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Paper: The High-Resolution OTF Survey of the 12CO in M31
Volume: 217, Imaging at Radio Through Submillimeter Wavelengths
Page: 72
Authors: Neininger, N.; Nieten, Ch.; Wielebinski, R.; Guélin, M.; Lucas, R.; Ungerechts, H.
Abstract: We are performing a high-sensitivity OTF survey of the 12CO(1-0) emission of the nearby galaxy M 31 with the IRAM 30-m telescope. The galaxy (of an angular size of ~2circ × 1circ) is covered with 12 separate fields. They are built up from scans that are typically 20' long -- which takes about 6 minutes. The scanning orientation is defined in a coordinate system intrinsic to the galaxy. Dump interval and inter-scan distance are chosen such as to ensure a full sampling of the 23'' beam. The integration time thus obtained is about 20 seconds per beam for each coverage and results in a final r.m.s. noise of 0.5 K kms-1 in a 60 kms-1-wide band. In order to minimize atmospheric effects, each field is covered at least twice, at orthogonal scanning orientations. While combining the individual coverages, a spatial Fourier filtering is applied. The OTF technique is very flexible and simple modifications of the observational parameters allow, e.g., to adjust the sensitivity or to map selected fields in the CO(2-1) line. The combination of high resolution and high sensitivity thus obtained provides a unique data set for the investigation of molecular clouds. CO turns out to be a good tracer for the molecular content of M 31 and its kinematical properties are currently under study.
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