Abstract
Observations of 2.6-mm carbon monoxide emission are reported for five galaxies: M82, NGC 253, M51, NGC 5236, and NGC 1068. An extensive map of the emission from M82 is presented, along with less extensive maps of NGC 253 and M51. Models for the CO distributions have been fitted to the mapping results for M82 and M51. Comparisons of OH, H2CO, and CO observations toward M82 and NGC 253 show that relative molecular abundances are similar to their Galactic values. The central CO profile in M82 closely resembles an averaged H-alpha emission profile for the same region. The estimated mass in molecular clouds is found to be greater than that in atomic hydrogen for most of the regions studied. Total CO column densities are estimated for the five galaxies, and a possible correlation is noted between these column densities and the nuclear 10-micron luminosities. Despite sensitive searches, no (C-13)O emission is observed toward NGC 253 and M82. These negative results imply either upper limits of about 10 for the optical depth of the (C-12)O features or lower limits to the C-12/C-13 abundance ratios of approximately 15 and 40 in M82 and NGC 253, respectively. Negative results for CO emission are reported for 24 other galaxies, including M31 and M63.
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call