Search

The Australia Telescope Compact Array (ATCA) has been used for an interferometric follow up observation at 104.3 GHz of the targets where either this or the 9.9-GHz maser was previously detected. We confirm the significant difference (by more than 1.5 orders of magnitude) from source to source of the flux density ratio for these two maser transitions. Based on the morphology and location of continuum sources, the most likely explanation of this discrepancy is the difference in the flux density of the seed radiation at the two frequencies. We also report absolute positions (with arcsec accuracy) for all detected 104.3 GHz masers. [ABSTRACT FROM AUTHOR]

We have performed a molecular line search towards the flaring 6.7-GHz masers G 24.33+0.13, and G 359.6−0.24 using the Australia Telescope Compact Array. We present spectra of the 6.7-GHz class II methanol and 22.2-GHz water masers towards these sources and provide a comparison with other recent flaring events these sources have experienced. We also detect the fourth example of a 23.4-GHz class I methanol maser and the 11th example of a 4.8-GHz formaldehyde maser towards G 24.33+0.13. Alongside these results, we also observe the previously detected ammonia (3,3) emission and report upper limits on the presence of various other cm-wavelength methanol, ammonia, and OH transitions. Our results are consistent with the flaring of G 24.33+0.13 being driven by a variable accretion rate in the host high mass young stellar object. [ABSTRACT FROM AUTHOR]

The Methanol MultiBeam survey (MMB) provides the most complete sample of Galactic massive young stellar objects (MYSOs) hosting 6.7 GHz class II methanol masers. We characterize the properties of these maser sources using dust emission detected by the Herschel Infrared Galactic Plane Survey (Hi-GAL) to assess their evolutionary state. Associating 731 (73 per cent) of MMB sources with compact emission at four Hi-GAL wavelengths, we derive clump properties and define the requirements of an MYSO to host a 6.7 GHz maser. The median far-infrared (FIR) mass and luminosity are 630 M⊙ and 2500 L⊙ for sources on the near side of Galactic centre and 3200 M⊙ and 10000 L⊙ for more distant sources. The median luminosity-to-mass ratio is similar for both at ∼4.2 L⊙  M⊙−1. We identify an apparent minimum 70  μ m luminosity required to sustain a methanol maser of a given luminosity (with |$L_{70} \propto L_{6.7}\, ^{0.6}$|⁠). The maser host clumps have higher mass and higher FIR luminosities than the general Galactic population of protostellar MYSOs. Using principal component analysis, we find 896 protostellar clumps satisfy the requirements to host a methanol maser but lack a detection in the MMB. Finding a 70  μ m flux density deficiency in these objects, we favour the scenario in which these objects are evolved beyond the age where a luminous 6.7 GHz maser can be sustained. Finally, segregation by association with secondary maser species identifies evolutionary differences within the population of 6.7GHz sources. [ABSTRACT FROM AUTHOR]

We have used the Australia Telescope Compact Array (ATCA) to make new observations of the 36.2-GHz (4−1 → 30E) methanol transition towards NGC 4945 and NGC 253. These observations have revealed the presence of new maser components towards these galaxies, and have provided the first clear evidence for variability in extragalactic class I methanol masers. Alongside the new observations of NGC 4945 and NGC 253, we present the results of recent 36.2-GHz methanol maser searches towards 12 galaxies, placing upper limits on the emission from the 36.2-GHz class I transition and the 37.7-GHz (72 → 81E) class II maser line towards these sources. Flux density values for the 7-mm continuum emission towards these sources are also reported where applicable. A re-analysis of the published 36.2-GHz methanol observations of Arp 220 undertaken as part of the search revealed some issues with previous imaging procedures. The re-analysis, combined with non-detections in independent follow-up observations, suggests that there is no 36.2-GHz methanol emission towards Arp 220 stronger than 3.5 mJy in a 10 km s−1 channel (5σ upper limit). [ABSTRACT FROM AUTHOR]

