Counting black holes: The cosmic stellar remnant population and implications for LIGO

We present an empirical approach for interpreting gravitational wave signals of binary black hole mergers under the assumption that the underlying black hole population is sourced by remnants of stellar evolution. Using the observed relationship between galaxy mass and stellar metallicity, we predict the black hole count as a function of galaxy stellar mass. We show, for example, that a galaxy like the Milky Way should host millions of ~30M⊙ black holes and dwarf satellite galaxies like Draco should host ~100 such remnants, with weak dependence on the assumed initial mass function and stellar evolution model. Most low-mass black holes (~10M⊙) typically reside within massive galaxies (M* ≃ 1011M⊙) while massive black holes (~50M⊙) typically reside within dwarf galaxies (M* ≃ 109M⊙) today. If roughly 1 per cent of black holes are involved in a binary black hole merger, then the reported merger rate densities from advanced Laser Interferometer Gravitational-Wave Observatory can be accommodated for a range of merger time-scales, and the detection of mergers with > 50M⊙ black holes should be expected within the next decade. Identifying the host galaxy population of the mergers provides a way to constrain both the binary neutron star or black hole formation efficiencies and the merger time-scale distributions; these events would be primarily localized in dwarf galaxies if the merger time-scale is short compared to the age of the Universe and in massive galaxies otherwise. As more mergers are detected, the prospect of identifying the host galaxy population, either directly through the detection of electromagnetic counterparts of binary neutron star mergers or indirectly through the anisotropy of the events, will become a realistic possibility

A Testable Conspiracy: Simulating Baryonic Effects on Self-interacting Dark Matter Halos

We investigate the response of self-interacting dark matter (SIDM) halos to the growth of galaxy potentials using idealized simulations, with each run in tandem with collisionless cold dark matter (CDM). We find that if the stellar potential strongly dominates in the central parts of a galaxy, then SIDM halos can be as dense as CDM halos on observable scales. For extreme cases, core collapse can occur, leading to SIDM halos that are denser and cuspier than their CDM counterparts. If the stellar potential is not dominant, then SIDM halos retain isothermal cores with densities far below CDM predictions. When a disk is present, the inner SIDM halo becomes more flattened in the disk plane than the CDM halo. These results are in excellent quantitative agreement with the predictions of Kaplinghat et al. We also simulated a cluster halo with a central stellar distribution similar to the brightest central galaxy of the cluster A2667. An SIDM halo simulated with the cross-section over mass provides a good match to the measured dark matter (DM) density profile, while an adiabatically contracted CDM halo is denser and cuspier. The profile of the same halo simulated with is not dense enough. Our findings are in agreement with previous results that is disfavored for DM collision velocities above about 1500 km s-1. More generally, the interaction between baryonic potentials and SIDM densities offers new directions for constraining SIDM cross-sections in galaxies where baryons are dynamically important

Core formation in dwarf haloes with self-interacting dark matter: No fine-tuning necessary

We investigate the effect of self-interacting dark matter (SIDM) on the density profiles of Vmax ≃ 40km s-1 isolated dwarf dark matter haloes-the scale of relevance for the too big to fail problem (TBTF)-using very high resolution cosmological zoom simulations. Each halo has millions of particles within its virial radius. We find that SIDM models with cross-sections per unitmass spanning the range s/m=0.5-50 cm2 g-1 alleviate TBTF and produce constantdensity cores of size 300-1000 pc, comparable to the half-light radii of M* ~ 105-7M⊙ dwarfs. The largest, lowest density cores develop for cross-sections in the middle of this range, σ/m ~ 5-10 cm2 g-1. Our largest SIDM cross-section run (σ/m = 50 cm2 g-1) develops a slightly denser core owing to mild core-collapse behaviour, but it remains less dense than the cold dark matter case and retains a constant-density core profile. Our work suggests that SIDM cross-sections as large or larger than 50 cm2 g-1 remain viable on velocity scales of dwarf galaxies (vrms ~ 40 km s-1). The range of SIDM cross-sections that alleviate TBTF and the cusp/core problem spans at least two orders of magnitude and therefore need not be particularly fine-tuned

Sweating the small stuff: Simulating dwarf galaxies, ultra-faint dwarf galaxies, and their own tiny satellites

We present Feedback in Realistic Environment (FIRE)/GIZMO hydrodynamic zoom-in simulations of isolated dark matter haloes, two each at the mass of classical dwarf galaxies (Mvir ≃ 1010 M o˙) and ultra-faint galaxies (Mvir ≃ 109 M o˙), and with two feedback implementations. The resulting central galaxies lie on an extrapolated abundance matching relation from M* ≃ 106 to 104 M o˙ without a break. Every host is filled with subhaloes, many of which form stars. Each of our dwarfs with M* ≃ 106 M o˙ has 1-2 well-resolved satellites with M* = 3-200 × 103 M o˙. Even our isolated ultra-faint galaxies have star-forming subhaloes. If this is representative, dwarf galaxies throughout the Universe should commonly host tiny satellite galaxies of their own. We combine our results with the Exploring the Local Volume in Simulations (ELVIS) simulations to show that targeting ~50 kpc regions around nearby isolated dwarfs could increase the chances of discovering ultra-faint galaxies by ~35 per cent compared to random pointings, and specifically identify the region around the Phoenix dwarf galaxy as a good potential target. The well-resolved ultra-faint galaxies in our simulations (M* ≃ 3-30 × 103 M o˙) form within Mpeak ≃ 0.5-3 × 109 M o˙ haloes. Each has a uniformly ancient stellar population (>10 Gyr) owing to reionization-related quenching. More massive systems, in contrast, all have late-time star formation. Our results suggest that Mhalo ≃ 5 × 109 M o˙ is a probable dividing line between haloes hosting reionization 'fossils' and those hosting dwarfs that can continue to form stars in isolation after reionization

