Exploring a new definition of the green valley and its implications

Angthopo, James; Ferreras, Ignacio; Silk, Joseph
Bibliographical reference

Monthly Notices of the Royal Astronomical Society: Letters, Volume 488, Issue 1, p.L99-L103

Advertised on:
9
2019
Number of authors
3
IAC number of authors
1
Citations
20
Refereed citations
17
Description
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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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.

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