We have constructed the largest sample of dust-associated class II 6.7 GHz methanol masers yet obtained. New measurements from the Methanol Multibeam (MMB) survey were combined with the 870  |$\mu {\rm m}$| APEX Telescope Large Area Survey of the Galaxy (ATLASGAL) and the 850  |$\mu {\rm m}$| JCMT Plane Survey (JPS). Together with two previous studies we have now identified the host clumps for 958 methanol masers across the Galactic Plane, covering approximately 99 per cent of the MMB catalogue and increasing the known sample of dust-associated masers by over 30 per cent. We investigate correlations between the physical properties of the clumps and masers using distances and luminosities drawn from the literature. Clumps hosting methanol masers are significantly more compact and have higher volume densities than the general population of clumps. We determine a minimum volume density threshold of n (H2) ≥ 104 cm−3 for the efficient formation of intermediate- and high-mass stars. We find 6.7 GHz methanol masers are associated with a distinct part of the evolutionary process (L bol/ M fwhm ratios of between 100.6 and 102.2) and have well-defined turning on and termination points. We estimate the lower limit for the mass of embedded objects to be ≥6 M⊙ and the statistical lifetime of the methanol maser stage to be ∼3.3 × 104 yr. This suggests that methanol masers are indeed reliable tracers of high-mass star formation, and indicates that the evolutionary period traced by this marker is relatively rapid. [ABSTRACT FROM AUTHOR]

We report the detection of new 12.178, 12.229, 20.347, and 23.121 GHz methanol masers in the massive star-forming region G358.93−0.03, which are flaring on similarly short time-scales (days) as the 6.668 GHz methanol masers also associated with this source. The brightest 12.178 GHz channel increased by a factor of over 700 in just 50 d. The masers found in the 12.229 and 20.347 GHz methanol transitions are the first ever reported and this is only the fourth object to exhibit associated 23.121 GHz methanol masers. The 12.178 GHz methanol maser emission appears to have a higher flux density than that of the 6.668 GHz emission, which is unusual. No associated near-infrared flare counterpart was found, suggesting that the energy source of the flare is deeply embedded. [ABSTRACT FROM AUTHOR]

We present observations of the 36-GHz (4−1 → 30  E) and 84-GHz (5−1 → 40  E) class I methanol maser transitions towards a sample of 94 known class I sites. These observations resulted in 93 and 92 detections in the 84- and 36-GHz transitions. While the majority of the 36-GHz sources have been previously reported, many of the sites are observed in the 84-GHz transition for the first time. The near-simultaneous observations of the two transitions revealed strikingly similar spectral profiles and a mean and median 36- to 84-GHz integrated flux density ratio of 2.6 and 1.4. Alongside the 36- and 84-GHz observations, we included rare class II methanol masers at 37.7, 38.3, 38.5, 86.6, and 86.9 GHz, a number of recombination lines, and thermal molecular transitions. We detect one new site of 86.6- and 86.9-GHz methanol masers, as well as six maser candidates in one or more of 37.7-, 38.3-, 38.5-, 86.6-, and 86.9-GHz methanol maser transitions. We detect a relatively higher rate of HC3N compared to that reported by MALT90 (once the respective detection limits were taken into account), who targeted dense dust clumps, suggesting that the class I methanol maser targets incorporate a relatively higher number of warm protostellar sources. We further find that there are similar relationships between the integrated flux density of both class I transitions with the integrated intensity of HC3N, HNC, HCO+, HNC, SiO, and H13CO+. We suggest that this indicates that the integrated flux densities of the 36- and 84-GHz transitions are closely linked to the available gas volume. [ABSTRACT FROM AUTHOR]

We have used the Australia Telescope Compact Array (ATCA) to conduct further observations of the 36.2-GHz (4−1 → 30E) methanol transition towards the nearby active galaxy NGC 4945. These observations have led to a more accurate determination of the offset between the maser emission and the nucleus of NGC 4945 with a typical synthesized beam of 6 arcsec × 4 arcsec (108 × 72 pc). This corresponds to a factor of 4 improvement with respect to the major axis of the beam. Other transitions of methanol and lines of other molecular species were obtained alongside the 36.2-GHz methanol emission, with strong detections of HC3N (J = 4 → 3) and CS (J = 1 → 0) presented here. We do not detect thermal methanol (5σ upper limit of 5 mJy in a 6 km s−1 channel) from the 48.4-GHz (10 → 00A+) ground-state transition, nor emission from the 44.1-GHz (70 → 61A+) class I maser transition (5σ upper limit of 6 mJy in a 3 km s−1 channel). We also present a comparison of the class I maser emission observed towards NGC 4945 with that from NGC 253 and towards the Galactic giant molecular cloud G 1.6-0.025. [ABSTRACT FROM AUTHOR]

