ORCID Profile
0000-0002-7633-431X
Current Organisation
University of Arizona
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Publisher: Springer Science and Business Media LLC
Date: 11-05-2022
DOI: 10.1038/S41586-022-04608-1
Abstract: Bright quasars, powered by accretion onto billion-solar-mass black holes, already existed at the epoch of reionization, when the Universe was 0.5-1 billion years old
Publisher: American Astronomical Society
Date: 28-04-2022
Abstract: We present the first near-IR spectroscopy and joint analyses of multiwavelength observations for SDSS J082747.14+425241.1, a dust-reddened, weak broad emission-line quasar (WLQ) undergoing a remarkable broad-absorption line (BAL) transformation. The systemic redshift is more precisely measured to be z = 2.070 ± 0.001 using H β compared to z = 2.040 ± 0.003 using Mg ii from the literature, signifying an extreme Mg ii blueshift of 2140 ± 530 km s −1 relative to H β . Using the H β -based single-epoch scaling relation with a systematic uncertainty of 0.3 dex, its black hole (BH) mass and Eddington ratio are estimated to be M BH ∼ 6.1 × 10 8 M ⊙ and λ Edd ∼ 0.71, indicative of being in a rapidly accreting phase. Our investigations confirm the WLQ nature and the LoBAL → HiBAL transformation, along with a factor of 2 increase in the Mg ii +Fe ii emission strength and a decrease of 0.1 in E ( B − V ) over two decades. The kinetic power of this LoBAL wind at R ∼ 15 pc from its BH is estimated to be ∼43% of the Eddington luminosity, sufficient for quasar feedback upon its host galaxy albeit with an order-of-magnitude uncertainty. This quasar provides a clear ex le of the long-sought scenario where LoBAL quasars are surrounded by dust cocoons, and wide-angle nuclear winds play a key role in the transition of red quasars evolving into the commonly seen blue quasars.
Publisher: Oxford University Press (OUP)
Date: 30-06-2020
Abstract: From near-infrared spectroscopic measurements of the Mg ii emission line doublet, we estimate the black hole (BH) mass of the quasar, SMSS J215728.21–360215.1, as being (3.4 ± 0.6) × 1010 M⊙ and refine the redshift of the quasar to be z = 4.692. SMSS J2157 is the most luminous known quasar, with a 3000 Å luminosity of (4.7 ± 0.5) × 1047 erg s−1 and an estimated bolometric luminosity of 1.6 × 1048 erg s−1, yet its Eddington ratio is only ∼0.4. Thus, the high luminosity of this quasar is a consequence of its extremely large BH – one of the most massive BHs at z & 4.
Publisher: Oxford University Press (OUP)
Date: 07-06-2022
Abstract: The presence of excess scatter in the Ly-α forest at z ∼ 5.5, together with the existence of sporadic extended opaque Gunn-Peterson troughs, has started to provide robust evidence for a late end of hydrogen reionization. However, low data quality and systematic uncertainties complicate the use of Ly-α transmission as a precision probe of reionization’s end stages. In this paper, we assemble a s le of 67 quasar sightlines at z & 5.5 with high signal-to-noise ratios of & per ≤15 km s−1 spectral pixel, relying largely on the new XQR-30 quasar s le. XQR-30 is a large program on VLT/X-Shooter which obtained deep (SNR & 20 per pixel) spectra of 30 quasars at z & 5.7. We carefully account for systematics in continuum reconstruction, instrumentation, and contamination by d ed Ly-α systems. We present improved measurements of the mean Ly-α transmission over 4.9 & z & 6.1. Using all known systematics in a forward modelling analysis, we find excellent agreement between the observed Ly-α transmission distributions and the homogeneous-UVB simulations Sherwood and Nyx up to z ≤ 5.2 (& σ), and mild tension (∼2.5σ) at z = 5.3. Homogeneous UVB models are ruled out by excess Ly-α transmission scatter at z ≥ 5.4 with high confidence (& .5σ). Our results indicate that reionization-related fluctuations, whether in the UVB, residual neutral hydrogen fraction, and/or IGM temperature, persist in the intergalactic medium until at least z = 5.3 (t = 1.1 Gyr after the big bang). This is further evidence for a late end to reionization.
