The H2O Southern Galactic Plane Survey (HOPS) - I. Techniques and H2O maser data

Abstract

We present first results of the H2O Southern Galactic Plane Survey (HOPS), using the Mopra Radio Telescope with a broad‐band backend and a beam size of about 2 arcmin. We have observed 100 deg2 of the southern Galactic plane at 12 mm (19.5–27.5 GHz), including spectral line emission from H2O masers, multiple metastable transitions of ammonia, cyanoacetylene, methanol and radio recombination lines. In this paper, we report on the characteristics of the survey and H2O maser emission. We find 540 H2O masers, of which 334 are new detections. The strongest maser is 3933 Jy and the weakest is 0.7 Jy, with 62 masers over 100 Jy. In 14 maser sites, the spread in the velocity of the H2O maser emission exceeds 100 km s−1. In one region, the H2O maser velocities are separated by 351.3 km s−1. The rms noise levels are typically between 1 and 2 Jy, with 95 per cent of the survey under 2 Jy. We estimate completeness limits of 98 per cent at around 8.4 Jy and 50 per cent at around 5.5 Jy. We estimate that there are between 800 and 1500 H2O masers in the Galaxy that are detectable in a survey with similar completeness limits to HOPS. We report possible masers in NH3 (11,9) and (8,6) emission towards G19.61−0.23 and in the NH3 (3,3) line towards G23.33−0.30.

The 6-GHz Multibeam Maser Survey – III. Comparison between the MMB and HOPS

“…HOPS observed 100 square degrees of the Southern Galactic plane for a number of spectral lines between 19.5 and 27.5 GHz, including water masers (Walsh et al 2011). Observations were made outside the traditional mm season which resulted in a slightly variable detection limit across the survey region.…”

“…HOPS itself is a good example of this; the initial survey with the Mopra radio telescope detected 540 water maser sites (Walsh et al 2011) and 31 of those sources were not detected in the much more sensitive ATCA follow-up observations. This indicates that ∼6 percent of the population detected in the initial survey fell below the detection limit of more sensitive observations conducted up to four years later.…”

“…Alongside the water maser observations, HOPS simultaneously observed a number of ammonia transitions (Walsh et al 2011). Purcell et al (2012 presented a catalogue of the ammonia (1,1) and (2,2) from the HOPS survey, which has a mean sensitivity of 0.20 K and catalogues 669 dense molecular clouds.…”

“…Following the completion of both the Methanol Multibeam (MMB) Survey (Green et al 2009) and the H2O Galactic Plane Survey (HOPS; Walsh et al 2011) we are now in a position to conduct a definitive comparison between statistically complete sample of the most common masers found towards high-mass star forming regions. Here we present a comparison of the occurrence of 6.7-GHz methanol masers, 12.2-GHz methanol masers, water masers and 6035-MHz excited-OH masers located within a 100 square degree portion of the southern Galactic plane made possible by the MMB and HOPS surveys described in Sections 1.1 and 1.2.…”

ISM gas studies towards the TeV PWN HESS J1825−137 and northern region

“…1) centred at (RA,Dec)=(18.425h,−13.3 • ) in the 12mm band from the 19 th to the 27 th of January 2012 with the 22 metre Mopra telescope. We combined our observations with the HOPS survey (Walsh et al 2011), which covered the Galactic plane within the Galactic latitude b=-0.5 to b=0.5 to achieve better sensitivity (see Table 1). Additionally, we observed a 40 × 40 subsection (small red dashed box in For these observations, we used the Mopra spectrometer MOPS in 'zoom' mode, which allowed the recording of sixteen sub-bands, each consisting of 4096 channels and a 137.5 MHz bandwidth, simultaneously.…”