We have used the Australia Telescope Compact Array (ATCA) to undertake the first high-angular-resolution observations of 37.7-GHz (7−2 → 8−1 E) methanol masers towards a sample of 11 high-mass star formation regions which host strong 6.7-GHz methanol masers. The 37.7-GHz methanol sites are coincident to within the astrometric uncertainty (0.4 arcsec) with the 6.7-GHz methanol masers associated with the same star formation region. However, spatial and spectral comparison of the 6.7- and 37.7-GHz maser emission within individual sources shows that the 37.7-GHz masers are less often, or to a lesser degree co-spatial than are the 12.2-GHz and 6.7-GHz masers. We also made sensitive, high-angular-resolution observations of the 38.3- and 38.5-GHz class II methanol transitions (62 → 53A− and 62 → 53A+, respectively) and the 36.2-GHz (4−1 → 30 E) class I methanol transition towards the same sample of 11 sources. The 37.7-, 38.3-, and 38.5-GHz methanol masers are unresolved in the current observations, which implies a lower limit on the brightness temperature of the strongest masers of more than 106 K. We detected the 38.3-GHz methanol transition towards seven sources, five of which are new detections and detected the 38.5-GHz transition towards six sources, four of which are new detections. We detected 36.2-GHz class I methanol masers towards all 11 sources, 6 of these are new detections for this transition, of which 4 sources do not have previously reported class I methanol masers from any transition. [ABSTRACT FROM AUTHOR]

We have compared the occurrence of 6.7- and 12.2-GHz methanol masers with 22-GHz water masers and 6035-MHz excited-state OH masers in the 100 deg2 region of the southern Galactic plane common to the Methanol Multibeam and H2O southern Galactic Plane Surveys. We find the most populous star formation species to be 6.7-GHz methanol, followed by water, then 12.2-GHz and, finally, excited-state OH masers. We present association statistics, flux density (and luminosity where appropriate) and velocity range distributions across the largest, fully surveyed portion of the Galactic plane for four of the most common types of masers found in the vicinity of star formation regions. Comparison of the occurrence of the four maser types with far-infrared dust temperatures shows that sources exhibiting excited-state OH maser emission are warmer than sources showing any of the other three maser types. We further find that sources exhibiting both 6.7- and 12.2-GHz methanol masers are warmer than sources exhibiting just 6.7-GHz methanol maser emission. These findings are consistent with previously made suggestions that both OH and 12.2-GHz methanol masers generally trace a later stage of star formation compared to other common maser types. [ABSTRACT FROM AUTHOR]

We present the results of the first complete unbaised survey of the Galactic plane for 6035-MHz excited-state hydroxyl (ex-OH) masers undertaken as part of the methanol multibeam (MMB) survey. These observations cover the Galactic longitude ranges 186°< l < 60° including the Galactic Centre. We report the detection of 127 ex-OH masers within the survey region, 47 being new sources. The positions of new detections were determined from interferometric observations with the Australia Telescope Compact Array. We discuss the association of 6035- MHz masers in our survey with the 6668-MHz masers from theMMBSurvey, finding 37 likely CH3OH-ex-OH maser pairs with physical separations of ≤0.03 pc and 55 pairings separated by ≤0.1 pc. Using these we calculate for the first time an ex-OH maser lifetime of between 3.3 × 10³ and 8.3 × 10³ yr. We also discuss the variability of the 6035-MHz masers and detection rates of counterpart 6030-MHz ex-OH masers (28 per cent of our sample having detection at both frequencies). [ABSTRACT FROM AUTHOR]

