C IV wind properties of the SDSS-V X-ray selected quasars: strong optical-to-UV emission is key regardless of X-ray strength

We present spectroscopic measurements for 226 sources from the Gemini Near Infrared Spectrograph–Distant Quasar Survey (GNIRS-DQS). Being the largest uniform, homogeneous survey of its kind, it represents a flux-limited sample (m i ≲ 19.0 mag, H ≲ 16.5 mag) of Sloan Digital Sky Survey (SDSS) quasars at 1.5 ≲ z ≲ 3.5 with a monochromatic luminosity ( ) at 5100 Å in the range of 1044–1046 erg s−1. A combination of the GNIRS and SDSS spectra covers principal quasar diagnostic features, chiefly the C iv λ1549, Mg ii λλ2798, 2803, Hβ λ4861, and [O iii] λλ4959, 5007 emission lines, in each source. The spectral inventory will be utilized primarily to develop prescriptions for obtaining more accurate and precise redshifts, black hole masses, and accretion rates for all quasars. Additionally, the measurements will facilitate an understanding of the dependence of rest-frame ultraviolet–optical spectral properties of quasars on redshift, luminosity, and Eddington ratio, and test whether the physical properties of the quasar central engine evolve over cosmic time.

We use the ROSAT All-Sky Survey (RASS) to study the soft X-ray properties of a homogeneous sample of 46 420 quasars selected from the third data release of the Sloan Digital Sky Survey (SDSS). Optical luminosities, both at rest frame 2500 (L 2500 ) and in [O III] (L [O III] ) span more than three orders of magnitude, while redshifts range over 0.1 < z < 5.4. We detect 3366 quasars directly in the observed 0.1-2.4 keV band. Subsamples of radio-loud quasars (RLQs) and radio-quiet quasars (RQQs) are obtained by cross-matching with the Faint Images of the Radio Sky at Twenty-cm (FIRST) catalogue. We study the distribution of X-ray luminosity as a function of optical luminosity, redshift and radio power using both individual detections and stacks of complete sets of similar quasars. At every optical luminosity and redshift log L 2 keV is, to a good approximation, normally distributed with dispersion 0.40, at least brightwards of the median X-ray luminosity. This median X-ray luminosity of quasars is a power law of optical luminosity with index 0.53 for L 2500 and 0.30 for L [O III] . RLQs are systematically brighter than RQQs by about a factor of 2 at given optical luminosity. The zero-points of these relations increase systematically with redshift, possibly in different ways for RLQs and RQQs. Evolution is particularly strong at low redshift and if the optical luminosity is characterized by L [O III] . At low redshift and at given L [O III] the soft X-ray emission from type II active galactic nucleus (AGN) is more than 100 times weaker than that from type I AGN.

We present a systematic X-ray and multiwavelength study of a sample of 47 active galactic nuclei (AGNs) with reverberation mapping measurements. This sample includes 21 super-Eddington accreting AGNs and 26 sub-Eddington accreting AGNs. Using high-state observations with simultaneous X-ray and UV/optical measurements, we investigate whether super-Eddington accreting AGNs exhibit different accretion disk–corona connections compared to sub-Eddington accreting AGNs. We find tight correlations between the X-ray-to-UV/optical spectral slope parameter (α OX) and the monochromatic luminosity at 2500 Å (L 2500Å) for both the super- and sub-Eddington subsamples. The best-fit α OX–L 2500Å relations are consistent overall, indicating that super-Eddington accreting AGNs are not particularly X-ray weak in general compared to sub-Eddington accreting AGNs. We find dependences of α OX on both the Eddington ratio (L Bol/L Edd) and black hole mass (M BH) parameters for our full sample. A multivariate linear regression analysis yields , with a scatter similar to that of the α OX–L 2500Å relation. The hard (rest-frame &gt;2 keV) X-ray photon index (Γ) is strongly correlated with L Bol/L Edd for the full sample and the super-Eddington subsample, but these two parameters are not significantly correlated for the sub-Eddington subsample. A fraction of super-Eddington accreting AGNs show strong X-ray variability, probably due to small-scale gas absorption, and we highlight the importance of employing high-state (intrinsic) X-ray radiation to study the accretion disk–corona connections in AGNs.

