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1. Chemical abundance of z ~ 6 quasar broad-line regions in the XQR-30 sample

   https://doi.org/10.1093/mnras/stac1001  

   Lai, Samuel ; Bian, Fuyan ; Onken, Christopher A. ; Wolf, Christian ; Mazzucchelli, Chiara ; Bañados, Eduardo ; Bischetti, Manuela ; Bosman, Sarah E. I. ; Becker, George ; Cupani, Guido ; et al ( April 2022 , Monthly Notices of the Royal Astronomical Society)

   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 individual 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.

    

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2. Metallicity in Quasar Broad-line Regions at Redshift ∼ 6

   https://doi.org/10.3847/1538-4357/ac3a69  

   Wang, Shu ; Jiang, Linhua ; Shen, Yue ; Ho, Luis C. ; Vestergaard, Marianne ; Bañados, Eduardo ; Willott, Chris J. ; Wu, Jin ; Zou, Siwei ; Yang, Jinyi ; et al ( January 2022 , The Astrophysical Journal)

   Broad-line regions (BLRs) in high-redshift quasars provide crucial information on chemical enrichment in the early universe. Here we present a study of BLR metallicities in 33 quasars at redshift 5.7 <z< 6.4. Using the near-IR spectra of the quasars obtained from the Gemini telescope, we measure their rest-frame UV emission-line flux and calculate flux ratios. We then estimate BLR metallicities with empirical calibrations based on photoionization models. The inferred median metallicity of our sample is a few times the solar value, indicating that the BLR gas had been highly metal enriched atz∼ 6. We compare our sample with a low-redshift quasar sample with similar luminosities and find no evidence of redshift evolution in quasar BLR metallicities. This is consistent with previous studies. The Feii/Mgiiflux ratio, a proxy for the Fe/αelement abundance ratio, shows no redshift evolution as well, further supporting rapid nuclear star formation atz∼ 6. We also find that the black hole mass–BLR metallicity relation atz∼ 6 is consistent with the relation measured at 2 <z< 5, suggesting that our results are not biased by a selection effect due to this relation.

    

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3. The SDSS-V Black Hole Mapper Reverberation Mapping Project: Unusual Broad-line Variability in a Luminous Quasar

   https://doi.org/10.3847/1538-4357/acbfb7  

   Fries, Logan B. ; Trump, Jonathan R. ; Davis, Megan C. ; Grier, C. J. ; Shen, Yue ; Anderson, Scott F. ; Dwelly, Tom ; Eracleous, Michael ; Homayouni, Y. ; Horne, Keith ; et al ( April 2023 , The Astrophysical Journal)

   We present a high-cadence multiepoch analysis of dramatic variability of three broad emission lines (Mgii, Hβ, and Hα) in the spectra of the luminous quasar (λL_λ(5100 Å) = 4.7 × 10⁴⁴erg s⁻¹) SDSS J141041.25+531849.0 atz= 0.359 with 127 spectroscopic epochs over nine years of monitoring (2013–2022). We observe anticorrelations between the broad emission-line widths and flux in all three emission lines, indicating that all three broad emission lines “breathe” in response to stochastic continuum variations. We also observe dramatic radial velocity shifts in all three broad emission lines, ranging from Δv∼ 400 km s⁻¹to ∼800 km s⁻¹, that vary over the course of the monitoring period. Our preferred explanation for the broad-line variability is complex kinematics in the gas in the broad-line region. We suggest a model for the broad-line variability that includes a combination of gas inflow with a radial gradient, an azimuthal asymmetry (e.g., a hot spot), superimposed on the stochastic flux-driven changes to the optimal emission region (“line breathing”). Similar instances of line-profile variability due to complex gas kinematics around quasars are likely to represent an important source of false positives in radial velocity searches for binary black holes, which typically lack the kind of high-cadence data we analyze here. The long-duration, wide-field, and many-epoch spectroscopic monitoring of SDSS-V BHM-RM provides an excellent opportunity for identifying and characterizing broad emission-line variability, and the inferred nature of the inner gas environment, of luminous quasars.

