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the uncertainties in neutron star radii and crust properties due to our limited knowledge of the equation of state are quantitatively analyzed. we first demonstrate the importance of a unified microscopic description for the different baryonic densities of the star. if the pressure functional is obtained matching a crust and a core equation of state based on models with different properties at nuclear matter saturation, the uncertainties can be as large as ∼30 % for the crust thickness and 4% for the radius. necessary conditions for causal and thermodynamically consistent matchings between the core and the crust are formulated and their consequences examined. a large set of unified equations of state for purely nucleonic matter is obtained based on twenty-four skyrme interactions and nine relativistic mean-field nuclear parametrizations. in addition, for relativistic models fifteen equations of state including a transition to hyperonic matter at high density are presented. all these equations of state have in common the property of describing a 2 m⊙ star and of being causal within stable neutron stars. spans of ∼3 and ∼4 km are obtained for the radius of, respectively, 1.0 m⊙ and 2.0 m⊙ stars. applying a set of nine further constraints from experiment and ab initio calculations the uncertainty is reduced to ∼1 and 2 km, respectively. these residual uncertainties reflect lack of constraints at large densities and insufficient information on the density dependence of the equation of state near the nuclear matter saturation point. the most important parameter to be constrained is shown to be the symmetry energy slope l . indeed, this parameter exhibits a linear correlation with the stellar radius, which is particularly clear for small mass stars around 1.0 m⊙ . the other equation-of-state parameters do not show clear correlations with the radius, within the present uncertainties. potential constraints on l , the neutron star radius, and the equation of state from observations of thermal states of neutron stars are also discussed. the unified equations of state are made available in the supplemental materials and via the compose database. | neutron star radii and crusts: uncertainties and unified equations of state |
context. recent years have seen building evidence that planet formation starts early, in the first ~0.5 myr. studying the dust masses available in young disks enables us to understand the origin of planetary systems given that mature disks are lacking the solid material necessary to reproduce the observed exoplanetary systems, especially the massive ones.aims: we aim to determine if disks in the embedded stage of star formation contain enough dust to explain the solid content of the most massive exoplanets.methods: we use atacama large millimeter/submillimeter array (alma) band 6 (1.1-1.3 mm) continuum observations of embedded disks in the perseus star-forming region together with very large array (vla) ka-band (9 mm) data to provide a robust estimate of dust disk masses from the flux densities measured in the image plane.results: we find a strong linear correlation between the alma and vla fluxes, demonstrating that emission at both wavelengths is dominated by dust emission. for a subsample of optically thin sources, we find a median spectral index of 2.5 from which we derive the dust opacity index β = 0.5, suggesting significant dust growth. comparison with alma surveys of orion shows that the class i dust disk mass distribution between the two regions is similar, but that the class 0 disks are more massive in perseus than those in orion. using the diana opacity model including large grains, with a dust opacity value of κ9 mm = 0.28 cm2 g-1, the median dust masses of the embedded disks in perseus are 158 m⊕ for class 0 and 52 m⊕ for class i from the vla fluxes. the lower limits on the median masses from alma fluxes are 47 m⊕ and 12 m⊕ for class 0 and class i, respectively, obtained using the maximum dust opacity value κ1.3 mm = 2.3 cm2 g-1. the dust masses of young class 0 and i disks are larger by at least a factor of ten and three, respectively, compared with dust masses inferred for class ii disks in lupus and other regions.conclusions: the dust masses of class 0 and i disks in perseus derived from the vla data are high enough to produce the observed exoplanet systems with efficiencies acceptable by planet formation models: the solid content in observed giant exoplanets can be explained if planet formation starts in class 0 phase with an efficiency of ~15%. a higher efficiency of ~30% is necessary if the planet formation is set to start in class i disks. | dust masses of young disks: constraining the initial solid reservoir for planet formation |
about 10 μs after the big bang, the universe was filled—in addition to photons and leptons—with strong-interaction matter consisting of quarks and gluons, which transitioned to hadrons at temperatures close to kt = 150 mev and densities several times higher than those found in nuclei. this quantum chromodynamics (qcd) matter can be created in the laboratory as a transient state by colliding heavy ions at relativistic energies. the different phases in which qcd matter may exist depend for example on temperature, pressure or baryochemical potential, and can be probed by studying the emission of electromagnetic radiation. electron-positron pairs emerge from the decay of virtual photons, which immediately decouple from the strong interaction, and thus provide information about the properties of qcd matter at various stages. here, we report the observation of virtual photon emission from baryon-rich qcd matter. the spectral distribution of the electron-positron pairs is nearly exponential, providing evidence for a source of temperature in excess of 70 mev with constituents whose properties have been modified, thus reflecting peculiarities of strong-interaction qcd matter. its bulk properties are similar to the dense matter formed in the final state of a neutron star merger, as apparent from recent multimessenger observation. | probing dense baryon-rich matter with virtual photons |
massive black holes (mbhs) inhabit galactic centres, and power luminous quasars and active galactic nuclei, shaping their cosmic environment with the energy they produce. the origins of mbhs remain a mystery, and the recent detection by ligo/virgo of a black hole of almost 150 solar masses has revitalized the questions of whether there is a continuum between `stellar' and `massive' black holes, and what the seeds of mbhs are. seeds could have formed in the first galaxies or could be related to the collapse of horizon-sized regions in the early universe. understanding the origins of mbhs straddles fundamental physics, cosmology and astrophysics, and bridges the fields of gravitational-wave physics and traditional astronomy. with several existing and upcoming facilities in the next 10-15 years, we foresee the possibility of discovering the avenues of formation of mbhs. this review links three main topics: the channels of black hole seed formation, the journey from seeds to mbhs, and the diagnostics on the origins of mbhs. we highlight and critically discuss current unsolved problems, touching on recent developments. | the origins of massive black holes |
hot subluminous stars of spectral type b and o are core helium-burning stars at the blue end of the horizontal branch or have evolved even beyond that stage. most hot subdwarf stars are chemically highly peculiar and provide a laboratory to study diffusion processes that cause these anomalies. the most obvious anomaly lies with helium, which may be a trace element in the atmosphere of some stars (sdb, sdo) while it may be the dominant species in others (he-sdb, he-sdo). strikingly, the distribution in the hertzsprung-russell diagram of he-rich versus he-poor hot subdwarf stars of the globular clusters ω cen and ngc 2808 differ from that of their field counterparts. the metal-abundance patterns of hot subdwarfs are typically characterized by strong deficiencies of some lighter elements as well as large enrichments of heavy elements. a large fraction of sdb stars are found in close binaries with white dwarf or very low-mass main sequence companions, which must have gone through a common-envelope (ce) phase of evolution. because the binaries are detached they provide a clean-cut laboratory to study this important but yet poorly understood phase of stellar evolution. hot subdwarf binaries with sufficiently massive white dwarf companions are viable candidate progenitors of type ia supernovae both in the double degenerate as well as in the single degenerate scenario as helium donors for double detonation supernovae. the hyper-velocity he-sdo star us 708 may be the surviving donor of such a double detonation supernova. substellar companions to sdb stars have also been found. for hw vir systems the companion mass distribution extends from the stellar into the brown dwarf regime. a giant planet to the acoustic-mode pulsator v391 peg was the first discovery of a planet that survived the red giant evolution of its host star. evidence for earth-size planets to two pulsating sdb stars have been reported and circumbinary giant planets or brown dwarfs have been found around hw vir systems from eclipse timings. the high incidence of circumbinary substellar objects suggests that most of the planets are formed from the remaining ce material (second generation planets). several types of pulsating star have been discovered among hot subdwarf stars, the most common are the gravity-mode sdb pulsators (v1093 her) and their hotter siblings, the p-mode pulsating v361 hya stars. another class of multi-periodic pulsating hot subdwarfs has been found in the globular cluster ω cen that is unmatched by any field star. asteroseismology has advanced enormously thanks to the high-precision kepler photometry and allowed stellar rotation rates to be determined, the interior structure of gravity-mode pulsators to be probed and stellar ages to be estimated. rotation rates turned out to be unexpectedly slow calling for very efficient angular momentum loss on the red giant branch or during the helium core flash. the convective cores were found to be larger than predicted by standard stellar evolution models requiring very efficient angular momentum transport on the red giant branch. the masses of hot subdwarf stars, both single or in binaries, are the key to understand the stars’ evolution. a few pulsating sdb stars in eclipsing binaries have been found that allow both techniques to be applied for mass determination. the results, though few, are in good agreement with predictions from binary population synthesis calculations. new classes of binaries, hosting so-called extremely low mass (elm) white dwarfs (m < 0.3 m ⊙), have recently been discovered, filling a gap in the mosaic of binary stellar evolution. like most sdb stars the elm white dwarfs are the stripped cores of red giants, the known companions are either white dwarfs, neutron stars (pulsars) or f- or a-type main sequence stars (“el cvn” stars). in the near future, the gaia mission will provide high-precision astrometry for a large sample of subdwarf stars to disentangle the different stellar populations in the field and to compare the field subdwarf population with the globular clusters’ hot subdwarfs. new fast-moving subdwarfs will allow the mass of the galactic dark matter halo to be constrained and additional unbound hyper-velocity stars may be discovered. subdwarf o/b stars and extremely low mass white dwarfs: atmospheric parameters and abundances, formation and evolution, binaries, planetary companions, pulsation, and kinematics. | hot subluminous stars |
our current knowledge of cosmic star-formation history during the first two billion years (corresponding to redshift z > 3) is mainly based on galaxies identified in rest-frame ultraviolet light1. however, this population of galaxies is known to under-represent the most massive galaxies, which have rich dust content and/or old stellar populations. this raises the questions of the true abundance of massive galaxies and the star-formation-rate density in the early universe. although several massive galaxies that are invisible in the ultraviolet have recently been confirmed at early epochs2-4, most of them are extreme starburst galaxies with star-formation rates exceeding 1,000 solar masses per year, suggesting that they are unlikely to represent the bulk population of massive galaxies. here we report submillimetre (wavelength 870 micrometres) detections of 39 massive star-forming galaxies at z > 3, which are unseen in the spectral region from the deepest ultraviolet to the near-infrared. with a space density of about 2 × 10-5 per cubic megaparsec (two orders of magnitude higher than extreme starbursts5) and star-formation rates of 200 solar masses per year, these galaxies represent the bulk population of massive galaxies that has been missed from previous surveys. they contribute a total star-formation-rate density ten times larger than that of equivalently massive ultraviolet-bright galaxies at z > 3. residing in the most massive dark matter haloes at their redshifts, they are probably the progenitors of the largest present-day galaxies in massive groups and clusters. such a high abundance of massive and dusty galaxies in the early universe challenges our understanding of massive-galaxy formation. | a dominant population of optically invisible massive galaxies in the early universe |
numerical relativity (nr) simulations provide the most accurate binary black hole gravitational waveforms, but are prohibitively expensive for applications such as parameter estimation. surrogate models of nr waveforms have been shown to be both fast and accurate. however, nr-based surrogate models are limited by the training waveforms' length, which is typically about 20 orbits before merger. we remedy this by hybridizing the nr waveforms using both post-newtonian and effective one-body waveforms for the early inspiral. we present nrhybsur3dq8, a surrogate model for hybridized nonprecessing numerical relativity waveforms, that is valid for the entire ligo band (starting at 20 hz) for stellar mass binaries with total masses as low as 2.25 m⊙. we include the ℓ≤4 and (5, 5) spin-weighted spherical harmonic modes but not the (4, 1) or (4, 0) modes. this model has been trained against hybridized waveforms based on 104 nr waveforms with mass ratios q ≤8 , and |χ1 z|,|χ2 z|≤0.8 , where χ1 z (χ2 z) is the spin of the heavier (lighter) black hole in the direction of orbital angular momentum. the surrogate reproduces the hybrid waveforms accurately, with mismatches ≲3 ×10-4 over the mass range 2.25 m⊙≤m ≤300 m⊙. at high masses (m ≳40 m⊙), where the merger and ringdown are more prominent, we show roughly 2 orders of magnitude improvement over existing waveform models. we also show that the surrogate works well even when extrapolated outside its training parameter space range, including at spins as large as 0.998. finally, we show that this model accurately reproduces the spheroidal-spherical mode mixing present in the nr ringdown signal. | surrogate model of hybridized numerical relativity binary black hole waveforms |
the geometry of the accretion flow around stellar-mass black holes can change on timescales of days to months1-3. when a black hole emerges from quiescence (that is, it `turns on' after accreting material from its companion) it has a very hard (high-energy) x-ray spectrum produced by a hot corona4,5 positioned above its accretion disk, and then transitions to a soft (lower-energy) spectrum dominated by emission from the geometrically thin accretion disk, which extends to the innermost stable circular orbit6,7. much debate persists over how this transition occurs and whether it is driven largely by a reduction in the truncation radius of the disk8,9 or by a reduction in the spatial extent of the corona10,11. observations of x-ray reverberation lags in supermassive black-hole systems12,13 suggest that the corona is compact and that the disk extends nearly to the central black hole14,15. observations of stellar-mass black holes, however, reveal equivalent (mass-scaled) reverberation lags that are much larger16, leading to the suggestion that the accretion disk in the hard-x-ray state of stellar-mass black holes is truncated at a few hundreds of gravitational radii from the black hole17,18. here we report x-ray observations of the black-hole transient maxi j1820+07019,20. we find that the reverberation time lags between the continuum-emitting corona and the irradiated accretion disk are 6 to 20 times shorter than previously seen. the timescale of the reverberation lags shortens by an order of magnitude over a period of weeks, whereas the shape of the broadened iron k emission line remains remarkably constant. this suggests a reduction in the spatial extent of the corona, rather than a change in the inner edge of the accretion disk. | the corona contracts in a black-hole transient |
context. the gaia second data release provides precise astrometry and photometry for more than 1.3 billion sources. this catalog opens a new era concerning the characterization of open clusters and test stellar models, paving the way for better understanding of the disk properties.aims: the aim of the paper is to improve the knowledge of cluster parameters, using only the unprecedented quality of the gaia photometry and astrometry.methods: we have made use of the membership determination based on the precise gaia astrometry and photometry. we applied an automated bayesian tool, base-9, to fit stellar isochrones on the observed g, gbp, grp magnitudes of the high probability member stars.results: we derive parameters such as age, distance modulus, and extinction for a sample of 269 open clusters, selecting only low reddening objects and discarding very young clusters, for which techniques other than isochrone-fitting are more suitable for estimating ages. full tables a.1-a.3 are 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/623/a108 | age determination for 269 gaia dr2 open clusters |
this paper discusses the transit model-fitting and multiple-planet search algorithms and performance of the kepler science data processing pipeline, developed by the kepler science operations center (soc). threshold crossing events (tces), which are transit candidate events, are generated by the transiting planet search (tps) component of the pipeline and subsequently processed in the data validation (dv) component. the transit model is used in dv to fit tces to characterize planetary candidates and to derive parameters that are used in various diagnostic tests to classify them. after the signature associated with the tce is removed from the light curve of the target star, the residual light curve goes through tps again to search for additional tces. the iterative process of transit model-fitting and multiple-planet search continues until no tce is generated from the residual light curve or an upper limit is reached. the transit model-fitting and multiple-planet search performance of the final release (9.3, 2016 january) of the pipeline is demonstrated with the results of the processing of four years (17 quarters) of flight data from the primary kepler mission. the transit model-fitting results are accessible from the nasa exoplanet archive. the final version of the soc codebase is available through github. | kepler data validation ii-transit model fitting and multiple-planet search |
