分类： 天文学 >> 天文学 提交时间： 2023-02-19
Da-Ming Yang
Jan-Torge Schindler
Riccardo Nanni
Joseph F. Hennawi
Eduardo Bañados
Xiaohui Fan
Anniek Gloudemans
Huub Rottgering
Feige Wang
Jinyi Yang
摘要： We present the high-$z$ quasar candidate archive (HzQCA), summarizing the spectroscopic observations of 174 $z\gtrsim5$ quasar candidates using Keck/LRIS, Keck/MOSFIRE, and Keck/NIRES. We identify 7 candidates as $z\sim 6$ quasars 3 of them newly reported here, and 51 candidates as brown dwarfs. In the remaining sources, 74 candidates are unlikely to be quasars; 2 sources are inconclusive; the others could not be fully reduced or extracted. Based on the classifications we investigate the distributions of quasars and contaminants in color space with photometry measurements from DELS ($z$), VIKING/UKIDSS ($YJHK_s$/$YJHK$), and un\textit{WISE} ($W1W2$). We find that the identified brown dwarfs are not fully consistent with the empirical brown dwarf model that is commonly used in quasar candidate selection methods. To refine spectroscopic confirmation strategies, we simulate synthetic spectroscopy of high-$z$ quasars and contaminants for all three instruments. The simulations utilize the spectroscopic data in HzQCA. We predict the required exposure times for quasar confirmation and propose and optimal strategy for spectroscopic follow-up observations. For example, we demonstrate that we can identify a $m_J=21.5$ at $z=7.6$ or a $m_J=23.0$ at $z=7.0$ within 15\,min of exposure time with LRIS. With the publication of the HzQCA we aim to provide guidance for future quasar surveys and candidate classification.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Eduardo Banados
Jan-Torge Schindler
Bram P. Venemans
Thomas Connor
Roberto Decarli
Emanuele Paolo Farina
Chiara Mazzucchelli
Romain A. Meyer
Daniel Stern
Fabian Walter
Xiaohui Fan
Joseph F. Hennawi
Yana Khusanova
Nidia Morrell
Riccardo Nanni
Gael Noirot
Antonio Pensabene
Hans-Walter Rix
Joseph Simon
Gijs A. Verdoes Kleijn
摘要： The identification of bright quasars at z>6 enables detailed studies of
supermassive black holes, massive galaxies, structure formation, and the state
of the intergalactic medium within the first billion years after the Big Bang.
We present the spectroscopic confirmation of 55 quasars at redshifts 5.6
分类： 天文学 >> 天文学 提交时间： 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
摘要： We report the results of near-infrared spectroscopic observations of 37 quasars in the redshift range $6.36.5$, 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.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Jan-Torge Schindler
Eduardo Bañados
Thomas Connor
Roberto Decarli
Xiaohui Fan
Emanuele Paolo Farina
Chiara Mazzucchelli
Riccardo Nanni
Hans-Walter Rix
Daniel Stern
Bram P. Venemans
Fabian Walter
摘要： We present the $z\!\approx\!6$ type-1 quasar luminosity function (QLF) based on the Pan-STARRS1 (PS1) quasar survey. The PS1 sample includes 125 quasars at $z\approx5.7-6.2$ with $-28\lesssim M_{1450}\lesssim-25$. Complemented by 48 fainter quasars from the SHELLQs survey, we evaluate the $z\approx6$ QLF over $-28\lesssim M_{1450}\lesssim-22$. Adopting a double power law with an exponential evolution of the quasar density ($\Phi(z)\propto10^{k(z-6)}$; $k=-0.7$), we use a maximum likelihood method to model our data. We find a break magnitude of $M^*=-26.38_{-0.60}^{+0.79}\,\text{mag}$, a faint end slope of $\alpha=-1.70_{-0.19}^{+0.29}$, and a steep bright end slope with $\beta=-3.84_{-1.21}^{+0.63}$. Based on our new QLF model we determine the quasar comoving spatial density at $z\!\approx\!6$ to be $n( M_{1450}<-26)=1.16_{-0.12}^{+0.13}\,\text{cGpc}^{-3}$. In comparison with the literature, we find the quasar density to evolve with a constant value of $k\approx-0.7$ from $z\approx7$ to $z\approx4$. Additionally, we derive an ionizing emissivity of $\epsilon_{912}(z=6) =7.23_{-1.02}^{+1.65}\times 10^{22}\,\text{erg}\,\text{s}^{-1}\text{Hz}^{-1}\text{cMpc}^{-3}$ based on the QLF measurement. Given standard assumptions and the recent measurement of the mean free path of Becker et al. (2021) at $z\approx6$ we calculate an HI photoionizing rate of $\Gamma_{\text{HI}}(z{=}6) \approx 6 \times10^{-16}\,\text{s}^{-1}$, strongly disfavoring a dominant role of quasars in hydrogen reionization.
分类： 天文学 >> 天文学 提交时间： 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
摘要： 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.
点击量
待评议
点击量
下载量
评论
