An ensemble study of turbulence in extended QSO nebulae at z≈0.5z\approx0.5--1

Turbulent motions in the circumgalactic medium (CGM) play a critical role in regulating the evolution of galaxies, yet their detailed characterization remains elusive. Using two-dimensional velocity maps constructed from spatially-extended [OII] and [OIII] emission, Chen et al. (2023b) measured the velocity structure functions (VSFs) of four quasar nebulae at $z\approx\!0.5$--1.1. One of these exhibits a spectacular Kolmogorov relation. Here we carry out an ensemble study using an expanded sample incorporating four new nebulae from three additional QSO fields. The VSFs measured for all eight nebulae are best explained by subsonic turbulence revealed by the line-emitting gas, which in turn strongly suggests that the cool gas ($T\!\sim\!10^4$ K) is dynamically coupled to the hot ambient medium. Previous work demonstrates that the largest nebulae in our sample reside in group environments with clear signs of tidal interactions, suggesting that environmental effects are vital in seeding and enhancing turbulence within the gaseous halos, ultimately promoting the formation of the extended nebulae. No discernible differences are observed in the VSF properties between radio-loud and radio-quiet QSO fields. We estimate the turbulent heating rate per unit volume, $Q_{\rm turb}$, in the QSO nebulae to be $\sim 10^{-26}$--$10^{-22}$ erg cm$^{-3}$ s$^{-1}$ for the cool phase and $\sim 10^{-28}$--$10^{-25}$ erg cm$^{-3}$ s$^{-1}$ for the hot phase. This range aligns with measurements in the intracluster medium and star-forming molecular clouds but is $\sim10^3$ times higher than the $Q_{\rm turb}$ observed inside cool gas clumps on scales $\lesssim1$ kpc using absorption-line techniques. We discuss the prospect of bridging the gap between emission and absorption studies by pushing the emission-based VSF measurements to below $\approx\!10$ kpc.Comment: 23 pages; 7 figures, and 4 tables in main text; 9 figures in Appendix; accepted by ApJ. Comments welcom

The first comprehensive study of a giant nebula around a radio-quiet quasar in the z<1z < 1 Universe

We present the first comprehensive study of a giant, $\approx \! \! 70$ kpc-scale nebula around a radio-quiet quasar at $z<1$. The analysis is based on deep integral field spectroscopy with MUSE of the field of HE$\,$0238$-$1904, a luminous quasar at $z=0.6282$. The nebula emits strongly in $\mathrm{[O \, II]}$, $\rm H \beta$, and $\mathrm{[O \, III]}$, and the quasar resides in an unusually overdense environment for a radio-quiet system. The environment likely consists of two groups which may be merging, and in total have an estimated dynamical mass of $M_{\rm dyn}\approx 4\times 10^{13}$ to $10^{14}\ {\rm M_\odot}$. The nebula exhibits largely quiescent kinematics and irregular morphology. The nebula may arise primarily through interaction-related stripping of circumgalactic and interstellar medium (CGM/ISM) of group members, with some potential contributions from quasar outflows. The simultaneous presence of the giant nebula and a radio-quiet quasar in a rich environment suggests a correlation between such circum-quasar nebulae and environmental effects. This possibility can be tested with larger samples. The upper limits on the electron number density implied by the$\mathrm{[O \, II]}$doublet ratio range from$\log(n_{\rm e, \, [O \, II]} / \mathrm{cm^{-3}}) < 1.2$to$2.8$. However, assuming a constant quasar luminosity and negligible projection effects, the densities implied from the measured line ratios between different ions (e.g.,$\mathrm{[O\,II]}$,$\mathrm{[O\,III]}$, and$\mathrm{[Ne\,V]}$) and photoionization simulations are often$10{-}400$times larger. This large discrepancy can be explained by quasar variability on a timescale of$\approx 10^4{-}10^5$ years.Comment: 19 pages, 9 figures, 3 tables; Submitted to MNRA

The Sloan Digital Sky Survey Reverberation Mapping Project : UV–optical accretion disk measurements with the Hubble Space Telescope

