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An Internet Database of Ultraviolet Continuum Light Curves for Seyfert Galaxies
Using the Multimission Archive at STScI (MAST), we have extractedspectra and determined continuum light curves for 175 Seyfert galaxiesthat have been observed with the International Ultraviolet Explorer andthe Faint Object Spectrograph on the Hubble Space Telescope. To obtainthe light curves as a function of Julian Date, we used fixed bins in theobject's rest frame and measured small regions (between 30 and 60Å) of each spectrum's continuum flux in the range 1150 to 3200Å. We provide access to the UV light curves and other basicinformation about the observations in tabular and graphical form via theInternet at http://www.chara.gsu.edu/PEGA/IUE.
| XMM-Newton observations of bright ROSAT selected active galactic nuclei with low intrinsic absorption
We present a sample of 21 ROSAT bright active galactic nuclei (AGNs),representing a range of spectral classes, and selected for follow-upsnapshot observations with XMM-Newton. The typical exposure was between5 and 10ks. The objects were primarily selected on the bases of X-raybrightness and not on hardness ratio; thus the sample cannot be strictlydefined as a `soft'sample. One of the main outcomes from the XMM-Newtonobservations was that all of the AGN, including 11 type 1.8-2 objects,required low levels of intrinsic absorption (NH<~1021cm-2). The low absorption in type 2 systems isa challenge to account for in the standard orientation-based unificationmodel, and we discuss possible physical and geometrical models whichcould elucidate the problem. Moreover, there does not appear to be anyrelation between the strength and shape of the soft excess, and thespectral classification of the AGN in this sample. We further identify anumber of AGN which deserve deeper observations or further analysis: forexample, the low-ionization nuclear emission regions (LINERs) NGC 5005and NGC 7331, where optically thin thermal and extended emission isdetected, and the narrow-line Seyfert 1 II Zw 177, which shows a broademission feature at ~ 5.8keV.
| On the X-Ray Baldwin Effect for Narrow Fe Kα Emission Lines
Most active galactic nuclei (AGNs) exhibit a narrow Fe Kα line at~6.4 keV in the X-ray spectra, due to the fluorescent emission from coldmaterial far from the inner accretion disk. Using XMM-Newtonobservations, Page et al. found that the equivalent width (EW) of thenarrow Fe Kα line decreases with increasing luminosity(EW~L-0.17+/-0.08), suggesting a decrease in the coveringfactor of the material emitting the line (presumably the torus). Bycombining the archival Chandra HETG observations of 34 type 1 AGNs withXMM observations in the literature, we build a much larger sample with101 AGNs. We find a similar X-ray Baldwin effect in the sample(EW~L-0.2015+/-0.0426) however, we note that theanticorrelation is dominated by the radio-loud AGNs in the sample, whoseX-ray spectra might be contaminated by the relativistic jet. Excludingthe radio-loud AGNs, we find a much weaker anticorrelation(EW~L-0.1019+/-0.0524). We present Monte Carlo simulationsshowing that such a weak anticorrelation can be attributed to therelative short timescale variations of the X-ray continuum.
| The Radius-Luminosity Relationship for Active Galactic Nuclei: The Effect of Host-Galaxy Starlight on Luminosity Measurements
We have obtained high-resolution images of the central regions of 14reverberation-mapped active galactic nuclei (AGNs) using the HubbleSpace Telescope Advanced Camera for Surveys High Resolution Camera toaccount for host-galaxy starlight contamination of measured AGNluminosities. We measure the host-galaxy starlight contribution to thecontinuum luminosity at 5100 Å through the typical ground-basedslit position and geometry used in the reverberation-mapping campaigns.We find that removing the starlight contribution results in asignificant correction to the luminosity of each AGN both for lowerluminosity sources, as expected, but also for the higher luminositysources such as the PG quasars. After accounting for the host galaxystarlight, we revisit the well-known broad-line region radius-luminosityrelationship for nearby AGNs. We find the power-law slope of therelationship for the Hβ line to be 0.518+/-0.039, shallower thanwhat was previously reported and consistent with the slope of 0.5expected from the naive theoretical assumption that all AGNs have, onaverage, the same ionizing spectrum and the same ionization parameterand gas density in the Hβ line-emitting region.