This is the fourth and final instalment of a series of catalogues presenting 12.2-GHz methanol maser observations made towards each of the 6.7-GHz methanol masers detected in the Methanol Multibeam (MMB) survey. This final portion of the survey covers the 20°-60° longitude range, increasing the 12.2-GHz follow-up range to the full MMB coverage of 186° ≥ l ≤ 60° and |b| ≤ 2°. Towards a total of 260 6.7-GHz MMB methanol masers (we were unable to observe five of the MMB sources in this longitude range) we detect 116 12.2-GHz masers counterparts, 64 of which were discovered in this survey. Including data from the literature, we find that there are 12.2-GHz methanol masers towards 47.1 per cent of the 6.7-GHz methanol masers in this portion of the Galaxy. Across the entire MMB survey range, we find a detection rate of 45.3 per cent. We find that the detection rate of 12.2-GHz methanol masers as a function of Galactic longitude is not uniform and there is an excess of masers with broad velocity ranges at longitudes near 30° and 330°. Comparing the occurrence of 12.2-GHz methanol masers with MMB-targeted CO observations has shown that those outflows associated with a 12.2-GHz source have a larger average dynamical time-scale than those associated with only 6.7-GHz methanol masers, supporting the notion that the 12.2-GHz masers are associated with a later phase of high-mass star formation. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We present a continuing study of a sample 44 molecular outflows, observed in 13CO lines, closely associated with 6.7-GHz methanol masers, hence called methanol maser associated outflows (MMAOs).We compare MMAO properties with those of outflows from other surveys in the literature. In general, MMAOs follow similar trends, but show a deficit in number at low masses and momenta, with a corresponding higher fraction at the high end of the distributions. A similar trend is seen for the dynamical time-scales of MMAOs. We argue that the lack of relatively low mass and young flows in MMAOs is due to the inherent selection-bias in the sample, i.e. its direct association with 6.7-GHz methanol masers. This implies that methanol masers must switch on after the onset of outflows (hence accretion), and not before a sufficient abundance of methanol is liberated from icy dust mantles. Consequently the average dynamical age of MMAOs is older than for the general population of molecular outflows. We propose an adjusted evolutionary sequence of outflow and maser occurrence in the hot core phase, where methanol masers turn on after the onset of the outflow phase. [ABSTRACT FROM AUTHOR]

We have selected the positions of 54 6.7 GHz methanol masers from the Methanol Multibeam Survey catalogue, covering a range of longitudes between 20° and 34° of the Galactic plane. These positions were mapped in the J = 3-2 transition of both the 13CO and C18O lines. A total of 58 13CO emission peaks are found in the vicinity of these maser positions. We search for outflows around all 13CO peaks, and find evidence for high-velocity gas in all cases, spatially resolving the red and blue outflow lobes in 55 cases. Of these sources, 44 have resolved kinematic distances, and are closely associated with the 6.7 GHz masers, a subset referred to as Methanol Maser Associated Outflows (MMAOs). We calculate the masses of the clumps associated with each peak using 870 μm continuum emission from the ATLASGAL survey. A strong correlation is seen between the clump mass and both outflow mass and mechanical force, lending support to models in which accretion is strongly linked to outflow. We find that the scaling law between outflow activity and clump masses observed for low-mass objects, is also followed by the MMAOs in this study, indicating a commonality in the formation processes of low-mass and high-mass stars. [ABSTRACT FROM PUBLISHER]

The Australia Telescope Compact Array has been used to search for 22-GHz water masers towards the 119 6.7-GHz methanol masers detected in the Methanol MultiBeam survey between Galactic longitudes 6° and 20°; we find water masers associated with 55 (∼46 per cent). Methanol masers with associated water masers have a higher mean integrated luminosity than those without and there is a general trend for sources with more luminous 6.7-GHz methanol masers to be associated with more luminous water maser emission. We have inspected the GLIMPSE (Galactic Legacy Infrared Mid-plane Survey Extraordinaire) three colour images of the regions surrounding the masers and cross-matched the maser positions with existing catalogues of Extended Green Objects and infrared dark clouds. We find more Extended Green Objects at sites where both methanol and water masers are present than at sites with only methanol masers, but no significant difference in the fraction embedded within infrared dark clouds. Analysis of the 1.1-mm dust emission shows dust clumps associated with masers that have greater flux densities and higher column densities than those without. Dust clumps associated with both water and 6.7-GHz methanol masers are generally the most compact clumps followed by those associated with only methanol then the clumps without associated maser emission. We conclude that protostars with both methanol and water masers are often older than those with only methanol; however, we suggest that the evolutionary phase traced by water masers is not as well defined as for 6.7-GHz methanol masers. [ABSTRACT FROM PUBLISHER]

