Astrophys. J., 647, 946-969 (2006/August-3)
Infalling faint [O II] emitters in Abell 851. II. Environment, kinematics, and star formation history.
SATO T. and MARTIN C.L.
Abstract (from CDS):
We report on the local environment, kinematics, and star formation history of [O II]-selected objects in the z~0.4 galaxy cluster Abell 851, using Keck optical spectra. A large fraction (~55%) of cluster [O II] emitters show strong Balmer absorptions (≳4 Å in Hδ equivalent width). These e(a)-type spectra have been attributed to dusty starburst galaxies by Poggianti & Wu, an interpretation supported by our reddening measurements, which show a high frequency of very reddened [E(B-V)≳0.5] galaxies. Our spectral modeling requires starburst ages of ≲1 Gyr, which is shorter than the cluster crossing timescale. We argue that this starburst phase occurs during cluster infall on the basis of the radial velocity distribution of the [O II] emitters, which present a deficit of systems near the cluster systemic velocity when compared to a virialized population (or a backsplash population). The spatial segregation of some redshifted and blueshifted groups strongly indicates that the accretion was recent. Throughout the cluster, the presence of [O II] emitters is strongly suppressed in dense environments. Our analysis supports previous suggestions that dusty starburst galaxies arise at the expense of gas-rich spiral galaxies [i.e., the e(c) type; Dressler and coworkers]. In addition, we describe a fainter population comprised largely of dwarf galaxies (Martin and coworkers) and find an even stronger suppression of [O II] emitters in high-density environments, indicative of more effective destruction by harassment and/or gas stripping. Comparison to previous morphological studies, limited to the cluster core, suggests that galaxy-galaxy interactions may trigger the starbursts. The high e(a) galaxy fraction in Abell 851 as compared to that in the field, however, suggests that some cluster-specific mechanism, likely related to the dynamical assembly of the cluster, also contributes to the high number of starbursts.
Cosmology: Observations - Galaxies: Clusters: General - Galaxies: Clusters: Individual: Name: Abell 851 - Galaxies: Clusters: Individual: Alphanumeric: Cl 0939+4713 - Galaxies: Dwarf - Galaxies: Evolution - Galaxies: Starburst
Table 4: [MLF2000] NNNN N=9 added.
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