Astronomy and Astrophysics – Astronomy
Scientific paper
Nov 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993a%26a...279..359b&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 279, no. 2, p. 359-375
Astronomy and Astrophysics
Astronomy
21
Andromeda Galaxy, Astronomical Models, Carbon Monoxide, Interstellar Magnetic Fields, Molecular Clouds, Molecular Spectra, Polarized Electromagnetic Radiation, Radio Astronomy, Radio Emission, Astronomical Spectroscopy, Continuums, H I Regions, H Ii Regions, Line Spectra, Radio Spectra
Scientific paper
In search of molecular clouds that might tangle the magnetic field in a region of varying polarized continuum emission in the SW of M 31 we observed (12)CO(1-0) with the 30-m dish at Pico Veleta/Spain. We took spectra along three lines, one parallel (6 min long) and two perpendicular (4 min long) to the spiral arms, centered on X approximately = 12.0 min S, Y approximately = 6 min W. We found three velocity components in (12)CO(1-0), which have counterparts in H I. On the basis of Braun's (1991) spiral arm model they may be identified with three arm segments at 5.7 kpc, 7.9 kpc and 12.7 kpc from the centre, respectively. The (12)CO(1-0) emission from the strongest velocity component shows several peaks coincident with positions of dust clouds, a clear deficiency across the OB-association A66 and significant enhancement around the H-alpha bubble P354. Hence all these objects are situated in the arm at R = 5.7 kpc. A comparison between the radio continuum emission at 1490 MHz (surface brightness of the total emission TA, degree of polarization p) and the gas surface brightness (ICO, Ngas = NHI + 2NH2) revealed the following relationships: (1) TA proportional to ICO exp 1.2 +/- 0.3, (2) TA proportional to Ngas emp 2.5 +/- 0.6, (3) p proportional to Ngas exp -2.0 +/- -0.8, and (4) p proportional to TA exp -1.15 +/- .21. Correlations with the total gas are considerably tighter than those with ICO or NHI alone, which indicates that the magnetic field is coupled to the total gas rather than to a specific component. We present the first observational correlation between the average magnetic field strength and the average gas volume density.
Bajaja Esteban
Beck Rainer
Berkhuijsen Elly M.
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