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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.
| On the origin of the iron Kα line cores in active galactic nuclei
X-ray observations made with Chandra and XMM-Newton have shown thatthere are relatively narrow cores to the iron Kα emission lines inactive galactic nuclei (AGN). Plausible origins for this core emissioninclude the outer regions of an accretion disc, a parsec-scale moleculartorus, and the optical broad-line region (BLR). Using data from theliterature it is shown that no correlation exists between the FeKα core width and the BLR (specifically Hβ) line width. Thisshows that in general the iron Kα core emission does not arisefrom the BLR. There is a similar lack of correlation between the widthof the Fe Kα core and black hole mass. The average Kα widthis about a factor of 2 lower than the Hβ width. It therefore seemslikely that, in many cases, the narrow core arises in the torus. Thereis a very wide range of observed Fe Kα core widths, however, andthis argues for multiple origins. The simplest explanation for theobserved line profiles in AGN is that they are due to a mixing of verynarrow emission from the inner edge of the torus, and broadened emissionfrom the accretion disc, in varying proportions from object to object.
| XMM-Newton study of the complex and variable spectrum of NGC 4051
We study the X-ray spectral variability of the narrow line Seyfert 1galaxy NGC 4051 as observed during two XMM-Newton observations. To gaininsight on the general behaviour, we first apply model-independenttechniques such as rms spectra and flux-flux plots. We then performtime-resolved spectral analysis by splitting the observations into 68spectra (2 ks each). The data show evidence for a neutral andconstant-reflection component and for constant emission fromphotoionized gas, which are included in all spectral models. The nuclearemission can be modelled both in terms of a `standard model' [pivotingpower-law plus a blackbody (BB) component for the soft excess] and of atwo-component one (power law plus ionized reflection from the accretiondisc). Both the models reproduce the source spectral variability andcannot be distinguished on a statistical ground. The distinction hasthus to be made on a physical basis. The standard model results indicatethat the soft excess does not follow the standard BB law (LBB~ T4), despite a variation in luminosity by about one orderof magnitude. The resulting temperature is consistent with beingconstant and has the same value as observed in the PG quasars. Moreover,although the spectral slope is correlated with flux, which is consistentwith spectral pivoting, the hardest photon indices are so flat (Γ~ 1.3-1.4) as to require rather unusual scenarios. Furthermore, the verylow flux states exhibit an inverted Γ-flux behaviour whichdisagrees with a simple pivoting interpretation. These problems can besolved in terms of the two-component model in which the soft excess isnot thermal, but due to the ionized reflection component. In thiscontext, the power law has a constant slope (about 2.2) and theslope-flux correlation is explained in terms of the relativecontribution of the power-law and reflection components which alsoexplains the shape of the flux-flux plot relationship. The variabilityof the reflection component from the inner disc closely follows thepredictions of the light-bending model, suggesting that most of theprimary nuclear emission is produced in the very innermost regions, onlya few gravitational radii (rg) from the central black hole.
| Revisiting the infrared spectra of active galactic nuclei with a new torus emission model
We describe improved modelling of the emission by dust in atoroidal-like structure heated by a central illuminating source withinactive galactic nuclei (AGNs). We have chosen a simple but realistictorus geometry, a flared disc, and a dust grain distribution functionincluding a full range of grain sizes. The optical depth within thetorus is computed in detail taking into account the differentsublimation temperatures of the silicate and graphite grains, whichsolves previously reported inconsistencies in the silicate emissionfeature in type 1 AGNs. We exploit this model to study the spectralenergy distributions (SEDs) of 58 extragalactic (both type 1 and type 2)sources using archival optical and infrared data. We find that both AGNand starburst contributions are often required to reproduce the observedSEDs, although in a few cases they are very well fitted by a pure AGNcomponent. The AGN contribution to the far-infrared luminosity is foundto be higher in type 1 sources, with all the type 2 requiring asubstantial contribution from a circumnuclear starburst. Our resultsappear in agreement with the AGN unified scheme, because thedistributions of key parameters of the torus models turn out to becompatible for type 1 and type 2 AGNs. Further support to theunification concept comes from comparison with medium-resolutioninfrared spectra of type 1 AGNs by the Spitzer observatory, showingevidence for a moderate silicate emission around 10 μm, which ourcode reproduces. From our analysis we infer accretion flows in the innernucleus of local AGNs characterized by high equatorial optical depths(AV~= 100), moderate sizes (Rmax < 100 pc) andvery high covering factors (f~= 80 per cent) on average.
