ORCID Profile
0000-0002-1363-5457
Current Organisation
University of Tasmania
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Publisher: Oxford University Press (OUP)
Date: 03-2006
Publisher: Oxford University Press (OUP)
Date: 22-10-2021
Abstract: 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 ex le of a 23.4-GHz class I methanol maser and the 11th ex le 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.
Publisher: Oxford University Press (OUP)
Date: 04-2010
Publisher: American Astronomical Society
Date: 10-08-2017
Publisher: American Astronomical Society
Date: 08-02-2012
Publisher: Oxford University Press (OUP)
Date: 04-2007
Publisher: Oxford University Press (OUP)
Date: 24-09-2010
Publisher: American Astronomical Society
Date: 10-06-2003
DOI: 10.1086/374862
Publisher: Elsevier BV
Date: 2000
Publisher: Springer Science and Business Media LLC
Date: 27-02-2023
Publisher: Oxford University Press (OUP)
Date: 17-03-2016
DOI: 10.1093/MNRAS/STW636
Publisher: American Astronomical Society
Date: 22-05-2017
Publisher: Oxford University Press (OUP)
Date: 29-04-2023
Abstract: We report the detection of ammonia masers in the non-metastable (6, 3), (7, 5), and (6, 5) transitions the latter being the first unambiguous maser detection of that transition ever made. Our observations include the first very long baseline interferometry detection of ammonia maser emission, which allowed effective constraining of the (6, 5) maser brightness temperature. The masers were detected towards G 358.931−0.030, a site of 6.7-GHz class II methanol maser emission that was recently reported to be undergoing a period of flaring activity. These ammonia masers appear to be flaring contemporaneously with the class II methanol masers during the accretion burst event of G 358.931−0.030. This newly detected site of ammonia maser emission is only the 12th such site discovered in the Milky Way. We also report the results of an investigation into the maser pumping conditions, for all three detected masing transitions, through radiative transfer calculations constrained by our observational data. These calculations support the hypothesis that the ammonia (6, 5) maser transition is excited through high colour temperature infrared emission, with the (6, 5) and (7, 5) transition line ratio implying dust temperatures & K. Additionally, we detect significant linearly polarized emission from the ammonia (6, 3) maser line. Alongside our observational and radiative transfer calculation results, we also report newly derived rest frequencies for the ammonia (6, 3) and (6, 5) transitions.
Publisher: American Astronomical Society
Date: 16-11-2018
Publisher: Springer Science and Business Media LLC
Date: 14-03-2013
Publisher: Oxford University Press (OUP)
Date: 15-08-1994
Publisher: American Astronomical Society
Date: 14-12-2007
DOI: 10.1086/527300
Publisher: Cambridge University Press (CUP)
Date: 2016
DOI: 10.1017/PASA.2016.48
Abstract: We have used the Australia Telescope Compact Array to search for a number of centimetre wavelength methanol transitions which are predicted to show weak maser emission towards star formation regions. Sensitive, high spatial, and spectral resolution observations towards four high-mass star formation regions which show emission in a large number of class II methanol maser transitions did not result in any detections. From these observations, we are able to place an upper limit of ≲ 1300 K on the brightness temperature of any emission from the 3 1 A + –3 1 A − , 17 −2 –18 −3 E ( v t = 1), 12 4 –13 3 A − , 12 4 –13 3 A + , and 4 1 A + –4 1 A − transitions of methanol in these sources on angular scales of 2 arcsec. This upper limit is consistent with current models for class II methanol masers in high-mass star formation regions and better constraints than those provided here will likely require observations with next-generation radio telescopes.
Publisher: American Astronomical Society
Date: 12-05-2020
Publisher: American Astronomical Society
Date: 02-2002
DOI: 10.1086/324383
Publisher: American Astronomical Society
Date: 20-11-1998
DOI: 10.1086/306373
Publisher: American Astronomical Society
Date: 28-07-2023
Abstract: We present the first results from the Southern Hemisphere Parallax Interferometric Radio Astrometry Legacy Survey: 10 μ as accurate parallaxes and proper motions for two Southern Hemisphere 6.7 GHz methanol masers obtained using the inverse MultiView calibration method. Using an array of radio telescopes in Australia and New Zealand, we measured trigonometric parallaxes and proper motions for the masers associated with the star formation region G232.62+00.99 of π = 0.610 ± 0.011 mas, μ x = −2.266 ± 0.021 mas yr −1 , and μ y = 2.249 ± 0.049 mas yr −1 , which implies its distance to be d = 1.637 ± 0.029 kpc. These measurements represent an improvement in accuracy by more than a factor of 3 over the previous measurements obtained through Very Long Baseline Array observations of the 12 GHz methanol masers associated with this region. We also measure the trigonometric parallax and proper motion for G323.74–00.26 as π = 0.364 ± 0.009 mas, μ x = −3.239 ± 0.025 mas yr −1 , and μ y = − 3.976 ± 0.039 mas yr −1 , which implies a distance of d = 2.747 ± 0.068 kpc. These are the most accurate measurements of trigonometric parallax obtained for 6.7 GHz class II methanol masers to date. We confirm that G232.62+00.99 is in the Local Arm and find that G323.74–00.26 is in the Scutum–Centaurus arm. We also investigate the structure and internal dynamics of both masers.
Publisher: Springer Science and Business Media LLC
Date: 04-0004
DOI: 10.1038/S41586-018-0001-X
Abstract: As pulsars lose energy, primarily in the form of magnetic dipole radiation, their rotation slows down accordingly. For some pulsars, this spin-down is interrupted by occasional abrupt spin-up events known as glitches
Publisher: IEEE
Date: 08-2014
Publisher: Oxford University Press (OUP)
Date: 18-07-2017
Publisher: American Astronomical Society
Date: 23-04-2015
Publisher: Oxford University Press (OUP)
Date: 07-10-2019
Abstract: We have constructed the largest s le of dust-associated class II 6.7 GHz methanol masers yet obtained. New measurements from the the Methanol MultiBeam (MMB) Survey were combined with the 870 $\\mu$m APEX Telescope Large Area Survey of the Galaxy (ATLASGAL) and the 850 $\\mu$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 s le 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 (Lbol/Mfwhm 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 yrs. 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.
Publisher: Oxford University Press (OUP)
Date: 21-01-2019
DOI: 10.1093/MNRAS/STZ192
Publisher: Cambridge University Press (CUP)
Date: 03-2007
DOI: 10.1017/S1743921307012999
Abstract: Interstellar masers are unique probes of the environments in which they arise. In studies of high-mass star formation their primary function has been as signposts of these regions and they have been used as probes of the kinematics and physical conditions in only a few sources. With a few notable exceptions, we know relatively little about the evolutionary phase the different maser species trace, nor their location with respect to other star formation tracers. While detailed studies of a small number of maser regions can reveal much about them, other information can only be obtained through large, systematic searches. In particular, such surveys are vital in efforts to determine an evolutionary sequence for the common maser species, and there is growing evidence that methanol masers may trace an earlier phase than the other common maser species of OH and water.
