Roman-Duval, J. and Israel, F. P. and Bolatto, A. and Hughes, A. and Leroy, A. and Meixner, M. and Gordon, K. and Madden, S. C. and Paradis, D. and Kawamura, A. and Li, A. and Sauvage, M. and Wong, T. and Bernard, J.-P. and Engelbracht, C. and Hony, S. and Kim, S. and Misselt, K. and Okumura, K. and Ott, J. and Panuzzo, P. and Pineda, J. L. and Reach, W. T. and Rubio, M. (2010) Dust/gas correlations from Herschel observations. Astronomy and Astrophysics, 518 . Art. No. L74. ISSN 0004-6361 http://resolver.caltech.edu/CaltechAUTHORS:20101202-155729224
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Context. Previous Spitzer and IRAS observations of the LMC suggest an excess of FIR emission with respect to the gas surface density traced by ^(12)CO rotational emission lines and H_I 21 cm emission. This so-called “FIR excess” is especially noticeable near molecular clouds in the LMC, and has usually been interpreted as indicating the presence of a self-shielded H_2 component not traced by CO in the envelopes of molecular clouds. Aims. Based on Herschel HERITAGE observations taken as part of the science demonstration phase, we examine the correlation between gas and dust surface densities at higher resolution than previously achieved. We consider three additional possible causes for the FIR excess: X factor, FIR dust emissivity, and gas-to-dust ratio variations between the diffuse and dense phases of the ISM. Methods. We examine the structure of NT80 and NT71, two molecular clouds detected in the NANTEN ^(12)CO survey of the LMC. Dust surface density maps were derived from the HERITAGE data. The gas phase is traced by MAGMA ^(12)CO and ATCA+Parkes H_I 21 cm observations of the LMC. These data provide unprecedented resolution (1') to examine the structure of molecular clouds. The dust emissivity, gas-to-dust ratio, and X factor required to match the dust and gas surface densities are derived, and their correlations with the dust surface density are examined. Results. We show that the dust surface density is spatially correlated with the atomic and molecular gas phases. The dust temperature is consistently lower in the dense phase of the ISM than in the diffuse phase. We confirm variations in the ratio of FIR emission to gas surface density derived from H_I and CO observations. There is an excess of FIR emission, spatially correlated with regions of intermediate H_I and dust surface densities (A_V = 1−2), and little or no CO.While there is no significant trend in the dust emissivity or gas-to-dust ratio with dust surface density, the X factor is enhanced at A_V = 1−2. We conclude that H_2 envelopes not traced by CO and X factor variations close to the CO boundary may be more likely to cause these deviations between FIR emission and gas surface density than gas-to-dust ratio or emissivity variations.
|Additional Information:||© 2010 ESO. Received 30 March 2010, Accepted 16 April 2010, Published online 16 July 2010. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. We acknowledge financial support from the NASA Herschel Science Center (NHSC), J.P.L. contracts #1381522, and #1381650. Part of this research was conducted at the Jet Propulsion Laboratory, California Institute of Technology under contract with the National Aeronautics and Space Administration. We thank the support from the European Space Agency, PACS and SPIRE teams, Herschel Science Center, and NHSC (B. Ali, K. Xu). M.R. is supported by FONDECYT No1080335 and FONDAP No15010003.|
|Subject Keywords:||dust, extinction, ISM: clouds, ISM: abundances, ISM: structure, galaxies: ISM, Magellanic Clouds|
|Official Citation:||Dust/gas correlations from Herschel observations J. Roman-Duval, F. P. Israel, A. Bolatto, A. Hughes, A. Leroy, M. Meixner, K. Gordon, S. C. Madden, D. Paradis, A. Kawamura, A. Li, M. Sauvage, T. Wong, J.-P. Bernard, C. Engelbracht, S. Hony, S. Kim, K. Misselt, K. Okumura, J. Ott, P. Panuzzo, J. L. Pineda, W. T. Reach and M. Rubio A&A 518 L74 (2010) DOI: 10.1051/0004-6361/201014575|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Benjamin Perez|
|Deposited On:||03 Dec 2010 16:02|
|Last Modified:||26 Dec 2012 12:42|
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