    

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4. METAL: The Metal Evolution, Transport, and Abundance in the Large Magellanic Cloud Hubble Program. III. Interstellar Depletions, Dust-to-Metal, and Dust-to-Gas Ratios versus Metallicity

   https://doi.org/10.3847/1538-4357/ac5248  

   Roman-Duval, Julia ; Jenkins, Edward B. ; Tchernyshyov, Kirill ; Clark, Christopher J. ; De Cia, Annalisa ; Gordon, Karl D. ; Hamanowicz, Aleksandra ; Lebouteiller, Vianney ; Rafelski, Marc ; Sandstrom, Karin ; et al ( March 2022 , The Astrophysical Journal)

   Abstract The metallicity and gas density dependence of interstellar depletions, the dust-to-gas (D/G), and dust-to-metal (D/M) ratios have important implications for how accurately we can trace the chemical enrichment of the universe, either by using FIR dust emission as a tracer of the ISM or by using spectroscopy of damped Ly α systems to measure chemical abundances over a wide range of redshifts. We collect and compare large samples of depletion measurements in the Milky Way (MW), Large Magellanic Cloud (LMC) ( Z = 0.5 Z ⊙ ), and Small Magellanic Cloud (SMC) ( Z = 0.2 Z ⊙ ). The relations between the depletions of different elements do not strongly vary between the three galaxies, implying that abundance ratios should trace depletions accurately down to 20% solar metallicity. From the depletions, we derive D/G and D/M. The D/G increases with density, consistent with the more efficient accretion of gas-phase metals onto dust grains in the denser ISM. For log N (H) > 21 cm −2 , the depletion of metallicity tracers (S, Zn) exceeds −0.5 dex, even at 20% solar metallicity. The gas fraction of metals increases from the MW to the LMC (factor 3) and SMC (factor 6), compensating for the reduction in total heavy element abundances and resulting in those three galaxies having the same neutral gas-phase metallicities. The D/G derived from depletions are respective factors of 2 (LMC) and 5 (SMC) higher than the D/G derived from FIR, 21 cm, and CO emission, likely due to the combined uncertainties on the dust FIR opacity and on the depletion of carbon and oxygen. 

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5. Probing Early Supermassive Black Hole Growth and Quasar Evolution with Near-infrared Spectroscopy of 37 Reionization-era Quasars at 6.3 < z ≤ 7.64

   https://doi.org/10.3847/1538-4357/ac2b32  

   Yang, Jinyi ; Wang, Feige ; Fan, Xiaohui ; Barth, Aaron J. ; Hennawi, Joseph F. ; Nanni, Riccardo ; Bian, Fuyan ; Davies, Frederick B. ; Farina, Emanuele P. ; Schindler, Jan-Torge ; et al ( December 2021 , The Astrophysical Journal)

   Abstract We report the results of near-infrared spectroscopic observations of 37 quasars in the redshift range 6.3 < z ≤ 7.64, 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 Mg ii emission lines are in the range (0.3–3.6) × 10 9 M ⊙ , which requires massive seed black holes with masses ≳10 3 –10 4 M ⊙ , assuming Eddington accretion since z = 30. The Eddington ratio distribution peaks at λ Edd ∼ 0.8 and has a mean of 1.08, suggesting high accretion rates for these quasars. The C iv –Mg ii emission-line velocity differences in our sample show an increase of C iv blueshift toward higher redshift, but the evolutionary trend observed from this sample is weaker than the previous results from smaller samples at similar redshift. The Fe ii /Mg ii 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 C iv line. Our sample yields a strong broad absorption line quasar fraction of ∼24%, higher than the fractions in lower-redshift quasar samples, although this could be affected by small sample statistics and selection effects. 

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