Matthias Dietrich

Black Hole Masses and Eddington Ratios at 0.3 < z < 4

We study the distribution of Eddington luminosity ratios, Lbol/LEdd, of active galactic nuclei (AGNs) discovered in the AGN and Galaxy Evolution Survey (AGES). We combine Hβ, Mg II, and C IV line widths with continuum luminosities to estimate black hole (BH) masses in 407 AGNs, covering the redshift range z ~ 0.3-4 and the bolometric luminosity range Lbol ~ 1045-1047 ergs s-1. The sample consists of X-ray or mid-infrared (24 μm) point sources with optical magnitude R ≤ 21.5 mag and optical emission-line spectra characteristic of AGNs. For the range of luminosity and redshift probed by AGES, the distribution of estimated Eddington ratios is well described as log-normal, with a peak at Lbol/LEdd 1/4 and a dispersion of 0.3 dex. Since additional sources of scatter are minimal, this dispersion must account for contributions from the scatter between estimated and true BH mass and the scatter between estimated and true bolometric luminosity. Therefore, we conclude that (1) neither of these sources of error can contribute more than ~0.3 dex rms, and (2) the true Eddington ratios of optically luminous AGNs are even more sharply peaked. Because the mass estimation errors must be smaller than ~0.3 dex, we can also investigate the distribution of Eddington ratios at fixed BH mass. We show for the first time that the distribution of Eddington ratios at fixed BH mass is peaked, and that the dearth of AGNs at a factor of ~10 below Eddington is real and not an artifact of sample selection. These results provide strong evidence that supermassive BHs gain most of their mass while radiating close to the Eddington limit, and they suggest that the fueling rates in luminous AGNs are ultimately determined by BH self-regulation of the accretion flow rather than galactic-scale dynamical disturbances.

The Black Hole-Bulge Relationship in Quasars

We use quasi-stellar object (QSO) emission-line widths to examine the MBH-σ* relationship as a function of redshift and to extend the relationship to larger masses. Supermassive black holes in galactic nuclei are closely related to the bulge of the host galaxy. The mass of the black hole MBH increases with the bulge luminosity and with the velocity dispersion of the bulge stars, σ*. An important clue to the origin of this correlation would be an observational determination of the evolution, if any, in the MBH-σ* relationship as a function of cosmic time. The high luminosity of QSOs affords the potential for studies at large redshifts. We derive black hole masses from the continuum luminosity and the width of the broad Hβ line and σ* from the width of the narrow [O III] lines. We find that radio-quiet QSOs conform to the established MBH-σ* relationship up to values of MBH ≈ 1010 M☉, with no discernible change in the relationship out to redshifts of z ≈ 3. These results are consistent with the idea that the growth of supermassive black holes and massive bulges occurred simultaneously.

REVERBERATION MAPPING MEASUREMENTS OF BLACK HOLE MASSES IN SIX LOCAL SEYFERT GALAXIES

We present the final results from a high sampling rate, multi-month, spectrophotometric reverberation mapping campaign undertaken to obtain either new or improved Hβ reverberation lag measurements for several relatively low-luminosity active galactic nuclei (AGNs). We have reliably measured the time delay between variations in the continuum and Hβ emission line in six local Seyfert 1 galaxies. These measurements are used to calculate the mass of the supermassive black hole at the center of each of these AGNs. We place our results in context to the most current calibration of the broad-line region (BLR) RBLR–L relationship, where our results remove outliers and reduce the scatter at the low-luminosity end of this relationship. We also present velocity-resolved Hβ time-delay measurements for our complete sample, though the clearest velocity-resolved kinematic signatures have already been published.

