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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.
| The K-band properties of Seyfert 2 galaxies
Aims. It is well known that the [O iii]λ5007 emission line andhard X-ray (2-10 keV) luminosities are good indicators of AGN activitiesand that the near and mid-infrared emission of AGN originates fromre-radiation of dusty clouds heated by the UV/optical radiation from theaccretion disk. In this paper we present a study of the near-infraredK-band (2.2 μm) properties for a sample of 65 Seyfert 2 galaxies. Methods: .By using the AGN/Bulge/Disk decomposition technique, weanalyzed the 2MASS K_S-band images for Seyfert 2 galaxies in order toderive the K_S-band magnitudes for the central engine, bulge, and diskcomponents. Results: .We find that the K_S-band magnitudes of thecentral AGN component in Seyfert 2 galaxies are tightly correlated withthe [O iii]λ5007 and the hard X-ray luminosities, which suggeststhat the AGN K-band emission is also an excellent indicator of thenuclear activities at least for Seyfert 2 galaxies. We also confirm thegood relation between the central black hole masses and bulge's K-bandmagnitudes for Seyfert 2s.
| A dichotomy in the orientation of dust and radio jets in nearby low-power radio galaxies
We examine the properties of central dust in nearby quiescent and activeearly-type galaxies. The active galaxies are low-power radio galaxieswith Fanaroff & Riley type I or I/II radio jets. We focus on (a) thecomparison of the dust distributions in the active and quiescent galaxysamples; and (b) the relation between the radio jet and dustorientations. Our main observational conclusions are: (i) in line withprevious studies, the dust detection rate is higher in radio-jetgalaxies than in non radio-jet galaxies; (ii) radio galaxies contain ahigher fraction of regular dust “ellipses” compared toquiescent galaxies which contain more often irregular dustdistributions; (iii) the morphology, size and orientation of dustellipses and lanes in quiescent early-types and active early-types withkpc-scale radio jets is very similar; (iv) dust ellipses are alignedwith the major axis of the galaxy, dust lanes do not show a preferredalignment except for large (>kpc) dust lanes which are aligned withthe minor axis of the galaxy; and (v) as projected on the sky, jets donot show a preferred orientation relative to the galaxy major axis (andhence dust ellipses), but jets are preferentially perpendicular to dustlanes. We show that the dust ellipses are consistent with being nearlycircular thin disks viewed at random viewing angles. The lanes arelikely warped dust structures, which may be in the process of settlingdown to become regular disks or are being perturbed by anon-gravitational force. We use the observed dust-jet orientations toconstrain the three-dimensional angle θDJ between jetand dust. For dust-lane galaxies, the jet is approximately perpendicularto the dust structure, while for dust-ellipse galaxies there is a muchwider distribution of θDJ. We discuss two scenariosthat could explain the dust/jet/galaxy orientation dichotomy. If lanesare indeed settling, then the jet orientation apparently is roughlyaligned with the angular momentum of the dust before it settles. Iflanes are perturbed by a jet-related force, it appears that it causesthe dust to move out of its equilibrium plane in the galaxy into a planewhich is perpendicular to the jet.
| The supermassive black hole in the Seyfert 2 galaxy NGC 5252
We present results from HST/STIS long-slit spectroscopy of the gasmotions in the nuclear region of the Seyfert 2 galaxy NGC 5252. Theobserved velocity field is consistent with gas in regular rotation withsuperposed localized patches of disturbed gas. The dynamics of thecircumnuclear gas can be accurately reproduced by adding to the stellarmass component a compact dark mass of MBH = 0.95(-0.45;+1.45) × 109 Mȯ, very likely asupermassive black hole (BH). Contrarily to results obtained in similarstudies rotational broadening is sufficient to reproduce also thebehaviour of line widths. The BH mass estimated for NGC 5252 is in goodagreement with the correlation between MBH and bulge mass.The comparison with the MBH vs. σcrelationship is less stringent (mostly due to the relatively large errorin σc); NGC 5252 is located above the best fit line bybetween 0.3 and 1.2 dex, i.e. 1-4 times the dispersion of thecorrelation. Both the galaxy's and BH mass of NGC 5252 are substantiallylarger than those usually estimated for Seyfert galaxies but, on theother hand, they are typical of radio-quiet quasars. Combining thedetermined BH mass with the hard X-ray luminosity, we estimate that NGC5252 is emitting at a fraction 0.005 of LEdd. In thissense, this active nucleus appears to be a quasar relic, now probablyaccreting at a low rate, rather than a low black hole mass counterpartof a QSO.Based on observations obtained at the Space Telescope Science Institute,which is operated by the Association of Universities for Research inAstronomy, Incorporated, under NASA contract NAS 5-26555.
