Day 856

Wednesday.


1503.06799
Rapid environmental quenching of satellite dwarf galaxies in the Local Group
Wetzel, Tollerud, Weisz

In the LG, nearly all of the dwarf galaxies (M*<1e9 Msun) that are satellite within 300kpc (the viral radius) of the MW and M31 have quiescent SF and little-to-no cold gas.  This contrasts strongly with comparatively isolated dwarf galaxies, which are almost all actively SF and gas-rich.  This near dichotomy implies a rapid transformation after falling into the halos of the MW or M31.  Combine the observed quiescent fractions for satellites of the MW and M31 with the infall times of satellites from the ELVIS suite of cosmo sims to determine the typical timescales over which environmental processes within the MW/M31 halos remove gas and quench SF in low-mass satellite galaxies.  The quenching timescales for satellites with M*<1e8Msun are short, <2Gyr, and quenching is more rapid at lower M*.  These quenching timescales can be 1-2 Gyr longer if environmental preprocessing in lower-mass groups prior to MW/M31 infall is important.  Compare with quenching timescales for more massive satellites from previous works and synthesize the nature of satellite quenching across the observable range of M*-1e3-11 Msun.  The environmental quenching timescale increases rapidly with satellite M*, peaking at ~9.5 Gyr for M*~1e9Msun, and rapidly decreases at higher M* to <5Gyr at M*>5e9Msun.  Overall, galaxies with M*~1e9Msun, similar to the Magellanic Clouds, exhibit the longest quenching teimscales, regardless of environmental or internal mechanisms.


1503.06830
Towards optimal estimation of the galaxy power spectrum
Smith, Marian

The galaxy PS encodes a wealth of information about cosmo and matter fluctuations.  Its unbiased and optimal estimation is therefore of great importance.  In this paper, generalize the framework of Feldman+1994 to take into account the fact that galaxies are not simply a Poisson sampling of the underling DM distribution.  Besides finite survey-volume effects and flux-limits, the optimal estimation scheme incorporates several of the key tenets of galaxy formation: galaxies form and reside exclusively in DM haloes; a given DM halo may host several galaxies of various luminosities; galaxies inherit part of their LS bias from their host halo.  Under these broad assumptions, prove that the optimal weights "do not" explicitly depend on galaxy luminosity, other than through defining the maximum survey volume and effective galaxy density at a given position.  Instead, they depend on the bias associated with the host halo; the first and second factorial moments of the halo occupation distribution; a selection function, which gives the fraction of galaxies that can be observed in a halo of mass M at position r in the survey; and an effective number density of galaxies.  If one wishes to reconstruct the matter PS, then, provided the model is correct, this scheme provides the only unbiased estimator.  The practical challenges with implementing this approach are also discussed.