text: 299,67,1285935591230767105,1064262393981820928,Benedikt Diemer,"Paper day #2: <LINK> Based on the new catalogs from yesterday, we look at the mass functions of splashback and SO masses. The splashback MF turns out to be remarkably universal! The image compares the MF for totally different cosmologies and redshifts. <LINK> A little background: the first theoretical model of the mass function, Press & Schechter 74, assumed that halos collapse when their progenitor peaks exceed a critical overdensity, delta_c. If delta_c is universal (not dependent on z and cosmology), then the MF is universal too. There are good reasons to believe this should not be the case! Nevertheless, ever since, people have argued about universality.  One important aspect is that, for a universal MF, the mass definition would need to capture the ""total mass"" of halos in some physical manner. There have been many claims of (non-)universality. In this paper, we show conclusively that SO mass functions are NOT universal for any definition (R500c, R200c, Rvir, R200m etc). The splashback MFs aren't perfectly universal either, but much more so! In particular, they more or less agree even between crazy self-similar universes and LCDM, plus across redshifts in the presence of dark energy. In my mind (but feel free to challenge me on this!), that indicates that splashback masses are a more physical definition; or at least that they come closer to including the entire mass of the halo in the sense of spherical collapse envisioned by theoretical models. Here's the figure with a legend: <LINK> @profbradgibson Haha yes Sir! I believe you have everything that's gonna come your way, for now ;)",https://arxiv.org/abs/2007.10346,"The mass function of dark matter halos is one of the most fundamental statistics in structure formation. Many theoretical models (such as Press-Schechter theory) are based on the notion that it could be universal, meaning independent of redshift and cosmology, when expressed in the appropriate variables. However, simulations exhibit persistent non-universalities in the mass functions of the virial mass and other commonly used spherical overdensity definitions. We systematically study the universality of mass functions over a wide range of mass definitions, for the first time including the recently proposed splashback mass, Msp. We confirm that, in LambdaCDM cosmologies, all mass definitions exhibit varying levels of non-universality that increase with peak height and reach between 20% and 500% at the highest masses we can test. Mvir, M200m, and Msp exhibit similar levels of non-universality. There are, however, two regimes where the splashback mass functions are significantly more universal. First, they are universal to 10% at z<2, whereas spherical overdensity definitions experience an evolution due to dark energy. Second, when additionally considering self-similar cosmologies with extreme power spectra, splashback mass functions are remarkably universal (to between 40% and 60%) whereas their spherical overdensity counterparts reach non-universalities between 180% and 450%. These results strongly support the notion that the splashback radius is a physically motivated definition of the halo boundary. We present a simple, universal fitting formula for splashback mass functions that accurately reproduces our simulation data. ",Universal at last? The splashback mass function of dark matter halos,8,"['Paper day #2: <LINK>\n\nBased on the new catalogs from yesterday, we look at the mass functions of splashback and SO masses. The splashback MF turns out to be remarkably universal! The image compares the MF for totally different cosmologies and redshifts. <LINK>', 'A little background: the first theoretical model of the mass function, Press &amp; Schechter 74, assumed that halos collapse when their progenitor peaks exceed a critical overdensity, delta_c. If delta_c is universal (not dependent on z and cosmology), then the MF is universal too.', 'There are good reasons to believe this should not be the case! Nevertheless, ever since, people have argued about universality. \n\nOne important aspect is that, for a universal MF, the mass definition would need to capture the ""total mass"" of halos in some physical manner.', ""There have been many claims of (non-)universality. In this paper, we show conclusively that SO mass functions are NOT universal for any definition (R500c, R200c, Rvir, R200m etc). The splashback MFs aren't perfectly universal either, but much more so!"", 'In particular, they more or less agree even between crazy self-similar universes and LCDM, plus across redshifts in the presence of dark energy.', 'In my mind (but feel free to challenge me on this!), that indicates that splashback masses are a more physical definition; or at least that they come closer to including the entire mass of the halo in the sense of spherical collapse envisioned by theoretical models.', ""Here's the figure with a legend: https://t.co/Ucvwj4k0Sw"", ""@profbradgibson Haha yes Sir! I believe you have everything that's gonna come your way, for now ;)""]",20,07,1613