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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.
| 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.
| 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.
| Molecular hydrogen and [FeII] in active galactic nuclei - II. Results for Seyfert 2 galaxies
Near-infrared spectroscopy is used to study the kinematics andexcitation mechanisms of H2 and [FeII] lines in a sampledominated by Seyfert 2 galaxies. The spectra simultaneously cover theJHK bands, allowing us to compare line fluxes emitted in the interval0.8-2.4 μm and avoiding aperture and seeing effects. TheH2 lines are systematically narrower than the narrow-lineregion lines, suggesting that, very likely, the H2 does notoriginate from the same parcel of gas that forms the narrow-line region.Emission-line ratios between H2 lines favour thermalexcitation mechanisms for the molecular gas in active galactic nuclei.It was found that non-thermal excitation contributes, at most, 30 percent of the observed H2. Thermal excitation is also confirmedby the rather similar vibrational and rotational temperatures in theobjects (~2000 K). The mass of hot H2 ranges from102 to 103Msolar, with nearly half ofobjects showing values of <500 Msolar. It shows that thefraction of molecular mass present in the nuclear region and emitting inthe near-infrared is a very small fraction of the warm molecular masspresent in the centre. A diagnostic diagram composed of the line ratiosH2/Brγ and [FeII]/Paβ proves to be a useful toolin the near-infrared for separating emission-line objects by theirdegree of nuclear activity. We found that active galactic nuclei arecharacterized by H2 2.121 μm/Brγ and [FeII] 1.257μm/Paβ flux ratios between 0.6 and 2. Starburst/HII galaxiesdisplay line ratios <0.6 while low-ionization nuclear emission-lineregions are characterized by values larger than 2 in either ratio.
| An atlas of calcium triplet spectra of active galaxies
We present a spectroscopic atlas of active galactic nuclei covering theregion around the λλ8498, 8542, 8662 calcium triplet(CaT). The sample comprises 78 objects, divided into 43 Seyfert 2s, 26Seyfert 1s, three starburst and six normal galaxies. The spectra pertainto the inner ~300 pc in radius, and thus sample the central kinematicsand stellar populations of active galaxies. The data are used to measurestellar velocity dispersions (σ*) with bothcross-correlation and direct fitting methods. These measurements arefound to be in good agreement with each other and with those in previousstudies for objects in common. The CaT equivalent width is alsomeasured. We find average values and sample dispersions ofWCaT of 4.6 +/- 2.0, 7.0 +/- 1.0 and 7.7 +/- 1.0 Å forSeyfert 1s, Seyfert 2s and normal galaxies, respectively. We furtherpresent an atlas of [SIII]λ9069 emission-line profiles for asubset of 40 galaxies. These data are analysed in a companion paperwhich addresses the connection between stellar and narrow-line regionkinematics, the behaviour of the CaT equivalent width as a function ofσ*, activity type and stellar population properties.
| Correlations among multiwavelength luminosities of star-forming galaxies
It has been known for two decades that a tight correlation existsbetween global far-infrared (FIR) and radio continuum (1.4 and 4.8 GHz)fluxes/luminosities from star-forming galaxies, which may be explainedby formation activities of massive stars in these galaxies. For thisvery reason, a correlation might also exist between X-ray and FIR/radioglobal luminosities of galaxies. We analyse data from the ROSAT All-SkySurvey and from IRAS to show that such correlation does indeed existbetween FIR (42.5-122.5μm) and soft X-ray (0.1-2.4 keV) luminositiesLX and LFIR in 17 normal star-forming galaxies(NSFGs), including 16 late-type galaxies and one host-dominant Seyfertgalaxy, as well as in 14 active star-forming galaxies (ASFGs) consistingof starburst-dominant Seyfert galaxies. The quantitative difference insuch correlations in NSFGs and in ASFGs may be interpreted in terms ofevolutionary variations from classic starburst galaxies tostarburst-dominant Seyfert galaxies. Meanwhile, some low-luminosityactive galactic nuclei (LLAGNs) tend to exhibit such a correlation thatwe infer for star-forming galaxies, implying that star-formingactivities might be more dominant in LLAGNs. In contrast, AGN-dominantSeyfert galaxies do not show such a LX versus LFIRcorrelation; this is most likely related to accretions towardssupermassive black holes (SMBHs) in galactic nuclei. In order toestablish a physical connection between theLX-LFIR correlation and global star formation rate(SFR) in galaxies, we empirically derive bothLX-LB and LFIR-LB relationswith the blue-band luminosity LB roughly representing themass of a galaxy. It appears that the more massive galaxies are, themore star formation regions exist in these galaxies. The global SFR isnot only associated with the mass of a galaxy but also closely relatedto the level of star-forming activities therein. We propose a relationbetween soft X-ray luminosity and SFR in star-forming galaxies. In orderto probe the LX-LFIR relation, we construct anempirical model in which both FIR and X-ray emissions consist of twocomponents with one being closely associated with star formation and theother one not. Based on this model, we infer a linear relation betweenFIR/soft X-ray in star formation regions and radio luminosities, and geta linear relation between LX and LFIR forstar-forming regions.
