The Role of Environment on the Formation of Early-Type Galaxies

TL;DR

This study investigates how environment influences the stellar populations of early-type galaxies, revealing that halo mass and galaxy position (central or satellite) affect star formation histories and ages.

Contribution

It provides new insights into the environmental effects on early-type galaxy evolution, highlighting the role of halo mass and galaxy type in stellar population differences.

Findings

Velocity dispersion is the main driver of star formation history.

Galaxies in low-mass halos are ~1 Gyr younger.

Satellite galaxies are younger than centrals of the same mass.

Abstract

(Abridged) We present a detailed study of the stellar populations of a volume-limited sample of early-type galaxies from SDSS, across a range of environments -- defined as the mass of the host dark matter halo. The stellar populations are explored through the SDSS spectra, via projection onto a set of two spectral vectors determined from Principal Component Analysis. We find the velocity dispersion of the galaxy to be the main driver behind the different star formation histories of early-type galaxies. However, environmental effects are seen to play a role (although minor). Galaxies populating the lowest mass halos have stellar populations on average ~1Gyr younger than the rest of the sample. The fraction of galaxies with small amounts of recent star formation is also seen to be truncated when occupying halos more massive than 3E13Msun. The sample is split into satellite and central galaxies for a further analysis of environment. Satellites are younger than central galaxies of the same stellar mass. The younger satellite galaxies in 6E12Msun halos have stellar populations consistent with the central galaxies found in the lowest mass halos of our sample (i.e. 1E12Msun). This result is indicative of galaxies in lower mass halos being accreted into larger halos.