Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Jinyi Yang
Xiaohui Fan
Feige Wang
Giorgio Lanzuisi
Riccardo Nanni
Massimo Cappi
George Chartas
Mauro Dadina
Roberto Decarli
Xiangyu Jin
Charles R. Keeton
Bram P. Venemans
Fabian Walter
Ran Wang
Xue-Bing Wu
Minghao Yue
Ann Zabludoff
Abstract： We report X-ray observations of the most distant known gravitationally lensed quasar, J0439+1634 at $z=6.52$, which is also a broad absorption line (BAL) quasar, using the XMM-Newton Observatory. With a 130 ks exposure, the quasar is significantly detected as a point source at the optical position with a total of 358$^{+19}_{-19}$ net counts using the EPIC instrument. By fitting a power-law plus Galactic absorption model to the observed spectra, we obtain a spectral slope of $\Gamma=1.45^{+0.10}_{-0.09}$. The derived optical-to-X-ray spectral slope $\alpha_{\rm{ox}}$ is $-2.07^{+0.01}_{-0.01}$, suggesting that the X-ray emission of J0439+1634 is weaker by a factor of 18 than the expectation based on its 2500 Angstrom luminosity and the average $\alpha_{\rm{ox}}$ vs. luminosity relationship. This is the first time that an X-ray weak BAL quasar at $z>6$ has been observed spectroscopically. Its X-ray weakness is consistent with the properties of BAL quasars at lower redshift. By fitting a model including an intrinsic absorption component, we obtain intrinsic column densities of $N_{\rm{H}}=2.8^{+0.7}_{-0.6}\times10^{23}\,\rm{cm}^{-2}$ and $N_{\rm{H}}= 4.3^{+1.8}_{-1.5}\times10^{23}\,\rm{cm}^{-2}$, assuming a fixed $\Gamma$ of 1.9 and a free $\Gamma$, respectively. The intrinsic rest-frame 2--10 keV luminosity is derived as $(9.4-15.1)\times10^{43}\,\rm{erg\,s}^{-1}$, after correcting for lensing magnification ($\mu=51.3$). The absorbed power-law model fitting indicates that J0439+1634 is the highest redshift obscured quasar with a direct measurement of the absorbing column density. The intrinsic high column density absorption can reduce the X-ray luminosity by a factor of $3-7$, which also indicates that this quasar could be a candidate of intrinsically X-ray weak quasar.
Peer Review Status:
Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Xiangyu Jin
Jinyi Yang
Xiaohui Fan
Feige Wang
Eduardo Bañados
Fuyan Bian
Frederick B. Davies
Anna-Christina Eilers
Emanuele Paolo Farina
Joseph F. Hennawi
Fabio Pacucci
Bram Venemans
Fabian Walter
Abstract： Cosmic reionization was the last major phase transition of hydrogen from
neutral to highly ionized in the intergalactic medium (IGM). Current
observations show that the IGM is significantly neutral at $z>7$, and largely
ionized by $z\sim5.5$. However, most methods to measure the IGM neutral
fraction are highly model-dependent, and are limited to when the
volume-averaged neutral fraction of the IGM is either relatively low
($\bar{x}_{\rm HI} \lesssim 10^{-3}$) or close to unity ($\bar{x}_{\rm HI}\sim
1$). In particular, the neutral fraction evolution of the IGM at the critical
redshift range of $z=6-7$ is poorly constrained. We present new constraints on
$\bar{x}_{\rm HI}$ at $z\sim5.1-6.8$, by analyzing deep optical spectra of $53$
quasars at $5.73
Peer Review Status:Awaiting Review
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