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The 2dF-SDSS LRG and QSO Survey: the star formation histories of luminous red galaxies

Roseboom, Isaac G.; Pimbblet, Kevin A.; Drinkwater, Michael J.; Cannon, Russell D.; De Propris, Roberto; Edge, Alastair C.; Eisenstein, Daniel J.; Nichol, Robert C.; Smail, Ian; Wake, David A.; Bland-Hawthorn, Joss; Bridges, Terry J.; Carson, Daniel; Colless, Matthew; Couch, Warrick J.; Croom, Scott M.; Driver, Simon P.; Hewett, Paul C.; Loveday, Jon; Ross, Nic; Schneider, Donald P.; Shanks, Tom; Sharp, Robert G. and Weilbacher, Peter (2006). The 2dF-SDSS LRG and QSO Survey: the star formation histories of luminous red galaxies. Monthly Notices of the Royal Astronomical Society, 373(1) pp. 349–360.

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We present a detailed investigation into the recent star formation histories of 5697 luminous red galaxies (LRGs) based on the Hδ (4101 Å), and [O II] (3727 Å) lines and the D4000 index. LRGs are luminous (L > 3(L*) galaxies which have been selected to have photometric properties consistent with an old, passively evolving stellar population. For this study, we utilize LRGs from the recently completed 2dF-SDSS LRG and QSO Survey (2SLAQ). Equivalent widths of the Hδ and [O II] lines are measured and used to define three spectral types, those with only strong Hδ absorption (k+a), those with strong [O II] in emission (em) and those with both (em+a). All other LRGs are considered to have passive star formation histories. The vast majority of LRGs are found to be passive (~80 per cent); however, significant numbers of k+a (2.7 per cent), em+a (1.2 per cent) and em LRGs (8.6 per cent) are identified. An investigation into the redshift dependence of the fractions is also performed. A sample of SDSS MAIN galaxies with colours and luminosities consistent with the 2SLAQ LRGs is selected to provide a low-redshift comparison. While the em and em+a fractions are consistent with the low-redshift SDSS sample, the fraction of k+a LRGs is found to increase significantly with redshift. This result is interpreted as an indication of an increasing amount of recent star formation activity in LRGs with redshift. By considering the expected lifetime of the k+a phase, the number of LRGs which will undergo a k+a phase can be estimated. A crude comparison of this estimate with the predictions from semi-analytic models of galaxy formation shows that the predicted level of k+a and em+a activities is not sufficient to reconcile the predicted mass growth for massive early types in a hierarchical merging scenario.

Item Type: Journal Item
Copyright Holders: 2006 The Authors., 2006 RAS Journal compilation
ISSN: 1365-2966
Project Funding Details:
Funded Project NameProject IDFunding Body
Not SetNot SetAlfred P. Sloan Foundation
Not SetNot SetParticipating Institutions
Not SetNot SetNational Aeronautics and Space Administration
Not SetNot SetNational Science Foundation
Not SetNot SetUS Department of Energy
Not SetNot SetJapanese Monbukagakusho
Not SetNot SetMax Planck Society
Not SetNot SetUQCS scholarship
Not SetNot SetEPSA University of Queensland Research Fellowship
Not SetNot SetRoyal Society
Keywords: surveys; galaxies - evolution; galaxies - formation
Academic Unit/School: Faculty of Science, Technology, Engineering and Mathematics (STEM) > Physical Sciences
Faculty of Science, Technology, Engineering and Mathematics (STEM)
Item ID: 38523
Depositing User: Miranda Callaway
Date Deposited: 26 Sep 2013 14:11
Last Modified: 07 Dec 2018 22:19
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