The Physical Origins of the Identified and Still Missing Components of the Warm–Hot Intergalactic Medium: Insights from Deep Surveys in the Field of Blazar 1ES1553+113

Abstract

The relationship between galaxies and the state/chemical enrichment of the warm–hot intergalactic medium (WHIM) expected to dominate the baryon budget at low- z provides sensitive constraints on structure formation and galaxy evolution models. We present a deep redshift survey in the field of 1ES1553+113, a blazar with a unique combination of ultraviolet (UV)+X-ray spectra for surveys of the circumgalactic/intergalactic medium (CGM/IGM). Nicastro et al. reported the detection of two O vii WHIM absorbers at z  = 0.4339 and 0.3551 in its spectrum, suggesting that the WHIM is metal rich and sufficient to close the missing baryons problem. Our survey indicates that the blazar is a member of a z  = 0.433 group and that the higher- z O vii candidate arises from its intragroup medium. The resulting bias precludes its use in baryon censuses. The z  = 0.3551 candidate occurs in an isolated environment 630 kpc from the nearest galaxy (with stellar mass ), which we show is unexpected for the WHIM. Finally, we characterize the galactic environments of broad H i Ly α absorbers (Doppler widths of b  = 40–80 km s −1 ; T ≲ 4 × 10 5 K) that provide metallicity-independent WHIM probes. On average, broad Ly α absorbers are ≈2× closer to the nearest luminous ( L > 0.25 L * ) galaxy (700 kpc) than narrow ( b < 30 km s −1 ; T  ≲ 4 × 10 5 K) ones (1300 kpc) but ≈2× further than O vi absorbers (350 kpc). These observations suggest that gravitational collapse heats portions of the IGM to form the WHIM, but with feedback that does not enrich the IGM far beyond galaxy/group halos to levels currently observable in UV/X-ray metal lines.