paper

On the dependence of galaxy assembly bias on the selection criteria, number density, and redshift of galaxy samples

arXiv:2504.06770 · doi:10.1051/0004-6361/202555093

Abstract

One of the key factors influencing galaxy clustering in the nonlinear regime is galaxy assembly bias, which describes the dependence of galaxy clustering on halo properties beyond halo mass. We study this effect by analyzing galaxy samples selected according to stellar mass, luminosity, and broad-band colors from the IllustrisTNG hydrodynamical simulation. We find that galaxy assembly bias depends strongly upon the selection criteria, number density, and redshift of the galaxy sample, with this effect increasing or decreasing galaxy clustering by as much as 25%. Interestingly, no single secondary halo property fully captures the strength of galaxy assembly bias for any galaxy population. Therefore, empirical models predicting galaxy assembly bias as a function of a single halo property cannot reproduce predictions from hydrodynamical simulations. Finally, we investigate how galaxy assembly bias arises from the interplay between halo assembly bias -- the dependence of halo clustering on properties other than halo mass -- and occupancy variation -- the correlation between galaxy occupation and secondary halo properties. We provide a fast analytical expression to predict the level of galaxy assembly bias induced by any halo property in simulated galaxy catalogs without the need for computationally expensive shuffling techniques.

arXiv comment9 pages, 8 figures, accepted by A&A

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