Using stellar population synthesis, we model the stellar contribution for a sample of 110 double-peaked broad-line active galactic nuclei (AGNs) from the Sloan Digital Sky Survey (SDSS). The stellar velocity dispersions (σ*) are obtained for 52 double-peaked AGNs with obvious stellar absorption features, ranging from 106 to 284 km s-1. We also use multicomponent profiles to fit O III λλ4959, 5007 and Hβ emission lines. Using the well-established Mbh-σ* relation, the black hole masses are calculated to range from 1.0 × 107 to 5.5 × 108 M☉, and the Eddington ratio from ~0.01 to ~1. Comparing these with the known RBLR-L relation, we can find the factor f, which indicates the BLRs' geometry, inclination, and kinematics. We find that f deviates greatly from 0.75, suggesting the nonvirial dynamics of broad-line regions. The peak separation is mildly correlated with the Eddington ratio and SMBH mass with almost the same correlation coefficients. This implies that it will be difficult to detect obvious double-peaked AGNs with higher Eddington ratios. Using the monochromatic luminosity at 5100 Å to trace the bolometric luminosity, we find that external illumination of the accretion disk is needed to produce the observed strength of the Hα emission line.

We measure long (2200-4000 ang) and short (1450-2200 ang) wavelength spectral slopes \alpha (F_\nu proportional to \nu^\alpha) for quasar spectra from the Sloan Digital Sky Survey. The long and short wavelength slopes are computed from 3646 and 2706 quasars with redshifts in the z=0.76-1.26 and z=1.67-2.07 ranges, respectively. We calculate mean slopes after binning the data by monochromatic luminosity at 2200 ang and virial mass estimates based on measurements of the MgII line width and 3000 ang continuum luminosity. We find little evidence for mass dependent variations in the mean slopes, but a significant luminosity dependent trend in the near UV spectral slopes is observed with larger (bluer) slopes at higher luminosities. The far UV slopes show no clear variation with luminosity and are generally lower (redder) than the near UV slopes at comparable luminosities, suggesting a slightly concave quasar continuum shape. We compare these results with Monte Carlo distributions of slopes computed from models of thin accretion disks, accounting for uncertainties in the mass estimates. The model slopes produce mass dependent trends which are larger than observed, though this conclusion is sensitive to the assumed uncertainties in the mass estimates. The model slopes are also generally bluer than observed, and we argue that reddening by dust intrinsic to the source or host galaxy may account for much of the discrepancy.

Using an empirical relation between the broad-line region size and optical continuum luminosity, we estimated the black hole mass and accretion rate for 135 active galactic nuclei (AGNs) with double-peaked broad emission lines in two samples, one from the Sloan Digital Sky Survey (SDSS) and the other from a survey of radio-loud broad emission line AGNs. With black hole masses ranging from 3 × 107 M☉ to 5 × 109 M☉, these AGNs have dimensionless accretion rates (Eddington ratios) between 0.001 and 0.1 and bolometric luminosity between 1043 and 1046 ergs s-1, both values being significantly larger than those of several previously known low-luminosity (Lbol < 1043 ergs s-1) double-peaked AGNs. The optical-X-ray spectra indices, αOX, of these high-luminosity double-peaked AGNs are between 1 and 1.9, systematically larger than those of low-luminosity objects, which are around 1. Modest correlations (with a Spearman rank correlation coefficient of 0.60) of the αOX value with the Eddington ratio and bolometric luminosity have been found, indicating that double-peaked AGNs with higher Eddington ratios or higher luminosity tend to have larger αOX values. Based on these results, we suggested that the accretion process in the central region of some high-luminosity double-peaked emission line AGNs (especially those with Eddington ratios larger than 0.01) is probably different from that of low-luminosity objects, in which a well-known ADAF-like accretion flow was thought to exist. It is likely that the accretion physics in some high-luminosity double-peaked AGNs is similar to that in normal type 1 AGNs, which is also supported by the presence of possible big blue bumps in the spectra of some double-peaked AGNs with higher Eddington ratios. We note that the prototype double-peaked emission line AGN, Arp 102B, which has a black hole mass of 108 M☉ and a dimensionless accretion rate of 0.001, may be an intermediate object between the high- and low-luminosity double-peaked AGNs. In addition, we found an apparent strong anticorrelation (with a Spearman rank correlation coefficient of -0.79) between the peak separation of double-peaked profiles and Eddington ratios. However, such an anticorrelation is probably induced by a strong correlation between the peak separation and emission-line widths and needs to be confirmed by future work. If it is real, it may provide us another clue to understanding why double-peaked broad emission lines were hardly found in luminous AGNs with Eddington ratios larger than 0.1.

