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Evidence of Magellanic-like moderate redshift H i-rich galaxies

Published online by Cambridge University Press:  01 July 2008

Brandon Lawton ,
Christopher W. Churchill ,
Brian A. York ,
Sara L. Ellison ,
Theodore P. Snow ,
Rachel A. Johnson ,
Sean G. Ryan  and
Chris R. Benn
Brandon Lawton
Affiliation:
Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA email: [email protected] Dept. of Astronomy, New Mexico State University, MSC 4500, P.O. Box 30001, Las Cruces, NM 88003, USA email: [email protected]
Christopher W. Churchill
Affiliation:
Dept. of Astronomy, New Mexico State University, MSC 4500, P.O. Box 30001, Las Cruces, NM 88003, USA email: [email protected]
Brian A. York
Affiliation:
Dept. of Physics and Astronomy, University of Victoria, 3800 Finnerty Rd., Victoria, V8W 1A1, British Columbia, Canada
Sara L. Ellison
Affiliation:
Dept. of Physics and Astronomy, University of Victoria, 3800 Finnerty Rd., Victoria, V8W 1A1, British Columbia, Canada
Theodore P. Snow
Affiliation:
Center for Astrophysics and Space Astronomy, University of Colorado at Boulder, 389 UCB, Boulder, CO 80309, USA
Rachel A. Johnson
Affiliation:
Oxford Astrophysics, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK
Sean G. Ryan
Affiliation:
Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield AL10 9AB, UK
Chris R. Benn
Affiliation:
Isaac Newton Group, Apartado 321, E-38700 Santa Cruz de La Palma, Spain
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Abstract

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We present equivalent width measurements and limits of six diffuse interstellar bands (DIBs, λ 4428, λ 5705, λ 5780, λ 5797, λ 6284, and λ 6613) in seven damped Lyα absorbers (DLAs) over the redshift range 0.091 ≤ z ≤ 0.524, sampling 20.3 ≤ log N(Hi) ≤ 21.7. Based upon the Galactic DIB–N(H i) relation, the λ 6284 DIB equivalent width upper limits in four of the seven DLAs are a factor of 4–10 times below the λ 6284 DIB equivalent widths observed in the Galaxy, but are not inconsistent with those present in the Magellanic Clouds. Assuming the Galactic DIB–E(B − V) relation, we determine reddening upper limits for the DLAs in our sample. Based upon the E(B − V) limits, the gas-to-dust ratios, N(H i)/E(B − V), of the four aforementioned DLAs are at least ~5 times higher than that of the Galactic ISM and are more consistent with the Large Magellanic Cloud. The ratios of two other DLAs are at least a factor of a few times higher. The best constraints on reddening derive from the upper limits for the λ 5780 and λ 6284 DIBs, which yield E(B − V) ≤ 0.08 mag for four of the seven DLAs and are more consistent with the Magellanic Clouds rather than the Galaxy. Our results suggest that, in DLAs, quantities related to dust, such as reddening and metallicity, appear to have a greater impact on DIB strengths than does H i gas abundance. The molecules responsible for the DIBs in DLA selected sightlines are underabundant relative to sightlines in the Galaxy of similarly high N(H i). Using DIBs to study the ISM of DLAs provide evidence that at least some population of DLAs are more Magellanic-like than Galactic-like.

Keywords

astrochemistrydustextinctiongalaxies: ISMMagellanic Cloudsquasars: absorption lines
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 4 , Symposium S256: The Magellanic System: Stars, Gas, and Galaxies , July 2008 , pp. 479 - 485
Copyright
Copyright © International Astronomical Union 2009

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