context. this work is part of the gaia data processing and analysis consortium papers published with the gaia early data release 3 (edr3). it is one of the demonstration papers aiming to highlight the improvements and quality of the newly published data by applying them to a scientific case.aims: we use the gaia edr3 data to study the structure and kinematics of the magellanic clouds. the large distance to the clouds is a challenge for the gaia astrometry. the clouds lie at the very limits of the usability of the gaia data, which makes the clouds an excellent case study for evaluating the quality and properties of the gaia data.methods: the basis of our work are two samples selected to provide a representation as clean as possible of the stars of the large magellanic cloud (lmc) and the small magellanic cloud (smc). the selection used criteria based on position, parallax, and proper motions to remove foreground contamination from the milky way, and allowed the separation of the stars of both clouds. from these two samples we defined a series of subsamples based on cuts in the colour-magnitude diagram; these subsamples were used to select stars in a common evolutionary phase and can also be used as approximate proxies of a selection by age.results: we compared the gaia data release 2 and gaia edr3 performances in the study of the magellanic clouds and show the clear improvements in precision and accuracy in the new release. we also show that the systematics still present in the data make the determination of the 3d geometry of the lmc a difficult endeavour; this is at the very limit of the usefulness of the gaia edr3 astrometry, but it may become feasible with the use of additional external data. we derive radial and tangential velocity maps and global profiles for the lmc for the several subsamples we defined. to our knowledge, this is the first time that the two planar components of the ordered and random motions are derived for multiple stellar evolutionary phases in a galactic disc outside the milky way, showing the differences between younger and older phases. we also analyse the spatial structure and motions in the central region, the bar, and the disc, providing new insightsinto features and kinematics. finally, we show that the gaia edr3 data allows clearly resolving the magellanic bridge, and we trace the density and velocity flow of the stars from the smc towards the lmc not only globally, but also separately for young and evolved populations. this allows us to confirm an evolved population in the bridge that is slightly shift from the younger population. additionally, we were able to study the outskirts of both magellanic clouds, in which we detected some well-known features and indications of new ones. velocity profiles are only available at the cds via anonymous ftp to cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/649/a7 | gaia early data release 3. structure and properties of the magellanic clouds |
gravitational wave astronomy opened dramatically in september 2015 with the ligo discovery of a distant and massive binary black hole coalescence. the more recent discovery of a binary neutron star merger, followed by a gamma ray burst (grb) and a kilonova, reinforces the excitement of this new era, in which we may soon see other sources of gravitational waves, including continuous, nearly monochromatic signals. potential continuous wave (cw) sources include rapidly spinning galactic neutron stars and more exotic possibilities, such as emission from axion bose einstein “clouds” surrounding black holes. recent searches in advanced ligo data are presented, and prospects for more sensitive future searches are discussed. | recent searches for continuous gravitational waves |
in a recent paper [1 p. v. p. cunha, c. a. r. herdeiro, e. radu, and h. f. runarsson, phys. rev. lett. 115, 211102 (2015).], it was shown that the lensing of light around rotating boson stars and kerr black holes with scalar hair can exhibit chaotic patterns. since no separation of variables is known (or expected) for geodesic motion on these backgrounds, we examine the 2d effective potentials for photon trajectories, to obtain a deeper understanding of this phenomenon. we find that the emergence of stable light rings on the background spacetimes allows the formation of "pockets" in one of the effective potentials, for open sets of impact parameters, leading to an effective trapping of some trajectories, dubbed "quasibound orbits." we conclude that pocket formation induces chaotic scattering, although not all chaotic orbits are associated to pockets. these and other features are illustrated in a gallery of examples, obtained with a new ray-tracing code, pyhole, which includes tools for a simple, simultaneous visualization of the effective potential, together with the spacetime trajectory, for any given point in a lensing image. an analysis of photon orbits allows us to further establish a positive correlation between photon orbits in chaotic regions and those with more than one turning point in the radial direction; we recall that the latter is not possible around kerr black holes. moreover, we observe that the existence of several light rings around a horizon (several fundamental orbits, including a stable one), is a central ingredient for the existence of multiple shadows of a single hairy black hole. we also exhibit the lensing and shadows by kerr black holes with scalar hair, observed away from the equatorial plane, obtained with pyhole. | chaotic lensing around boson stars and kerr black holes with scalar hair |
the detection of a kilo/macronova electromagnetic counterpart (at 2017gfo) of the first gravitational-wave signal compatible with the merger of two neutron stars (gw170817) has confirmed the occurrence of r-process nucleosynthesis in this kind of event. the blue and red components of at 2017gfo have been interpreted as the signature of multi-component ejecta in the merger dynamics. however, the explanation of at 2017gfo in terms of the properties of the ejecta and of the ejection mechanisms is still incomplete. in this work, we analyze at 2017gfo with a new semi-analytic model of kilo/macronova inferred from general-relativistic simulations of the merger and long-term numerical models of the merger aftermath. the model accounts for the anisotropic emission from the three known mass ejecta components: dynamic, winds, and secular outflows from the disk. the early multi-band light curves of at 2017gfo can only be explained by the presence of a relatively low-opacity component of the ejecta at high latitudes. this points to the key role of weak interactions in setting the ejecta properties and determining the nucleosynthetic yields. our model also constrains the total ejected mass associated to at 2017gfo to be between 0.042 and 0.077 {m}⊙ , the observation angle of the source to be between π /12 and 7π /36, and the mass of the disk to be ≳ 0.08 {m}⊙ . | at 2017gfo: an anisotropic and three-component kilonova counterpart of gw170817 |
large surveys of galaxy clusters with the hubble space telescope (hst) and spitzer, including the cluster lensing and supernova survey with hubble and the frontier fields, have demonstrated the power of strong gravitational lensing to efficiently deliver large samples of high-redshift galaxies. we extend this strategy through a wider, shallower survey named relics, the reionization lensing cluster survey, described here. our 188-orbit hubble treasury program observed 41 clusters at 0.182 ≤ z ≤ 0.972 with advanced camera for surveys (acs) and wfc3/ir imaging spanning 0.4-1.7 μm. we selected 21 of the most massive clusters known based on planck psz2 estimates and 20 additional clusters based on observed or inferred lensing strength. relics observed 46 wfc3/ir pointings (∼200 arcmin2) each with two orbits divided among four filters (f105w, f125w, f140w, and f160w) and acs imaging as needed to achieve single-orbit depth in each of three filters (f435w, f606w, and f814w). as previously reported by salmon et al., we discovered over 300 z ∼ 6-10 candidates, including the brightest z ∼ 6 candidates known, and the most distant spatially resolved lensed arc known at z ∼ 10. spitzer irac imaging (945 hr awarded, plus 100 archival, spanning 3.0-5.0 μm) has crucially enabled us to distinguish z ∼ 10 candidates from z ∼ 2 interlopers. for each cluster, two hst observing epochs were staggered by about a month, enabling us to discover 11 supernovae, including 3 lensed supernovae, which we followed up with 20 orbits from our program. reduced hst images, catalogs, and lens models are available on mast, and reduced spitzer images are available on irsa. | relics: reionization lensing cluster survey |
the release of spin-down energy by a magnetar is a promising scenario to power several classes of extreme explosive transients. however, it lacks a firm basis because magnetar formation still represents a theoretical challenge. using the first three-dimensional simulations of a convective dynamo based on a protoneutron star interior model, we demonstrate that the required dipolar magnetic field can be consistently generated for sufficiently fast rotation rates. the dynamo instability saturates in the magnetostrophic regime with the magnetic energy exceeding the kinetic energy by a factor of up to 10. our results are compatible with the observational constraints on galactic magnetar field strength and provide strong theoretical support for millisecond protomagnetar models of gamma-ray burst and superluminous supernova central engines. | magnetar formation through a convective dynamo in protoneutron stars |
the short gamma-ray burst, grb 170817a, that followed the binary neutron star merger gravitational waves signal, gw170817, is not a usual short gamma-ray burst (sgrb). it is weaker by three orders of magnitude than the weakest sgrb seen before and its spectrum, showing a hard early signal followed by a softer thermal spectrum, is unique. we show, first, that the γ-rays must have emerged from at least mildly relativistic outflow, implying that a relativistic jet was launched following the merger. we then show that the observations are consistent with the predictions of a mildly relativistic shock breakout: a minute γ-ray energy as compared with the total energy and a rather smooth light curve with a hard to soft evolution. we present here a novel analytic study and detailed numerical 2d and 3d relativistic hydrodynamic and radiation simulations that support the picture in which the observed γ-rays arose from a shock breakout of a cocoon from the merger's ejecta . the cocoon can be formed either by a choked jet which does not generate an sgrb (in any direction) or by a successful jet which generates an undetected regular sgrb along the system's axis pointing away from us. remarkably, for the choked jet model, the macronova signal produced by the ejecta (which is partially boosted to high velocities by the cocoon's shock) and the radio that is produced by the interaction of the shocked cocoon material with the surrounding matter agree with the observed ultraviolet/optical/infrared emission and with current radio observations. finally, we discuss the possibility that the jet propagation within the ejecta may photodissociate some of the heavy elements and may affect the composition of a fraction of ejecta and, in turn, the opacity and the early macronova light. | a cocoon shock breakout as the origin of the γ-ray emission in gw170817 |
the radiation from stars and active galactic nuclei (agns) creates photodissociation regions (pdrs) and x-ray-dominated regions (xdrs), where the chemistry or heating is dominated by far-ultraviolet (fuv) radiation or x-ray radiation, respectively. pdrs include a wide range of environments, from the diffuse interstellar medium (ism) to dense star-forming regions. xdrs are found in the center of galaxies hosting agns, in protostellar disks, and in the vicinity of x-ray binaries. in this review, we describe the dominant thermal, chemical, and radiation transfer processes in pdrs and xdrs, as well as give a brief description of models and their use for analyzing observations. we then present recent results from milky way, nearby extragalactic, and high-redshift observations. several important results include the following: velocity-resolved pdr lines reveal the kinematics of the neutral atomic gas and provide constraints on the stellar feedback process. their interpretation is, however, in dispute, as observations suggest a prominent role for stellar winds, whereas they are much less important in theoretical models. a significant fraction of molecular mass resides in co-dark gas especially in low-metallicity and/or highly irradiated environments. the co ladder and [ci]/[cii] ratios can determine if fuv or x rays dominate the ism heating of extragalactic sources. with atacama large millimeter/submillimeter array, pdr and xdr tracers are now routinely detected on galactic scales over cosmic time. this makes it possible to link the star-formation history of the universe to the evolution of the physical and chemical properties of the gas. | photodissociation and x-ray-dominated regions |
the interstellar medium (ism) contains filamentary structure over a wide range of scales. understanding the role of this structure, both as a conduit of gas across the scales and a diagnostic tool of local physics, is a major focus of star formation studies. we review recent progress in studying filamentary structure in the ism, interpreting its properties in terms of physical processes, and exploring formation and evolution scenarios. we include structures from galactic-scale filaments to tenth-of-a-parsec scale filaments, comprising both molecular and atomic structures, from both observational and theoretical perspectives. in addition to the literature overview, we assemble a large amount of catalog data from different surveys and provide the most comprehensive census of filamentary structures to date. our census consists of 22 803 filamentary structures, facilitating a holistic perspective and new insights. we use our census to conduct a meta-analysis, leading to a description of filament properties over four orders of magnitudes in length and eight in mass. our analysis emphasize the hierarchical and dynamical nature of filamentary structures. filaments do not live in isolation, nor they generally resemble static structures close to equilibrium. we propose that accretion during filament formation and evolution sets some of the key scaling properties of filaments. this highlights the role of accretion during filament formation and evolution and also in setting the initial conditions for star formation. overall, the study of filamentary structures during the past decade has been observationally driven. while great progress has been made on measuring the basic properties of filaments, our understanding of their formation and evolution is clearly lacking. in this context, we identify a number of directions and questions we consider most pressing for the field. | initial conditions for star formation: a physical description of the filamentary ism |
the ionizing photon escape fraction [lyman continuum (lyc) fesc] of star-forming galaxies is the single greatest unknown in the reionization budget. stochastic sightline effects prohibit the direct separation of lyc leakers from non-leakers at significant redshifts. here we circumvent this uncertainty by inferring fesc using resolved (r > 4000) lyman α (lyα) profiles from the x-shooter lyα survey at z = 2 (xls-z2). with empirically motivated criteria, we use lyα profiles to select leakers ($f_{\mathrm{ esc}} > 20{{\ \rm per\ cent}}$) and non-leakers ($f_{\mathrm{ esc}} < 5{{\ \rm per\ cent}}$) from a representative sample of >0.2l* lyman α emitters (laes). we use median stacked spectra of these subsets over λrest ≈ 1000-8000 å to investigate the conditions for lyc fesc. our stacks show similar mass, metallicity, muv, and βuv. we find the following differences between leakers versus non-leakers: (i) strong nebular c iv and he ii emission versus non-detections; (ii) [o iii]/[o ii] ≈ 8.5 versus ≈3; (iii) hα/hβ indicating no dust versus e(b - v) ≈ 0.3; (iv) mg ii emission close to the systemic velocity versus redshifted, optically thick mg ii; and (v) lyα fesc of ${\approx} 50{{\ \rm per\ cent}}$ versus ${\approx} 10{{\ \rm per\ cent}}$. the extreme equivalent widths (ews) in leakers ([o iii]+$\mathrm{ h}\beta \approx 1100$ å rest frame) constrain the characteristic time-scale of lyc escape to ≈3-10 myr bursts when short-lived stars with the hardest ionizing spectra shine. the defining traits of leakers - extremely ionizing stellar populations, low column densities, a dust-free, high-ionization state interstellar medium (ism) - occur simultaneously in the $f_{\rm esc} > 20{{\ \rm per\ cent}}$ stack, suggesting they are causally connected, and motivating why indicators like [o iii]/[o ii] may suffice to constrain fesc at z > 6 with the james webb space telescope (jwst). the leakers comprise half of our sample, have a median lyc$f_{\rm esc} \approx 50{{\ \rm per\ cent}}$ (conservative range: $20\!-\!55{{\ \rm per\ cent}}$), and an ionizing production efficiency $\log ({\xi _{\rm {ion}}/\rm {hz\ erg^{-1}}})\approx 25.9$ (conservative range: 25.7-25.9). these results show laes - the type of galaxies rare at z ≈ 2, but that become the norm at higher redshift - are highly efficient ionizers, with extreme ξion and prolific fesc occurring in sync. | the synchrony of production and escape: half the bright lyα emitters at z ≈ 2 have lyman continuum escape fractions ≈50 per cent |
we report x-ray diffraction studies of the electronic ordering instabilities in the kagome material csv3sb5 as a function of temperature and applied magnetic field. our zero-field measurements between 10 and 120 k reveal an unexpected reorganization of the three-dimensional electronic order in the bulk of csv3sb5: at low temperatures, a 2 ×2 ×2 superstructure modulation due to electronic order is observed, which upon warming changes to a 2 ×2 ×4 superstructure at 60 k. the electronic order-order transition discovered here involves a change in the stacking of electronically ordered v3sb5 layers, which coincides with anomalies previously observed in magnetotransport measurements. this implies that the temperature-dependent three-dimensional electronic order plays a decisive role for transport properties, which are related to the berry curvature of the v bands. we also show that the bulk electronic order in csv3sb5 breaks the sixfold rotational symmetry of the underlying p 6 /m m m lattice and perform a crystallographic analysis of the 2 ×2 ×2 phase. the latter yields two possible superlattices, namely a staggered star-of-david and a staggered inverse star-of-david structure. applied magnetic fields up to 10 t have no effect on the x-ray diffraction signal. this, however, does not rule out time-reversal symmetry breaking in csv3sb5. | temperature-driven reorganization of electronic order in csv3sb5 |
we propose a conceptual distinction between hard and soft realizations of deconfinement from nuclear to quark matter. in the high density region of hard deconfinement the repulsive hard cores of baryons overlap each other and bulk thermodynamics is dominated by the core properties that can be experimentally accessed in high-energy scattering experiments. we find that the equation of state estimated from a single baryon core is fairly consistent with those empirically known from neutron star phenomenology. we next discuss a novel concept of soft deconfinement, characterized by quantum percolation of quark wave functions, at densities lower than the threshold for hard deconfinement. we make a brief review of quantum percolation in the context of nuclear and quark matter and illustrate a possible scenario of quark deconfinement at high baryon densities. | hard-core deconfinement and soft-surface delocalization from nuclear to quark matter |
