Chandra Discovery of a Tree in the X-Ray Forest toward PKS 2155–304: The Local Filament?

By F. Nicastro, A. Zezas, J. Drake, M. Elvis, Fabrizio Fiore, A. Fruscione, M. Marengo, S. Mathur, S. Bianchi. 2002

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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 2155-304. The Chandra HRCS/LETG spectrum of this z = 0.116 source clearly shows, at ≥5 σ level, unresolved (FWHM ≤ 800 km s-1 at a 2 σ confidence level) O VII Kα and Ne IX Kα resonant absorption lines at 21.603 and 13.448 Å (i.e., cz = 14 km s-1 in the rest frame, from the O VII Kα line). O VIII Kα and O VII Kβ from the same system are also detected at a lower significance level (i.e., ~3 σ), while upper limits are set on O VIII Kβ, Ne X Kα, and Ne IX Kβ. 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 = 106 ± 9 km s-1) and slightly redshifted (cz = 36 ± 6 km s-1), and one broader (FWHM = 158 ± 26 km s-1) and blueshifted (cz = -135 ± 14 km s-1). 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.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/e30da93ffd427710f5111b46f702ecabb34eea51

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Citations in the corpus

CONSTRAINING THE MILKY WAY'S HOT GAS HALO WITH O vii AND O viii EMISSION LINES (2014, background): “…other hand, the absorption lines are only seen in ∼30 bright active galactic nucleus (AGN) and mjmil@umich.edu, jbregman@umich.edu blazar spectra (Nicastro et al. 2002; Rasmussen et al. 2003; Wang et al. 2005; Williams et al. 2005; Fang et al. 2006; Bregman & Lloyd-Davies 2007; Yao & Wang 2007;…”
Highly Ionized High-Velocity Gas in the Vicinity of the Galaxy (2002, background): “Indeed, preliminary results from several authors (Fang et al. 2003; Nicastro et al. 2002) demonstrate that O vii absorption is present near zero velocity along at least two high-latitude sight lines, which is consistent with the presence of a large, nearby reservoir of hot gas.”
The Progenitors of Dwarf Spheroidal Galaxies (2002, background): “Recent UV and X-ray absorption line studies suggest that intermediate-temperature ionized gas is present in galaxy groups, with local densities perhaps as high as 10−4 cm−3 (Fang et al. 2002; Nicastro et al. 2002; Sembach et al. 2003).”
Toward a Self-Consistent Model of the Ionized Absorber in NGC 3783 (2003, background): “This feature would be produced by intergalactic absorption at zero redshift, or by Galactic absorption (see Nicastro et al. 2002).”
Where Are the Baryons? II. Feedback Effects (2005, background): “…and XMM-Newton (Tripp et al. 2000; Tripp & Savage 2000; Oegerle et al. 2000; Scharf et al. 2000; Tittley&Henriksen 2001; Savage et al. 2002; Fang et al. 2002a, 2002b; Nicastro et al. 2002; Mathur et al. 2003; Kaastra et al. 2003; Finoguenov et al. 2003; Sembach et al. 2004; Nicastro et al. 2005).”
The Search for the Missing Baryons at Low Redshift (2007, background): “X-Ray absorption line studies are practical for the brightest AGNs and the first identification of absorption line gas at z ≈ 0 was reported by Nicastro et al. (2002) for Chandra observations of PKS 2155-304, shortly followed by Rasmussen et al. (2003), who reported on XMM observations toward 3C…”
A High-Resolution Survey of Low-Redshift QSO Absorption Lines: Statistics and Physical Conditions of O VI Absorbers (2007, background): “X-ray absorption lines have been robustly detected at zabs ≈ 0 (e.g., Nicastro et al. 2002; Fang et al. 2006), but there is evidence that the zabs ≈ 0 X-ray absorbers arise in gas clouds that are relatively close to the Milky Way (Futamoto et al. 2004; Wang et al. 2005; Fang et al. 2006), perhaps…”
THE STRUCTURE OF THE MILKY WAY'S HOT GAS HALO (2013, background): “These X-ray lines have primarily been observed in absorption of active galactic nuclei (AGNs) and blazar spectra (Nicastro et al. 2002; Rasmussen et al. 2003; Wang et al. 2005; Williams et al. 2005; Fang et al. 2006; Yao & Wang 2007; Hagihara et al. 2010) as well as Galactic X-ray binary spectra…”
DO HOT HALOS AROUND GALAXIES CONTAIN THE MISSING BARYONS? (2010, background): “It extends out to at least 50 kpc, although its density declines to the intergalactic medium (IGM) density by a radius of 80 kpc or so.”