Funding: Y.H., J.R.T., and G.F.A. acknowledge support from NASA grants HST-GO-15650 and 18-2ADAP18-0177 and NSF grant CAREER-1945546. K.H. acknowledges support from STFC grant ST/R000824/1. C.J.G. acknowledges support from NSF grant AST-2009949. Y.S. acknowledges support from NSF grants AST-1715579 and AST-2009947. P.H. acknowledges support from the Natural Sciences and Engineering Research Council of Canada (NSERC), funding reference number 2017-05983. L.C.H. was supported by the National Science Foundation of China (11721303, 11991052) and the National Key R&D Program of China (2016YFA0400702).We present accretion-disk structure measurements from UV–optical reverberation mapping (RM) observations of a sample of eight quasars at 0.24 < z < 0.85. Ultraviolet photometry comes from two cycles of Hubble Space Telescope monitoring, accompanied by multiband optical monitoring by the Las Cumbres Observatory network and Liverpool Telescopes. The targets were selected from the Sloan Digital Sky Survey Reverberation Mapping project sample with reliable black hole mass measurements from Hβ RM results. We measure significant lags between the UV and various optical griz bands using JAVELIN and CREAM methods. We use the significant lag results from both methods to fit the accretion-disk structure using a Markov Chain Monte Carlo approach. We study the accretion disk as a function of disk normalization, temperature scaling, and efficiency. We find direct evidence for diffuse nebular emission from Balmer and Fe ii lines over discrete wavelength ranges. We also find that our best-fit disk color profile is broadly consistent with the Shakura & Sunyaev disk model. We compare our UV–optical lags to the disk sizes inferred from optical–optical lags of the same quasars and find that our results are consistent with these quasars being drawn from a limited high-lag subset of the broader population. Our results are therefore broadly consistent with models that suggest longer disk lags in a subset of quasars, for example, due to a nonzero size of the ionizing corona and/or magnetic heating contributing to the disk response.Publisher PDFPeer reviewe

The Sloan Digital Sky Survey Reverberation Mapping Project : the MBH–host relations at 0.2 ∼< z ∼< 0.6 from reverberation mapping and Hubble Space Telescope imaging

Funding: Y.S. acknowledges support from an Alfred P. Sloan Research Fellowship and NSF grants AST-1715579, AST-2009947. Support for Program number HST-GO-14109 was provided through a grant from the STScI under NASA contract NAS5-26555. L.C.H. was supported by the National Key R&D Program of China (2016YFA0400702) and the National Science Foundation of China (11721303, 11991052). E.D.B. is supported by Padua University grants DOR1715817/17, DOR1885254/18, and DOR1935272/19 and by MIUR grant PRIN 201720173ML3WW_001. J.V.H.S.and K.H. acknowledge funds from a Science and Technology Facilities Council grant ST/R000824/1.We present the results of a pilot Hubble Space Telescope (HST) imaging study of the host galaxies of ten quasars from the Sloan Digital Sky Survey Reverberation Mapping (SDSS-RM) project. Probing more than an order of magnitude in BH and stellar masses, our sample is the first statistical sample to study the BH-host correlations beyond z>0.3 with reliable BH masses from reverberation mapping rather than from single-epoch spectroscopy. We perform image decomposition in two HST bands (UVIS-F606W and IR-F110W) to measure host colors and estimate stellar masses using empirical relations between broad-band colors and the mass-to-light ratio. The stellar masses of our targets are mostly dominated by a bulge component. The BH masses and stellar masses of our sample broadly follow the same correlations found for local RM AGN and quiescent bulge-dominant galaxies, with no strong evidence of evolution in the MBH-M*bulge relation to z~0.6. We further compare the host light fraction from HST imaging decomposition to that estimated from spectral decomposition. We found a good correlation between the host fractions derived with both methods. However, the host fraction derived from spectral decomposition is systematically smaller than that from imaging decomposition by ~30%, indicating different systematics in both approaches. This study paves the way for upcoming more ambitious host galaxy studies of quasars with direct RM-based BH masses at high redshift.PostprintPeer reviewe

The Sloan Digital Sky Survey Reverberation Mapping Project : how broad emission line widths change when luminosity changes

