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Title: KECK ECHELLETTE SPECTROGRAPH AND IMAGER OBSERVATIONS OF METAL-POOR DAMPED Ly{alpha} SYSTEMS

Abstract

We present the first results from a survey of SDSS quasars selected for strong H I damped Ly{alpha} (DLA) absorption with corresponding low equivalent width absorption from strong low-ion transitions (e.g., C II {lambda}1334 and Si II {lambda}1260). These metal-poor DLA candidates were selected from the SDSS fifth release quasar spectroscopic database, and comprise a large new sample for probing low-metallicity galaxies. Medium-resolution echellette spectra from the Keck Echellette Spectrograph and Imager spectrograph for an initial sample of 35 systems were obtained to explore the metal-poor tail of the DLA distribution and to investigate the nucleosynthetic patterns at these metallicities. We have estimated saturation corrections for the moderately underresolved spectra, and systems with very narrow Doppler parameters (b {<=} 5 km s{sup -1}) will likely have underestimated abundances. For those systems with Doppler parameters b > 5 km s{sup -1}, we have measured low-metallicity DLA gas with [X/H] <-2.4 for at least one of C, O, Si, or Fe. Assuming non-saturated components, we estimate that several DLA systems have [X/H] <-2.8, including five DLA systems with both low equivalent widths and low metallicity in transitions of both C II and O I. All of the measured DLA metallicities, however, exceedmore » or are consistent with a metallicity of at least 1/1000 of solar, regardless of the effects of saturation in our spectra. Our results indicate that the metal-poor tail of galaxies at z {approx} 3 drops exponentially at [X/H] {approx}<-3. If the distribution of metallicity is Gaussian, the probability of identifying interstellar medium gas with lower abundance is extremely small, and our results suggest that DLA systems with [X/H] < -4.0 are extremely rare, and could comprise only 8 x 10{sup -7} of DLA systems. The relative abundances of species within these low-metallicity DLA systems are compared with stellar nucleosynthesis models, and are consistent with stars having masses of 30 M{sub sun} < M{sub *} < 100 M{sub sun}. The observed ratio of [C/O] for values of [O/H] <-2.5 exceeds values seen in moderate metallicity DLA systems, and also exceeds theoretical nucleosynthesis predictions for higher mass Population III stars. We also have observed a correlation between the column density N(C IV) with [Si/H] metallicity, suggestive of a trend between mass of the DLA system and its metallicity.« less

Authors:
; ;  [1];  [2];  [3]
  1. Department of Physics and Astronomy, Pomona College, 610 N. College Ave., Claremont, CA 91711 (United States)
  2. Department of Astronomy and Astrophysics, UCO/Lick Observatory, University of California, 1156 High Street, Santa Cruz, CA 95064 (United States)
  3. Department of Astronomy, California Institute of Technology, 1200 E. California Blvd., MS 105-24, Pasadena, CA 91125 (United States)
Publication Date:
OSTI Identifier:
21464863
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 721; Journal Issue: 1; Other Information: DOI: 10.1088/0004-637X/721/1/1
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABSORPTION; ABUNDANCE; GALAXIES; MASS; METALS; NUCLEOSYNTHESIS; PROBABILITY; QUASARS; SPECTRA; STARS; COSMIC RADIO SOURCES; ELEMENTS; SORPTION; SYNTHESIS

