A huge reservoir of ionized gas around the milky way: Accounting for the missing mass?

A. Gupta, S. Mathur, Y. Krongold, F. Nicastro, M. Galeazzi

Research output: Contribution to journalArticlepeer-review

172 Scopus citations


Most of the baryons from galaxies have been "missing" and several studies have attempted to map the circumgalactic medium (CGM) of galaxies in their quest. We report on X-ray observations made with the Chandra X-Ray Observatory probing the warm-hot phase of the CGM of our Milky Way at about 106K. We detect O VII and O VIII absorption lines at z = 0 in extragalactic sight lines and measure accurate column densities using both Kα and Kβ lines of O VII. We then combine these measurements with the emission measure of the Galactic halo from literature to derive the density and the path length of the CGM. We show that the warm-hot phase of the CGM is massive, extending over a large region around the Milky Way, with a radius of over 100kpc. The mass content of this phase is over 10 billion solar masses, many times more than that in cooler gas phases and comparable to the total baryonic mass in the disk of the Galaxy. The missing mass of the Galaxy appears to be in this warm-hot gas phase.

Original languageEnglish (US)
Article numberL8
JournalAstrophysical Journal Letters
Issue number1
StatePublished - 2012


  • Galaxy: halo
  • X-rays: galaxies
  • cosmology: observations
  • intergalactic medium
  • quasars: absorption lines

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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