Funding: National Science Foundation of China (11721303, 11890693, 11991052) and the National Key R&D Program of China (2016YFA0400702, 2016YFA0400703). YS acknowledges support from an Alfred P. Sloan Research Fellowship and NSF grant AST-1715579. CJG, WNB, JRT, and DPS acknowledge support from NSF grants AST-1517113 and AST-1516784. KH acknowledges support from STFC grant ST/R000824/1. PBH acknowledges support from NSERC grant 2017-05983. YH acknowledges support from NASA grant HST-GO-15650.Quasar broad emission lines are largely powered by photoionization from the accretion continuum. Increased central luminosity will enhance line emissivity in more distant clouds, leading to increased average distance of the broad-line-emitting clouds and decreased averaged line width, known as the broad-line region (BLR) "breathing". However, different lines breathe differently, and some high-ionization lines, such as C IV, can even show "anti-breathing" where the line broadens when luminosity increases. Using multi-year photometric and spectroscopic monitoring data from the Sloan Digital Sky Survey Reverberation Mapping project, we quantify the breathing effect (Δlog W=αΔlog L) of broad Hα, Hβ, Mg II, C IV,and C III] for statistical quasar samples over z≈0.1−2.5. We found that Hβ displays the most consistent normal breathing expected from the virial relation (α∼−0.25), Mg II and Hα on average show no breathing (α∼0), and C IV (and similarly C III] and Si IV mostly shows anti-breathing (α>0). The anti-breathing of C IV can be well understood by the presence of a non-varying core component in addition to a reverberating broad-base component, consistent with earlier findings. The deviation from canonical breathing introduces extra scatter (aluminosity-dependent bias) in single-epoch virial BH mass estimates due to intrinsic quasar variability, which underlies the long argued caveats of C IV single-epoch masses. Using the line dispersion instead of FWHM leads to less, albeit still substantial, deviations from canonical breathing in most cases. Our results strengthen the need for reverberation mapping to provide reliable quasar BH masses, and quantify the level of variability-induced bias in single-epoch BH masses based on various lines.PostprintPeer reviewe

The Sloan Digital Sky Survey Reverberation Mapping Project : low-ionization broad-line widths and implications for virial black hole mass estimation

Funding: UK STFC grant ST/R000824/1 (KH).The width of the broad emission lines in quasars is commonly characterized by either the FWHM or the square root of the second moment of the line profile (σ line) and used as an indicator of the virial velocity of the broad-line region (BLR) in the estimation of black hole (BH) mass. We measure FWHM and σ line for Hα, Hβ, and Mg ii broad lines in both the mean and rms spectra of a large sample of quasars from the Sloan Digital Sky Survey Reverberation Mapping project. We introduce a new quantitative recipe to measure σ line that is reproducible, is less susceptible to noise and blending in the wings, and scales with the intrinsic width of the line. We compare the four definitions of line width (FWHM and σ line in mean and rms spectra, respectively) for each of the three broad lines and among different lines. There are strong correlations among different width definitions for each line, providing justification for using the line width measured in single-epoch spectroscopy as a virial velocity indicator. There are also strong correlations among different lines, suggesting that alternative lines to Hβ can be used to estimate virial BH masses. We further investigate the correlations between virial BH masses using different line width definitions and the stellar velocity dispersion of the host galaxies and the dependence of line shape (characterized by the ratio FWHM/σ line) on physical properties of the quasar. Our results provide further evidence that FWHM is more sensitive to the orientation of a flattened BLR geometry than σ line, but the overall comparison between the virial BH mass and host stellar velocity dispersion does not provide conclusive evidence that one particular width definition is significantly better than the others.Publisher PDFPeer reviewe

The Sloan Digital Sky Survey Reverberation Mapping Project: Initial C IV lag results from four years of data

K.H. acknowledges support from STFC grant ST/M001296/1.We present reverberation-mapping (RM) lags and black hole mass measurements using the C iv λ1549 broad emission line from a sample of 348 quasars monitored as a part of the Sloan Digital Sky Survey RM Project. Our data span four years of spectroscopic and photometric monitoring for a total baseline of 1300 days, allowing us to measure lags up to ~750 days in the observed frame (this corresponds to a rest-frame lag of ~300 days in a quasar at z = 1.5 and ~190 days at z = 3). We report significant time delays between the continuum and the C iv λ1549 emission line in 48 quasars, with an estimated false-positive detection rate of 10%. Our analysis of marginal lag measurements indicates that there are on the order of ~100 additional lags that should be recoverable by adding more years of data from the program. We use our measurements to calculate black hole masses and fit an updated C iv radius–luminosity relationship. Our results significantly increase the sample of quasars with C iv RM results, with the quasars spanning two orders of magnitude in luminosity toward the high-luminosity end of the C iv radius–luminosity relation. In addition, these quasars are located at some of the highest redshifts (z ≈ 1.4–2.8) of quasars with black hole masses measured with RM. This work constitutes the first large sample of C iv RM measurements in more than a dozen quasars, demonstrating the utility of multiobject RM campaigns.Publisher PDFPeer reviewe