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arXiv · 1611.00367

The Galaxy End Sequence

Stephen Eales·Pieter de Vis·Matthew Smith·Kiran Appah·Laure Ciesla·Chris Duffield·Simon Schofield
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Abstract

A common assumption is that galaxies fall in two distinct regions on a plot of specific star-formation rate (SSFR) versus galaxy stellar mass: a star-forming Galaxy Main Sequence (GMS) and a separate region of `passive' or `red and dead galaxies'. Starting from a volume-limited sample of nearby galaxies designed to contain most of the stellar mass in this volume, and thus being a fair representation of the Universe at the end of 12 billion years of galaxy evolution, we investigate the distribution of galaxies in this diagram today. We show that galaxies follow a strongly curved extended GMS with a steep negative slope at high galaxy stellar masses. There is a gradual change in the morphologies of the galaxies along this distribution, but there is no clear break between early-type and late-type galaxies. Examining the other evidence that there are two distinct populations, we argue that the `red sequence' is the result of the colours of galaxies changing very little below a critical value of the SSFR, rather than implying a distinct population of galaxies, and that Herschel observations, which show at least half of early-type galaxies contain a cool interstellar medium, also imply continuity between early-type and late-type galaxies. This picture of a unitary population of galaxies requires more gradual evolutionary processes than the rapid quenching processes needed to to explain two distinct populations. We challenge theorists to reproduce the properties of this `Galaxy End Sequence'.

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Stephen Eales, Pieter de Vis, Matthew Smith, Kiran Appah, Laure Ciesla, Chris Duffield, Simon Schofield. 2016-11-01. The Galaxy End Sequence. https://doi.org/10.1093/mnras%2Fstw2875

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