Strategies for Detecting the Missing Hot Baryons in the Universe

Abstract

About 30-50% of the baryons in the local Universe are unaccounted for and are likely in a hot phase, 10^5.5-10^8 K. A hot halo (10^6.3 K) is detected around the Milky Way through the O VII and O VIII resonance absorption and emission lines in the soft X-ray band. Current instruments are not sensitive enough to detect this gas in absorption around other galaxies and galaxy groups, the two most likely sites. We show that resonant line absorption by this hot gas can be detected with current technology, with a collecting area exceeding about 300 cm^2 and a resolution R > 2000. For a few notional X-ray telescope configurations that could be constructed as Explorer or Probe missions, we calculate the differential number of O VII and O VIII absorbers as a function of equivalent width through redshift space, dN/dz. The hot halos of individual external galaxies produce absorption that should be detectable out to about their virial radii. For the Milky Way, one can determine the radial distribution of density, temperature, and metallicity, after making optical depth corrections. Spectroscopic observations can determine the rotation of a hot gaseous halo.

36 pages with 5 tables and 9 figures

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• Hot Extended Galaxy Halos Around Local L* Galaxies From Sunyaev-Zeldovich Measurements
• Detection of the Missing Baryons toward the Sightline of H1821+643
• Massive Black Holes from Dissipative Dark Matter
• Black Hole Growth and Feedback in Isolated Romulus25 Dwarf Galaxies
• The World Space Observatory Ultraviolet (WSO-UV), as a bridge to future UV astronomy
• The Milky Way's Hot Gas Kinematics: Signatures in Current and Future OVII Absorption Line Observations
• A hot gaseous galaxy halo candidate with Mg X absorption
• X-ray performance of critical-angle transmission grating prototypes for the Arcus mission
• Stellar Feedback and the Energy Budget of Late-Type Galaxies: Missing Baryons and Core Creation
• Monochromatic neutrino lines from sneutrino dark matter
• Limiting Spectral Resolution of a Reflection Grating Made via Electron-Beam Lithography
• The Hosts of X-ray Absorption Lines Toward AGNs
• Characterizing the Variable X-ray and UV-Optical Flux Behavior of Blazars
• Future Detections of the Warm-Hot Intergalactic Medium using Bright Power Law Sources with NewAthena