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Exploring a new definition of the green valley and its implications

Angthopo, J; Ferreras, I; Silk, J; (2019) Exploring a new definition of the green valley and its implications. Monthly Notices of the Royal Astronomical Society: Letters , 488 (1) L99-L103. 10.1093/mnrasl/slz106. Green open access

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Abstract

The distribution of galaxies on a colour–magnitude diagram reveals a bimodality, featuring a passively evolving red sequence and a star-forming blue cloud. The region between these two, the green valley (GV), represents a fundamental transition where quenching processes operate. We exploit an alternative definition of the GV using the 4000 Å break strength, an indicator that is more resilient than colour to dust attenuation. We compare and contrast our GV definition with the traditional one, based on dust-corrected colour, making use of data from the Sloan Digital Sky Survey. Our GV selection – that does not need a dust correction and thus does not carry the inherent systematics – reveals very similar trends regarding nebular activity (star formation, AGN, quiescence) to the standard dust-corrected 0.1(g − r). By use of high-SNR stacked spectra of the quiescent GV subsample, we derive the simple stellar population (SSP) age difference across the GV, a rough proxy of the quenching time-scale (Δt). We obtain an increasing trend with velocity dispersion (σ), from Δt ∼ 1.5 Gyr at σ = 100 km s−1, up to 3.5 Gyr at σ = 200 km s−1, followed by a rapid decrease in the most massive GV galaxies (Δt ∼ 1 Gyr at σ = 250 km s−1), suggesting two different modes of quenching, or the presence of an additional channel (rejuvenation).

Type: Article
Title: Exploring a new definition of the green valley and its implications
Open access status: An open access version is available from UCL Discovery
DOI: 10.1093/mnrasl/slz106
Publisher version: https://doi.org/10.1093/mnrasl/slz106
Language: English
Additional information: This version is the version of record. For information on re-use, please refer to the publisher’s terms and conditions.
Keywords: Science & Technology, Physical Sciences, Astronomy & Astrophysics, galaxies: evolution, galaxies: formation, galaxies: interactions, galaxies: stellar content, STAR-FORMATION HISTORIES, DIGITAL SKY SURVEY, EARLY-TYPE GALAXIES, STELLAR POPULATIONS, RED SEQUENCE, LINE SPECTRA, EVOLUTION, COMBO-17, BULGES, BLUE
UCL classification: UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Physics and Astronomy
URI: https://discovery.ucl.ac.uk/id/eprint/10083056
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