STAR FORMATION ACTIVITY IN THE LARGE MAGELLANIC CLOUD: FAR-INFRARED EMISSION FROM IRAS HIGH-RESOLUTION DATA

摘要

We present an investigation of the properties of 21 molecular clouds in the LMC. Our data consist of 60 μm and 100 μm IRAS images that we compare with fully sampled ~(12)CO (J = 1 → 0) maps. The CO data were taken on the 15 m Swedish-ESO Submillimeter Telescope (SEST), which has a beamwidth at 2.6 mm of 45″, or 10 pc at the distance of the LMC. We use the IRAS high-resolution reprocessed data, with approximate resolutions of 60″ and 75″ at 60 μm and 100 μm, respectively. The clouds mapped are in three regions: two complexes south of 30 Doradus, and one at the H Ⅱ region N11. We measure the far-infrared luminosities for each cloud that has a good CO-FIR correspondence and compare these results with those from similar studies done on Milky Way molecular clouds. The far-infrared luminosities range from 3.5 x 10~4 to 2.8 x 10~6 solar luminosity, with an average value of 4 x 10~5 solar luminosity. This average is lower than that seen for H Ⅱ regions in the inner Milky Way, as reported by Scoville & Good in 1989 and slightly higher than that for outer Galaxy clouds as reported by Mead et al. in 1990. Virial masses of these clouds are from 4 x 10~4 to 1 x 10~6 solar mass. Star formation activity (L_(FIR)/M_(VIR)), defined as the ratio of the luminosity from recently formed stars to the total cloud mass, has a range of 2 orders of magnitude for any M_(VIR). In addition, we find that L_(FIR)/M_(VIR) is independent of cloud mass over the entire range of measured virial masses. These results indicate that although less luminous in CO and FIR than their inner Milky Way counterparts, LMC molecular clouds are undergoing significant massive star for-mation. L_(FIR) is used to determine the numbers and types of stars embedded in the GMCs. We compare these findings with those from the Milky Way and discuss the implications for star formation theories.