| Connecting the cosmic infrared background to the X-ray background
We estimate the contribution of active galactic nuclei (AGN) and oftheir host galaxies to the infrared background. We use the luminosityfunction and evolution of AGN recently determined by the hard X-raysurveys, and new spectral energy distributions connecting the X-ray andthe infrared emission, divided in intervals of absorption. These twoingredients allow us to determine the contribution of AGN to theinfrared background by using mostly observed quantities, with only minorassumptions. We find that AGN emission contributes little to theinfrared background (<5 per cent over most of the infrared bands),implying that the latter is dominated by star formation. However, AGNhost galaxies may contribute significantly to the infrared background,and more specifically 10-20 per cent in the 1-20 μm range and ~5 percent at λ < 60μm. We also give the contribution of AGN andof their host galaxies to the source number counts in various infraredbands, focusing on those which will be observed with Spitzer. We alsoreport a significant discrepancy between the expected contribution ofAGN hosts to the submillimetre background and bright submillimetrenumber counts with the observational constraints. We discuss the causesand implications of this discrepancy and the possible effects on theSpitzer far-infrared bands.
| The star formation history of Seyfert 2 nuclei
We present a study of the stellar populations in the central ~200 pc ofa large and homogeneous sample comprising 79 nearby galaxies, most ofwhich are Seyfert 2s. The star formation history of these nuclei isreconstructed by means of state-of-the-art population synthesismodelling of their spectra in the 3500-5200 Åinterval. Aquasar-like featureless continuum (FC) is added to the models to accountfor possible scattered light from a hidden active galactic nucleus(AGN).We find the following. (1) The star formation history of Seyfert 2nuclei is remarkably heterogeneous: young starbursts, intermediate-ageand old stellar populations all appear in significant and widely varyingproportions. (2) A significant fraction of the nuclei show a strong FCcomponent, but this FC is not always an indication of a hidden AGN: itcan also betray the presence of a young, dusty starburst. (3) We detectweak broad Hβ emission in several Seyfert 2s after cleaning theobserved spectrum by subtracting the synthesis model. These are mostlikely the weak scattered lines from the hidden broad-line regionenvisaged in the unified model, given that in most of these casesindependent spectropolarimetry data find a hidden Seyfert 1. (4) The FCstrengths obtained by the spectral decomposition are substantiallylarger for the Seyfert 2s which present evidence of broad lines,implying that the scattered non-stellar continuum is also detected. (5)There is no correlation between the star formation in the nucleus andeither the central or overall morphology of the parent galaxies.
| Spectropolarimetry of Compton-thin Seyfert 2 galaxies
We present new spectropolarimetry of a sample of nearby Compton-thinSeyfert 2 galaxies (i.e. those with NH < 1023cm-2). We show that the detection rate of scattered broadHα in this sample is considerably higher than in Seyfert 2galaxies as a whole. Our results also show that in this low obscurationset it is possible to find scattered broad Hα even when the globalproperties of the galaxy are largely dominated by the host galaxy andnot the active galactic nucleus. These results argue against theexistence of a population of `pure' Seyfert 2 galaxies.
| The infrared continuum of active galactic nuclei
We discuss the different physical processes contributing to the infraredcontinuum of active galactic nuclei (AGNs), assuming that bothphotoionization from the active centre and shocks ionize and heat thegas and dust contained in an ensemble of clouds surrounding the nucleus.In our model, radiation transfer of primary and secondary radiationthroughout a cloud is calculated consistently with collisional processesdue to the shock. We consider that the observed continuum corresponds toreprocessed radiation from both dust and gas in the clouds. Collisionalprocesses are important in the presence of shocks. The grains aresputtered crossing the shock front. The models are constrained bysputtering as well as by the far-infrared data. The model is applied tothe continuum of Seyfert galaxies from which the best estimate of thenuclear, stellar subtracted, emission is available. The results showthat radiation-dominated high-velocity clouds are more numerous inSeyfert 1-1.5 whereas shock-dominated low-velocity clouds are dominantin Seyfert type 2. This result is in full agreement with the unifiedmodel for AGNs, by which high-velocity clouds, placed deeper into thecentral region and therefore reached by a more intense radiation, shouldplay a more significant role in the spectra of broad-line objects. Wecould therefore conclude that in type 2 objects, radiation is partlysuppressed by a central dusty medium with a high dust-to-gas ratio. Oncethe model approach is tested, a grid of models is used to provide aphenomenological analysis of the observed infrared spectral energydistribution. This empirical method is a useful tool to rapidly accessthe physical conditions of the AGN emitting clouds. For this, analyticalforms are derived for the two processes contributing to the infraredemission: dust emission and thermal bremsstrahlung produced by thenarrow-line region clouds. Their relative contribution provides ameasurement of the dust-to-gas ratio.
| Chandra observations of the flat spectrum Seyfert-2 galaxies NGC 2110 and NGC 7582.
