Gass: The Parkes Galactic All-Sky Survey. I. Survey Description, Goals, and Initial Data Release

McClure-Griffiths, N. M.; Pisano, D. J.; Calabretta, M. R.; Ford, H. Alyson; Lockman, Felix J.; Staveley‐Smith, L.; Kalberla, P. M. W.; Bailin, Jeremy; Dedes, L.; Janowiecki, Steven; Gibson, Brad K.; Murphy, Tara; Nakanishi, Hiroyuki; Newton‐McGee, K.

doi:10.1088/0067-0049/181/2/398

Cited by 338 publications

(344 citation statements)

References 48 publications

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“…We used the GASS data (McClure-Griffiths et al 2009;Kalberla et al 2010) to investigate the LA structure. The analyzed area covers 70 • × 85 • degrees.…”

Section: Discussionmentioning

confidence: 99%

“…Observations and initial data processing of the survey were described by McClure-Griffiths et al (2009). We extracted data from the final data release (Kalberla et al 2010) that were corrected for stray radiation, instrumental effects, and radio-frequency interference (RFI).…”

Section: The Datamentioning

confidence: 99%

“…In this paper we focus on the Hi 21-cm emission distribution of the LA as observed with the Galactic All-Sky Survey (GASS, McClure-Griffiths et al 2009;Kalberla et al 2010). Assuming a linear distance of about 50 kpc from the Sun (Cioni et al 2000), single-dish radio telescopes like the Parkes 64-m dish offer a linear resolution of about 200 pc at Hi 21-cm wavelength.…”

Section: Introductionmentioning

confidence: 99%

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The four leading arms of the Magellanic Cloud system

Venzmer¹,

Kerp²,

Kalberla³

2012

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Context. The Magellanic Cloud system (MCS) interacts via tidal and drag forces with the Milky Way galaxy. Aims. Using the Parkes Galactic All-Sky Survey (GASS) of atomic hydrogen we explore the role of drag on the evolution of the so-called Leading Arm (LA).Methods. We present a new image recognition algorithm that allows us to differentiate features within a 3D data cube (longitude, latitude, radial velocity) and to parameterize individual coherent structures. We compiled an Hi object catalog of LA objects within an area of 70 • × 85 • (1.6 sr) of the LA region. This catalog comprises information of location, column density, line width, shape and asymmetries of the individual LA objects above the 4-σ threshold of ΔT b 200 mK.Results. We present evidence of a fourth arm segment (LA4). For all LA objects we find an inverse correlation of velocities v GSR in Galactic Standard of Rest frame with Magellanic longitude. High-mass objects tend to have higher radial velocities than low-mass ones. About 1/4 of all LA objects can be characterized as head-tail (HT) structures. Conclusions. Using image recognition with objective criteria, it is feasible to isolate most of LA emission from the diffuse Milky Way Hi gas. Some blended gas components (we estimate 5%) escape detection, but we find a total gas content of the LA that is about 50% higher than previously assumed. These methods allow the deceleration of the LA clouds to be traced towards the Milky Way disk by drag forces. The derived velocity gradient strongly supports the assumption that the whole LA originates entirely in the Large Magellanic Cloud (LMC). LA4 is observed opposite to LA1, and we propose that both arms are related, spanning about 52 kpc in space. HT structures trace drag forces even at tens of kpc altitudes above the Milky Way disk.

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“…We used the GASS data (McClure-Griffiths et al 2009;Kalberla et al 2010) to investigate the LA structure. The analyzed area covers 70 • × 85 • degrees.…”

Section: Discussionmentioning

confidence: 99%

Section: The Datamentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The four leading arms of the Magellanic Cloud system

Venzmer¹,

Kerp²,

Kalberla³

2012

A&A

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“…Such high spatial resolution data do not exist. The Galactic All Sky Survey, GASS (McClure-Griffiths et al 2009), has a resolution of only 16 , which does not help for our investigation. ATCA interferometric 21 cm data on the other hand are only available for velocities v > 30 km s −1 .…”

Section: It Would Have Been Favourable If the H I Column Densitiesmentioning

confidence: 99%

Interstellar absorptions towards the LMC:

Nasoudi-Shoar¹,

Richter

Boer³

et al. 2010

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Observations show that the interstellar medium (ISM) contains sub-structure on scales less than 1 pc, detected in the form of spatial and temporal variations in column densities or optical depth. Despite the number of detections, the nature and ubiquity of the smallscale structure in the ISM is not yet fully understood. We use UV absorption data mainly from the Far Ultraviolet Spectroscopic Explorer (FUSE) and partly from the Space Telescope Imaging Spectrograph (STIS) of six Large Magellanic Cloud (LMC) stars (Sk -67 • 111, LH 54-425, Sk -67 • 107, Sk -67 • 106, Sk -67 • 104, and Sk -67 • 101) that are all located within 5 of each other, and analyse the physical properties of the Galactic disc gas in front of the LMC on sub-pc scales. We analyse absorption lines of a number of ions within the UV spectral range. Most importantly, interstellar molecular hydrogen, neutral oxygen, and fine-structure levels of neutral carbon have been used in order to study changes in the density and the physical properties of the Galactic disc gas over small angular scales. At an assumed distance of 1 kpc, the 5 separation between Sk -67 • 111 and Sk -67 • 101 implies a linear extent of 1.5 pc.We report on column densities of H 2 , C i, N i, O i, Al ii, Si ii, P ii, S iii, Ar i, and Fe ii in our six lines of sight, as well as C i*, C i**, Mg ii, Si iv, S ii, Mn ii, and Ni ii for four of them. While most species do not show any significant variation in their column densities, we find an enhancement of almost 2 dex for H 2 from Sk -67 • 111 to Sk -67 • 101, accompanied by only a small variation in the O i column density. Based on the formation-dissociation equilibrium, we trace these variations to the actual density variations in the molecular gas. On the smallest spatial scale of <0.08 pc, between Sk -67 • 107 and LH 54-425, we find a gas density variation of a factor of 1.8. The line of sight towards LH 54-425 does not follow the relatively smooth change seen from Sk -67 • 101 to Sk -67 • 111, suggesting that sub-structure might exist on a smaller spatial scale than the linear extent of our sight-lines. The results show that we sample a mix of both neutral and ionised gas in our six lines of sight. Towards Sk -67 • 101 to Sk -67 • 107, we derive the temperature T exc 70 K for the inner self-shielded part of the gas based on the rotational excitation levels of H 2 , and an average density of n H 60 cm −3 , typical of that for CNM. The gas towards LH 54-425 and Sk -67 • 111 shows different properties, and T exc 200 K. Our observations suggest that the detected H 2 in these six lines of sight (with the extent of <1.5 pc) is not necessarily physically connected, but that we are sampling molecular cloudlets with pathlengths <0.1−1.8 pc and possibly different densities.

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“…The robust polynomial fitting algorithm used by livedata has been described by McClure-Griffiths et al (2009). In this instance an initial mask 41 channels wide was set to exclude Galactic HI emission.…”

Section: Ghz Radio Continuummentioning

confidence: 99%