Publisher: Research Square Platform LLC
Date: 29-04-2021
DOI: 10.21203/RS.3.RS-402900/V1
Abstract: Theoretical models and numerical simulations suggest that high mass star (with mass 8 solar mass) can be formed either via monolithic collapse of a massive core or competitive accretion, but the dominant mechanism is currently unclear. Although recent high resolution observations with the Atacama Large Millimeter/submillimeter Array (ALMA) have detected physical and kinematic features, such as disks, outflows and filamentary structures surrounding the high mass young stellar objects (HMYSO), direct detection of the infalling gas towards the HMYSO is still the key to distinguish the different scenarios. Chemically fresh gas inflows have been detected towards low-mass stars being formed, which are consistent with the accretion-disk-outflow process. In this work we report the detection of a chemically fresh inflow which is feeding HMYSO growth in the nearby high mass star-forming region G352.63-1.07. High quality images of the dust and molecular lines from both ALMA and the Submillimeter Array (SMA) have consistently revealed a gravitationally-controlled gas inflow towards a rotating structure (disk or torus) around the HMYSO. The HMYSO is also observed to have an outflow, but it can be clearly separated from the inflow. These kinematic features provide observational evidence to support the conjecture that high-mass stars can be formed in a similar process to that observed in the low-mass counterparts. The chemically fresh infalling streamers could also be related with the disk configuration, fragmentation and accretion bursts that occur in both simulations and observations.
Publisher: American Astronomical Society
Date: 12-2005
DOI: 10.1086/497592
Publisher: American Astronomical Society
Date: 11-2004
DOI: 10.1086/424941
Publisher: Oxford University Press (OUP)
Date: 07-2009
Publisher: Oxford University Press (OUP)
Date: 21-07-2006
Publisher: American Astronomical Society
Date: 10-02-2006
DOI: 10.1086/498673
Publisher: American Astronomical Society
Date: 14-11-2011
Publisher: Oxford University Press (OUP)
Date: 30-06-2021
Abstract: The highly variable BL Lac object PKS B1144 − 379 was monitored at 6.7 GHz using the Ceduna Radio Telescope with high cadence from 2003 to 2011. Intraday variations due to interstellar scintillation (ISS) were observed throughout the period. To complement our earlier analysis of the ISS and variability of this object, we have investigated the physical origin of changes in the modality of flux density distributions, calculated for ∼14 d observing blocks. Our analysis shows that the flux density distribution is primarily bimodal, but it changes to unimodal during the core brightening and jet expansion phases of the source. The presence of unimodal flux density distributions during these two phases is most likely due to the compactness of the scintillating component and the intrinsic evolution of the source. The existence of unimodality in the flux density distributions associated with specific phases of the source evolution also suggests that changes in the modality are unlikely due to multiple scattering screens. We propose that the physical origin of changes in the modality of the flux density distribution for PKS B1144 − 379 is most likely due to the combination of multiple bright jet features with interstellar scintillation along the line of sight between observer and source. This new approach complements our previous investigations of the temporal evolution of PKS B1144 − 379 that used interstellar scintillation and very long baseline interferometry, and the combination of these techniques provides a crucial starting point for understanding the system.
Publisher: Oxford University Press (OUP)
Date: 17-01-2014
Publisher: Oxford University Press (OUP)
Date: 05-2010
Publisher: American Association for the Advancement of Science (AAAS)
Date: 05-01-2018
Abstract: Human malaria is caused by half a dozen species of Plasmodium protozoan parasites, each with distinctive biology. P. vivax , which causes relapsing malaria, specifically parasitizes immature red blood cells called reticulocytes. Gruszczyk et al. identified TfR1 (host transferrin receptor 1) as an alternative receptor for P. vivax . TfR1 binds to a specific P. vivax surface protein. However, the parasite that causes cerebral malaria, P. falciparum , does not share TfR1 as a receptor: P. falciparum could still infect cells in which TfR1 expression was knocked down, but P. vivax could not. Monoclonal antibodies to the P. vivax protein successfully hindered P. vivax infection of red blood cells. Science , this issue p. 48
Publisher: American Astronomical Society
Date: 30-08-2011
Publisher: Oxford University Press (OUP)
Date: 02-2010
Publisher: Oxford University Press (OUP)
Date: 04-1994
Publisher: American Astronomical Society
Date: 28-05-2015
Publisher: American Astronomical Society
Date: 03-2004
DOI: 10.1086/381957
Publisher: Japan Society for Aeronautical and Space Sciences
Date: 2009
DOI: 10.2322/TSTJ.7.TK_1
Publisher: Oxford University Press (OUP)
Date: 15-11-2019
Publisher: American Astronomical Society
Date: 05-12-2017
Publisher: American Astronomical Society
Date: 09-10-2012
Publisher: American Astronomical Society
Date: 03-09-2013
Publisher: Oxford University Press (OUP)
Date: 07-02-2014
DOI: 10.1093/MNRAS/STU032
Publisher: Oxford University Press (OUP)
Date: 21-09-2005
Publisher: American Astronomical Society
Date: 10-02-2020
Publisher: Oxford University Press (OUP)
Date: 11-05-2007
Publisher: American Geophysical Union (AGU)
Date: 04-2010
DOI: 10.1029/2009RS004203
Publisher: Oxford University Press (OUP)
Date: 05-11-2020
Abstract: 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).
Publisher: American Astronomical Society
Date: 06-2004
DOI: 10.1086/421001
Publisher: American Astronomical Society
Date: 12-2021
Abstract: We report the detection of a chemically fresh inflow that is feeding high-mass young-stellar-object (HMYSO) growth in the nearby high-mass star-forming region G352.63 made with both the Atacama Large Millimeter/submillimeter Array (ALMA) and the Submillimeter Array (SMA). High-quality images of the dust and molecular lines from both ALMA and SMA have consistently revealed a gravitationally controlled cold (∼10 K) gas inflow of chemically fresh molecules (e.g., CCH and HC 3 N) toward the central HMYSO and its surrounding dense gas structure, which has a possible torus- or disk-like morphology. The HMYSO is also observed to have an outflow, which is nearly perpendicular to the torus and its parental filament, and thus can be clearly separated from the inflows. These kinematic features provide observational evidence to support the conjecture that the infalling streamers in high-mass star-forming regions could proceed in a similar process to that observed in low-mass counterparts. The chemically fresh infalling streamers could also be involved in the disk or torus configuration, fragmentation, and accretion bursts that occur in both simulations and observations.
