Abstract
The H2O Southern Galactic Plane Survey (HOPS) has mapped a 100 degree strip of the Galactic plane (-70deg > l > 30deg, |b| < 0.5deg) using the 22-m Mopra antenna at 12-mm wavelengths. Observations were conducted in on-the-fly mode using the Mopra spectrometer (MOPS), targeting water masers, thermal molecular emission and radio-recombination lines. Foremost among the thermal lines are the 23 GHz transitions of NH3 J,K = (1,1) and (2,2), which trace the densest parts of molecular clouds (n > 10^4 cm^{-3}). In this paper we present the NH3 (1,1) and (2,2) data, which have a resolution of 2 arcmin and cover a velocity range of +/-200 km/s. The median sensitivity of the NH3 data-cubes is sigma_Tmb = 0.20 +/1 0.06 K. For the (1,1) transition this sensitivity equates to a 3.2 kpc distance limit for detecting a 20 K, 400 Msun cloud at the 5-sigma level. Similar clouds of mass 5,000 Msun would be detected as far as the Galactic centre, while 30,000 Msun clouds would be seen across the Galaxy. We have developed an automatic emission finding procedure based on the ATNF DUCHAMP software and have used it to create a new catalogue of 669 dense molecular clouds. The catalogue is 100 percent complete at the 5-sigma detection limit (Tmb = 1.0 K). A preliminary analysis of the ensemble cloud properties suggest that the near kinematic distances are favoured. The cloud positions are consistent with current models of the Galaxy containing a long bar. Combined with other Galactic plane surveys this new molecular-line dataset constitutes a key tool for examining Galactic structure and evolution. Data-cubes, spectra and catalogues are available to the community via the HOPS website.
Highlights
HOPS (H2O Southern Galactic Plane Survey) is a project utilising the Mopra radio telescope1 to simultaneously map spectral-line emission along the southern Galactic plane across the full 12-mm band
The aim of the survey is to provide an untargeted census of 22.235 GHz H2O (616−523) masers and thermal line emission towards the inner Galaxy
In contrast to other large molecular line surveys of the Galactic plane, which use relatively abundant CO isotopologues (e.g. Dame et al 2001, Jackson et al 2006) HOPS has focused on the inversion-rotation transitions of NH3
Summary
HOPS (H2O Southern Galactic Plane Survey) is a project utilising the Mopra radio telescope to simultaneously map spectral-line emission along the southern Galactic plane across the full 12-mm band (frequencies of 19.5 to 27.5 GHz). NH3 is excited in gas with kinetic temperatures greater than ∼ 5 K (Pickett et al 1998) and is found associated with cool (T < 10 K) dense clouds. Such regions are too cold for more common gas tracers, like CO, to remain in the gas phase. Comparison of the (1,1) and higher J,K inversion transitions can be used to estimate the rotational temperature of the gas In this second paper we present the HOPS NH3 (1,1) and NH3 (2,2) datasets and the automatic finding procedure used to create catalogues of emission. A third paper (Longmore et al in prep.) will published the properties of the catalogue derived by fitting the NH3 (1,1) and NH3 (2,2) spectra with model line profiles (i.e. temperature, density, mass and evolutionary state)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