| XMM-Newton observations of the Seyfert 1 AGN H0557-385
We present XMM-Newton observations of the Seyfert 1 active galacticnucleus (AGN) H0557-385. We have conducted a study into the warmabsorber present in this source, and using high-resolution ReflectionGrating Spectrometer (RGS) data we find that the absorption can becharacterized by two phases: a phase with log ionization parameter ξof 0.50 (where ξ is in units of ergcms-1) and a column of0.2 × 1021cm-2, and a phase with log ξ of1.62 and a column of 1.3 × 1022cm-2. An ironKα line is detected. Neutral absorption is also present in thesource, and we discuss possible origins for this. On the assumption thatthe ionized absorbers originate as an outflow from the inner edge of thetorus, we use a new method for finding the volume filling factor. Bothphases of H0557-385 have small volume filling factors (<=1 per cent).We also derive the volume filling factors for a sample of 23 AGN usingthis assumption and for the absorbers with logξ > 0.7, we findreasonable agreement with the filling factors obtained through thealternative method of equating the momentum flow of the absorbers to themomentum loss of the radiation field. By comparing the filling factorsobtained by the two methods, we infer that some absorbers with logξ< 0.7 occur at significantly larger distances from the nucleus thanthe inner edge of the torus.
| Discovery of a relativistic Fe line in PG 1425+267 with XMM-Newton and study of its short time-scale variability
We report results from the XMM-Newton observation of the radio-loudquasar PG 1425+267 (z= 0.366). The X-ray data above 2keV exhibit adouble-peaked emission feature in the Fe K band. The higher energy peakis found at 6.4keV and is consistent with being narrow, while the lowerenergy one is detected at 5.3keV and is much broader than the detectorresolution. We confirm the significance of the detection of the broadred part of the line via Monte Carlo simulations (99.1 per centconfidence level). We explore two possible origins of the line profile,i.e., a single relativistic iron line from the accretion disc, and thesuperposition of a narrow 6.4-keV line from distant material and arelativistic one. We find that a contribution from a distant reflectoris not required by the data. We also perform a time-resolved analysissearching for short time-scale variability of the emission line. Resultstentatively suggest that the line is indeed variable on shorttime-scales (at the 97.3 per cent confidence level according tosimulations) and better quality data are needed to confirm it on morefirm statistical grounds. We also detect clear signatures of a warmabsorber in the soft X-ray energy band.
| Comptonization and Reprocessing Processes in Accretion Disks: Applications to the Seyfert 1 Galaxies NGC 5548 and NGC 4051
Simultaneous multi-wavelength observations have revealed complexvariability in AGNs. To explain the variability we considered atheoretical model consisting of an inner hot comptonizing corona and anouter thin accretion disk, with interactions between the two componentsin the form of comptonization and reprocessing. We found that thevariability of AGNs is strongly affected by the parameters of the model,namely, the truncated disk radius rmin, the corona radiusrs, the temperature KTe and the optical depthτ0 of the corona. We applied this model to the two bestobserved Seyfert 1 galaxies, NGC 5548 and NGC 4051. Our model canreproduce satisfactory the observed SEDs. Our fits indicate that NGC5548 may have experienced dramatic changes in physical parametersbetween 19891990 and 1998, and that NGC 4051 has a much largertruncated disk radius (700 Schwarzschild radii) than NGC 5548 (severaltens of Schwarzschild radii). Since we adopted a more refined treatmentof the comptonization process rather than simply assuming a cut-offpower law, our results should be more reasonable than the previous ones.
| On the Fraction of X-Ray-obscured Quasars in the Local Universe
Recent wide-area hard X-ray and soft gamma-ray surveys have shown thatthe fraction of X-ray-obscured active galactic nuclei (AGNs) in thelocal universe significantly decreases with intrinsic luminosity. Inthis Letter we point out that two corrections have to be made to thesamples: (1) radio-loud AGNs have to be excluded, since their X-rayemission might be dominated by the jet component, and (2) Compton-thicksources have to be excluded too, since their hard X-ray and softgamma-ray emission are also strongly attenuated by Compton scattering.The soft gamma-ray-selected AGN samples obtained by Swift and INTEGRALprovide the best opportunity to study the fraction of obscured AGNs inthe local universe in the least biased way. We choose these samples tocheck if the corrections could alter the above result on the fraction ofobscured AGNs. We find that before the corrections both samples showsignificant anticorrelation between LX and NH,indicating an obvious decrease in the fraction of obscured AGNs withluminosity. However, after the corrections, we find only marginalevidence of anticorrelation (at the 98% confidence level) in the Swiftsample and no evidence at all in the INTEGRAL sample, which consists ofa comparable number of objects. We conclude that current samples onlyshow a marginal decrease in the fraction of obscured AGNs in the localuniverse and that much larger samples are required in order to reach amore robust conclusion.
