Confirming the Detection of an Intergalactic X-ray Absorber Toward PKS 2155-304

Abstract

We present new observations on PKS 2155-304 with the Chandra Low Energy Transmission Grating Spectrometer (LETG), using the Advanced CCD Imaging Spectrometer (ACIS). We confirm the detection of an absorption line plausibly identified as OVIII Ly-alpha from the warm-hot intergalactic medium associated with a small group of galaxies along the line of sight, as originally reported by Fang et al. 2002 (here after FANG02). Combining the previous observations in FANG02 and five new, long observations on the same target, we increase the total exposure time by a factor of three, and the total counts per resolution element by a factor of five. The measured line equivalent width is smaller than that observed in FANG02, but still consistent at 90% confidence. We also analyze the XMM-Newton observations on the same target, as well as observations using the Chandra LETG and the High Resolution Camera (HRC) combination. These observations have been used to challenge our reported detection. While no line is seen in either the XMM-Newton and the Chandra LETG+HRC data, we find that our result is consistent with the upper limits from both data sets. We attribute the non-detection to (1) higher quality of the Chandra LETG+ACIS spectrum, and (2) the rather extended wings of the line spread functions of both the XMM RGS and the Chandra LETG+HRC. We discuss the implication of our observation on the temperature and density of the absorber. We also confirm the detection of z ~ 0 OVII absorption and, comparing with previous Chandra analysis, we obtain much tighter constraints on the line properties.

10 pages, 8 figures, accepted for publication in ApJ

References in corpus (7)

• X-Ray Absorption from the Milky Way Halo and the Local Group
• Physical Properties, Baryon Content, and Evolution of the LyαForest: New Insights from High Resolution Observations at z < 0.4
• On the Putative Detection of z>0 X-ray Absorption Features in the Spectrum of Markarian 421
• Chandra and Far Ultraviolet Spectroscopic Explorer Observations of z~0 Warm-Hot Gas Toward PKS 2155-304
• Warm-Hot Intergalactic Medium Associated with the Coma Cluster
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• The Low-z Intergalactic Medium. III. HI and Metal Absorbers at z<0.4
• Discovery of Galactic OIV and OV X-ray absorption due to transition temperature gas in the PKS 2155-304 spectrum
• Effect of the Metallicity on the X-ray Emission from the Warm-Hot Intergalactic Medium
• Warm-hot gas in groups and galaxies toward H2356-309
• Discovery of a large-scale galaxy filament near a candidate intergalactic X-ray absorption system
• X-ray and Sunyaev-Zeldovich properties of the WHIM
• Systematic errors in the maximum likelihood regression of Poisson count data: introducing the overdispersed chi-square distribution
• On the nature of the z=0 X-ray absorbers: I. Clues from an external group
• A search for the missing baryons with X--ray absorption lines towards the blazar 1ES 1553+113
• On the nature of the z=0 X-ray absorbers: II. The contrast between local and AGN host galaxy absorption