Hagai Netzer

Reverberation Measurements for 17 Quasars and the Size-Mass-Luminosity Relations in Active Galactic Nuclei

Correlated variations in the line and continuum emission from active galactic nuclei (AGNs) can be used to determine the size and geometry of the broad emission-line regions (BLRs). We have spectro- photometrically monitored a well-de—ned sample of 28 Palomar-Green quasars in order to obtain mea- surements of their BLRs and to investigate the relationships between quasar luminosity, central black hole mass, and BLR size in AGNs. Spectrophotometry was obtained every 1¨4 months for 7.5 yr, yield- ing 20¨70 observing epochs per object. Both the continuum and emission-line —uxes of all of the quasars were observed to change during the duration of the observing program. Seventeen of the 28 objects were observed with adequate sampling independent observing epochs) to search for correlated variations (Z20 between the Balmer emission lines and the continuum —ux. For each of these 17 objects, a signi—cant correlation was observed, with the Balmer-line variations lagging those of the continuum by D100 days (rest frame). Our work increases the available luminosity range for studying the size-mass-luminosity relations in AGNs by 2 orders of magnitude and doubles the number of objects suitable for such studies. Combining our results with comparable published data available for Seyfert 1 galaxies, we —nd the BLR size scales with the rest-frame 5100 luminosity as L0.70B0.03. This determination of the scaling of the Ae size of the BLR as a function of luminosity is signi—cantly diUerent from those previously published and suggests that the eUective ionization parameter in AGNs may be a decreasing function of luminosity. We are also able to constrain, subject to our assumption that gravity dominates the motions of the BLR gas, the scaling relationship between the mass of the central black holes and the luminosity in AGNs. We —nd that the central mass scales with 5100 luminosity as M P L0.5B0.1. This is inconsistent with all Ae AGNs having optical luminosity that is a constant fraction of the Eddington luminosity. Subject headings: galaxies: activequasars: emission linesquasars: general

Central masses and broad-line region sizes of active galactic nuclei. II. A Homogeneous analysis of a large reverberation-mapping database

We present improved black hole masses for 35 active galactic nuclei (AGNs) based on a complete and consistent reanalysis of broad emission-line reverberation-mapping data. From objects with multiple line measurements, we find that the highest precision measure of the virial product cτΔV2/G, where τ is the emission-line lag relative to continuum variations and ΔV is the emission-line width, is obtained by using the cross-correlation function centroid (as opposed to the cross-correlation function peak) for the time delay and the line dispersion (as opposed to FWHM) for the line width and by measuring the line width in the variable part of the spectrum. Accurate line-width measurement depends critically on avoiding contaminating features, in particular the narrow components of the emission lines. We find that the precision (or random component of the error) of reverberation-based black hole mass measurements is typically around 30%, comparable to the precision attained in measurement of black hole masses in quiescent galaxies by gas or stellar dynamical methods. Based on results presented in a companion paper by Onken et al., we provide a zero-point calibration for the reverberation-based black hole mass scale by using the relationship between black hole mass and host-galaxy bulge velocity dispersion. The scatter around this relationship implies that the typical systematic uncertainties in reverberation-based black hole masses are smaller than a factor of 3. We present a preliminary version of a mass-luminosity relationship that is much better defined than any previous attempt. Scatter about the mass-luminosity relationship for these AGNs appears to be real and could be correlated with either Eddington ratio or object inclination.

THE RELATIONSHIP BETWEEN LUMINOSITY AND BROAD-LINE REGION SIZE IN ACTIVE GALACTIC NUCLEI

We reinvestigate the relationship between the characteristic broad-line region size (RBLR) and the Balmer emission-line, X-ray, UV, and optical continuum luminosities. Our study makes use of the best available determinations of RBLR for a large number of active galactic nuclei (AGNs) from Peterson et al. Using their determinations of RBLR for a large sample of AGNs and two different regression methods, we investigate the robustness of our correlation results as a function of data subsample and regression technique. Although small systematic differences were found depending on the method of analysis, our results are generally consistent. Assuming a power-law relation RBLR ∝ Lα, we find that the mean best-fitting α is about 0.67 ± 0.05 for the optical continuum and the broad Hβ luminosity, about 0.56 ± 0.05 for the UV continuum luminosity, and about 0.70 ± 0.14 for the X-ray luminosity. We also find an intrinsic scatter of ~40% in these relations. The disagreement of our results with the theoretical expected slope of 0.5 indicates that the simple assumption of all AGNs having on average the same ionization parameter, BLR density, column density, and ionizing spectral energy distribution is not valid and there is likely some evolution of a few of these characteristics along the luminosity scale.

