Satellites around massive galaxies since z~2

TL;DR

This study investigates the prevalence of satellite galaxies around massive galaxies since redshift 2, finding a consistent satellite fraction over time and differences between spheroid and disk morphologies, informing galaxy evolution models.

Contribution

It provides the first extensive analysis of satellite fractions around massive galaxies up to z=2, highlighting morphological differences and estimating merger counts over cosmic time.

Findings

Approximately 30% of massive galaxies have satellites with mass ratios down to 1:100 up to z=1.

The satellite fraction is about 15% for 1:10 mass ratio satellites up to z=2.

Spheroid-like galaxies have 2-3 times more satellites than disk-like galaxies.

Abstract

Accretion of minor satellites has been postulated as the most likely mechanism to explain the significant size evolution of the massive galaxies over cosmic time. Using a sample of 629 massive (Mstar~10^11 Msun) galaxies from the near-infrared Palomar/DEEP-2 survey, we explore which fraction of these objects has satellites with 0.01 Msat < Mcentral < 1 (1:100) up to z=1 and which fraction has satellites with 0.1 Msat < Mcentral < 1 (1:10) up to z=2 within a projected radial distance of 100 kpc. We find that the fraction of massive galaxies with satellites, after the background correction, remains basically constant and close to ~30% for satellites with a mass ratio down to 1:100 up to z=1, and ~15% for satellites with a 1:10 mass ratio up to z=2. The family of spheroid-like massive galaxies presents a 2-3 times larger fraction of objects with satellites than the group of disk-like massive galaxies. A crude estimation of the number of 1:3 mergers a massive spheroid-like galaxy experiences since z~2 is around 2. For a disk-like galaxy this number decreases to ~1.