Journal
ASTROPHYSICAL JOURNAL LETTERS
Volume 701, Issue 1, Pages L12-L15Publisher
IOP PUBLISHING LTD
DOI: 10.1088/0004-637X/701/1/L12
Keywords
galaxies: ISM; gamma rays: bursts; ISM: molecules; ISM: structure; quasars: absorption lines; stars: formation
Categories
Funding
- Alfred P. Sloan Foundation
- NASA/JPL
- National Science Foundation [0807739, AST-0709235]
- NSERC Discovery Grant
- Direct For Mathematical & Physical Scien [0807739] Funding Source: National Science Foundation
- Division Of Astronomical Sciences [0807739] Funding Source: National Science Foundation
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We argue that the lack of observed damped Ly alpha (DLA) systems that simultaneously have high Hi 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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