Publisher: Springer Science and Business Media LLC
Date: 16-03-2023
Publisher: Oxford University Press (OUP)
Date: 14-03-2022
Abstract: We present the full data release for the Southern Parkes Large-Area Survey in Hydroxyl (SPLASH), a sensitive, unbiased single-dish survey of the Southern Galactic Plane in all four ground-state transitions of the OH radical at 1612, 1665, 1667, and 1720 MHz. The survey covers the inner Galactic Plane, Central Molecular Zone, and Galactic Centre over the range |b| & 2°, 332$^{\circ }\, \lt l \lt $ 10°, with a small extension between 2$^{\circ }\, \lt b \lt $ 6°, 358$^{\circ }\, \lt l \lt $ 4°. SPLASH is the most sensitive large-scale survey of OH to-date, reaching a characteristic root-mean-square sensitivity of ∼15 mK for an effective velocity resolution of ∼0.9 km s−1. The spectral line datacubes are optimized for the analysis of extended, quasi-thermal OH, but also contain numerous maser sources, which have been confirmed interferometrically and published elsewhere. We also present radio continuum images at 1612, 1666, and 1720 MHz. Based on initial comparisons with 12CO(J = 1–0), we find that OH rarely extends outside CO cloud boundaries in our data, but suggest that large variations in CO-to-OH brightness temperature ratios may reflect differences in the total gas column density traced by each. Column density estimation in the complex, continuum-bright Inner Galaxy is a challenge, and we demonstrate how failure to appropriately model sub-beam structure and the line-of-sight source distribution can lead to order-of-magnitude errors. Anomalous excitation of the 1612 and 1720 MHz satellite lines is ubiquitous in the inner Galaxy, but is disabled by line overlap in and around the Central Molecular Zone.
Publisher: Oxford University Press (OUP)
Date: 06-2005
Publisher: Oxford University Press (OUP)
Date: 1995
Publisher: American Astronomical Society
Date: 05-2012
Publisher: Cambridge University Press (CUP)
Date: 08-2012
DOI: 10.1017/S1743921313000203
Abstract: Determining an evolutionary clock for high-mass star formation is an important step towards realizing a unified theory of star formation, as it will enable qualitative studies of the associated high-mass stars to be executed. Our recent studies have shown that masers have great potential to accurately trace the evolution of these regions. We have investigated the relative evolutionary phases associated with the presence of combinations of water, methanol and hydroxyl masers. Comparison between the characteristics of coincident sources has revealed strong evidence for an evolutionary sequence for the different maser species, a result that we now aim to corroborate through comparisons with chemical clocks. Using our new, large s les of methanol masers at 6.7 GHz (MMB survey Green et al. (2009)) and 12.2 GHz (Breen et al . 2012), 22 GHz water masers (Breen & Ellingsen 2012), OH masers together with complementary data, we find strong evidence that it is not only the presence or absence of the different maser species that indicates the evolutionary stage of the associated high-mass star formation region (see e.g. Breen et al . (2010)), but that the properties of those masers can give even finer evolutionary details. Most notably, the intensity and velocity range of detected maser emission increases as the star forming region evolves (Breen et al . 2011). Subsequent work we have undertaken (Ellingsen et al . 2011) has shown that the presence of rare 37.7 GHz methanol masers may signal the end of the methanol maser phase. They show that 37.7 GHz methanol masers are associated only with the most luminous 6.7 and 12.2 GHz methanol masers, which combined with the rarity of these objects is consistent with them being a short lived phase towards the end of the 6.7 GHz methanol maser lifetime. An independent confirmation of our maser evolutionary timeline can be gained through comparisons with chemical clocks. MALT90 is a legacy survey of 1000s of dense star forming cores at 90GHz, simultaneously observing 16 molecular lines with the Mopra radio telescope (see e.g. Foster et al . 2011). It provides the perfect dataset to test the maser evolutionary timeline due to the targeted lines and the fact that at least one-quarter of the MALT90 sources correspond to maser sites, providing a large enough s le for meaningful analysis. From our preliminary analysis, we find that star formation regions showing similar maser properties also show similar thermal line properties as would be expected if our evolutionary scenario were accurate.
Publisher: American Astronomical Society
Date: 13-09-2017
Publisher: Oxford University Press (OUP)
Date: 14-04-2016
DOI: 10.1093/GJI/GGW150
Publisher: American Astronomical Society
Date: 03-10-2006
DOI: 10.1086/507991
Publisher: Oxford University Press (OUP)
Date: 19-12-2016
Publisher: Oxford University Press (OUP)
Date: 06-06-2020
Publisher: American Astronomical Society
Date: 14-11-2014
Publisher: Springer Science and Business Media LLC
Date: 2005
Publisher: Oxford University Press (OUP)
Date: 11-05-2007
Publisher: Oxford University Press (OUP)
Date: 09-2007
Publisher: American Astronomical Society
Date: 10-01-1997
DOI: 10.1086/310434
Publisher: Oxford University Press (OUP)
Date: 14-02-2020
Abstract: The Methanol MultiBeam survey (MMB) provides the most complete s le 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 μm 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 μm 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.
Publisher: Oxford University Press (OUP)
Date: 04-07-2013
Publisher: Springer Science and Business Media LLC
Date: 13-01-2020
Publisher: EDP Sciences
Date: 02-2014
Publisher: Oxford University Press (OUP)
Date: 03-2005
Publisher: Oxford University Press (OUP)
Date: 02-2009
Publisher: American Astronomical Society
Date: 20-10-2002
DOI: 10.1086/342646
Publisher: Oxford University Press (OUP)
Date: 10-2004
Publisher: Oxford University Press (OUP)
Date: 16-03-2018
DOI: 10.1093/MNRAS/STY694
Publisher: Oxford University Press (OUP)
Date: 08-2014
Publisher: Oxford University Press (OUP)
Date: 08-11-2016
Publisher: Oxford University Press (OUP)
Date: 11-1998
Publisher: Cambridge University Press (CUP)
Date: 04-1995
DOI: 10.1017/S1323358000020026
Abstract: Sites of recent star formation often radiate strong maser emission from methanol transitions near 6-6 and 12 GHz. We have studied many of these masers over several years and find that intensity variations are common on both transitions. We present observations which demonstrate marked variability in 48 sources. We explore the characteristics of the variability and find it to be typically quasi-periodic, on a timescale of between a month and several years. The litude of the variation is most commonly less than a factor of two, but can reach factors of ten. The variability of different features in a source is usually independent. Variability of features seen at both 6·6 and 12 GHz is sometimes correlated, with larger litudes usually seen at 12 GHz. A likely inference is that variations are occasionally due to a change in the pump rate throughout the masing region, but most are consistent with a change in the masing path length due to large-scale motions. In addition, it is likely that the majority of 6·6-GHz masers are saturated whereas the 12-GHz masers may be somewhat less saturated.
