Carbon Monoxide and Dust Column Densities: The Dust-To-Gas Ratio and Structure of Three Giant Molecular Cloud Cores

Astronomy and Astrophysics – Astronomy

Scientific paper

Rate now

  [ 0.00 ] – not rated yet Voters 0   Comments 0

Details

Scientific paper

We have observed emission in the three lowest rotational transitions of the optically thin species C(18) O and the dust continuum emission at three millimeter/submillimeter wavelengths. By employing the proper combination of the intensities of the three lowest rotational transitions, we can obtain the total molecular column density, with relatively little sensitivity to density and temperature variations along the line of sight. We use the line and continuum data to determine column densities of the dust and gas across three Giant Molecular Cloud cores. We find that two of the three sources, M17 and Cepheus A, have the same gas column density to dust opticaldepth ratio, given by log[N(C(18) O/tau (790 micron )] = 18.8. In the third source, the Orion Molecular Cloud, the gas to dust ratio is typically a factor of three lower. We have good evidence for the correlation of the continuum emission in different bands for the Orion Molecular Cloud, and find the frequency dependence of the optical depth in the densest regions near the embedded sources to be given by tau ~ nu (1.9) . For positions away from the embedded sources there is a larger scatter in the data points, with a suggestion that the frequency-dependence is steeper, tau ~ nu (2.4) . This may be an indication of a change in the grain properties between less dense and very dense regions, and is consistent with the results of grain growth. Using standard values for the fractional abundance of C(18) O relative to H_2, the mean densities of the cloud cores are 3 - 5 x 10(4) cm{-3}. These regions appear to be close to virial equilibrium. The dense gas (revealed by multiple transition studies of tracers such as CS and HC_3N to have n(H_2) =~ 10(6) cm{-3}) has a volume filling factor of only a few percent.

No associations

LandOfFree

Say what you really think

Search LandOfFree.com for scientists and scientific papers. Rate them and share your experience with other people.

Rating

Carbon Monoxide and Dust Column Densities: The Dust-To-Gas Ratio and Structure of Three Giant Molecular Cloud Cores does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with Carbon Monoxide and Dust Column Densities: The Dust-To-Gas Ratio and Structure of Three Giant Molecular Cloud Cores, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Carbon Monoxide and Dust Column Densities: The Dust-To-Gas Ratio and Structure of Three Giant Molecular Cloud Cores will most certainly appreciate the feedback.

Rate now

     

Profile ID: LFWR-SCP-O-1173689

  Search
All data on this website is collected from public sources. Our data reflects the most accurate information available at the time of publication.