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Galactic All-Sky Survey (GASS)

The Galactic All-Sky Survey (GASS) provides comprehensive observations of the entire HI sky south of δ=0°. It captures data with an angular resolution of ~15' and a sensitivity of ~70 mK, covering velocity ranges from -450 km/s to +400 km/s with a spectral resolution of ~1 km/s. Over 1500 hours of observations were conducted within two years. The survey aims to study phenomena such as HI shells, the Galactic Fountain, and high-velocity clouds (HVCs). GSH 242-03+37, identified by Heiles (1979), is one of the largest HI shells discovered, revealing insights into the dynamics and structures of our galaxy.

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Galactic All-Sky Survey (GASS)

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  1. Galactic All-Sky Survey (GASS)

  2. GASS Observations • Entire HI sky south of =0 • Fully sampled • Angular resolution ~15’ • Sensitivity ~ 70 mK • Spectral resolution ~ 1 km/s • 450 km/s to 400 km/s • Scanning entire sky twice • ~1500 hours in 2 years Scientific Goals • HI Shells • Galactic Fountain, HVCs • Galactic Structure

  3. Galactic All-Sky Survey

  4. GSH 242-03+37 McClure-Griffiths et al., in prep

  5. GASS and GSH 242-03+37 • GSH 242-03+47 was discovered by Heiles (1979) • No further imaging, though obvious in LDS • One of the largest HI shells in the Galaxy • Distance: 3.5 kpc • Radius: 500 pc • Expansion velocity: 20 km/s • Expansion energy: 1054 ergs! • Break-outs above and below the plane • Capped above the plane at ~1 kpc • Amazingly similar morphology to GSH 277+00+36 • Instability modes at work?

  6. GSH 242-03+37 • Red: ROSAT 1/4 keV • Blue: HI from GASS • The Xray emission from the shell interior indicates that there is hot (~106 K) gas in the shell interior • Is this hot gas venting to the halo? • Sensitivity of ROSAT too low to tell

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