Contents
Images
Upload your image
DSS Images Other Images
Related articles
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.
| The multi-wavelength correlations and the evolution of spectral index on the quasar 3C 273
The observed data from 2 keV to 5 GHz were complied to investigatepossible correlations between different frequency variations by means ofdiscrete correlation function (DCF) analysis. The results show thatthere are significant flux correlations between different radio bandsand the weak correlations between radio and optical variability. Thevariations of higher frequency components would lead those of lowerfrequency components. Due to the sparse and uneven data in the X-rayband, the correlations between X-ray and the lower energy bands (radioand optical) cannot be confirmed. In addition, we give the spectralindex evolution in each energy band and find out that there are stronganti-correlation between spectral index and flux, in the sense that thespectral index decreases with the flux increases.
| 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.
| 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.
| Photoionized Hβ emission in NGC 5548: it breathes!
Emission-line regions in active galactic nuclei (AGNs) and otherphotoionized nebulae should become larger in size when the ionizingluminosity increases. This `breathing' effect is observed for theHβ emission in NGC 5548 by using Hβ and optical continuumlight curves from the 13-yr (1989-2001) AGN Watch monitoring campaign.To model the breathing, we use two methods to fit the observed lightcurves in detail: (i) parametrized models and, (ii) the MEMECHOreverberation-mapping code. Our models assume that optical continuumvariations track the ionizing radiation, and that the Hβ variationsrespond with time-delays τ due to light travel-time. By fitting thedata using a delay-map Ψ(τ, Fc) that is allowed tochange with continuum flux Fc, we find that the strength ofthe Hβ response decreases and the time-delay increases withionizing luminosity. The parametrized breathing models allow thetime-delay and the Hβ flux to depend on the continuum flux so that,τ~Fβc andFHβ~Fαc. Our fits give 0.1< β < 0.46 and 0.57 < α < 0.66. α isconsistent with previous work by Gilbert and Peterson, and Goad, Koristaand Knigge. Although we find β to be flatter than previouslydetermined by Peterson et al. using cross-correlation methods, it iscloser to the predicted values from recent theoretical work by Koristaand Goad.
| 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.
| The AGN Outflow in the HDF-S Target QSO J2233-606 from a High-Resolution VLT UVES Spectrum
We present a detailed analysis of the intrinsic UV absorption in thecentral HDF-S target QSO J2233-606, based on a high-resolution, high-S/N(~25-50) spectrum obtained with VLT UVES. This spectrum samples thecluster of intrinsic absorption systems outflowing from the AGN atradial velocities v~-5000 to -3800 km s-1 in the key far-UVdiagnostic lines: the lithium-like CNO doublets and H I Lyman series. Wefit the absorption troughs using a global model of all detected lines tosolve for the independent velocity-dependent covering factors of thecontinuum and emission-line sources and ionic column densities. Thisreveals increasing covering factors in components with greater outflowvelocity. Narrow substructure is revealed in the optical depth profiles,suggesting that the relatively broad absorption is comprised of a seriesof multiple components. We perform velocity-dependent photoionizationmodeling, which allows a full solution to the C, N, and O abundances, aswell as the velocity-resolved ionization parameter and total columndensity. The absorbers are found to have supersolar abundances, with[C/H] and [O/H]~0.5-0.9, and [N/H]~1.1-1.3, consistent with enhancednitrogen production expected from secondary nucleosynthesis processes.Independent fits to each kinematic component give consistent results forthe abundances. The lowest ionization material in each of the strongabsorbers is modeled with similar ionization parameters. Components ofhigher ionization (indicated by stronger O VI relative to C IV and N V)are present at velocities just redward of each low-ionization absorber.We explore the implications of these results for thekinematic-geometric-ionization structure of the outflow.Based on public data released from the Ultraviolet and Visual EchelleSpectrograph (UVES) commissioning at the VLT-UT2 (Kueyen) telescope,European Southern Observatory (ESO), Paranal, Chile.
