CO and IRAS observations of the Chamaeleon molecular clouds
F. Boulanger, L. Bronfman, T. M. Dame, P. Thaddeus;
AaA, 1998, 332, 273
ABSTRACT:We present an extensive survey of the CO emission from the conspicuous complex of dark nebulae in Chamaeleon.
The CO observations together with
IRAS, extinction and H I data are used to study the distribution of
interstellar matter in the complex.
The comparison of the cloud 100mum emission
with \Av shows that the far-infrared brightness traces the gas over most of
the surface of the complex, specifically where Av < 2 mag and outside a small
number of regions heated by embedded stars.
For the complex as a whole and for
its largest clouds, masses computed from the far infrared emission
roughly agree with those derived from the CO surveys using the standard
Galactic value of the CO-to-H_2 conversion factor.
However, among the smaller
clouds the H_2 masses computed from CO emission are lower than those derived
from the 100mum data by as much as a factor of 10.
The molecular emission is
observed to be primarily associated with the 100mum emission characterized by
cold IRAS colors: low 60/100mum flux ratio and no 12 and 25mum emission while
the 100mum emission with warm IRAS colors is poorly traced by CO
emission.
The observed correlation between the spectral distribution of the dust
emission with the molecular emission may be related to the effect of the far-UV
extinction of dust on the formation of CO.
In some regions it is clear that the warm
infrared component cannot be accounted for by matter detected in the CO and H I
surveys; we suggest that these regions contain molecular gas without detected
CO emission.
KEYWORDS: ism: dust, clouds, infrared: ism: continuum, ism: chamaeleon clouds, radio lines: ism
CODE: boulanger98a