stellar-mass primordial black holes (pbh) have been recently reconsidered as a dark matter (dm) candidate after the aligo discovery of several binary black hole (bh) mergers with masses of tens of m⊙ . matter accretion on such massive objects leads to the emission of high-energy photons, capable of altering the ionization and thermal history of the universe. this, in turn, affects the statistical properties of the cosmic microwave background (cmb) anisotropies. previous analyses have assumed spherical accretion. we argue that this approximation likely breaks down and that an accretion disk should form in the dark ages. using the most up-to-date tools to compute the energy deposition in the medium, we derive constraints on the fraction of dm in pbh. provided that disks form early on, even under conservative assumptions for accretion, these constraints exclude a monochromatic distribution of pbh with masses above ∼2 m⊙ as the dominant form of dm. the bound on the median pbh mass gets more stringent if a broad, log-normal mass function is considered. a deepened understanding of nonlinear clustering properties and bh accretion disk physics would permit an improved treatment and possibly lead to more stringent constraints. | cmb bounds on disk-accreting massive primordial black holes |
multiple codes are available to derive atmospheric parameters and individual chemical abundances from high-resolution spectra of afgkm stars. almost all spectroscopists have their own preferences regarding which code and method to use. but the intrinsic differences between codes and methods lead to complex systematics that depend on multiple variables such as the selected spectral regions and the radiative transfer code used. i expand ispec, a popular open-source spectroscopic tool, to support the most well-known radiative transfer codes and assess their similarities and biases when using multiple set-ups based on the equivalent-width method and the synthetic spectral-fitting technique (interpolating from a pre-computed grid of spectra or synthesizing with interpolated model atmospheres). this work shows that systematic differences on atmospheric parameters and abundances between most of the codes can be reduced when using the same method and executing a careful spectral feature selection. however, it may not be possible to ignore the remaining differences, depending on the particular case and the required precision. regarding methods, equivalent-width-based and spectrum-fitting analyses exhibit large differences that are caused by their intrinsic differences, which is significant given the popularity of these two methods. the results help to identify the key caveats of modern spectroscopy that all scientists should be aware of before trusting their own results or being tempted to combine atmospheric parameters and abundances from the literature. | modern stellar spectroscopy caveats |
water and simple organic molecular ices dominate the mass of solid materials available for planetesimal and planet formation beyond the water snow line. here we analyze alma long baseline 2.9, 1.3 and 0.87 mm continuum images of the young star hl tau, and suggest that the emission dips observed are due to rapid pebble growth around the condensation fronts of abundant volatile species. specifically, we show that the prominent innermost dip at 13 au is spatially resolved in the 0.87 mm image, and its center radius is coincident with the expected mid-plane condensation front of water ice. in addition, two other prominent dips, at distances of 32 and 63 au, cover the mid-plane condensation fronts of pure ammonia or ammonia hydrates and clathrate hydrates (especially with co and n2) formed from amorphous water ice. the spectral index map of hl tau between 1.3 and 0.87 mm shows that the flux ratios inside the dips are statistically larger than those of nearby regions in the disk. this variation can be explained by a model with two dust populations, where most of the solid mass resides in a component that has grown to decimeter size scales inside the dips. such growth is in accord with recent numerical simulations of volatile condensation, dust coagulation, and settling. | evidence of fast pebble growth near condensation fronts in the hl tau protoplanetary disk |
galaxy observations are influenced by many physical parameters: stellar masses, star formation rates (sfrs), star formation histories (sfhs), metallicities, dust, black hole activity, and more. as a result, inferring accurate physical parameters requires high-dimensional models that capture or marginalize over this complexity. here we reassess inferences of galaxy stellar masses and sfrs using the 14-parameter physical model prospector- α built in the prospector bayesian inference framework. we fit the photometry of 58,461 galaxies from the 3d-hst catalogs at 0.5 < z < 2.5. the resulting stellar masses are ∼0.1-0.3 dex larger than the fiducial masses while remaining consistent with dynamical constraints. this change is primarily due to the systematically older sfhs inferred with prospector. the sfrs are ∼0.1-1+ dex lower than uv+ir sfrs, with the largest offsets caused by emission from “old” (t > 100 myr) stars. these new inferences lower the observed cosmic sfr density by ∼0.2 dex and increase the observed stellar mass growth by ∼0.1 dex, finally bringing these two quantities into agreement and implying an older, more quiescent universe than found by previous studies at these redshifts. we corroborate these results by showing that the prospector- α sfhs are both more physically realistic and much better predictors of the evolution of the stellar mass function. finally, we highlight examples of observational data that can break degeneracies in the current model; these observations can be incorporated into priors in future models to produce new and more accurate physical parameters. | an older, more quiescent universe from panchromatic sed fitting of the 3d-hst survey |
context. the gaia-eso public spectroscopic survey is an ambitious project designed to obtain astrophysical parameters and elemental abundances for 100 000 stars, including large representative samples of the stellar populations in the galaxy, and a well-defined sample of 60 (plus 20 archive) open clusters. we provide internally consistent results calibrated on benchmark stars and star clusters, extending across a very wide range of abundances and ages. this provides a legacy data set of intrinsic value, and equally a large wide-ranging dataset that is of value for the homogenisation of other and future stellar surveys and gaia's astrophysical parameters.aims: this article provides an overview of the survey methodology, the scientific aims, and the implementation, including a description of the data processing for the giraffe spectra. a companion paper introduces the survey results.methods: gaia-eso aspires to quantify both random and systematic contributions to measurement uncertainties. thus, all available spectroscopic analysis techniques are utilised, each spectrum being analysed by up to several different analysis pipelines, with considerable effort being made to homogenise and calibrate the resulting parameters. we describe here the sequence of activities up to delivery of processed data products to the eso science archive facility for open use.results: the gaia-eso survey obtained 202 000 spectra of 115 000 stars using 340 allocated vlt nights between december 2011 and january 2018 from giraffe and uves.conclusions: the full consistently reduced final data set of spectra was released through the eso science archive facility in late 2020, with the full astrophysical parameters sets following in 2022. a companion article reviews the survey implementation, scientific highlights, the open cluster survey, and data products. | the gaia-eso public spectroscopic survey: motivation, implementation, giraffe data processing, analysis, and final data products |
the apex telescope large area survey of the galaxy (atlasgal) is an unbiased 870 μm submillimetre survey of the inner galactic plane (|ℓ| < 60° with |b| < 1.5°). it is the largest and most sensitive ground-based submillimetre wavelength galactic survey to date and has provided a large and systematic inventory of all massive, dense clumps in the galaxy (≥1000 m⊙ at a heliocentric distance of 20 kpc) and includes representative samples of all of the earliest embedded stages of high-mass star formation. here, we present the first detailed census of the properties (velocities, distances, luminosities and masses) and spatial distribution of a complete sample of ∼8000 dense clumps located in the galactic disc (5° < |ℓ| < 60°). we derive highly reliable velocities and distances to ∼97 per cent of the sample and use mid- and far-infrared survey data to develop an evolutionary classification scheme that we apply to the whole sample. comparing the evolutionary subsamples reveals trends for increasing dust temperatures, luminosities and linewidths as a function of evolution indicating that the feedback from the embedded protoclusters is having a significant impact on the structure and dynamics of their natal clumps. we find that the vast majority of the detected clumps are capable of forming a massive star and 88 per cent are already associated with star formation at some level. we find the clump mass to be independent of evolution suggesting that the clumps form with the majority of their mass in situ. we estimate the statistical lifetime of the quiescent stage to be ∼5 × 104 yr for clump masses ∼1000 m⊙ decreasing to ∼1 × 104 yr for clump masses >10000 m⊙. we find a strong correlation between the fraction of clumps associated with massive stars and peak column density. the fraction is initially small at low column densities, but reaching 100 per cent for column densities above 1023 cm-2; there are no clumps with column densities above this value that are not already associated with massive star formation. all of the evidence is consistent with a dynamic view of star formation wherein the clumps form rapidly and are initially very unstable so that star formation quickly ensues. | atlasgal - properties of a complete sample of galactic clumps |
studies of exoplanet demographics require large samples and precise constraints on exoplanet host stars. using the homogeneous kepler stellar properties derived using the gaia data release 2 by berger et al., we recompute kepler planet radii and incident fluxes and investigate their distributions with stellar mass and age. we measure the stellar mass dependence of the planet radius valley to be $d\mathrm{log}{r}_{{\rm{p}}}$ / $d\mathrm{log}{m}_{\star }$ = ${0.26}_{-0.16}^{+0.21}$ , consistent with the slope predicted by a planet mass dependence on stellar mass (0.24-0.35) and core-powered mass loss (0.33). we also find the first evidence of a stellar age dependence of the planet populations straddling the radius valley. specifically, we determine that the fraction of super-earths (1-1.8 ${r}_{\oplus }$ ) to sub-neptunes (1.8-3.5 ${r}_{\oplus }$ ) increases from 0.61 ± 0.09 at young ages (<1 gyr) to 1.00 ± 0.10 at old ages (>1 gyr), consistent with the prediction by core-powered mass loss that the mechanism shaping the radius valley operates over gyr timescales. additionally, we find a tentative decrease in the radii of relatively cool (fp < 150 ${f}_{\oplus }$ ) sub-neptunes over gyr timescales, which suggests that these planets may possess h/he envelopes instead of higher mean molecular weight atmospheres. we confirm the existence of planets within the hot sub-neptunian "desert" (2.2 r⊕ < rp < 3.8 ${r}_{\oplus }$ , fp > 650 ${f}_{\oplus }$ ) and show that these planets are preferentially orbiting more evolved stars compared to other planets at similar incident fluxes. in addition, we identify candidates for cool (fp < 20 ${f}_{\oplus }$ ) inflated jupiters, present a revised list of habitable zone candidates, and find that the ages of single and multiple transiting planet systems are statistically indistinguishable. | the gaia-kepler stellar properties catalog. ii. planet radius demographics as a function of stellar mass and age |
we improve the current upper bound on the axion-photon coupling derived from stellar evolution using the r 2 parameter, the ratio of stellar populations on the asymptotic giant branch to horizontal branch in globular clusters. we compare this with data from simulations using the stellar evolution code mesa which include the effects of axion production. particular attention is given to quantifying in detail the effects of uncertainties on the r and r 2 parameters due to the modelling of convective core boundaries. using a semiconvective mixing scheme we constrain the axion-photon coupling to be gaγγ < 0.47 × 10-10 gev-1. this rules out new regions of qcd axion and axion-like particle parameter space. complementary evidence from asteroseismology suggests that this could improve to as much as gaγγ < 0.34 × 10-10 gev-1 as the uncertainties surrounding mixing across convective boundaries are better understood. | advancing globular cluster constraints on the axion-photon coupling |
the relationship between stellar populations and the ionizing flux with which they irradiate their surroundings has profound implications for the evolution of the intergalactic medium (igm). we quantify the ionizing flux arising from synthetic stellar populations which incorporate the evolution of interacting binary stars. we determine that these show ionizing flux boosted by 60 per cent at 0.05 ≤ z ≤ 0.3 z⊙ and a more modest 10-20 per cent at near-solar metallicities relative to star-forming populations in which stars evolve in isolation. the relation of ionizing flux to observables such as 1500 å continuum and ultraviolet spectral slope is sensitive to attributes of the stellar population including age, star formation history and initial mass function (imf). for a galaxy forming 1 m⊙ yr-1, observed at >100 myr after the onset of star formation, we predict a production rate of photons capable of ionizing hydrogen, nion = 1.4 × 1053 s-1 at z = z⊙ and 3.5 × 1053 s-1 at 0.1 z⊙, assuming a salpeter-like imf. we evaluate the impact of these issues on the ionization of the igm, finding that the known galaxy populations can maintain the ionization state of the universe back to z ∼ 9, assuming that their luminosity functions continue to muv = -10, and that constraints on the igm at z ∼ 2-5 can be satisfied with modest lyman-continuum photon escape fractions of 4-24 per cent depending on assumed metallicity. | stellar population effects on the inferred photon density at reionization |
we present an atlas of ultraviolet and infrared images of ∼15,750 local (d ≲ 50 mpc) galaxies, as observed by nasa’s wide-field infrared survey explorer (wise) and galaxy evolution explorer (galex) missions. these maps have matched resolution (fwhm 7.″5 and 15″), matched astrometry, and a common procedure for background removal. we demonstrate that they agree well with resolved intensity measurements and integrated photometry from previous surveys. this atlas represents the first part of a program (the z = 0 multiwavelength galaxy synthesis) to create a large, uniform database of resolved measurements of gas and dust in nearby galaxies. the images and associated catalogs will be publicly available at the nasa/ipac infrared science archive. this atlas allows us estimate local and integrated star formation rates (sfrs) and stellar masses (m ⋆) across the local galaxy population in a uniform way. in the appendix, we use the population synthesis fits of salim et al. to calibrate integrated m ⋆ and sfr estimators based on galex and wise. because they leverage a sloan digital sky survey (sdss)-based training set of >100,000 galaxies, these calibrations have high precision and allow us to rigorously compare local galaxies to sdss results. we provide these sfr and m ⋆ estimates for all galaxies in our sample and show that our results yield a “main sequence” of star-forming galaxies comparable to previous work. we also show the distribution of intensities from resolved galaxies in nuv-to-wise1 versus wise1-to-wise3 space, which captures much of the key physics accessed by these bands. | a z = 0 multiwavelength galaxy synthesis. i. a wise and galex atlas of local galaxies |
accurate distances to local molecular clouds are critical for understanding the star and planet formation process, yet distance measurements are often obtained inhomogeneously on a cloud-by-cloud basis. we have recently developed a method that combines stellar photometric data with gaia dr2 parallax measurements in a bayesian framework to infer the distances of nearby dust clouds to a typical accuracy of ∼5%. after refining the technique to target lower latitudes and incorporating deep optical data from decam in the southern galactic plane, we have derived a catalog of distances to molecular clouds in reipurth (2008, star formation handbook, vols. i and ii) which contains a large fraction of the molecular material in the solar neighborhood. comparison with distances derived from maser parallax measurements towards the same clouds shows our method produces consistent distances with ≲10% scatter for clouds across our entire distance spectrum (150 pc-2.5 kpc). we hope this catalog of homogeneous distances will serve as a baseline for future work. table a.1 is also 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/cat/j/a+a/633/a51. it is also available on the harvard dataverse at https://doi.org/10.7910/dvn/07l7yz an interactive 3d version of fig. 2 is available at https://www.aanda.org | a compendium of distances to molecular clouds in the star formation handbook |
the σ orionis cluster is important for studying protoplanetary disk evolution, as its intermediate age (∼3-5 myr) is comparable to the median disk lifetime. we use alma to conduct a high-sensitivity survey of dust and gas in 92 protoplanetary disks around σ orionis members with m * ≳ 0.1 m ⊙. our observations cover the 1.33 mm continuum and several co j = 2-1 lines: out of 92 sources, we detect 37 in the millimeter continuum and 6 in 12co, 3 in 13co, and none in c18o. using the continuum emission to estimate dust mass, we find only 11 disks with m dust ≳ 10 m ⊕, indicating that after only a few myr of evolution most disks lack sufficient dust to form giant planet cores. stacking the individually undetected continuum sources limits their average dust mass to 5× lower than that of the faintest detected disk, supporting theoretical models that indicate rapid dissipation once disk clearing begins. comparing the protoplanetary disk population in σ orionis to those of other star-forming regions supports the steady decline in average dust mass and the steepening of the m dust-m * relation with age; studying these evolutionary trends can inform the relative importance of different disk processes during key eras of planet formation. external photoevaporation from the central o9 star is influencing disk evolution throughout the region: dust masses clearly decline with decreasing separation from the photoionizing source, and the handful of co detections exist at projected separations of >1.5 pc. collectively, our findings indicate that giant planet formation is inherently rare and/or well underway by a few myr of age. | an alma survey of protoplanetary disks in the σ orionis cluster |
we present the simultaneous measurement of the interaction rates rp p, rbe, rp e p of p p , 7be, and p e p solar neutrinos performed with a global fit to the borexino data in an extended energy range (0.19-2.93) mev with particular attention to details of the analysis methods. this result was obtained by analyzing 1291.51 days of borexino phase-ii data, collected after an extensive scintillator purification campaign. using counts per day (cpd )/100 ton as unit, we find rp p=134 ±10 (stat )-10+6(sys ) , rb e=48.3 ±1.1 (stat )-0.7+0.4(sys ) ; and rpe p hz=2.43 ±0.36 (stat )-0.22+0.15(sys ) assuming the interaction rate rcno of cno-cycle (carbon, nitrogen, oxigen) solar neutrinos according to the prediction of the high metallicity standard solar model, and rpe p lz=2.65 ±0.36 (stat )-0.24+0.15(sys ) according to that of the low metallicity model. an upper limit rcno<8.1 cpd /100 ton (95% c.l.) is obtained by setting in the fit a constraint on the ratio rp p/rp e p (47.7 ±0.8 cpd /100 ton or 47.5 ±0.8 cpd /100 ton according to the high or low metallicity hypothesis). | simultaneous precision spectroscopy of p p , 7be, and p e p solar neutrinos with borexino phase-ii |