| Principal components in active galactic nuclei variability data and the estimation of the flux contributions from different components
It has been found that the near-infrared flux variations of Seyfertgalaxies satisfy relations of the formFi~αij+βijFj,where Fi, Fj are the fluxes in filters i and j;and αi,j, βi,j are constants. Theserelations have been used to estimate the constant contributions of thenon-variable underlying galaxies. The paper attempts a formal treatmentof the estimation procedure, allowing for the possible presence of athird component, namely non-variable hot dust. In an analysis of asample of 38 Seyfert galaxies, inclusion of the hot dust componentimproves the model fit in approximately half the cases. All derived dusttemperatures are below 300 K, in the range 540-860 K or above 1300 K. Anoteworthy feature is the estimation of confidence intervals for thecomponent contributions: this is achieved by bootstrapping. It is alsopointed out that the model implies that such data could be fruitfullyanalysed in terms of principal components.
| The Physical Connections among Infrared QSOs, Palomar-Green QSOs, and Narrow-Line Seyfert 1 Galaxies
We study the properties of infrared-selected QSOs (IR QSOs), opticallyselected Palomar-Green QSOs (PG QSOs), and narrow-line Seyfert 1galaxies (NLS1s). We compare their properties from the IR to the opticaland examine various correlations among the black hole mass, accretionrate, star formation rate, and optical and IR luminosities. We find thatthe IR excess in IR QSOs is mostly in the far-IR, and their IR spectralindices suggest that the excess emission is from low-temperature dustheated by starbursts rather than active galactic nuclei (AGNs). The IRexcess is therefore a useful criterion to separate the relativecontributions of starbursts and AGNs. We further find a tightcorrelation between the star formation rate and the accretion rate ofcentral AGNs for IR QSOs. The ratio of the star formation rate and theaccretion rate is about several hundred for IR QSOs but decreases withthe central black hole mass. This shows that the tight correlationbetween the stellar mass and the central black hole mass is preserved inmassive starbursts during violent mergers. We suggest that the higherEddington ratios of NLS1s and IR QSOs imply that they are in the earlystage of evolution toward classical Seyfert 1 galaxies and QSOs,respectively.
