Large-scale characteristics of interstellar dust from COBE DIRBE observations
T. J. Sodroski, C. Bennett, N. Boggess, E. Dwek, B. A. Franz, M. G. Hauser, T. Kelsall, S. H. Moseley, N. Odegard, R. F. Silverberg, J. L. Weiland;
ApJ, 1994, 428, 638
ABSTRACT:Observations from the COBE Diffuse Infrared Background Experiment of the 140 and 240 micrometer emissions from the
Galatic plane region (absolute value of b less than 10 deg) are combined with
radio surveys that trace the molecular (H2), neutral atomic (H I), and
extended low-density (n(sub e) approximately 10 to 100/cm(exp 3)) ionized (H
II) gas phases of the interstellar medium to derive physical conditions
such as the dust temperature, dust-to-gas mass ratio, and far-infrared
emissivity (1) averaged over these gas phases along each line of sight and (2)
within each of these three gas phases.
This analysis shows large-scale
longitudinal and latitudinal gradients in the dust temperature and a decrease in
dust temperature with increasing Galactocentric distance.
The derived
dust temperatures are significantly different from those derived in
similar analyses using the Infrared Astronomical Satellite (IRAS) 60 and 100
micrometer data, suggesting that small (5 A approximately less than radius
approximately less than 200 A) transiently heated dust particles contribute
significantly o the Galactic 60 micrometer emission.
It is found that 60% to 75% of the
far-infrared luminosity arises from cold (approximately 17 to 22 K) dust associated
with diffuse H I clouds, 15% to 30% from cold (approximately 19 K) dust
associated with molecular gas, and less than 10% from warm (approximately 29 K)
dust in extended low-density H II regions, consistent with the results of
the IRAS analyses of the Galactic 60 and 100 micrometer emission.
Within 2
deg of longitude of the Galactic center, the derived gas-to-dust mass
ratio along the line of sight, G(sub d), reverses its general trend of
decreasing G(sub d) toward the inner Galaxy and increases by a factor of
approximately 2 to 3 toward the Galactic center.
One possible explanation for this
result is that the ratio of H2 column density to (12)CO intensity is lower in the
Galactic center region than in the Galactic disk.
KEYWORDS: atoms, carbon monoxide, galaxies, gases, hydrogen, infrared radiation, interstellar matter, ions, molecules, radio observation, cosmic background explorer satellite, luminosity, photometry, spatial resolution, temperature dependence
PERSOKEY:milky way, ,
CODE: sodroski94