we explore hierarchical black hole (bh) mergers in nuclear star clusters (nscs), globular clusters (gcs) and young star clusters (yscs), accounting for both original and dynamically assembled binary bhs (bbhs). we find that the median mass of both first- and nth-generation dynamical mergers is larger in gcs and yscs with respect to nscs because the lighter bhs are ejected by supernova kicks from the lower mass clusters. also, first- and nth-generation bh masses are strongly affected by the metallicity of the progenitor stars: the median mass of the primary bh of a nth-generation merger is ~24-38 m⊙ (~9-15 m⊙) in metal-poor (metal-rich) nscs. the maximum bh mass mainly depends on the escape velocity: bhs with mass up to several thousand m⊙ form in nscs, while yscs and gcs host bhs with mass up to several hundred m⊙. furthermore, we calculate the fraction of mergers with at least one component in the pair-instability mass gap (fpi) and in the intermediate-mass bh regime (fimbh). in the fiducial model for dynamical bbhs with metallicity z = 0.002, we find fpi ≈ 0.05, 0.02 and 0.007 (fimbh ≈ 0.01, 0.002 and 0.001) in nscs, gcs and yscs, respectively. both fpi and fimbh drop by at least one order of magnitude at solar metallicity. finally, we investigate the formation of gw190521 by assuming that it is either a nearly equal-mass bbh or an intermediate-mass ratio inspiral. | hierarchical black hole mergers in young, globular and nuclear star clusters: the effect of metallicity, spin and cluster properties |
nasa’s kepler space telescope was designed to determine the frequency of earth-sized planets orbiting sun-like stars, but these planets are on the very edge of the mission’s detection sensitivity. accurately determining the occurrence rate of these planets will require automatically and accurately assessing the likelihood that individual candidates are indeed planets, even at low signal-to-noise ratios. we present a method for classifying potential planet signals using deep learning, a class of machine learning algorithms that have recently become state-of-the-art in a wide variety of tasks. we train a deep convolutional neural network to predict whether a given signal is a transiting exoplanet or a false positive caused by astrophysical or instrumental phenomena. our model is highly effective at ranking individual candidates by the likelihood that they are indeed planets: 98.8% of the time it ranks plausible planet signals higher than false-positive signals in our test set. we apply our model to a new set of candidate signals that we identified in a search of known kepler multi-planet systems. we statistically validate two new planets that are identified with high confidence by our model. one of these planets is part of a five-planet resonant chain around kepler-80, with an orbital period closely matching the prediction by three-body laplace relations. the other planet orbits kepler-90, a star that was previously known to host seven transiting planets. our discovery of an eighth planet brings kepler-90 into a tie with our sun as the star known to host the most planets. | identifying exoplanets with deep learning: a five-planet resonant chain around kepler-80 and an eighth planet around kepler-90 |
hot gas giant exoplanets can lose part of their atmosphere due to strong stellar irradiation, and these losses can affect their physical and chemical evolution. studies of atmospheric escape from exoplanets have mostly relied on space-based observations of the hydrogen lyman-α line in the far ultraviolet region, which is strongly affected by interstellar absorption. using ground-based high-resolution spectroscopy, we detected excess absorption in the helium triplet at 1083 nanometers during the transit of the saturn-mass exoplanet wasp-69b, at a signal-to-noise ratio of 18. we measured line blueshifts of several kilometers per second and posttransit absorption, which we interpret as the escape of part of the atmosphere trailing behind the planet in comet-like form. | ground-based detection of an extended helium atmosphere in the saturn-mass exoplanet wasp-69b |
we present a set of 148 independent n-body simulations of globular clusters (gcs) computed using the code cmc (cluster monte carlo). at an age of ∼10-13 gyr, the resulting models cover nearly the full range of cluster properties exhibited by the milky way gcs, including total mass, core and half-light radii, metallicity, and galactocentric distance. we use our models to investigate the role that stellar-mass black holes play in the process of core collapse. furthermore, we study how dynamical interactions affect the formation and evolution of several important types of sources in gcs, including low-mass x-ray binaries, millisecond pulsars, blue stragglers, cataclysmic variables, type ia supernovae, calcium-rich transients, and merging compact binaries. while our focus here is on old, low-metallicity gcs, our cmc simulations follow the evolution of clusters over a hubble time, and they include a wide range of metallicities (up to solar), so that our results can also be used to study younger and higher-metallicity star clusters. finally, the output from these simulations is available for download at https://cmc.ciera.northwestern.edu/home/. | modeling dense star clusters in the milky way and beyond with the cmc cluster catalog |
the redshifted 21 cm line is an emerging tool in cosmology, in principle permitting three-dimensional surveys of our universe that reach unprecedentedly large volumes, previously inaccessible length scales, and hitherto unexplored epochs of our cosmic timeline. large radio telescopes have been constructed for this purpose, and in recent years there has been considerable progress in transforming 21 cm cosmology from a field of considerable theoretical promise to one of observational reality. increasingly, practitioners in the field are coming to the realization that the success of observational 21 cm cosmology will hinge on software algorithms and analysis pipelines just as much as it does on careful hardware design and telescope construction. this review provides a pedagogical introduction to state-of-the-art ideas in 21 cm data analysis, covering a wide variety of steps in a typical analysis pipeline, from calibration to foreground subtraction to map making to power spectrum estimation to parameter estimation. | data analysis for precision 21 cm cosmology |
over the past decades, rest-frame ultraviolet (uv) observations have provided large samples of uv luminous galaxies at redshift (z) greater than 6 (refs. 1-3), during the so-called epoch of reionization. while a few of these uv-identified galaxies revealed substantial dust reservoirs4-7, very heavily dust-obscured sources at these early times have remained elusive. they are limited to a rare population of extreme starburst galaxies8-12 and companions of rare quasars13,14. these studies conclude that the contribution of dust-obscured galaxies to the cosmic star formation rate density at z > 6 is sub-dominant. recent alma and spitzer observations have identified a more abundant, less extreme population of obscured galaxies at z = 3−6 (refs. 15,16). however, this population has not been confirmed in the reionization epoch so far. here, we report the discovery of two dust-obscured star-forming galaxies at z = 6.6813 ± 0.0005 and z = 7.3521 ± 0.0005. these objects are not detected in existing rest-frame uv data and were discovered only through their far-infrared [c ii] lines and dust continuum emission as companions to typical uv-luminous galaxies at the same redshift. the two galaxies exhibit lower infrared luminosities and star-formation rates than extreme starbursts, in line with typical star-forming galaxies at z ≈ 7. this population of heavily dust-obscured galaxies appears to contribute 10-25% to the z > 6 cosmic star formation rate density. | normal, dust-obscured galaxies in the epoch of reionization |
m dwarf stars, which have masses less than 60 per cent that of the sun, make up 75 per cent of the population of the stars in the galaxy. the atmospheres of orbiting earth-sized planets are observationally accessible via transmission spectroscopy when the planets pass in front of these stars. statistical results suggest that the nearest transiting earth-sized planet in the liquid-water, habitable zone of an m dwarf star is probably around 10.5 parsecs away. a temperate planet has been discovered orbiting proxima centauri, the closest m dwarf, but it probably does not transit and its true mass is unknown. seven earth-sized planets transit the very low-mass star trappist-1, which is 12 parsecs away, but their masses and, particularly, their densities are poorly constrained. here we report observations of lhs 1140b, a planet with a radius of 1.4 earth radii transiting a small, cool star (lhs 1140) 12 parsecs away. we measure the mass of the planet to be 6.6 times that of earth, consistent with a rocky bulk composition. lhs 1140b receives an insolation of 0.46 times that of earth, placing it within the liquid-water, habitable zone. with 90 per cent confidence, we place an upper limit on the orbital eccentricity of 0.29. the circular orbit is unlikely to be the result of tides and therefore was probably present at formation. given its large surface gravity and cool insolation, the planet may have retained its atmosphere despite the greater luminosity (compared to the present-day) of its host star in its youth. because lhs 1140 is nearby, telescopes currently under construction might be able to search for specific atmospheric gases in the future. | a temperate rocky super-earth transiting a nearby cool star |
we perform long-term general relativistic neutrino radiation hydrodynamics simulations (in axisymmetry) for a massive neutron star (mns) surrounded by a torus, which is a canonical remnant formed after the binary neutron star merger. we take into account the effects of viscosity, which is likely to arise in the merger remnant due to magnetohydrodynamical turbulence. the viscous effect plays key roles for the mass ejection from the remnant in two phases of the evolution. in the first t ≲ 10 ms, a differential rotation state of the mns is changed to a rigidly rotating state. a shock wave caused by the variation of its quasi-equilibrium state induces significant mass ejection of mass ∼(0.5-2.0) × {10}-2 {m}⊙for the α-viscosity parameter of 0.01-0.04. for the longer-term evolution with ∼0.1-10 s, a significant fraction of the torus material is ejected. we find that the total mass of the viscosity-driven ejecta (≳ {10}-2 {m}⊙ ) could dominate over that of the dynamical ejecta (≲ {10}-2 {m}⊙ ). the electron fraction, ye , of the ejecta is always high enough (ye≳ 0.25) that this post-merger ejecta is lanthanide-poor; hence, the opacity of the ejecta is likely to be ∼10-100 times lower than that of the dynamical ejecta. this indicates that the electromagnetic signal from the ejecta would be rapidly evolving, bright, and blue if it is observed from a small viewing angle (≲45°) for which the effect of the dynamical ejecta is minor. | mass ejection from the remnant of a binary neutron star merger: viscous-radiation hydrodynamics study |
we present predictions for neutron star tidal deformabilities obtained from a bayesian analysis of the nuclear equation of state, assuming a minimal model at high-density that neglects the possibility of phase transitions. the bayesian posterior probability distribution is constructed from priors obtained from microscopic many-body theory based on realistic two- and three-body nuclear forces, while the likelihood functions incorporate empirical information about the equation of state from nuclear experiments. the neutron star crust equation of state is constructed from the liquid drop model, and the core-crust transition density is found by comparing the energy per baryon in inhomogeneous matter and uniform nuclear matter. from the cold β -equilibrated neutron star equation of state, we then compute neutron star tidal deformabilities as well as the mass-radius relationship. finally, we investigate correlations between the neutron star tidal deformability and properties of finite nuclei. | bayesian modeling of the nuclear equation of state for neutron star tidal deformabilities and gw170817 |
the monte carlo evaluation of path integrals is one of a few general purpose methods to approach strongly coupled systems. it is used in all branches of physics, from qcd and nuclear physics to the correlated electron systems. however, many systems of great importance (dense matter inside neutron stars, the repulsive hubbard model away from half filling, and dynamical and nonequilibrium observables) are not amenable to the monte carlo method as it currently stands due to the so-called sign problem. a new set of ideas recently developed to tackle the sign problem based on the complexification of field space and the picard-lefshetz theory accompanying it is reviewed. the mathematical ideas underpinning this approach, as well as the algorithms developed thus far, are described together with nontrivial examples where the method has already been proved successful. directions of future work, including the burgeoning use of machine learning techniques, are delineated. | complex paths around the sign problem |
new spectroscopic surveys offer the promise of stellar parameters and abundances (“stellar labels”) for hundreds of thousands of stars; this poses a formidable spectral modeling challenge. in many cases, there is a subset of reference objects for which the stellar labels are known with high(er) fidelity. we take advantage of this with the cannon, a new data-driven approach for determining stellar labels from spectroscopic data. the cannon learns from the “known” labels of reference stars how the continuum-normalized spectra depend on these labels by fitting a flexible model at each wavelength; then, the cannon uses this model to derive labels for the remaining survey stars. we illustrate the cannon by training the model on only 542 stars in 19 clusters as reference objects, with {t}{eff}, {log} g, and [{fe}/{{h}}] as the labels, and then applying it to the spectra of 55,000 stars from apogee dr10. the cannon is very accurate. its stellar labels compare well to the stars for which apogee pipeline (aspcap) labels are provided in dr10, with rms differences that are basically identical to the stated aspcap uncertainties. beyond the reference labels, the cannon makes no use of stellar models nor any line-list, but needs a set of reference objects that span label-space. the cannon performs well at lower signal-to-noise, as it delivers comparably good labels even at one-ninth the apogee observing time. we discuss the limitations of the cannon and its future potential, particularly, to bring different spectroscopic surveys onto a consistent scale of stellar labels. | the cannon: a data-driven approach to stellar label determination |
the lyman continuum (lyc) cannot be observed at the epoch of reionization (z ≳ 6) owing to intergalactic h i absorption. to identify lyc emitters (lces) and infer the fraction of escaping lyc, astronomers have developed various indirect diagnostics of lyc escape. using measurements of the lyc from the low-redshift lyman continuum survey (lzlcs), we present the first statistical test of these diagnostics. while optical depth indicators based on lyα, such as peak velocity separation and equivalent width, perform well, we also find that other diagnostics, such as the [o iii]/[o ii] flux ratio and star formation rate surface density, predict whether a galaxy is an lce. the relationship between these galaxy properties and the fraction of escaping lyc flux suggests that lyc escape depends strongly on h i column density, ionization parameter, and stellar feedback. we find that lces occupy a range of stellar masses, metallicities, star formation histories, and ionization parameters, which may indicate episodic and/or different physical causes of lyc escape. | the low-redshift lyman continuum survey. ii. new insights into lyc diagnostics |
compact object mergers: population astrophysics and statistics (compas; https://compas.science) is a public rapid binary population synthesis code. compas generates populations of isolated stellar binaries under a set of parameterized assumptions in order to allow comparisons against observational data sets, such as those coming from gravitational-wave observations of merging compact remnants. it includes a number of tools for population processing in addition to the core binary evolution components. compas is publicly available via the github repository https://github.com/teamcompas/compas/, and is designed to allow for flexible modifications as evolutionary models improve. this paper describes the methodology and implementation of compas. it is a living document that will be updated as new features are added to compas; the current document describes compas v02.21.00. | rapid stellar and binary population synthesis with compas |
general relativistic magnetohydrodynamic (grmhd) simulations have revolutionized our understanding of black hole accretion. here, we present a gpu-accelerated grmhd code h-amr with multifaceted optimizations that, collectively, accelerate computation by 2-5 orders of magnitude for a wide range of applications. first, it introduces a spherical grid with 3d adaptive mesh refinement that operates in each of the three dimensions independently. this allows us to circumvent the courant condition near the polar singularity, which otherwise cripples high-resolution computational performance. second, we demonstrate that local adaptive time stepping on a logarithmic spherical-polar grid accelerates computation by a factor of ≲10 compared to traditional hierarchical time-stepping approaches. jointly, these unique features lead to an effective speed of ~109 zone cycles per second per node on 5400 nvidia v100 gpus (i.e., 900 nodes of the olcf summit supercomputer). we illustrate h-amr's computational performance by presenting the first grmhd simulation of a tilted thin accretion disk threaded by a toroidal magnetic field around a rapidly spinning black hole. with an effective resolution of 13,440 × 4608 × 8092 cells and a total of ≲22 billion cells and ~0.65 × 108 time steps, it is among the largest astrophysical simulations ever performed. we find that frame dragging by the black hole tears up the disk into two independently precessing subdisks. the innermost subdisk rotation axis intermittently aligns with the black hole spin, demonstrating for the first time that such long-sought alignment is possible in the absence of large-scale poloidal magnetic fields. | h-amr: a new gpu-accelerated grmhd code for exascale computing with 3d adaptive mesh refinement and local adaptive time stepping |
exoplanets with substantial hydrogen/helium atmospheres have been discovered in abundance, many residing extremely close to their parent stars. the extreme irradiation levels that these atmospheres experience cause them to undergo hydrodynamic atmospheric escape. ongoing atmospheric escape has been observed to be occurring in a few nearby exoplanet systems through transit spectroscopy both for hot jupiters and for lower-mass super-earths and mini-neptunes. detailed hydrodynamic calculations that incorporate radiative transfer and ionization chemistry are now common in one-dimensional models, and multidimensional calculations that incorporate magnetic fields and interactions with the interstellar environment are cutting edge. however, comparison between simulations and observations remains very limited. while hot jupiters experience atmospheric escape, the mass-loss rates are not high enough to affect their evolution. however, for lower-mass planets, atmospheric escape drives and controls their evolution, sculpting the exoplanet population that we observe today. | atmospheric escape and the evolution of close-in exoplanets |