| The MBH-σ* Relation in Local Active Galaxies
We examine whether active galaxies obey the same relation between blackhole mass and stellar velocity dispersion as inactive systems, using thelargest published sample of velocity dispersions for active nuclei todate. The combination of 56 original measurements with objects from theliterature not only increases the sample from the 15 consideredpreviously to 88 objects but allows us to cover an unprecedented rangein both stellar velocity dispersion (30-268 km s-1) and blackhole mass (105-108.6 Msolar). In theMBH-σ* relation of active galaxies, we finda lower zero point than the best-fit relation of Tremaine et al. forinactive galaxies, and an upper limit on the intrinsic scatter of 0.4dex. There is also evidence of a flatter slope at low black hole masses.We discuss potential contributors to the observed offsets, includingvariations in the geometry of the broad-line region, evolution in theMBH-σ* relation, and differential growthbetween black holes and galaxy bulges.
| Determining Central Black Hole Masses in Distant Active Galaxies and Quasars. II. Improved Optical and UV Scaling Relationships
We present four improved empirical relationships useful for estimatingthe central black hole mass in nearby AGNs and distant luminous quasarsalike using either optical or UV single-epoch spectroscopy. These massscaling relationships between line widths and luminosity are based onrecently improved empirical relationships between the broad-line regionsize and luminosities in various energy bands and are calibrated to theimproved mass measurements of nearby AGNs based on emission-linereverberation mapping. The mass scaling relationship based on theHβ line luminosity allows mass estimates for low-redshift sourceswith strong contamination of the optical continuum luminosity by stellaror nonthermal emission, while that based on the C IV λ1549 linedispersion allows mass estimates in cases where only the line dispersion(as opposed to the FWHM) can be reliably determined. We estimate thatthe absolute uncertainties in masses given by these mass scalingrelationships are typically around a factor of 4. We include in anappendix mass estimates for all of the Bright Quasar Survey (PG) quasarsfor which direct reverberation-based mass measurements are notavailable.Based in part on observations made with the NASA/ESA Hubble SpaceTelescope, obtained from the Data Archive at the Space Telescope ScienceInstitute, which is operated by the Association of Universities forResearch in Astronomy, Inc., under NASA contract NAS 5-26555.
| Local and Large-Scale Environment of Seyfert Galaxies
We present a three-dimensional study of the local (<=100h-1 kpc) and the large-scale (<=1 h-1 Mpc)environment of the two main types of Seyfert AGN galaxies. For thispurpose we use 48 Seyfert 1 galaxies (with redshifts in the range0.007<=z<=0.036) and 56 Seyfert 2 galaxies (with0.004<=z<=0.020), located at high galactic latitudes, as well astwo control samples of nonactive galaxies having the same morphological,redshift, and diameter size distributions as the corresponding Seyfertsamples. Using the Center for Astrophysics (CfA2) and Southern SkyRedshift Survey (SSRS) galaxy catalogs (mB~15.5) and our ownspectroscopic observations (mB~18.5), we find that within aprojected distance of 100 h-1 kpc and a radial velocityseparation of δv<~600 km s-1 around each of ourAGNs, the fraction of Seyfert 2 galaxies with a close neighbor issignificantly higher than that of their control (especially within 75h-1 kpc) and Seyfert 1 galaxy samples, confirming a previoustwo-dimensional analysis of Dultzin-Hacyan et al. We also find that thelarge-scale environment around the two types of Seyfert galaxies doesnot vary with respect to their control sample galaxies. However, theSeyfert 2 and control galaxy samples do differ significantly whencompared to the corresponding Seyfert 1 samples. Since the maindifference between these samples is their morphological typedistribution, we argue that the large-scale environmental differencecannot be attributed to differences in nuclear activity but rather totheir different type of host galaxies.
| The Host Galaxies of Narrow-Line Seyfert 1 Galaxies: Nuclear Dust Morphology and Starburst Rings
We present a study of the nuclear morphology of a sample of narrow- andbroad-line Seyfert 1 galaxies (NLS1s and BLS1s, respectively) based onbroadband images in the Hubble Space Telescope archives. In our previousstudy we found that large-scale stellar bars at >1 kpc from thenucleus are more common in NLS1s than BLS1s. In this paper we find thatNLS1s preferentially have grand-design dust spirals within ~1 kpc oftheir centers. We also find that NLS1s have a higher fraction of nuclearstar-forming rings than BLS1s. We find that many of the morphologicaldifferences are due to the presence or absence of a large-scale stellarbar within the spiral host galaxy. In general, barred Seyfert 1 galaxiestend to have grand-design dust spirals at their centers, confirming theresults of other researchers. The high fraction of grand-design nucleardust spirals and stellar nuclear rings observed in NLS1s' host galaxiessuggests a means for efficient fueling of their nuclei to support theirhigh Eddington ratios.