We present a study of the mid-infrared environments and association with star formation tracers of 6.7 GHz methanol masers taken from the Methanol Multi-Beam (MMB) survey. Our ultimate goal is to establish the mass of the host star and its evolutionary stage for each maser site. As a first step, the GLIMPSE survey of the Galactic plane is utilized to investigate the environment of 776 methanol masers and we find that while the majority of the masers are associated with mid-infrared counterparts, a significant fraction (17 per cent) are not associated with any detectable mid-infrared emission. A number of the maser counterparts are clearly extended with respect to the GLIMPSE point spread function and we implement an adaptive non-circular aperture photometry (ANCAP) technique to determine the fluxes of the maser counterparts. The ANCAP technique doubles the number of masers with flux information at all four wavelengths compared to the number of the corresponding counterparts obtained from the GLIMPSE Point Source Catalog. The colours of the maser counterparts are found to be very similar to the smaller study carried out by Ellingsen. The MMB masers are weakly associated with extended green objects and Red MSX Survey embedded sources (YSO and H ii region classifications) with 18 and 12 per cent of masers associated with these objects, respectively. The majority of MMB masers (60 per cent) have detectable GLIMPSE infrared counterparts but have not been identified with previously recognized tracers of massive star formation; this confirms that the MMB survey has the potential to identify massive star-forming regions independent of infrared selection. [ABSTRACT FROM PUBLISHER]

ABSTRACT We present the second portion of a catalogue of 12.2-GHz methanol masers detected towards 6.7-GHz methanol masers observed in the unbiased Methanol Multibeam (MMB) survey. Using the Parkes radio telescope we have targeted all 207 6.7-GHz methanol masers in the longitude range 186°-330° for 12.2-GHz counterparts. We report the detection of 83 12.2-GHz methanol masers, and one additional source which we suspect is thermal emission, equating to a detection rate of 40 per cent. Of the 83 maser detections, 39 are reported here for the first time. We discuss source properties, including variability and highlight a number of unusual sources. We present a list of 45 candidates that are likely to harbour methanol masers in the 107.0-GHz transition. [ABSTRACT FROM AUTHOR]

ABSTRACT We present a catalogue of 12.2-GHz methanol masers detected towards 6.7-GHz methanol masers observed in the unbiased Methanol Multibeam (MMB) survey in the longitude range 330° (through 360°) to 10°. This is the first portion of the catalogue which, when complete, will encompass all of the MMB detections. We report the detection of 185 12.2-GHz sources towards 400 6.7-GHz methanol maser targets, equating to a detection rate of 46 per cent. Of the 185 12.2-GHz detections, 118 are reported here for the first time. We draw attention to a number of 'special' sources, particularly those with emission at 12.2-GHz stronger than their 6.7-GHz counterpart, and conclude that these unusual sources are not associated with a specific evolutionary stage. [ABSTRACT FROM AUTHOR]

We report the results of a search for class II methanol masers at 37.7, 38.3, and 38.5 GHz toward a sample of 70 high-mass star formation regions. We primarily searched toward regions known to show emission either from the 107 GHz class II methanol maser transition, or from the 6.035 GHz excited OH transition. We detected maser emission from 13 sources in the 37.7 GHz transition, eight of these being new detections. We detected maser emission from three sources in the 38 GHz transitions, one of which is a new detection. We find that 37.7 GHz methanol masers are only associated with the most luminous 6.7 and 12.2 GHz methanol maser sources, which in turn are hypothesized to be the oldest class II methanol sources. We suggest that the 37.7 GHz methanol masers are associated with a brief evolutionary phase (of 1000-4000 years) prior to the cessation of class II methanol maser activity in the associated high-mass star formation region. [ABSTRACT FROM AUTHOR]

ABSTRACT We present results from the third portion of the Methanol Multibeam Galactic plane survey of masers at 6668 MHz. It covers the longitude range 330°-345°, yielding 198 masers, of which more than 40 per cent are new discoveries. The maser population in this longitude range is the densest anywhere in the Galaxy, with many sources delineating a large portion of the Norma spiral arm close to its tangent point, and a cluster defining the southern tangent point of the 3-kpc ring. Two sources lie outside the solar circle, on the far side of the Galaxy, more than 15 kpc away. [ABSTRACT FROM AUTHOR]