Publisher: Oxford University Press (OUP)
Date: 07-2009
Publisher: Oxford University Press (OUP)
Date: 05-10-2011
Publisher: Oxford University Press (OUP)
Date: 11-10-2006
Publisher: American Astronomical Society
Date: 15-11-2010
Publisher: Informa UK Limited
Date: 02-2003
Publisher: Cambridge University Press (CUP)
Date: 03-2007
DOI: 10.1017/S1743921307012720
Abstract: We report the results of a blind search for 22 GHz water masers in two regions, covering approximately half a square degree, within the G 333.2–0.6 giant molecular cloud. The complete search of the two regions was carried out with the 26 m Mount Pleasant radio telescope and resulted in the detection of nine water masers, five of which are new detections. Australia Telescope Compact Array (ATCA) observations of these detections have allowed us to obtain positions with arcsecond accuracy, allowing meaningful comparison with infrared and molecular data for the region. We find that for the regions surveyed there are more water masers than either 6.7 GHz methanol, or main-line OH masers. The water masers are concentrated towards the central axis of the star formation region, in contrast to the 6.7 GHz methanol masers which tend to be located near the periphery. The colours of the GLIMPSE point sources associated with the water masers are slightly less red than those associated with methanol masers. Statistical investigation of the properties of the 13 CO and 1.2 mm dust clumps with and without associated water masers shows that the water masers are associated with the more massive, denser and brighter 13 CO and 1.2 mm dust clumps. We present statistical models that can predict those 13 CO and 1.2 mm dust clumps likely to have associated water masers.
Publisher: EDP Sciences
Date: 23-05-2003
Publisher: Cambridge University Press (CUP)
Date: 2012
DOI: 10.1017/S1743921312007120
Abstract: The Australia Telescope Compact Array has been used to observe all the 603 6.7 GHz methanol masers detected in the Methanol Multi-Beam survey between l = 310° - 20°. To date we have measured positions with arcsecond accuracy for all the observations in the l = 6° - 20°.
Publisher: American Astronomical Society
Date: 06-2022
Abstract: Very Long Baseline Interferometry (VLBI) astrometry is a well established technique for achieving ±10 μ as parallax accuracies at frequencies well above 10 GHz. At lower frequencies, uncompensated interferometer delays associated with the ionosphere play the dominant role in limiting the astrometric accuracy. Multiview is a novel VLBI calibration method, which uses observations of multiple quasars to accurately model and remove time-variable, directional-dependent changes to the interferometer delay. Here we extend the Multiview technique by phase-referencing data to the target source (“inverse Multiview”) and test its performance. Multiple observations with a four-antenna VLBI array operating at 8.3 GHz show single-epoch astrometric accuracies near 20 μ as for target–reference quasar separations up to about 7°. This represents an improvement in astrometric accuracy by up to an order of magnitude compared to standard phase-referencing.
Publisher: Oxford University Press (OUP)
Date: 11-05-1996
Publisher: American Astronomical Society
Date: 29-05-2019
Abstract: We report the detection of a new class I methanol maser candidate from the 5 2 −4 1 E transition (266.8 GHz). This methanol transition has been detected toward a nearby high-mass star-forming region G352.630-1.067 (distance ∼0.7 kpc), in Submillimeter Array (SMA) observations. The new candidate transition has a similar spatial distribution as the 4 2 −3 1 E (218.4 GHz) and 8 −1 −7 0 E (229.7 GHz) transitions, which are known class I maser transitions. Thermal methanol emission in this source is confined to a central hot core, while the three class I maser transitions are detected in two additional regions. These two maser-only emission regions are clearly associated with shocked gas traced by 2 μ m Ks -band and thermal v = 0, J = 5−4 SiO molecular emission. In contrast to the thermal methanol emission from the hot core, the three class I maser transitions show an positive trend in the rotation diagram for the two maser regions. Large velocity gradient modeling of the 266.8, 218.4, and 229.7 GHz transitions shows that the 266.8 GHz transition can be a maser for a wide range of conditions. The intensity ratios for the three methanol transitions detected in maser regions can be reproduced under conditions that are typical for class I methanol maser sites. These facts all support the hypothesis that the detected emission from the 266.8 GHz methanol (5 2 −4 1 E ) transition is masing.
Publisher: Oxford University Press (OUP)
Date: 09-2003
Publisher: Oxford University Press (OUP)
Date: 24-08-2011
Publisher: Cambridge University Press (CUP)
Date: 2012
DOI: 10.1017/S1743921312006837
Abstract: Determining an evolutionary clock for high-mass star formation is an important step towards realising a unified theory of star formation, as it will enable qualitative studies of the associated high-mass stars to be executed. We have carried out detailed studies of a large number of sources suspected of undergoing high-mass star formation and have found that common maser transitions offer the best opportunity to determine an evolutionary scheme for these objects. We have investigated the relative evolutionary phases of massive star formation associated with the presence or absence of combinations of water, methanol and main-line hydroxyl masers. The locations of the different maser species have been compared with the positions of 1.2 mm dust clumps, radio continuum, GLIMPSE point sources and Extended Green Objects. Comparison between the characteristics of coincident sources has revealed strong evidence for an evolutionary sequence for the different maser species in high-mass star formation regions. We present our proposed sequence for the presence of the common maser species associated with young high-mass stars and highlight recent advances. We discuss future investigations that will be made in this area by comparing data from the Methanol Multibeam (MMB) Survey with chemical clocks from the Millimetre Astronomy Legacy Team 90 GHz (MALT90) Survey.
