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H ɪ, CO, and Planck/IRAS dust properties in the high latitude cloud complex, MBM 53, 54, 55 and HLCG 92-35. Possible evidence for an optically thick HI envelope around the CO clouds

Citation

Fukui, Y and Okamoto, R and Kaji, R and Yamamoto, H and Torii, K and Hayakawa, T and Tachihara, K and Dickey, JM and Okuda, T and Ohama, A and Kuroda, Y and Kuwahara, T, H ɪ, CO, and Planck/IRAS dust properties in the high latitude cloud complex, MBM 53, 54, 55 and HLCG 92-35. Possible evidence for an optically thick HI envelope around the CO clouds, The Astrophysical Journal, 796, (1) Article 59. ISSN 0004-637X (2014) [Refereed Article]


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Copyright 2014 The American Astronomical Society

DOI: doi:10.1088/0004-637X/796/1/59

Abstract

We present an analysis of the Hɪ and CO gas in conjunction with the Planck/IRAS submillimeter/far-infrared dust properties toward the most outstanding high latitude clouds MBM53, 54, 55 and HLCG 92 − 35 at b = −30° to−45°. The CO emission, dust opacity at 353 GHz (τ353), and dust temperature (Td) show generally good spatial correspondence. On the other hand, the correspondence between the Hɪ emission and the dust properties is less clear than in CO. The integrated Hɪ intensity W and τ353 show a large scatter with a correlation coefficient of ∼0.6 for a Td range from 16K to 22K. We find, however, that W and τ353 show better correlation for smaller ranges of Td every 0.5K, generally with a correlation coefficient of 0.7–0.9.We set up a hypothesis that the Hɪ gas associated with the highest Td ≥ 21.5K is optically thin, whereas the Hɪ emission is generally optically thick for Td lower than 21.5K. We have determined a relationship for the optically thin Hɪ gas between atomic hydrogen column density and τ353, N (cm−2) = (1.5 × 1026)· τ353, under the assumption that the dust properties are uniform and we have applied this to estimate N from τ353 for the whole cloud. N was then used to solve for τs and N over the region. The result shows that the Hɪ is dominated by optically thick gas having a low spin temperature of 20–40K and a density of 40–160 cm−3. The Hɪ envelope has a total mass of ∼1.2 × 104 M, an order of magnitude larger than that of the CO clouds. The Hɪ envelope properties derived by this method do not rule out a mixture of Hɪ and H2 in the dark gas, but we present indirect evidence that most of the gas mass is in the atomic state.

Item Details

Item Type:Refereed Article
Keywords:radio astronomy, interstellar medium, Galactic astronomy, radio spectroscopy
Research Division:Physical Sciences
Research Group:Astronomical and Space Sciences
Research Field:Galactic Astronomy
Objective Division:Expanding Knowledge
Objective Group:Expanding Knowledge
Objective Field:Expanding Knowledge in the Physical Sciences
Author:Dickey, JM (Professor John Dickey)
ID Code:97434
Year Published:2014
Funding Support:Australian Research Council (DP110104101)
Web of Science® Times Cited:25
Deposited By:Mathematics and Physics
Deposited On:2014-12-17
Last Modified:2018-01-25
Downloads:163 View Download Statistics

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