ABSTRACT We have conducted a sensitive water maser search with the Australia Telescope Compact Array towards 267 1.2-mm dust clumps presented in the literature. We combine our new observations with previous water maser observations to extend our sample to 294 1.2-mm dust clumps, towards which we detect 165 distinct water maser sites towards 128 1.2-mm dust clumps. Within the fields of our observations, we additionally find four water masers with no apparent associated 1.2-mm dust continuum emission. Our overall detection rate of 44 per cent appears to vary as a function of Galactic longitude. We find that there is an excellent correspondence between the locations of the detected water masers with the peak of the target 1.2-mm dust clump sources. As expected from previous similar studies, the water masers are chiefly detected towards the bigger, brighter and more massive 1.2-mm dust clumps. We find further evidence to suggest that the water masers tend to increase in flux density (and therefore luminosity), as well as velocity range, as the sources evolve. We also show that the current sample of water maser sources suffers less from evolutionary biases than previous targeted searches. We have compared the locations of the water masers with dust clumps which have a previously determined association with 6.7-GHz methanol masers and 8-GHz radio continuum. We find that the fraction of 1.2-mm dust clump sources in our sample that are associated only with water masers (41) is higher than that of the sources associated only with methanol masers (13). This suggests that water masers can be present at an even earlier evolutionary stage than 6.7-GHz methanol masers. Comparison of the water maser detection rates associated with different combinations of methanol maser and radio continuum, as well as those with neither tracer, shows that the highest detection rate is towards those sources which also exhibit methanol maser emission. We have tested a previously hypothesized model for water maser presence towards 1.2-mm dust clumps. We not only find water masers towards a high proportion of the clumps that the model predicts would have associated water masers, but also find a number of water masers towards sources with a low calculated probability. We propose that this is likely an artefact of the poorly determined distances to the sources. We suggest refinements and future work which will further constrain the nature of the driving sources associated with water masers. [ABSTRACT FROM AUTHOR]

We present definitive detection statistics for 12.2 GHz methanol masers toward a complete sample of 6.7 GHz methanol masers detected in the Methanol Multibeam survey south of declination -20°. In total, we detect 250 12.2 GHz methanol masers toward 580 6.7 GHz methanol masers. This equates to a detection rate of 43.1%, which is lower than that of previous significant searches of comparable sensitivity. Both the velocity ranges and the flux densities of the target 6.7 GHz sources surpass that of their 12.2 GHz companion in almost all cases. Eighty percent of the detected 12.2 GHz methanol maser peaks are coincident in velocity with the 6.7 GHz maser peak. Our data support an evolutionary scenario whereby the 12.2 GHz sources are associated with a somewhat later evolutionary stage than the 6.7 GHz sources devoid of this transition. Furthermore, we find that the 6.7 GHz and 12.2 GHz methanol sources increase in luminosity as they evolve. In addition to this, evidence for an increase in velocity range with evolution is presented. This implies that it is not only the luminosity but also the volume of gas conducive to the different maser transitions that increases as the sources evolve. Comparison with GLIMPSE mid-infrared sources has revealed a coincidence rate between the locations of the 6.7 GHz methanol masers and GLIMPSE point sources similar to that achieved in previous studies. Overall, the properties of the GLIMPSE sources with and without 12.2 GHz counterparts are similar. There is a higher 12.2 GHz detection rate toward those 6.7 GHz methanol masers that are coincident with extended green objects. [ABSTRACT FROM AUTHOR]

We report the first detection of a methanol maser in the A transition at 23.4 GHz, discovered during the HO southern Galactic Plane Survey (HOPS) with the 22-m Mopra Radio Telescope. In the region covered by HOPS, the 23.4-GHz maser was found at only one location, G0.16, which was also a prominent source of maser emission in the E series near 25 GHz. The Australia Telescope Compact Array (ATCA) was used to follow up these detections at high angular resolution and prove the maser nature of the observed emission. The analysis shows that the new methanol maser at 23.4 GHz is a class I maser, which has properties similar to the 9.9- and 25-GHz masers (i.e. traces strong shocks with higher than average temperature and density). All class I masers were found to originate at the same spatial location (within the measurement uncertainty of 0.5 arcsec) in the vicinity of the dominant infrared source, but at a clearly distinct position from nearby OH, HO and class II methanol masers at 6.7 GHz. All maser species are distributed approximately on a line, but it is not clear at present whether this has any physical significance. We also detected a weak (1.3 mJy) continuum source at 25 GHz near the OH maser (at the most northern site, associated with a class II methanol maser and an HO maser renowned for its extremely wide spread of velocity components). The continuum source has not been reported at lower frequencies and is therefore a candidate hypercompact H region. We also used the ATCA to find the strongest and only the fifth known 9.9-GHz maser towards G0.16 and another 23.4-GHz maser towards G0.06 not seen in HOPS. [ABSTRACT FROM AUTHOR]

