Day 660

Tuesday.

1405.3985
Running with BICEP2: implications for small-scale problems in CDM
Garrison-Kimmel, Horiuchi, Abazajian, Bullock, Kaplinghat

The BICEP2 results suggest a roll-off in power towards small scales in the primordial matter power spectrum.  Among the simplest possibilities is a running of the spectral index.  Show that the preferred level of running alleviates small-scale issues within the LCDM model, more so even than viable WDM models.  Use cosmological zoom-in simulations of fMW-size halo along with full-box simulations to compare predictions among four separate cosmologies: a BICEP2-inspired running indue model (alpha_s=-0.024), two fixed-tilt LCDM models motivated by Planck, and a 2.6 keV thermal WDM model.  Find that the running BICEP2 model reduces the central densities of large dwarf-size haloes (Vmax~30-80 km/s) and alleviates the too-big-to-fail problem significantly compared to the adopted Planck and WDM cases.  Further, the BICEP2 model suppresses the count of small sub haloes by ~50% relative to Planck models, and yields a significantly lower "boost" factor for DM annihilation signals.  Findings highlight the need to understand the shape of the primordial PS in order to correctly interpret small-scale data.

1405.4318
Baryonic and dark matter distribution in cosmological simulations of spiral galaxies
Mollitor, Nezri, Teyssier

High-res cosmo hydrosim of MW-sized haloes; consistently tuned SFR and SNe feedback.  Obtain an extended disk and a flat rotation curve in one of the simulated galaxies; DM density in the solar neighborhood in agreement with observations [what are the observational constraint of DM in the Solar neighborhood?].  DM distribution show the interaction with the baryons and how the DM is first contracted by SF and then cored by feedback processes.  Analysing the clump spectrum, find a shift in mass with regard to corresponding DM-only sims and obtain a distribution of luminous satellites comparable with MW spheroidal dwarf galaxies.

1405.4523
Abundance of field galaxies
Klypin et al

Present new measurements of the abundance of galaxies with a given circular velocity of the Local Volume: a region centered on the MW and extending to distance 10 Mpc.  The sample of 750 mostly dwarf galaxies provides a unique opportunity to study the abundance and properties of galaxies down to absolute magnitudes MB=-10, and virial masses 1e9 Msun.  Find that the standard LCDM model gives remarkable accurate estimates for the velocity function of galaxies with circular velocities V>60 km/s and corresponding virial masses Mvir>3e10 Msun, but it badly fails by over-predicting 5x the abundance of large dwarfs with velocities V=30-50 km/s.  The WDM models cannot explain the data either, regardless of mass of the WDM particle.  Just as in previous observational studies, find a shallow asymptotic slope dN/dlogV=V^alpha, alpha=-1 of the velocity function, which is inconsistent with the standard LCDM model that predicts the slope alpha=-3.  Though reminiscent of the known overabundance of satellites problem, the overabundance of field galaxies is a much more difficult problem.  For the LCDM model to survive, in the 10 Mpc radius of the MW there should be 1000 dark galaxies with virial mass Mvir=1e10 Msun, extremely low surface brightness and no detectable HI gas.  So far none of this type of galaxies have been discovered.