Day 90

Monday.  6:00am.


1001.1737
A cosmic variance cookbook
Moster, Somerville, Newman, Rix


Deep pencil beam surveys (<1 deg. sq.) are important for studying the high-z universe, but inferences about galaxy populations properties are limited by 'cosmic variance'.  Cosmic variance for a given galaxy population can be determined using predictions from CDM theory and the galaxy bias.  Provide tools for experiment design and interpretation.  For a given survey geometry, present the cosmic variance of DM as a function of mean redshift z and redshift bin size dz.  Use HOD to predict galaxy clustering, derive galaxy bias as a function of mead redshift for galaxy samples of a given stellar mass range.  In the linear regime, the cosmic variance of these galaxy samples is the product of the galaxy bias and the DM cosmic variance.  Present a simple recipe using a fitting function to compute cosmic variance as a function of the angular dimensions of the field, z, dz and stellar mass m*.  Also provide tabulated values and software tool.  For GOODS (10'x16') at z=2 and dz=0.5, the relative cosmic variance for galaxies with m*>1e11 Msun is 38%, while it is 27% for GEMS (28'x28') and ~12% for COSMOS (84'x84').  This implies that cosmic variance is a significant source of uncertainty at z=2 for small fields and massive galaxies, while for larger fields and intermediate mass galaxies cosmic variance is less serious.


* What is the SUBARU (27'x34', close to GEMS) field variance?  ... around 10% for MW galaxies or brighter.  Cool!


MPIfR Special Colloquium
29 Sept. 2011, 11:00, MPIfR 0.02
Dynamiacs in young star clusters: from planets to massive stars
Christoph Olczak


Numerical simulations play a vital role in exploring the initial conditions under which star clusters form, and the impact of these (often harsh) environments on the formation and evolution of their stellar and substellar members.  Stellar interactions can have a huge variety: prevent or trigger planet formation, modify disk structure, affect stellar multiplicity, leave characteristic signatures that can be traced observationally.  Also, present a recently developed efficient measure of mass segregation in stellar systems.  Mass segregation occurs rapidly even for spherical systems without substructure.  Provides strong constraints on their initial conditions.