| O VI Asymmetry and an Accelerated Outflow in an Obscured Seyfert: FUSE and HST STIS Spectroscopy of Mrk 533
We present far-ultraviolet spectra of the Seyfert 2 galaxy Mrk 533obtained with FUSE. These spectra show narrow asymmetrical O VIλλ1032,1038 emission lines with stronger wings shortwardof the peak wavelength, but the degree of asymmetry of these wings invelocity is much lower than that of the wings of the lines of lowerionization. In the combined O VI profile there are marginal indicationsof local absorptions in the outflow. The C III λ977 line is seenweakly with a similar profile, but with very low signal-to-noise ratio(S/N). These FUV spectra are among the first for a Seyfert of type 2,i.e., a purportedly obscured Seyfert. The HST STIS spectral image of Mrk533 allows delineation of the various components of the outflow, and weinfer that the outflow is accelerated. We discuss the results in termsof nuclear geometry and kinematics.
| Cosmic Evolution of Black Holes and Spheroids. I. The MBH-σ Relation at z = 0.36
We test the evolution of the correlation between black hole mass andbulge velocity dispersion (MBH-σ), using a carefullyselected sample of 14 Seyfert 1 galaxies at z=0.36+/-0.01. We measurevelocity dispersion from stellar absorption lines around Mg b (5175Å) and Fe (5270 Å) using high-S/N Keck spectra and estimateblack hole mass from the Hβ line width and the optical luminosityat 5100 Å, based on the empirically calibrated photoionizationmethod. We find a significant offset from the local relation, in thesense that velocity dispersions were smaller for given black hole massesat z=0.36 than locally. We investigate various sources of systematicuncertainties and find that those cannot account for the observedoffset. The measured offset isΔlogMBH=0.62+/-0.10+/-0.25 i.e.,Δlogσ=0.15+/-0.03+/-0.06, where the error bars include arandom component and an upper limit to the systematics. At face value,this result implies a substantial growth of bulges in the last 4 Gyr,assuming that the local MBH-σ relation is the universalevolutionary endpoint. Along with two samples of active galaxies withconsistently determined black hole mass and stellar velocity dispersiontaken from the literature, we quantify the observed evolution with thebest-fit linear relation:ΔlogMBH=(1.66+/-0.43)z+(0.04+/-0.09) with respect tothe local relationship of Tremaine and coworkers, andΔlogMBH=(1.55+/-0.46)z+(0.01+/-0.12) with respect tothat of Ferrarese. This result is consistent with the growth of blackholes predating the final growth of bulges at these mass scales(<σ>=170 km s-1).
| Lens-Aided Multi-Angle Spectroscopy (LAMAS) Reveals Small-Scale Outflow Structure in Quasars
Spectral differences between lensed quasar image components are common.Since lensing is intrinsically achromatic, these differences aretypically explained as the effect of either microlensing, or as lightpath time delays sampling intrinsic quasar spectral variability. Here weadvance a novel third hypothesis: some spectral differences are due tosmall line-of-sight differences through quasar disk wind outflows. Inparticular, we propose that variable spectral differences seen only incomponent A of the widest separation lens SDSS J1004+4112 are due todifferential absorption along the sight lines. The absorber propertiesrequired by this hypothesis are akin to known broad absorption line(BAL) outflows but must have a broader, smoother velocity profile. Weinterpret the observed C IV emission-line variability as furtherevidence for spatial fine structure transverse to the line of sight.Since outflows are likely to be rotating, such absorber fine structurecan consistently explain some of the UV and X-ray variability seen inAGNs. The implications are many: (1) Spectroscopic differences in otherlensed objects may be due to this ``lens-aided multi-anglespectroscopy'' (LAMAS). (2) Outflows have fine structure on size scalesof arcseconds, as seen from the nucleus. (3) Assuming either broadabsorption line region sizes proposed in recent wind models, ortypically assumed continuum emission region sizes, LAMAS and/orvariability provide broadly consistent absorber size scale estimates of~1015 cm. (4) Very broad smooth absorption may be ubiquitousin quasar spectra, even when no obvious troughs are seen.
| 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.