Not Available
| Emission Line Properties of Active Galactic Nuclei from a Post-COSTAR Hubble Space Telescope Faint Object Spectrograph Spectral Atlas
We present consistent emission-line measurements for active galacticnuclei (AGNs), useful for reliable statistical studies of emission lineproperties. This paper joins a series including similar measurements of993 spectra from the Large Bright Quasar Survey and 174 spectra of AGNsobtained from the Faint Object Spectrograph (FOS) on the Hubble SpaceTelescope (HST) prior to the installation of COSTAR. This time weconcentrate on 220 spectra obtained with the FOS after the installationof COSTAR, completing the emission line analysis of all FOS archivalspectra. We use the same automated technique as in previous papers,which accounts for Galactic extinction, models blended optical and UViron emission, includes Galactic and intrinsic absorption lines, andmodels emission lines using multiple Gaussians. We present UV andoptical emission line parameters (equivalent widths, fluxes, FWHM, andline positions) for a large number (28) of emission lines includingupper limits for undetected lines. Further scientific analyses will bepresented in subsequent papers.
| A Green Bank Telescope Search for Water Masers in Nearby Active Galactic Nuclei
Using the Green Bank Telescope, we have conducted a survey for 1.3 cmwater maser emission toward the nuclei of nearby active galaxies, themost sensitive large survey for H2O masers to date. Among 145galaxies observed, maser emission was newly detected in 11 sources andconfirmed in one other. Our survey targeted nearby (v<12,000 kms-1), mainly type 2 active galactic nuclei (AGNs) north ofδ=-20deg and includes a few additional sources as well.We find that more than one-third of Seyfert 2 galaxies have strong maseremission, although the detection rate declines beyond v~5000 kms-1 because of sensitivity limits. Two of the masersdiscovered during this survey are found in unexpected hosts: NGC 4151(Seyfert 1.5) and NGC 2782 (starburst). We discuss the possiblerelations between the large X-ray column to NGC 4151 and a possiblehidden AGN in NGC 2782 to the detected masers. Four of the masersdiscovered here, NGC 591, NGC 4388, NGC 5728, and NGC 6323, havehigh-velocity lines symmetrically spaced about the systemic velocity, alikely signature of molecular gas in a nuclear accretion disk. The masersource in NGC 6323, in particular, reveals the classic spectrum of a``disk maser'' represented by three distinct groups of Dopplercomponents. Future single-dish and VLBI observations of these fourgalaxies could provide a measurement of the distance to each galaxy andof the Hubble constant, independent of standard candle calibrations.
| Comparison of Nuclear Starburst Luminosities between Seyfert 1 and 2 Galaxies Based on Near-Infrared Spectroscopy
We report on infrared K- (2-2.5 μm) and L-band (2.8-4.1 μm) slitspectroscopy of 23 Seyfert 1 galaxies in the CfA and 12 μm samples. Apolycyclic aromatic hydrocarbon (PAH) emission feature at 3.3 μm inthe L band is primarily used to investigate nuclear star-formingactivity in these galaxies. The 3.3 μm PAH emission is detected in 10sources (=43%), demonstrating that detection of nuclear star formationin a significant fraction of Seyfert 1 galaxies is now feasible. For thePAH-detected nuclei, the surface brightness values of the PAH emissionare as high as those of typical starbursts, suggesting that the PAHemission probes the putative nuclear starbursts in the dusty tori aroundthe central active galactic nuclei (AGNs). The magnitudes of the nuclearstarbursts are quantitatively estimated from the observed 3.3 μm PAHemission luminosities. The estimated starburst luminosities relative tosome indicators of AGN powers in these Seyfert 1 galaxies are comparedwith 32 Seyfert 2 galaxies in the same samples that we have previouslyobserved. We find that there is no significant difference in nuclearstarburst to AGN luminosity ratios of Seyfert 1 and 2 galaxies and thatnuclear starburst luminosity positively correlates with AGN power inboth types. Our results favor a slightly modified AGN unification model,which predicts that nuclear starbursts occurring in the dusty tori ofSeyfert galaxies are physically connected to the central AGNs, ratherthan the classical unification paradigm, in which the dusty tori simplyhide the central AGNs of Seyfert 2 galaxies and reprocess AGN radiationas infrared dust emission in Seyfert galaxies. No significantdifferences in nuclear star formation properties are recognizablebetween Seyfert 1 galaxies in the CfA and 12 μm samples.