(Abridged) We construct a catalog of radio sources detected by the GB6 (6 cm), FIRST and NVSS (20 cm), and WENSS (92 cm) radio surveys, and the SDSS optical survey. The 2.7 million entries in the publicly-available master catalog are comprised of the closest three FIRST to NVSS matches (within 30 arcsec) and vice-versa, and unmatched sources from each survey. Entries are supplemented by data from the other radio and optical surveys, where available. We perform data analysis a ~3000 deg^2 region of sky where the surveys overlap, which contains 140,000 NVSS-FIRST sources, of which 64,000 are detected by WENSS and 12,000 by GB6. About one third of each sample is detected by SDSS. An automated classification method based on 20 cm fluxes defines three radio morphology classes: complex, resolved, and compact. Radio color-magnitude- morphology diagrams for these classes show structure suggestive of strong underlying physical correlations. Complex and resolved sources tend to have a steep spectral slope (alpha ~ -0.8) that is nearly constant from 6 to 92 cm, while the compact class contains a significant number of flat-spectrum (alpha ~ 0) sources. In the optically-detected sample, quasars dominate the flat-spectrum compact sources while steep-spectrum and resolved objects contain substantial numbers of both quasars and galaxies. Differential radio counts of quasars and galaxies are similar at bright flux levels (>100 mJy at 20 cm), while at fainter levels the quasar counts are significantly reduced below galaxy counts. The optically-undetected sample is strongly biased toward steep-spectrum sources. In samples of quasars and galaxies with SDSS spectra, we find that radio properties such as spectral slope, morphology, and radio loudness are correlated with optical color and luminosity.

We discuss the optical and radio properties of ~30,000 FIRST (radio, 20 cm, sensitive to 1 mJy) sources positionally associated within 15 with a Sloan Digital Sky Survey (SDSS) (optical, sensitive to r* ~ 22.2) source in 1230 deg2 of sky. The matched sample represents ~30% of the 108,000 FIRST sources and 0.1% of the 2.5 ? 107 SDSS sources in the studied region. SDSS spectra are available for 4300 galaxies and 1154 quasars from the matched sample and for a control sample of 140,000 galaxies and 20,000 quasars in 1030 deg2 of sky. Here we analyze only core sources, which dominate the sample; the fraction of SDSS-FIRST sources with complex radio morphology is determined to be less than 10%. This large and unbiased catalog of optical identifications provides much firmer statistical footing for existing results and allows several new findings. The majority (83%) of the FIRST sources identified with an SDSS source brighter than r* = 21 are optically resolved; the fraction of resolved objects among the matched sources is a function of the radio flux, increasing from ~50% at the bright end to ~90% at the FIRST faint limit. Nearly all optically unresolved radio sources have nonstellar colors indicative of quasars. We estimate an upper limit of ~5% for the fraction of quasars with broadband optical colors indistinguishable from those of stars. The distribution of quasars in the radio flux?optical flux plane suggests the existence of the quasar radio dichotomy; 8% ? 1% of all quasars with i* 2.22) galaxies, especially those with r* > 17.5. Magnitude- and redshift-limited samples show that radio galaxies have a different optical luminosity distribution than nonradio galaxies selected by the same criteria; when galaxies are further separated by their colors, this result remains valid for both blue and red galaxies. For a given optical luminosity and redshift, the observed optical colors of radio galaxies are indistinguishable from those of all SDSS galaxies selected by identical criteria. The distributions of radio-to-optical flux ratio are similar for blue and red galaxies in redshift-limited samples; this similarity implies that the difference in their luminosity functions and resulting selection effects are the dominant cause for the preponderance of red radio galaxies in flux-limited samples. The fraction of radio galaxies whose emission-line ratios indicate an AGN (30%), rather than starburst, origin is 6 times larger than the corresponding fraction for all SDSS galaxies (r* < 17.5). We confirm that the AGN-to-starburst galaxy number ratio increases with radio flux and find that radio emission from AGNs is more concentrated than radio emission from starburst galaxies.

