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We report observations of the J =(1--0) C18O molecular emission line toward the L977 molecular cloud. To study the correlation between C18O emission and dust extinction we constructed a Gaussian smoothed map of the infrared extinction measured by Alves et al. (1998) at the same angular resolution (50) as our molecular--line observations. This enabled a direct comparison of C18O integrated intensities and column densities with dust extinction over a relatively large range of cloud depth (2 < Av < 30 mag) at 240 positions inside L977. We find a good linear correlation between these two column density tracers for cloud depths corresponding to Av < ~10 magnitudes. For cloud depths above this threshold there is a notable break in the linear correlation. Although either optically thick C18O emission or extremely low (Tex < 5 K) excitation temperatures at high extinctions could produce this departure from linearity, CO depletion in the denser, coldest regions of L977 may be the most likely cause of the break in the observed correlation. We directly derive the C18O abundance in this cloud over a broad range of cloud depths and find it to be virtually the same as that derived for IC 5146 from the data of Lada et al. (1994). In regions of very high extinction (Av > 10 mag), such as dense cores, our results suggest that C18O would be a very poor tracer of mass. Consequently, using C18O as a column density tracer in molecular clouds can lead to a 10 to 30% underestimation of overall cloud mass. We estimate the minimum total column density required to shield C18O from the interstellar radiation field to be 1.6 +/- 0.5 magnitudes of visual extinction.
We report results of a near--infrared imaging survey of L977, a dark cloud in Cygnus seen in projection against the plane of the Milky Way. We use measurements of the near--infrared color excess and positions of the 1628 brightest stars in our survey
We report the discovery and characterization of a power law correlation between the local surface densities of Spitzer-identified, dusty young stellar objects and the column density of gas (as traced by near-IR extinction) in eight molecular clouds w
We perform numerical simulations of dusty, supersonic turbulence in molecular clouds. We model 0.1, 1 and 10 {mu}m sized dust grains at an initial dust-to-gas mass ratio of 1:100, solving the equations of combined gas and dust dynamics where the dust
Dust and gas energetics are incorporated into a cluster-scale simulation of star formation in order to study the effect of heating and cooling on the star formation process. We build on our previous work by calculating separately the dust and gas tem
We present $^{12}$CO(1-0) and $^{12}$CO(2-1) observations of a sample of 20 star-forming dwarfs selected from the Herschel Virgo Cluster Survey, with oxygen abundances ranging from 12 + log(O/H) ~ 8.1 to 8.8. CO emission is observed in ten galaxies a