| Spectral line variability amplitudes in active galactic nuclei
We present the results of a long-term variability campaign of verybroad-line AGNs with line widths broader than FWHM > 5000 kms-1. The main goal of our investigation was to study whetherthe widths of the optical broad emission lines are correlated with theoptical intensity variations on timescales of years. Our AGN sampleconsisted of 10 objects. We detected a significant correlation betweenoptical continuum variability amplitudes and Hβ emission linewidths (FWHM) and, to a lesser degree, between Hβ line intensityvariations and Hβ equivalent widths. We add the spectroscopic dataof variable AGNs from the literature to supplement our sample. The AGNsfrom other optical variability campaigns with different line-widthshelped to improve the statistical significance of our very broad-lineAGN sample. After including the data on 35 additional galaxies, thecorrelation between optical continuum variability amplitudes and Hβemission line widths becomes even more significant and the probabilitythat this is a random correlation drops to 0.7 percent.
| Supermassive Black Holes in Galactic Nuclei: Past, Present and Future Research
This review discusses the current status of supermassive black holeresearch, as seen from a purely observational standpoint. Since theearly ‘90s, rapid technological advances, most notably the launchof the Hubble Space Telescope, the commissioning of the VLBA andimprovements in near-infrared speckle imaging techniques, have not onlygiven us incontrovertible proof of the existence of supermassive blackholes, but have unveiled fundamental connections between the mass of thecentral singularity and the global properties of the host galaxy. It isthanks to these observations that we are now, for the first time, in aposition to understand the origin, evolution and cosmic relevance ofthese fascinating objects.
| O I Line Emission in the Quasar PG 1116+215
By observing the near-infrared spectrum of the quasar PG 1116+215 at z =0.176 and combining with the HST/FOS spectrum, we obtained the relativestrengths of three permitted O I lines(λ1304, λ8446, and λ11287) in a quasar for thefirst time. The photon flux ratios of the O I lines of the quasar were compared with those previously measured in a Seyfert 1 and six narrow-line Seyfert 1s. No significant differences were found in the O I line flux ratios between the quasar and the other Seyferts, suggesting that the gas density in the O I and Fe II line-emitting regions in the quasar is of the same order as those in low-luminosity AGNs. It was also found that the line width of O Iλ11287 is significantly narrower than that of Lyα, which isconsistent with O I and Fe II emission occurring in the partly ionized regions at the outermost portion of the broad-line region where velocities are small.
| The Relationship of Hard X-Ray and Optical Line Emission in Low-Redshift Active Galactic Nuclei
In this paper we assess the relationship of the population of activegalactic nuclei (AGNs) selected by hard X-rays to the traditionalpopulation of AGNs with strong optical emission lines. First, we studythe emission-line properties of a new hard-X-ray-selected sample of 47local AGNs (classified optically as Type 1 and 2 AGNs). We find that thehard X-ray (3-20 keV) and [O III] λ5007 optical emission-lineluminosities are well-correlated over a range of about 4 orders ofmagnitude in luminosity (mean luminosity ratio 2.15 dex with a standarddeviation of σ=0.51 dex). Second, we study the hard X-rayproperties of a sample of 55 local AGNs selected from the literature onthe basis of the flux in the [O III] line. The correlation between thehard X-ray (2-10 keV) and [O III] luminosity for the Type 1 AGNs isconsistent with what is seen in the hard-X-ray-selected sample. However,the Type 2 AGNs have a much larger range in the luminosity ratio, andmany are very weak in hard X-rays (as expected for heavily absorbedAGNs). We then compare the hard X-ray (3-20 keV) and [O III] luminosityfunctions of AGNs in the local universe. These have similar faint-endslopes, with a luminosity ratio of 1.60 dex (0.55 dex smaller than themean value for individual hard-X-ray-selected AGNs). We conclude that atlow redshift, selection by narrow optical emission lines will recovermost AGNs selected by hard X-rays (with the exception of BL Lacobjects). However, selection by hard X-rays misses a significantfraction of the local AGN population with strong emission lines.