| Spectral Variability of Quasars in the Sloan Digital Sky Survey. II. The C IV Line
We examine the variability of the high-ionization C IV λ1549 linein a sample of 105 quasars observed at multiple epochs by the SloanDigital Sky Survey. We find a strong correlation between the change inthe C IV line flux and the change in the line width, but no correlationsbetween the change in flux and changes in line center and skewness. Therelation between line flux change and line width change is consistentwith a model in which a broad line base varies with greater amplitudethan the line core. The objects studied here are more luminous and athigher redshift than those normally studied for variability, ranging inredshift from 1.65 to 4.00 and in absolute r-band magnitude from roughly-24 to -28. Using moment analysis line-fitting techniques, we measureline fluxes, centers, widths, and skewnesses for the C IV line at twoepochs for each object. The well-known Baldwin effect is seen for theseobjects, with a slope of β=-0.22. The sample has a median intrinsicBaldwin effect slope of βint=-0.85 the C IV lines inthese high-luminosity quasars appear to be less responsive to continuumvariations than those in lower luminosity AGNs. In addition, we find noevidence for variability of the well-known blueshift of the C IV linewith respect to the low-ionization Mg II λ2798 line in thehighest flux objects, indicating that this blueshift might be useful asa measure of orientation.Presented as part of a dissertation to the Department of Astronomy andAstrophysics of the University of Chicago, in partial fulfillment of therequirements for the Ph.D. degree.
| 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 Bright Ages Survey. I. Imaging Data
This is the first paper in a series presenting and analyzing data for aK-selected sample of galaxies collected in order to identify and studygalaxies at moderate to high redshift in rest-wavelength optical light.The sample contains 842 objects over six separate fields covering 75.6arcmin2 down to K=20-20.5. We combine the K band withUBVRIzJH multiband imaging, reaching depths of R~26. Two of the fieldsstudied also have deep HST WFPC2 imaging, totaling more than 60 hr inthe F300W, F450W, F606W, and F814W filters. Using artificial galaxymodeling and extraction, we measure 85% completeness limits down toK=19.5-20, depending on the field examined. The derived K-band numbercounts are in good agreement with previous studies. We find a densityfor extremely red objects (EROs; R-K>5) of 1.55+/-0.16arcmin-2 for K<19.7, dominated by the 1714+5015 field(centered on 53w002), with an ERO number density more than 3 times thatof the other sample fields. If we exclude the counts for 1714+5015, ourdensity is 0.95+/-0.14 arcmin-2. Both ERO densities areconsistent with previous measurements due to the significant knowncosmic variance of these red sources. Keck spectroscopic redshifts wereobtained for 18 of the EROs, all but one of which are emission galaxies.None of the EROs in the 1714+5015 field for which we obtainedspectroscopic redshifts are associated with the known z=2.39overdensity, although there are three different galaxy redshift pairs(z=0.90, 1.03, and 1.22).
| A Sample of IRAS Infrared-selected Seyfert 1.5 Galaxies: Infrared Color α(60, 25)-dominated Eigenvector 1
The well-documented E1 relationships are first extended to infraredcolor α(60, 25) and flux ratio [O III]/Hβn bycomparing emission-line properties to continuum properties in infraredwavelengths. Both direct correlations and a principal component analysisare used in a sample of 50 IRAS IR-selected Seyfert 1.5 galaxies. Inaddition, to confirm the correlations of E1 in Boroson & Green, oureigenvector 1 turns out to be dominated by the mid-infrared colorα(60, 25) and most strongly affected by RFe, [OIII]/Hβn, and EW(Hβb). Our analysisindicates that the objects with large E1 tend to coexist with relativelyyoung nuclear stellar populations, which implies that E1 is related tothe nuclear star formation history. The IR-dominated eigenvector 1 cantherefore be inferred to be interpreted as the ``age'' of an AGN. Inconfirmation of the work of Xu and coworkers, it is clear that theextreme Seyfert galaxies with both large RFe and large [OIII]/Hβn are rare in our universe.
