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Journal Articles Monthly Notices of the Royal Astronomical Society: Letters Year : 2019

Exploring a new definition of the green valley and its implications

James Angthopo
  • Function : Author
Ignacio Ferreras
  • Function : Author

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).
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Dates and versions

insu-03747920 , version 1 (09-08-2022)

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James Angthopo, Ignacio Ferreras, Joseph Silk. Exploring a new definition of the green valley and its implications. Monthly Notices of the Royal Astronomical Society: Letters, 2019, 488, pp.L99-L103. ⟨10.1093/mnrasl/slz106⟩. ⟨insu-03747920⟩
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