The Nature of Dusty Starburst Galaxies in a Rich Cluster at z = 0.4: The Progenitors of Lenticulars?
Abstract
We present the results of a Spitzer Infrared Spectrograph survey of 24 μm selected luminous infrared galaxies (LIRGs, L IR > 1011 L sun) in the rich cluster Cl 0024+16 at z = 0.4. Optically, these LIRGs resemble unremarkable spiral galaxies with e(a)/e(c) spectral classifications and [O II]-derived star formation rates (SFRs) of lsim2 M sun yr-1, generally indistinguishable from the "quiescent" star-forming population in the cluster. Our IRS spectra show that the majority of the 24 μm detected galaxies exhibit polycyclic aromatic hydrocarbon emission with implied SFRs ~ 30-60 M sun yr-1, with only one (< 10%) in the sample displaying unambiguous evidence of an active galactic nucleus in the mid-infrared. This confirms the presence of a large population of obscured starburst galaxies in distant clusters, which comprise the bulk of the star formation occurring in these environments at z ~ 0.5. We suggest that, although several mechanisms could be at play, these dusty starbursts could be the signature of an important evolutionary transition converting gas-rich spiral galaxies in distant clusters into the passive, bulge-dominated lenticular galaxies that become increasingly abundant in the cores of rich clusters in the ~ 4 Gyr to the present day.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- January 2009
- DOI:
- 10.1088/0004-637X/691/1/783
- arXiv:
- arXiv:0809.4260
- Bibcode:
- 2009ApJ...691..783G
- Keywords:
-
- galaxies: active:;
- galaxies: clusters: individual: Cl0024+16;
- galaxies: evolution;
- galaxies: starburst;
- Astrophysics
- E-Print:
- 11 pages, 5 figures (Fig 5 degraded in quality). Accepted for publication in ApJ