Giant Molecular Clouds in M31. I. Molecular Cloud Properties

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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 sufficient signal-to-noise 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 a similar interstellar radiation field, metallicity, Toomre Q parameter, and midplane volume density as the inner Milky Way, so the similarity of GMC populations between the two systems is not surprising.

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