| Spatially Resolved Narrow-Line Region Kinematics in Active Galactic Nuclei
We have analyzed Hubble Space Telescope spectroscopy of 24 nearby activegalactic nuclei (AGNs) to investigate spatially resolved gas kinematicsin the narrow-line region (NLR). These observations effectively isolatethe nuclear line profiles on less than 100 pc scales and are used toinvestigate the origin of the substantial scatter between the widths ofstrong NLR lines and the stellar velocity dispersion σ*of the host galaxy, a quantity that relates with substantially lessscatter to the mass of the central, supermassive black hole and moregenerally characterize variations in the NLR velocity field with radius.We find that line widths measured with STIS at a range of spatial scalessystematically underestimate both σ* and the line widthmeasured from ground-based observations, although they do havecomparably large scatter to the relation between ground-based NLR linewidth and σ*. There are no obvious trends in theresiduals when compared with a range of host galaxy and nuclearproperties. The widths and asymmetries of [O III] λ5007 and [SII] λλ6716, 6731 as a function of radius exhibit a widerange of behavior. Some of the most common phenomena are substantialwidth increases from the STIS to the large-scale, ground-based apertureand almost no change in line profile between the unresolved nuclearspectrum and ground-based measurements. We identify asymmetries in asurprisingly large fraction of low-ionization [S II] line profiles andseveral examples of substantial red asymmetries in both [O III] and [SII]. These results underscore the complexity of the circumnuclearmaterial that constitutes the NLR and suggest that the scatter in theNLR width and σ* correlation cannot be substantiallyreduced with a simple set of empirical relations.
| Kinematics of the Narrow-Line Region in the Seyfert 2 Galaxy NGC 1068: Dynamical Effects of the Radio Jet
We present a study of high-resolution long-slit spectra of thenarrow-line region (NLR) in NGC 1068 obtained with the Space TelescopeImaging Spectrograph aboard the Hubble Space Telescope (HST). Thespectra were retrieved from the Multimission Archive at the SpaceTelescope Science Institute obtained from two visits and seven orbits ofHST time. We also obtained MERLIN radio maps of the center of NGC 1068to examine the dependence of the NLR cloud velocities on the radiostructure. The radial velocities and velocity dispersions of the brightNLR clouds appear to be unaffected by the radio knots, indicating thatthe radio jet is not the principal driving force on the outflowing NLRclouds. However, the velocities of the fainter NLR clouds are split nearknots in the jet, indicating a possible interaction. Biconical outflowmodels were generated to match the data and for comparison to previousmodels done with lower dispersion observations. The general trend is anincrease in radial velocity roughly proportional to distance from thenucleus followed by a linear decrease after roughly 100 pc similar tothat seen in other Seyfert galaxies, indicating common acceleration anddeceleration mechanisms.Based on observations made with the NASA/ESA Hubble Space Telescope. TheSpace Telescope Science Institute is operated by the Association ofUniversities for Research in Astronomy, Inc., under NASA contractNAS5-26555.
| A Survey of Kiloparsec-Scale Radio Outflows in Radio-Quiet Active Galactic Nuclei
Seyfert galaxies commonly host compact jets spanning 10-100 pc scales,but larger structures are resolved out in long-baseline aperturesynthesis surveys. Previous, targeted studies showed thatkiloparsec-scale radio structures (KSRs) may be a common feature ofSeyfert and LINER galaxies, and the origin of KSRs may be starbursts oractive galactic nuclei (AGNs). We report a new Very Large Array surveyof a complete sample of Seyfert and LINER galaxies. Out of all of thesurveyed radio-quiet sources, we find that 44% (19 out of 43) showextended radio structures at least 1 kpc in total extent that do notmatch the morphology of the disk or its associated star-forming regions.The detection rate is a lower limit owing to the combined effects ofprojection and resolution. The infrared colors of the KSR host galaxiesare unremarkable compared to other Seyfert galaxies, and the large-scaleoutflows orient randomly with respect to the host galaxy axes. The KSRSeyfert galaxies instead stand out by deviating significantly from thefar-infrared-radio correlation for star-forming galaxies, with tendencytoward radio excess, and they are more likely to have a relativelyluminous, compact radio source in the nucleus; these results argue thatKSRs are powered by the AGNs rather than starbursts. The high detectionrate indicates that Seyfert galaxies generate radio outflows over asignificant fraction of their lifetime, which is much longer than thedynamical timescale of an AGN-powered jet but is comparable instead tothe buoyancy timescale. The likely explanation is that the KSRsoriginate from jet plasma that has been decelerated by interaction withthe nuclear interstellar medium (ISM). Based on a simple ram pressureargument, the kinetic power of the jet on kiloparsec scales is about 3orders of magnitude weaker than the power of the jet on 10-100 pcscales. This result is consistent with the interaction model, in whichcase virtually all of the jet power must be lost to the ISM within theinner kiloparsec.