Publisher: Springer Science and Business Media LLC
Date: 19-05-2010
Publisher: Oxford University Press (OUP)
Date: 17-04-2017
DOI: 10.1093/MNRAS/STX887
Publisher: Oxford University Press (OUP)
Date: 15-06-1995
Publisher: American Astronomical Society
Date: 17-03-2016
Publisher: Oxford University Press (OUP)
Date: 09-08-2018
Publisher: American Astronomical Society
Date: 31-01-2019
Publisher: American Astronomical Society
Date: 25-10-2018
Publisher: American Astronomical Society
Date: 03-06-2013
Publisher: Oxford University Press (OUP)
Date: 06-08-2014
Publisher: American Astronomical Society
Date: 04-2000
DOI: 10.1086/301283
Publisher: Oxford University Press (OUP)
Date: 23-03-2016
DOI: 10.1093/MNRAS/STW680
Publisher: American Astronomical Society
Date: 28-12-2017
Publisher: EDP Sciences
Date: 02-2022
DOI: 10.1051/0004-6361/202142811
Abstract: Context. Gravitational collapse is one of the most important processes in high-mass star formation. Compared with the classic blue-skewed profiles, redshifted absorption against continuum emission is a more reliable method to detect inward motions within high-mass star formation regions. Aims. We aim to test if methanol transitions can be used to trace infall motions within high-mass star formation regions. Methods. Using the Effelsberg-100 m, IRAM-30 m, and APEX-12 m telescopes, we carried out observations of 37 and 16 methanol transitions towards two well-known collapsing dense clumps, W31C (G10.6−0.4) and W3(OH), to search for redshifted absorption features or inverse P-Cygni profiles. Results. Redshifted absorption is observed in 14 and 11 methanol transitions towards W31C and W3(OH), respectively. The infall velocities fitted from a simple two-layer model agree with previously reported values derived from other tracers, suggesting that redshifted methanol absorption is a reliable tracer of infall motions within high-mass star formation regions. Our observations indicate the presence of large-scale inward motions, and the mass infall rates are roughly estimated to be ≳10 −3 M ⊙ yr −1 , which supports the global hierarchical collapse and clump-fed scenario. Conclusions. With the aid of bright continuum sources and the overcooling of methanol transitions leading to enhanced absorption, redshifted methanol absorption can trace infall motions within high-mass star formation regions hosting bright H II regions.
Publisher: American Astronomical Society
Date: 10-07-2012
Publisher: Oxford University Press (OUP)
Date: 02-1998
Publisher: American Astronomical Society
Date: 20-02-2020
Publisher: EDP Sciences
Date: 2012
Publisher: Oxford University Press (OUP)
Date: 10-10-2012
Publisher: American Astronomical Society
Date: 20-07-2017
Publisher: American Geophysical Union (AGU)
Date: 08-2015
DOI: 10.1002/2015JB012210
Publisher: Oxford University Press (OUP)
Date: 09-01-2023
Abstract: We present the first high spatial resolution radio continuum survey of the southern Galactic plane. The CORNISH project has mapped the region defined by 295° & l & 350° |b| & 1° at 5.5 GHz, with a resolution of 2.5 arcsec (FWHM). As with the CORNISH-North survey, this is designed to primarily provide matching radio data to the Spitzer GLIMPSE survey region. The CORNISH-South survey achieved a root mean square noise level of ∼0.11 mJy beam−1, using the 6A configuration of the Australia Telescope Compact Array (ATCA). In this paper, we discuss the observations, data processing and measurements of the source properties. Above a 7σ detection limit, 4701 sources were detected, and their ensemble properties show similar distributions with their northern counterparts. The catalogue is highly reliable and is complete to 90 per cent at a flux density level of 1.1 mJy. We developed a new way of measuring the integrated flux densities and angular sizes of non-Gaussian sources. The catalogue primarily provides positions, flux density measurements, and angular sizes. All sources with IR counterparts at 8 μm have been visually classified, utilizing additional imaging data from optical, near-IR, mid-IR, far-IR, and sub-millimetre galactic plane surveys. This has resulted in the detection of 524 H ii regions of which 255 are ultra-compact H ii regions, 287 planetary nebulae, 79 radio stars, and 6 massive young stellar objects. The rest of the sources are likely to be extragalactic. These data are particularly important in the characterization and population studies of compact ionized sources such as UCHII regions and PNe towards the Galactic mid-plane.
Publisher: American Astronomical Society
Date: 09-12-2016
Publisher: American Astronomical Society
Date: 15-12-2016
Publisher: Oxford University Press (OUP)
Date: 06-02-2012
Publisher: Oxford University Press (OUP)
Date: 25-06-2014
DOI: 10.1093/GJI/GGU183
Publisher: Informa UK Limited
Date: 08-2001
Publisher: American Astronomical Society
Date: 24-04-2009
Publisher: Oxford University Press (OUP)
Date: 29-02-2012
Publisher: Oxford University Press (OUP)
Date: 13-08-2013
Publisher: Cambridge University Press (CUP)
Date: 2012
DOI: 10.1017/S174392131200748X
Abstract: We review properties of all known collisionally pumped (class I) methanol maser series based on observations with the Australia Telescope Compact Array (ATCA) and the Mopra radio telescope. Masers at 36, 84, 44 and 95 GHz are most widespread, while 9.9, 25, 23.4 and 104 GHz masers are much rarer, tracing the most energetic shocks. A survey of many southern masers at 36 and 44 GHz suggests that these two transitions are highly complementary. The 23.4 GHz maser is a new type of rare class I methanol maser, detected only in two high-mass star-forming regions, G357.97-0.16 and G343.12-0.06, and showing a behaviour similar to 9.9, 25 and 104 GHz masers. Interferometric positions suggest that shocks responsible for class I masers could arise from a range of phenomena, not merely an outflow scenario. For ex le, some masers might be caused by interaction of an expanding H ii region with its surrounding molecular cloud. This has implications for evolutionary sequences incorporating class I methanol masers if they appear more than once during the evolution of the star-forming region. We also make predictions for candidate maser transitions in the ALMA frequency range.
Publisher: Oxford University Press (OUP)
Date: 26-04-2016
DOI: 10.1093/MNRAS/STW965
Publisher: Springer Science and Business Media LLC
Date: 13-07-2020
Publisher: Oxford University Press (OUP)
Date: 30-05-2001
Publisher: Springer Science and Business Media LLC
Date: 23-02-2014
Publisher: Oxford University Press (OUP)
Date: 30-01-2013
DOI: 10.1093/MNRAS/STS523
Publisher: American Astronomical Society
Date: 10-06-2001
DOI: 10.1086/321349
Publisher: Springer New York
Date: 2010
Publisher: Cambridge University Press (CUP)
Date: 2016
DOI: 10.1017/PASA.2016.13
Abstract: We applied three statistical classification techniques—linear discriminant analysis (LDA), logistic regression, and random forests—to three astronomical datasets associated with searches for interstellar masers. We compared the performance of these methods in identifying whether specific mid-infrared or millimetre continuum sources are likely to have associated interstellar masers. We also discuss the interpretability of the results of each classification technique. Non-parametric methods have the potential to make accurate predictions when there are complex relationships between critical parameters. We found that for the small datasets the parametric methods logistic regression and LDA performed best, for the largest dataset the non-parametric method of random forests performed with comparable accuracy to parametric techniques, rather than any significant improvement. This suggests that at least for the specific ex les investigated here accuracy of the predictions obtained is not being limited by the use of parametric models. We also found that for LDA, transformation of the data to match a normal distribution led to a significant improvement in accuracy. The different classification techniques had significant overlap in their predictions further astronomical observations will enable the accuracy of these predictions to be tested.