| Probing the Ionizing Continuum of Narrow-Line Seyfert 1 Galaxies. I. Observational Results
We present optical spectra and emission-line ratios of 12 narrow-lineSeyfert 1 (NLS1) galaxies that we observed to study the ionizing EUVcontinuum. A common feature in the EUV continuum of active galacticnuclei is the big blue bump (BBB), generally associated with thermalaccretion disk emission. While Galactic absorption prevents directaccess to the EUV range, it can be mapped by measuring the strength of avariety of forbidden optical emission lines that respond to differentEUV continuum regions. We find that narrow emission line ratiosinvolving [O II] λ3727, Hβ, [O III] λ5007, [O I]λ6300, Hα, [N II] λ6583, and [S II]λλ6716, 6731 indicate no significant difference betweenNLS1 galaxies and broad-line Seyfert 1 (BLS1) galaxies, which suggeststhat the spectral energy distributions of their ionizing EUV-soft X-raycontinua are similar. The relative strength of important forbiddenhigh-ionization lines like [Ne V] λ3426 compared to He IIλ4686 and the relative strength of [Fe X] λ6374 appear toshow the same range as in BLS1 galaxies. However, a trend of weaker F([OI] λ6300)/F(Hα) emission-line ratios is indicated for NLS1galaxies compared to BLS1 galaxies. To recover the broad emission lineprofiles, we used Gaussian components. This approach indicates that thebroad Hβ profile can be well described with a broad component(FWHM~=3275+/-800 km s-1) and an intermediate broad component(FWHM~=1200+/-300 km s-1). The width of the broad componentis in the typical range of normal BLS1 galaxies. The emission-line fluxthat is associated with the broad component in these NLS1 galaxiesamounts to at least 60% of the total flux. Thus, it dominates the totalline flux, similar to BLS1 galaxies.
| Small-Scale Systems of Galaxies. II. Properties of the NGC 4756 Group of Galaxies
This paper is part of a series that focuses on investigating galaxyformation and evolution in small-scale systems of galaxies inlow-density environments. We present results from a study of the NGC4756 group, which is dominated by the elliptical galaxy NGC 4756. Thecharacteristics of the group are investigated through (1) the detailedinvestigation of the morphological, photometric, and spectroscopicproperties of nine galaxies among the dominant members of the group; (2)the determination of the photometric parameters of the faint galaxypopulation in an area of 34'×34' centered onNGC 4756 and (3) an analysis of the X-ray emission in the area based onarchival data.The nine member galaxies are located in the core part of the NGC 4756group (a strip ~300 kpc in diameter, H0=70 km s-1Mpc-1), which has a very loose configuration. The centralpart of the NGC 4756 group contains a significant fraction of early-typegalaxies. Three new group members with previously unknown systemicvelocities are identified, one of which is type dE. At about 7.5 arcminsouthwest of NGC 4756 a substructure of the group is detected, includingIC 829, MCG -2-33-35, MCG -2-33-36, and MCG -2-33-38, that meets theHickson criteria for being a compact group. Most of the galaxies in thissubstructure show interaction signatures. We do not detect apparent finestructure and signatures of recent interaction events in the early-typegalaxy population, with the exception of a strong dust lane in theelliptical galaxy MCG -2-33-38. However, this galaxy displays signaturesof nuclear activity. Strong [O III], [N II], and [S II] line emission,combined with comparatively weak but broad Hα emission, suggestsan intermediate Seyfert type classification. Although the area isheavily contaminated by the background cluster A1631, X-ray data suggestthe presence of a hot intergalactic medium related to the detected X-rayemission of the group. The present results are discussed in the contextof group evolution.Based on observations obtained at the European Southern Observatory, LaSilla, Chile (program 65.P-252).
| Long-term infrared photometry of Seyferts
Long-term (up to 10 000 d) monitoring has been undertaken for 41Seyferts in the near-infrared (1.25-3.45 μm). All but two showedvariability, with amplitudes at K in the range <0.1 to >1.1 mag.The time-scale for detectable change is from about one week to a fewyears.Where contemporary observations of variability in X-rays, ultraviolet(UV) or visible light exist, it is found that the near-infrared variesin a similar way, though in some cases the shorter-wavelength infrared(IR) bands are diluted by underlying galaxy radiation.A simple cross-correlation study indicates that there is evidence fordelays of up to several hundred d between the variations seen at theshortest wavelengths (U or J) and the longest (L) in many galaxies. Inparticular, the data for Fairall 9 now extend to twice the intervalcovered in earlier publications and the delay between its UV and IRoutputs is seen to persist.An analysis of the fluxes shows that, for any given galaxy, the coloursof the variable component of its nucleus are usually independent of thelevel of activity. The state of activity of the galaxy can beparameterized.Taken over the whole sample, the colours of the variable components fallwithin moderately narrow ranges. In particular, the H-K colour isappropriate to a blackbody of temperature 1600 K. The H-K excess for aheavily reddened nucleus can be determined and used to findEB-V, which can be compared to the values found from thevisible region broad line ratios.Using flux-flux diagrams, the flux within the aperture from theunderlying galaxies can often be determined without the need for modelsurface brightness profiles. In many galaxies it is apparent that theremust be an additional constant contribution from warm dust.