| The Link between Star Formation and Accretion in LINERs: A Comparison with Other Active Galactic Nucleus Subclasses
We present archival high-resolution X-ray imaging observations of 25nearby LINERs observed by ACIS on board Chandra. This sample builds onour previously published proprietary and archival X-ray observations andincludes the complete set of LINERs with published black hole masses andFIR luminosities that have been observed by Chandra. Of the 82 LINERsobserved by Chandra, 41 (50%) display hard nuclear cores consistent withan AGN. The nuclear 2-10 keV luminosities of these AGN-LINERs range from~2×1038 to ~1×1044 ergss-1. Reinforcing our previous work, we find a significantcorrelation between the Eddington ratio,Lbol/LEdd, and the FIR luminosity,LFIR, as well as the IR brightness ratio,LFIR/LB, in the host galaxy of AGN-LINERs thatextends over 7 orders of magnitude in Lbol/LEdd.Combining our AGN-LINER sample with galaxies from other AGN subclasses,we find that this correlation is reinforced in a sample of 129 AGNs,extending over almost 9 orders of magnitude inLbol/LEdd. Using archival and previously publishedobservations of the 6.2 μm PAH feature from ISO, we find that it isunlikely that dust heating by the AGN dominates the FIR luminosity inour sample of AGNs. Our results may therefore imply a fundamental linkbetween the mass accretion rate (M˙), as measured by the Eddingtonratio, and the star formation rate (SFR), as measured by the FIRluminosity. Apart from the overall correlation, we find that thedifferent AGN subclasses occupy distinct regions in the LFIRand Lbol/LEdd plane. Assuming a constant radiativeefficiency for accretion, our results may imply a variation in theSFR/M˙ ratio as a function of AGN activity level, a result that mayhave significant consequences for our understanding of galaxy formationand black hole growth.
| The Relationship between Luminosity and Broad-Line Region Size in Active Galactic Nuclei
We reinvestigate the relationship between the characteristic broad-lineregion size (RBLR) and the Balmer emission-line, X-ray, UV,and optical continuum luminosities. Our study makes use of the bestavailable determinations of RBLR for a large number of activegalactic nuclei (AGNs) from Peterson et al. Using their determinationsof RBLR for a large sample of AGNs and two differentregression methods, we investigate the robustness of our correlationresults as a function of data subsample and regression technique.Although small systematic differences were found depending on the methodof analysis, our results are generally consistent. Assuming a power-lawrelation RBLR~Lα, we find that the meanbest-fitting α is about 0.67+/-0.05 for the optical continuum andthe broad Hβ luminosity, about 0.56+/-0.05 for the UV continuumluminosity, and about 0.70+/-0.14 for the X-ray luminosity. We also findan intrinsic scatter of ~40% in these relations. The disagreement of ourresults with the theoretical expected slope of 0.5 indicates that thesimple assumption of all AGNs having on average the same ionizationparameter, BLR density, column density, and ionizing spectral energydistribution is not valid and there is likely some evolution of a few ofthese characteristics along the luminosity scale.
| A Comparison of Stellar and Gaseous Kinematics in the Nuclei of Active Galaxies
To investigate the relationship between black holes and their hostgalaxies, many groups have used the width of the [O III] λ5007line as a substitute for the stellar velocity dispersion(σ*) of galaxy bulges. We directly test this assumptionwith a large and homogeneous sample of narrow-line active galacticnuclei from the Sloan Digital Sky Survey. We consider multipletransitions ([O II] λ3727, [O III] λ5007, and [S II]λλ6716, 6731) and various techniques for quantifying theline width in order to obtain a calibration between the gas velocitydispersion, σg, and σ*. We find thatσg of the low-ionization lines tracesσ*, as does σg for the core of [O III]after its asymmetric blue wing is properly removed, although in allcases the correlation between σg andσ* has considerable scatter. While the gas kinematicsof the narrow-line region of active galaxies are primarily governed bythe gravitational potential of the stars, the accretion rate, as tracedby the Eddington luminosity ratio, seems to play an important secondaryrole. Departures from virial motions correlate systematically withaccretion rate. We discuss the implications of these results forprevious studies that use [O III] line widths to infer stellar velocitydispersions in quasars and narrow-line Seyfert 1 galaxies.
| The Hubble Space Telescope View of LINER Nuclei: Evidence for a Dual Population?
