Article

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

The Astrophysical Journal Supplement Series (Impact Factor: 14.14). 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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    • "Easily detectable strong narrow-line interference was flagged during the basic data reduction with Livedata [5]. This kind of RFI occurs typically at fixed topocentric frequencies. "
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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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