The Radius-Luminosity Relationship For Active Galactic Nuclei: The Effect of Host-Galaxy Starlight On Luminosity Measurements. II. The Full Sample of Reverberation-Mapped AGNs

We present high-resolution Hubble Space Telescope images of all 35 active galactic nuclei (AGNs) with optical reverberation-mapping results, which we have modeled to create a nucleus-free image of each AGN host galaxy. From the nucleus-free images, we determine the host-galaxy contribution to ground-based spectroscopic luminosity measurements at 5100 A. After correcting the luminosities of the AGNs for the contribution from starlight, we re-examine the Hβ R BLR-L relationship. Our best fit for the relationship gives a power-law slope of 0.52 with a range of 0.45-0.59 allowed by the uncertainties. This is consistent with our previous findings, and thus still consistent with the naive assumption that all AGNs are simply luminosity-scaled versions of each other. We discuss various consistency checks relating to the galaxy modeling and starlight contributions, as well as possible systematic errors in the current set of reverberation measurements from which we determine the form of the R BLR-L relationship.

Broad emission features in QSOs and active galactic nuclei. II - New observations and theory of Fe II and H I emission

Seven QSOs of low to intermediate redshift are characterized on the basis of: 320-850-nm spectra obtained with the UVITS spectrograph and image-dissector scanner at the f/9 Cassegrain focus of the 2.7-m reflecting telescope at McDonald Observatory; improved model calculations for the Fe II, Mg II, and Balmer lines and the Balmer continuum; and the theoretical results of Netzer and Wills (1983). The data are presented in tables, spectra, and difference spectra and described in detail. Fe II is found to be the largest contributor to the emission line spectrum, with strong UV Fe II lines in all QSOs (regardless of the strength of the optical Fe II lines) and an abundance ratio suggesting a factor-of-three overabundance of Fe relative to Mg and probably H. A discrepancy between the observed Fe II strength and the predictions of dustless standard photoionization models is noted, and the addition of a high-density component to the models is suggested.

SPITZER QUASAR AND ULIRG EVOLUTION STUDY (QUEST). I. THE ORIGIN OF THE FAR-INFRARED CONTINUUM OF QSOs

This paper addresses the origin of the far-infrared (FIR) continuum of QSOs, based on the Quasar and ULIRG Evolution Study (QUEST) of nearby QSOs and ULIRGs using observations with the Spitzer Space Telescope. For 27 Palomar-Green QSOs at z ≲ 0.3, we derive luminosities of diagnostic lines ([Ne II] 12.8 μm, [Ne V] 14.3 μm, [O IV] 25.9 μm) and emission features (PAH 7.7 μm emission, which is related to star formation), as well as continuum luminosities over a range of mid- to far-infrared wavelengths between 6 and 60 μm. We detect star-formation-related PAH emission in 11/26 QSOs and fine-structure line emission in all of them, often in multiple lines. The detection of PAHs in the average spectrum of sources that lack individual PAH detections provides further evidence for the widespread presence of PAHs in QSOs. Similar PAH/FIR and [Ne II]/FIR ratios are found in QSOs and in starburst-dominated ULIRGs and lower luminosity starbursts. We conclude that the typical QSO in our sample has at least 30% but likely most of the far-infrared luminosity (~10^(10)-10^(12) L_☉) arising from star formation, with a tendency for larger star formation contribution at the largest FIR luminosities. In the QSO sample, we find correlations between most of the quantities studied including combinations of AGN tracers and starburst tracers. The common scaling of AGN and starburst luminosities (and fluxes) is evidence for a starburst-AGN connection in luminous AGN. Strong correlations of far-infrared continuum and starburst related quantities (PAH, low-excitation [Ne II]) offer additional support for the starburst origin of far-infrared emission.