We study a complete, distance-limited sample of 25 LINERs, 21 of whichhave been imaged with the Hubble Space Telescope. In nine objects wedetect an unresolved nucleus. To study their physical properties, wecompare the radio and optical properties of the nuclei of LINERs withthose of other samples of local active galactic nuclei (AGNs), namely,Seyfert galaxies and low-luminosity radio galaxies (LLRGs). Our resultsshow that the LINER population is not homogeneous, as there are twosubclasses: (1) the first class is similar to the LLRG class, as itextends the population of radio-loud nuclei to lower luminosities; (2)the second is similar to Seyfert galaxies and extends the properties ofradio-quiet nuclei toward the lowest luminosities. The objects areoptimally discriminated in the plane formed by the black hole massversus nuclear radio loudness: all radio-loud LINERs haveMBH>~108Msolar, while Seyfertgalaxies and radio-quiet LINERs haveMBH<~108Msolar. The different natureof the various classes of local AGNs are best understood when thefraction of the Eddington luminosity they irradiate,Lo/LEdd, is plotted against the nuclearradio-loudness parameter: Seyfert galaxies are associated withrelatively high radiative efficienciesLo/LEdd>~10-4 (and high accretionrates onto low-mass black holes); LLRGs are associated with lowradiative efficiencies (and low accretion rates onto high-mass blackholes); all LINERs have low radiative efficiency (and accretion rates)and can be radio-loud or radio-quiet, depending on their black holemass.Based on observations obtained at the Space Telescope Science Institute,which is operated by the Association of Universities for Research inAstronomy, Inc., under NASA contract NAS5-26555.
| Simulating the Spitzer Mid-Infrared Color-Color Diagrams
We use a simple parameterization of the mid-IR spectra of a wide rangeof galaxy types in order to predict their distribution in the InfraredArray Camera (IRAC) 3.6, 4.5, 5.8, and 8.0 μm and MultibandPhotometer for Spitzer 24 μm color-color diagrams. We distinguishthree basic spectral types by the energetically dominant component inthe 3-12 μm regime: stellar-dominated, polycyclic aromatichydrocarbon (PAH)-dominated, and continuum-dominated. We use a Markovchain Monte Carlo approach to arrive at a more systematic and robustrepresentation of the mid-IR spectra of galaxies than do moretraditional approaches. We find that IRAC color-color plots are wellsuited to distinguishing the above spectral types, while the addition of24 μm data allows us to suggest practical three-color cuts thatpreferentially select higher redshift sources of a specific type. Wecompare our simulations with the color-color plot obtained by theSpitzer First Look Survey and find reasonable agreement. Lastly, wediscuss other applications as well as future directions for this work.
| Origin of Radio Emission from Nearby Low-Luminosity Active Galactic Nuclei
We use the observational data in radio, optical, and X-ray wave bandsfor a sample of active galactic nuclei (AGNs) with measured black holemasses to explore the origin of radio emission from nearbylow-luminosity active galactic nuclei (LLAGNs). The maximal luminosityof an advection-dominated accretion flow (ADAF) can be calculated for agiven black hole mass, as there is a critical accretion rate above whichthe ADAF is no longer present. We find that the radio luminosities arehigher than the maximal luminosities expected from the ADAF model formost sources in this sample. This implies that the radio emission ispredominantly from the jets in these sources. The radio emission from asmall fraction of the sources (15/60; referred to as radio-weak sources)in this sample can be explained by the ADAF model. However, comparingthe observed multiband emission data with the spectra calculated for theADAF or adiabatic inflow-outflow solution (ADIOS) cases, we find thatneither ADAF nor ADIOS models can reproduce the observed multibandemission simultaneously, with reasonable magnetic field strengths, forthese radio-weak sources. A variety of other possibilities arediscussed, and we suggest that the radio emission is probably dominatedby jet emission even in these radio-weak LLAGNs.
| Connecting the cosmic infrared background to the X-ray background
We estimate the contribution of active galactic nuclei (AGN) and oftheir host galaxies to the infrared background. We use the luminosityfunction and evolution of AGN recently determined by the hard X-raysurveys, and new spectral energy distributions connecting the X-ray andthe infrared emission, divided in intervals of absorption. These twoingredients allow us to determine the contribution of AGN to theinfrared background by using mostly observed quantities, with only minorassumptions. We find that AGN emission contributes little to theinfrared background (<5 per cent over most of the infrared bands),implying that the latter is dominated by star formation. However, AGNhost galaxies may contribute significantly to the infrared background,and more specifically 10-20 per cent in the 1-20 μm range and ~5 percent at λ < 60μm. We also give the contribution of AGN andof their host galaxies to the source number counts in various infraredbands, focusing on those which will be observed with Spitzer. We alsoreport a significant discrepancy between the expected contribution ofAGN hosts to the submillimetre background and bright submillimetrenumber counts with the observational constraints. We discuss the causesand implications of this discrepancy and the possible effects on theSpitzer far-infrared bands.
