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Title:
Deep Spectroscopy of Ultra-Strong Emission-Line Galaxies
Authors:
Hu, Esther M.; Cowie, Lennox L.; Kakazu, Yuko; Barger, Amy J.
Affiliation:
AA(Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822, USA ), AB(Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822, USA ), AC(Institut d'Astrophysique, Paris, 98 bis Boulevard Arago, F-75014 Paris ), AD(Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822, USA ; Department of Astronomy, University of Wisconsin-Madison, 475 North Charter Street, Madison, WI 53706, USA ; Department of Physics and Astronomy, University of Hawaii, 2505 Correa Road, Honolulu, HI 96822, USA)
Publication:
The Astrophysical Journal, Volume 698, Issue 2, pp. 2014-2022 (2009). (ApJ Homepage)
Publication Date:
06/2009
Origin:
IOP
ApJ Keywords:
cosmology: observations, galaxies: abundances, galaxies: distances and redshifts, galaxies: evolution, galaxies: starburst
DOI:
10.1088/0004-637X/698/2/2014
Bibliographic Code:
2009ApJ...698.2014H

Abstract

Ultra-strong emission-line galaxies (USELs) with extremely high equivalent widths (EW(Hβ) gsim 30 Å) can be used to pick out galaxies of extremely low metallicity in the z = 0-1 redshift range. Large numbers of these objects are easily detected in deep narrow band searches. Since most have detectable [O III]λ4363, their metallicities can be determined using the direct method. These large samples hold out the possibility for determining whether there is a metallicity floor for the galaxy population. In this, the second of our papers on the topic, we describe the results of an extensive spectroscopic follow-up of the Kakazu et al. catalog of 542 USELs carried out with the DEIMOS spectrograph on Keck. We have obtained high S/N spectra of 348 galaxies. The two lowest metallicity galaxies in our sample have 12 + log(O/H) = 6.97 ± 0.17 and 7.25 ± 0.03—values comparable to the lowest metallicity galaxies found to date. We determine an empirical relation between metallicity and the R23 parameter for our sample, and we compare this to the relationship for low-redshift galaxies. The determined metallicity-luminosity relation for this sample is compared with that of magnitude selected samples in the same redshift range. The emission-line-selected galaxies show a metal-luminosity relation where the metallicity decreases with luminosity, and they appear to define the lower bound of the galaxy metallicity distribution at a given continuum luminosity. We also compute the Hα luminosity function of the USELs as a function of redshift and use this to compute an upper bound on the Lyα emitter luminosity function over the z = 0-1 redshift range.

Based in part on data obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA and was made possible by the generous financial support of the W. M. Keck Foundation.

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