Publisher: Oxford University Press (OUP)
Date: 10-05-2016
Abstract: 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 the MMB Survey, 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 s le having detection at both frequencies).
Publisher: American Astronomical Society
Date: 30-08-2011
Publisher: Elsevier BV
Date: 07-2008
Publisher: American Astronomical Society
Date: 29-04-2011
Publisher: IOP Publishing
Date: 02-2019
Publisher: Oxford University Press (OUP)
Date: 05-09-2022
DOI: 10.1093/PASJ/PSAC067
Abstract: In 2019 September, a sudden flare of the 6.7 GHz methanol maser was observed toward the high-mass young stellar object (HMYSO) G24.33+0.14. This may represent the fourth detection of a transient mass accretion event in an HMYSO after S255IR NIRS3, NGC 6334I-MM1, and G358.93−0.03-MM1. G24.33+0.14 is unique among these sources as it clearly shows a repeating flare with an 8 yr interval. Using the Atacama Large Millimeter/submillimeter Array (ALMA), we observed the millimeter continuum and molecular lines toward G24.33+0.14 in the pre-flare phase in 2016 August (ALMA Cycle 3) and the mid-flare phase in 2019 September (ALMA Cycle 6). We identified three continuum sources in G24.33+0.14, and the brightest source, C1, which is closely associated with the 6.7 GHz maser emission, shows only a marginal increase in flux density with a flux ratio (Cycle 6$/$Cycle 3) of 1.16 ± 0.01, considering an additional absolute flux calibration uncertainty of $10\\%$. We identified 26 transitions from 13 molecular species other than methanol, and they exhibit similar levels of flux differences with an average flux ratio of 1.12 ± 0.15. In contrast, eight methanol lines observed in Cycle 6 are brighter than those in Cycle 3 with an average flux ratio of 1.23 ± 0.13, and the higher excitation lines tend to show a larger flux increase. If this systematic increasing trend is real, it would suggest radiative heating close to the central HMYSO due to an accretion event which could expand the size of the emission region and/or change the excitation conditions. Given the low brightness temperatures and small flux changes, most of the methanol emission is likely to be predominantly thermal, except for the 229.759 GHz (8−1–70 E) line known as a class I methanol maser. The flux change in the millimeter continuum of G24.33+0.14 is smaller than in S255IR NIRS3 and NGC 6334I-MM1 but is comparable with that in G358.93−0.03-MM1, suggesting different amounts of accreted mass in these events.
Publisher: American Geophysical Union (AGU)
Date: 06-2017
DOI: 10.1002/2017JB014141
Publisher: Oxford University Press (OUP)
Date: 03-1996
Publisher: Oxford University Press (OUP)
Date: 07-2011
Publisher: Oxford University Press (OUP)
Date: 02-09-2020
Abstract: The University of Tasmania Ceduna radio telescope has been used to investigate rapid variability in the radio flux density of the BL Lac object PKS B1144−379 at 6.7 GHz. High-cadence monitoring of this extreme scintillator was carried out over a period of approximately 9 yr, between 2003 and 2011. We have used structure functions created from the intensity time-series to determine the characteristic time-scale of the variability. The characteristic time-scale is consistently observed to increase during certain periods of each year, demonstrating the annual cycle expected for scintillation through an interstellar scattering screen. The best-fitting annual cycle model for each year suggests that the scintillation pattern has an anisotropic structure and that the upper limit of its scattering screen is at a distance of ∼0.84 kpc. Higher anisotropy in some of the annual cycle fits suggests that changes in the intrinsic source structure might be influencing the variability time-scale. We found a prominent annual cycle is only present in the variability time-scale for certain years, where other evidence suggests that the core is compact. From our measurements, we calculated that the core angular size varied between 5.65 and 15.90 μas (0.05–0.13 pc). The core component was found to be at its most compact during two flares in the total flux density, which were observed in 2005 and 2008. We conclude that the long-term variability in the radio flux density of PKS B1144−379 is due to intrinsic changes in the source and that these affect our ability to measure an annual cycle in its variability time-scale.
Publisher: Oxford University Press (OUP)
Date: 14-08-2017
Publisher: Oxford University Press (OUP)
Date: 13-07-2013
Publisher: Oxford University Press (OUP)
Date: 05-12-2017
Publisher: American Astronomical Society
Date: 03-2005
DOI: 10.1086/427399
Publisher: Springer Berlin Heidelberg
Date: 2007
Publisher: Oxford University Press (OUP)
Date: 20-05-2015
DOI: 10.1093/MNRAS/STV847
Publisher: Oxford University Press (OUP)
Date: 04-05-2010
Publisher: Oxford University Press (OUP)
Date: 21-04-2006
Publisher: Oxford University Press (OUP)
Date: 16-03-2013
Publisher: Oxford University Press (OUP)
Date: 09-08-2018
Publisher: American Astronomical Society
Date: 06-05-2011
Publisher: Cambridge University Press (CUP)
Date: 11-2009
DOI: 10.1017/S1743921310011786
Abstract: The methanol multi-beam (MMB) survey has produced the largest and most complete catalogue of Galactic 6.7-GHz methanol masers to date. 6.7-GHz methanol masers are exclusively associated with high-mass star formation, and as such provide invaluable insight into the Galactic distribution and properties of high-mass star formation regions. I present the statistical properties of the MMB catalogue and, through the calculation of kinematic distances, investigate the resolution of distance ambiguities and explore the Galactic distribution.
