To be or not to be: hot WHIM absorption in the blazar PKS 2155-304 sight line?

Abstract

The cosmological missing baryons at z<1 most likely hide in the hot (T$\gtrsim 10^{5.5}$ K) phase of the Warm Hot Intergalactic Medium (WHIM). While the hot WHIM is hard to detect due to its high ionisation level, the warm (T$\lesssim 10^{5.5}$ K) phase of the WHIM has been very robustly detected in the FUV band. We adopted the assumption that the hot and warm WHIM phases are co-located and thus used the FUV-detected warm WHIM as a tracer for the cosmologically interesting hot WHIM. We utilised the assumption by performing an X-ray follow-up in the sight line of a blazar PKS 2155-304 at the redshifts where previous FUV measurements of OVI, SiIV and BLA absorption have indicated the existence of the warm WHIM. We looked for the OVII He$\alpha$ and OVIII Ly$\alpha$ absorption lines, the most likely hot WHIM tracers. Despite of the very large exposure time ($\approx$ 1 Ms), the XMM-Newton/RGS1 data yielded no significant detection which corresponds to upper limits of $\log N(\mathrm{OVII})({\mathrm{cm}}^{-2}))\le 14.5-15.2$ and $\log N(\mathrm{OVIII})({\mathrm{cm}}^{-2}))\le 14.9-15.2$. An analysis of LETG/HRC data yielded consistent results. However, the LETG/ACIS data yielded a detection of an absorption line - like feature at $\lambda \approx$ 20 Å at simple one parameter uncertainty - based confidence level of 3.7 $\sigma$, consistently with several earlier LETG/ACIS reports. Given the high statistical quality of the RGS1 data, the possibility of RGS1 accidentally missing the true line at $\lambda \sim$ 20 Å is very low, 0.006%. Neglecting this, the LETG/ACIS detection can be interpreted as Ly$\alpha$ transition of OVIII at one of the redshifts (z$\approx$ 0.054) of FUV-detected warm WHIM. Given the very convincing X-ray spectral evidence for and against the existence of the $\lambda \sim$ 20 Å feature, we cannot conclude whether or not it is a true astrophysical absorption line.

arXiv commentAccepted for A&A

References in corpus (37)

• The EAGLE project: Simulating the evolution and assembly of galaxies and their environments
• Where are the Baryons?
• Baryons in the Warm-Hot Intergalactic Medium
• The Baryon Census in a Multiphase Intergalactic Medium: 30% of the Baryons May Still Be Missing
• Highly-Ionized High-Velocity Gas in the Vicinity of the Galaxy
• Observations of the MIssing Baryons in the warm-hot intergalactic medium
• Characterizing the Circumgalactic Medium of Nearby Galaxies with HST/COS and HST/STIS Absorption-Line Spectroscopy
• The Low-z Intergalactic Medium. III. HI and Metal Absorbers at z<0.4
• The abundance, distribution, and physical nature of highly ionized oxygen OVI, OVII, and OVIII in IllustrisTNG
• Physical Properties, Baryon Content, and Evolution of the LyαForest: New Insights from High Resolution Observations at z < 0.4
• Chandra Detection of OVIII Ly-alpha Absorption from an Overdense Region in the Intergalactic Medium
• The Properties of Low Redshift Intergalactic O VI Absorbers Determined from High S/N Observations of 14 QSOs with the Cosmic Origins Spectrograph
• Simulating the physical properties of dark matter and gas inside the cosmic web
• An HST/COS legacy survey of high-velocity ultraviolet absorption in the Milky Way's circumgalactic medium and the Local Group
• The effects of baryons on the halo mass function
• X-Ray Absorption By WHIM in the Sculptor Wall
• Confirmation of X-Ray Absorption by WHIM in the Sculptor Wall
• The low-redshift intergalactic medium as seen in archival legacy Hubble/STIS and FUSE data
• Absorption-Line Detections of $10^{5-6}$ K Gas in Spiral-Rich Groups of Galaxies
• The Multiphase Intergalactic Medium towards PKS 2155-304
• A Cluster of Low-Redshift Lyman-alpha Clouds toward PKS 2155-304. I. Limits on Metals and D/H
• The interstellar oxygen-K absorption edge as observed by XMM-Newton
• Studying the WHIM with Gamma Ray Bursts
• Confirming the Detection of an Intergalactic X-ray Absorber Toward PKS 2155-304
• The large-scale environment from cosmological simulations I: The baryonic cosmic web
• Missing baryons traced by the galaxy luminosity density in the large-scale WHIM filaments
• Chandra and Far Ultraviolet Spectroscopic Explorer Observations of z~0 Warm-Hot Gas Toward PKS 2155-304
• Coincidences between OVI and OVII Lines: Insights from High Resolution Simulations of the Warm-Hot Intergalactic Medium
• Calibration and in orbit performance of the reflection grating spectrometer onboard XMM-Newton
• A view of PKS 2155-304 with XMM-Newton Reflection Grating Spectrometers
• Diffuse Low-Ionization Gas in the Galactic Halo Casts Doubts on $z\simeq 0.03$ WHIM Detections
• X-raying the Intergalactic OVI Absorbers
• Discovery of Galactic OIV and OV X-ray absorption due to transition temperature gas in the PKS 2155-304 spectrum
• Warm-hot gas in groups and galaxies toward H2356-309
• On the presence of ultra-fast outflows in the WAX sample of Seyfert galaxies
• Far-UV Emission Properties of FR1 Radio Galaxies
• Detection of A Transient X-ray Absorption Line Intrinsic to the BL Lacertae Object H 2356-309

Cited by in corpus (11)

• An EAGLE view of the missing baryons
• 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
• Hot WHIM counterparts of FUV OVI absorbers: Evidence in the line-of-sight towards quasar 3C 273
• The challenge of measuring and mapping the missing baryons
• Cosmic metal invaders: Intergalactic OVII as a tracer of the warm-hot intergalactic medium within cosmic filaments in the EAGLE simulation
• Tracing the 10${}^7$K Warm-Hot Intergalactic Medium with UV absorption lines
• Systematic errors in the maximum likelihood regression of Poisson count data: introducing the overdispersed chi-square distribution
• A search for the missing baryons with X--ray absorption lines towards the blazar 1ES 1553+113
• A high-resolution view of the filament of gas between Abell 399 and Abell 401 from the Atacama Cosmology Telescope and MUSTANG-2
• Relation between the local width and linear halo mass density of cosmic filaments
• Profiles of cosmic filaments since z=4.0 in cosmological hydrodynamical simulation