| Spitzer IRS Spectra of a Large Sample of Seyfert Galaxies: A Variety of Infrared Spectral Energy Distributions in the Local Active Galactic Nucleus Population
We are conducting a large observing program with the Spitzer SpaceTelescope to determine the mid- to far-IR spectral energy distributionsof a well-defined sample of 87 nearby, 12 μm-selected Seyfertgalaxies. In this paper we present the results of Spitzer IRSlow-resolution spectroscopy of a statistically representative subsampleof 51 of the galaxies (59%), with an analysis of the continuum shapesand a comparison of the Seyfert types. We find that the spectra clearlydivide into groups based on their continuum shapes and spectralfeatures. The largest group (47% of the sample of 51) shows a very redcontinuum suggestive of cool dust and strong emission featuresattributed to polycyclic aromatic hydrocarbons. Sixteen objects (31%)have a power-law continuum with spectral indices of α5-20μm=-2.3 to -0.9 that flatten to α20-35μm=-1.1 to 0.0 at ~20 μm. Clear silicate emission featuresat 10 and 18 μm are found in two of these objects (Mrk 6 and Mrk335). A further 16% of the sample show power-law continua withunchanging slopes of α5-35 μm=-1.7 to -1.1. Twoobjects are dominated by a broad silicate absorption feature. One objectin the sample shows an unusual spectrum dominated by emission features,which is unlike any of the other spectra. Some spectral features areclearly related to a starburst contribution to the IR spectrum, whilethe mechanisms producing observed power-law continuum shapes, attributedto an active galactic nucleus (AGN) component, may be dust or nonthermalemission. The IR spectral types appear to be related to the Seyferttypes. Principal component analysis results suggest that the relativecontribution of starburst emission may be the dominant cause of variancein the observed spectra. The derived starburst component of eachspectrum, however, contributes <40% of the total flux density. Wecompare the IR emission with the optically thin radio emissionassociated with the AGN and find that Seyfert 1 galaxies have higherratios of IR to radio emission than Seyfert 2 galaxies, as predicted bythe unified model if the torus is optically thick in the mid-IR.However, smooth-density torus models predict a much larger differencebetween Seyfert types 1 and 2 than the factor of 2 difference observedin our sample; the observed factor of ~2 difference between the type 1and type 2 galaxies in their IR-to-radio ratios above 15 μm requiresthe standard smooth-density torus models to be optically thin at thesewavelengths. However, the resulting low torus opacity requires that thehigh observed columns detected in X-ray absorption be produced in gaswith a very low dust-to-gas ratio (perhaps within the dust sublimationregion). On the other hand, our observations may be consistent withclumpy torus models containing a steep radial distribution of opticallythick dense clumps. The selection of our sample at 12 μm, where thetorus may be optically thick, implies that there may beorientation-dependent biases in the sample; however, we do not find thatthe sample is biased toward Seyfert 2 galaxies with more luminouscentral engines, as would be expected. We find that the Seyfert 2galaxies typically show stronger starburst contributions than theSeyfert 1 galaxies in the sample, contrary to what is expected based onthe unified scheme for AGNs. This may be due to the selection effectthat only those Seyfert 2 galaxies with strong starburst contributionshad high enough integrated 12 μm flux densities to fall above theflux limit of the sample.
| 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.
| On the X-ray, optical emission line and black hole mass properties of local Seyfert galaxies
We investigate the relation between X-ray nuclear emission, opticalemission line luminosities and black hole masses for a sample of 47Seyfert galaxies. The sample, which has been selected from the Palomaroptical spectroscopic survey of nearby galaxies (Ho et al. 1997a, ApJS,112, 315), covers a wide range of nuclear powers, from L2-10keV ~ 1043 erg/s down to very low luminosities(L2-10 keV ~ 1038 erg/s). Best available data fromChandra, XMM-Newton and, in a few cases, ASCA observations have beenconsidered. Thanks to the good spatial resolution available from theseobservations and a proper modeling of the various spectral components,it has been possible to obtain accurate nuclear X-ray luminosities notcontaminated by off-nuclear sources and/or diffuse emission. X-rayluminosities have then been corrected taking into account the likelycandidate Compton thick sources, which are a high fraction (>30%)among type 2 Seyferts in our sample. The main result of this study isthat we confirm strong linear correlations between 2-10 keV,[OIII]λ5007, Hα luminosities which show the same slope asquasars and luminous Seyfert galaxies, independent of the level ofnuclear activity displayed. Moreover, despite the wide range ofEddington ratios (L/L_Edd) tested here (six orders of magnitude, from0.1 down to ~10-7), no correlation is found between the X-rayor optical emission line luminosities and the black hole mass. Ourresults suggest that Seyfert nuclei in our sample are consistent withbeing a scaled-down version of more luminous AGN.
