Halo and Subhalo Demographics with Planck Cosmological Parameters: Bolshoi-Planck and MultiDark-Planck Simulations

TL;DR

This paper provides detailed halo and subhalo abundance functions, halo accretion rates, and galaxy-halo relations from Planck cosmology simulations, highlighting implications for galaxy evolution and observational consistency.

Contribution

It introduces new fitting functions for halo/subhalo demographics and accretion rates based on Planck cosmology, and analyzes galaxy-halo velocity relations and their evolution.

Findings

Higher matter density leads to more massive halos at high redshift.

Halo spin parameter is nearly independent of redshift, affecting galaxy size evolution.

Galaxy velocity relations must evolve at z > 1 to match observed stellar mass densities.

Abstract

We report and provide fitting functions for the abundance of dark matter halos and subhalos as a function of mass, circular velocity, and redshift from the new Bolshoi-Planck and MultiDark-Planck $\Lambda$CDM cosmological simulations, based on the Planck cosmological parameters. We also report the halo mass accretion rates, which may be connected with galaxy star formation rates. We show that the higher cosmological matter density of the Planck parameters compared with the WMAP parameters leads to higher abundance of massive halos at high redshifts. We find that the median halo spin parameter $\lambda_{\rm B} = J(2M_{\rm vir}R_{\rm vir}V_{\rm vir})^{-1}$ is nearly independent of redshift, leading to predicted evolution of galaxy sizes that is consistent with observations, while the significant decrease with redshift in median $\lambda_{\rm P} = J|E|^{-1/2}G^{-1}M^{-5/2}$ predicts more decrease in galaxy sizes than is observed. Using the Tully-Fisher and Faber-Jackson relations between galaxy velocity and mass, we show that a simple model of how galaxy velocity is related to halo maximum circular velocity leads to increasing overprediction of cosmic stellar mass density as redshift increases beyond redshifts $z\sim1$, implying that such velocity-mass relations must change at redshifts $z>1$. By making a realistic model of how observed galaxy velocities are related to halo circular velocity, we show that recent optical and radio observations of the abundance of galaxies are in good agreement with our $\Lambda$CDM simulations. Our halo demographics are based on updated versions of the \rockstar\ and \ctrees\ codes, and this paper includes appendices explaining all of their outputs. This paper is an introduction to a series of related papers presenting other analyses of the Bolshoi-Planck and MultiDark-Planck simulations.