Results of the SEST Key Programme: CO in the Magellanic Clouds

Free access article

Issue		A&A Volume 389, Number 3, July III 2002


Page(s)		977 - 992
Section		Diffuse matter in space
DOI		http://dx.doi.org/10.1051/0004-6361:20020397

A&A 389, 977-992 (2002)
DOI: 10.1051/0004-6361:20020397

VIII. The giant molecular complex No. 37 of the LMC

G. Garay¹, L. E. B. Johansson², L.-Å. Nyman³, R. S. Booth², F. P. Israel⁴, M. L. Kutner⁵, J. Lequeux⁶ and M. Rubio¹

¹ Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile
² Onsala Space Observatory, 439 92 Onsala, Sweden
³ European Southern Observatory, Casilla 19001, Santiago 19, Chile
⁴ Sterrewacht, Postbus 9513, 2300 Leiden, The Netherlands
⁵ NRAO, 949 N. Cherry Av., Campus Building 65, Tucson, Arizona 85721-0655, USA
⁶ DEMIRM, Observatoire de Paris, 61 Av. de l'Observatoire, 75014 Paris, France

(Received 29 November 2001 / Accepted 12 March 2002 )

Abstract
We report observations of the CO(1 $\rightarrow$ 0), CO(2 $\rightarrow$ 1) and ¹³CO(1 $\rightarrow$ 0) line emission from the giant molecular complex No. 37 of the Large Magellanic Cloud, made with linear resolutions between 6 and 12 pc. The observations were undertaken with the Swedish-ESO Submillimetre Telescope (SEST) as part of the Key Programme: CO in the Magellanic Clouds. We find that the CO(1 $\rightarrow$ 0) emission arises from six large, distinct, molecular clouds, with CO luminosities in the range $1\times10^4$ to $5\times10^4$ K km s ^-1 pc ² and sizes between 22 and 38 pc, and seven smaller clumps, with CO luminosities in the range between $7\times10^2$ and $2\times10^3$ K km s ^-1 pc ². The opacities in the CO(1 $\rightarrow$ 0) line at the peak position of the large clouds are remarkably smaller than those derived for Galactic molecular clouds. Relationships between line width, size and CO luminosities are discussed. The total CO luminosity of the complex determined from the SEST observations, of $1.8\times10^5$ K km s ^-1 pc ², is in excellent agreement with that determined from the low spatial resolution (~140 pc) observations of Cohen et al. On the other hand, the total mass of molecular gas in the complex derived from the SEST observations, assuming that the individual clouds are virialized, is $2.4\times10^6$ $M_{\odot}$ , which is a factor of 6 lower than that estimated by Cohen et al. under the same assumption. We conclude that the value of the velocity integrated CO emission to H ₂ column density conversion factor in the LMC determined from low angular resolution observations has been overestimated by a factor of ~3. We derive a conversion factor for clouds in Complex-37 of ${\sim}6\times10^{20} {\rm cm^{-2}~K^{-1}~km^{-1}~s}$ , which is similar to that for clouds in the outer Galaxy.

Key words: galaxies: Magellanic Clouds -- ISM: clouds -- ISM: molecules -- radio lines: ISM

Offprint request: G. Garay, guido@das.uchile.cl

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