Extinction toward the galactic center from observations of interstellar lines

Journal Article · Sat Aug 15 04:00:00 EDT 1981 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/159134· OSTI ID:5625337

Federman, S R; Evans, II, N J

A substantial galactic gradient in the /sup 13/Co--to-dust ratio has been suggested recently by Blitz and Shu. They used the /sup 13/CO emission seen toward the galactic center and a local calibration of the /sup 13/CO--to-emission ratio to predict the extinction to the galactic center. The result is far greater than the extinction deduced from infrared observations. In this paper, H/sub 2/CO absorption observations against Sgr A are used to select the molecular material lying in front of the galactic center, and a similar analysis is carried out. The ratio of visual extinction to equivalent width of the 6 cm line of H/sub 2/CO is similar for several nearby interstellar clouds. The value for the ratio A/sub v//W(H/sub 2/CO) is approx.12 mag (km s/sup -1/)/sup -1/. When this ratio is applied to published data for the galactic center an extinction of <86 mag is derived. By considering only the molecular components in front of the infrared cluster, the estimate for the extinction is lowered to 15--46 mag. These results are consistent with the results from infrared observations toward the galactic center. Extinction estimates based on other interstellar species were also considered. Atomic gas appears to contribute less than 10 mag of extinction. An analysis of /sup 13/CO emission toward the galactic center reveals that the results for this molecule are similar to those for H/sub 2/CO if the result of Dickman is used to determine A/sub v/. The large value that Blitz and Shu deduced for A/sub v/ from /sup 13/CO is a consequence of their inclusion of molecular components which do not lie in front of the infrared cluster. We find no compelling evidence for a substantial gradient in the /sup 13/CO--to-dust ratio. If the assumptions used by Solomon, Scoville, and Sanders to deduce cloud masses are used instead of the result of Dickman, extinctions are found which are 3--5 times greater than those deduced from H/sub 2/CO. consequently, the mass estimates of Solomon et al. appear to be 3--5 times too high.

• Research Organization: Astronomy Department and Electrical Engineering Research Laboratory, University of Texas at Austin
• OSTI ID: 5625337
• Journal Information: Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 248:1; ISSN ASJOA
• Country of Publication: United States
• Language: English

Related Subjects

640105* -- Astrophysics &amp; Cosmology-- Galaxies
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ABSORPTION
ABUNDANCE
ALDEHYDES
CARBON COMPOUNDS
CARBON MONOXIDE
CARBON OXIDES
CHALCOGENIDES
CHEMICAL COMPOSITION
CHEMISTRY
COSMIC DUST
COSMIC GASES
COSMOCHEMISTRY
DATA ANALYSIS
DUSTS
EMISSION
FLUIDS
FORMALDEHYDE
GALAXIES
GALAXY NUCLEI
GASES
INFRARED SPECTRA
INTERSTELLAR SPACE
MILKY WAY
ORGANIC COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
SPACE
SPECTRA