Galaxy populations in groups and clusters: evidence for a characteristic stellar mass scale at $M_\ast\sim 10^{9.5}M_\odot$

TL;DR

This study analyzes galaxy populations in groups and clusters, revealing a characteristic stellar mass scale at around 10^{9.5} solar masses where galaxy properties such as old stellar populations and structural dichotomies change notably.

Contribution

It provides the first detailed measurement of the conditional luminosity function down to very faint magnitudes, identifying a mass scale linked to galaxy evolution and structural properties.

Findings

Faint-end upturn in red satellite CLF with slope ~-1.8, independent of halo mass.

Old galaxy fraction drops to a minimum at M_r ~ -18, corresponding to M_* ~ 10^{9.5} M_sun.

The characteristic mass scale is consistent across different halo masses and relates to galaxy structural dichotomies.

Abstract

We use the most recent data release (DR9) of the DESI legacy imaging survey and SDSS galaxy groups to measure the conditional luminosity function (CLF) for groups with halo mass $M_{\rm h}\ge 10^{12}M_{\odot}$ and redshift $0.01\le z\le 0.08$, down to a limiting $r$-band magnitude of $M_{\rm r}=-10\sim-12$. For a given halo mass we measure the CLF for the total satellite population, as well as separately for the red and blue populations classified using the $(g-z)$ color. We find a clear faint-end upturn in the CLF of red satellites, with a slope $\alpha\approx-1.8$ which is almost independent of halo mass. This faint-end upturn is not seen for blue satellites and for the total population. Our stellar population synthesis modeling shows that the $(g-z)$ color provides a clean red/blue division, and that group galaxies in the red population defined by $(g-z)$ are all dominated by old stellar populations. The fraction of old galaxies as a function of galaxy luminosity shows a minimum at a luminosity $M_{\rm r}\sim-18$, corresponding to a stellar mass $M_\ast\sim10^{9.5}M_\odot$. This mass scale is independent of halo mass and is comparable to the characteristic luminosity at which galaxies show a dichotomy in surface brightness and size, suggesting that the dichotomy in the old fraction and in galaxy structure may have a common origin. The rising of the old fraction at the faint end for Milky Way (MW)-sized halos found here is in good agreement with the quenched fraction measured both for the MW/M31 system and from the ELVES survey. We discuss the implications of our results for the formation and evolution of low-mass galaxies, and for the stellar mass functions of low-mass galaxies to be observed at high redshift.