| Circumnuclear Structure and Black Hole Fueling: Hubble Space Telescope NICMOS Imaging of 250 Active and Normal Galaxies
Why are the nuclei of some galaxies more active than others? If mostgalaxies harbor a central massive black hole, the main difference isprobably in how well it is fueled by its surroundings. We investigatethe hypothesis that such a difference can be seen in the detailedcircumnuclear morphologies of galaxies using several quantitativelydefined features, including bars, isophotal twists, boxy and diskyisophotes, and strong nonaxisymmetric features in unsharp-masked images.These diagnostics are applied to 250 high-resolution images of galaxycenters obtained in the near-infrared with NICMOS on the Hubble SpaceTelescope. To guard against the influence of possible biases andselection effects, we have carefully matched samples of Seyfert 1,Seyfert 2, LINER, starburst, and normal galaxies in their basicproperties, taking particular care to ensure that each was observed witha similar average scale (10-15 pc pixel-1). Severalmorphological differences among our five different spectroscopicclassifications emerge from the analysis. The H II/starburst galaxiesshow the strongest deviations from smooth elliptical isophotes, whilethe normal galaxies and LINERs have the least disturbed morphology. TheSeyfert 2s have significantly more twisted isophotes than any othercategory, and the early-type Seyfert 2s are significantly more disturbedthan the early-type Seyfert 1s. The morphological differences betweenSeyfert 1s and Seyfert 2s suggest that more is at work than simply theviewing angle of the central engine. They may correspond to differentevolutionary stages.
| Near-infrared K-Band Spectroscopic Investigation of Seyfert 2 Nuclei in the CfA and 12 Micron Samples
We present near-infrared K-band slit spectra of the nuclei of 25 Seyfert2 galaxies in the CfA and 12 μm samples. The strength of the COabsorption features at 2.3-2.4 μm produced by stars is measured interms of a spectroscopic CO index. A clear anticorrelation between theobserved CO index and the nuclear K-L color is present, suggesting thata featureless hot dust continuum heated by an active galactic nucleus(AGN) contributes significantly to the observed K-band fluxes in thenuclei of Seyfert 2 galaxies. After correction for this AGNcontribution, we estimate nuclear stellar K-band luminosities for allsources and CO indices for sources with modestly large observed COindices. The corrected CO indices for 10 (=40%) Seyfert 2 nuclei arefound to be as high as those observed in star-forming or elliptical(=spheroidal) galaxies. We combine the K-band data with measurements ofthe L-band 3.3 μm polycyclic aromatic hydrocarbon (PAH) emissionfeature, another powerful indicator for star formation, and find thatthe 3.3 μm PAH to K-band stellar luminosity ratios are substantiallysmaller than those of starburst galaxies. Our results suggest that the3.3 μm PAH emission originates in the putative nuclear starbursts inthe dusty tori surrounding the AGNs, because of its high surfacebrightness, whereas the K-band CO absorption features detected at thenuclei are dominated by old bulge (=spheroid) stars and thus may not bea powerful indicator for the nuclear starbursts. We see no cleardifference in the strength of the CO absorption and PAH emissionfeatures between the CfA and 12 μm Seyfert 2 galaxies.
| On-axis spectroscopy of the z =0.144 radio-loud quasar HE 1434-1600: an elliptical host with a highly ionized ISM
VLT on-axis optical spectroscopy of the z=0.144 radio-loud quasar HE1434-1600 is presented. The spatially resolved spectra of the hostgalaxy are deconvolved and separated from those of the central quasar inorder to study the dynamics of the stars and gas as well as the physicalconditions of the ISM. We find that the host of HE 1434-1600 is anelliptical galaxy that resides in a group of at least 5 member galaxies,and that most likely experienced a recent collision with its nearestcompanion. Compared with other quasar host galaxies, HE 1434-1600 has ahighly ionized ISM. The ionization state corresponds to that of typicalSeyferts, but the ionized regions are not distributed in a homogeneousway around the QSO, and are located preferentially several kiloparsecsaway from it. While the stellar absorption lines do not show anysignificant velocity field, the gas emission lines do. The observed gasvelocity field is hard to reconcile with dynamical models involvingrotating disk, modified Hubble laws or power laws, that all requireextreme central masses (M>109 Mȯ) toprovide only poor fit to the data. Power law models, which best fit thedata, provide a total mass of M(<10 kpc) = 9.2 ×1010 Mȯ. We conclude that the recentinteraction between HE 1434-1600 and its closest companion has stronglyaffected the gas velocity and ionization state, from the center of thegalaxy to its most external parts.Based on observations made with the ESO Very Large Telescope ANTU/UT1 atESO-Paranal observatory, Chile (program 65.P-0361(A)).
