The Faint End of the Cluster Galaxy Luminosity Function at High Redshift

TL;DR

This study measures the faint end slope of the galaxy luminosity function in high-redshift clusters, finding it similar to the field and low-redshift clusters, indicating early establishment of the LF shape.

Contribution

It provides the first measurement of the faint end slope of the cluster galaxy LF at z=1.35 using Spitzer IRAC data, showing no significant evolution from low redshift.

Findings

Faint end slope alpha ~ -0.9 at z=1.35

No significant evolution of LF shape from low redshift

LF shape largely established by z~1.3

Abstract

We measure the faint end slope of the galaxy luminosity function (LF) for cluster galaxies at 1<z<1.5 using Spitzer IRAC data. We investigate whether this slope, alpha, differs from that of the field LF at these redshifts, and with the cluster LF at low redshifts. The latter is of particular interest as low-luminosity galaxies are expected to undergo significant evolution. We use seven high-redshift spectroscopically confirmed galaxy clusters drawn from the IRAC Shallow Cluster Survey to measure the cluster galaxy LF down to depths of M* + 3 (3.6 microns) and M* + 2.5 (4.5 microns). The summed LF at our median cluster redshift (z=1.35) is well fit by a Schechter distribution with alpha[3.6] = -0.97 +/- 0.14 and alpha[4.5] = -0.91 +/- 0.28, consistent with a flat faint end slope and is in agreement with measurements of the field LF in similar bands at these redshifts. A comparison to alpha in low-redshift clusters finds no statistically significant evidence of evolution. Combined with past studies which show that M* is passively evolving out to z~1.3, this means that the shape of the cluster LF is largely in place by z~1.3. This suggests that the processes that govern the build up of the mass of low-mass cluster galaxies have no net effect on the faint end slope of the cluster LF at z<1.3.