Publisher: Oxford University Press (OUP)
Date: 02-03-2011
Publisher: Oxford University Press (OUP)
Date: 20-02-2014
DOI: 10.1093/MNRAS/STU116
Publisher: Oxford University Press (OUP)
Date: 06-2002
Publisher: Oxford University Press (OUP)
Date: 17-03-2015
DOI: 10.1093/MNRAS/STV173
Publisher: Oxford University Press (OUP)
Date: 29-09-2020
Abstract: We have used catalogues from several Galactic plane surveys and dedicated observations to investigate the relationship between various maser species and Galactic star-forming clumps, as identified by the APEX Telescope Large Area Survey of the Galaxy (ATLASGAL) survey. The maser transitions of interest are the 6.7 and 12.2-GHz methanol masers, 22.2-GHz water masers, and the masers emitting in the four ground-state hyperfine structure transitions of hydroxyl. We find clump association rates for the water, hydroxyl and methanol masers to be 56, 39, and 82 per cent, respectively, within the Galactic longitude range of 60○ & ℓ & −60○. We investigate the differences in physical parameters between maser associated clumps and the full ATLASGAL s le, and find that clumps coincident with maser emission are more compact with increased densities and luminosities. However, we find the physical conditions within the clumps are similar for the different maser species. A volume density threshold of n(H2) & 104.1 cm−3 for the 6.7-GHz methanol maser found in our previous study is shown to be consistent across for all maser species investigated. We find limits that are required for the production of maser emission to be 500 L⊙ and 6 M⊙, respectively. The evolutionary phase of maser associated clumps is investigated using the L/M ratio of clumps coincident with maser emission, and these have similar L/M ranges (∼100.2−102.7 L⊙/M⊙) regardless of the associated transitions. This implies that the conditions required for the production of maser emission only occur during a relatively narrow period during a star’s evolution. Lower limits of the statistical lifetimes for each maser species are derived, ranging from ∼0.4−2 × 104 yr and are in good agreement with the ‘straw man’ evolutionary model previously presented.
Publisher: Cambridge University Press (CUP)
Date: 03-2007
DOI: 10.1017/S1743921307012616
Abstract: General characteristics of methanol (CH 3 OH) maser emission are summarized. It is shown that methanol maser sources are concentrated in the spiral arms. Most of the methanol maser sources from the Perseus arm are associated with embedded stellar clusters and a considerable portion is situated close to compact H II regions. Almost 1/3 of the Perseus Arm sources lie at the edges of optically identified H II regions which means that massive star formation in the Perseus Arm is to a great extent triggered by local phenomena. A multiline analysis of the methanol masers allows us to determine the physical parameters in the regions of maser formation. Maser modelling shows that class II methanol masers can be pumped by the radiation of the warm dust as well as by free-free emission of a hypercompact region (hcH II ) with a turnover frequency exceeding 100 GHz. Methanol masers of both classes can reside in the vicinity of hcH II s. Modelling shows that periodic changes of maser fluxes can be reproduced by variations of the dust temperature by a few percent which may be caused by variations in the brightness of the central young stellar object reflecting the character of the accretion process. Sensitive observations have shown that the masers with low flux densities can still have considerable lification factors. The analysis of class I maser surveys allows us to identify four distinct regimes that differ by the series of their brightest lines.
Publisher: Cambridge University Press (CUP)
Date: 2011
DOI: 10.1071/AS11029
Abstract: We have used the University of Tasmania Mt Pleasant 26-m radio telescope to investigate the polarisation characteristics of a s le of strong 6.7 GHz methanol masers, the first spectral line polarisation observations to be undertaken with this instrument. As part of this process we have developed a new technique for calibrating linear polarisation spectral line observations. This calibration method gives results consistent with more traditional techniques, but requires much less observing time on the telescope. We have made the first polarisation measurements of a number of 6.7 GHz methanol masers and find linear polarisation at levels from a few to 10% in most of the sources we observed, consistent with previous results. We also investigated the circular polarisation produced by Zeeman splitting in the 6.7 GHz methanol maser G9.62+0.20 to get an estimate of the line of sight magnetic field strength of 35±7 mG.
Publisher: Oxford University Press (OUP)
Date: 25-06-2010
Publisher: American Astronomical Society
Date: 06-05-2019
Publisher: American Astronomical Society
Date: 20-02-2020
Publisher: American Astronomical Society
Date: 20-11-1996
DOI: 10.1086/310353
Publisher: IEEE
Date: 08-2011
Publisher: American Astronomical Society
Date: 03-05-2013
Publisher: American Geophysical Union (AGU)
Date: 03-2019
DOI: 10.1029/2018JB016959
Publisher: Oxford University Press (OUP)
Date: 28-04-2013
DOI: 10.1093/MNRAS/STT558
Publisher: Oxford University Press (OUP)
Date: 08-02-2023
Abstract: We present broad-band radio flux-density measurements supernova (SN) 1996cr, made with MeerKAT, ATCA, and ALMA, and images made from very long baseline interferometry (VLBI) observations with the Australian Long Baseline Array. The spectral energy distribution of SN 1996cr in 2020, at age t ∼8700 d, is a power-law, with flux density, S ∝ ν−0.588 ± 0.011 between 1 and 34 GHz, but may steepen at & GHz. The spectrum has flattened since t = 5370 d (2010). Also since t = 5370 d, the flux density has declined rapidly, with $S_{\\rm 9 \\, GHz} \\propto t^{-2.9}$. The VLBI image at t = 8859 d shows an approximately circular structure with a central minimum reminiscent of an optically-thin spherical shell of emission. For a distance of 3.7 Mpc, the average outer radius of the radio emission at t = 8859 d was (5.1 ± 0.3) × 1017 cm, and SN 1996cr has been expanding with a velocity of 4650 ± 1060 km s−1 between t = 4307 and 8859 d. It must have undergone considerable deceleration before t = 4307 d. Deviations from a circular shell structure in the image suggest a range of velocities up to ∼7000 km s−1, and hint at the presence of a ring- or equatorial-belt-like structure rather than a complete spherical shell.
Publisher: Oxford University Press (OUP)
Date: 07-2004
Publisher: Oxford University Press (OUP)
Date: 07-2004
Publisher: Oxford University Press (OUP)
Date: 22-09-2021
Abstract: We have investigated the evolution of the BL Lac object PKS B1144−379 using the University of Tasmania Ceduna 30-m radio telescope at a frequency of 6.7 GHz and very long baseline interferometry (VLBI) data at 8.6 GHz. Variability time-scales associated with two flares detected in 2005 November and 2008 August were derived from long-term variations in total flux density monitored by Ceduna between 2003 and 2011. A kinematic study of the parsec-scale jet of PKS B1144−379 was performed using VLBI data obtained between 1997 and 2018. Quasi-periodic flarings with a period of ∼3–4 yr were observed. Over the 20-yr interval, the average jet position angle was found to be ~150°.
