Galaxy Zoo: Evidence for Diverse Star Formation Histories through the Green Valley
R. J. Smethurst, C. J. Lintott, B. D. Simmons, K. Schawinski, P. J., Marshall, S. Bamford, L. Fortson, S. Kaviraj, K. L. Masters, T. Melvin, R. C., Nichol, R. A. Skibba, K. W. Willett

TL;DR
This study uses a Bayesian model to analyze galaxy star formation histories, revealing multiple evolutionary pathways through the green valley linked to galaxy morphology and quenching timescales.
Contribution
It introduces a novel Bayesian approach to distinguish galaxy evolutionary routes based on morphology and star formation quenching timescales.
Findings
Smooth galaxies quench rapidly via major mergers.
Disc galaxies evolve slowly through secular processes.
Multiple pathways through the green valley are supported by data.
Abstract
Does galaxy evolution proceed through the green valley via multiple pathways or as a single population? Motivated by recent results highlighting radically different evolutionary pathways between early- and late-type galaxies, we present results from a simple Bayesian approach to this problem wherein we model the star formation history (SFH) of a galaxy with two parameters, [t, \tau] and compare the predicted and observed optical and near-ultraviolet colours. We use a novel method to investigate the morphological differences between the most probable SFHs for both disc-like and smooth-like populations of galaxies, by using a sample of 126,316 galaxies (0.01 < z < 0.25) with probabilistic estimates of morphology from Galaxy Zoo. We find a clear difference between the quenching timescales preferred by smooth- and disc-like galaxies, with three possible routes through the green valley…
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