Publisher: Oxford University Press (OUP)
Date: 11-04-2022
Abstract: The elemental abundances in the broad-line regions of high-redshift quasars trace the chemical evolution in the nuclear regions of massive galaxies in the early Universe. In this work, we study metallicity-sensitive broad emission-line flux ratios in rest-frame UV spectra of 25 high-redshift (5.8 & z & 7.5) quasars observed with the VLT/X-shooter and Gemini/GNIRS instruments, ranging over $\\log \\left({{M}_{\\rm {BH}}/\\rm {M}_{\\odot }}\\right) = 8.4-9.8$ in black hole mass and $\\log \\left(\\rm {L}_{\\rm {bol}}/\\rm {erg \\, s}^{-1}\\right) = 46.7-47.7$ in bolometric luminosity. We fit in idual spectra and composites generated by binning across quasar properties: bolometric luminosity, black hole mass, and blueshift of the C iv line, finding no redshift evolution in the emission-line ratios by comparing our high-redshift quasars to lower redshift (2.0 & z & 5.0) results presented in the literature. Using cloudy-based locally optimally emitting cloud photoionization model relations between metallicity and emission-line flux ratios, we find the observable properties of the broad emission lines to be consistent with emission from gas clouds with metallicity that are at least 2–4 times solar. Our high-redshift measurements also confirm that the blueshift of the C iv emission line is correlated with its equivalent width, which influences line ratios normalized against C iv. When accounting for the C iv blueshift, we find that the rest-frame UV emission-line flux ratios do not correlate appreciably with the black hole mass or bolometric luminosity.
Publisher: American Astronomical Society
Date: 20-08-2018
Publisher: American Astronomical Society
Date: 06-2022
Abstract: We present a new investigation of the intergalactic medium near reionization using dark gaps in the Ly β forest. With its lower optical depth, Ly β offers a potentially more sensitive probe to any remaining neutral gas compared to the commonly used Ly α line. We identify dark gaps in the Ly β forest using spectra of 42 QSOs at z em 5.5, including new data from the XQR-30 VLT Large Programme. Approximately 40% of these QSO spectra exhibit dark gaps longer than 10 h −1 Mpc at z ≃ 5.8. By comparing the results to predictions from simulations, we find that the data are broadly consistent both with models where fluctuations in the Ly α forest are caused solely by ionizing ultraviolet background 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 = 28 h −1 Mpc) and dark ( τ eff ≳ 6) gap persisting down to z ≃ 5.5 in the Ly β forest of the z = 5.85 QSO PSO J025−11. This gap may support late reionization models with a volume-weighted average neutral hydrogen fraction of 〈 x H I 〉 ≳ 5% by z = 5.6. Finally, we infer constraints on 〈 x H I 〉 over 5.5 ≲ z ≲ 6.0 based on the observed Ly β dark gap length distribution and a conservative relationship between gap length and neutral fraction derived from simulations. We find 〈 x H I 〉 ≤ 0.05, 0.17, and 0.29 at z ≃ 5.55, 5.75, and 5.95, respectively. These constraints are consistent with models where reionization ends significantly later than z = 6.
Publisher: American Astronomical Society
Date: 17-08-2016
Abstract: We present a new investigation of the intergalactic medium (IGM) near the end of reionization using “dark gaps” in the Ly α forest. Using spectra of 55 QSOs at z em 5.5, including new data from the XQR-30 VLT Large Programme, we identify gaps in the Ly α forest where the transmission averaged over 1 comoving h −1 Mpc bins falls below 5%. Nine ultralong ( L 80 h −1 Mpc) dark gaps are identified at z 6. In addition, we quantify the fraction of QSO spectra exhibiting gaps longer than 30 h −1 Mpc, F 30 , as a function of redshift. We measure F 30 ≃ 0.9, 0.6, and 0.15 at z = 6.0, 5.8, and 5.6, respectively, with the last of these long dark gaps persisting down to z ≃5.3. Comparing our results with predictions from hydrodynamical simulations, we find that the data are consistent with models wherein reionization extends significantly below redshift six. Models wherein the IGM is essentially fully reionized that retain large-scale fluctuations in the ionizing UV background at z ≲6 are also potentially consistent with the data. Overall, our results suggest that signatures of reionization in the form of islands of neutral hydrogen and/or large-scale fluctuations in the ionizing background remain present in the IGM until at least z ≃ 5.3.