Sweating the small stuff: Simulating dwarf galaxies, ultra-faint dwarf galaxies, and their own tiny satellites

We present Feedback in Realistic Environment (FIRE)/GIZMO hydrodynamic zoom-in simulations of isolated dark matter haloes, two each at the mass of classical dwarf galaxies (Mvir ≃ 1010 M o˙) and ultra-faint galaxies (Mvir ≃ 109 M o˙), and with two feedback implementations. The resulting central galaxies lie on an extrapolated abundance matching relation from M* ≃ 106 to 104 M o˙ without a break. Every host is filled with subhaloes, many of which form stars. Each of our dwarfs with M* ≃ 106 M o˙ has 1-2 well-resolved satellites with M* = 3-200 × 103 M o˙. Even our isolated ultra-faint galaxies have star-forming subhaloes. If this is representative, dwarf galaxies throughout the Universe should commonly host tiny satellite galaxies of their own. We combine our results with the Exploring the Local Volume in Simulations (ELVIS) simulations to show that targeting ~50 kpc regions around nearby isolated dwarfs could increase the chances of discovering ultra-faint galaxies by ~35 per cent compared to random pointings, and specifically identify the region around the Phoenix dwarf galaxy as a good potential target. The well-resolved ultra-faint galaxies in our simulations (M* ≃ 3-30 × 103 M o˙) form within Mpeak ≃ 0.5-3 × 109 M o˙ haloes. Each has a uniformly ancient stellar population (>10 Gyr) owing to reionization-related quenching. More massive systems, in contrast, all have late-time star formation. Our results suggest that Mhalo ≃ 5 × 109 M o˙ is a probable dividing line between haloes hosting reionization 'fossils' and those hosting dwarfs that can continue to form stars in isolation after reionization

FIRE in the field: Simulating the threshold of galaxy formation

We present a suite of 15 cosmological zoom-in simulations of isolated dark matter haloes, all with masses of Mhalo ≈ 1010M⊙ at z = 0, in order to understand the relationship among halo assembly, galaxy formation and feedback's effects on the central density structure in dwarf galaxies. These simulations are part of the Feedback in Realistic Environments (FIRE) project and are performed at extremely high resolution (mbaryon = 500M⊙, mdm = 2500M⊙). The resultant galaxies have stellar masses that are consistent with rough abundance matching estimates, coinciding with the faintest galaxies that can be seen beyond the virial radius of the Milky Way (M*/M⊙ ≈ 105 - 107). This non-negligible spread in stellar mass at z = 0 in haloes within a narrow range of virial masses is strongly correlated with central halo density or maximum circular velocity Vmax, both of which are tightly linked to halo formation time. Much of this dependence of M* on a second parameter (beyond Mhalo) is a direct consequence of the Mhalo ~ 1010M⊙ mass scale coinciding with the threshold for strong reionization suppression: the densest, earliest-forming haloes remain above the UV-suppression scale throughout their histories while late-forming systems fall below the UV-suppression scale over longer periods and form fewer stars as a result. In fact, the latest-forming, lowest-concentration halo in our suite fails to form any stars. Haloes that form galaxies with M ≳ 2 × 106 M⊙ have reduced central densities relative to dark-matter-only simulations, and the radial extent of the density modifications is well-approximated by the galaxy half-mass radius r1/2. Lower-mass galaxies do not modify their host dark matter haloes at the mass scale studied here. This apparent stellar mass threshold of M ≈ 2 × 106-2 × 10-4 Mhalo is broadly consistent with previous work and provides a testable prediction of FIRE feedback models in Λcold dark matter

Reheating neutron stars with the annihilation of self-interacting dark matter

[[abstract]]Compact stellar objects such as neutron stars (NS) are ideal places for capturing dark matter (DM) particles. We study the effect of self-interacting DM (SIDM) captured by nearby NS that can reheat it to an appreciated surface temperature through absorbing the energy released due to DM annihilation. When DM-nucleon cross section σχn is small enough, DM self-interaction will take over the capture process and make the number of captured DM particles increased as well as the DM annihilation rate. The corresponding NS surface temperature resulted from DM self-interaction is about hundreds of Kelvin and is potentially detectable by the future infrared telescopes. Such observations could act as the complementary probe on DM properties to the current DM direct searches.[[notice]]補正完