Limits on Hot Galactic Halo Gas from X-ray Absorption Lines

Abstract

Although the existence of large-scale hot gaseous halos around massive disk galaxies have been theorized for a long time, there is yet very little observational evidence. We report the Chandra and XMM-Newton grating spectral detection of OVII and NeIX Kalpha absorption lines along the sight-line of 4U 1957+11. The line absorption is consistent with the interstellar medium in origin. Attributing these line absorptions to the hot gas associated with the Galactic disk, we search for the gaseous halo around the Milky Way by comparing this sight-line with more distant ones (toward X-ray binary LMC X-3 and the AGN Mrk 421). We find that all the line absorptions along the LMC X-3 and Mrk 421 sight-lines are attributable to the hot gas in a thick Galactic disk, as traced by the absorption lines in the spectra of 4U~1957+11 after a Galactic latitude dependent correction. We constrain the OVII column density through the halo to be N(OVII) < 5E15 cm^{-2} (95% confidence limit), and conclude that the hot gas contribution to the metal line absorptions, if existing, is negligible.

4 pages, Accepted for publication in the ApJ Letters, no change except for fixing a typo in an author's name

References in corpus (6)

• The magnetic nature of disk accretion onto black holes
• X-Ray Absorption from the Milky Way Halo and the Local Group
• Where are the ``Missing'' Galactic Baryons?
• High-Resolution X-ray Spectroscopy of the Interstellar Medium II: Neon and Iron Absorption Edges
• An XMM-Newton Observation of the Massive Edge-on Sb Galaxy NGC 2613
• The density profiles of hot galactic halo gas

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• Disk Dominated States of 4U 1957+11: Chandra, XMM, and RXTE Observations of Ostensibly the Most Rapidly Spinning Galactic Black Hole
• Structual Study of Galactic Hot Gas toward Markarian 421 from X-Ray Absorption and Emission Lines
• The SRG/eROSITA diffuse soft X-ray background. I. The local hot bubble in the western Galactic hemisphere
• Looking through the photoionisation wake: Vela X-1 at ${\phi }_{\mathrm{orb}}\approx 0.75$ with Chandra/HETG
• NICER/NuSTAR Characterization of 4U 1957+11: A Near Maximally Spinning Black Hole Potentially in the Mass Gap
• Unusual X-ray Oxygen Line Ratios of SN 1987A Arising From the Absorption of Galactic Hot Interstellar Medium
• Spectral characteristics of the black hole binary 4U 1957+115: A multi-mission perspective