Molecular spiral arms in M51

Abstract

The controversy surrounding the delineation of molecular spiral structure in the Galaxy emphasizes that spiral structure can best be understood by observing external galaxies with high angular resolution. M51, the galaxy in which spiral structure was first discerned, is the obvious galaxy to observe. Lo et al. (1987) observed CO emission from the nuclear region of M51; however, only a very short segment of the spiral arms was mapped since the half-power point of their primary beam was ~2 kpc from the nucleus.

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