Day 1507

Monday.

1811.11791
Dwarf galaxies in CDM, WDM and SIDM: Disentangling baryons and dark matter physics
Fitts, et al

Present a suite of FIRE-2 cosmo zoom-in simulations of isolated field dwarf galaxies, all with masses of M_halo ~ 1e10 Msun at z=0, across a range of DM models.  For the first time, compare how both self-interacting dark matter (SIDM) and/or warm dark matter (WDM) models affect the assembly histories as well as the central density structure in fully hydrodynamical simulations of dwarfs.  Overall, the inclusion of self-interactions does little to affect the mass assembly of these haloes (both DM and baryonic), while WDM models generally delay DM halo formation and reduce galaxies' stellar masses at z=0.  Dwarfs with smaller stellar half-mass radii (r_1/2<500 pc) have lower sigma_*/V_max ratios, reinforcing the idea that smaller dwarfs may reside in haloes that are more massive than is naively expected.  Surprisingly, the majority of dwarfs simulated with self-interactions (regardless of the warmth of the DM) actually experience contraction of their inner density profiles with the addition of baryons relative to the cores produced in DM-only runs, though the simulated dwarfs are always less centrally dense than in LambdaCDM.  The V_1/2-r_1/2 relation is overall consistent with observations of Local Field dwarfs, though compact objects such as Tucana provide a unique challenge.  Spatially-resolved rotation curves in the central regions (<400 pc) of small dwarfs could provide a way to distinguish between CDM, WDM and SIDM: at the masses probed in this simulation suite, cored density profiles in dwarfs with small r_1/2 values can only originate from DM self-interactions.


1811.11976
Hubble flow variations as a test for inhomogeneous cocsmology
Saulder, et al

Backreactions from large-scale inhomogeneities may provide an elegant explanation for the observed accelerated expansion of the universe without the need to introduce DE.  Propose a cosmological test for a specific model of inhomogeneous cosmology, called timescale cosmology.  Using large-scale galaxy surveys such as SDSS and 2MRS, test the variation of expansion expected in the LCDM model versus a more generic differential expansion using calibrations of bounds suggested by timescale cosmology.  The test measures the systematic variations of the Hubble flow towards distant galaxies groups as function of the matter distribution in the line of sight to those galaxy groups.  Compare the observed systematic variation of the Hubble flow to mock catalogues from the Millennium Simulation in the case of the LCDM model, and a deformed version of the same simulation that exhibits more pronounced differential expansion.  Perform a series of statistical tests, ranging from linear regressions to Kolmogorov-Smirnov tests, on the obtained data.  They consistency yield results preferring LCDM cosmology over the approximated model of timescale cosmology.  Analysis of observational data shows no evidence that the variation of expansion differs from that of the standard LCDM model.


1811.12412
First detection of scale-dependent linear halo bias in N-body simulations with massive neutrinos
Chiang, et al

Using N-body isms with massive neutrino density perturbations, detect the scale-dependent linear halo bias with high significance.  This is the first time that this effect is detected in simulations containing neutrino density perturbations on all scales, confirming the same finding from separate universe simulations.  The scale dependence is the result of the additional scale in the system, i.e. the massive neutrino free-streaming length, and it persists even if the bias is defined with respect to the CDM plus baryon (instead of total matter) power spectrum . The separate universe approach provides a good model for the scale-dependent linear bias, and the effect is approximately 0.25 f_nu and 0.43 f_nu for haloes with bias of 1.7 and 3.5, respectively.  WhIle the size of the effect is small, it is not insignificant in terms of f_nu and should therefore be included to accurately constrain neutrino mass from clustering statistics of biased tracers.  More importantly, the feature is a distinct signature of free-streaming particles and cannot be mimicked by other components of the standard cosmological model.