| Classification of Spectra from the Infrared Space Observatory PHT-S Database
We have classified over 1500 infrared spectra obtained with the PHT-Sspectrometer aboard the Infrared Space Observatory according to thesystem developed for the Short Wavelength Spectrometer (SWS) spectra byKraemer et al. The majority of these spectra contribute to subclassesthat are either underrepresented in the SWS spectral database or containsources that are too faint, such as M dwarfs, to have been observed byeither the SWS or the Infrared Astronomical Satellite Low ResolutionSpectrometer. There is strong overall agreement about the chemistry ofobjects observed with both instruments. Discrepancies can usually betraced to the different wavelength ranges and sensitivities of theinstruments. Finally, a large subset of the observations (~=250 spectra)exhibit a featureless, red continuum that is consistent with emissionfrom zodiacal dust and suggest directions for further analysis of thisserendipitous measurement of the zodiacal background.Based on observations with the Infrared Space Observatory (ISO), aEuropean Space Agency (ESA) project with instruments funded by ESAMember States (especially the Principle Investigator countries: France,Germany, Netherlands, and United Kingdom) and with the participation ofthe Institute of Space and Astronautical Science (ISAS) and the NationalAeronautics and Space Administration (NASA).
| Comparison of Nuclear Starburst Luminosities between Seyfert 1 and 2 Galaxies Based on Near-Infrared Spectroscopy
We report on infrared K- (2-2.5 μm) and L-band (2.8-4.1 μm) slitspectroscopy of 23 Seyfert 1 galaxies in the CfA and 12 μm samples. Apolycyclic aromatic hydrocarbon (PAH) emission feature at 3.3 μm inthe L band is primarily used to investigate nuclear star-formingactivity in these galaxies. The 3.3 μm PAH emission is detected in 10sources (=43%), demonstrating that detection of nuclear star formationin a significant fraction of Seyfert 1 galaxies is now feasible. For thePAH-detected nuclei, the surface brightness values of the PAH emissionare as high as those of typical starbursts, suggesting that the PAHemission probes the putative nuclear starbursts in the dusty tori aroundthe central active galactic nuclei (AGNs). The magnitudes of the nuclearstarbursts are quantitatively estimated from the observed 3.3 μm PAHemission luminosities. The estimated starburst luminosities relative tosome indicators of AGN powers in these Seyfert 1 galaxies are comparedwith 32 Seyfert 2 galaxies in the same samples that we have previouslyobserved. We find that there is no significant difference in nuclearstarburst to AGN luminosity ratios of Seyfert 1 and 2 galaxies and thatnuclear starburst luminosity positively correlates with AGN power inboth types. Our results favor a slightly modified AGN unification model,which predicts that nuclear starbursts occurring in the dusty tori ofSeyfert galaxies are physically connected to the central AGNs, ratherthan the classical unification paradigm, in which the dusty tori simplyhide the central AGNs of Seyfert 2 galaxies and reprocess AGN radiationas infrared dust emission in Seyfert galaxies. No significantdifferences in nuclear star formation properties are recognizablebetween Seyfert 1 galaxies in the CfA and 12 μm samples.