| High-Resolution Absorption Spectroscopy of Multiphase, High-Metallicity Gas Associated with the Luminous Quasar HE 0226-4110
We present FUSE and HST STIS observations of the absorption-line systemnear the emission redshift of the radio-quiet, X-ray-bright quasar HE0226-4110 (z=0.495, V=15.2). The spectra cover the rest-frame wavelengthrange 610-1150 Å, and we detect a wide range of ionizationspecies, including four adjacent stages of oxygen: O III-VI, whichreveal a striking change in gas kinematics with ionization. Examinatonof the O VI λλ1031, 1037 doublet profiles reveals noevidence for partial coverage or unresolved saturated structure. O IIIis only detected in a narrow feature that is also traced by the H I andC III lines, suggesting that they arise in the same gas. Absorption atthe same velocity is also present in other species (N IV, O IV-VI, SIV, and possibly Ne VIII ), but the kinematics differ from the O III,implying production in separate gaseous phases. The combination of H I,O III , and C III information yields an estimate of both thephotoionization parameter and the metallicity of the O III-bearing gas:[O/H]=+0.12+0.16-0.03,logU=-2.29+0.02-0.23. We discuss two possiblelocations for the gas in this associated absorption-line system: thenarrow emission line region of the quasar, and the halo of the quasarhost galaxy. An additional narrow (and thus photoionized) component thatis only detected in O VI appears 58 km s-1 redward of the OIII-bearing gas with -0.35<~logU<~0.02. Additional structure isdetected in the associated absorber in the form of two broad componentsthat only appear in moderate- to high-ionization species.Based on observations made with the NASA/ESA Hubble Space Telescope,which is operated by the Association of Universities for Research inAstronomy, Inc., under NASA contract NAS 5-26555. Also based onobservations made with the NASA-CNES-CSA Far Ultraviolet SpectroscopicExplorer, which is operated for NASA by Johns Hopkins University underNASA contract NAS 5-32985.
| Multiwavelength Monitoring of the Dwarf Seyfert 1 Galaxy NGC 4395. II. X-Ray and Ultraviolet Continuum Variability
We report on two Chandra observations, and a simultaneous Hubble SpaceTelescope ultraviolet observation, of the dwarf Seyfert 1 galaxy NGC4395. Each Chandra observation had a duration of ~30 ks, with aseparation of ~50 ks. The spectrum was observed to harden between theseobservations via a scaling down of the soft-band flux. Theinterobservation variability is in a different sense from the observedvariability within each observation and is most likely the result ofincreased absorption. Spectral variations were seen during the firstobservation suggesting that the X-ray emission is produced in more thanone disconnected region. We have also reanalyzed a ~17 ks Chandraobservation conducted in 2000. During the three Chandra observations the2-10 keV flux is about a factor of 2 lower than seen during anXMM-Newton observation conducted in 2003. Moreover, the fractionalvariability amplitude exhibited during the XMM-Newton observation issignificantly softer than seen during the Chandra observations. A powerspectral analysis of the first of the two new Chandra observationsrevealed a peak at 341 s with a formal detection significance of 99%. Asimilar peak was seen previously in the 2000 Chandra data. However, thedetection of this feature is tentative given that it was found inneither the second of our two new Chandra observations nor theXMM-Newton data, and it is much narrower than expected. The Hubble SpaceTelescope observation was conducted during part of the second Chandravisit. A zero-lag correlation between the ultraviolet and X-ray fluxeswas detected with a significance of ~99.5%, consistent with thepredictions of the two-phase model for the X-ray emission from activegalactic nuclei.
| 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.
| A Galactic Origin for the Local Ionized X-Ray Absorbers
Recent Chandra and XMM-Newton observations of distant quasars have shownstrong local (z~0) X-ray absorption lines from highly ionized gas,primarily He-like oxygen. The nature of these X-ray absorbers, i.e.,whether they are part of the hot gas associated with the Milky Way orpart of the intragroup medium in the Local Group, remains a puzzle dueto the uncertainties in the distance. We present in this paper a surveyof 20 AGNs with Chandra and XMM-Newton archival data. About 40% of thetargets show local O VII He α absorption with column densitiesaround 1016 cm-2; in particular, O VII absorptionis present in all the high-quality spectra. We estimate that the skycovering fraction of this O VII-absorbing gas is at least 63%, at 90%confidence, and likely to be unity given enough high-quality spectra. Onthe basis of (1) the expected number of absorbers along sight linestoward distant AGNs, (2) joint analysis with X-ray emissionmeasurements, and (3) mass estimation, we argue that the observed X-rayabsorbers are part of the hot gas associated with our Galaxy. Futureobservations will significantly improve our understanding of thecovering fraction and provide robust tests of this result.
