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A coincidence of disturbed morphology and blue UV colour: minor-merger-driven star formation in early-type galaxies at z ~ 0.6

Kaviraj, Sugata and Tan, Kok-Meng and Ellis, Richard S. and Silk, Joseph (2011) A coincidence of disturbed morphology and blue UV colour: minor-merger-driven star formation in early-type galaxies at z ~ 0.6. Monthly Notices of the Royal Astronomical Society, 411 (4). pp. 2148-2160. ISSN 0035-8711. doi:10.1111/j.1365-2966.2010.17754.x.

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We exploit multiwavelength photometry of early-type galaxies (ETGs) in the Cosmological Evolution Survey (COSMOS) to demonstrate that the low-level star formation activity in the ETG population at intermediate redshift is likely to be driven by minor mergers. Splitting the ETGs into galaxies that show disturbed morphologies indicative of recent merging and those that appear relaxed, we find that ~32 per cent of the ETG population appears to be morphologically disturbed. While the relaxed objects are almost entirely contained within the UV red sequence, their morphologically disturbed counterparts dominate the scatter to blue UV colours, regardless of luminosity. Empirically and theoretically determined major-merger rates in the redshift range z < 1 are several times too lowto account for the fraction of disturbed ETGs in our sample, suggesting that minor mergers represent the principal mechanism driving the observed star formation activity in our sample. The young stellar components forming in these events have ages between 0.03 and 0.3 Myr and typically contribute ≤ 10 per cent of the stellar mass of the remnant. Together with recent work which demonstrates that the structural evolution of nearby ETGs is consistent with one or more minor mergers, our results indicate that the overall evolution of massive ETGs may be heavily influenced by minor merging at late epochs and highlights the need to systematically study this process in future observational surveys.

Item Type:Article
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Ellis, Richard S.0000-0001-7782-7071
Additional Information:© 2011 The Authors. Monthly Notices of the Royal Astronomical Society © 2011 RAS. Accepted 2010 September 22. Received 2010 August 17; in original form 2009 December 25. Article first published online: 31 Jan 2011. The anonymous referee is gratefully acknowledged for a thorough report which significantly improved the original manuscript. SK acknowledges an Imperial College Junior Research Fellowship, a Research Fellowship from the Royal Commission for the Exhibition of 1851, a Senior Research Fellowship from Worcester College, Oxford, and support from the BIPAC institute at Oxford. Some of this work was supported by a Leverhulme Early-Career Fellowship (SK). RSE acknowledges support from the Royal Society. Roger Davies, Kevin Bundy, Martin Bureau, Chris Conselice, Jerry Sellwood and Sukyoung Yi are thanked for interesting discussions and useful comments. Some of this research utilized the undergraduate computing facilities in the Department of Physics at the University of Oxford.
Funding AgencyGrant Number
Leverhulme Early-Career FellowshipUNSPECIFIED
Imperial College Junior Research FellowshipUNSPECIFIED
Royal Commission Research FellowshipUNSPECIFIED
Worcester College Senior Research FellowshipUNSPECIFIED
Subject Keywords:galaxies: elliptical and lenticular, cD; galaxies: evolution; galaxies: formation; galaxies: interactions; ultraviolet: galaxies
Issue or Number:4
Record Number:CaltechAUTHORS:20110323-080916064
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Official Citation:A coincidence of disturbed morphology and blue UV colour: minor-merger-driven star formation in early-type galaxies at z∼ 0.6 (pages 2148–2160) Sugata Kaviraj, Kok-Meng Tan, Richard S. Ellis and Joseph Silk Article first published online: 31 JAN 2011 | DOI: 10.1111/j.1365-2966.2010.17754.x
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:23058
Deposited On:23 Mar 2011 17:23
Last Modified:09 Nov 2021 16:10

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