Continuum and Emission-Line Strength Relations for a Large Active Galactic Nuclei Sample

We report on the analysis of a large sample of 744 type 1 active galactic nuclei, including quasars and Seyfert 1 galaxies across the redshift from 0 z 5 and spanning nearly 6 orders of magnitude in continuum luminosity. We discuss correlations of continuum and emission-line properties in the rest-frame ultraviolet and optical spectral ranges. The well-established Baldwin effect is detected for almost all emission lines from O VI ?1034 to [O III] ?5007. Their equivalent widths are significantly anticorrelated with the continuum strength, while they are nearly independent of redshift. This is the well-known Baldwin effect. Its slope ?, measured as log W? ? log ?L?(1450 ?), shows a tendency to become steeper toward higher luminosity. The slope of the Baldwin effect also increases with the ionization energy needed to create the individual lines. In contrast to this general trend, the N V ?1240 equivalent width is nearly independent of continuum luminosity and remains nearly constant. The overall line behaviors are consistent with softer UV continuum shapes and perhaps increasing gas metallicity in more luminous active galactic nuclei.

Steps toward Determination of the Size and Structure of the Broad-Line Region in Active Galactic Nuclei. XVI. A 13 Year Study of Spectral Variability in NGC 5548

We present the final installment of an intensive 13 year study of variations of the optical continuum and broad Hemission line in the Seyfert 1 galaxy NGC 5548. The database consists of 1530 optical continuum measurements and 1248 Hmeasurements. The Hvariations follow the continuum variations closely, with a typical time delay of about 20 days. However, a year-by-year analysis shows that the magnitude of emission-line time delay is correlated with the mean continuum flux. We argue that the data are consistent with the simple model prediction between the size of the broad-line region and the ionizing luminosity, r / L 1=2 ion . Moreover, the apparently linear nature of the correlation between the Hresponse time and the nonstellar optical continuum Fopt arises as a consequence of the changing shape of the continuum as it varies, specifically Fopt / F 0:56 UV . Subject headings: galaxies: active — galaxies: individual (NGC 5548) — galaxies: nuclei — galaxies: Seyfert

A reverberation-based mass for the central black hole in NGC 4151

We have undertaken a new ground-based monitoring campaign to improve the estimates of the mass of the central black hole in NGC 4151. We measure the lag time of the broad H? line response compared to the optical continuum at 5100 ? and find a lag of 6.6 days. We combine our data with the recent reanalysis of UV emission lines by Metzroth and coworkers to calculate a weighted mean of the black hole mass, MBH = (4.57) ? 107 M?. The absolute calibration of the black hole mass is based on normalization of the AGN black hole mass-stellar velocity dispersion (MBH-?*) relationship to that of quiescent galaxies by Onken and coworkers. The scatter in the MBH-?* relationship suggests that reverberation-mapping-based mass measurements are typically uncertain by a factor of 3-4.

Systematic Uncertainties in Black Hole Masses Determined from Single-Epoch Spectra

We explore the nature of systematic errors that can arise in measurement of black hole masses from single-epoch (SE) spectra of active galactic nuclei (AGNs) by utilizing the many epochs available for NGC 5548 and PG1229+204 from reverberation mapping (RM) databases. In particular, we examine systematics due to AGN variability, contamination due to constant spectral components (i.e., narrow lines and host galaxy flux), data quality (i.e., signal-to-noise ratio (S/N)), and blending of spectral features. We investigate the effect that each of these systematics has on the precision and accuracy of SE masses calculated from two commonly used line width measures by comparing these results to recent RM studies. We calculate masses by characterizing the broad H? emission line by both the full width at half maximum and the line dispersion, and demonstrate the importance of removing narrow emission-line components and host starlight. We find that the reliability of line width measurements rapidly decreases for S/N lower than ~ 10-20 (per pixel), and that fitting the line profiles instead of direct measurement of the data does not mitigate this problem but can, in fact, introduce systematic errors. We also conclude that a full spectral decomposition to deblend the AGN and galaxy spectral features is unnecessary, except to judge the contribution of the host galaxy to the luminosity and to deblend any emission lines that may inhibit accurate line width measurements. Finally, we present an error budget which summarizes the minimum observable uncertainties as well as the amount of additional scatter and/or systematic offset that can be expected from the individual sources of error investigated. In particular, we find that the minimum observable uncertainty in SE mass estimates due to variability is 0.1 dex for high S/N (20 pixel?1) spectra.