Long-term optical variability properties of the Palomar—Green quasars

We present results from a monitoring programme of 42 quasars from the Palomar–Green sample. The objects were observed for seven years at the Wise Observatory, as part of a long-term effort to monitor AGN of various types. This is the most extensive programme of its kind carried out to date on a well-defined, optically selected quasar sample. The typical sampling interval is ∼ 40 d. One-third of the quasars were observed at ∼ 60 epochs, and the rest at ∼ 30 epochs in two bands (B and R) with a photometric accuracy of ∼ 0.01 mag. We present light curves for all of the sources, and discuss the sample variability properties. All of the quasars in the sample varied during the campaign with intrinsic rms amplitudes of 5 <σB<34 per cent and 4 <σR<26 per cent. The rms amplitude and colour for the entire sample are σB=14 per cent, σR=12 per cent and σB-R=5 per cent. On time-scales of 100 to 1000 d the power spectra of the sources have a power-law shape, Pν≺ν−γ, with γ≈ 2.0 and a spread ≲ 0.6. At least half of the quasars, particularly those that are most variable, become bluer when they brighten, and the rest do not show this behaviour. We quantify this phenomenon, which has been observed previously mainly in Seyfert galaxies. The quasars which are most variable tend also to exhibit asymmetry in their variations, in the sense that the brightening phases last longer than the fading phases. We have searched for correlations between the measured variability properties and other parameters of the quasars, such as luminosity, redshift, radio loudness and X-ray slope. We find several new correlations, and reproduce some of the correlations reported by previous studies. Among them are an anticorrelation of variability amplitude with luminosity, a trend of the autocorrelation time-scale with luminosity, and an increase in variability amplitude with Hβ equivalent width. However, all of these trends have a large scatter despite the low observational uncertainties.

X-Ray Observations of Optically Selected, Radio-quiet Quasars. I. The ASCA Results

We present the result of 27 ASCA observations of 26 radio-quiet quasars (RQQs) from the Palomar-Green (PG) survey. The sample is not statistically complete, but it is reasonably representative of RQQs in the PG survey. For many of the sources, the ASCA data are presented here for the first time. All the RQQs were detected except for two objects, both of which contain broad absorption lines in the optical band. We find the variability characteristics of the sources to be consistent with Seyfert 1 galaxies. A power law offers an acceptable description of the time-averaged spectra in the 2-10 keV (quasar frame) band for all but one data set. The best-fitting values of the photon index vary from object to object over the range 1.5 ?2-10 3, with a mean ?2-10 2 and dispersion ?(?2-10) 0.25. The distribution of ?2-10 is therefore similar to that observed in other RQ active galactic nuclei (AGNs) and seems to be unrelated to X-ray luminosity. No single model adequately describes the full 0.6-10 keV (observed frame) continuum of all the RQQs. Approximately 50% of the sources can be adequately described by a single power law or by a power law with only very subtle deviations. All but one of the remaining data sets were found to have convex spectra (flattening as one moves to higher energies). The exception is PG 1411+442, in which a substantial column density (NH,z ~ 2 ? 1023 cm-2) obscures ~98% of the continuum. We find only five (maybe six) of 14 objects with z 0.25 to have soft excesses at energies 1 keV, but we find no universal shape for these spectral components. The spectrum of PG 1244+026 contains a rather narrow emission feature centered at an energy ~1 keV (quasar frame). The detection rate of absorption due to ionized material in these RQQs is lower than that seen in Seyfert 1 galaxies. In part, this may be due to selection effects. However, when detected, the absorbers in the RQQs exhibit a similar range of column density and ionization parameter as Seyfert 1 galaxies. We find evidence of Fe K-shell emission in at least eight RQQs. These are all low-luminosity objects, and the line parameters are consistent with those of other low-luminosity RQ AGNs. However the construction of the mean data/model ratios for various luminosity ranges reveals a trend whereby the profile and strength of the Fe K-shell emission changes as a function of luminosity.