| Motion and properties of nuclear radio components in Seyfert galaxies seen with VLBI
We report EVN, MERLIN and VLBA observations at 18 cm, 6 cm and 3.6 cm ofthe Seyfert galaxies NGC 7674, NGC5506, NGC 2110 and Mrk1210 to study their structure and proper motions on pc scalesand to add some constraints on the many possible causes of theradio-quietness of Seyferts. The component configurations inNGC 7674 and NGC 2110 are simple,linear structures, whereas the configurations in NGC5506 and Mrk 1210 have multiple componentswith no clear axis of symmetry. We suggest that NGC7674 is a low-luminosity compact symmetric object. Comparingthe images at different epochs, we find a proper motion in NGC7674 of (0.92±0.07) c between the two centralcomponents separated by 282 pc and, in NGC 5506, wefind a 3 σ upper limit of 0.50 c for the components separated by3.8 pc. Our results confirm and extend earlier work showing that theoutward motion of radio components in Seyfert galaxies isnon-relativistic on pc scales. We briefly discuss whether thisnon-relativistic motion is intrinsic to the jet-formation process orresults from deceleration of an initially relativistic jet byinteraction with the pc or sub-pc scale interstellar medium. We combinedour sample with a list compiled from the literature of VLBI observationsmade of Seyfert galaxies, and found that most Seyfert nuclei have atleast one flat-spectrum component on the VLBI scale, which was not seenin the spectral indices measured at arcsec resolution. We found alsothat the bimodal alignment of pc and kpc radio structures displayed byradio galaxies and quasars is not displayed by this sample of Seyferts,which shows a uniform distribution of misalignment between0° and 90°. The frequent misalignmentcould result from jet precession or from deflection of the jet byinteraction with gas in the interstellar medium.
| Radio emission from AGN detected by the VLA FIRST survey
Using the most recent (April 2003) version of the VLA FIRST survey radiocatalog, we have searched for radio emission from >2800 AGN takenfrom the most recent (2001) version of the Veron-Cetty and Veron AGNcatalog. These AGN lie in the 9033 square degrees of sky alreadycovered by the VLA FIRST survey. Our work has resulted in positivedetection of radio emission from 775 AGN of which 214 are new detectionsat radio wavelengths.Tables 3 and 4 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/416/35
| Investigating the central engine of Seyfert 2 galaxies with and without Polarized Broad Lines
We study the hard X-ray emission of two samples of Seyfert 2 galaxieswith and without Polarized Broad Lines (PBL). In the hard X-ray domain,absorption effects do not significantly modify the intrinsic emissionallowing us a direct access to the central engine. The purpose of thisstudy is to compare the primary emission of the two Seyfert 2 subclassesin order to investigate the nature of their central engine and to testunified models according to which they both have a hidden Seyfert 1nucleus. We compute the average hard X-ray spectra of Seyfert 2 galaxieswith and without PBL observed with BeppoSAX/PDS (15-136 keV). The twospectra have a common general behavior at first sight, but investigatingdeeper we find differences in the intrinsic properties of the twocategories of Seyfert 2 galaxies. Sy 2 with polarized broad lines havephysical conditions close to those of Sy 1 galaxies whereas Sy 2 withoutPBL differ substantially, suggesting that they may have a particularplace in the scheme of Seyfert galaxies.Appendix A is only available in electronic form athttp://www.edpsciences.org
| The mid-IR emission of Seyfert galaxies: Relevance for CANARICAM
New results on the mid-IR emission of Seyfert galaxies are presented.The observations were performed using the TIMMI-2 instrument at the 3.6m ESO telescope. We have obtained diffraction-limited images. In somecases the emission can be resolved and varies with wavelength. Therelevance for these studies for CANARICAM is briefly discussed.
| Science with Tunable Filters
In just two years, the OSIRIS tunable filter spectrograph on the 10 mGTC will herald a new era in spectrophotometric imaging, from 350 nm to1 μ m. Like its forebear, the TTF at the Anglo-Australian Telescope(AAT), OSIRIS will offer a wide variety of observing modes linked tocharge shuffling in order to achieve exquisite differential imaging. Insome respects, simply repeating the many science cases conducted at theAAT will lead to advances in a number of fields. This is all butguaranteed by the better apparatus, observing conditions and largeraperture. However, the expected improvement in sensitivity suggests manynew avenues: large surveys of extended sources, absorption line imaging,time series and coronographic imaging, to name a few. OSIRIS willprovide some of the deepest photometric ``diffuse light'' images todate, much better than what can be achieved with an integral fieldspectrograph, and over a much wider field of view.
