Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992aas...18111502r&link_type=abstract
American Astronomical Society, 181st AAS Meeting, #115.02D; Bulletin of the American Astronomical Society, Vol. 24, p.1302
Astronomy and Astrophysics
Astronomy
Scientific paper
Sagittarius A (Sgr A) West has been observed in the H92alpha \ line at 8.3 GHz using the Very Large Array with an angular resolution of ~ 1('') , a velocity resolution of 14 km s(-1) and an r.m.s. noise of ~ 0.15 mJy beam(-1) . The global kinematics and electron temperatures of the HII region have been determined. This determination of the kinematics has been done with almost an order of magnitude greater resolution and sensitivity than previous radio recombination line observations. These observations have a factor of two greater angular and velocity resolution than recent [Ne II] imaging spectral line observations; this kinematic determination does not support the one-armed spiral model suggested by the [Ne II] observations. Rather, three major kinematic features are identified: the western arc; the northern arm; and the extended bar. The western arc is modeled as part of a ring with an inner radius of 25('') (1 pc) and is in circular rotation about a point near Sgr A*. The modeled ring with a position angle of 22(deg) and inclination of 56(deg) has a rotational velocity of 105 km s(-1) and the interior mass appears to be ~ 3.5 times 10(6) M_sun. The previously reported high electron temperatures south of Sgr A* have been explained as a superposition of the bar (at v_LSR = 0 km s(-1) ) and the northern arm (at v_LSR = --250 km s(-1) ) and a uniform electron temperature of ~ 7000 K is observed throughout Sgr A West. Additionally, observation of stimulated emission at the position of the non-thermal point source Sgr A* has been interpreted as evidence of an infalling cloud from the circum-nuclear disk. The He92alpha line has been possibly detected at the 2.5sigma level, with a Y(+) (He(+) /H(+) ) of ~ 5%. Finally, the data were used to derive a 3sigma upper limit to the line-of-sight magnetic field strength in the northern arm of Sgr A West of ~ 8 mG.
Goss William Miller
Roberts Daniel A.
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