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J/ApJ/654/240       Giant molecular clouds in M31            (Rosolowsky+, 2007)

Giant molecular clouds in M31. I. Molecular cloud properties. Rosolowsky E. <Astrophys. J., 654, 240-251 (2007)> =2007ApJ...654..240R
ADC_Keywords: Galaxies, nearby ; Molecular clouds ; Radio lines Keywords: galaxies: individual (Andromeda) - galaxies: ISM - ISM: clouds - radio lines: ISM Abstract: We present Berkeley-Illinois-Maryland Association (BIMA) millimeter interferometer observations of giant molecular clouds (GMCs) along a spiral arm in M31. The observations consist of a survey using the compact configuration of the interferometer and follow-up, higher resolution observations on a subset of the detections in the survey. The data are processed using an analysis algorithm designed to extract GMCs and correct their derived properties for observational biases, thereby facilitating comparison with Milky Way data. The algorithm identifies 67 GMCs, of which 19 have a sufficient signal-to-noise ratio to accurately measure their properties. The GMCs in this portion of M31 are indistinguishable from those found in the Milky Way, having a similar size-line width relationship and distribution of virial parameters, confirming the results of previous, smaller studies. The velocity gradients and angular momenta of the GMCs are comparable to the values measured in M33 and the Milky Way, and in all cases are below expected values based on the local galactic shear. The studied region of M31 has an interstellar radiation field, metallicity, Toomre Q parameter, and midplane volume density similar to those of the inner Milky Way, so the similarity of GMC populations between the two systems is not surprising. Description: We observed 12CO (J=1->0) emission from M31 during the spring and fall observing seasons of 2002 with the D and C configurations of the BIMA millimeter interferometer File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table2.dat 43 67 Molecular Cloud Properties in M31
Byte-by-byte Description of file: table2.dat
Bytes Format Units Label Explanations
1 A1 --- Type [HL] (H)igh or (L)ow S/N Clouds (5) 3- 4 I2 --- [R2007] Sequential number 6- 10 I5 arcsec oRA Relative position along RA (1) 12- 16 I5 arcsec oDE Relative position along DE (1) 18- 19 I2 10+4solMass Mlum Luminous mass (2) 21- 22 I2 pc Re ? Deconvolved radius (2) (3) 24- 27 F4.2 km/s sigmav Line width (2) 29- 32 F4.1 --- Tmax/sigma Maximum temperature to line width rms ratio 34- 37 F4.2 km/s/pc |∇v| Velocity gradient magnitude (2) 38 A1 --- u_|∇v| [d] Uncertainty flag on |nablav| (4) 40- 43 I4 deg ∇PA Gradient position angle (2)
Note (1): Position given in arcseconds relative to the center of M31 at RA=00:42:44.3, DE=+41:16:09 (J2000) Note (2): Typical errors in properties: * luminous mass (MLum), 20% * radius (Re), 15% * line width (sigmav), 15% * velocity gradient magnitude (|∇v|), 50% * gradient position angle (φ∇). Note (3): No values of the deconvolved radius (Re) are reported if the cloud cannot be resolved with the present data. Note (4): d = The uncertainty in the gradient of this cloud is larger than 0.15km/s/pc and it is not included in the gradient analysis. Note (5): High S/N clouds have Tmax/sigma≥10.
History: From electronic version of the journal
(End) Patricia Vannier [CDS] 25-Nov-2008
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