Stellar Populations in Satellite Galaxies in Close Pairs

TL;DR

This study investigates stellar populations in satellite galaxies near primary galaxies, confirming age conformity but not metallicity or abundance ratio conformity, and suggests environment-related effects at high velocity dispersions.

Contribution

It provides new evidence for age conformity in satellite galaxies using spectral fitting of SDSS data, and explores the role of environment and velocity dispersion in stellar population properties.

Findings

Confirmed age conformity in satellite galaxies.

No evidence for metallicity or alpha-element abundance conformity.

Possible environment effects at high velocity dispersions.

Abstract

Satellite galaxies that are near to massive primary galaxies in close pairs can have stellar population ages that are more similar to their primaries than expected. This is one way in which close pairs of galaxies show galactic conformity, which is thought to be driven by assembly bias. Such conformity is seen in ages, morphologies and star formation rates in different samples. This paper revisits a high signal-to-noise SDSS spectroscopic sample, by spectral fitting of new stellar population models, to investigate satellite galaxy properties of age, metallicity and alpha-element abundance. We find the clear signature of age conformity, as previously seen, but no clear evidence for conformity in metallicity or abundance ratios. The offsets showing age conformity are not caused by age-metallicity degeneracies. There is a suggestion in these data that lower velocity dispersion satellites have increased [alpha/Fe] compared to a control sample of passive galaxies, however this needs further observations to be verified. Our results also suggest an intriguing turnover in the age trends of the satellites at the highest velocity dispersion, perhaps reflecting the onset of environment-related processes in the most massive groups.