| The structure and X-ray radiation spectra of illuminated accretion disks in AGN. III. Modeling fractional variability
Context: .Random magnetic flares above the accretion disks of ActiveGalactic Nuclei can account for the production of the primary radiationand for the rapid X-ray variability that have been frequently observedin these objects. The primary component is partly reprocessed in thedisk atmosphere, forming a hot spot underneath the flare source andgiving rise to distinct spectral features. Aims: .Extending thework of Czerny et al. (2004, A&A, 420, 1), we model the fractionalvariability amplitude due to distributions of hot spots co-orbiting onthe accretion disk around a supermassive black hole. We compare ourresults to the observed fractional variability spectrum of the Seyfertgalaxy MCG-6-30-15. Methods: .According to defined radialdistributions, our code samples random positions for the hot spotsacross the disk. The local spot emission is computed as reprocessedradiation coming from a compact primary source above the disk. Thestructure of the hot spot and the anisotropy of the re-emission aretaken into account. We compute the fractional variability spectraexpected from such spot ensembles and investigate dependencies on theparameters describing the radial spot distribution. We consider thefractional variability F{ var} with respect to the spectralmean and the so-called point-to-point definition F{ pp}. Ourmethod includes relativistic corrections due to the curved space-time inthe vicinity of a rotating supermassive black hole at the disk center;the black hole's angular momentum is a free parameter and is subject tothe fitting procedure. Results: .We confirm that therms-variability spectra involve intrinsic randomness at a significantlevel when the number of flares appearing during the total observationtime is too small. Furthermore, the fractional variability expressed byF{ var} is not always compatible with F{ pp}. Inthe special case of MCG-6-30-15, we can reproduce the short-timescalevariability and model the suppressed variability in the energy range ofthe Kα line without any need to postulate reprocessing fartheraway from the center. The presence of the dip in the variabilityspectrum requires an increasing rate of energy production by the flarestoward the center of the disk. The depth of the feature is wellrepresented only if we assume a fast rotation of the central black holeand allow for considerable suppression of the primary flare emission.The modeled line remains consistent with the measured equivalent widthof the iron Kα line complex. The model can reproduce thefrequently observed suppression of the variability in the spectral rangearound 6.5 keV, thereby setting constraints on the black hole spin andon the disk inclination.
| 4U 1344-60: a bright intermediate Seyfert galaxy at z = 0.012 with a relativistic Fe Kα emission line
We present analysis of the optical and X-ray spectra of the low Galacticlatitude bright (F_2-10 = 3.6 × 10-11 ergcm-2 s-1) source 4U 1344-60. On the basis of theoptical data we propose to classify 4U 1344-60 as an intermediate typeSeyfert galaxy and we measure a value of z = 0.012±0.001 for itsredshift. From the XMM-Newton observation we find that the overall X-rayspectral shape of 4U 1344-60 is complex and can be described by apower-law continuum (Γ≈ 1.55) obscured by two neutralabsorption components (N_Hf ~ 1022 cm-2and N_Hp ~ 4 × 1022 cm-2), thelatter covering only the ~50% of the primary X-ray source. The X-raydata therefore lend support to our classification of 4U 1344-60. Itexhibits a broad and skewed Fe Kα line at ~6.4 keV, which suggeststhe existence of an accretion disk that is able to reprocess the primarycontinuum down to a few gravitational radii. Such a line represents oneof the clearest examples of a relativistic line observed by XMM-Newtonso far. Our analysis has also revealed the marginal presence of twonarrow line-like emission features at ~4.9 and ~5.2 keV.
| The host galaxy/AGN connection in nearby early-type galaxies. A new view of the origin of the radio-quiet/radio-loud dichotomy?
