GASKAP—The Galactic ASKAP Survey

Dickey, John M.; McClure-Griffiths, N. M.; Gibson, Steven J.; Gómez, José F.; Imai, Hiroshi; Jones, P. A.; Stanimirović, Snežana; Loon, Jacco Th. van; Walsh, A. J.; Alberdi, A.; Anglada, Guillem; Uscanga, L.; Arce, Héctor G.; Bailey, Mandy; Begum, Ayesha; Wakker, Bart P.; Bekhti, N. Ben; Kalberla, P. M. W.; Winkel, B.; Bekki, Kenji; For, Bi-Qing; Staveley‐Smith, L.; Westmeier, T.; Burton, M. G.; Cunningham, M. R.; Dawson, J. R.; Ellingsen, S. P.; Diamond, P. J.; Green, J.A.; Hill, Alex S.; Koribalski, B. S.; McConnell, D.; Rathborne, Jill; Voronkov, M. A.; Douglas, K. A.; English, Jayanne; Ford, H. Alyson; Lockman, Felix J.; Foster, Tyler; Green, A.; Bland-Hawthorn, Joss; Gulyaev, Sergei; Hoare, M. G.; Joncas, G.; Kang, Ji-hyun; Kerton, C. R.; Koo, Bon‐Chul; Leahy, D. A.; Lo, Nadia; Migenes, V.; Nakashima, Jun-ichi; Zhang, Yong; Nidever, David L.; Peek, J. E. G.; Tafoya, Daniel; Wu, Tian; Wu, Dan

doi:10.1017/pasa.2012.003

Cited by 84 publications

(50 citation statements)

References 150 publications

(216 reference statements)

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“…We are planing to use the method presented in this paper in future Galactic H i absorption surveys and map the T s distribution across a large range of H i self-absorption clouds. One such an upcoming survey is the Galactic Australian SKA Pathfinder Survey (GASKAP; Dickey et al 2013) with the Australian Square Kilometre Array Pathfinder (ASKAP). GASKAP will map the plane of the Milky Way and the Magellanic system in H i and OH lines in high-spatial and high-frequency resolution.…”

Section: Discussionmentioning

confidence: 99%

Calibrating the HISA temperature: Measuring the temperature of the Riegel–Crutcher cloud

Dénes

McClure-Griffiths

Dickey

et al. 2018

Monthly Notices of the Royal Astronomical Society

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H i self absorption (HISA) clouds are clumps of cold neutral hydrogen (H i) visible in front of warm background gas, which makes them ideal places to study the properties of the cold atomic component of the interstellar medium (ISM). The Riegel-Crutcher (R-C) cloud is the most striking HISA feature in the Galaxy. It is one of the closest HISA clouds to us and is located in the direction of the Galactic Centre, which provides a bright background. High-resolution interferometric measurements have revealed the filamentary structure of this cloud, however it is difficult to accurately determine the temperature and the density of the gas without optical depth measurements. In this paper we present new H i absorption observations with the Australia Telescope Compact Array (ATCA) against 46 continuum sources behind the Riegel-Crutcher cloud to directly measure the optical depth of the cloud. We decompose the complex H i absorption spectra into Gaussian components using an automated machine learning algorithm. We find 300 Gaussian components, from which 67 are associated with the R-C cloud (0 < v LSR < 10 km s −1 , FWHM < 10 km s −1 ). Combining the new H i absorption data with H i emission data from previous surveys we calculate the spin temperature and find it to be between 20 and 80 K. Our measurements uncover a temperature gradient across the cloud with spin temperatures decreasing towards positive Galactic latitudes. We also find three new OH absorption lines associated with the cloud, which support the presence of molecular gas.

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Section: Discussionmentioning

confidence: 99%

Calibrating the HISA temperature: Measuring the temperature of the Riegel–Crutcher cloud

Dénes

McClure-Griffiths

Dickey

et al. 2018

Monthly Notices of the Royal Astronomical Society

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“…The large-scale distribution of 18-cm OH emission in the galaxy could shed light on the features of the galactic molecular ISM not revealed by conventional CO mapping observations. Future observations by the 500m FAST telescope (Li & Pan 2016), and the SKA (Dickey et al 2012) may help to reveal a portion of this dark molecular ISM content through OH absorption studies; however, the low excitation temperature of the 18-cm OH lines (Engelke & Allen 2018) remains an impediment to the straightforward interpretation of OH observations in the inner Galaxy in the presence of substantial ambient nonthermal continuum emission. An all-sky survey for OH emission in the outer Galaxy would not be hindered by the much weaker continuum of the galactic background there; however, an effective OH emission survey may be presently out of reach of current instruments owing to the long integration times required to obtain the necessary sensitivity.…”

