CHIMPS: the 13CO/C18O (J = 3 → 2) Heterodyne Inner Milky Way Plane Survey
Monthly Notices of the Royal Astronomical Society
Oxford University Press
We present the 13CO/C18O (J = 3 → 2) Heterodyne Inner Milky Way Plane Survey (CHIMPS) which has been carried out using the Heterodyne Array Receiver Program on the 15 m James Clerk Maxwell Telescope (JCMT) in Hawaii. The high-resolution spectral survey currently covers |b| ≤ 0 ∘..∘5 and 28deg≲l≲46deg28deg≲l≲46deg, with an angular resolution of 15 arcsec in 0.5 km s−1 velocity channels. The spectra have a median rms of ∼0.6 K at this resolution, and for optically thin gas at an excitation temperature of 10 K, this sensitivity corresponds to column densities of NH2 ∼ 3 × 1020 cm−2 and NH2 ∼ 4 × 1021 cm−2 for 13CO and C18O, respectively. The molecular gas that CHIMPS traces is at higher column densities and is also more optically thin than in other publicly available CO surveys due to its rarer isotopologues, and thus more representative of the three-dimensional structure of the clouds. The critical density of the J = 3 → 2 transition of CO is ≳104 cm−3 at temperatures of ≤20 K, and so the higher density gas associated with star formation is well traced. These data complement other existing Galactic plane surveys, especially the JCMT Galactic Plane Survey which has similar spatial resolution and column density sensitivity, and the Herschel infrared Galactic Plane Survey. In this paper, we discuss the observations, data reduction and characteristics of the survey, presenting integrated-emission maps for the region covered. Position–velocity diagrams allow comparison with Galactic structure models of the Milky Way, and while we find good agreement with a particular four-arm model, there are some significant deviations.
AJR would like to thank David Berry and especially Malcolm Currie for their assistance with ORAC-DR and other Starlink applications. AJR also acknowledges the support of an STFC-funded studentship, and the support of the Royal Astronomical Society for overseas travel to present CHIMPS data. The James Clerk Maxwell Telescope has historically been operated by the Joint Astronomy Centre on behalf of the Science and Technology Facilities Council of the United Kingdom, the National Research Council of Canada and the Netherlands Organisation for Scientific Research. This research used the facilities of the Canadian Astronomy Data Centre operated by the National Research Council of Canada with the support of the Canadian Space Agency. This research made use of the NASA Astrophysical Data System. This research has also made use of the SIMBAD data base, operated at CDS, Strasbourg, France. This research made use of ASTROPY, a community-developed core PYTHON package for Astronomy (Astropy Collaboration 2013). This research also made use of APLPY, an open-source plotting package for PYTHON hosted at http://aplpy.github.com. MZ acknowledges support from the China Ministry of Science and Technology under the State Key Development Program for Basic Research (2012CB821800)
This is the final version of the article. Available from OUP] via the DOI in this record.
Vol. 456, pp. 2885 - 2899