An X-ray WHIM metal absorber from a Mpc-scale empty region of space

TL;DR

This paper reports the detection of a warm-hot intergalactic medium (WHIM) metal absorber at z≈0.112 in X-ray spectra, located in a low galaxy density region, suggesting it is part of a large-scale intergalactic filament.

Contribution

First detection of a CV-Kα WHIM absorber in a low galaxy density region, indicating the presence of intergalactic filaments outside galaxy halos.

Findings

Detected CV-Kα absorption at z≈0.112 with 2.9σ significance.

Absorber located 2.2 Mpc from the nearest galaxy, unlikely associated with galactic halo.

Possible association with a large-scale galaxy filament extending 30 Mpc.

Abstract

We report a detection of an absorption line at ~44.8 {\AA} in a > 500 ks Chandra HRC-S/LETG X-ray grating spectrum of the blazar H 2356-309. This line can be identified as intervening CV-K{\alpha} absorption, at z\approx0.112, produced by a warm (log T = 5.1 K) intergalactic absorber. The feature is significant at a 2.9{\sigma} level (accounting for the number of independent redshift trials). We estimate an equivalent hydrogen column density of log N_H=19.05 (Z/Zsun)^-1 cm^-2. Unlike other previously reported FUV/X-ray metal detections of warm-hot intergalactic medium (WHIM), this CV absorber lies in a region with locally low galaxy density, at ~2.2 Mpc from the closest galaxy at that redshift, and therefore is unlikely to be associated with an extended galactic halo. We instead tentatively identify this absorber with an intervening Warm-Hot Intergalactic Medium filament possibly permeating a large-scale, 30 Mpc extended, structure of galaxies whose redshift centroid, within a cylinder of 7.5 Mpc radius centered on the line of sight to H 2356-309, is marginally consistent (at a 1.8{\sigma} level) with the redshift of the absorber.