The evolution of low-mass central galaxies in the vicinity of massive structures and its impact on the two-halo conformity

TL;DR

This study examines how the evolutionary history of low-mass central galaxies near massive structures influences large-scale galaxy conformity signals, revealing the role of former satellites and their environmental effects across different simulations and redshifts.

Contribution

It provides new insights into the impact of former satellite galaxies on two-halo conformity signals and compares results across two different cosmological simulations.

Findings

Former satellites are more common among quenched centrals near massive structures.

Removing former satellites aligns the evolutionary trends of quenched centrals with control samples.

The two-halo conformity signal evolves differently in the two simulations, decreasing in one and increasing in the other from z=0 to z=1.

Abstract

We investigated the population of low-mass central galaxies with Mstar = $10^{9.5}-10^{10}$ Msun/h, inhabiting regions near massive groups and clusters of galaxies using the TNG300 and MDPL2-SAG simulations. We set out to study their evolutionary histories, aiming to find hints about the large-scale conformity signal they produce. We also used a control sample of central galaxies with the same stellar mass range located far away from massive structures. For both samples, we find a subpopulation of galaxies accreted by another halo in the past, but now considered central galaxies; we refer to these objects as former satellites. The number of former satellites is higher for quenched central galaxies near massive systems, with fractions of 45% and 17% in TNG300 and MDPL2-SAG. Our results in TNG300 show that former satellites pollute the sample of central galaxies because they suffered environmental processes when they were satellites hosted typically by massive dark matter halos (M200 $\geq 10^{13}$ Msun/h) since z$\lesssim$0.5. After removing former satellites, the evolutionary trends for quenched central galaxies near massive structures are fairly similar to those of the quenched control galaxies, showing small differences at low redshift. For MDPL2-SAG instead, former satellites were hosted by less massive halos, with a mean halo mass around $10^{11.4}$ Msun/h, and the evolutionary trends remain equal before and after removing former satellite galaxies. We also measured the two-halo conformity, i.e, the correlation in the sSFR between low-mass central galaxies and their neighbors at Mpc scales, and how former satellites contribute to the signal at three different redshifts: z=0, 0.3, and 1. The time evolution of the conformity signal in the simulations presents apparent contradictory results: it decreases from z=0 to z=1 in MDPL2-SAG, while it increases in TNG300 (abridged).