Galaxy environments over cosmic time: the non-evolving radial galaxy distributions around massive galaxies since z=1.6

TL;DR

This study analyzes the environments of massive galaxies from redshift 1.6 to 0.04, finding that their satellite distributions have remained largely unchanged over 9.5 billion years, indicating static halo evolution or balanced mergers and accretion.

Contribution

It provides the first comprehensive analysis of the non-evolving radial galaxy distributions around massive galaxies over a significant cosmic time span.

Findings

Massive galaxies typically have 2-3 satellites with significant mass.

The radial distribution of satellites shows no significant evolution in slope or normalization.

The results support static halo evolution or a balance between mergers and accretion.

Abstract

We present a statistical study of the environments of massive galaxies in four redshift bins between z=0.04 and z=1.6, using data from the Sloan Digital Sky Survey (SDSS) and the NEWFIRM Medium Band Survey (NMBS). We measure the projected radial distribution of galaxies in cylinders around a constant number density selected sample of massive galaxies and utilize a statistical subtraction of contaminating sources. Our analysis shows that massive primary galaxies typically live in group halos and are surrounded by 2 to 3 satellites with masses more than one-tenth of the primary galaxy mass. The cumulative stellar mass in these satellites roughly equals the mass of the primary galaxy itself. We further find that the radial number density profile of galaxies around massive primaries has not evolved significantly in either slope or overall normalization in the past 9.5 Gyr. A simplistic interpretation of this result can be taken as evidence for a lack of mergers in the studied groups and as support for a static evolution model of halos containing massive primaries. Alternatively, there exists a tight balance between mergers and accretion of new satellites such that the overall distribution of galaxies in and around the halo is preserved. The latter interpretation is supported by a comparison to a semi-analytic model, which shows a similar constant average satellite distribution over the same redshift range.