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What drives the star formation in early-type galaxies at late epochs? - the case for minor mergers

Published online by Cambridge University Press:  13 April 2010

Sugata Kaviraj
Affiliation:
MSSL, University College London, Holmbury St Mary, Surrey RH5 6NT, UK email: skaviraj@astro.ox.ac.uk Dept. of Physics, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK Dept. of Astrophysics, Imperial College London, London SW7 2AZ
Richard Ellis
Affiliation:
Dept. of Physics, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK California Institute of Technology, 105-24 Astronomy, Pasadena, CA 91125, USA
Sukyoung Yi
Affiliation:
Dept. of Astronomy, Yonsei University, 134 Shinchon-dong, Seoul 120-179, Korea
Joseph Silk
Affiliation:
Dept. of Physics, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK
Kevin Schawinski
Affiliation:
Yale Center for Astronomy and Astrophysics, New Haven CT 06520-8121, USA
Eric Gawiser
Affiliation:
Dept. of Physics and Astronomy, Rutgers University, Piscataway, NJ 08854, USA
Pieter van Dokkum
Affiliation:
Yale Center for Astronomy and Astrophysics, New Haven CT 06520-8121, USA
C. Megan Urry
Affiliation:
Yale Center for Astronomy and Astrophysics, New Haven CT 06520-8121, USA
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Abstract

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Multi-wavelength photometry of early-type galaxies (ETGs) in the COSMOS survey is used to demonstrate that the low-level star formation activity in the ETG population at late epochs (z < 1) is likely to be driven by repeated minor mergers. While relaxed ETGs are almost entirely contained within the UV red sequence, their morphologically disturbed counterparts are largely found in the blue cloud, regardless of luminosity. Since empirically determined major-merger rates in the redshift range z < 1 are a few factors too low to account for the number fraction of disturbed ETGs, this suggests that minor mergers are the principal mechanism that drives star formation activity in ETGs at low and intermediate redshift.

Type
Contributed Papers
Copyright
Copyright © International Astronomical Union 2010

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