Astronomy and Astrophysics – Astronomy
Scientific paper
May 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996adil...rp...01p&link_type=abstract
NCSA Astronomy Digital Image Library
Astronomy and Astrophysics
Astronomy
Scientific paper
We present the high-resolution (6.6" by 3.7") CS J=2-1 map of the nearby starburst galaxy NGC 253, made with the 6-element BIMA array. Dense molecular gas traced by the CS transition is seen within a ~ 30" by 10" (~ 430 by 140 pc) region of the nucleus. An LVG analysis estimates that the typical H$_2$ volume density is of the order of 3 X 10^4 per cubic cm, and H2, CS column densities in the line of sight are 7 X 10^15 per square cm and 2 X 10^23 per square cm, respectively. The total mass of dense gas is about 2.2 X 10^8 solar masses, accounting for half the gas mass traced by CO J = 1-0 emission and 17% of the dynamical mass. The morphology and kinematics of the CS emission are inconsistent with gas on circular orbits around the dynamic center. Instead, they are well explained by gas moving along closed orbits in a bar potential with the major axis of the bar at an angle of 34 degrees from the line of sight in the galactic plane. We speculate that most massive stars form in clouds on the inner x(2) orbits, which are oriented perpendicular to the bar. This provides a viable explanation for the fact that 2-cm radio continuum knots (Turner and Ho 1985, ApJ, 299, L77) are distributed along a line perpendicular to the bar.
Lo Kwok Yung
Peng Richard
Sutton Edmund C.
Whiteoak John B.
Zhou Shuhua
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