| A Possible Signature of Connection between Blazars and Seyfert Galaxies
The accretion rates (dot{M}) and their correlation with cosmologicalredshifts for a sample of blazars and Seyfert galaxies are presented.The sample includes 77 blazars (28 FSRQs, 26 LBLs, and 23 HBLs) and 60Seyfert galaxies, of which the extended spectral energy distributioninformation and redshifts are available. Within the framework ofaccreting black holes, the accretion rates for these sources wereestimated based on their bolometric luminosities. The result shows thatthe accretion rates are significantly different for each subclass of theblazars and Seyfert galaxies. Their averages are, respectively, 50.2,17.0, 1.0, 0.1Modot yr-1 for the FSRQs, LBLs, HBLs, and theSeyfert galaxies, exhibiting a well descending sequence ofFSRQs-LBLs-HBLs-Seyfert galaxies. They are strongly correlated with theredshifts for both blazars and Seyfert galaxies. The linear correlationcoefficients are 0.81 and 0.68 with a chance probab ility of p <0.0001, respectively. A plot of dot{M} - z shows that the blazars andthe Seyfert galaxies distribute in a distinguishable regions with aconnection at z 0.7 and almost all the sources lie in a narrowregion of z1.40 ≤ dot{M} ≤ 250 z1.40,illustrating a strong correlation between the two quantities for thewhole sample. The regression line is dot{M} = (14.5 ± 1.2)z1.40±0.06 Modot yr-1 with a linearcoefficient of 0.93 and a chance probability of p < 0.0001,suggesting a connection between blazars and Seyfert galaxies. Thisconnection might imply that the two classes are on the same evolutionarysequence. Although the correlations of the data are formally solid, theconclusion may be affected by one source of considerable uncertainty atthe data level, which is also discussed.
| Taurus Tunable Filter - Seven Years of Observing
The Taurus Tunable Filter (TTF) has now been in regular use for sevenyears on the Anglo-Australian Telescope (AAT). The instrument was alsoused for three years (1996-1999) on the William Herschel Telescope(WHT). We present a brief review of the different applications in orderto illustrate the versatility of tunable filters in optical/IRspectrophotometric imaging. Tunable filters are now either planned orunder development for 6-10m class telescopes which ensures their use foryears to come.
| The infrared-X-ray continuum correlation in active galactic nuclei
The correlation between the soft X-ray and near-infrared emission fromactive galactic nuclei (AGNs) is analysed using composite models. Wefind new evidence for differences in the ranges of parameters thatcharacterize the narrow-line region (NLR) of Seyfert galaxies andlow-ionization nuclear emission regions (LINERs). Soft X-rays show lessvariability, so they are better fitted for this kind of analysis. In ourmodels, soft X-rays are emitted in the post-shock region of clouds withrelatively high shock velocities Vs > 250 kms-1. Consequently, dust emission peaks in the mid-infrared.On the other hand, in the photoionized zone, dust is at lowertemperature and usually does not contribute to the mid-infraredemission. The results are sensible enough to allow the same modellingmethod to be applied to different types of AGN. We found that shockvelocities are between 300 and 1000 km s-1, with the NLR oflow-luminosity active galactic nuclei (LLAGNs) and type 2 Seyfertgalaxies (Sy2s) showing lower velocities than type 1 Seyfert galaxies(Sy1s). The intensity of the ionizing radiation flux at the Lyman limitfrom the central source is low for LINERs and low-luminosity AGNs (logFh= 9 to 10), increasing towards Sy2s (log Fh~ 11)and Sy1s (11 <=Fh<= 12). Results obtained by modellingthe Einstein and the ROSAT samples of galaxies are in full agreement.Dust-to-gas ratios by number are >=10-14 in LINERs andLLAGNs, between 10-15 and 3 × 10-13 in Sy1sand up to 5 × 10-13 in Sy2s. In order to fit theinfrared and X-ray continua, an η factor is defined, which accountsfor the emitting area of the cloud. If the infrared emission is due tobremsstrahlung and comes from the same cloud that produces the softX-rays, the η values obtained from both emissions must be the same.Therefore, if (η)IR < (η)softX, theremust be a strong contribution of soft X-rays from the active centre.From the η values, we expect to identify the objects that couldpresent strong variability.
| A Fundamental Plane of black hole activity
We examine the disc-jet connection in stellar mass and supermassiveblack holes by investigating the properties of their compact emission inthe X-ray and radio bands. We compile a sample of ~100 active galacticnuclei with measured masses, 5-GHz core emission, and 2-10 keVluminosities, together with eight galactic black holes with a total of~50 simultaneous observations in the radio and X-ray bands. Using thissample, we study the correlations between the radio (LR) andthe X-ray (LX) luminosity and the black hole mass (M). Wefind that the radio luminosity is correlated with bothM andLX, at a highly significant level. In particular, we showthat the sources define a `Fundamental Plane' in the three-dimensional(logLR, logLX, logM) space, given bylogLR= (0.60+0.11-0.11)logLX+ (0.78+0.11-0.09) logM+7.33+4.05-4.07, with a substantial scatter ofσR= 0.88. We compare our results to the theoreticalrelations between radio flux, black hole mass, and accretion ratederived by Heinz & Sunyaev. Such relations depend only on theassumed accretion model and on the observed radio spectral index.Therefore, we are able to show that the X-ray emission from black holesaccreting at less than a few per cent of the Eddington rate is unlikelyto be produced by radiatively efficient accretion, and is marginallyconsistent with optically thin synchrotron emission from the jet. On theother hand, models for radiatively inefficient accretion flows seem toagree well with the data.
