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.
We present the fifth portion of an unbiased survey of the Galactic plane, |b| ≤ 2°, for 6668-MHz methanol masers. This section of the survey completes the Galactic longitude range visible to the ...Parkes radio telescope, incorporating the longitude range 20°–60°. Within this section of the survey we find 265 methanol masers, 64 new to the survey, bringing the total number of methanol masers detected across the full longitude coverage (186°, through 0°, to 60°) to 972 sources.
Radio continuum observations using the Australia telescope compact array at 5.5, 9.0, 17.0 and 22.8 GHz have detected free–free emission associated with 45 of 49 massive young stellar objects and ...H ii regions. Of these, 26 sources are classified as ionized jets (12 of which are candidates), 2 as ambiguous jets or disc winds, 1 as a disc-wind, 14 as H ii regions and 2 were unable to be categorized. Classification as ionized jets is based upon morphology, radio flux and spectral index, in conjunction with previous observational results at other wavelengths. Radio luminosity and momentum are found to scale with bolometric luminosity in the same way as low-mass jets, indicating a common mechanism for jet production across all masses. In 13 of the jets, we see associated non-thermal/optically thin lobes resulting from shocks either internal to the jet and/or at working surfaces. 10 jets display non-thermal (synchrotron emission) spectra in their lobes, with an average spectral index of α = −0.55 consistent with Fermi acceleration in shocks. This shows that magnetic fields are present, in agreement with models of jet formation incorporating magnetic fields. Since the production of collimated radio jets is associated with accretion processes, the results presented in this paper support the picture of disc-mediated accretion for the formation of massive stars with an upper limit on the jet phase lasting approximately 6.5 × 104 yr. Typical mass-loss rates in the jet are found to be 1.4 × 10−5 M⊙ yr−1 with associated momentum rates of the order of (1–2) × 10−2 M⊙ km s−1 yr−1.
Here, we describe the Compact Array Broad-band Backend (CABB) and present first results obtained with the upgraded Australia Telescope Compact Array (ATCA). The 16-fold increase in observing ...bandwidth, from 2 × 128 to 2 × 2048 MHz, high-bit sampling and the addition of 16 zoom windows (each divided into further 2048 channels) provide major improvements for all ATCA observations. The benefits of the new system are: (1) hugely increased radio continuum and polarization sensitivity as well as image fidelity; (2) substantially improved capability to search for and map emission and absorption lines over large velocity ranges; (3) simultaneous multi-line and continuum observations; (4) increased sensitivity, survey speed and dynamic range due to high-bit sampling and (5) high-velocity resolution, while maintaining full polarization output. The new CABB system encourages all observers to make use of both spectral line and continuum data to achieve their full potential.
Given the dramatic increase of the ATCA capabilities in all bands (ranging from 1.1 to 105 GHz) CABB enables scientific projects that were not feasible before the upgrade, such as simultaneous observations of multiple spectral lines, on-the-fly mapping, fast follow-up of radio transients (e.g. the radio afterglow of new supernovae) and maser observation at high-velocity resolution and full polarization. The first science results presented here include wide-band spectra, high dynamic-range images and polarization measurements, highlighting the increased capability and discovery potential of the ATCA.
Recently, a comparison between the locations of 6.7-GHz methanol masers and dust continuum emission has renewed speculation that these masers can be associated with evolved stars. The implication of ...such a scenario would be profound, especially for the interpretation of large surveys for 6.7-GHz masers, individual studies where high-mass star formation has been inferred from the presence of 6.7-GHz methanol masers and for the pumping mechanisms of these masers. We have investigated the two instances where 6.7-GHz methanol masers have been explicitly suggested to be associated with evolved stars, and we find the first to be associated with a standard high-mass star formation region, and the second to be a spurious detection. We also find no evidence to suggest that the methanol maser action can be supported in the environments of evolved stars. We thereby confirm their exclusive association with high-mass star formation regions.
We present the unambiguous discovery of six new class II methanol maser transitions, three of which are torsionally excited (vt = 1). The newly discovered 6.18 GHz 17−2 → 18−3 E (vt = 1), 7.68 GHz ...124 → 133 A− (vt = 0), 7.83 GHz 124 → 133 A+ (vt = 0), 20.9 GHz 101 → 112 A+ (vt = 1), 44.9 GHz 20 → 31 E (vt = 1), and 45.8 GHz 93 → 102 E (vt = 0) methanol masers were detected toward G 358.931−0.030, where the known 6.68 GHz maser has recently been reported to be undergoing a period flaring. The detection of the vt = 1 torsionally excited lines corroborates one of the missing puzzle pieces in class II maser pumping, but the intensity of the detected emission provides an additional challenge, especially in the case of the very highly excited 6.18 GHz line. Together with the newly detected vt = 0 lines, these observations provide significant new information that can be utilized to improve class II methanol maser modeling. We additionally present detections of 6.68, 19.9, 23.1, and 37.7 GHz class II masers, as well as 36.2 and 44.1 GHz class I methanol masers, and provide upper limits for the 38.3 and 38.5 GHz class II lines. Near simultaneous Australia Telescope Compact Array observations confirm that all 10 of the class II methanol maser detections are co-spatial to ∼0.2 arcsec, which is within the uncertainty of the observations. We find significant levels of linearly polarized emission in the 6.18, 6.67, 7.68, 7.83, 20.9, 37.7, 44.9, and 45.8 GHz transitions, and low levels of circular polarization in the 6.68, 37.7, and 45.8 GHz transitions.