| The Difference between the α-disks of Seyfert 1 Galaxies and Quasars
In a previous paper, it was suggested that contamination of the nuclearluminosity by the host galaxy plays an important role in determining theparameters of the standard α disk of AGNs. Using the nuclearabsolute B band magnitude instead of the total absolute B bandmagnitude, we have recalculated the central black hole masses, accretionrates and disk inclinations for 20 Seyfert 1 galaxies and 17Palomar-Green (PG) quasars. It is found that a small value of αis needed for the Seyfert 1 galaxies than for the PG quasars. Thisdifference in α possibly leads to the different properties ofSeyfert 1 galaxies and quasars. Furthermore, we find most of the objectsin this sample are not accreting at super-Eddington rates if we adoptthe nuclear optical luminosity in our calculation.
| Classification of Spectra from the Infrared Space Observatory PHT-S Database
We have classified over 1500 infrared spectra obtained with the PHT-Sspectrometer aboard the Infrared Space Observatory according to thesystem developed for the Short Wavelength Spectrometer (SWS) spectra byKraemer et al. The majority of these spectra contribute to subclassesthat are either underrepresented in the SWS spectral database or containsources that are too faint, such as M dwarfs, to have been observed byeither the SWS or the Infrared Astronomical Satellite Low ResolutionSpectrometer. There is strong overall agreement about the chemistry ofobjects observed with both instruments. Discrepancies can usually betraced to the different wavelength ranges and sensitivities of theinstruments. Finally, a large subset of the observations (~=250 spectra)exhibit a featureless, red continuum that is consistent with emissionfrom zodiacal dust and suggest directions for further analysis of thisserendipitous measurement of the zodiacal background.Based on observations with the Infrared Space Observatory (ISO), aEuropean Space Agency (ESA) project with instruments funded by ESAMember States (especially the Principle Investigator countries: France,Germany, Netherlands, and United Kingdom) and with the participation ofthe Institute of Space and Astronautical Science (ISAS) and the NationalAeronautics and Space Administration (NASA).
| Comparison of Nuclear Starburst Luminosities between Seyfert 1 and 2 Galaxies Based on Near-Infrared Spectroscopy
We report on infrared K- (2-2.5 μm) and L-band (2.8-4.1 μm) slitspectroscopy of 23 Seyfert 1 galaxies in the CfA and 12 μm samples. Apolycyclic aromatic hydrocarbon (PAH) emission feature at 3.3 μm inthe L band is primarily used to investigate nuclear star-formingactivity in these galaxies. The 3.3 μm PAH emission is detected in 10sources (=43%), demonstrating that detection of nuclear star formationin a significant fraction of Seyfert 1 galaxies is now feasible. For thePAH-detected nuclei, the surface brightness values of the PAH emissionare as high as those of typical starbursts, suggesting that the PAHemission probes the putative nuclear starbursts in the dusty tori aroundthe central active galactic nuclei (AGNs). The magnitudes of the nuclearstarbursts are quantitatively estimated from the observed 3.3 μm PAHemission luminosities. The estimated starburst luminosities relative tosome indicators of AGN powers in these Seyfert 1 galaxies are comparedwith 32 Seyfert 2 galaxies in the same samples that we have previouslyobserved. We find that there is no significant difference in nuclearstarburst to AGN luminosity ratios of Seyfert 1 and 2 galaxies and thatnuclear starburst luminosity positively correlates with AGN power inboth types. Our results favor a slightly modified AGN unification model,which predicts that nuclear starbursts occurring in the dusty tori ofSeyfert galaxies are physically connected to the central AGNs, ratherthan the classical unification paradigm, in which the dusty tori simplyhide the central AGNs of Seyfert 2 galaxies and reprocess AGN radiationas infrared dust emission in Seyfert galaxies. No significantdifferences in nuclear star formation properties are recognizablebetween Seyfert 1 galaxies in the CfA and 12 μm samples.
| The Relationship Between Black Hole Mass and Velocity Dispersion in Seyfert 1 Galaxies
Black hole masses in active galactic nuclei are difficult to measureusing conventional dynamical methods but can be determined using thetechnique of reverberation mapping. However, it is important to verifythat the results of these different methods are equivalent. This can bedone indirectly, using scaling relations between the black hole and thehost galaxy spheroid. For this purpose, we have obtained newmeasurements of the bulge stellar velocity dispersion,σ*, in Seyfert 1 galaxies. These are used inconjunction with the MBH-σ* relation tovalidate nuclear black hole masses, MBH, in active galaxiesdetermined through reverberation mapping. We find that Seyfert galaxiesfollow the same MBH-σ* relation as nonactivegalaxies, indicating that reverberation mapping measurements ofMBH are consistent with those obtained using other methods.We also reconsider the relationship between bulge absolute magnitude,Mbul, and black hole mass. We find that Seyfert galaxies areoffset from nonactive galaxies, but that the deviation can be entirelyunderstood as a difference in bulge luminosity, not black hole mass;Seyfert galaxy hosts are brighter than normal galaxies for a given valueof their velocity dispersion, perhaps as a result of younger stellarpopulations.