we consider the formation of binary black hole (bh) mergers through the evolution of field massive triple stars. in this scenario, favorable conditions for the inspiral of a bh binary are initiated by its gravitational interaction with a distant companion, rather than by a common-envelope phase invoked in standard binary evolution models. we use a code that follows self-consistently the evolution of massive triple stars, combining the secular triple dynamics (lidov-kozai cycles) with stellar evolution. after a bh triple is formed, its dynamical evolution is computed using either the orbit-averaged equations of motion, or a high-precision direct integrator for triples with weaker hierarchies for which the secular perturbation theory breaks down. most bh mergers in our models are produced in the latter non-secular dynamical regime. we derive the properties of the merging binaries and compute a bh merger rate in the range (0.3-1.3) gpc-3 yr-1, or up to ≈2.5 gpc-3 yr-1 if the bh orbital planes have initially random orientation. finally, we show that bh mergers from the triple channel have significantly higher eccentricities than those formed through the evolution of massive binaries or in dense star clusters. measured eccentricities could therefore be used to uniquely identify binary mergers formed through the evolution of triple stars. while our results suggest up to ≈10 detections per year with advanced-ligo, the high eccentricities could render the merging binaries harder to detect with planned space based interferometers such as lisa. | binary black hole mergers from field triples: properties, rates, and the impact of stellar evolution |
the combined observation of gravitational and electromagnetic waves from the coalescence of two neutron stars marks the beginning of multimessenger astronomy with gravitational waves (gws). the development of accurate gravitational waveform models is a crucial prerequisite to extract information about the properties of the binary system that generated a detected gw signal. in binary neutron star systems (bns), tidal effects also need to be incorporated in the modeling for an accurate waveform representation. building on previous work [phys. rev. d 96, 121501 (2017), 10.1103/physrevd.96.121501], we explore the performance of inspiral-merger waveform models that are obtained by adding a numerical relativity (nr) based approximant for the tidal part of the phasing (nrtidal) to existing models for nonprecessing and precessing binary black hole systems, as implemented in the lsc algorithm library suite. the resulting bns waveforms are compared and contrasted to a set of target waveforms which we obtain by hybridizing nr waveforms (covering the last ∼10 orbits up to the merger and extending through the postmerger phase) with inspiral waveforms calculated from 30 hz obtained with a state-of-the-art effective-one-body waveform model. while due to the construction procedure of the target waveforms, there is no error budget available over the full frequency range accessible by advanced gw detectors, the waveform set presents only an approximation of the real signal. we probe that the combination of the self-spin terms and of the nrtidal description is necessary to obtain minimal mismatches (≲0.01 ) and phase differences (≲1 rad ) with respect to the target waveforms. we also discuss possible improvements and drawbacks of the nrtidal approximant in its current form. | matter imprints in waveform models for neutron star binaries: tidal and self-spin effects |
the explosion of ultra-stripped stars in close binaries can lead to ejecta masses <0.1 m⊙ and may explain some of the recent discoveries of weak and fast optical transients. in tauris et al., it was demonstrated that helium star companions to neutron stars (nss) may experience mass transfer and evolve into naked ∼1.5 m⊙ metal cores, barely above the chandrasekhar mass limit. here, we elaborate on this work and present a systematic investigation of the progenitor evolution leading to ultra-stripped supernovae (sne). in particular, we examine the binary parameter space leading to electron-capture (ec sne) and iron core-collapse sne (fe ccsne), respectively, and determine the amount of helium ejected with applications to their observational classification as type ib or type ic. we mainly evolve systems where the sn progenitors are helium star donors of initial mass mhe = 2.5-3.5 m⊙ in tight binaries with orbital periods of porb = 0.06-2.0 d, and hosting an accreting ns, but we also discuss the evolution of wider systems and of both more massive and lighter - as well as single - helium stars. in some cases, we are able to follow the evolution until the onset of silicon burning, just a few days prior to the sn explosion. we find that ultra-stripped sne are possible for both ec sne and fe ccsne. ec sne only occur for mhe = 2.60-2.95 m⊙ depending on porb. the general outcome, however, is an fe ccsn above this mass interval and an onemg or co white dwarf for smaller masses. for the exploding stars, the amount of helium ejected is correlated with porb - the tightest systems even having donors being stripped down to envelopes of less than 0.01 m⊙. we estimate the rise time of ultra-stripped sne to be in the range 12 h-8 d, and light-curve decay times between 1 and 50 d. a number of fitting formulae for our models are provided with applications to population synthesis. ultra-stripped sne may produce nss in the mass range 1.10-1.80 m⊙ and are highly relevant for ligo/virgo since most (possibly all) merging double ns systems have evolved through this phase. finally, we discuss the low-velocity kicks which might be imparted on these resulting nss at birth. | ultra-stripped supernovae: progenitors and fate |
by compiling a comprehensive census of literature studies, we investigate the evolution of the main sequence (ms) of star-forming galaxies (sfgs) in the widest range of redshift (0 < z < 6) and stellar mass (108.5-1011.5 m⊙) ever probed. we convert all observations to a common calibration and find a remarkable consensus on the variation of the ms shape and normalization across cosmic time. the relation exhibits a curvature towards the high stellar masses at all redshifts. the best functional form is governed by two parameters: the evolution of the normalization and the turnover mass (m0(t)), which both evolve as a power law of the universe age. the turn-over mass determines the ms shape. it marginally evolves with time, making the ms slightly steeper towards z ~ 4-6. at stellar masses below m0(t), sfgs have a constant specific sfr (ssfr), while above m0(t) the ssfr is suppressed. we find that the ms is dominated by central galaxies. this allows to turn m0(t) into the corresponding host halo mass. this evolves as the halo mass threshold between cold and hot accretion regimes, as predicted by the theory of accretion, where the central galaxy is fed or starved of cold gas supply, respectively. we, thus, argue that the progressive ms bending as a function of the universe age is caused by the lower availability of cold gas in haloes entering the hot accretion phase, in addition to black hole feedback. we also find qualitatively the same trend in the largest sample of star-forming galaxies provided by the illustristng simulation. nevertheless, we still note large quantitative discrepancies with respect to observations, in particular at the high-mass end. these can not be easily ascribed to biases or systematics in the observed sfrs and the derived ms. | the main sequence of star-forming galaxies across cosmic times |
we present a new set of high-resolution hydrodynamic cosmological zoom-in simulations that apply the feedback in realistic environments physics to both local group (lg)-like and isolated milky way (mw)-like volumes (10 host systems in total with a baryonic particle mass ≃ 3500-7000 m_⊙). we study the stellar mass functions, circular velocity or mass profiles, and velocity dispersions of the dwarf galaxy populations. the simulations reproduce the stellar mass function and central densities of mw satellite dwarfs for m_\ast ≥ 10^{5.5} m_⊙ and predict the existence of ∼3 unidentified galaxies with m_\ast ∼ 10^5 m_⊙ within 300 kpc of the mw. overall, we find no evidence for the classical missing satellites or too-big-to-fail (tbtf) problems for satellite galaxies in our sample. among the satellites, tbtf is resolved primarily by subhalo disruption and overall mass-loss; central density profiles of subhaloes are of secondary importance. for non-satellite galaxies, our lg-like simulations predict as many as ∼10 as-of-yet unseen galaxies at distances 0.3-1 mpc from both hosts, with m_\ast ∼eq 10^{5-6} m_⊙ (in haloes with vmax ∼ 20 km s-1), albeit with large halo-to-halo variance. none of our simulations produces a compact, baryon-dominated, high-density dwarf elliptical-type galaxy (with vcirc ≳ 35 km s-1 at r<1 kpc), of which six may appear in the lg (but none in the mw). it may therefore remain a challenge to reproduce the full diversity of the dwarf population, including both the highest and lowest density systems. | the local group on fire: dwarf galaxy populations across a suite of hydrodynamic simulations |
the latest observation of hl tau by alma revealed spectacular concentric dust rings in its circumstellar disk. we attempt to explain the multiple ring structure as a consequence of aggregate sintering. sintering is known to reduce the sticking efficiency of dust aggregates and occurs at temperatures slightly below the sublimation point of the constituent material. we present a dust growth model that incorporates sintering and use it to simulate global dust evolution due to sintering, coagulation, fragmentation, and radial inward drift in a modeled hl tau disk. we show that aggregates consisting of multiple species of volatile ices experience sintering, collisionally disrupt, and pile up at multiple locations slightly outside the snow lines of the volatiles. at wavelengths of 0.87-1.3 mm, these sintering zones appear as bright, optically thick rings with a spectral slope of ≈ 2, whereas the non-sintering zones appear as darker, optically thinner rings of a spectral slope of ≈ 2.3-2.5. the observational features of the sintering and non-sintering zones are consistent with those of the major bright and dark rings found in the hl tau disk, respectively. radial pileup and vertical settling occur simultaneously if disk turbulence is weak and if monomers constituting the aggregates are ∼ 1 μ {{m}} in radius. for the radial gas temperature profile of t=310{(r/1{au})}-0.57 {{k}}, our model perfectly reproduces the brightness temperatures of the optically thick bright rings and reproduces their orbital distances to an accuracy of ≲ 30%. | sintering-induced dust ring formation in protoplanetary disks: application to the hl tau disk |
we describe the processing of the phangs-alma survey and present the phangs-alma pipeline, a public software package that processes calibrated interferometric and total power data into science-ready data products. phangs-alma is a large, high-resolution survey of co(2-1) emission from nearby galaxies. the observations combine alma's main 12 m array, the 7 m array, and total power observations, and use mosaics of dozens to hundreds of individual pointings. we describe the processing of the u - v data, imaging and deconvolution, linear mosaicking, combining interferometer and total power data, noise estimation, masking, data product creation, and quality assurance. our pipeline has a general design and can also be applied to very large array and alma observations of other spectral lines and continuum emission. we highlight our recipe for deconvolution of complex spectral line observations, which combines multiscale clean, single-scale clean, and automatic mask generation in a way that appears robust and effective. we also emphasize our two-track approach to masking and data product creation. we construct one set of "broadly masked" data products, which have high completeness but significant contamination by noise, and another set of "strictly masked" data products, which have high confidence but exclude faint, low signal-to-noise emission. our quality assurance tests, supported by simulations, demonstrate that 12 m+7 m deconvolved data recover a total flux that is significantly closer to the total power flux than the 7 m deconvolved data alone. in the appendices, we measure the stability of the alma total power calibration in phangs-alma and test the performance of popular short-spacing correction algorithms. | phangs-alma data processing and pipeline |
'hot super-earths' (or 'mini-neptunes') between one and four times earth's size with period shorter than 100 d orbit 30-50 per cent of sun-like stars. their orbital configuration - measured as the period ratio distribution of adjacent planets in multiplanet systems - is a strong constraint for formation models. here, we use n-body simulations with synthetic forces from an underlying evolving gaseous disc to model the formation and long-term dynamical evolution of super-earth systems. while the gas disc is present, planetary embryos grow and migrate inward to form a resonant chain anchored at the inner edge of the disc. these resonant chains are far more compact than the observed super-earth systems. once the gas dissipates, resonant chains may become dynamically unstable. they undergo a phase of giant impacts that spreads the systems out. disc turbulence has no measurable effect on the outcome. our simulations match observations if a small fraction of resonant chains remain stable, while most super-earths undergo a late dynamical instability. our statistical analysis restricts the contribution of stable systems to less than 25 per cent. our results also suggest that the large fraction of observed single-planet systems does not necessarily imply any dichotomy in the architecture of planetary systems. finally, we use the low abundance of resonances in kepler data to argue that, in reality, the survival of resonant chains happens likely only in ∼5 per cent of the cases. this leads to a mystery: in our simulations only 50-60 per cent of resonant chains became unstable, whereas at least 75 per cent (and probably 90-95 per cent) must be unstable to match observations. | breaking the chains: hot super-earth systems from migration and disruption of compact resonant chains |
we combine high-resolution spectroscopic data from apogee-2 survey data release 16 (dr16) with broad-band photometric data from several sources as well as parallaxes from gaia data release 2 (dr2). using the bayesian isochrone-fitting code starhorse, we derived the distances, extinctions, and astrophysical parameters for around 388 815 apogee stars. we achieve typical distance uncertainties of ∼6% for apogee giants, ∼2% for apogee dwarfs, and extinction uncertainties of ∼0.07 mag, when all photometric information is available, and ∼0.17 mag if optical photometry is missing. starhorse uncertainties vary with the input spectroscopic catalogue, available photometry, and parallax uncertainties. to illustrate the impact of our results, we show that thanks to gaia dr2 and the now larger sky coverage of apogee-2 (including apogee-south), we obtain an extended map of the galactic plane. we thereby provide an unprecedented coverage of the disc close to the galactic mid-plane (|zgal| < 1 kpc) from the galactic centre out to rgal ∼ 20 kpc. the improvements in statistics as well as distance and extinction uncertainties unveil the presence of the bar in stellar density and the striking chemical duality in the innermost regions of the disc, which now clearly extend to the inner bulge. we complement this paper with distances and extinctions for stars in other public released spectroscopic surveys: 324 999 in galah dr2, 4 928 715 in lamost dr5, 408 894 in rave dr6, and 6095 in ges dr3. data are 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/cat/j/a+a/638/a76 | from the bulge to the outer disc: starhorse stellar parameters, distances, and extinctions for stars in apogee dr16 and other spectroscopic surveys |
the hubble constant (h0 ) estimated from the local cepheid-supernova distance ladder is in 3 -σ tension with the value extrapolated from cosmic microwave background (cmb) data assuming the standard cosmological model. whether this tension represents new physics or systematic effects is the subject of intense debate. here, we investigate how new, independent h0 estimates can arbitrate this tension, assessing whether the measurements are consistent with being derived from the same model using the posterior predictive distribution (ppd). we show that, with existing data, the inverse distance ladder formed from boss baryon acoustic oscillation measurements and the pantheon supernova sample yields an h0 posterior near identical to the planck cmb measurement. the observed local distance ladder value is a very unlikely draw from the resulting ppd. turning to the future, we find that a sample of ∼50 binary neutron star "standard sirens" (detectable within the next decade) will be able to adjudicate between the local and cmb estimates. | prospects for resolving the hubble constant tension with standard sirens |
following our first detection reported in izotov et al., we present the detection of lyman continuum (lyc) radiation of four other compact star-forming galaxies observed with the cosmic origins spectrograph (cos) onboard the hubble space telescope. these galaxies, at redshifts of z ∼ 0.3, are characterized by high emission-line flux ratios [o iii] λ5007/[o ii] λ3727 ≳ 5. the escape fractions of the lyc radiation fesc(lyc) in these galaxies are in the range of ∼6-13 per cent, the highest values found so far in low-redshift star-forming galaxies. narrow double-peaked ly α emission lines are detected in the spectra of all four galaxies, compatible with predictions for lyc leakers. we find escape fractions of ly α, fesc(ly α) ∼ 20-40 per cent, among the highest known for ly α emitting galaxies. surface brightness profiles produced from the cos acquisition images reveal bright star-forming regions in the centre and exponential discs in the outskirts with disc scalelengths α in the range ∼0.6-1.4 kpc. our galaxies are characterized by low metallicity, ∼1/8-1/5 solar, low stellar mass ∼(0.2-4) × 109 m⊙, high star formation rates, sfr ∼ 14-36 m⊙ yr-1, and high sfr densities, σ ∼ 2-35 m⊙ yr-1 kpc-2. these properties are comparable to those of high-redshift star-forming galaxies. finally, our observations, combined with our first detection reported in izotov et al., reveal that a selection for compact star-forming galaxies showing high [o iii] λ5007/[o ii] λ3727 ratios appears to pick up very efficiently sources with escaping lyc radiation: all five of our selected galaxies are lyc leakers. | detection of high lyman continuum leakage from four low-redshift compact star-forming galaxies |
astrophysical black hole candidates are thought to be the kerr black holes of general relativity, but there is not yet direct observational evidence that the spacetime geometry around these objects is described by the kerr solution. the study of the properties of the electromagnetic radiation emitted by gas or stars orbiting these objects can potentially test the kerr black hole hypothesis. this paper reviews the state of the art of this research field, describing the possible approaches to test the kerr metric with current and future observational facilities and discussing current constraints. | testing black hole candidates with electromagnetic radiation |
