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Quenching star formation at intermediate redshifts: downsizing of the mass flux density in the green valley

Published online by Cambridge University Press:  17 July 2013

Thiago S. Gonçalves
Affiliation:
Observatório do Valongo, Universidade Federal do Rio de Janeiro, Ladeira Pedro Antonio, 43, Saúde, Rio de Janeiro–RJ, CEP 22240-060 email: tsg@astro.ufrj.br
D. Christopher Martin
Affiliation:
California Institute of Technology
Karín Menéndez-Delmestre
Affiliation:
Observatório do Valongo, Universidade Federal do Rio de Janeiro, Ladeira Pedro Antonio, 43, Saúde, Rio de Janeiro–RJ, CEP 22240-060 email: tsg@astro.ufrj.br
Ted K. Wyder
Affiliation:
California Institute of Technology
Anton Koekemoer
Affiliation:
Space Telescope Science Institute
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Abstract

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The bimodality in galaxy properties has been observed at low and high redshift, with a clear distinction between star-forming galaxies in the blue cloud and passively evolving objects in the red sequence; the absence of galaxies with intermediate properties indicates that the quenching of star formation and subsequent transition between populations must happen rapidly. In this work, we present a study of over 100 transiting galaxies in the so-called “green valley” at intermediate redshifts (z ~ 0.8). By using very deep spectroscopy with the DEIMOS instrument at the Keck telescope, we are able to infer the star formation histories of these objects and measure the stellar mass flux density transiting from the blue cloud to the red sequence when the Universe was half its current age. Our results indicate that the process happened more rapidly, affecting more massive galaxies in the past, suggesting a top-down scenario whereby the massive end of the red sequence assembles first. This represents another aspect of downsizing, with the mass flux density moving towards smaller galaxies in recent times.

Type
Contributed Papers
Copyright
Copyright © International Astronomical Union 2013 

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