Publisher: Springer Science and Business Media LLC
Date: 28-06-2023
Publisher: American Astronomical Society
Date: 05-02-2019
Publisher: Oxford University Press (OUP)
Date: 25-03-2022
Abstract: Bright, high-redshift (z & 6) QSOs are powerful probes of the ionization state of the intervening intergalactic medium (IGM). The detection of Ly α d ing wing absorption imprinted in the spectrum of high-z QSOs can provide strong constraints on the epoch of reionization (EoR). In this work, we perform an independent Ly α d ing wing analysis of two known z & 7 QSOs DESJ0252−0503 at z = 7.00 (Wang et al.) and J1007+2115 at z = 7.51 (Yang et al.). For this, we utilize our existing Bayesian framework which simultaneously accounts for uncertainties in: (i) the intrinsic Ly α emission profile (reconstructed from a covariance matrix of measured emission lines extended in this work to include N v) and (ii) the distribution of ionized (H ii) regions within the IGM using a 1.63 Gpc3 reionization simulation. This approach is complementary to that used in the aforementioned works as it focuses solely redward of Ly α (1218 & λ & 1230 Å) making it more robust to modelling uncertainties while also using a different methodology for (i) and (ii). We find, for an EoR morphology driven by galaxies within Mh ≳ 109 M⊙ haloes, $\\bar{x}_{\\mathrm{H\\, {\\scriptscriptstyle I}}{}} = 0.64\\substack{+0.19 \\\\-0.23}$ (68 per cent) at z = 7 and $\\bar{x}_{\\mathrm{H\\, {\\scriptscriptstyle I}}{}} = 0.27\\substack{+0.21 \\\\-0.17}$ at z = 7.51 consistent within 1σ to the previous works above, though both are slightly lower in litude. Following the inclusion of N v into our reconstruction pipeline, we perform a reanalysis of ULASJ1120+0641 at z = 7.09 (Mortlock et al.) and ULASJ1342+0928 at z = 7.54 (Bañados et al.) finding $\\bar{x}_{\\mathrm{H\\, {\\scriptscriptstyle I}}{}} = 0.44\\substack{+0.23 \\\\-0.24}$ at z = 7.09 and $\\bar{x}_{\\mathrm{H\\, {\\scriptscriptstyle I}}{}} = 0.31\\substack{+0.18 \\\\-0.19}$ at z = 7.54. Finally, we combine the QSO d ing wing constraints for all four z ≳ 7 QSOs to obtain a single, unified constraint of $\\bar{x}_{\\mathrm{H\\, {\\scriptscriptstyle I}}{}} = 0.49\\substack{+0.11 \\\\-0.11}$ at z = 7.29.
Publisher: American Astronomical Society
Date: 30-03-2017
Publisher: Oxford University Press (OUP)
Date: 10-12-2020
Abstract: We present the results of a new, deeper, and complete search for high-redshift 6.5 & z & 9.3 quasars over 977 deg2 of the VISTA Kilo-Degree Infrared Galaxy (VIKING) survey. This exploits a new list-driven data set providing photometry in all bands Z, Y, J, H, Ks, for all sources detected by VIKING in J. We use the Bayesian model comparison (BMC) selection method of Mortlock et al., producing a ranked list of just 21 candidates. The sources ranked 1, 2, 3, and 5 are the four known z & 6.5 quasars in this field. Additional observations of the other 17 candidates, primarily DESI Legacy Survey photometry and ESO FORS2 spectroscopy, confirm that none is a quasar. This is the first complete s le from the VIKING survey, and we provide the computed selection function. We include a detailed comparison of the BMC method against two other selection methods: colour cuts and minimum-χ2 SED fitting. We find that: (i) BMC produces eight times fewer false positives than colour cuts, while also reaching 0.3 mag deeper, (ii) the minimum-χ2 SED-fitting method is extremely efficient but reaches 0.7 mag less deep than the BMC method, and selects only one of the four known quasars. We show that BMC candidates, rejected because their photometric SEDs have high χ2 values, include bright ex les of galaxies with very strong [O iii] λλ4959,5007 emission in the Y band, identified in fainter surveys by Matsuoka et al. This is a potential contaminant population in Euclid searches for faint z & 7 quasars, not previously accounted for, and that requires better characterization.
Publisher: American Astronomical Society
Date: 11-04-2017
Location: United States of America
No related grants have been discovered for Feige Wang.