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1. The Time Domain Spectroscopic Survey: Changing-look Quasar Candidates from Multi-epoch Spectroscopy in SDSS-IV

   https://doi.org/10.3847/1538-4357/ac743f  

   Green, Paul J. ; Pulgarin-Duque, Lina ; Anderson, Scott F. ; MacLeod, Chelsea L. ; Eracleous, Michael ; Ruan, John J. ; Runnoe, Jessie ; Graham, Matthew ; Roulston, Benjamin R. ; Schneider, Donald P. ; et al ( July 2022 , The Astrophysical Journal)

   Active galactic nuclei (AGN) can vary significantly in their rest-frame optical/UV continuum emission, and with strong associated changes in broad line emission, on much shorter timescales than predicted by standard models of accretion disks around supermassive black holes. Most suchchanging-lookorchanging-stateAGN—and at higher luminosities, changing-look quasars (CLQs)—have been found via spectroscopic follow-up of known quasars showing strong photometric variability. The Time Domain Spectroscopic Survey of the Sloan Digital Sky Survey IV (SDSS-IV) includes repeat spectroscopy of large numbers of previously known quasars, many selected irrespective of photometric variability, and with spectral epochs separated by months to decades. Our visual examination of these repeat spectra for strong broad line variability yielded 61 newly discovered CLQ candidates. We quantitatively compare spectral epochs to measure changes in continuum and Hβbroad line emission, finding 19 CLQs, of which 15 are newly recognized. The parent sample includes only broad line quasars, so our study tends to find objects that have dimmed, i.e., turn-off CLQs. However, we nevertheless find four turn-on CLQs that meet our criteria, albeit with broad lines in both dim and bright states. We study the response of Hβand Mgiiemission lines to continuum changes. The Eddington ratios of CLQs are low, and/or their Hβbroad line width is large relative to the overall quasar population. Repeat quasar spectroscopy in the upcoming SDSS-V black hole Mapper program will reveal significant numbers of CLQs, enhancing our understanding of the frequency and duty cycle of such strong variability, and the physics and dynamics of the phenomenon.

    

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2. A New Infrared Criterion for Selecting Active Galactic Nuclei to Lower Luminosities

   https://doi.org/10.3847/1538-3881/ac5e33  

   Hviding, Raphael E. ; Hainline, Kevin N. ; Rieke, Marcia ; Juneau, Stéphanie ; Lyu 吕, Jianwei 建伟 ; Pucha, Ragadeepika ( April 2022 , The Astronomical Journal)

   We present a spectroscopic and photometric analysis of a sample of 416,288 galaxies from the Sloan Digital Sky Survey (SDSS) matched to mid-infrared (mid-IR) data from the Wide-field Infrared Survey Explorer (WISE). By using a new spectroscopic fitting package, GELATO (Galaxy/AGN Emission Line Analysis TOol), we are able to retrieve emission line fluxes and uncertainties for SDSS spectra and robustly determine the presence of broad lines and outflowing components, enabling us to investigate WISE color space as a function of optical spectroscopic properties. In addition, we pursue spectral energy distribution template fitting to assess the relative active galactic nucleus (AGN) contribution and nuclear obscuration to compare to existing mid-IR selection criteria with WISE. We present a selection criterion in mid-IR color space to select AGNs with an ∼80% accuracy and a completeness of ∼16%. This is the first mid-IR color selection defined by solely using the distribution of Type I and Type II optical spectroscopic AGNs in WISE mid-IR color space. Our selection is an improvement of ∼50% in the completeness of targeting spectroscopic AGNs with WISE down to an SDSSr< 17.77 mag. In addition, our new criterion targets a less-luminous population of AGNs, with on average lower [Oiii] luminosities by ∼30% ( > 0.1 dex) compared to typical WISE color–color selections. With upcoming large photometric surveys without corresponding spectroscopy, our method presents a way to select larger populations of AGNs at lower AGN luminosities and higher nuclear obscuration levels than traditional mid-IR color selections.

    

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3. VLT/UVES observation of the SDSS J2357−0048 outflow

   https://doi.org/10.1093/mnras/stac2638  

   Byun, Doyee ; Arav, Nahum ; Hall, Patrick B. ( September 2022 , Monthly Notices of the Royal Astronomical Society)

   We found a broad absorption line (BAL) outflow in the VLT/UVES spectrum of the quasar SDSS J235702.54−004824.0, in which we identified four subcomponents. We measured the column densities of the ions in one of the subcomponents (v = −1600 km s−1), which include O i and Fe ii. We found the kinetic luminosity of this component to be at most $\sim 2.4{{\ \rm per\ cent}}$ of the quasar’s Eddington luminosity. This is near the amount required to contribute to active galactic nucleus feedback. We also examined the time variability of a C iv mini-BAL found at v = −8700 km s−1, which shows a shallower and narrower absorption feature attached to it in previous SDSS observations from 2000 to 2001, but not in the spectra from 2005 and onwards.

    

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4. 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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5. An elliptical accretion disk following the tidal disruption event AT 2020zso

   https://doi.org/10.1051/0004-6361/202142616  

   Wevers, T. ; Nicholl, M. ; Guolo, M. ; Charalampopoulos, P. ; Gromadzki, M. ; Reynolds, T. M. ; Kankare, E. ; Leloudas, G. ; Anderson, J. P. ; Arcavi, I. ; et al ( October 2022 , Astronomy & Astrophysics)

   Aims. The modelling of spectroscopic observations of tidal disruption events (TDEs) to date suggests that the newly formed accretion disks are mostly quasi-circular. In this work we study the transient event AT 2020zso, hosted by an active galactic nucleus (AGN; as inferred from narrow emission line diagnostics), with the aim of characterising the properties of its newly formed accretion flow. Methods. We classify AT 2020zso as a TDE based on the blackbody evolution inferred from UV/optical photometric observations and spectral line content and evolution. We identify transient, double-peaked Bowen (N  III ), He  I , He  II, and H α emission lines. We model medium-resolution optical spectroscopy of the He  II (after careful de-blending of the N  III contribution) and H α lines during the rise, peak, and early decline of the light curve using relativistic, elliptical accretion disk models. Results. We find that the spectral evolution before the peak can be explained by optical depth effects consistent with an outflowing, optically thick Eddington envelope. Around the peak, the envelope reaches its maximum extent (approximately 10 15 cm, or ∼3000–6000 gravitational radii for an inferred black hole mass of 5−10 × 10 5 M ⊙ ) and becomes optically thin. The H α and He  II emission lines at and after the peak can be reproduced with a highly inclined ( i  = 85 ± 5 degrees), highly elliptical ( e  = 0.97 ± 0.01), and relatively compact ( R in = several 100 R g and R out = several 1000 R g ) accretion disk. Conclusions. Overall, the line profiles suggest a highly elliptical geometry for the new accretion flow, consistent with theoretical expectations of newly formed TDE disks. We quantitatively confirm, for the first time, the high inclination nature of a Bowen (and X-ray dim) TDE, consistent with the unification picture of TDEs, where the inclination largely determines the observational appearance. Rapid line profile variations rule out the binary supermassive black hole hypothesis as the origin of the eccentricity; these results thus provide a direct link between a TDE in an AGN and the eccentric accretion disk. We illustrate for the first time how optical spectroscopy can be used to constrain the black hole spin, through (the lack of) disk precession signatures (changes in inferred inclination). We constrain the disk alignment timescale to > 15 days in AT2020zso, which rules out high black hole spin values ( a  < 0.8) for M BH  ∼ 10 6 M ⊙ and disk viscosity α  ≳ 0.1. 

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