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Evidence for an X-ray Emitting Galactic Bulge: Shadows Cast by Distant Molecular Gas

Sangwook Park·John P. Finley·Steven L. Snowden·Thomas M. Dame
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Abstract

A mosaic of 7 ROSAT PSPC pointed observations in the direction of (l,b ~ 10,0 deg) reveals deep X-ray shadows in the 0.5-2.0 keV band cast by dense molecular gas. The comparison between the observed on-cloud and off-cloud X-ray fluxes indicates that ~43% of the diffuse X-ray background in this direction in both the 3/4 keV and 1.5 keV bands originates behind the molecular gas, which is located at 2-4 kpc from the Sun. Given the short mean free path of X-rays in the 3/4 keV band in the Galactic plane (~1 kpc assuming an average space density of 1 cm^-3), this large percentage of the observed flux which originates beyond the molecular gas most likely indicates a strong enhancement in the distribution of X-ray emitting gas in the Galactic center region, possibly associated with a Galactic X-ray bulge.

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Sangwook Park, John P. Finley, Steven L. Snowden, Thomas M. Dame. 1996-12-04. Evidence for an X-ray Emitting Galactic Bulge: Shadows Cast by Distant Molecular Gas. https://doi.org/10.1086/310501

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