DIRECT EVIDENCE OF COLD GAS IN DLA 0812+32B
- Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge, CB3 0HA (United Kingdom)
- Department of Physics and Center for Astrophysics and Space Sciences, University of California, San Diego, 9500 Gilman Dr., La Jolla, CA 92093-0424 (United States)
We present the first direct evidence for cold gas in a high redshift DLA galaxy. We measured several multiplets of weak neutral carbon (C I) transitions in order to perform a curve of growth analysis. A DELTA chi{sup 2} test constrains the best-fit Doppler parameter, b = 0.33{sup +0.05}{sub -0.04} km s{sup -1} and log N(C I) = 13.30 +- 0.2 cm{sup -2}. This Doppler parameter constrains the kinetic temperature of the gas to T <= 78 K (T <= 115 K, 2sigma). We used the associated C I fine structure lines to constrain the volume density of the gas, n(H I) approx40-200 cm{sup -3} (2sigma), resulting in a lower limit on the cloud size of approximately 0.1-1 parsec. While it is difficult to determine the metallicity of the cold component, the absence of Cr II indicates that the cold cloud suffers a high level of dust depletion. Additionally, the large amount of Lyman and Werner-band molecular hydrogen absorption (log N(H{sub 2}){sub total} = 19.88 cm{sup -2}, f{sub H{sub 2}} >= 0.06) with an excitation temperature of T{sub ex} = 46 K as determined by the rotational J = 0 and J = 1 states, is consistent with the presence of cold gas. We propose that this cloud may be gravitationally confined and may represent a transition gas phase from primarily neutral atomic gas, to a colder, denser molecular phase that will eventually host star formation.
- OSTI ID:
- 21367446
- Journal Information:
- Astrophysical Journal, Vol. 704, Issue 1; Other Information: DOI: 10.1088/0004-637X/704/1/247; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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