Day 661

Wednesday.

1405.4855
Halo bias in mixed dark matter cosmologies
LoVerde

In a universe with multiple types of matter fluctuations (e.g., with massive neutrinos), the relation between the halo field and the matter fluctuations may be more complicated than "CDM haloes trace the LSS of matter".   Develop a method for calculating the bias factor relating fluctuations n the halo number density to fluctuations in the mass density in the presence of multiple fluctuation components of the energy density.  In the presence of massive neutrinos, find a small but pronounced features in the halo bias near the neutrino free streaming scale.  The neutrino feature is a small step with amplitude that increases with halo mass and neutrino mass density. The scale-dependent halo bias lessens the suppression of the small-scale halo power spectrum and should therefore weaken constraints on neutrino mass from the galaxy auto-power spectrum and correlation function.  On the other hand, the feature in the bias is itself a novel signature of massive neutrinos that can be studied independently.  

1405.4856
Cookie-cutter haloes: the remarkable constancy of the stellar mass function of satellite galaxies at 0.2<z<1.2
Tal et al

Observational study of the stellar MF of satellite galaxies around central galaxies at 0.2<z<1.2.  4 bins of central galaxy mass in 3 redshift bins.  Results show that the stellar MF of satellite galaxies increases with central galaxy mass, and that the distribution of satellite masses at fixed central mass is at most weakly dependent on redshift.   Conclude that the average mass distribution of galaxies in groups is remarkably universal even out to z=1.2 and that it can be uniquely characterized by the group central galaxy mass.  This further suggests that as central galaxies grow in stellar mass, they do so in tandem with the mass growth of their satellites.  Finally, we classify all galaxies as either star forming or quiescent, and derive the mass functions of each subpopulation separately.  Find that the mass distribution of both star forming and quiescent satellites show minimal redshift dependence at fixed central mass.  However, while the fraction of quiescent satellite galaxies increases rapidly with increasing central galaxy mass, that of star forming satellites decreases.

1405.4858
Spherical collapse in $\nu \Lambda CDM$
LoVerde

The abundance of massive DM haloes hosting galaxy clusters provide an important test of the masses of relic neutrino species.  The dominant effect of neutrino mass is to lower the typical amplitude of density perturbations that eventually form haloes, but for neutrino masses >0.4eV the threshold for halo formation can be changed significantly as well.  Study the spherical collapse model for halo formation in cosmologies with neutrino masses in the range M_nu,i = 0.05eV-1eV and find that halo formation is differently sensitive to Omega_nu and m_nu.  That is, different neutrino hierarchies with common Omega_nu are in principle distinguishable.  The added sensitivity to m_nu is small but potentially important for scenarios with heavier sterile neutrinos.  Massive neutrinos cause the evolution of density perturbations to be scale-dependent at high redshift which complicates the usual mapping between the collapse threshold and halo abundance.  Propose one way of handling this and compute the correction to the halo mass function within this framework.  For Sum m_nu,i<0.3eV, prescription for the halo abundance is only ~<15% different than the standard calculation.  However for larger neutrino masses the differences approach 50-100% which, if verified by simulations, could alter neutrino mass constraints from cluster abundance.

1405.5014
Microlensing of the broad-line region in the quadruply imaged quasar HE0435-1223
Braibant, Hutsemékers, Sluse, Anguita, García-Vergara

Using IR spectra of the z=1.693 quadruply lensed quasar HE0435-1223 acquired in 2009 with the spectrograph SINFONI at the ESO VLT, detected a clear microlensing effect in images A and D.  While microlensing affects the blue and red wings of the Halpha line profile in image D very differently, it de-magnifies the line core in image A.  The combination of these different effects sets constrains on the line-emitting region; these constraints suggest that a rotating ring is at the origin of the Halpha line.  Visible spectra obtained in 2004 and 2012 indicate that the MgII line profile is micro lensed in the same way as the Halpha line.  Results therefore favor flattened geometries for the low-ionization line-emitting region, for example, a Keplerian disk.  Biconical models cannot be ruled out but require more fine-tuning.  Flux ratios between the different images are also derived and confirm flux anomalies with respect to estimates from lens models with smooth mass distributions.