This is the third in a series of three papers exploring the connectionbetween the multiwavelength properties of AGN in nearby early-typegalaxies and the characteristics of their hosts. Starting from aninitial sample of 332 galaxies, we selected 116 AGN candidates requiringthe detection of a radio source with a flux limit of ~1 mJy, as measuredfrom 5 GHz VLA observations. In Paper I we classified the objects withavailable archival HST images into "core" and "power-law" galaxies,discriminating on the basis of the nuclear slope of their brightnessprofiles. We used HST and Chandra data to isolate the nuclear emissionof these galaxies in the optical and X-ray bands, thus enabling us (oncecombined with the radio data) to study the multiwavelength behaviour oftheir nuclei. The properties of the nuclei hosted by the 29 coregalaxies were presented in Paper II Core galaxies invariably host aradio-loud nucleus, with a median radio-loudness of Log R = 3.6 and anX-ray based radio-loudness parameter of Log RX = -1.3. Herewe discuss the properties of the nuclei of the 22 "power-law" galaxies.They show a substantial excess of optical and X-ray emission withrespect to core galaxies at the same level of radio luminosity.Conversely, their radio-loudness parameters, Log R 1.6 and LogRX -3.3, are similar to those measured in Seyfertgalaxies. Thus the radio-loudness of AGN hosted by early-type galaxiesappears to be univocally related to the host's brightness profile:radio-loud AGN are only hosted by core galaxies, while radio-quiet AGNare found only in power-law galaxies. The brightness profile isdetermined by the galaxy's evolution, through its merger history; ourresults suggest that the same process sets the AGN flavour. In thisscenario, the black holes hosted by the merging galaxies rapidly sinktoward the centre of the newly formed object, setting its nuclearconfiguration, described by e.g. the total mass, spin, mass ratio, orseparation of the SMBHs. These parameters are most likely at the originof the different levels of the AGN radio-loudness. This connection mightopen a new path toward understanding the origin of theradio-loud/radio-quiet AGN dichotomy and provide us with a further toolfor exploring the co-evolution of galaxies and supermassive black holes.
| Modeling the warm absorber in active galactic nuclei
We present a wide grid of models for the structure and transmissionproperties of warm absorbers in active galactic nuclei (AGN). Contraryto commonly used constant density models, our absorbing cloud is assumedto be under constant total (gas plus radiation) pressure. Thisassumption implies the coexistence of material at different temperaturesand ionization states, which is a natural consequence of pressure andthermal equilibrium. Our photoionization code allows us to compute theprofiles of the density, the temperature, the gas pressure, theradiation pressure and the ionization state across the cloud, and tocalculate the radiative transfer of continuum and lines includingCompton scattering. Therefore, equivalent widths of both saturated andunsaturated lines are properly modeled. For each pair of the incidentspectrum slope and the ionization parameter at the cloud surface thereis a natural upper limit to the total column densities of the cloud dueto thermal instabilities. These maximum values are comparable to theobservational constraints on the column density of warm absorbers whichmay give support to constant total pressure models. In all models wenote considerable absorption around 6.4 keV which modifies the intrinsicrelativistically broadened iron line profile originating in an accretiondisk illuminated atmosphere. Our models can be applied to fitting thespectroscopic data from the XMM-Newton and Chandra satellites.
| X-ray spectral survey with XMM-Newton of a complete sample of nearby Seyfert galaxies
Results obtained from an X-ray spectral survey of nearby Seyfertgalaxies using XMM-Newton are reported. The sample was opticallyselected, well defined, complete in B magnitude, and distance limited:it consists of the nearest (D 22 Mpc) 27 Seyfert galaxies (9 oftype 1, 18 of type 2) taken from the Ho et al. (1997a, ApJS, 112, 315)sample. This is one of the largest atlases of hard X-ray spectra oflow-luminosity active galaxies ever assembled. All nuclear sourcesexcept two Seyfert 2s are detected between 2 and 10 keV, half for thefirst time ever, and average spectra are obtained for all of them.Nuclear luminosities reach values down to 1038 ergs-1. The shape of the distribution of X-ray parameters isaffected by the presence of Compton-thick objects (30% among type2s). The latter have been identified either directly from their intenseFeK line and flat X-ray spectra, or indirectly with flux diagnosticdiagrams which use isotropic indicators. After taking into account thesehighly absorbed sources, we find that (i) the intrinsic X-ray spectralproperties (i.e., spectral shapes and luminosities above 2 keV) areconsistent between type 1 and type 2 Seyferts, as expected from "unifiedmodels"; (ii) Seyfert galaxies as a whole are distributed fairlycontinuously over the entire range of N_H, between 1020 and1025 cm-2; and (iii) while Seyfert 1s tend to havelower NH and Seyfert 2s tend to have the highest, we find 30%and 10% exceptions, respectively. Overall the sample is of sufficientquality to well represent the average intrinsic X-ray spectralproperties of nearby active galactic nuclei, including a proper estimateof the distribution of their absorbing columns. Finally, we concludethat, with the exception of a few cases, the present study agrees withpredictions of unified models of Seyfert galaxies, and extends theirvalidity down to very low luminosities.
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