| 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.
| BeppoSAX View of Radio-loud Active Galactic Nuclei
A systematic analysis of a large sample of radio-loud active galacticnuclei (AGNs) available in the BeppoSAX public archive has beenperformed. The sample includes 3 narrow-line radio galaxies (NLRGs), 10broad-line radio galaxies (BLRGs), 6 steep-spectrum radio quasars(SSRQs), and 16 flat-spectrum radio quasars (FSRQs). According to theunified models, these classes correspond to objects with increasingviewing angles. As expected, the presence of a nonthermal beamedcomponent emerges clearly in FSRQs. This class shows in fact afeatureless continuum (with the exception of 3C 273) and a significantlyflatter average spectral slope. However, traces of a nonthermalDoppler-enhanced radiation are elusive in the other classes. We findthat the iron line equivalent widths (EWs) are generally weaker inradio-loud AGNs than in Seyfert 1 galaxies, and we confirm the presenceof an X-ray Baldwin effect; that is, a decrease of EW with the 2-10 keVluminosity from Seyfert galaxies to BLRGs and quasars. Since theEW-L2-10 keV anticorrelation is present also in radio-quietAGNs alone, this effect cannot be ascribed entirely to a strongly beamedjet component. Possible alternative interpretations are explored.
| 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.
| Reverberation Measurements of the Inner Radius of the Dust Torus in Nearby Seyfert 1 Galaxies
The most intense monitoring observations yet made in the optical andnear-infrared wave bands were carried out for Seyfert 1 galaxies NGC5548, NGC 4051, NGC 3227, and NGC 7469 by the MAGNUM telescope, andclear time-delayed responses of the K-band flux variations to the V-bandflux variations were found for all of these galaxies. Their H-K colortemperatures of 1500-1800 K, estimated from their observed fluxvariation gradients, support a view that the bulk of the K flux shouldoriginate in the thermal radiation of hot dust surrounding the centralengine and that the lag time should correspond to light-travel distancebetween them. Cross-correlation analysis measures their lag times to be47-53 (NGC 5548), 11-18 (NGC 4051), about 20 (NGC 3227), and 65-87 (NGC7469) days. The lag times are tightly correlated with the opticalluminosities, as expected from dust reverberation(Δt~L0.5), while weakly with the central virial masses,which suggests that the inner radii of the dust tori around activenuclei have one-to-one correspondences with their central luminosities.In the lag time versus central luminosity diagram, the K-band lag timesplace an upper boundary on the similar lag times of broad emission linesin the literature, which not only supports the unified scheme of AGNsbut also implies a physical transition from the BLR out to the dusttorus that encircles the BLR. Correlated short-term V-band and X-rayflux variations in NGC 5548 are also found with a delay of 1 or 2 days,indicating the thermal reprocessing of X-ray emission by the centralaccretion flow.
| 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 First INTEGRAL AGN Catalog
We present the first INTEGRAL AGN catalog, based on observationsperformed from launch of the mission in 2002 October until 2004 January.The catalog includes 42 AGNs, of which 10 are Seyfert 1, 17 are Seyfert2, and 9 are intermediate Seyfert 1.5. The fraction of blazars is rathersmall, with five detected objects, and only one galaxy cluster and nostarburst galaxies have been detected so far. A complete subset consistsof 32 AGNs with a significance limit of 7 σ in the INTEGRAL ISGRI20-40 keV data. Although the sample is not flux limited, thedistribution of sources shows a ratio of obscured to unobscured AGNs of1.5-2.0, consistent with luminosity-dependent unified models for AGNs.Only four Compton-thick AGNs are found in the sample. Based on theINTEGRAL data presented here, the Seyfert 2 spectra are slightly harder(Γ=1.95+/-0.01) than Seyfert 1.5 (Γ=2.10+/-0.02) and Seyfert1 (Γ=2.11+/-0.05).
| 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.
| 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.
