Tentative detection of warm intervening gas towards PKS 0548-322 with XMM-Newton

Abstract

We present the results of a long (~93 ksec) XMM-Newton observation of the bright BL-Lac object PKS 0548-322 (z=0.069). Our Reflection Grating Spectrometer (RGS) spectrum shows a single absorption feature at an observed wavelength lambda=23.33 A, which we interpret as OVI Ka absorption at z=0.058, i.e., ~3000 km/s from the background object. The observed equivalent width of the absorption line ~30 mA, coupled with the lack of the corresponding absorption edge in the EPIC pn data, implies an OVI column density ~ 2 10^{16} cm-2 and turbulence with a Doppler velocity parameter b>100 km/s. Within the limitations of our RGS spectrum, no OVII or OV Ka absorption are detected. Under the assumption of ionisation equilibrium by both collisions and the extragalactic background, this is only marginally consistent if the gas temperature is ~250,000 K, with significantly lower or higher values being excluded by our limits on OV or OVII. If confirmed, this would be the first X-ray detection of a large amount of intervening warm absorbing gas through OVI absorption. The existence of such a high column density absorber, much stronger than any previously detected one in OVI, would place stringent constraints on the large-scale distribution of baryonic gas in the Universe.

arXiv comment9 pages, 10 ps figures, accepted by MNRAS

References in corpus (17)

• The European Photon Imaging Camera on XMM-Newton: The MOS Cameras
• Where are the Baryons?
• Baryons in the Warm-Hot Intergalactic Medium
• Surveys for z > 3 Damped Lyman-alpha Absorption Systems
• Chandra Discovery of a Tree in the X-ray Forest towards PKS 2155-304: the Local Filament?
• Chandra Detection of OVIII Ly-alpha Absorption from an Overdense Region in the Intergalactic Medium
• X-Ray IGM in the Local Group
• The X-Ray Forest: A New Prediction of Hierarchical Structure Formation Models
• Revealing the Warm-Hot Intergalactic Medium with OVI Absorption
• Chandra Detection of Local OVII He-alpha Absorption Along the Sight Line Toward 3C 273
• X-ray Absorption by the Low-redshift Intergalactic Medium: A Numerical Study of the Lambda CDM model
• The interstellar oxygen-K absorption edge as observed by XMM-Newton
• On the intensity of the cosmic X-ray background
• Probing Cosmology with the X-ray Forest
• X-ray absorption via K-alpha resonance complexes in oxygen ions
• A warm hot intergalactic medium towards 3C 120?
• Intrinsic absorbers in BL Lac objects: the XMM-Newton view

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