THE RELATION BETWEEN GAS AND DUST IN THE TAURUS MOLECULAR CLOUD
- Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109-8099 (United States)
- Department of Astronomy, LGRT 619, University of Massachusetts, 710 North Pleasant Street, Amherst, MA 01003 (United States)
- Observatoire Astronomique de Strasbourg, 67000 Strasbourg (France)
- Astrophysics Group, School of Physics, University of Exeter, Stocker Road, Exeter, EX4 4QL (United Kingdom)
We report a study of the relation between dust and gas over a 100 deg{sup 2} area in the Taurus molecular cloud. We compare the H{sub 2} column density derived from dust extinction with the CO column density derived from the {sup 12}CO and {sup 13}CO J = 1 {yields} 0 lines. We derive the visual extinction from reddening determined from 2MASS data. The comparison is done at an angular size of 200'' corresponding to 0.14 pc at a distance of 140 pc. We find that the relation between visual extinction A{sub V} and N(CO) is linear between A{sub V} {approx_equal} 3 and 10 mag in the region associated with the B213-L1495 filament. In other regions, the linear relation is flattened for A{sub V{approx}}> 4 mag. We find that the presence of temperature gradients in the molecular gas affects the determination of N(CO) by {approx}30%-70% with the largest difference occurring at large column densities. Adding a correction for this effect and accounting for the observed relation between the column density of CO and CO{sub 2} ices and A{sub V}, we find a linear relationship between the column of carbon monoxide and dust for observed visual extinctions up to the maximum value in our data {approx_equal}23 mag. We have used these data to study a sample of dense cores in Taurus. Fitting an analytical column density profile to these cores we derive an average volume density of about 1.4 x 10{sup 4} cm{sup -3} and a CO depletion age of about 4.2 x 10{sup 5} yr. At visual extinctions smaller than {approx}3 mag, we find that the CO fractional abundance is reduced by up to two orders of magnitude. The data show a large scatter suggesting a range of physical conditions of the gas. We estimate the H{sub 2} mass of Taurus to be about 1.5 x 10{sup 4} M{sub sun}, independently derived from the A{sub V} and N(CO) maps. We derive a CO integrated intensity to H{sub 2} conversion factor of about 2.1 x 10{sup 20} cm{sup -2} (K km s{sup -1}){sup -1}, which applies even in the region where the [CO]/[H{sub 2}] ratio is reduced by up to two orders of magnitude. The distribution of column densities in our Taurus maps resembles a log-normal function but shows tails at large and low column densities. The length scale at which the high column density tail starts to be noticeable is about 0.4 pc.
- OSTI ID:
- 21464838
- Journal Information:
- Astrophysical Journal, Vol. 721, Issue 1; Other Information: DOI: 10.1088/0004-637X/721/1/686; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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