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

The Astrophysical Journal Supplement Series (Impact Factor: 16.24). 01/2009; 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

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    ABSTRACT: We establish with certainty that the Magellanic Stream (MS) is some 40{sup 0} longer than previously known and that the entire MS and Leading Arm system is thus at least 200{sup 0} long. With the Green Bank Telescope (GBT), we conducted a {approx}200 deg{sup 2}, 21 cm survey at the tip of the MS to substantiate the continuity of the MS between the Hulsbosch and Wakker data and the MS-like emission reported by Braun and Thilker. Our survey, in combination with the Arecibo survey by Stanimirovic et al., shows that the MS gas is continuous in this region and that the MS is at least {approx}140{sup 0} long. The MS tip is composed of a multitude of forks and filaments. We identify a new filament on the eastern side of the MS that significantly deviates from the equator of the MS coordinate system for more than {approx}45{sup 0}. Additionally, we find a previously unknown velocity inflection in the MS tip near MS longitude L{sub MS} {approx}-120{sup 0} at which the velocity reaches a minimum and then starts to increase. We find that five compact high-velocity clouds cataloged by de Heij et al. as well as Wright's Cloud are plausibly associated with the MS because they match the MS in position and velocity. The mass of the newly confirmed {approx}40{sup 0} extension of the MS tip is {approx}2 x 10{sup 7} M{sub sun} (d/120 kpc){sup 2} (including Wright's Cloud increases this by {approx}50%) and increases the total mass of the MS by {approx}4%. However, projected model distances of the MS at the tip are generally quite large and, if true, indicate that the mass of the extension might be as large as {approx}10{sup 8} M{sub sun}. From our combined map of the entire MS, we find that the total column density (integrated transverse to the MS) drops markedly along the MS and follows an exponential decline with L{sub MS} of N{sub H{sub i}} = 5.9 x 10{sup 21}exp(L{sub MS}/19.{sup 0}3) cm{sup -2}. Under the assumption that the observed sinusoidal velocity pattern of the LMC filament of the MS is due to the origin of the MS from a rotating LMC, we estimate that the age of the {approx}140{sup 0} long MS is {approx}2.5 Gyr. This coincides with bursts of star formation in the Magellanic Clouds and a possible close encounter of these two galaxies with each other that could have triggered the formation of the MS. These newly observed characteristics of the MS offer additional constraints for MS simulations. In the Appendix, we describe a previously little discussed problem with a standing wave pattern in GBT H I data and detail a method for removing it.
    The Astrophysical Journal 11/2010; 723(2). · 6.73 Impact Factor

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