ABSTRACT We have used the Australia Telescope Compact Array to survey the Galactic Centre for the 22-GHz transition of water. The survey provides an unbiased search for water masers within a 0.5 deg2 region about the Centre, and the small synthesized beam directly yields positions to arcsecond accuracy. The detected sources were re-observed 4 months later and showed considerable changes in their spectra, with two sources found in the follow-up that were not seen in the original survey, yielding a total of 27 maser detections. Comparison with methanol and OH surveys shows that, at current sensitivity levels, water masers greatly outnumber the other species. 12 of our maser detections had previously been reported, discovered during searches towards interesting targets in the survey area. The majority of our sources are quite weak, consistent with excitation by young massive stars mostly near the Galactic Centre. Our spectra reveal high-velocity outflows at one-quarter of the water maser sites, a statistic similar to sites in the remainder of the Galaxy. [ABSTRACT FROM AUTHOR]

We present the second portion of an unbiased survey of the Galactic plane for 6668-MHz methanol masers. This section of the survey spans the longitude range 6° to 20°. We report the detection of 119 maser sources, of which 42 are new discoveries. The masers are tightly constrained to the Galactic plane, with only four outside a latitude range of . This longitude region includes the brightest known 6668-MHz methanol maser, 9.621+0.196, as well as the two brightest newly discovered sources in the southern survey as a whole. We list all the sources associated with the 3-kpc arms within longitude and consider further candidates beyond 15° longitude. We identify three new sources associated with the Galactic bar and comment on the density of masers in relation to the bar orientation. [ABSTRACT FROM AUTHOR]

The Australia Telescope Compact Array has been used to measure positions with arcsecond accuracy for 379 masers at the 22-GHz transition of water. The principal observation targets were 202 OH masers of the variety associated with star formation regions (SFRs) in the Southern Galactic plane. At a second epoch, most of these targets were observed again, and new targets of methanol masers were added. Many of the water masers reported here are new discoveries and others had been reported, with position uncertainties exceeding 10 arcsec, from Parkes telescope single-dish observations many years ago. Variability in the masers is often acute, with very few features directly corresponding to those discovered two decades ago. Within our current observations, less than a year apart, spectra are often dissimilar, but positions at the later epoch, even when measured for slightly different features, mostly correspond to the detected maser site measured earlier, to within the typical extent of the whole site, of a few arcseconds. The precise water positions show that approximately 79 per cent (160 of 202) of the OH maser sites show coincident water maser emission, the best estimate yet obtained for this statistic; however, there are many instances where additional water sites are present offset from the OH target, and consequently less than half of the water masers coincide with a 1665-MHz ground-state OH maser counterpart. Our less uniform sample of methanol targets is not suitable for a full investigation of their association with water masers, but we are able to explore differences between the velocities of peak emission from the three species and quantify the typically larger deviations shown by water maser peaks from systemic velocities. Clusters of two or three distinct but nearby sites, each showing one or several of the principal molecular masing transitions, are found to be common. We also report the detection of ultracompact H ii regions towards some of the sites. In combination with an investigation of correlations with IR sources from the Spitzer Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) catalogue, these comparative studies allow further progress in the use of the maser properties to assign relative evolutionary stages in star formation to individual sites. [ABSTRACT FROM AUTHOR]

