X-ray spectroscopy of the z = 6.4 quasar SDSS J1148+5251

Feb 23, 2017
8 pages
Published in:
  • Mon.Not.Roy.Astron.Soc. 467 (2017) 3, 3590-3597
  • Published: Jun 1, 2017
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Abstract: (Oxford University Press)
We present the 78 ks Chandra observations of the z = 6.4 quasar SDSS J1148+5251. The source is clearly detected in the energy range 0.3–7 keV with 42 counts (with a significance ≳9σ). The X-ray spectrum is best fitted by a power law with photon index Γ = 1.9 absorbed by a gas column density of NH=2.01.5+2.0×1023cm2{\rm N}_{\rm H}=2.0^{+2.0}_{-1.5}\times {10}^{23}\,{\rm cm}^{-2}. We measure an intrinsic luminosity at 2–10 and 10–40 keV equal to ∼ 1.5 × 10^45 erg s^− 1, comparable with luminous local and intermediate-redshift quasar properties. Moreover, the X-ray to optical power-law slope value (α_OX = −1.76 ± 0.14) of J1148 is consistent with the one found in quasars with similar rest-frame 2500 Å luminosity (L_2500 ∼ 10^32 erg s^− 1 Å^− 1). Then we use Chandra data to test a physically motivated model that computes the intrinsic X-ray flux emitted by a quasar starting from the properties of the powering black hole and assuming that X-ray emission is attenuated by intervening, metal-rich (Z ≥ Z_⊙) molecular clouds (MC) distributed on ∼kpc scales in the host galaxy. Our analysis favours a black hole mass M_BH ∼ 3 × 10^9 M_⊙ and a molecular hydrogen mass MH22×1010 MM_{\rm H_2}\sim 2\times {10}^{10}\ {\rm M_{\odot }}, in good agreement with estimates obtained from previous studies. We finally discuss strengths and limits of our analysis.
Note:
  • 9 pages, 3 figures, 1 table, MNRAS in press
  • galaxies: ISM
  • quasars: individual: SDSS J1148+5251
  • quasars: super-massive black holes
  • X-rays: galaxies
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