Article

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

The Astrophysical Journal Supplement Series (Impact Factor: 11.22). 01/2009; 181(2). DOI: 10.1088/0067-0049/181/2/398
Source: arXiv

ABSTRACT

The Parkes Galactic All-Sky Survey (GASS) is a survey of Galactic atomic hydrogen (HI) emission in the Southern sky covering declinations $\delta \leq 1^{\circ}$ using the Parkes Radio Telescope. The survey covers $2\pi$ steradians with an effective angular resolution of ~16', at a velocity resolution of 1.0 km/s, and with an rms brightness temperature noise of 57 mK. GASS is the most sensitive, highest angular resolution survey of Galactic HI emission ever made in the Southern sky. In this paper we outline the survey goals, describe the observations and data analysis, and present the first-stage data release. The data product is a single cube at full resolution, not corrected for stray radiation. Spectra from the survey and other data products are publicly available online. Comment: 35 pages, 16 figures, accepted for publication in ApJS. Full resolution version available at ftp://ftp.atnf.csiro.au/pub/people/nmcclure/papers/GASS.1.ps.gz

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    • "More than 5000 galaxies have been detected and led to an accurate estimate of the HI mass function [2]. HIPASS was supplemented by a subsequent survey conducted with the Parkes telescope, the Galactic All Sky Survey (GASS, [3], [4]), which mapped the HI of the Milky Way Galaxy. For the Parkes surveys auto-correlators were used. "
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    ABSTRACT: We report on the current status of the Effelsberg-Bonn HI Survey, a new large-scale single-dish observing campaign to map the 21-cm line emission across the full northern hemisphere. Using state-of-the-art spectrometers it is feasible to survey the Milky Way Galaxy as well as the local universe within a single run. The improvement in terms of sensitivity, angular resolution, and data quality is demonstrated in comparison to present day datasets.
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    ABSTRACT: The GASS is a survey of Galactic atomic hydrogen (HI) emission in the southern sky observed with the Parkes 64-m Radio Telescope. With a sensitivity of 60 mK for a channel width of 1 km/s the GASS is the most sensitive and most accurate survey of the Galactic HI emission in the southern sky. We discuss RFI mitigation strategies that have been applied during the data reduction. Most of the RFI could be cleaned by using prior information on the HI distribution as well as statistical methods based on median filtering. Narrow line RFI spikes have been flagged during the first steps of the data processing. Most of these lines were found to be constant over long periods of time, such data were replaced by interpolating profiles from the Leiden/Argentine/Bonn (LAB) survey. Remaining RFI was searched for at any position by a statistical comparison of all observations within a distance of 0.1 deg. The median and mean of the line emission was calculated. In cases of significant deviations between both it was checked in addition whether the associated rms fluctuations exceeded the typical scatter by a factor of 3. Such data were replaced by the median, which is found to be least biased by RFI and other artifacts. The median estimator was found to be equivalent to the mean, which was obtained after rejecting outliers.
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    ABSTRACT: In the spectra of 139 early-type Large Magellanic Cloud (LMC) stars observed with FUSE and with deep radio Parkes HI 21-cm observations along those stars, we search for and analyze the absorption and emission from high-velocity gas at +90<v<+175 km/s. The HI column density of the high-velocity clouds (HVCs) along these sightlines ranges from <10^18.4 to 10^19.2 cm^-2. The incidence of the HVC metal absorption is 70%, significantly higher than the HI emission occurrence of 32%. We find that the mean metallicity of the HVC is [OI/HI] = -0.51 (+0.12,-0.16). There is no strong evidence for a large variation in the HVC metallicity, implying that thes e HVCs have a similar origin and are part of the same complex. The mean and scatter of the HVC metallicities are more consistent with the present-day LMC oxygen abundance than that of the Small Magellanic Cloud or the Milky Way. We find that on average [SiII/OI] = +0.48 (+0.15,- 0.25) and [FeII/OI] = +0.33 (+0.14,-0.21), implying that the HVC complex is dominantly ionized. The HVC complex has a multiphase structure with a neutral (OI, FeII), weakly ionized (FeII, NII), and highly ionized (OVI) components, and has evidence of dust but no molecules. All the observed properties of the HVC can be explained by an energetic outflow from the LMC. This is the first example of a large (>10^6 M_sun) HVC complex that is linked to stellar feedback occurring in a dwarf spiral galaxy. Comment: Accepted for publication in the ApJ
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