Population Statistics of Galaxy Halos in Cosmological Simulations

[摘要] The number of massive structures in the universe is determined by a small set of cosmological parameters characterizing its content, geometry, and expansion rate.Survey counts of massive clusters of galaxies can constrain these parameters, but require a statistical model relating total cluster mass to relevant, observable signals, such X-ray luminosity, X-raytemperature, and galaxy count.I present empirical and computational efforts to improve estimates of this statistical relationship, with an emphasis on measures of the hot intracluster gas.First, I present my work calibrating therelationship between galaxy cluster mass and X-ray luminosity.This work compared observed cluster counts from the REFLEX survey toexpectations for $Lambda$CDM cosmologies derived from a halo mass function. In this comparison, I obtained the first measurement of the scatter and discuss possible systematic biases in parameter estimates due to the scatter.I extended my work on mass selection functions to a full suite of X-ray and Sunyaev-Zeldovich (SZ) signals in the Millennium Gas Simulations (MGS).The MGS are hydrodynamic simulations in a 500 Mpc/h box, with two treatments of the gasphysics: a model with only shock-heating and gravity (GO) and a simple preheating model (PH).From the MGS, I present scaling relations among multiple signals, including a covariance matrix,for about 4000 massive halos. Finally, I investigate the total halo mass function with two pairs of simulations: the MGS and a pair of high-resolution simulations which include a GOmodel and a refined treatment including cooling, star formation, and supernova feedback (CSF).The CSF and PH models have baryon fractionswhich differ from the GO models, and therefore systematic shifts in halo mass at fixed number density. These mass shifts result in a 30% deviation in number density at fixed mass from a halo mass function calibrated with only dark matter, significantly higher than the 5% statistical uncertainty halo mass function.

[发布机构] University of Michigan

[效力级别] Computer Simulations

[关键词] Astrophysics;Computer Simulations;Galaxy Clusters;X-ray Observations;Astronomy;Science;Astronomy and Astrophysics