Citation Formats

Penprase, Bryan E., Toro-Martinez, Irene, Beeler, Daniel J., Prochaska, J. Xavier, and Sargent, Wallace L. W., E-mail: penprase@dci.pomona.ed, E-mail: wws@astro.caltech.ed, E-mail: xavier@ucolick.or. KECK ECHELLETTE SPECTROGRAPH AND IMAGER OBSERVATIONS OF METAL-POOR DAMPED Ly{alpha} SYSTEMS. United States: N. p., 2010. Web. doi:10.1088/0004-637X/721/1/1.
Penprase, Bryan E., Toro-Martinez, Irene, Beeler, Daniel J., Prochaska, J. Xavier, & Sargent, Wallace L. W., E-mail: penprase@dci.pomona.ed, E-mail: wws@astro.caltech.ed, E-mail: xavier@ucolick.or. KECK ECHELLETTE SPECTROGRAPH AND IMAGER OBSERVATIONS OF METAL-POOR DAMPED Ly{alpha} SYSTEMS. United States. doi:10.1088/0004-637X/721/1/1.
Penprase, Bryan E., Toro-Martinez, Irene, Beeler, Daniel J., Prochaska, J. Xavier, and Sargent, Wallace L. W., E-mail: penprase@dci.pomona.ed, E-mail: wws@astro.caltech.ed, E-mail: xavier@ucolick.or. Mon . "KECK ECHELLETTE SPECTROGRAPH AND IMAGER OBSERVATIONS OF METAL-POOR DAMPED Ly{alpha} SYSTEMS". United States. doi:10.1088/0004-637X/721/1/1.
@article{osti_21464863,
title = {KECK ECHELLETTE SPECTROGRAPH AND IMAGER OBSERVATIONS OF METAL-POOR DAMPED Ly{alpha} SYSTEMS},
author = {Penprase, Bryan E. and Toro-Martinez, Irene and Beeler, Daniel J. and Prochaska, J. Xavier and Sargent, Wallace L. W., E-mail: penprase@dci.pomona.ed, E-mail: wws@astro.caltech.ed, E-mail: xavier@ucolick.or},
abstractNote = {We present the first results from a survey of SDSS quasars selected for strong H I damped Ly{alpha} (DLA) absorption with corresponding low equivalent width absorption from strong low-ion transitions (e.g., C II {lambda}1334 and Si II {lambda}1260). These metal-poor DLA candidates were selected from the SDSS fifth release quasar spectroscopic database, and comprise a large new sample for probing low-metallicity galaxies. Medium-resolution echellette spectra from the Keck Echellette Spectrograph and Imager spectrograph for an initial sample of 35 systems were obtained to explore the metal-poor tail of the DLA distribution and to investigate the nucleosynthetic patterns at these metallicities. We have estimated saturation corrections for the moderately underresolved spectra, and systems with very narrow Doppler parameters (b {<=} 5 km s{sup -1}) will likely have underestimated abundances. For those systems with Doppler parameters b > 5 km s{sup -1}, we have measured low-metallicity DLA gas with [X/H] <-2.4 for at least one of C, O, Si, or Fe. Assuming non-saturated components, we estimate that several DLA systems have [X/H] <-2.8, including five DLA systems with both low equivalent widths and low metallicity in transitions of both C II and O I. All of the measured DLA metallicities, however, exceed or are consistent with a metallicity of at least 1/1000 of solar, regardless of the effects of saturation in our spectra. Our results indicate that the metal-poor tail of galaxies at z {approx} 3 drops exponentially at [X/H] {approx}<-3. If the distribution of metallicity is Gaussian, the probability of identifying interstellar medium gas with lower abundance is extremely small, and our results suggest that DLA systems with [X/H] < -4.0 are extremely rare, and could comprise only 8 x 10{sup -7} of DLA systems. The relative abundances of species within these low-metallicity DLA systems are compared with stellar nucleosynthesis models, and are consistent with stars having masses of 30 M{sub sun} < M{sub *} < 100 M{sub sun}. The observed ratio of [C/O] for values of [O/H] <-2.5 exceeds values seen in moderate metallicity DLA systems, and also exceeds theoretical nucleosynthesis predictions for higher mass Population III stars. We also have observed a correlation between the column density N(C IV) with [Si/H] metallicity, suggestive of a trend between mass of the DLA system and its metallicity.},
doi = {10.1088/0004-637X/721/1/1},
journal = {Astrophysical Journal},
number = 1,
volume = 721,
place = {United States},
year = {Mon Sep 20 00:00:00 EDT 2010},
month = {Mon Sep 20 00:00:00 EDT 2010}
}