| Compact Nuclear Starbursts in Seyfert 2 Galaxies from the CfA and 12 Micron Samples
We present infrared 2.8-4.1 μm slit spectra of 32 Seyfert 2 galaxiesin the CfA and 12 μm samples. The 3.3 μm polycyclic aromatichydrocarbon (PAH) emission feature was used to estimate the absolutemagnitude of a compact nuclear starburst (less than a few hundredparsecs in size) that is presumed to have occurred in the outer regionof an obscuring dusty molecular torus around a central supermassiveblack hole. We detected 3.3 μm PAH emission in 11 of the 32 Seyfert 2nuclei in our sample, providing evidence for the presence of compactnuclear starbursts in a significant fraction of Seyfert 2 nuclei.However, the rest-frame equivalent widths of the 3.3 μm PAH emissionand the 3.3 μm PAH-to-infrared luminosity ratios measured in thisstudy suggest that compact nuclear starbursts generally do notcontribute significantly to the observed 3-4 μm nuclear fluxes or tothe infrared luminosities of Seyfert 2 galaxies. Absorption features at3.4 μm from bare dust were clearly detected in only two of thenuclei, and features at 3.1 μm from ice-covered dust were detected inonly one nucleus. If the dust properties in the direction of theseSeyfert 2 nuclei do not differ significantly from the Galacticinterstellar medium, then these small absorption optical depths suggestthat dust extinction toward the 3-4 μm continuum emitting region inthe innermost part of the obscuring dusty torus is modest:AV<50-60 mag. Finally, the 3.3 μm PAH emissionluminosities measured in this study were found to be significantlycorrelated with IRAS 12 and 25 μm and nuclear N-band (10.6 μm)luminosities. If these three luminosities trace the power of the activegalactic nucleus (AGN), then the luminosities of compact nuclearstarbursts and AGNs are correlated. This correlation is in agreementwith theories predicting that the presence of a compact nuclearstarburst in the torus leads to an enhancement of the mass accretionrate onto the central supermassive black hole.
| The Relation between Black Hole Mass, Bulge Mass, and Near-Infrared Luminosity
We present new accurate near-infrared (NIR) spheroid (bulge) structuralparameters obtained by a two-dimensional image analysis of all galaxieswith a direct black hole (BH) mass determination. As expected, NIR bulgeluminosities Lbul and BH masses are tightly correlated, andif we consider only those galaxies with a secure BH mass measurement andan accurate Lbul (27 objects), the spread ofMBH-Lbul is similar toMBH-σe, where σe is theeffective stellar velocity dispersion. We find an intrinsic rms scatterof ~=0.3 dex in logMBH. By combining the bulge effectiveradii Re measured in our analysis with σe,we find a tight linear correlation (rms~=0.25 dex) betweenMBH and the virial bulge mass(~Reσ2e), with~0.002. A partial correlationanalysis shows that MBH depends on both σeand Re and that both variables are necessary to drive thecorrelations between MBH and other bulge properties.
| BeppoSAX Average Spectra of Seyfert Galaxies
We have studied the average 3-200 keV spectra of Seyfert galaxies oftype 1 and 2, using data obtained with BeppoSAX. The average Seyfert 1spectrum is well fitted by a power-law continuum with photon spectralindex Γ~1.9, a Compton reflection component R~0.6-1 (depending onthe inclination angle between the line of sight and the reflectingmaterial), and a high-energy cutoff at around 200 keV; there is also aniron line at 6.4 keV characterized by an equivalent width of 120 eV.Seyfert 2 galaxies, on the other hand, show stronger neutral absorption[NH=(3-4)×1022 atoms cm-2], asexpected, but are also characterized by an X-ray power law that issubstantially harder (Γ~1.75) and with a cutoff at lower energies(Ec~130 keV); the iron line parameters are insteadsubstantially similar to those measured in type 1 objects. There areonly two possible solutions to this problem: to assume more reflectionin Seyfert 2 galaxies than observed in Seyfert 1 galaxies or morecomplex absorption than estimated in the first instance. The firstpossibility is ruled out by the Seyfert 2 to Seyfert 1 ratio, while thesecond provides an average Seyfert 2 intrinsic spectrum very similar tothat of the Seyfert 1. The extra absorber is likely an artifact due tosumming spectra with different amounts of absorption, although we cannotexclude its presence in at least some individual sources. Our resultargues strongly for a very similar central engine in both types ofgalaxies, as expected under the unified theory.