ground- and space-based planet searches employing radial velocity techniques and transit photometry have detected thousands of planet-hosting stars in the milky way. with so many planets discovered, the next step toward identifying potentially habitable planets is atmospheric characterization. while the sun-earth system provides a good framework for understanding the atmospheric chemistry of earth-like planets around solar-type stars, the observational and theoretical constraints on the atmospheres of rocky planets in the habitable zones (hzs) around low-mass stars (k and m dwarfs) are relatively few. the chemistry of these atmospheres is controlled by the shape and absolute flux of the stellar spectral energy distribution (sed), however, flux distributions of relatively inactive low-mass stars are poorly understood at present. to address this issue, we have executed a panchromatic (x-ray to mid-ir) study of the seds of 11 nearby planet-hosting stars, the measurements of the ultraviolet spectral characteristics of low-mass exoplanetary systems (muscles) treasury survey. the muscles program consists visible observations from hubble and ground-based observatories. infrared and astrophysically inaccessible wavelengths (euv and lyα) are reconstructed using stellar model spectra to fill in gaps in the observational data. in this overview and the companion papers describing the muscles survey, we show that energetic radiation (x-ray and ultraviolet) is present from magnetically active stellar atmospheres at all times for stars as late as m6. the emission line luminosities of c iv and mg ii are strongly correlated with band-integrated luminosities and we present empirical relations that can be used to estimate broadband fuv and xuv (≡x-ray + euv) fluxes from individual stellar emission line measurements. we find that while the slope of the sed, fuv/nuv, increases by approximately two orders of magnitude form early k to late m dwarfs (≈0.01-1), the absolute fuv and xuv flux levels at their corresponding hz distances are constant to within factors of a few, spanning the range 10-70 erg cm-2 s-1 in the hz. despite the lack of strong stellar activity indicators in their optical spectra, several of the m dwarfs in our sample show spectacular uv flare emission in their light curves. we present an example with flare/quiescent ultraviolet flux ratios of the order of 100:1 where the transition region energy output during the flare is comparable to the total quiescent luminosity of the star eflare(uv) ∼ 0.3 l*δt (δt = 1 s). finally, we interpret enhanced l(line)/lbol ratios for c iv and n v as tentative observational evidence for the interaction of planets with large planetary mass-to-orbital distance ratios (mplan/aplan) with the transition regions of their host stars. based on observations made with the nasa/esa hubble space telescope, obtained from the data archive at the space telescope science institute. stsci is operated by the association of universities for research in astronomy, inc. under nasa contract nas 5-26555. | the muscles treasury survey. i. motivation and overview |
the direct detection of gravitational waves from merging binary black holes opens up a window into the environments in which binary black holes form. one signature of such environments is the angular distribution of the black hole spins. binary systems that formed through dynamical interactions between already-compact objects are expected to have isotropic spin orientations (that is, the spins of the black holes are randomly oriented with respect to the orbit of the binary system), whereas those that formed from pairs of stars born together are more likely to have spins that are preferentially aligned with the orbit. the best-measured combination of spin parameters for each of the four likely binary black hole detections gw150914, lvt151012, gw151226 and gw170104 is the ‘effective’ spin. here we report that, if the magnitudes of the black hole spins are allowed to extend to high values, the effective spins for these systems indicate a 0.015 odds ratio against an aligned angular distribution compared to an isotropic one. when considering the effect of ten additional detections, this odds ratio decreases to 2.9 × 10-7 against alignment. the existing preference for either an isotropic spin distribution or low spin magnitudes for the observed systems will be confirmed (or overturned) confidently in the near future. | distinguishing spin-aligned and isotropic black hole populations with gravitational waves |
we present the first systematic study of strong binary-single and binary-binary black hole (bh) interactions with the inclusion of general relativity. by including general relativistic effects in the equations of motion during strong encounters, the dissipation of orbital energy from the emission of gravitational waves (gws) can lead to captures and subsequent inspirals with appreciable eccentricities when entering the sensitive frequency ranges of the ligo and virgo gw detectors. it has been shown that binary-single interactions significantly contribute to the rate of eccentric mergers, but no studies have looked exclusively into the contribution from binary-binary interactions. to this end, we perform binary-binary and binary-single scattering experiments with general relativistic dynamics up through the 2.5 post-newtonian order included, both in a controlled setting to gauge the importance of non-dissipative post-newtonian terms and derive scaling relations for the cross section of gw captures, as well as experiments tuned to the strong interactions from state-of-the art globular cluster (gc) models to assess the relative importance of the binary-binary channel in facilitating gw captures and the resultant eccentricity distributions of inspiral from channel. although binary-binary interactions are 10-100 times less frequent in gcs than binary-single interactions, their longer lifetime and more complex dynamics leads to a higher probability for gw captures to occur during the encounter. we find that binary-binary interactions contribute 25%-45% of the eccentric mergers that occur during strong bh encounters in gcs, regardless of the properties of the cluster environment. the inclusion of higher multiplicity encounters in dense star clusters therefore have major implications on the predicted rates of highly eccentric binaries potentially detectable by the ligo/virgo network. because gravitational waveforms of eccentric inspirals are distinct from those generated by merging binaries that have circularized, measurements of eccentricity in such systems would highly constrain their formation scenario. | eccentric black hole mergers in dense star clusters: the role of binary-binary encounters |
the observation of gravitational waves from an asymmetric binary opens the possibility for heavy neutron stars, but these pose challenges to models of the neutron star equation of state. we construct heavy neutron stars by introducing nontrivial structure in the speed of sound sourced by deconfined qcd matter, which cannot be well recovered by spectral representations. their moment of inertia, love number, and quadrupole moment are very small, so a tenfold increase in sensitivity may be needed to test this possibility with gravitational waves, which is feasible with third generation detectors. | neutron star equation of state in light of gw190814 |
we present the results of a search for high-redshift (z > 9) galaxy candidates in the jwst uncover survey, using deep nircam and niriss imaging in seven bands over ~45 arcmin2 and ancillary hubble space telescope (hst) observations. the nircam observations reach a 5σ limiting magnitude of ~29.2 ab. the identification of high-z candidates relies on a combination of a dropout selection and photometric redshifts. we find 16 candidates at 9 < z < 12 and three candidates at 12 < z < 13, eight candidates are deemed very robust. their lensing amplification ranges from μ = 1.2 to 11.5. candidates have a wide range of (lensing corrected) luminosities and young ages, with low stellar masses [6.8 < log(m⋆/m⊙) < 9.5] and low star formation rates (sfr = 0.2-7 m⊙ yr-1), confirming previous findings in early jwst observations of z > 9. a few galaxies at z ~ 9-10 appear to show a clear balmer break between the f356w and f444w/f410m bands, which helps constrain their stellar mass. we estimate blue uv continuum slopes between β = -1.8 and -2.3, typical for early galaxies at z > 9 but not as extreme as the bluest recently discovered sources. we also find evidence for a rapid redshift-evolution of the mass-luminosity relation and a redshift evolution of the uv continuum slope for a given range of intrinsic magnitude, in line with theoretical predictions. these findings suggest that deeper jwst observations are needed to reach the fainter galaxy population at those early epochs, and follow-up spectroscopy will help better constrain the physical properties and star formation histories of a larger sample of galaxies. | jwst uncover: discovery of z > 9 galaxy candidates behind the lensing cluster abell 2744 |
in the present article, we have constructed a static charged anisotropic compact star model of einstein field equations for a spherically symmetric space-time geometry. specifically, we have extended the charged isotropic heintzmann solution to an anisotropic domain. to address this work, we have employed the gravitational decoupling through the so called minimal geometric deformation approach. the charged anisotropic model is representing the realistic compact objects such as rxj1856-37 and sax j1808.4-3658(ss2). we have reported our results in details for the compact star rxj1856-37 on the ground of physical properties such as pressure, density, velocity of sound, energy conditions, stability conditions, tolman-oppenheimer-volkoff equation and redshift etc. | charged anisotropic compact objects by gravitational decoupling |
the physical processes that establish the morphological evolution and the structural diversity of galaxies are key unknowns in extragalactic astrophysics. here we report the finding of the morphologically-mature galaxy jades-gs+53.18343-27.79097, which existed within the first 700 million years of the universe's history. this star-forming galaxy with a stellar mass of $10^{8.6}$ solar masses consists of three components, a highly-compact core with a half-light radius of 144 pc, a strongly star-forming disc with a radius of 468 pc, and a star-forming clump, which all show distinctive star-formation histories. the central stellar mass density of this galaxy is within a factor of two of the most massive present-day ellipticals, while being globally 1000 times less massive. the radial profile of the specific star-formation rate is strongly rising toward the outskirts. this evidence strongly suggests the first detection of inside-out growth of a galaxy as a proto-bulge and a star-forming disc in the epoch of reionization. | inside-out growth in the early universe: a core in a vigorously star-forming disc |
we investigate the incidence and properties of ionized gas outflows in a sample of 52 galaxies with stellar mass between $10^7$ m$_{\odot}$ and $10^9$ m$_{\odot}$ observed with ultra-deep jwst/nirspec msa spectroscopy as part of the jwst advanced deep extragalactic survey (jades). the high-spectral resolution (r2700) nirspec observations allowed us to identify for the first time the signature of outflows in the rest-frame optical nebular lines in low-mass galaxies at $z>3$. the incidence fraction of ionized outflows, traced by broad components, is about 25-40$\%$ depending on the intensity of the emission lines. the low incidence fraction might be due to both the sensitivity limit and the fact that outflows are not isotropic but have a limited opening angle which results in a detection only when this is directed toward our line of sight. evidence for outflows increases slightly with stellar mass and star-formation rate. the median velocity and mass loading factor (i.e., the ratio between mass outflow rate and star formation rate) of the outflowing ionized gas are 500 km s$^{-1}$ and $\eta=2.1^{+2.5}_{-1.6}$, respectively. these are two and 100 times higher, respectively than the typical values observed in local dwarf galaxies. these outflows are able to escape the gravitational potential of the galaxy and enrich the circum-galactic medium and, potentially, the inter-galactic medium. our results indicate that outflows can significantly impact the star formation activity in low-mass galaxies within the first 2 gyr of the universe. | jades: the incidence rate and properties of galactic outflows in low-mass galaxies across 3 < z < 9 |
the detection of five new fast radio bursts (frbs) found in the 1.4-ghz high time resolution universe high-latitude survey at parkes, is presented. the rate implied is 7^{+5}_{-3}× 10^3 (95 per cent) frbs sky-1 d-1 above a fluence of 0.13 jy ms for an frb of 0.128 ms duration to 1.5 jy ms for 16 ms duration. one of these frbs has a two-component profile, in which each component is similar to the known population of single component frbs and the two components are separated by 2.4 ± 0.4 ms. all the frb components appear to be unresolved following deconvolution with a scattering tail and accounting for intrachannel smearing. the two-component burst, frb 121002, also has the highest dispersion measure (1629 pc cm-3) of any frb to-date. many of the proposed models to explain frbs use a single high-energy event involving compact objects (such as neutron-star mergers) and therefore cannot easily explain a two-component frb. models that are based on extreme versions of flaring, pulsing, or orbital events, however, could produce multiple component profiles. the compatibility of these models and the frb rate implied by these detections is discussed. | five new fast radio bursts from the htru high-latitude survey at parkes: first evidence for two-component bursts |
neutron matter is an intriguing nuclear system with multiple connections to condensed matter and astrophysics. considerable progress has been made over the past 20 years in exploring the properties of pure neutron fluids. we begin by reviewing research exploring the behavior of very low density neutron matter, which forms a strongly paired superfluid and is thus similar to cold fermi atoms, although at energy scales that differ by many orders of magnitude. we then review the behavior of higher-density neutron matter, discussing research that ties the study of neutron matter to the determination of the properties of neutron-rich nuclei and neutron star crusts. finally, we review the impact that neutron matter at even higher densities has on the mass-radius relation of neutron stars, thereby making contact with astrophysical observations. | neutron matter from low to high density |
aims: recent observations by the atacama large millimeter/submillimeter array (alma) of disks around young stars revealed distinct asymmetries in the dust continuum emission. in this work we wish to study axisymmetric and non-axisymmetric structures that are generated by the magneto-rotational instability in the outer regions of protoplanetary disks. we combine the results of state-of-the-art numerical simulations with post-processing radiative transfer (rt) to generate synthetic maps and predictions for alma.methods: we performed non-ideal global 3d magneto-hydrodynamic (mhd) stratified simulations of the dead-zone outer edge using the fargo mhd code pluto. the stellar and disk parameters were taken from a parameterized disk model applied for fitting high-angular resolution multi-wavelength observations of various circumstellar disks. we considered a stellar mass of m∗ = 0.5 m⊙ and a total disk mass of about 0.085 m∗. the 2d initial temperature and density profiles were calculated consistently from a given surface density profile and monte carlo radiative transfer. the 2d ohmic resistivity profile was calculated using a dust chemistry model. we considered two values for the dust-to-gas mass ratio, 10-2 and 10-4, which resulted in two different levels of magnetic coupling. the initial magnetic field was a vertical net flux field. the radiative transfer simulations were performed with the monte carlo-based 3d continuum rt code mc3d. the resulting dust reemission provided the basis for the simulation of observations with alma.results: all models quickly turned into a turbulent state. the fiducial model with a dust-to-gas mass ratio of 10-2 developed a large gap followed by a jump in surface density located at the dead-zone outer edge. the jump in density and pressure was strong enough to stop the radial drift of particles at this location. in addition, we observed the generation of vortices by the rossby wave instability at the jump location close to 60 au. the vortices were steadily generated and destroyed at a cycle of 40 local orbits. the rt results and simulated alma observations predict that it is feasible to observe these large-scale structures that appear in magnetized disks without planets. neither the turbulent fluctuations in the disk nor specific times of the model can be distinguished on the basis of high-angular resolution submillimeter observations alone. the same applies to the distinction between gaps at the dead-zone edges and planetary gaps, to the distinction between turbulent and simple unperturbed disks, and to the asymmetry created by the vortex. | gaps, rings, and non-axisymmetric structures in protoplanetary disks. from simulations to alma observations |
we present the densely sampled early light curve of the type ii supernova (sn) 2023ixf, first observed within hours of explosion in the nearby pinwheel galaxy (messier 101; 6.7 mpc). comparing these data to recently updated models of shock-cooling emission, we find that the progenitor likely had a radius of 410 ± 10 r ⊙. our estimate is model dependent but consistent with a red supergiant. these models provide a good fit to the data starting about 1 day after the explosion, despite the fact that the classification spectrum shows signatures of circumstellar material around sn 2023ixf during that time. photometry during the first day after the explosion, provided almost entirely by amateur astronomers, does not agree with the shock-cooling models or a simple power-law rise fit to data after 1 day. we consider the possible causes of this discrepancy, including precursor activity from the progenitor star, circumstellar interaction, and emission from the shock before or after it breaks out of the stellar surface. the very low luminosity (-11 mag > m > -14 mag) and short duration of the initial excess lead us to prefer a scenario related to prolonged emission from the sn shock traveling through the progenitor system. | shock cooling and possible precursor emission in the early light curve of the type ii sn 2023ixf |
