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Title:
On the Absence of High Metallicity-High Column Density Damped Lyα Systems: Molecule Formation in a Two-Phase Interstellar Medium
Authors:
Krumholz, Mark R.; Ellison, Sara L.; Prochaska, J. Xavier; Tumlinson, Jason
Affiliation:
AA(Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064, USA ), AB(Department of Physics and Astronomy, University of Victoria, BC V8P 5C2, Canada ), AC(Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064, USA ), AD(Space Telescope Science Institute, Baltimore, MD 21218, USA)
Publication:
The Astrophysical Journal Letters, Volume 701, Issue 1, pp. L12-L15 (2009). (ApJL Homepage)
Publication Date:
08/2009
Origin:
IOP
ApJ Keywords:
galaxies: ISM, gamma rays: bursts, ISM: molecules, ISM: structure, quasars: absorption lines, stars: formation
DOI:
10.1088/0004-637X/701/1/L12
Bibliographic Code:
2009ApJ...701L..12K

Abstract

We argue that the lack of observed damped Lyα (DLA) systems that simultaneously have high H I column densities and high metallicities results naturally from the formation of molecules in the cold phase of a two-phase atomic medium in pressure balance. Our result applies equally well in diffuse systems where the ultraviolet radiation field is dominated by the extragalactic background and in dense star-forming ones, where the local radiation field is likely to be orders of magnitude higher. We point out that such a radiation-insensitive model is required to explain the absence of high column-high metallicity systems among DLAs observed using gamma-ray burst (GRB) afterglows, since these are likely subjected to strong radiation fields created by active star formation in the GRB host galaxy. Moreover, we show that the observed relationship between the maximum atomic gas column in DLAs sets a firm upper limit on the fraction of the mass in these systems that can be in the warm, diffuse phase. Finally, we argue that our result explains the observed lack of in situ star formation in DLA systems.
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