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.

DOI: https://doi.org/10.1111/j.1365-2966.2006.11024.x

Abstract

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.

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About

• Item ORO ID
• 38523
• Item Type
• Journal Item
• ISSN
• 1365-2966
• Project Funding Details

• Funded Project Name	Project ID	Funding Body
  Not Set	Not Set	Alfred P. Sloan Foundation
  Not Set	Not Set	Participating Institutions
  Not Set	Not Set	National Aeronautics and Space Administration
  Not Set	Not Set	National Science Foundation
  Not Set	Not Set	US Department of Energy
  Not Set	Not Set	Japanese Monbukagakusho
  Not Set	Not Set	Max Planck Society
  Not Set	Not Set	UQCS scholarship
  Not Set	Not Set	EPSA University of Queensland Research Fellowship
  Not Set	Not Set	Royal Society

• Keywords
• surveys; galaxies - evolution; galaxies - formation
• Academic Unit or School
• Faculty of Science, Technology, Engineering and Mathematics (STEM) > Physical Sciences
  Faculty of Science, Technology, Engineering and Mathematics (STEM)
• Copyright Holders
• © 2006 The Authors., © 2006 RAS Journal compilation
• Depositing User
• Miranda Callaway