We report the results of a sensitive search for 12.2-GHz methanol maser emission towards a sample of eight high-mass star formation regions in the Large Magellanic Cloud (LMC) which have been detected in other maser transitions. We detected one source towards the star formation region N105a. This is the first detection of a 12.2-GHz methanol maser outside our Galaxy. We also made near-contemporaneous observations of the 6.7-GHz methanol and 22-GHz water masers towards these sources, resulting in the detection of water maser emission in six new sources, including one associated with the strongest 6.7-GHz maser in the Magellanic Clouds IRAS 6815. The majority of the maser sources are closely associated with objects identified as likely young stellar objects (YSO) on the basis of Spitzer Space Telescope observations. We find that the YSOs associated with masers tend to be more luminous and have redder infrared colours than the sample as a whole. Spectral energy distribution modelling of the YSOs shows that the masers are associated with sources of higher central mass, total luminosity and ambient density than the majority of YSOs in the LMC. This is consistent with the well-established relationship between luminous methanol and water masers and young, high-mass objects observed in the Galaxy. [ABSTRACT FROM AUTHOR]

We have conducted a Galactic plane survey of methanol masers at 6668 MHz using a seven-beam receiver on the Parkes telescope. Here we present results from the first part, which provides sensitive unbiased coverage of a large region around the Galactic Centre. Details are given for 183 methanol maser sites in the longitude range 345° through the Galactic Centre to 6°. Within 6° of the Galactic Centre, we found 88 maser sites, of which more than half (48) are new discoveries. The masers are confined to a narrow Galactic latitude range, indicative of many sources at the Galactic Centre distance and beyond, and confined to a thin disc population; there is no high-latitude population that might be ascribed to the Galactic bulge. Within 2° of the Galactic Centre the maser velocities all lie between −60 and , a range much smaller than the range observed in CO. Elsewhere, the maser with highest positive velocity occurs, surprisingly, near longitude 355° and is probably attributable to the Galactic bar. The maser with the most negative velocity is near longitude 346°, within the longitude–velocity locus of the near side of the ‘3-kpc arm’. It has the most extreme velocity of a clear population of masers associated with the near and far sides of the 3-kpc arm. Closer to the Galactic Centre the maser space density is generally low, except within 0.25 kpc of the Galactic Centre itself, the ‘Galactic Centre zone’, where it is 50 times higher, which is hinted at by the longitude distribution, and confirmed by the unusual velocities. [ABSTRACT FROM AUTHOR]

We report the results of a search for 12.2-GHz methanol maser emission, targeted towards 113 known 6.7-GHz methanol masers associated with 1.2-mm dust continuum emission. Observations were carried out with the Australia Telescope National Facility (ATNF) Parkes 64-m radio telescope in the period 2008 June 20–25. We detect 68 12.2-GHz methanol masers with flux densities in excess of our 5σ detection limit of 0.55 Jy, 30 of which are new discoveries. This equates to a detection rate of 60 per cent, similar to previous searches of comparable sensitivity. We have made a statistical investigation of the properties of the 1.2-mm dust clumps with and without associated 6.7-GHz methanol maser and find that 6.7-GHz methanol masers are associated with 1.2-mm dust clumps with high-flux densities, masses and radii. We additionally find that 6.7-GHz methanol masers with higher peak luminosities are associated with less dense 1.2-mm dust clumps than those 6.7-GHz methanol masers with lower luminosities. We suggest that this indicates that more luminous 6.7-GHz methanol masers are generally associated with a later evolutionary phase of massive star formation than less luminous 6.7-GHz methanol maser sources. Analysis of the 6.7-GHz associated 1.2-mm dust clumps with and without associated 12.2-GHz methanol maser emission shows that clumps associated with both class II methanol maser transitions are less dense than those with no associated 12.2-GHz methanol maser emission. Furthermore, 12.2-GHz methanol masers are preferentially detected towards 6.7-GHz methanol masers with associated OH masers, suggesting that 12.2-GHz methanol masers are associated with a later evolutionary phase of massive star formation. We have compared the colours of the Spitzer Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) point sources associated with the maser sources in the following two subgroups: 6.7-GHz methanol masers with and without associated 12.2-GHz methanol masers; and 6.7-GHz methanol masers with high- and those with low-peak luminosities. There is little difference in the nature of the associated GLIMPSE point sources in any of these subgroups, and we propose that the masers themselves are probably much more sensitive than mid-infrared data to evolutionary changes in the massive star formation regions that they are associated with. We present an evolutionary sequence for masers in high-mass star formation regions, placing quantitative estimates on the relative lifetimes for the first time. [ABSTRACT FROM AUTHOR]