OH as a Probe of The Milky Way's Hidden Gas: First Results from SPLASH

AbstractSPLASH (the Southern Parkes Large-Area Survey in Hydroxyl) is a deep survey of ground-state OH absorption and emission from the Galactic Plane, as well as an unbiased search for OH masers. Key early results include the detection of a rich and complex distribution of diffuse, optically thin OH with strongly non-thermal excitation temperatures, and the detection of numerous new maser sources. The survey aims to use OH as a probe of CO-dark H2 ISM Galactic scales, with future plans including comprehensive comparisons with CO and Hi, as well as non-LTE excitation modelling of the four ground-state lines.

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ATLASGAL, the APEX Telescope Large Area Survey of the Galaxy

Proceedings of the International Astronomical Union ◽

10.1017/s1743921310011580 ◽

2009 ◽

Vol 5 (H15) ◽

pp. 780-780

Author(s):

F. Schuller ◽

K. M. Menten ◽

F. Wyrowski ◽

H. Beuther ◽

S. Bontemps ◽

...

Keyword(s):

Galactic Plane ◽

High Mass ◽

Current Status ◽

Continuum Emission ◽

Mass Star ◽

Large Area ◽

Submillimeter Wavelengths ◽

The Galaxy ◽

First Results ◽

Area Survey

AbstractSubmillimeter continuum emission traces high molecular column densities and, thus, dense cloud regions in which new stars are forming. Surveys of the Galactic plane in such emission have the potential of delivering an unbiased view of high-mass star formation throughout the Milky Way. Here we present the scope, current status and first results of ATLASGAL, an ongoing survey of the Galactic plane using the Large APEX Bolometer Camera (LABOCA) on the Atacama Pathfinder Experiment (APEX) telescope at the Chajnantor plateau in Chile. Aimed at mapping 360 square degrees at 870 μm, with a uniform sensitivity of 50 mJy/beam, this survey will provide the first unbiased sample of cold dusty clumps in the Galaxy at submillimeter wavelengths. These will be targets for molecular line follow-up observations and high resolution studies with ALMA and the EVLA.

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Modelled 3D distribution of OH/IR stars in the Galactic disc

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab176 ◽

2021 ◽

Vol 502 (2) ◽

pp. 3012-3020

Author(s):

Y Uno ◽

H Imai ◽

K Shinano ◽

H-H Qiao ◽

J R Dawson ◽

...

Keyword(s):

Simple Model ◽

Galactic Plane ◽

Phase 1 ◽

Galactic Disc ◽

Large Area ◽

Luminosity Functions ◽

Ir Stars ◽

The Galaxy ◽

Area Survey ◽

Maser Sources

ABSTRACT We have modelled the 3D distribution of OH/IR stars in the Galactic plane, traced by 1612 MHz OH maser sources with classic double horned spectral profiles. We statistically analysed over 700 maser sources detected by the HI/OH/Recombination line survey of the Milky Way (THOR) and the Australia Telescope Compact Array interferometric follow-up observations of the Southern Parkes Large-Area Survey in Hydroxyl (SPLASH). With a simple model constructed from a classical density distribution of stars and luminosity functions of OH maser sources in the Galaxy, we estimate the scale height, or the half thickness of the OH/IR star distribution along the Galactic disc to be 90–290 pc. The simple model also implies that there are ∼4000 OH/IR stars hosting 1612 MHz OH masers along the Galactic Plane. Therefore, next generation telescopes such as the Australian Square Kilometre Array Pathfinder (ASKAP) and SKA Phase 1 will detect about 80 per cent of such OH/IR stars in the Galaxy at a 10 mJy detection limit. Comparing the data of previously detected circumstellar 1612 MHz OH maser sources with those of THOR and SPLASH, the maser source lifetime is estimated to be ∼300 yr. This is likely a lower limit, since non-detections of masers in some cases could be affected by the flux variation of the maser source.

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Detailed distributions of the CO J = (2 − 1)/J = (1 − 0) intensity ratios toward a large area of the central molecular zone

Proceedings of the International Astronomical Union ◽

10.1017/s1743921314000295 ◽

2013 ◽

Vol 9 (S303) ◽

pp. 106-108

Author(s):

Kazufumi Torii ◽

Rei Enokiya ◽

Yasuo Fukui ◽

Hiroaki Yamamoto ◽

Akiko Kawamura ◽

...