The Mass of the Black Hole in the Seyfert 1 Galaxy NGC 4593 from Reverberation Mapping

We present new observations leading to an improved black hole mass estimate for the Seyfert 1 galaxy NGC 4593 as part of a reverberation-mapping campaign conducted at the MDM Observatory. Cross-correlation analysis of the Hβ emission-line light curve with the optical continuum light curve reveals an emission-line time delay of τcent = 3.73 ± 0.75 days. By combining this time delay with the Hβ line width, we derive a central black hole mass of MBH = (9.8 ± 2.1) × 106 M☉, an improvement in precision of a factor of several over past results.

ACTIVE GALACTIC NUCLEUS EMISSION-LINE PROPERTIES VERSUS THE EDDINGTON RATIO

We analyze UV spectra for a large sample of 578 type 1 active galactic nuclei and derive Eddington ratios, L/LEdd, from the bolometric luminosities and emission-line widths for each object in the sample. The sample spans 5 orders of magnitude in supermassive black hole (SMBH) mass, 7 orders of magnitude in luminosity, and a redshift range 0 ≤ z ≤ 5. We include a sample of 26 low-redshift narrow-line Seyfert 1 galaxies (NLS1s) for comparative analysis. The NLS1s have slightly larger than average L/LEdd ratios (and smaller SMBH masses) for their luminosities, but those L/LEdd values are still substantially below the average for luminous quasars. A large fraction (27%) of the objects overall have L/LEdd > 1, which might be explained by nonspherically symmetric accretion. We find no trend between L/LEdd and either redshift or SMBH mass. Composite spectra sorted by L/LEdd show an unusual emission-line behavior: nearly constant peak heights and decreasing FWHMs with increasing L/LEdd. This is in marked contrast to the emission-line behaviors with luminosity, SMBH mass, and FWHM(C IV), which clearly show trends analogous to the Baldwin effect: decreasing line peaks and equivalent widths with increasing luminosity, SMBH mass, and FWHM. The origins of the unusual behavior with L/LEdd are not understood, but one implication is that metallicity estimates based on emission-line ratios involving nitrogen show no trend with L/LEdd in the composite spectra created from different ranges in L/LEdd. The NLS1 composite, however, shows a slightly high metallicity for its SMBH mass and luminosity. Our earlier work suggests that host galaxy mass, correlated with SMBH mass and AGN luminosity, is the fundamental parameter affecting broad emission line region metallicities. Some secondary effect, not related to L/LEdd, must be enhancing the metallicities in NLS1s.

The structure of the broad-line region in active galactic nuclei. I. Reconstructed velocity-delay maps

We present velocity-resolved reverberation results for five active galactic nuclei. We recovered velocity-delay maps using the maximum entropy method for four objects: Mrk 335, Mrk 1501, 3C?120, and PG?2130+099. For the fifth, Mrk 6, we were only able to measure mean time delays in different velocity bins of the H? emission line. The four velocity-delay maps show unique dynamical signatures for each object. For 3C?120, the Balmer lines show kinematic signatures consistent with both an inclined disk and infalling gas, but the He II??4686 emission line is suggestive only of inflow. The Balmer lines in Mrk 335, Mrk 1501, and PG?2130+099 show signs of infalling gas, but the He II emission in Mrk 335 is consistent with an inclined disk. We also see tentative evidence of combined virial motion and infalling gas from the velocity-binned analysis of Mrk 6. The maps for 3C?120 and Mrk 335 are two of the most clearly defined velocity-delay maps to date. These maps constitute a large increase in the number of objects for which we have resolved velocity-delay maps and provide evidence supporting the reliability of reverberation-based black hole mass measurements.