Publisher: American Astronomical Society
Date: 04-2005
DOI: 10.1086/428374
Publisher: American Astronomical Society
Date: 15-10-2010
Publisher: American Astronomical Society
Date: 03-1996
DOI: 10.1086/176924
Publisher: American Physical Society (APS)
Date: 29-12-2011
Publisher: EDP Sciences
Date: 07-2023
DOI: 10.1051/0004-6361/202346227
Abstract: Context. Class I methanol masers are known to be associated with shocked outflow regions around massive protostars, indicating a possible link between the maser properties and those of their host clumps. Aims. The main goals of this study are (1) to search for new class I methanol masers, (2) to statistically study the relationship between class I masers and shock tracers, (3) to compare the properties between class I masers and their host clumps, also as a function of their evolutionary stage, and (4) to constrain the physical conditions that excite multiple class I masers simultaneously. Methods. We analysed the 3 mm wavelength spectral line survey of 408 clumps identified by the APEX Telescope Large Area Survey of the Galaxy (ATLASGAL), which were observed with the IRAM 30-meter telescope, focusing on the class I methanol masers with frequencies near 84, 95, and 104.3 GHz. Results. We detect narrow maser-like features towards 54, 100, and 4 sources in the maser lines near 84, 95, and 104.3 GHz, respectively. Among them, 50 masers at 84 GHz, 29 masers at 95 GHz, and 4 rare masers at 104.3 GHz are new discoveries. The new detections increase the number of known 104.3 GHz masers from five to nine. The 95 GHz class I methanol maser is generally stronger than the 84 GHz maser counterpart. We find nine sources showing class I methanol masers, but no SiO emission, indicating that class I methanol masers might be the only signpost of protostellar outflow activity in extremely embedded objects at the earliest evolutionary stage. Class I methanol masers that are associated with sources that show SiO line wings are more numerous and stronger than those without such wings. The total integrated intensity of class I methanol masers is well correlated with the integrated intensity and velocity coverage of the SiO (2−1) emission. The properties of class I methanol masers are positively correlated with the bolometric luminosity, clump mass, and peak H 2 column density of their associated clumps, but are uncorrelated with the luminosity-to-mass ratio, dust temperature, and mean H 2 volume density. Conclusions. We suggest that the properties of class I masers are related to shocks traced by SiO. Based on our observations, we conclude that class I methanol masers at 84 and 95 GHz can trace a similar evolutionary stage to the H 2 O maser, and appear prior to 6.7 and 12.2 GHz methanol and OH masers. Despite their small number, the 104.3 GHz class I masers appear to trace a shorter and more evolved stage compared to the other class I masers.
Publisher: American Astronomical Society
Date: 04-2023
Abstract: We have conducted a systematic line survey, primarily focused on transitions of the methanol and ammonia molecules, and monitoring observations of masers toward the high-mass star-forming region NGC 6334I. These observations were undertaken between 2019 and 2022 in the C, K, Ka , and Q bands with the Tianma Radio Telescope. In total, 63 CH 3 OH (including 11 class I and nine class II maser or maser candidate), 18 13 CH 3 OH, and 34 NH 3 (including seven maser or maser candidate) transitions were detected. The emission is likely associated with the luminosity outburst source MM1. Rotation diagram analysis of multiple ammonia transitions shows that the gas temperature in the molecular core was a factor of 2 higher than that measured in previous observations in the pre-burst stage. This suggests that the molecular core has likely been heated by radiation originating from the luminosity outburst. Maser variability in the methanol and excited-state OH masers shows a general trend that the maser components associated with the luminosity outburst have decreased in their intensity since 2020. The decay in the maser luminosity indicates that the outburst is possibly declining, and as a result, the duration of the MM1 luminosity outburst may be shorter than the predicted 40 yr duration. Compared to the masers detected toward another luminosity outburst source, G358.93-0.03, abundant class I methanol masers and strong water maser flares were also detected toward NGC 633I, but masers from rare class II methanol transitions and new molecules were absent toward NGC 6334I. The large number of detections of maser transitions toward the two burst sources provided a database for further maser modeling to explore the physical environments associated with accretion burst events.
Publisher: American Astronomical Society
Date: 30-07-2019
Publisher: Oxford University Press (OUP)
Date: 27-02-2015
DOI: 10.1093/MNRAS/STV178
Publisher: Oxford University Press (OUP)
Date: 14-01-2013
DOI: 10.1093/MNRAS/STS621
Publisher: American Astronomical Society
Date: 02-04-2018
Publisher: American Astronomical Society
Date: 02-2022
Abstract: We report the detection of class I methanol maser at the 36.2 GHz transition toward the nearby starburst galaxy Maffei 2 with the Karl G. Jansky Very Large Array. Observations of the 36.2 GHz transition at two epochs separated by ∼4 yr show consistencies in both the spatial distribution and flux density of the methanol emission in this transition. Similar to the detections in other nearby starbursts the class I methanol masers sites are offset by a few hundred pc from the center of the galaxy and appear to be associated with the bar edges of Maffei 2. Narrow spectral features with line widths of a few km s −1 are detected, supporting the hypothesis that they are masing. Compared to other nearby galaxies with the detections in the 36.2 GHz methanol maser transition, the maser detected in Maffei 2 has about an order of magnitude higher isotropic luminosity, and thus represents the first confirmed detection of class I methanol megamasers. The spatial distribution of the 36.2 GHz maser spot clusters may trace the rotational gas flow of the galactic bar, providing direct evidence that the class I methanol maser is related to shocks induced by galactic bar rotation. A tentative detection in the 6.7 GHz class II methanol maser (at a 5 σ level) is also reported. This is comparable in luminosity to some of the 6.7 GHz maser sources detected in Galactic star-forming regions. The 6.7 GHz methanol emission appears to be associated with star formation activity in a smaller volume, rather than related to the larger-scale galactic activities.
Start Date: 2015
End Date: 2015
Funder: CSIRO-Commonwealth Scientific & Industrial Research Organisation
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End Date: 2015
Funder: Smithsonian Institution
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End Date: 2015
Funder: Australian Research Council
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End Date: 2015
Funder: Max Planck Institute for Radio Astronomy
View Funded ActivityStart Date: 2010
End Date: 2013
Funder: Australian Research Council
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End Date: 2015
Funder: Geoscience Australia
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End Date: 2015
Funder: Auckland University of Technology
View Funded ActivityStart Date: 2009
End Date: 2018
Funder: CSIRO-Commonwealth Scientific & Industrial Research Organisation
View Funded ActivityStart Date: 2005
End Date: 2005
Funder: Swinburne University of Technology
View Funded ActivityStart Date: 2006
End Date: 2009
Funder: CSIRO-Commonwealth Scientific & Industrial Research Organisation
View Funded ActivityStart Date: 2005
End Date: 2005
Funder: Geoscience Australia
View Funded ActivityStart Date: 2005
End Date: 2005
Funder: CSIRO-Atmospheric Research
View Funded ActivityStart Date: 2005
End Date: 2006
Funder: Australian Research Council
View Funded ActivityStart Date: 2005
End Date: 2005
Funder: Australian Research Council
View Funded ActivityStart Date: 2016
End Date: 2016
Funder: Australian Research Council
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