Keyword(s):

Angular Resolution ◽

Galactic Center ◽

Galactic Plane ◽

Area Coverage ◽

High Angular Resolution ◽

Molecular Gas ◽

Large Area ◽

First Results ◽

Intensity Ratios ◽

Sgr A

AbstractWe present the first results of the new CO J = (2 − 1) observations toward the central molecular zone (CMZ) using the NANTEN2 telescope at an angular resolution of 100″. Large area coverage of 4° × 2° in l and b and a high angular resolution of 100″ enable us to investigate detailed structures of the molecular gas in the CMZ including peculiar molecular filaments perpendicularly to the Galactic plane to b > |0.5°|. The major components of the CMZ, e.g., Sgr A, Sgr B and Sgr C cloud complexes, show high CO J = (2 − 1)/J = (1 − 0) ratios around 0.9, indicating highly excited conditions of the molecular gas, while the local foreground components show less than 0.4. The molecular filaments show the typical ratios of 0.6–0.7 indicate that they are indeed located in the Galactic center.

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Current stage of the ATCA follow-up for SPLASH

Proceedings of the International Astronomical Union ◽

10.1017/s1743921317009747 ◽

2017 ◽

Vol 13 (S336) ◽

pp. 295-296

Author(s):

Hai-Hua Qiao ◽

Andrew J. Walsh ◽

Zhi-Qiang Shen

Keyword(s):

Ground State ◽

Supernova Remnants ◽

Unknown Origin ◽

High Accuracy ◽

Large Area ◽

Evolved Stars ◽

Area Survey ◽

Current Stage ◽

Compact Array

AbstractFour ground-state OH transitions were detected in emission, absorption and maser emission in the Southern Parkes Large-Area Survey in Hydroxyl (SPLASH). We re-observed these OH masers with the Australia Telescope Compact Array to obtain positions with high accuracy (~1 arcsec). According to the positions, we categorised these OH masers into different classes, i.e. star formation, evolved stars, supernova remnants and unknown origin. We found one interesting OH maser source (G336.644-0.695) in the pilot region, which has been studied in detail in Qiaoet al.(2016a). In this paper, we present the current stage of the ATCA follow-up for SPLASH and discuss the potential future researches derived from the ATCA data.

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ATLASGAL – physical parameters of dust clumps associated with 6.7 GHz methanol masers

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz2691 ◽

2019 ◽

Cited By ~ 2

Author(s):

S J Billington ◽

J S Urquhart ◽

C König ◽

T J T Moore ◽

D J Eden ◽

...

Keyword(s):

Galactic Plane ◽

Evolutionary Process ◽

Volume Density ◽

High Mass ◽

Physical Parameters ◽

Mass Star ◽

Large Area ◽

The Galaxy ◽

Area Survey ◽

Methanol Masers

Abstract We have constructed the largest sample 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 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 (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.

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ATLASGAL – relationship between dense star-forming clumps and interstellar masers

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2936 ◽

2020 ◽

Vol 499 (2) ◽

pp. 2744-2759

Author(s):

S J Billington ◽

J S Urquhart ◽

C König ◽

H Beuther ◽

S L Breen ◽

...

Keyword(s):

Galactic Plane ◽

Evolutionary Model ◽

Volume Density ◽

Physical Parameters ◽

Large Area ◽

Maser Emission ◽

Star Forming ◽

Area Survey ◽

Methanol Masers ◽

Water Masers

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 sample, 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.

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Ground-state OH maser distributions in the Galactic Centre region

Proceedings of the International Astronomical Union ◽

10.1017/s1743921316011765 ◽

2016 ◽

Vol 11 (S322) ◽

pp. 141-142 ◽

Cited By ~ 1

Author(s):

Hai-Hua Qiao ◽

Andrew J. Walsh ◽

Zhi-Qiang Shen ◽

Joanne R. Dawson

Keyword(s):

Star Formation ◽

Ground State ◽

Planetary Nebula ◽

Supernova Remnant ◽

High Accuracy ◽

Galactic Centre ◽

Large Area ◽

Area Survey ◽

Centre Region ◽

Compact Array

AbstractGround-state OH masers identified in the Southern Parkes Large-Area Survey in Hydroxyl were observed with the Australia Telescope Compact Array to obtain positions with high accuracy (~1 arcsec). We classified these OH masers into evolved star OH maser sites, star formation OH maser sites, supernova remnant OH maser sites, planetary nebula OH maser sites and unknown maser sites using their accurate positions. Evolved star and star formation OH maser sites in the Galactic Centre region (between Galactic longitudes of −5° to +5° and Galactic latitudes of −2° and +2°) were studied in detail to understand their distributions.

