The interstellar gas in the central part of the galaxy.

Abstract

view Abstract Citations (3) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The interstellar gas in the central part of the galaxy. Oort, J. H. ; Rougoor, G. W. Abstract The high-velocity wings of the 21-cm line profiles in directions near that of the galactic center (Kwee et al. 1954) have been studied intensively in the past few years. Following are some features of the motion and distribution of neutral hydrogen in the central region of the Galaxy following from the observations. I) A spiral or circular arm visible from 1 = 3050 to 1 = 3340 and possibly extending to greater longitude, at R 3 kpc, which has a radial motion of about 50 km/sec directed away from the center; at the same time it takes part in the galactic rotation with a velocity of about 200 km/sec.' The arm is seen against the continuous radiation of the source Sagittarius A (Van Woerden et al. 1957). It is by far the most regular of all the arms that have so far been observed in the Galaxy. Its temperature is about 1000K, the random motions average 5 km/sec in one coordinate, and the half-density thickness in the z-direction is 130 pc. 2) A spiral arm on the far side of the center, broken up into bits with radial motions between 75 and 150 km/sec, probably also situated between R = 2 and 3 kpc. 3) A rather empty region between R = 0.5 and 1.5 or 2 kpc. 4) A concentration within 500 pc from the center, with no radial motion and a rotational velocity of the order of 200 km/sec. Similar high rotational velocities close to the center have been observed optically in some elliptical nebulae and in M81. It seems likely that the expansion is caused by magnetic fields (Oort and Rougoor 1958). The total amount of gas moving out of the region of 3 kpc radius is roughly 1.5 solar masses per year. At this rate the central disk would be emptied in a few tens of millions of years. It seems probable that replenishment comes from condensation of the galactic corona into the cool clouds of the disk, between 1? = 1.5 and 2.5 kpc. The magnetic lines of force would then have to enter the plane at right angles and bend there to extend outward in the plane of the disk. REFERENCES Kwee, K. K., Muller, C. A. and Westerhout, G. 1954, B. A. N. 12, 211. Oort, J. H. and Rougoor, G. W. 1958, Kon. Ned. Ac. Wet, Afd. Nat. 67, 139. van Woerden, H., Rougoor, G. W. and Oort, J. H. 1957, C. R. Acad. Sci. Paris 244, 1691. Sterrewacht, Leiden, The Netherlands Publication: The Astronomical Journal Pub Date: May 1959 DOI: 10.1086/107903 Bibcode: 1959AJ.....64..130O full text sources ADS |