分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We describe the first results from the All-sky BRIght, Complete Quasar Survey (AllBRICQS), which aims to discover the last remaining optically bright quasars. We present 156 spectroscopically confirmed quasars (140 newly identified) having |b|>10deg. 152 of the quasars have Gaia DR3 magnitudes brighter than B_P=16.5 or R_P=16 mag, while four are slightly fainter. The quasars span a redshift range of z=0.07-3.93. In particular, we highlight the properties of J0529-4351 at z=3.93, which, if unlensed, is one of the most intrinsically luminous quasars in the Universe. The AllBRICQS sources have been selected by combining data from the Gaia and WISE all-sky satellite missions, and we successfully identify quasars not flagged as candidates by Gaia Data Release 3. We expect the completeness to be approximately 96% within our magnitude and latitude limits, while the preliminary results indicate a selection purity of approximately 96%. The optical spectroscopy used for source classification will also enable detailed quasar characterisation, including black hole mass measurements and identification of foreground absorption systems. The AllBRICQS sources will greatly enhance the number of quasars available for high-signal-to-noise follow-up with present and future facilities.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Studies of excess infrared radiation around white dwarfs provide important constraints on the evolution of planetary systems and low-mass stars beyond the main sequence stage. In this paper series, we focus on identifying and characterizing bright white dwarfs with an infrared excess. Here, we present 188 infrared excess candidates from Gaia and unWISE, 147 of which are new discoveries. Further characterization of this sample can significantly increase the current list of white dwarf debris disks and white dwarfs with low-mass companions.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Yongda Zhu
George D. Becker
Sarah E. I. Bosman
Laura C. Keating
Valentina D'Odorico
Rebecca L. Davies
Holly M. Christenson
Eduardo Bañados
Fuyan Bian
Manuela Bischetti
Huanqing Chen
Frederick B. Davies
Anna-Christina Eilers
Xiaohui Fan
Prakash Gaikwad
Bradley Greig
Martin G. Haehnelt
Girish Kulkarni
Samuel Lai
Andrea Pallottini
摘要： We present a new investigation of the intergalactic medium (IGM) near reionization using dark gaps in the Lyman-$\beta$ (Ly$\beta$) forest. With its lower optical depth, Ly$\beta$ offers a potentially more sensitive probe to any remaining neutral gas compared to commonly used Ly$\alpha$ line. We identify dark gaps in the Ly$\beta$ forest using spectra of 42 QSOs at $z_{\rm em}>5.5$, including new data from the XQR-30 VLT Large Programme. Approximately $40\%$ of these QSO spectra exhibit dark gaps longer than $10h^{-1}{\rm Mpc}$ at $z\simeq5.8$. By comparing the results to predictions from simulations, we find that the data are broadly consistent both with models where fluctuations in the Ly$\alpha$ forest are caused solely by ionizing ultraviolet background (UVB) fluctuations and with models that include large neutral hydrogen patches at $z<6$ due to a late end to reionization. Of particular interest is a very long ($L=28h^{-1}{\rm Mpc}$) and dark ($\tau_{\rm eff} \gtrsim 6$) gap persisting down to $z\simeq 5.5$ in the Ly$\beta$ forest of the $z_{\rm}=5.85$ QSO PSO J025$-$11. This gap may support late reionization models with a volume-weighted average neutral hydrogen fraction of $ \langle x_{\rm HI}\rangle \gtrsim 5\%$ by $z=5.6$. Finally, we infer constraints on $\langle x_{\rm HI}\rangle$ over $5.5 \lesssim z \lesssim 6.0$ based on the observed Ly$\beta$ dark gap length distribution and a conservative relationship between gap length and neutral fraction derived from simulations. We find $\langle x_{\rm HI}\rangle \leq 0.05$, 0.17, and 0.29 at $z\simeq 5.55$, 5.75, and 5.95, respectively. These constraints are consistent with models where reionization ends significantly later than $z = 6$.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We develop an accretion disc (AD) fitting method, utilising thin and slim disc models and Bayesian inference with the Markov-Chain Monte-Carlo approach, testing it on the most luminous known quasar, SMSS J215728.21-360215.1, at redshift $z=4.692$. With a spectral energy distribution constructed from near-infrared spectra and broadband photometry, the AD models find a black hole mass of $\log(M_{\rm{AD}}/M_{\odot}) = 10.31^{+0.17}_{-0.14}$ with an anisotropy-corrected bolometric luminosity of $\log{(L_{\rm{bol}}/\rm{erg\,s^{-1}})} = 47.87 \pm 0.10$, and derive an Eddington ratio of $0.29^{+0.11}_{-0.10}$ as well as a radiative efficiency of $0.09^{+0.05}_{-0.03}$. Using the near-infrared spectra, we estimate the single-epoch virial black hole mass estimate to be $\log(M_{\rm{SE}}/M_{\odot}) = 10.33 \pm 0.08$, with a monochromatic luminosity at 3000\AA\ of $\log{(L(\rm{3000\text{\AA}})/\rm{erg\,s^{-1}})} = 47.66 \pm 0.01$. As an independent approach, AD fitting has the potential to complement the single-epoch virial mass method in obtaining stronger constraints on properties of massive quasar black holes across a wide range of redshifts.
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