The mean star formation rate of X-ray selected active galaxies and its evolution from z ~ 2.5: results from PEP-Herschel

We study relationships between star-formation rate (SFR) and the accretion luminosity and nuclear obscuration of X-ray selected active galactic nuclei (AGNs) using a combination of deep far-infrared (FIR) and X-ray data in three key extragalactic survey fields (GOODS-South, GOODS-North and COSMOS), as part of the PACS Evolutionary Probe (PEP) program. The use of three fields with differing areas and depths enables us to explore trends between the global FIR luminosity of the AGN hosts and the luminosity of the active nucleus across 4.5 orders of magnitude in AGN luminosity (LAGN) and spanning redshifts from the Local Universe to z = 2.5. Using imaging from the Herschel/PACS instrument in 2−3 bands, we combine FIR detections and stacks of undetected objects to arrive at mean fluxes for subsamples in bins of redshift and X-ray luminosity. We constrain the importance of AGN-heated dust emission in the FIR and confirm that the majority of the FIR emission of AGNs is produced by cold dust heated by star-formation in their host galaxies. We uncover characteristic trends between the mean FIR luminosity (L60) and accretion luminosity of AGNs, which depend both on LAGN and redshift. At low AGN luminosities, accretion and SFR are uncorrelated at all redshifts, consistent with a scenario where most low-luminosity AGNs are primarily fueled by secular processes in their host galaxies. At high AGN luminosities, a significant correlation is observed between L60 and LAGN, but only among AGNs at low and moderate redshifts (z 1) suggesting that the role of mergers is less important at these epochs. At all redshifts, we find essentially no relationship between L60 and nuclear obscuration across five orders of magnitude in obscuring Hydrogen column density (NH), suggesting that various mechanisms are likely to be responsible for obscuring X-rays in active galaxies. We discuss a broad scenario which can account for these trends: one in which two different modes of AGN fueling operate in the low- and high-luminosity regimes of SMBH accretion. We postulate that the dominant mode of accretion among high-luminosity AGNs evolves with redshift. Our study, as well as a body of evidence from the literature and emerging knowledge about the properties of high redshift galaxies, supports this scenario.

FAST MOLECULAR OUTFLOWS IN LUMINOUS GALAXY MERGERS: EVIDENCE FOR QUASAR FEEDBACK FROM HERSCHEL

We report the results from a systematic search for molecular (OH 119 μm) outflows with Herschel/PACS in a sample of 43 nearby (z < 0.3) galaxy mergers, mostly ultraluminous infrared galaxies (ULIRGs) and QSOs. We find that the character of the OH feature (strength of the absorption relative to the emission) correlates with that of the 9.7 μm silicate feature, a measure of obscuration in ULIRGs. Unambiguous evidence for molecular outflows, based on the detection of OH absorption profiles with median velocities more blueshifted than –50 km s^(–1), is seen in 26 (70%) of the 37 OH-detected targets, suggesting a wide-angle (~145°) outflow geometry. Conversely, unambiguous evidence for molecular inflows, based on the detection of OH absorption profiles with median velocities more redshifted than +50 km s^(–1), is seen in only four objects, suggesting a planar or filamentary geometry for the inflowing gas. Terminal outflow velocities of ~–1000 km s^(–1) are measured in several objects, but median outflow velocities are typically ~–200 km s^(–1). While the outflow velocities show no statistically significant dependence on the star formation rate, they are distinctly more blueshifted among systems with large active galactic nucleus (AGN) fractions and luminosities [log(L_(AGN)/L_☉) ≥ 11.8 ± 0.3]. The quasars in these systems play a dominant role in driving the molecular outflows. However, the most AGN dominated systems, where OH is seen purely in emission, show relatively modest OH line widths, despite their large AGN luminosities, perhaps indicating that molecular outflows subside once the quasar has cleared a path through the obscuring material.