supernova (sn) explosions deposit prodigious energy and momentum in their environments, with the former regulating multiphase thermal structure and the latter regulating turbulence and star formation rates in the interstellar medium (ism). however, systematic studies quantifying the impact of sne in realistic inhomogeneous ism conditions have been lacking. using three-dimensional hydrodynamic simulations, we investigate the dependence of radial momentum injection on both physical conditions (considering a range of mean density n0 = 0.1-100 cm-3) and numerical parameters. our inhomogeneous simulations adopt two-phase background states that result from thermal instability in atomic gas. although the supernova remnant (snr) morphology becomes highly complex for inhomogeneous backgrounds, the radial momentum injection is remarkably insensitive to environmental details. for our two-phase simulations, the final momentum produced by a single sn is given by 2.8×105 m⊙ km s-1 n0-0.17. this is only 5% less than the momentum injection for a homogeneous environment with the same mean density, and only 30% greater than the momentum at the time of shell formation. the maximum mass in hot gas is also quite insensitive to environmental inhomogeneity. strong magnetic fields alter the hot gas mass at very late times, but the momentum injection remains the same. initial experiments with multiple spatially correlated sne show a momentum per event nearly as large as single-sn cases. we also present a full numerical parameter study to assess convergence requirements. for convergence in the momentum and other quantities, we find that the numerical resolution δ and the initial size of the snr rinit must satisfy δ, rinit < rsf/3, where the shell formation radius is given by r sf=30 pc n0-0.46 for two-phase models (or 30% smaller for a homogeneous medium). | momentum injection by supernovae in the interstellar medium |
supermassive black hole feedback is thought to be responsible for the lack of star formation, or quiescence, in a significant fraction of galaxies. we explore how observable correlations between the specific star formation rate (ssfr), stellar mass (mstar), and black hole mass (mbh) are sensitive to the physics of black hole feedback in a galaxy formation model. we use the illustristng simulation suite, specifically the tng100 simulation and 10 model variations that alter the parameters of the black hole model. focusing on central galaxies at z = 0 with mstar > 1010 m⊙, we find that the ssfr of galaxies in illustristng decreases once the energy from black hole kinetic winds at low accretion rates becomes larger than the gravitational binding energy of gas within the galaxy stellar radius. this occurs at a particular mbh threshold above which galaxies are found to sharply transition from being mostly star forming to mostly quiescent. as a result of this behaviour, the fraction of quiescent galaxies as a function of mstar is sensitive to both the normalization of the mbh-mstar relation and the mbh threshold for quiescence in illustristng. finally, we compare these model results to observations of 91 central galaxies with dynamical mbh measurements with the caveat that this sample is not representative of the whole galaxy population. while illustristng reproduces the observed trend that quiescent galaxies host more massive black holes, the observations exhibit a broader scatter in mbh at a given mstar and show a smoother decline in ssfr with mbh. | the relationship between black hole mass and galaxy properties: examining the black hole feedback model in illustristng |
given that the macromolecular building blocks of life were likely produced photochemically in the presence of ultraviolet (uv) light, we identify some general constraints on which stars produce sufficient uv for this photochemistry. we estimate how much light is needed for the uv photochemistry by experimentally measuring the rate constant for the uv chemistry (`light chemistry', needed for prebiotic synthesis) versus the rate constants for the bimolecular reactions that happen in the absence of the uv light (`dark chemistry'). we make these measurements for representative photochemical reactions involving so$_3^{2-}$ and hs$^-$. by balancing the rates for the light and dark chemistry, we delineate the "abiogenesis zones" around stars of different stellar types based on whether their uv fluxes are sufficient for building up this macromolecular prebiotic inventory. we find that the so$_3^{2-}$ 'light chemistry' is rapid enough to build up the prebiotic inventory for stars hotter than k5 (4400 k). we show how the abiogenesis zone overlaps with the liquid water habitable zone. stars cooler than k5 may also drive the formation of these building blocks if they are very active. the hs$^-$ 'light chemistry' is too slow to work even for the early earth. | the origin of rna precursors on exoplanets |
we present the first results from the mapping obscuration to reionization with alma (mora) survey, the largest atacama large millimeter/submillimeter array (alma) blank-field contiguous survey to date (184 arcmin2) and the only at 2 mm to search for dusty star-forming galaxies (dsfgs). we use the 13 sources detected above 5σ to estimate the first alma galaxy number counts at this wavelength. these number counts are then combined with the state-of-the-art galaxy number counts at 1.2 and 3 mm and with a backward evolution model to place constraints on the evolution of the ir luminosity function and dust-obscured star formation in the past 13 billion years. our results suggest a steep redshift evolution on the space density of dsfgs and confirm the flattening of the ir luminosity function at faint luminosities, with a slope of ${\alpha }_{\mathrm{lf}}=-{0.42}_{-0.04}^{+0.02}$ <!-- --> . we conclude that the dust-obscured component, which peaks at z ≈ 2-2.5, has dominated the cosmic history of star formation for the past ∼12 billion years, back to z ∼ 4. at z = 5, the dust-obscured star formation is estimated to be ∼35% of the total star formation rate density and decreases to 25%-20% at z = 6-7, implying a minor contribution of dust-enshrouded star formation in the first billion years of the universe. with the dust-obscured star formation history constrained up to the end of the epoch of reionization, our results provide a benchmark to test galaxy formation models, to study the galaxy mass assembly history, and to understand the dust and metal enrichment of the universe at early times. | the evolution of the ir luminosity function and dust-obscured star formation over the past 13 billion years |
with jwst, new opportunities to study the evolution of galaxies in the early universe are emerging. spitzer constraints on rest-optical properties of z ≳ 7 galaxies demonstrated the power of using galaxy stellar masses and star formation histories (sfhs) to indirectly infer the cosmic star formation history. however, only the brightest individual z ≳ 8 objects could be detected with spitzer, making it difficult to robustly constrain activity at z ≳ 10. here, we leverage the greatly improved rest-optical sensitivity of jwst at z ≳ 8 to constrain the ages of seven uv-bright ($m_{\rm uv}\lesssim -19.5$) galaxies selected to lie at z ~ 8.5-11, then investigate implications for z ≳ 15 star formation. we infer the properties of individual objects with two spectral energy distribution modelling codes, then infer a distribution of ages for bright z ~ 8.5-11 galaxies. we find a median age of ~20 myr, younger than that inferred at z ~ 7 with a similar analysis, consistent with an evolution towards larger specific star formation rates at early times. the age distribution suggests that only ~3 per cent of bright z ~ 8.5-11 galaxies would be similarly luminous at z ≳ 15, implying that the number density of bright galaxies declines by at least an order of magnitude between z ~ 8.5-11 and $z \sim 15$. this evolution is challenging to reconcile with some early jwst results suggesting the abundance of bright galaxies does not significantly decrease towards very early times, but we suggest this tension may be eased if young stellar populations form on top of older stellar components, or if bright z ~ 15 galaxies are observed during a burst of star formation. | on the ages of bright galaxies 500 myr after the big bang: insights into star formation activity at z ≳ 15 with jwst |
we describe updates to the redmapper algorithm, a photometric red-sequence cluster finder specifically designed for large photometric surveys. the updated algorithm is applied to 150 {{deg}}2 of science verification (sv) data from the dark energy survey (des), and to the sloan digital sky survey (sdss) dr8 photometric data set. the des sv catalog is locally volume limited and contains 786 clusters with richness λ \gt 20 (roughly equivalent to {m}{{500c}}≳ {10}14 {h}70-1 {m}⊙ ) and 0.2\lt z\lt 0.9. the dr8 catalog consists of 26,311 clusters with 0.08\lt z\lt 0.6, with a sharply increasing richness threshold as a function of redshift for z≳ 0.35. the photometric redshift performance of both catalogs is shown to be excellent, with photometric redshift uncertainties controlled at the {σ }z/(1+z)∼ 0.01 level for z≲ 0.7, rising to ∼0.02 at z∼ 0.9 in des sv. we make use of chandra and xmm x-ray and south pole telescope sunyaev-zeldovich data to show that the centering performance and mass-richness scatter are consistent with expectations based on prior runs of redmapper on sdss data. we also show how the redmapper photo-z and richness estimates are relatively insensitive to imperfect star/galaxy separation and small-scale star masks. | the redmapper galaxy cluster catalog from des science verification data |
durgapal's fifth isotropic solution describing spherically symmetric and static matter distribution is extended to an anisotropic scenario. to do so we employ the gravitational decoupling through the minimal geometric deformation scheme. this approach allows to split einstein's field equations in two simply set of equations, one corresponding to the isotropic sector and other to the anisotropic sector described by an extra gravitational source. the isotropic sector is solved by the durgapal's model and the anisotropic sector is solved once a suitable election on the minimal geometric deformation is imposes. the obtained model is representing some strange stars candidates and fulfill all the requirements in order to be a well behaved physical solution to the einstein's field equations. | compact anisotropic models in general relativity by gravitational decoupling |
for the first ~3 yrs after the binary neutron star merger event gw 170817, the radio and x-ray radiation has been dominated by emission from a structured relativistic off-axis jet propagating into a low-density medium with n < 0.01 cm-3. we report on observational evidence for an excess of x-ray emission at δt > 900 days after the merger. with lx≈ 5 × 1038 erg s-1 at 1234 days, the recently detected x-ray emission represents a ≥3.2σ (gaussian equivalent) deviation from the universal post-jet-break model that best fits the multiwavelength afterglow at earlier times. in the context of jetfit afterglow models, current data represent a departure with statistical significance ≥3.1σ, depending on the fireball collimation, with the most realistic models showing excesses at the level of ≥3.7σ. a lack of detectable 3 ghz radio emission suggests a harder broadband spectrum than the jet afterglow. these properties are consistent with the emergence of a new emission component such as synchrotron radiation from a mildly relativistic shock generated by the expanding merger ejecta, i.e., a kilonova afterglow. in this context, we present a set of ab initio numerical relativity binary neutron star (bns) merger simulations that show that an x-ray excess supports the presence of a high-velocity tail in the merger ejecta, and argues against the prompt collapse of the merger remnant into a black hole. radiation from accretion processes on the compact-object remnant represents a viable alternative. neither a kilonova afterglow nor accretion-powered emission have been observed before, as detections of bns mergers at this phase of evolution are unprecedented. | evidence for x-ray emission in excess to the jet-afterglow decay 3.5 yr after the binary neutron star merger gw 170817: a new emission component |
we consider the problem of learning an unknown function $f_{\star}$ on the $d$-dimensional sphere with respect to the square loss, given i.i.d. samples $\{(y_i,{\boldsymbol x}_i)\}_{i\le n}$ where ${\boldsymbol x}_i$ is a feature vector uniformly distributed on the sphere and $y_i=f_{\star}({\boldsymbol x}_i)+\varepsilon_i$. we study two popular classes of models that can be regarded as linearizations of two-layers neural networks around a random initialization: the random features model of rahimi-recht (rf); the neural tangent kernel model of jacot-gabriel-hongler (nt). both these approaches can also be regarded as randomized approximations of kernel ridge regression (with respect to different kernels), and enjoy universal approximation properties when the number of neurons $n$ diverges, for a fixed dimension $d$. we consider two specific regimes: the approximation-limited regime, in which $n=\infty$ while $d$ and $n$ are large but finite; and the sample size-limited regime in which $n=\infty$ while $d$ and $n$ are large but finite. in the first regime we prove that if $d^{\ell + \delta} \le n\le d^{\ell+1-\delta}$ for small $\delta > 0$, then \rf\, effectively fits a degree-$\ell$ polynomial in the raw features, and \nt\, fits a degree-$(\ell+1)$ polynomial. in the second regime, both rf and nt reduce to kernel methods with rotationally invariant kernels. we prove that, if the number of samples is $d^{\ell + \delta} \le n \le d^{\ell +1-\delta}$, then kernel methods can fit at most a a degree-$\ell$ polynomial in the raw features. this lower bound is achieved by kernel ridge regression. optimal prediction error is achieved for vanishing ridge regularization. | linearized two-layers neural networks in high dimension |
can a dynamically robust bosonic star (bs) produce an (effective) shadow that mimics that of a black hole (bh)? we focus on models of spherical bss with free scalar or vector fields, as well as with polynomial or axionic self-interacting fields. the bh shadow is linked to the existence of light rings (lrs). for free bosonic fields, yielding mini-bss, it is known that these stars can become ultra-compact — i.e., possess lrs — but only for perturbatively unstable solutions. we show this remains the case even when different self-interactions are considered. however, an effective shadow can arise in a different way: if bss reproduce the existence of an innermost stable circular orbit (isco) for timelike geodesics (located at risco = 6m for a schwarzschild bh of mass m), the accretion flow morphology around bhs is mimicked and an effective shadow arises in an astrophysical environment. even though spherical bss may accommodate stable timelike circular orbits all the way down to their centre, we show the angular velocity ω along such orbits may have a maximum away from the origin, at rω; this scale was recently observed to mimic the bh's isco in some scenarios of accretion flow. then: (i) for free scalar fields or with quartic self-interactions, rω ≠ 0 only for perturbatively unstable bss; (ii) for higher scalar self-interactions, e.g. axionic, rω ≠ 0 is possible for perturbatively stable bss, but no solution with rω = 6m was found in the parameter space explored; (iii) but for free vector fields, yielding proca stars, perturbatively stable solutions with rω ≠ 0 exist, and indeed rω = 6m for a particular solution. thus, dynamically robust spherical proca stars succeed in the imitation game: they can mimic the shadow of a (near-)equilibrium schwarzschild bh with the same m, in an astrophysical environment, despite the absence of a lr, at least under some observation conditions, as we confirm by explicitly comparing the lensing of such proca stars and schwarzschild bhs. | the imitation game: proca stars that can mimic the schwarzschild shadow |
this paper describes the data release of the sloan digital sky survey-ii (sdss-ii) supernova survey conducted between 2005 and 2007. light curves, spectra, classifications, and ancillary data are presented for 10,258 variable and transient sources discovered through repeat ugriz imaging of sdss stripe 82, a 300 deg2 area along the celestial equator. this data release is comprised of all transient sources brighter than r ≃ 22.5 mag with no history of variability prior to 2004. dedicated spectroscopic observations were performed on a subset of 889 transients, as well as spectra for thousands of transient host galaxies using the sdss-iii boss spectrographs. photometric classifications are provided for the candidates with good multi-color light curves that were not observed spectroscopically, using host galaxy redshift information when available. from these observations, 4607 transients are either spectroscopically confirmed, or likely to be, supernovae, making this the largest sample of supernova candidates ever compiled. we present a new method for sn host-galaxy identification and derive host-galaxy properties including stellar masses, star formation rates, and the average stellar population ages from our sdss multi-band photometry. we derive salt2 distance moduli for a total of 1364 sn ia with spectroscopic redshifts as well as photometric redshifts for a further 624 purely photometric sn ia candidates. using the spectroscopically confirmed subset of the three-year sdss-ii sn ia sample and assuming a flat λcdm cosmology, we determine ω m= 0.315 ± 0.093 (statistical error only) and detect a non-zero cosmological constant at 5.7σ. | the data release of the sloan digital sky survey-ii supernova survey |
we present an updated release of the basti (a bag of stellar tracks and isochrones) stellar model and isochrone library for a solar-scaled heavy element distribution. the main input physics that have been changed from the previous basti release include the solar metal mixture, electron conduction opacities, a few nuclear reaction rates, bolometric corrections, and the treatment of the overshooting efficiency for shrinking convective cores. the new model calculations cover a mass range between 0.1 and 15 m ⊙, 22 initial chemical compositions between [fe/h] = -3.20 and +0.45, with helium to metal enrichment ratio dy/dz = 1.31. the isochrones cover an age range between 20 myr and 14.5 gyr, consistently take into account the pre-main-sequence phase, and have been translated to a large number of popular photometric systems. asteroseismic properties of the theoretical models have also been calculated. we compare our isochrones with results from independent databases and with several sets of observations to test the accuracy of the calculations. all stellar evolution tracks, asteroseismic properties, and isochrones are made available through a dedicated web site. | the updated basti stellar evolution models and isochrones. i. solar-scaled calculations |
the most efficient axion production mechanism in a supernova (sn) core is the nucleon-nucleon bremsstrahlung. this process has been often modeled at the level of the vacuum one-pion exchange (ope) approximation. starting from this naive recipe, we revise the calculation including systematically different effects, namely a non-vanishing mass for the exchanged pion, the contribution from the two-pions exchange, effective in-medium nucleon masses and multiple nucleon scatterings. moreover, we allow for an arbitrary degree of nucleon degeneracy. a self consistent treatment of the axion emission rate including all these effects is currently missing. the aim of this work is to provide such an analysis. furthermore, we demonstrate that the ope potential with all the previous corrections gives rise to similar results as the on-shell t-matrix, and is \pagebreak therefore well justified for our and similar studies. we find that the axion emissivity is reduced by over an order of magnitude with respect to the basic ope calculation, after all these effects are accounted for. the implications for the axion mass bound and the impact for the next generation experimental axion searches is also discussed. | improved axion emissivity from a supernova via nucleon-nucleon bremsstrahlung |
