Tj. Sodroski et al., LARGE-SCALE CHARACTERISTICS OF INTERSTELLAR DUST FROM COBE DIRBE OBSERVATIONS, The Astrophysical journal, 428(2), 1994, pp. 638-646
Observations from the COBE Diffuse infrared Background Experiment of t
he 140 and 240 mum emission from the Galactic plane region (Absolute v
alue of b < 10-degrees) are combined with radio surveys that trace the
molecular (H-2), neutral atomic (H I), and extended low-density (n(e)
approximately 10-100 cm-3) ionized (H II) gas phases of the interstel
lar 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 thes
e three gas phases. This analysis shows large-scale longitudinal and l
atitudinal gradients in the dust temperature and a decrease in dust te
mperature with increasing Galactocentric distance. The derived dust te
mperatures are significantly different from those derived in similar a
nalyses using the Infrared Astronomical Satellite (IRAS) 60 and 100 mu
m data, suggesting that small (5 angstrom less than or similar to radi
us less than or similar to 200 angstrom) transiently heated dust parti
cles contribute significantly to the Galactic 60 mum emission. It is f
ound that 60%-75% of the far-infrared luminosity arises from cold (app
roximately 17-22 K) dust associated with diffuse H I clouds, 15%-30% f
rom cold (approximately 19 K) dust associated with molecular gas, and
less than 10% from warm (approximately 29 K) dust in extended low-dens
ity H II regions, consistent with the results of the IRAS analyses of
the Galactic 60 and 100 mum emission. Within 2-degrees of longitude of
the Galactic center, the derived gas-to-dust mass ratio along the lin
e of sight, G(d), reverses its general trend of decreasing G(d) toward
the inner Galaxy and increases by a factor of approximately 2-3 towar
d the Galactic center. One possible explanation for this result is tha
t the ratio of H-2 column density to (CO)-C-12 intensity is lower in t
he Galactic center region than in the Galactic disk.