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

• Main Authors: Park, Sangwook, Finley, John P, Snowden, Steven L, Dame, Thomas M
• Format: Journal Article
• Language: English
• Published: 04-12-1996
• Subjects: Physics - Astrophysics of Galaxies; Physics - Cosmology and Nongalactic Astrophysics; Physics - Earth and Planetary Astrophysics; Physics - High Energy Astrophysical Phenomena; Physics - Instrumentation and Methods for Astrophysics; Physics - Solar and Stellar Astrophysics
• DOI: 10.48550/arxiv.astro-ph/9612039

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.