title: Discrete sources as the origin of the Galactic X-ray ridge emission.
abstract: An unresolved X-ray glow (at energies above a few kiloelectronvolts) was discovered about 25 years ago and found to be coincident with the Galactic disk-the Galactic ridge X-ray emission. This emission has a spectrum characteristic of a approximately 10(8) K optically thin thermal plasma, with a prominent iron emission line at 6.7 keV. The gravitational well of the Galactic disk, however, is far too shallow to confine such a hot interstellar medium; instead, it would flow away at a velocity of a few thousand kilometres per second, exceeding the speed of sound in the gas. To replenish the energy losses requires a source of 10(43) erg s(-1), exceeding by orders of magnitude all plausible energy sources in the Milky Way. An alternative is that the hot plasma is bound to a multitude of faint sources, which is supported by the recently observed similarities in the X-ray and near-infrared surface brightness distributions (the latter traces the Galactic stellar distribution). Here we report that at energies of approximately 6-7 keV, more than 80 per cent of the seemingly diffuse X-ray emission is resolved into discrete sources, probably accreting white dwarfs and coronally active stars.
authors.affiliation: Excellence Cluster Universe, Technische Universität München, 85748, Garching, Germany. mikej@mpa-garching.mpg.de
authors.forename: M
authors.initials: M
authors.lastname: Revnivtsev
authors.forename: S
authors.initials: S
authors.lastname: Sazonov
authors.forename: E
authors.initials: E
authors.lastname: Churazov
authors.forename: W
authors.initials: W
authors.lastname: Forman
authors.forename: A
authors.initials: A
authors.lastname: Vikhlinin
authors.forename: R
authors.initials: R
authors.lastname: Sunyaev