New 9.9-GHz methanol masers Voronkov, M. A.; Caswell, J. L.; Ellingsen, S. P. ...
Monthly notices of the Royal Astronomical Society,
07/2010, Letnik:
405, Številka:
4
Journal Article
Recenzirano
Odprti dostop
The Australia Telescope Compact Array has been used to make the first extensive search for the class I methanol masers at 9.9 GHz. In total, 48 regions of high-mass star formation were observed. In ...addition to masers in W33-Met (G12.80−0.19) and G343.12−0.06 (IRAS 16547−4247) which have already been reported in the literature, two new 9.9-GHz masers have been found towards G331.13−0.24 and G19.61−0.23. We have determined absolute positions (accurate to roughly a second of arc) for all the detected masers and suggest that some class I masers may be associated with shocks driven into molecular clouds by expanding H ii regions. Our observations also imply that the evolutionary stage of a high-mass star-forming region when the class I masers are present can outlast the stage when the class II masers at 6.7-GHz are detectable, and overlaps significantly with the stage when OH masers are active.
The 6-GHz multibeam maser survey – I. Techniques Green, J. A.; Caswell, J. L.; Fuller, G. A. ...
Monthly notices of the Royal Astronomical Society,
January 2009, Letnik:
392, Številka:
2
Journal Article
Recenzirano
Odprti dostop
A new seven-beam 6–7 GHz receiver has been built to survey the Galaxy and the Magellanic Clouds for newly forming high-mass stars that are pinpointed by strong methanol maser emission at 6668 MHz. ...The receiver was jointly constructed by Jodrell Bank Observatory (JBO) and the Australia Telescope National Facility (ATNF) and allows simultaneous coverage at 6668 and 6035 MHz. It was successfully commissioned at Parkes in 2006 January and is now being used to conduct the Parkes–Jodrell multibeam maser survey of the Milky Way. This will be the first systematic survey of the entire Galactic plane for masers of not only 6668-MHz methanol, but also 6035-MHz excited-state hydroxyl. The survey is two orders of magnitude faster than most previous systematic surveys and has an rms noise level of ∼0.17 Jy. This paper describes the observational strategy, techniques and reduction procedures of the Galactic and Magellanic Cloud surveys, together with deeper, pointed, follow-up observations and complementary observations with other instruments. It also includes an estimate of the survey detection efficiency. The 111 d of observations with the Parkes telescope have so far yielded >800 methanol sources, of which ∼350 are new discoveries. The whole project will provide the first comprehensive Galaxy-wide catalogue of 6668-MHz and 6035-MHz masers.
Southern class I methanol masers at 36 and 44 GHz Voronkov, M. A; Caswell, J. L; Ellingsen, S. P ...
Monthly notices of the Royal Astronomical Society,
04/2014, Letnik:
439, Številka:
3
Journal Article
Recenzirano
Odprti dostop
The Australia Telescope Compact Array (ATCA) has been used for high angular resolution imaging of 71 southern class I methanol maser sources quasi-simultaneously at 36 and 44 GHz. The data reveal a ...high level of morphological and kinematical complexity, and allow us to demonstrate associations, at arcsecond precision, of the class I maser emission with outflows, expanding H ii regions, dark clouds, shocks traced by the 4.5-μm emission and 8.0-μm filaments. More than 700 maser component features were found at each of the two methanol transitions, but with only 23 per cent recognizable at both transitions; the morphology of class I emission is much better revealed by our survey of both transitions, compared with either one alone. We found that the number of masers falls exponentially with the projected linear distance from the associated class II 6.7-GHz methanol maser. This distribution has a scale of 263±15 mpc, irrespective of the transition. The class I masers associated with OH masers were found to have a tendency to be more spread out, both spatially and in the velocity domain. This is consistent with the expectation that such sources are more evolved. Apart from a small number of high-velocity components (which are largely blueshifted and predominantly seen at 36 GHz), the velocity distribution was found to be Gaussian, peaking near the systemic velocity of the region, which had been estimated as the middle of the velocity interval of the associated class II methanol maser at 6.7 GHz. The mean indicated a small, but significant blueshift asymmetry of −0.57 km s−1 (uncertainties are 0.06 and 0.07 km s−1 for the 36- and 44-GHz masers, respectively) with respect to the 6.7-GHz masers. The standard deviation of the velocity distribution was found to be 3.65 ± 0.05 and 3.32 ± 0.07 km s−1 for the 36- and 44-GHz masers, respectively. We also suggest a refined rest frequency value of 36 169.238 ± 0.011 MHz for the 4− 1-30 E methanol transition.
PDF
