Keck Echellette Spectrograph and Imager Observations of Metal-poor Damped Lyα Systems
Abstract
We present the first results from a survey of SDSS quasars selected for strong H I damped Lyα (DLA) absorption with corresponding low equivalent width absorption from strong low-ion transitions (e.g., C II λ1334 and Si II λ1260). 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^(–1)) will likely have underestimated abundances. For those systems with Doppler parameters b > 5 km s^(–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 ~ 3 drops exponentially at [X/H] ≾ –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 × 10^(–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_⊙ < M * < 100 M_⊙. 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.
Additional Information
© 2010 The American Astronomical Society. Received 2009 December 19; accepted 2010 June 16; published 2010 August 26. Some of the data presented herein were 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. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The observations from the Keck telescope were made possible by Pomona College travel grants to B.E.P., I.T.M., and D.J.B and a Pomona SURP grant to I.T.M. The authors also recognize the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. J.X.P. acknowledges funding through an NSF CAREER grant (AST–0548180) and an additional NSF grant (AST–0709235). W.W.S and B.E.P. acknowledge support from an NSF grant (AST-0606868).Attached Files
Published - Penprase2010p11576Astrophys_J.pdf
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Additional details
- Eprint ID
- 20563
- Resolver ID
- CaltechAUTHORS:20101027-104110922
- W. M. Keck Foundation
- Pomona College
- NSF
- AST-0548180
- NSF
- AST-0709235
- NSF
- AST-0606868
- Created
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2010-11-12Created from EPrint's datestamp field
- Updated
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2021-11-09Created from EPrint's last_modified field