Stellar populations in satellite galaxies in close pairs

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 Sloan Digital Sky Survey (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.