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The Rapid ASKAP Continuum Survey I: Design and first results

Publications of the Astronomical Society of Australia ◽

10.1017/pasa.2020.41 ◽

2020 ◽

Vol 37 ◽

Author(s):

D. McConnell ◽

C. L. Hale ◽

E. Lenc ◽

J. K. Banfield ◽

George Heald ◽

...

Keyword(s):

Spectral Index ◽

Spatial Resolution ◽

Western Australia ◽

Large Area ◽

Square Kilometre Array ◽

Sky Survey ◽

Data Release ◽

First Results ◽

Area Survey

Abstract The Rapid ASKAP Continuum Survey (RACS) is the first large-area survey to be conducted with the full 36-antenna Australian Square Kilometre Array Pathfinder (ASKAP) telescope. RACS will provide a shallow model of the ASKAP sky that will aid the calibration of future deep ASKAP surveys. RACS will cover the whole sky visible from the ASKAP site in Western Australia and will cover the full ASKAP band of 700–1800 MHz. The RACS images are generally deeper than the existing NRAO VLA Sky Survey and Sydney University Molonglo Sky Survey radio surveys and have better spatial resolution. All RACS survey products will be public, including radio images (with $\sim$ 15 arcsec resolution) and catalogues of about three million source components with spectral index and polarisation information. In this paper, we present a description of the RACS survey and the first data release of 903 images covering the sky south of declination $+41^\circ$ made over a 288-MHz band centred at 887.5 MHz.

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Investigation of the double-lobed sources of the Cygnus constellation core

Publications of the Astronomical Society of Australia ◽

10.1017/pasa.2021.43 ◽

2021 ◽

Vol 38 ◽

Author(s):

J. Saponara ◽

P. Benaglia ◽

I. Andruchow ◽

C. H. Ishwara-Chandra ◽

H. T. Intema

Keyword(s):

Spectral Index ◽

Angular Resolution ◽

Galactic Plane ◽

Central Nucleus ◽

Electromagnetic Spectrum ◽

Large Area ◽

X Ray ◽

First Results ◽

First Time ◽

Better Than

Abstract We present a collection of double-lobed sources towards a $20\,\mathrm{deg}^2$ area of the Cygnus region at the northern sky, observed at 325 and 610 MHz with the Giant Metrewave Radio Telescope. The 10 $^{\prime\prime}$ resolution achieved at 325 MHz is 5.5 times better than previous studies, while at 610 MHz, these are the first results ever of such a large area, mapped with 6 $^{\prime\prime}$ angular resolution. After a thorough visual inspection of the images at the two bands, we found 43 double-lobed source candidates, proposed as such due to the presence of 2 bright peaks, within a few arcminutes apart, joined by a bridge or a central nucleus. All but two are presented here as a double-lobed candidates for the first time. Thirty nine of the candidates were covered at both bands, and we provide the spectral index information for them. We have searched for positional coincidences between the detected sources/components and other objects from the literature, along the electromagnetic spectrum. Twenty-three candidates possess radio counterpart(s), 12 present infrared counterparts, and 1 showed an overlapping X-ray source. We analysed each candidate considering morphology, counterparts, and spectral indices. Out of the 43 candidates, 37 show characteristics compatible with an extragalactic nature, 2 of probably Galactic origin, 3 remain as dubious cases, though with feature(s) compatible with an extragalactic nature, and the remaining one, evidence of physically unrelated components. The median spectral index of the 40 putative extragalactic sources is $-1.0$ . Their celestial surface density at 610 MHz resulted in $1.9\,\mathrm{per\ deg}^2$ , across a region lying at the Galactic plane.

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