| Observations Supporting the Existence of an Intrinsic Magnetic Moment inside the Central Compact Object within the Quasar Q0957+561
Recent brightness fluctuation and autocorrelation analysis of timeseries data and microlensing size scales, seen in Q0957+561A and B, haveproduced important information about the existence and characteristicphysical dimensions of a new nonstandard magnetically dominated internalstructure contained within this quasar. This new internal quasarstructure, which we call the Schild-Vakulik structure, can beconsistently explained in terms of a new class of gravitationallycollapsing solutions to the Einstein field equations that describehighly redshifted Eddington-limited magnetospheric eternally collapsingobjects that contain intrinsic magnetic moments. Since observations ofthe Schild-Vakulik structure within Q0957+561 imply that this quasarcontains an observable intrinsic magnetic moment, this represents strongevidence that the quasar does not have an event horizon.
| 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 Statistics and Local Luminosity Function of a Complete Hard X-Ray Sample of the Brightest Active Galactic Nuclei
We have measured the X-ray spectral properties of a completeflux-limited sample of bright active galactic nuclei (AGNs) from theHEAO-1 all-sky catalogs to investigate their statistics and providegreater constraints on the bright end of the hard X-ray luminosityfunction (HXLF) and the AGN population synthesis model of the X-raybackground. Spectral studies using data from ASCA, XMM-Newton, and/orBeppoSAX observations have been made for almost all AGNs in this sample.The spectral measurements enable us to construct the neutral absorbingcolumn density (logNH) distribution and separate HXLFs forabsorbed (logNH[cm-2]>21.5) and unabsorbed AGNsin the local universe. Our results show evidence of a difference in theshapes of the HXLFs of absorbed and unabsorbed AGNs in that the absorbedAGN HXLF drops more rapidly at higher luminosities than that ofunabsorbed AGNs, similar to what has been previously reported. In theLX-NH plot we find no AGNs in the high-luminosity,high-intrinsic-absorption regime (logLX[ergss-1]>44.5 and logNH[cm-2]>21.5)in our sample, in which we expect approximately five AGNs if we assumethat the absorbed and unabsorbed AGNs have identical HXLF shapes. Wealso find that the fluxes observed with ASCA or XMM-Newton are smallerthan that observed with HEAO-1 by a factor of 0.29 on average, which isexpected for reobservation of sources with a factor of ~2.5 variabilityamplitude scale.
| Low-Luminosity Active Galaxies and Their Central Black Holes
Central black hole masses for 117 spiral galaxies representingmorphological stages S0/a through Sc and taken from the largespectroscopic survey of Ho et al. are derived using Ks-banddata from the Two Micron All Sky Survey. Black hole masses are foundusing a calibrated black hole-Ks bulge luminosity relation,while bulge luminosities are measured by means of a two-dimensionalbulge-disk decomposition routine. The black hole masses are correlatedagainst a variety of parameters representing properties of the nucleusand host galaxy. Nuclear properties such as line width (FWHM [N II]), aswell as emission-line ratios (e.g., [O III]/Hβ, [O I]/Hα, [NII]/Hα, and [S II]/Hα), show a very high degree ofcorrelation with black hole mass. The excellent correlation with linewidth supports the view that the emission-line gas is in virialequilibrium with either the black hole or bulge potential. The very goodemission-line ratio correlations may indicate a change in ionizingcontinuum shape with black hole mass in the sense that more massiveblack holes generate harder spectra. Apart from theinclination-corrected rotational velocity, no excellent correlations arefound between black hole mass and host galaxy properties. Significantdifferences are found between the distributions of black hole masses inearly-, mid-, and late-type spiral galaxies (subsamples A, B, and C) inthe sense that early-type galaxies have preferentially larger centralblack holes, consistent with observations that Seyfert galaxies arefound preferentially in early-type systems. The line width distributionsshow a marked difference among subsamples A, B, and C in the sense thatearlier type galaxies have larger line widths. There are also cleardifferences in line ratios between subsamples A+B and C that likely arerelated to the level of ionization in the gas. Finally, aKs-band Simien & de Vaucouleurs diagram shows excellentagreement with the original B-band relation, although there is a largedispersion at a given morphological stage.
| 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.
| 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.
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
Catalogs and designations:
|
