ChandraDiscovery of a Tree in the X‐Ray Forest toward PKS 2155−304: The Local Filament?

Abstract

We present the first X-ray detection of resonant absorption from warm/hot local gas either in our Galaxy, or in the intergalactic space surrounding our Galaxy, along the line of sight toward the blazar PKS 2155À304. The Chandra HRCS/LETG spectrum of this z À330 km s À1 in the rest frame, from the O vii K line). O viii K and O vii K from the same system are also detected at a lower significance level (i.e., $3 ), while upper limits are set on O viii K, Ne x K, and Ne ix K. The Far Ultraviolet Spectroscopic Explorer spectrum of this source shows complex O vi 2s!2p absorption at the same redshift as the X-ray system, made by at least two components: one relatively narrow (FWHM ¼ 106 AE 9 km s À1 ) and slightly redshifted (cz ¼ 36 AE 6 km s À1 ), and one broader (FWHM ¼ 158 AE 26 km s À1 ) and blueshifted (cz ¼ À135 AE 14 km s À1 ). We demonstrate that the physical states of the UV and X-ray absorbers are hard to reconcile with a single, purely collisionally ionized, equilibrium plasma. We propose instead that the X-ray and at least the broader and blueshifted UV absorber are produced in a low-density intergalactic plasma, collapsing toward our Galaxy, consistent with the predictions of a warm-hot intergalactic medium from numerical simulations. We find that any reasonable solution requires overabundance of Ne compared to O by a factor of $2, with respect to the solar value. We propose several scenarios to account for this observation.

XMM-NewtonRGS observation of the warm absorber in Mrk 279

“…We modelled these components by means of a collisionally ionised plasma (hot model in SPEX) fixing their parameters to the values listed above. The ionised component likely originates in the interstellar medium of our Galaxy, but an extragalactic origin cannot be ruled out (Nicastro et al 2002). Further discussion of the absorbing gas along the line of sight of Mrk 279 can be found in Williams et al (2006).…”

The Rotation of the Hot Gas Around the Milky Way

“…Our analysis sample includes 37 known O VII absorbers at z=0 with RGS data (Fang et al 2002(Fang et al , 2006(Fang et al , 2015Nicastro et al 2002;McKernan et al 2004;Williams et al 2005Williams et al , 2006Williams et al , 2007Yao et al 2009b;Gupta et al 2012; Table 1). These include active galactic nuclei (AGNs) as well as several X-ray binaries in the Milky Way's halo and Magellanic Clouds.…”

FUV and X-Ray Absorption in the Warm-Hot Intergalactic Medium

“…Nicastro et al (2002) first identified the resonance lines in the Chandra LETGS spectrum of PKS 2155−304 (O VII n = 1−2, n = 1−3, O VIII Lyα, Ne IX n = 1−2). Fang et al (2003) found absorption in the LETGS spectrum of 3C273.…”

“…7. Nicastro et al (2002) initially interpreted the absorption as arising in an extended intergalactic filament. The argument that drives this interpretation is based on the assumption that O VI, O VII, and O VIII are all located in a single phase of the absorbing gas.…”