| Supermassive Black Holes in Active Galactic Nuclei. II. Calibration of the Black Hole Mass-Velocity Dispersion Relationship for Active Galactic Nuclei
We calibrate reverberation-based black hole (BH) masses in activegalactic nuclei (AGNs) by using the correlation between BH mass,MBH, and bulge/spheroid stellar velocity dispersion,σ*. We use new measurements of σ* forsix AGNs and published velocity dispersions for 10 others, inconjunction with improved reverberation-mapping results, to determinethe scaling factor required to bring reverberation-based BH masses intoagreement with the quiescent galaxy MBH-σ*relationship. The scatter in the AGN BH masses is found to be less thana factor of 3. The current observational uncertainties preclude the useof the scaling factor to discriminate between broad-line region models.
| 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 broademission-line reverberation-mapping data. From objects with multipleline measurements, we find that the highest precision measure of thevirial product cτΔV2/G, where τ is theemission-line lag relative to continuum variations and ΔV is theemission-line width, is obtained by using the cross-correlation functioncentroid (as opposed to the cross-correlation function peak) for thetime delay and the line dispersion (as opposed to FWHM) for the linewidth and by measuring the line width in the variable part of thespectrum. Accurate line-width measurement depends critically on avoidingcontaminating features, in particular the narrow components of theemission lines. We find that the precision (or random component of theerror) of reverberation-based black hole mass measurements is typicallyaround 30%, comparable to the precision attained in measurement of blackhole masses in quiescent galaxies by gas or stellar dynamical methods.Based on results presented in a companion paper by Onken et al., weprovide a zero-point calibration for the reverberation-based black holemass scale by using the relationship between black hole mass andhost-galaxy bulge velocity dispersion. The scatter around thisrelationship implies that the typical systematic uncertainties inreverberation-based black hole masses are smaller than a factor of 3. Wepresent a preliminary version of a mass-luminosity relationship that ismuch better defined than any previous attempt. Scatter about themass-luminosity relationship for these AGNs appears to be real and couldbe correlated with either Eddington ratio or object inclination.
| On the Relationship between the Optical Emission-Line and X-Ray Luminosities in Seyfert 1 Galaxies
We have explored the relationship between the [O III] λ5007 andthe 2-10 keV luminosities for a sample of broad- and narrow-line Seyfert1 galaxies (BLSy1s and NLSy1s, respectively). We find that both types ofSeyfert galaxies span the same range in luminosity and possess similar[O III]/X-ray ratios. The NLSy1s are more luminous than BLSy1s whennormalized to their central black hole masses, a fact attributed tohigher mass accretion rates. However, we find no evidence for elevated[O III]/X-ray ratios in NLSy1s, which would have been expected if theyhad excess extreme-ultraviolet (EUV) continuum emission compared toBLSy1s. Also, other studies suggest that the gas in narrow-line regions(NLRs) of NLSy1s and BLSy1s spans a similar range in ionization,contrary to what is expected if those of the former are exposed to astronger flux of EUV radiation. The simplest interpretation is that,like BLSy1s, a large EUV bump is not present in NLSy1s. However, we showthat the [O III]/X-ray ratio can be lowered as a result of absorption ofthe ionizing continuum by gas close to the central source, althoughthere is no evidence that intrinsic line-of-sight absorption is morecommon among NLSy1s, as would be expected if there were a larger amountof circumnuclear gas. Other possible explanations include (1)anisotropic emission of the ionizing radiation; (2) higher gas densitiesin the NLRs of NLSy1s, resulting in lower average ionization; or (3) thepresence of strong winds in the nuclei of NLSy1s that may drive off muchof the gas in the NLR, resulting in lower cover fraction and weaker [OIII] emission.
| Galaxy Interaction and the Starburst-Seyfert Connection
Galaxy interactions are studied in terms of the starburst-Seyfertconnection. The starburst requires a high rate of gas supply. Since theefficiency for supplying the gas is high in a galaxy interaction,although the companion is not necessarily discernible, Seyfert galaxieswith circumnuclear starbursts are expected to be interacting. Since thelarge amounts of circumnuclear gas and dust obscure the broad-lineregion, they are expected to be observed as Seyfert 2 galaxies. Theactive galactic nucleus itself does not require a high rate of gassupply. Seyfert galaxies without circumnuclear starbursts are notnecessarily expected to be interacting even at the highest luminosities.They are not necessarily expected to evolve from Seyfert galaxies withcircumnuclear starbursts. We derive these and other theoreticalexpectations and confirm them with statistics on observational data ofmagnitude-limited samples of Seyfert galaxies.
| Why Are Massive Black Holes Small in Disk Galaxies?