We investigate the relation between the optical (g-band) and X-ray (0.5–10 keV) luminosities of accreting nonmagnetic white dwarfs. According to the present-day counts of the populations of star systems in our Galaxy, these systems have the highest space density among the close binary systems with white dwarfs. We show that the dependence of the optical luminosity of accreting white dwarfs on their X-ray luminosity forms a fairly narrow one-parameter curve. The typical half-width of this curve does not exceed 0.2–0.3 dex in optical and X-ray luminosities, which is essentially consistent with the amplitude of the aperiodic flux variability for these objects. At X-ray luminosities L x ∼ 1032 erg s−1 or lower, the optical g-band luminosity of the accretion flow is shown to be related to its X-ray luminosity by a factor ∼2–3. At even lower X-ray luminosities (L x ≲ 1030 erg s−1), the contribution from the photosphere of the white dwarf begins to dominate in the optical spectrum of the binary system and its optical brightness does not drop below M g ∼ 13–14. Using the latter fact, we show that in current and planned X-ray sky surveys, the family of accreting nonmagnetic white dwarfs can be completely identified to the distance determined by the sensitivity of an optical sky survey in this region. For the Sloan Digital Sky Survey (SDSS) with a limiting sensitivity m g ∼ 22.5, this distance is ∼400–600 pc.

The ensemble variability properties of nearly 23,000 quasars are studied using the Palomar-QUEST Survey. The survey has covered 15,000 square degrees multiple times over 3.5 years using 7 optical filters, and has been calibrated specifically for variability work. Palomar-QUEST allows for the study of rare objects using multiple epochs of consistently calibrated, homogeneous data, obviating the common problem of generating comparable measurements from disparate datasets. A power law fit to the quasar structure function versus time yields an index of 0.432 +/- 0.024 for our best measured sample. We see the commonly reported anticorrelation between average optical variability amplitude and optical luminosity, and measure the logarithmic decrease in variability amplitude to scale as the logarithm of the luminosity times 0.205 +/- 0.002. Black hole mass is positively correlated with variability amplitude over three orders of magnitude in mass. Quasar variability amplitude is seen to decrease with Eddington ratio as a step function with a transition around Eddington ratio of 0.5. The higher variability at low Eddington ratios is due to excess power at timescales shorter than roughly 300 days. X-ray and radio measurements exist for subsets of the quasar sample. We observe an anticorrelation between optical variability amplitude and X-ray luminosity. No significant correlation is seen between average optical variability properties and radio luminosity. The timescales of quasar fluctuations are suggestive of accretion disk instabilities. The relationships seen between variability, Eddington ratio, and radio and X-ray emission are discussed in terms of a possible link between the behavior of quasars and black hole X-ray binaries.

We present single-epoch black hole mass (M BH) estimators based on the rest-frame ultraviolet (UV) Mg ii 2798 Å and optical Hβ 4861 Å emission lines. To enlarge the luminosity range of active galactic nuclei (AGNs), we combine the 31 reverberation-mapped AGNs with relatively low luminosities from Bahk et al., 47 moderate-luminosity AGNs from Woo et al., and 425 high-luminosity AGNs from the Sloan Digital Sky Survey. The combined sample has a monochromatic luminosity at 5100 Å in the range erg s−1, over the range 5.5 &lt; log(M BH/M ⊙) &lt; 9.5. Based on the fiducial mass from the line dispersion or FWHM of Hβ paired with the continuum luminosity at 5100 Å, we calibrate the best-fit parameters in the black hole mass estimators using the Mg ii line. We find that the differences in the line profiles between Mg ii and Hβ have significant effects on calibrating the UV M BH estimators. By exploring the systematic discrepancy between the UV and optical M BH estimators as a function of AGN properties, we suggest adding a correction term in the equation for the UV mass estimator. We also find a ∼0.1 dex bias in the M BH estimation due to the difference in the spectral slope in the range 2800–5200 Å. Depending on whether the selection of M BH estimator is based on either line dispersion or FWHM and either continuum or line luminosity, the derived UV mass estimators show ≳0.1 dex intrinsic scatter with respect to the fiducial Hβ-based M BH.