| The Lack of Broad-Line Regions in Low Accretion Rate Active Galactic Nuclei as Evidence of Their Origin in the Accretion Disk
In this Letter, we present evidence suggesting that the absence orpresence of hidden broad-line regions (HBLRs) in Seyfert 2 galaxies isregulated by the rate at which matter accretes onto a centralsupermassive black hole, in units of the Eddington rate. Evidence isbased on data from a subsample of type 2 active galactic nucleiextracted from the Tran spectropolarimetric sample and made up of allthose sources that also have good-quality X-ray spectra available andfor which a bulge luminosity can be estimated. We use the intrinsic(i.e., unabsorbed) X-ray luminosities of these sources and their blackhole masses (estimated by using the well-known relationship betweennuclear mass and bulge luminosity in galaxies) to derive the nuclearaccretion rate in Eddington units. We find that virtually all HBLRsources have accretion rates larger than a threshold value ofmthres~=10-3 (in Eddington units), while non-HBLRsources lie at m<~mthres. These data nicely fitpredictions from a model proposed by Nicastro in which the broad-lineregions (BLRs) are formed by accretion disk instabilities occurring inproximity of the critical radius at which the disk changes from gaspressure dominated to radiation pressure dominated. This radiusdiminishes with decreasing m for low enough accretion rates (andtherefore luminosities), the critical radius becomes smaller than theinnermost stable orbit and BLRs cannot form.
| The Infrared Spectral Energy Distribution of the Seyfert 2 Prototype NGC 5252
The complete mid- to far-infrared continuum energy distributioncollected with the Infrared Space Observatory of the Seyfert 2 prototypeNGC 5252 is presented. ISOCAM images taken in the 3-15 μm show aresolved central source that is consistent at all bands with a region ofabout 1.3 kpc in size. Because of the lack of ongoing star formation inthe disk of the galaxy, this resolved emission is associated with eitherdust heated in the nuclear active region or bremsstrahlung emission fromthe nuclear and extended ionized gas. The size of the mid-IR emissioncontrasts with the standard unification scenario envisaging a compactdusty structure surrounding and hiding the active nucleus and thebroad-line region. The mid-IR data are complemented by ISOPHOT aperturephotometry in the 25-200 μm range. The overall IR spectral energydistribution is dominated by a well-defined component peaking at ~100μm, a characteristic temperature of T~=20 K, and an associated dustmass of 2.5×107 Msolar, which greatlydominates the total dust mass content of the galaxy. The heatingmechanism of this dust is probably the interstellar radiation field.After the contribution of this cold dust component is subtracted, thebulk of the residual emission is attributed to dust heated within thenuclear environment. Its luminosity consistently accounts for thereprocessing of the X-ray to UV emission derived for the nucleus of thisgalaxy. The comparison of NGC 5252's spectral energy distribution withcurrent torus models favors large nuclear disk structure on thekiloparsec scale.
| Chandra Snapshot Observations of Low-Luminosity Active Galactic Nuclei with a Compact Radio Source
The results of Chandra snapshot observations of 11 low-ionizationnuclear emission-line regions (LINERs), three low-luminosity Seyfertgalaxies, and one H II-LINER transition object are presented. Our sampleconsists of all the objects with a flat- or inverted-spectrum, compactradio core in the Very Large Array survey of 48 low-luminosity AGNs(LLAGNs) by Nagar and coworkers in 2000. An X-ray nucleus is detected inall galaxies except one, and their X-ray luminosities are in the range5×1038-8×1041 ergs s-1. TheX-ray spectra are generally steeper than expected from thermalbremsstrahlung emission from an advection-dominated accretion flow. TheX-ray-to-Hα luminosity ratios for 11 of 14 objects are in goodagreement, with the value characteristic of LLAGNs and more luminousAGNs, and indicate that their optical emission lines are predominantlypowered by an LLAGN. For three objects, this ratio is less thanexpected. Comparing with properties in other wavelengths, we find thatthese three galaxies are most likely to be heavily obscured AGNs. We usethe ratio RX=νLν(5 GHz)/LX, whereLX is the luminosity in the 2-10 keV band, as a measure ofradio loudness. In contrast to the usual definition of radio loudness[Ro=Lν(5 GHz)/Lν(B)],RX can be used for heavily obscured(NH>~1023 cm-2, AV>50mag) nuclei. Further, with the high spatial resolution of Chandra, thenuclear X-ray emission of LLAGNs is often easier to measure than thenuclear optical emission. We investigate the values of RX forLLAGNs, luminous Seyfert galaxies, quasars, and radio galaxies andconfirm the suggestion that a large fraction of LLAGNs are radio-loud.
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