A detailed look at the stellar populations in green valley galaxies

Angthopo, James; Ferreras, Ignacio; Silk, Joseph
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Monthly Notices of the Royal Astronomical Society

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The green valley (GV) represents an important transitional state from actively star-forming galaxies to passively evolving systems. Its traditional definition, based on colour, rests on a number of assumptions that can be subjected to non-trivial systematics. In Angthopo, Ferreras & Silk (2019), we proposed a new definition of the GV based on the 4000 Å break strength. In this paper, we explore in detail the properties of the underlying stellar populations by use of ∼230 thousand high-quality spectra from the Sloan Digital Sky Survey (SDSS), contrasting our results with a traditional approach via dust-corrected colours. We explore high-quality stacked SDSS spectra, and find a population trend that suggests a substantial difference between low- and high-mass galaxies, with the former featuring younger populations with star formation quenching, and the latter showing older (post-quenching) populations that include rejuvenation events. Subtle but measurable differences are found between a colour-based approach and our definition, especially as our selection of GV galaxies produces a cleaner 'stratification' of the GV, with more homogeneous population properties within sections of the GV. Our definition based on 4000 Å break strength gives a clean representation of the transition to quiescence, easily measurable in the upcoming and future spectroscopic surveys.
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Traces of Galaxy Formation: Stellar populations, Dynamics and Morphology

We are a large, diverse, and very active research group aiming to provide a comprehensive picture for the formation of galaxies in the Universe. Rooted in detailed stellar population analysis, we are constantly exploring and developing new tools and ideas to understand how galaxies came to be what we now observe.

Martín Navarro