Tracking Down a Critical Halo Mass for Killing Galaxies through the Growth of the Red-Sequence

TL;DR

This study investigates the build-up of red-sequence galaxies across different environments and redshifts, revealing a critical halo mass threshold affecting galaxy quenching and highlighting discrepancies in current models.

Contribution

It introduces a simple toy model with a halo mass threshold for galaxy strangulation, improving understanding of red-sequence evolution and challenging existing semi-analytic predictions.

Findings

Higher DGR in clusters than in the field at all redshifts.

DGR evolution supports the 'down-sizing' star formation scenario.

Semi-analytic models overpredict the DGR and its environmental dependence.

Abstract

Red-sequence galaxies record the history of terminated star-formation in the Universe and can thus provide important clues to the mechanisms responsible for this termination. We construct composite samples of published cluster and field galaxy photometry in order to study the build-up of galaxies on the red-sequence, as parameterised by the dwarf-to-giant ratio (DGR). We find that the DGR in clusters is higher than that of the field at all redshifts, implying that the faint end of the red-sequence was established first in clusters. We find that the DGR evolves with redshift for both samples, consistent with the ``down-sizing'' picture of star formation. We examine the predictions of semi-analytic models for the DGR and find that neither the magnitude of its environmental dependence nor its evolution is correctly predicted in the models. Red-sequence DGRs are consistently too high in the models, the most likely explanation being that the strangulation mechanism used to remove hot gas from satellite galaxies is too efficient. Finally we present a simple toy model including a threshold mass, below which galaxies are not strangled, and show that this can predict the observed evolution of the field DGR.