Astronomy and Astrophysics – Astronomy
Scientific paper
Oct 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998stin...0057365r&link_type=abstract
Technical Report, astro-ph/9810244-VOL2 Dept. of Physics and Astronomy
Astronomy and Astrophysics
Astronomy
Star Formation, Star Formation Rate, Interstellar Matter, Galaxies, High Resolution, Maps, Spectral Emission, Radio Spectra, Line Spectra, Gas Density, Molecular Gases, Carbon Monoxide, Virial Theorem, Gravitational Instability
Scientific paper
We have used the Owens Valley Millimeter Array to map (12)CO (J=1-0) along a 3.5 kpc segment of M83's eastern spiral arm at resolutions of 6.5" x 3-5", 10", and 16". The CO emission in most of this segment lies along the sharp dust lane demarking the inner edge of the spiral arm, but beyond a certain point along the arm the emission shifts downstream from the dust lane to become better aligned with the young stars seen in blue and H.beta images. This morphology resembles that of the western arm of M100. Three possibilities, none of which is wholly satisfactory, are considered to explain the deviation of the CO arm from the dust lane: heating of the CO by UV radiation from young stars, heating by low-energy cosmic rays, and a molecular medium consisting of two (diffuse and dense) components which react differently to the density wave. Regardless, the question of what CO emission traces along this spiral arm is a complicated one. Masses based on CO emission and the virial theorem for ten emission features roughly agree and are in the range 1.5-16 x 106 solar mass. These are lower than the masses of GMAs in M5l, but the discrepancy is probably due to the much higher linear resolution of these observations. Despite the uncertainty in what CO emission is tracing, we do not require a conversion factor of CO brightness to H2 column density much different from the standard Galactic value if these structures are bound. Surprisingly, for the two fields where we can compare with single-dish data, only 2-5% of the single-dish flux is seen in our observations. A possible explanation is that M83 contains much smoothly distributed molecular gas that is resolved out by the interferometer. Strong tangential streaming is observed where the arm crosses the kinematic major axis of the galaxy, implying that the shear becomes locally prograde in the arms. The amplitude of the tangential streaming is used along with a low-resolution single-dish radial profile of CO emission to infer a very high gas surface density of about 230 solar mass /sq pc and an arm-interarm contrast greater than 2.3 in the part of the arm near the major axis. Using two different criteria, we find that the gas at this location is well above the threshold for gravitational instability - much more clearly so than in either M51 or M100. This finding is consistent with the unusually high H.alpha surface brightness and star formation efficiency in M83: star formation may be particularly active because of strong gravitational instabilities.
Higdon James J.
Lord Steven D.
Rand Richard J.
No associations
LandOfFree
The Eastern Arm of M83 Revisited: High-Resolution Mapping of (12)CO 1-0 Emission does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with The Eastern Arm of M83 Revisited: High-Resolution Mapping of (12)CO 1-0 Emission, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and The Eastern Arm of M83 Revisited: High-Resolution Mapping of (12)CO 1-0 Emission will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1101191