The Starburst Properties of M82, M83, and IC342

Details The Starburst Properties of M82, M83, and IC342 The Starburst Properties of M82, M83, and IC342

Dec 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992aas...181.4909w&link_type=abstract

American Astronomical Society, 181st AAS Meeting, #49.09; Bulletin of the American Astronomical Society, Vol. 24, p.1201

Astronomy and Astrophysics

Astronomy

1

Scientific paper

We have used millimeter and submillimeter-wave observations of multi-transitional isotopic and main-line CO (and CS) to probe the central few kpcs of three nearby starburst galaxies: M82, IC342, and M83. A detailed analysis of the data was performed using both LTE and non-LTE techniques. Our analysis reveals that the molecular mediums associated with starbursts activity appear to be composed of multiple components. The gas temperatures of these components range from 10 to ~ 45 K. Gas densities of ~ 10(5) cm(-3) are indicated. In general, the starbursts in M82 and M83 have similar characteristics. The starburst occurring in IC342 is much more subdued, with many of the derived cloud properties similar to that observed in the central kiloparsec of the Milky Way. Main and isotopic line ratios toward IC342 and perhaps toward M83 suggest that the molecular clouds are optically thick in the lower transitions of CO and externally heated. A comparison of (12) CO and (13) CO J=3->2 observations along the major and minor axes of M82 indicates gas optical depths are highest in the molecular ring. A comparison of (13) CO and C(18) O J=3->2 observations towards the central region of M82 reveals that in order for the CO emission to be optically thin (as suggested by the CO main line ratios), the (13) CO to C(18) O abundance ratio must be ~ 3. The derived gas mass, M_g, toward the centers of M82, M83, and IC342 (within the central 630-1300 pc) is ~ 5times 10(7) M_sun. The star formation efficiency is found to be 77, 60, and 10% for M82, M83, and IC342 respectively. Assuming a Salpeter initial mass function, the observed luminosities indicate star formation rates of 16, 6, and 2.5 M_sun/yr for the three galaxies. The average cloud sizes are 0.6, <=1 and >=11 pc in M82, M83 and IC342, respectively. The corresponding numbers of such clouds in these galaxies are 10(4) , >=10(4) and <=30. We find that the higher the star formation efficiency, the smaller the cloud size. We conclude that small clouds are a result and not a cause of high star formation efficiencies. There appears to be a correlation between star formation efficiency and gas surface density (sigma_g ), where sigma_g = 174, 140 and 82 M_sun/pc(2) for M82, M83 and IC342, respectively.

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