A potential mechanism is proposed to account for the fact thatsupermassive black holes (SMBHs) in disk galaxies appear to be smallerthan those in elliptigalaxies in the same luminosity range. We considerthe formation of SMBHs by radiation drag (the Poynting-Robertsoneffect), which extracts angular momentum from interstellar matter andthereby drives the mass accretion onto a galactic center. In particular,we quantitatively scrutinize the efficiency of radiation drag in agalaxy composed of bulge and disk, and we elucidate the relation betweenthe final mass of SMBH and the bulge-to-disk ratio of the galaxy. As aresult, it is found that the BH-to-galaxy mass ratio,MBH/Mgalaxy, decreases with a smallerbulge-to-disk ratio, because of the effects of geometridilution andopacity, and is reduced maximally by 2 orders of magnitude, resulting inMBH/Mgalaxy~10-5. In contrast, if onlythe bulge components in galaxies are focused, the BH-to-bulge mass ratiobecomes MBH/Mbulge~10-3, which issimilar to that found in elliptigalaxies. Thus, it turns out that themass of an SMBH primarily correlates with a bulge, not with a disk,consistent with observational data.
| Exploring Narrow-Line Seyfert 1 Galaxies through the Physical Properties of Their Hosts
In this work we address the still open question of the nature ofnarrow-line Seyfert 1 galaxies (NLS1s): are they really active nucleiwith lower mass black holes (BHs) than Seyfert 1 galaxies (S1s) andquasars? Our approach is based on the recently discovered physicalconnections between nuclear supermassive BHs and their hosting spheroids(spiral bulges or elliptical galaxies). In particular, we compare BHmasses of NLS1s and S1s, analyzing the properties of their hosts bymeans of spectroscopic and photometric data in the optical wavelengthdomain. We find that NLS1s fill the low BH mass and bulge luminosityvalues of the MBH-MB relation, a result stronglysuggesting that NLS1s are active nuclei in which less massive BHs arehosted by less massive bulges. The correlation is good, with arelatively small scatter fitting simultaneously NLS1s, S1s, and quasars.On the other hand, NLS1s seem to share the same stellar velocitydispersion range as S1s in the MBH-σ*relation, indicating that NLS1s have a smaller BH/bulge mass ratio thanS1s. These two conflicting results support in any case the idea thatNLS1s could be young S1s. Finally, we do not confirm the significantlynonlinear BH-bulge relation claimed by some authors.Partially based on observations made with the Asiago 1.82 m telescope ofthe Padova Astronomical Observatory.
| Black hole mass estimation using a relation between the BLR size and emission line luminosity of AGN
An empirical relation between the broad line region (BLR) size andoptical continuum luminosity is often adopted to estimate the BLR sizeand then the black hole mass of AGNs. However, optical luminosity maynot be a good indicator of photoionizing luminosity for extremelyradio-loud AGNs because the jets usually contribute significantly to theoptical continuum. Therefore, the black hole masses derived forblazar-type AGNs with this method are probably overestimated. Here wefirst derived a tight empirical relation between the BLR size and theHβ emission line luminosity, R(light-days)=24.05(LH_β/1042 ergss-1)0.68, from a sample of 34 AGNs with the BLRsize estimated with the reverberation mapping technique. Then we appliedthis relation to estimate the black hole masses of some AGNs and foundthat for many extremely radio-loud AGNs the black hole masses obtainedwith the R-LH_β relation are systematically lower thanthose derived previously with the R-L_{5100 Å} relation, while forradio-quiet and slightly radio-loud AGNs the results obtained with thesetwo methods are almost the same. The difference of black hole massesestimated with these two relations increases with the radio-loudness forextremely radio-loud AGNs, which is consistent with the fact that theirequivalent widths of the Hβ emission line become smallerat greater radio-loudness. If the small Hβ equivalentwidths of extremely radio-loud AGNs are indeed caused by the beamingeffect, we argue that the optical emission line luminosity may be abetter tracer of ionizing luminosity for blazar-type AGNs and the blackhole masses derived with the R-LH_β relation areprobably more accurate.
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