modern and future surveys effectively provide a panchromatic view for large numbers of extragalactic objects. consistently modeling these multiwavelength survey data is a critical but challenging task for extragalactic studies. the code investigating galaxy emission (cigale) is an efficient python code for spectral energy distribution (sed) fitting of galaxies and active galactic nuclei (agns). recently, a major extension of cigale (named x-cigale) has been developed to account for agn/galaxy x-ray emission and improve agn modeling at uv-to-ir wavelengths. here, we apply x-cigale to different samples, including cosmological evolution survey (cosmos) spectroscopic type 2 agns, chandra deep field-south x-ray detected normal galaxies, sloan digital sky survey quasars, and cosmos radio objects. from these tests, we identify several weaknesses of x-cigale and improve the code accordingly. these improvements are mainly related to agn intrinsic x-ray anisotropy, x-ray binary emission, agn accretion-disk sed shape, and agn radio emission. these updates improve the fit quality and allow for new interpretation of the results, based on which we discuss physical implications. for example, we find that agn intrinsic x-ray anisotropy is moderate, and can be modeled as ${l}_{x}(\theta )\propto 1+\cos \theta $ , where θ is the viewing angle measured from the agn axis. we merge the new code into the major branch of cigale, and publicly release this new version as cigale v2022.0 on https://cigale.lam.fr. | fitting agn/galaxy x-ray-to-radio seds with cigale and improvement of the code |
the neutron skin thickness δ rnp of heavy nuclei is essentially determined by the symmetry energy density slope l (ρ ) at ρc=0.11 fm−3≈2 /3 ρ0 (ρ0 is nuclear saturation density), roughly corresponding to the average density of finite nuclei. the prex collaboration recently reported a model-independent extraction of δ rnp208=0.283 ±0.071 fm for the δ rnp of 208pb, suggesting a rather stiff symmetry energy esym(ρ ) with l (ρc)≥52 mev. we show that the esym(ρ ) cannot be too stiff and l (ρc)≤73 mev is necessary to be compatible with (1) the ground-state properties and giant monopole resonances of finite nuclei, (2) the constraints on the equation of state of symmetric nuclear matter at suprasaturation densities from flow data in heavy-ion collisions, (3) the largest neutron star (ns) mass reported so far for psr j0740 +6620 , (4) the ns tidal deformability extracted from gravitational wave signal gw170817, and (5) the mass-radius of psr j0030 +045 measured simultaneously by nicer. this allows us to obtain 52 ≤l (ρc)≤73 mev and 0.212 ≤δ rnp208≤0.271 fm and further esym(ρ0) =34.3 ±1.7 mev, l (ρ0)=83.1 ±24.7 mev, and esym(2 ρ0 ) =62.8 ±15.9 mev. a number of critical implications on nuclear physics and astrophysics are discussed. | constraints on the symmetry energy from prex-ii in the multimessenger era |
we introduce serra, a suite of zoom-in high-resolution ($1.2\times 10^4 \, {\rm m}_{\odot }$, $\simeq 25\, {\rm {pc}}$ at z = 7.7) cosmological simulations including non-equilibrium chemistry and on-the-fly radiative transfer. the outputs are post-processed to derive galaxy ultraviolet (uv) + far-infrared (fir) continuum and emission line properties. results are compared with available multiwavelength data to constrain the physical properties [e.g. star formation rates (sfrs), stellar/gas/dust mass, metallicity] of high-redshift 6 ≲ z ≲ 15 galaxies. this flagship paper focuses on the z = 7.7 sub-sample, including 202 galaxies with stellar mass $10^7 \, {\rm m}_{\odot }\lesssim m_\star \lesssim 5\times 10^{10}\, {\rm m}_{\odot }$, and specific star formation rate ranging from ${\rm ssfr} \sim 100\, {\rm gyr}^{-1}$ in young, low-mass galaxies to $\sim 10\, {\rm gyr}^{-1}$ for older, massive ones. at this redshift, serra galaxies are typically bursty, i.e. they are located above the schmidt-kennicutt relation by a factor $\kappa _s = 3.03^{+4.9}_{-1.8}$, consistent with recent findings for [o iii] and [c ii] emitters at high z. they also show relatively large infrared excess (irx = lfir/luv) values as a result of their compact/clumpy morphology effectively blocking the stellar uv luminosity. note that this conclusion might be affected by insufficient spatial resolution at the molecular cloud level. we confirm that early galaxies lie on the standard [c ii]$\!-\!\rm sfr$ relation; their observed l[oiii]/l[cii] ≃ 1-10 ratios can be reproduced by a part of the serra galaxies without the need of a top-heavy initial mass function and/or anomalous c/o abundances. [o i] line intensities are similar to local ones, making alma high-z detections challenging but feasible ($\sim 6\, \rm h$ for an sfr of $50\, \, {\rm m}_{\odot }\, {\rm yr}^{-1}$). | a survey of high-z galaxies: serra simulations |
according to the cpt theorem, which states that the combined operation of charge conjugation, parity transformation and time reversal must be conserved, particles and their antiparticles should have the same mass and lifetime but opposite charge and magnetic moment. here, we test cpt symmetry in a nucleus containing a strange quark, more specifically in the hypertriton. this hypernucleus is the lightest one yet discovered and consists of a proton, a neutron and a λ hyperon. with data recorded by the star detector1-3 at the relativistic heavy ion collider, we measure the λ hyperon binding energy bλ for the hypertriton, and find that it differs from the widely used value4 and from predictions5-8, where the hypertriton is treated as a weakly bound system. our results place stringent constraints on the hyperon-nucleon interaction9,10 and have implications for understanding neutron star interiors, where strange matter may be present11. a precise comparison of the masses of the hypertriton and the antihypertriton allows us to test cpt symmetry in a nucleus with strangeness, and we observe no deviation from the expected exact symmetry. | measurement of the mass difference and the binding energy of the hypertriton and antihypertriton |
gaia dr2 provides unprecedented precision in measurements of the distance and kinematics of stars in the solar neighborhood. through applying unsupervised machine learning on dr2's 5d data set (3d position + 2d velocity), we identify a number of clusters, associations, and comoving groups within 1 kpc and | b| < 30^\circ (many of which have not been previously known). we estimate their ages with the precision of ∼0.15 dex. many of these groups appear to be filamentary or string-like, oriented in parallel to the galactic plane, and some span hundreds of parsec in length. most of these string lack a central cluster, indicating that their filamentary structure is primordial, rather than the result of tidal stripping or dynamical processing. the youngest strings (<100 myr) are orthogonal to the local arm. the older ones appear to be remnants of several other arm-like structures that cannot be presently traced by dust and gas. the velocity dispersion measured from the ensemble of groups and strings increase with age, suggesting a timescale for dynamical heating of ∼300 myr. this timescale is also consistent with the age at which the population of strings begins to decline, while the population in more compact groups continues to increase, suggesting that dynamical processes are disrupting the weakly bound string populations, leaving only individual clusters to be identified at the oldest ages. these data shed a new light on the local galactic structure and a large-scale cloud collapse. | untangling the galaxy. i. local structure and star formation history of the milky way |
we study the spatially resolved excitation properties of the ionized gas in a sample of 646 galaxies using integral field spectroscopy data from the sloan digital sky survey iv mapping nearby galaxies at apache point observatory (manga) programme. making use of baldwin-philips-terlevich diagnostic diagrams we demonstrate the ubiquitous presence of extended (kpc scale) low-ionization emission-line regions (liers) in both star-forming and quiescent galaxies. in star-forming galaxies lier emission can be associated with diffuse ionized gas, most evident as extraplanar emission in edge-on systems. in addition, we identify two main classes of galaxies displaying lier emission: `central lier' (clier) galaxies, where central lier emission is spatially extended, but accompanied by star formation at larger galactocentric distances, and `extended lier' (elier) galaxies, where lier emission is extended throughout the whole galaxy. in elier and clier galaxies, lier emission is associated with radially flat, low h α equivalent width of line emission (<3 å) and stellar population indices demonstrating the lack of young stellar populations, implying that line emission follows tightly the continuum due to the underlying old stellar population. the h α surface brightness radial profiles are always shallower than 1/r2 and the line ratio [o iii] λ5007/[o ii] λλ3727,29 (a tracer of the ionization parameter of the gas) shows a flat gradient. this combined evidence strongly supports the scenario in which lier emission is not due to a central point source but to diffuse stellar sources, the most likely candidates being hot, evolved (post-asymptotic giant branch) stars. shocks are observed to play a significant role in the ionization of the gas only in rare merging and interacting systems. | sdss iv manga - spatially resolved diagnostic diagrams: a proof that many galaxies are liers |
we investigate the properties of haloes, galaxies and black holes to z = 0 in the high-resolution hydrodynamical simulation massiveblack-ii (mbii) which evolves a λ cold dark matter cosmology in a comoving volume vbox = (100 mpc h-1)3. mbii is the highest resolution simulation of this size which includes a self-consistent model for star formation, black hole accretion and associated feedback. we provide a simulation browser web application which enables interactive search and tagging of the mbii data set and publicly release our galaxy catalogues. we find that baryons affect strongly the halo mass function (mf), with 20-33 per cent change in the halo abundance below the knee of the mf (mhalo < 1013.2 m⊙ h-1 at z = 0) when compared to dark-matter-only simulations. we provide a fitting function for the halo mf out to redshift z = 11 and discuss its limitations. we study the halo occupation distribution and clustering of galaxies, in particular the evolution and scale dependence of stochasticity and bias finding reasonable agreement with observational data. the shape of the cosmic spectral energy distribution of galaxies in mbii is consistent with observations, but lower in amplitude. the galaxy stellar mass function (gsmf) function is broadly consistent with observations at z ≥ 2. at z < 2, the population of passive low-mass (m* < 109 m⊙) galaxies in mbii makes the gsmf too steep compared to observations whereas at the high-mass end (m* > 1011 m⊙) galaxies hosting bright agns make significant contributions to the gsmf. the quasar bolometric luminosity function is also largely consistent with observations. we note however that more efficient agn feedback is necessary for the largest, rarest objects/clusters at low redshifts. | the massiveblack-ii simulation: the evolution of haloes and galaxies to z ∼ 0 |
a review of solar cycle prediction methods and their performance is given, including early forecasts for cycle 25. the review focuses on those aspects of the solar cycle prediction problem that have a bearing on dynamo theory. the scope of the review is further restricted to the issue of predicting the amplitude (and optionally the epoch) of an upcoming solar maximum no later than right after the start of the given cycle. prediction methods form three main groups. precursor methods rely on the value of some measure of solar activity or magnetism at a specified time to predict the amplitude of the following solar maximum. the choice of a good precursor often implies considerable physical insight: indeed, it has become increasingly clear that the transition from purely empirical precursors to model-based methods is continuous. model-based approaches can be further divided into two groups: predictions based on surface flux transport models and on consistent dynamo models. the implicit assumption of precursor methods is that each numbered solar cycle is a consistent unit in itself, while solar activity seems to consist of a series of much less tightly intercorrelated individual cycles. extrapolation methods, in contrast, are based on the premise that the physical process giving rise to the sunspot number record is statistically homogeneous, i.e., the mathematical regularities underlying its variations are the same at any point of time, and therefore it lends itself to analysis and forecasting by time series methods. in their overall performance during the course of the last few solar cycles, precursor methods have clearly been superior to extrapolation methods. one method that has yielded predictions consistently in the right range during the past few solar cycles is the polar field precursor. nevertheless, some extrapolation methods may still be worth further study. model based forecasts are quickly coming into their own, and, despite not having a long proven record, their predictions are received with increasing confidence by the community. | solar cycle prediction |
the phase-space structure of zero-temperature quarkyonic matter is a fermi sphere of quark matter surrounded by a shell of nucleonic matter. we construct a quasiparticle model of quarkyonic matter based on the constituent quark model, where the quark and nucleon masses are related by mq=mn/nc , and nc is the number of quark colors. the region of occupied states is for quarks kq<kf/nc and for nucleons kf<kn<kf+δ . we first consider the general problem of quarkyonic matter with hard-core nucleon interactions. we then specialize to a quasiparticle model where the hard-core nucleon interactions are accounted for by an excluded volume. in this model, we show that the nucleonic shell forms past some critical density related to the hard-core size and for large densities becomes a thin shell. we explore the basic features of such a model and argue this model has the semiquantitative behavior needed to describe neutron stars. | dynamically generated momentum space shell structure of quarkyonic matter via an excluded volume model |
we present 294 pulsars found in gev data from the large area telescope (lat) on the fermi gamma-ray space telescope. another 33 millisecond pulsars (msps) discovered in deep radio searches of lat sources will likely reveal pulsations once phase-connected rotation ephemerides are achieved. a further dozen optical and/or x-ray binary systems colocated with lat sources also likely harbor gamma-ray msps. this catalog thus reports roughly 340 gamma-ray pulsars and candidates, 10% of all known pulsars, compared to ≤11 known before fermi. half of the gamma-ray pulsars are young. of these, the half that are undetected in radio have a broader galactic latitude distribution than the young radio-loud pulsars. the others are msps, with six undetected in radio. overall, ≥236 are bright enough above 50 mev to fit the pulse profile, the energy spectrum, or both. for the common two-peaked profiles, the gamma-ray peak closest to the magnetic pole crossing generally has a softer spectrum. the spectral energy distributions tend to narrow as the spindown power $\dot{e}$ decreases to its observed minimum near 1033 erg s‑1, approaching the shape for synchrotron radiation from monoenergetic electrons. we calculate gamma-ray luminosities when distances are available. our all-sky gamma-ray sensitivity map is useful for population syntheses. the electronic catalog version provides gamma-ray pulsar ephemerides, properties, and fit results to guide and be compared with modeling results. | the third fermi large area telescope catalog of gamma-ray pulsars |
the building of planetary systems is controlled by the gas and dust dynamics of protoplanetary disks. while the gas is simultaneously accreted onto the central star and dissipated away by winds, dust grains aggregate and collapse to form planetesimals and eventually planets. this dust and gas dynamics involves instabilities, turbulence and complex non-linear interactions which ultimately control the observational appearance and the secular evolution of these disks. this chapter is dedicated to the most recent developments in our understanding of the dynamics of gaseous and dusty disks, covering hydrodynamic and magnetohydrodynamic turbulence, gas-dust instabilities, dust clumping and disk winds. we show how these physical processes have been tested from observations and highlight standing questions that should be addressed in the future. | hydro-, magnetohydro-, and dust-gas dynamics of protoplanetary disks |
planet formation theories predict that some planets may be ejected from their parent systems as result of dynamical interactions and other processes. unbound planets can also be formed through gravitational collapse, in a way similar to that in which stars form. a handful of free-floating planetary-mass objects have been discovered by infrared surveys of young stellar clusters and star-forming regions as well as wide-field surveys, but these studies are incomplete for objects below five jupiter masses. gravitational microlensing is the only method capable of exploring the entire population of free-floating planets down to mars-mass objects, because the microlensing signal does not depend on the brightness of the lensing object. a characteristic timescale of microlensing events depends on the mass of the lens: the less massive the lens, the shorter the microlensing event. a previous analysis of 474 microlensing events found an excess of ten very short events (1-2 days)—more than known stellar populations would suggest—indicating the existence of a large population of unbound or wide-orbit jupiter-mass planets (reported to be almost twice as common as main-sequence stars). these results, however, do not match predictions of planet-formation theories and surveys of young clusters. here we analyse a sample of microlensing events six times larger than that of ref. 11 discovered during the years 2010-15. although our survey has very high sensitivity (detection efficiency) to short-timescale (1-2 days) microlensing events, we found no excess of events with timescales in this range, with a 95 per cent upper limit on the frequency of jupiter-mass free-floating or wide-orbit planets of 0.25 planets per main-sequence star. we detected a few possible ultrashort-timescale events (with timescales of less than half a day), which may indicate the existence of earth-mass and super-earth-mass free-floating planets, as predicted by planet-formation theories. | no large population of unbound or wide-orbit jupiter-mass planets |
the recent detections of the binary black hole mergers gw150914 and gw151226 have inaugurated the field of gravitational-wave astronomy. for the two main formation channels that have been proposed for these sources, isolated binary evolution in galactic fields and dynamical formation in dense star clusters, the predicted masses and merger rates overlap significantly, complicating any astrophysical claims that rely on measured masses alone. here, we examine the distribution of spin-orbit misalignments expected for binaries from the field and from dense star clusters. under standard assumptions for black hole natal kicks, we find that black hole binaries similar to gw150914 could be formed with significant spin-orbit misalignment only through dynamical processes. in particular, these heavy-black hole binaries can only form with a significant spin-orbit anti-alignment in the dynamical channel. our results suggest that future detections of merging black hole binaries with measurable spins will allow us to identify the main formation channel for these systems. | illuminating black hole binary formation channels with spins in advanced ligo |
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