We employ the Chandra Multiwavelength Project (ChaMP) and the Sloan Digital Sky Survey (SDSS) to study the fraction of X-ray-active galaxies in the field out to z = 0.7. We utilize spectroscopic redshifts from SDSS and ChaMP, as well as photometric redshifts from several SDSS catalogs, to compile a parent sample of more than 100,000 SDSS galaxies and nearly 1,600 Chandra X-ray detections. Detailed ChaMP volume completeness maps allow us to investigate the local fraction of active galactic nuclei (AGN), defined as those objects having broad-band X-ray luminosities L_X (0.5-8 keV) > 10^42 erg s^-1, as a function of absolute optical magnitude, X-ray luminosity, redshift, mass, and host color/morphological type. In five independent samples complete in redshift and i-band absolute magnitude, we determine the field AGN fraction to be between 0.16 +/- 0.06% (for z < 0.125 and -18 > M_i > -20) and 3.80 +/- 0.92% (for z < 0.7 and M_i < -23). We find striking agreement between our ChaMP/SDSS field AGN fraction and the Chandra cluster AGN fraction, for samples restricted to similar redshift and absolute magnitude ranges: 1.19 +/- 0.11% of ChaMP/SDSS field galaxies with 0.05 < z < 0.31 and absolute R-band magnitude more luminous than M_R < -20 are AGN. Our results are also broadly consistent with measures of the field AGN fraction in narrow, deep fields, though differences in the optical selection criteria, redshift coverage, and possible cosmic variance between fields introduce larger uncertainties in these comparisons.

We perform a systematic search for long-term extreme variability quasars (EVQs) in the overlapping Sloan Digital Sky Survey and 3 Year Dark Energy Survey imaging, which provide light curves spanning more than 15 years. We identified ∼1000 EVQs with a maximum change in g-band magnitude of more than 1 mag over this period, about 10% of all quasars searched. The EVQs have L bol ∼ 1045–1047 erg s−1 and L/L Edd ∼ 0.01–1. Accounting for selection effects, we estimate an intrinsic EVQ fraction of ∼30%–50% among all quasars over a baseline of ∼15 yr. We performed detailed multi-wavelength, spectral, and variability analyses for the EVQs and compared them to their parent quasar sample. We found that EVQs are distinct from a control sample of quasars matched in redshift and optical luminosity: (1) their UV broad emission lines have larger equivalent widths; (2) their Eddington ratios are systematically lower; and (3) they are more variable on all timescales. The intrinsic difference in quasar properties for EVQs suggests that internal processes associated with accretion are the main driver for the observed extreme long-term variability. However, despite their different properties, EVQs seem to be in the tail of a continuous distribution of quasar properties, rather than standing out as a distinct population. We speculate that EVQs are normal quasars accreting at relatively low rates, where the accretion flow is more likely to experience instabilities that drive the changes in flux by a factor of a few on multi-year timescales.

It has been inferred from large unbiased samples that $10$–$15{{\ \rm per\ cent}}$ of all quasars are radio-loud (RL). Using the quasar catalogue from the Sloan Digital Sky Survey, we show that the radio-loud fraction (RLF) for high broad line (HBL) quasars, containing H β full width at half-maximum greater than 15 000 km s−1, is $\sim 57 {{\ \rm per\ cent}}$. While there is no significant difference between the RL and radio-quiet (RQ) populations in our sample in terms of their black hole mass, Eddington ratio, and covering fraction (CF), optical continuum luminosity of the RL quasars are higher. The similarity in the distribution of their CF indicates that our analysis is unbiased in terms of the viewing angle of the HBL RL and RQ quasars. Hence, we conclude that the accretion disc luminosity of the RL quasars in our HBL sample is higher, which indicates a connection between a brighter disc and a more prominent jet. By comparing them with the non-HBL H β broad emission line quasars, we find that the HBL sources have the lowest Eddington ratios in addition to having a very high RLF. That is consistent with the theories of jet formation, in which jets are launched from low Eddington ratio accreting systems. We find that the [O iii] narrow emission line is stronger in the RL compared to RQ quasars in our HBL sample, which is consistent with previous findings in the literature, and may be caused by the interaction of the narrow line gas with the jet.

We present a new accurate catalog of narrow-line Seyfert 1 galaxies (NLS1s) in the southern hemisphere from the Six-degree Field Galaxy Survey (6dFGS) final data release, which is currently the most extensive spectroscopic survey available in the southern sky whose database has not yet been systematically explored. We classified 167 sources as NLS1s based on their optical spectral properties. We derived flux-calibrated spectra for the first time that the 6dFGS does not provide. By analyzing these spectra, we obtained strong correlations between the monochromatic luminosity at 5100 Å and the luminosities of Hβ and [O III]λ5007 lines. The central black hole mass and the Eddington ratio have average values of 8.6 × 106M⊙ and 0.96 LEdd respectively, which are typical values for NLS1s. In the sample, 23 (13.8%) NLS1s were detected at radio frequencies, and 12 (7.0%) of them are radio-loud. Our results confirmed that radio-loud sources tend to have higher redshift, a more massive black hole, and higher radio and optical luminosities than radio-quiet sources.