Other
Scientific paper
Jan 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010aas...21533007l&link_type=abstract
American Astronomical Society, AAS Meeting #215, #330.07; Bulletin of the American Astronomical Society, Vol. 42, p.429
Other
Scientific paper
I present the first results from a near-IR spectroscopic campaign of galaxies in the Cl1604 supercluster at z=0.9 and the RX J1821.6+6827 cluster at z=0.81 to investigate the nature of [OII] λ3727A emission in cluster galaxies at high redshift. A large fraction of the 401 cluster galaxies feature detectable [OII] emission with no other signs of current star-formation activity as well as strong absorption features indicative of a well-established older stellar population. The combination of these features suggests that the primary source of [OII] emission in these galaxies is not a result of star-formation, but rather due to emission from a Low-Ionization Nuclear Emission-Line Region (LINER) or Seyfert. Using the NIRSPEC spectrograph on the Keck II 10-m telescope, 19 such galaxies were targeted as our main sample, along with six members of other spectral types. A majority (60%) of the galaxies in our main sample are classified as LINER/Seyfert based primarily on the emission-line ratio of [NII] λ6584A and Hα λ6563A, a fraction that increases for red-sequence galaxies. Many LINER/Seyfert galaxies also exhibit high [OII] equivalent widths (EWs) relative to those of Hα, similar to populations of LINER/Seyfert galaxies observed at low redshift. In addition, LINER/Seyfert galaxies exhibit average L([OII])/L(Hα) ratios that are significantly higher than those of star-forming galaxies, suggesting that [OII] is a poor indicator of star-formation in many high-redshift cluster members. From the prevalence of absorption-line dominated [OII] emitters in both structures, we estimate that at least 20% of galaxies in high-redshift clusters with log(Mstellar) > 10-10.5 Msolar contain a LINER/Seyfert component. The effects such a population has on both the global star formation rate of cluster galaxies and the post-starburst fraction is investigated, concluding that LINER/Seyferts must be accounted for if these quantities are to be physically meaningful.
Gal Roy R.
Kocevski Dale D.
Lemaux Brian
Lubin Lori Maxine
Shapley Alice
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