Section: Discussionmentioning

confidence: 99%

The Structure of Dark Molecular Gas in the Galaxy. II. Physical State of “CO-dark” Gas in the Perseus Arm

Busch

Allen

Engelke

et al. 2019

ApJ

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We report the results from a new, highly sensitive (∆T mb ∼ 3mK) survey for thermal OH emission at 1665 and 1667 MHz over a dense, 9 x 9-pixel grid covering a 1 • × 1 • patch of sky in the direction of l = 105. • 00, b = +2. • 50 towards the Perseus spiral arm of our Galaxy. We compare our Green Bank Telescope (GBT) 1667 MHz OH results with archival 12 CO(1-0) observations from the Five College Radio Astronomy Observatory (FCRAO) Outer Galaxy Survey within the velocity range of the Perseus Arm at these galactic coordinates. Out of the 81 statistically-independent pointings in our survey area, 86% show detectable OH emission at 1667 MHz, and 19% of them show detectable CO emission. We explore the possible physical conditions of the observed features using a set of diffuse molecular cloud models. In the context of these models, both OH and CO disappear at current sensitivity limits below an A v of 0.2, but the CO emission does not appear until the volume density exceeds 100-200 cm −3 . These results demonstrate that a combination of low column density A v and low volume density n H can explain the lack of CO emission along sight lines exhibiting OH emission. The 18-cm OH main lines, with their low critical density of n * ∼ 1 cm −3 , are collisionally excited over a large fraction of the quiescent galactic environment and, for observations of sufficient sensitivity, provide an optically-thin radio tracer for diffuse H 2 .

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“…With both methods, we confirm that there is less power on smaller scales, corresponding to longer interferometer spacings, in a rough power law, but we do not trust the derived value of the power law slope, for the reasons above. We suggest that better statistical results for the high latitude H i power spectrum may be obtained with the GASKAP project (Dickey et al 2013) which will have a wider field of view and more antennas compared to the ATCA. Figure 4.…”

Section: Statistical Investigation Of the Pattern Of Foreground Ismmentioning

confidence: 99%

Exploring the pattern of the Galactic HI foreground of GRBs with the ATCA

Dénes

Jones

Tóth

et al. 2019

Monthly Notices of the Royal Astronomical Society

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The afterglow of a gamma ray burst (GRB) can give us valuable insight into the properties of its host galaxy. To correctly interpret the spectra of the afterglow we need to have a good understanding of the foreground interstellar medium (ISM) in our own Galaxy. The common practice to correct for the foreground is to use neutral hydrogen (H i) data from the Leiden/Argentina/Bonn (LAB) survey. However, the poor spatial resolution of the single dish data may have a significant effect on the derived column densities. To investigate this, we present new high-resolution H i observations with the Australia Telescope Compact Array (ATCA) towards 4 GRBs. We combine the interferometric ATCA data with single dish data from the Galactic All Sky Survey (GASS) and derive new Galactic H i column densities towards the GRBs. We use these new foreground column densities to fit the Swift XRT X-ray spectra and calculate new intrinsic hydrogen column density values for the GRB host galaxies. We find that the new ATCA data shows higher Galactic H i column densities compared to the previous single dish data, which results in lower intrinsic column densities for the hosts. We investigate the line of sight optical depth near the GRBs and find that it may not be negligible towards one of the GRBs, which indicates that the intrinsic hydrogen column density of its host galaxy may be even lower. In addition, we compare our results to column densities derived from far-infrared data and find a reasonable agreement with the H i data.

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GASKAP—The Galactic ASKAP Survey

Cited by 84 publications

References 150 publications

Calibrating the HISA temperature: Measuring the temperature of the Riegel–Crutcher cloud

Calibrating the HISA temperature: Measuring the temperature of the Riegel–Crutcher cloud

The Structure of Dark Molecular Gas in the Galaxy. II. Physical State of “CO-dark” Gas in the Perseus Arm

Exploring the pattern of the Galactic HI foreground of GRBs with the ATCA

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