized neutron stars that display a wide array of x-ray activity including short bursts, large outbursts, giant flares, and quasi-periodic oscillations, often coupled with interesting timing behavior including enhanced spin-down, glitches, and antiglitches. the bulk of this activity is explained by the evolution and decay of an ultrastrong magnetic field, stressing and breaking the neutron-star crust, which in turn drives twists of the external magnetosphere and powerful magnetospheric currents. the population of detected magnetars has grown to about 30 objects and shows unambiguous phenomenological connection with highly magnetized radio pulsars. recent progress in magnetar theory includes explanation of the hard x-ray component in the magnetar spectrum and development of surface heating models, explaining the sources' remarkable radiative output. | magnetars |
on september 14, 2015, the laser interferometer gravitational-wave observatory (ligo) detected a gravitational-wave transient (gw150914); we characterize the properties of the source and its parameters. the data around the time of the event were analyzed coherently across the ligo network using a suite of accurate waveform models that describe gravitational waves from a compact binary system in general relativity. gw150914 was produced by a nearly equal mass binary black hole of masses 3 6-4+5m⊙ and 2 9-4+4m⊙ ; for each parameter we report the median value and the range of the 90% credible interval. the dimensionless spin magnitude of the more massive black hole is bound to be <0.7 (at 90% probability). the luminosity distance to the source is 41 0-180+160 mpc , corresponding to a redshift 0.0 9-0.04+0.03 assuming standard cosmology. the source location is constrained to an annulus section of 610 deg2 , primarily in the southern hemisphere. the binary merges into a black hole of mass 6 2-4+4m⊙ and spin 0.6 7-0.07+0.05. this black hole is significantly more massive than any other inferred from electromagnetic observations in the stellar-mass regime. | properties of the binary black hole merger gw150914 |
combining the gw observations of merging systems of binary neutron stars and quasi-universal relations, we set constraints on the maximum mass that can be attained by nonrotating stellar models of neutron stars. more specifically, exploiting the recent observation of the gw event gw170817 and drawing from basic arguments on kilonova modeling of grb 170817a together with the quasi-universal relation between the maximum mass of nonrotating stellar models {m}{tov} and the maximum mass supported through uniform rotation {m}\max=({1.20}-0.05+0.02){m}{tov}, we set limits for the maximum mass to be {2.01}-0.04+0.04≤slant {m}{tov}/{m}⊙ ≲ {2.16}-0.15+0.17, where the lower limit in this range comes from pulsar observations. our estimate, which follows a very simple line of arguments and does not rely on the modeling of the electromagnetic signal in terms of numerical simulations, can be further refined as new detections become available. we briefly discuss the impact that our conclusions have on the equation of state of nuclear matter. | using gravitational-wave observations and quasi-universal relations to constrain the maximum mass of neutron stars |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.