Campus, PAB 241
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 are 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 utilize Chandra LETG spectra of luminous AGN, along with previous redshift measurements of UV absorption line systems, and apply a stacking method to gain unparalleled sensitivity. Based on the stacked data, we probe the most abundant helium-like and hydrogen-like metal lines in the spectra of AGN. In addition, we constrain the contribution of the WHIM to the overall ! baryon budget.