X-ray spectroscopy of the z=6.4 quasar J1148+5251 [GA]

http://arxiv.org/abs/1702.07349


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 $\gtrsim9\sigma$). The X-ray spectrum is best-fitted by a power-law with photon index $\Gamma=1.9$ absorbed by a gas column density of $\rm N_{\rm H}=2.0^{+2.0}_{-1.5}\times10^{23}\,\rm cm^{-2}$. We measure an intrinsic luminosity at 2-10 keV and 10-40 keV equal to $\sim 1.5\times 10^{45}~\rm erg~s^{-1}$, comparable with luminous local and intermediate-redshift quasar properties. Moreover, the X-ray to optical power-law slope value ($\alpha_{\rm OX}=-1.76\pm 0.14$) of J1148 is consistent with the one found in quasars with similar rest-frame 2500 \AA ~luminosity ($L_{\rm 2500}\sim 10^{32}~\rm erg~s^{-1}$\AA$^{-1}$). 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 ($Z\geq \rm Z_{\odot}$) molecular clouds distributed on $\sim$kpc scales in the host galaxy. Our analysis favors a black hole mass $M_{\rm BH} \sim 3\times 10^9 \rm M_\odot$ and a molecular hydrogen mass $M_{\rm H_2}\sim 2\times 10^{10} \rm M_\odot$, in good agreement with estimates obtained from previous studies. We finally discuss strengths and limits of our analysis.

Read this paper on arXiv…

S. Gallerani, L. Zappacosta, M. Orofino, et. al.
Mon, 27 Feb 17
45/49

Comments: 9 pages, 3 figures, 1 table, MNRAS in press

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