Exploring the missing baryons using absorption studies
Abstract
In the low-redshift (z < 2) universe, about one-third of the baryons remain unaccounted for, which poses the long-standing missing baryon problem. The missing baryons are believed to reside in filaments connecting galaxies in the form of warm-hot intergalactic medium (WHIM). Although UV absorption studies explored the warm phase of the WHIM, it is hypothesized that notable fraction of the missing baryons is in the hot X-ray phase. However, X-ray spectroscopy is limited by the low effective area of currently available instrumentation, thus the conclusive observational evidence is still lacking. In this work, we used a novel approach and utilized Chandra LETG spectra of a luminous AGN, along with previous redshift measurements of UV absorption line systems, and applied a stacking method to gain unparalleled sensitivity. Based on the stacked data, we detect an OVII absorption line that exhibits a Gaussian line profile and is statistically significant at the 3.3 sigma level. Since the redshifts of the UV absorption line systems were known a priori, this is the first definitive detection of an X-ray absorption line originating from the WHIM. Based on this detection we constrain the contribution of the WHIM to the overall baryon budget.
- Publication:
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AAS/High Energy Astrophysics Division
- Pub Date:
- March 2019
- Bibcode:
- 2019HEAD...1740004B