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
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Jinyi Yang
Feige Wang
Xiaohui Fan
Aaron J. Barth
Joseph F. Hennawi
Riccardo Nanni
Fuyan Bian
Frederick B. Davies
Emanuele P. Farina
Jan-Torge Schindler
Eduardo Banados
Roberto Decarli
Anna-Christina Eilers
Richard Green
Hengxiao Guo
Linhua Jiang
Jiang-Tao Li
Bram Venemans
Fabian Walter
Xue-Bing Wu
Abstract： We report the results of near-infrared spectroscopic observations of 37 quasars in the redshift range $6.3< z\le7.64$, including 32 quasars at $z>6.5$, forming the largest quasar near-infrared spectral sample at this redshift. The spectra, taken with Keck, Gemini, VLT, and Magellan, allow investigations of central black hole mass and quasar rest-frame ultraviolet spectral properties. The black hole masses derived from the MgII emission lines are in the range $(0.3-3.6)\times10^{9}\,M_{\odot}$, which requires massive seed black holes with masses $\gtrsim10^{3-4}\,M_{\odot}$, assuming Eddington accretion since $z=30$. The Eddington ratio distribution peaks at $\lambda_{\rm Edd}\sim0.8$ and has a mean of 1.08, suggesting high accretion rates for these quasars. The CIV - MgII emission line velocity differences in our sample show an increase of CIV blueshift towards higher redshift, but the evolutionary trend observed from this sample is weaker than the previous results from smaller samples at similar redshift. The FeII/MgII flux ratios derived for these quasars up to $z=7.6$, compared with previous measurements at different redshifts, do not show any evidence of strong redshift evolution, suggesting metal-enriched environments in these quasars. Using this quasar sample, we create a quasar composite spectrum for $z>6.5$ quasars and find no significant redshift evolution of quasar broad emission lines and continuum slope, except for a blueshift of the CIV line. Our sample yields a strong broad absorption line quasar fraction of $\sim$24%, higher than the fractions in lower redshift quasar samples, although this could be affected by small sample statistics and selection effects.
Peer Review Status:Awaiting Review
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