Open AccessTentative detection of warm intervening gas towards PKS 0548‐322 with XMM–Newton
Author(s) -
Barcons X.,
Paerels F. B. S.,
Carrera F. J.,
Ceballos M. T.,
Sako M.
Publication year - 2005
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1111/j.1365-2966.2005.08993.x
Subject(s) - physics , absorption (acoustics) , astrophysics , absorption spectroscopy , spectral line , ionization , line (geometry) , epic , equivalent width , wavelength , analytical chemistry (journal) , astronomy , optics , emission spectrum , ion , geometry , mathematics , quantum mechanics , art , chemistry , literature , chromatography
We present the results of a long (∼93 ks) 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 λ= 23.33 ± 0.01 Å , which we interpret as O vi Kα absorption at z = 0.058 , i.e. ∼3000 km s −1 from the background object. The observed equivalent width of the absorption line, ∼30 mÅ, coupled with the lack of the corresponding absorption edge in the EPIC pn data, implies a column density of N O VI ∼ 2 × 10 16 cm −2 and turbulence with a Doppler velocity parameter b > 100 km s −1 . Within the limitations of our RGS spectrum, no O vii or O v Kα absorption are detected. Under the assumption of ionization equilibrium by both collisions and the extragalactic background, this is only marginally consistent if the gas temperature is ∼2.5 × 10 5 K , with significantly lower or higher values being excluded by our limits on O v or O vii . If confirmed, this would be the first X‐ray detection of a large amount of intervening warm absorbing gas through O vi absorption. The existence of such a high column density absorber, much stronger than any previously detected one in O vi , would place stringent constraints on the large‐scale distribution of baryonic gas in the Universe.