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Register a new userStructual Study of Galactic Hot Gas toward Markarian 421 from X-Ray Absorption and Emission Lines
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We present a structural study of the hot ISM in the Galactic halo along the sight line toward the bright active galactic nucleus Mkn 421. The OVII and OVIII absorption lines were measured with the Low Energy Transmission Grating Spectrograph aboard Chandra toward Mkn 421, and the OVII and OVIII emission lines were observed in the adjacent fields of the sight line with the X-ray Imaging Spectrometer aboard Suzaku. We jointly analyzed the absorption and the emission spectra assuming exponential distributions of the gas temperature and density from the Galactic plane, and constrained the temperature and density at the plane to be $(3.2^{+0.6}_{-0.7})times 10^6,mathrm{K}$ and $(1.2^{+0.5}_{-0.4})times 10^{-3},mathrm{cm^{-3}}$, with the scale heights of $1.6^{+1.7}_{-0.7},mathrm{kpc}$ and $>2.8,mathrm{kpc}$ respectively. The results are consistent with those obtained in the LMC X-3 direction and the PKS 2155-304 direction, describing a thick disk-like hot gas with its height of a few kpc from the Galactic plane.
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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.
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Recently, with the Chandra X-ray Telescope we have detected several local X-ray absorption lines along lines-of-sight towards distant quasars. These absorption lines are produced by warm/hot gas located in local intergalactic space and/or in our Galaxy. I will present our observations and discuss the origin of the X-ray absorption and its implications in probing the warm/hot component of local baryons.
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