The Importance of Satellite Quenching for the Build-Up of the Red Sequence of Present Day Galaxies

TL;DR

This study investigates how satellite-specific mechanisms like strangulation and ram-pressure stripping contribute to the transformation of blue disk galaxies into red, early-type galaxies, emphasizing the role of satellite quenching in building the red sequence.

Contribution

It provides observational evidence that satellite quenching mechanisms predominantly affect galaxy color rather than morphology, and quantifies the significance of satellite quenching across different stellar masses.

Findings

Satellites are redder and more concentrated than centrals of the same stellar mass.

Color transformation occurs without significant morphological change.

Approximately 70% of low-mass red satellites quenched after becoming satellites.

Abstract

In the current paradigm, red sequence galaxies are believed to have formed as blue disk galaxies that subsequently had their star formation quenched. Since red-sequence galaxies typically have an early-type morphology, the transition from the blue to the red sequence also involves a morphological transformation. In this paper we study the impact of transformation mechanisms that operate only on satellite galaxies, such as strangulation, ram-pressure stripping and galaxy harassment. Using a large galaxy group catalogue constructed from the SDSS, we compare the colors and concentrations of satellites galaxies to those of central galaxies of the same stellar mass, adopting the hypothesis that the latter are the progenitors of the former. On average, satellites are redder and more concentrated than central galaxies of the same stellar mass. Central-satellite pairs that are matched in both stellar mass and color, however, show no average concentration difference, indicating that the transformation mechanisms affect color more than morphology. The color and concentration differences of matched central-satellite pairs are completely independent of the halo mass of the satellite galaxy, indicating that satellite-specific transformation mechanisms are equally efficient in haloes of all masses. This strongly favors strangulation as the main quenching mechanism for satellite galaxies. Finally, we determine the relative importance of satellite quenching for the build-up of the red sequence. We find that roughly 70 percent of red sequence satellite galaxies with a stellar mass of 10^9 Msun had their star formation quenched as satellites. This drops rapidly to zero with increasing stellar mass, indicating that a significant fraction of red satellites were already quenched before they became a satellite.