| 10 Micron Imaging of Seyfert Galaxies from the 12 Micron Sample
We present small-aperture (1.5") photometry and new high-resolutionimages at 10 μm (N band) for 87 Seyfert galaxies from the Extended 12μm Sample drawn from the IRAS database. With this data we hope totest the predictions of the unified model for active galactic nuclei andto search for bright, extended circumnuclear 10 μm emission. Wedetected 62 Seyfert galaxies, 18 of which have no previously publishedsmall-aperture photometry. All the detected sources, both Seyfert 1'sand Seyfert 2's, show a central point source. The 31 Seyfert 1's and 31Seyfert 2's that we detected have similar luminosity distributions.Except for previously known bright extended 10 μm structure aroundArp 220, NGC 1068, and NGC 7469, we see definitive evidence for brightextended emission around only one new object: Mrk 1239. Four otherSeyfert 1's and six other Seyfert 2's show evidence of faint, low-levelextended emission. One Seyfert 1 and two Seyfert 2's show evidence ofsignificantly increased flux over previously published small-aperturevalues. We also compared the N-band data with the J-Ks colorthat we derived from the Two Micron All Sky Survey (2MASS). There is adistinct trend of redder central bulge J-Ks colorscorresponding to brighter absolute N-band magnitudes. In color-magnitudespace there is a definite grouping of Seyfert 1's and Seyfert 2's, withtwo sets of outliers.
| Molecular hydrogen and [Fe II] in Active Galactic Nuclei
Near-infrared spectroscopy is used to study the kinematics andexcitation mechanisms of H2 and [Fe II] lines in a sample ofmostly Seyfert 1 galaxies. The spectral coverage allows simultaneousobservation of the JHK bands, thus eliminating the aperture and seeingeffects that have usually plagued previous works. The H2lines are unresolved in all objects in which they were detected whilethe [Fe II] lines have widths implying gas velocities of up to 650 ~kms-1. This suggests that, very likely, the H2 and[Fe II] emission does not originate from the same parcel of gas.Molecular H2 lines were detected in 90% of the sample,including PG objects, indicating detectable amounts of molecularmaterial even in objects with low levels of circumnuclear starburstactivity. Analysis of the observations favors thermal excitationmechanisms for the H2 lines. Indeed, in NGC 3227, Mrk 766,NGC 4051 and NGC 4151, the molecular emission is found to be purelythermal but with heating processes that vary between the objects.Thermal excitation is also confirmed by the rather similar vibrationaland rotational temperatures in the objects for which data wereavailable. [Fe II] lines are detected in all of the sample AGN. The [FeII] 1.254 μm/Paβ ratio is compatible with excitation of the [FeII] lines by the active nucleus in most Seyfert 1 galaxies, but in Mrk766 the ratio implies a stellar origin. A correlation betweenH2/Brγ and [Fe II]/Paβ is found for our sampleobjects supplemented by data from the literature. The correlation ofthese line ratios is a useful diagnostic tool in the NIR to separateemitting line objects by their level of nuclear activity. X-rayexcitation models are able to explain the observed H2 andpart of the [Fe II] emission but fail to explain the observations inSeyfert 2 galaxies. Most likely, a combination of X-ray heating, shocksdriven by the radio jet and circumnuclear star formation contributes, indifferent proportions, to the H2 and [Fe II] lines observed.In most of our sample objects, the [Fe II] 1.257 μm/1.644 μm ratiois found to be 30% lower than the intrinsic value based on currentatomic data. This implies either that the extinction towards the [FeII]-emitting clouds is very similar in most objects or there arepossible inaccuracies in the A-values in the Fe II transitions.Based on observations taken at the Infrared Telescope Facility, which isoperated by the University of Hawaii under Cooperative Agreement no. NCC5-538 with the National Aeronautics and Space Administration, Office ofSpace Science, Planetary Astronomy Program.
| The B-band luminosities of quasar host galaxies
We report on the analysis of B-band imaging data of 57 low-redshiftquasi-stellar objects (quasars/QSOs) and Seyfert 1 galaxies selectedfrom the Hamburg/ESO Survey, for which host-galaxy-dependent selectionbiases are greatly reduced compared with other optical surveys. Only oneobject in the sample is known to be radio-loud.We adopted a procedure to remove the active galactic nuclei (AGN)contribution by subtracting a scaled point spread function from each QSOimage. To reclaim the integrated host galaxy flux we correct foroversubtraction based on simulations. This method is quite insensitiveto the host galaxy morphological type, which we can unambiguouslyestablish for 15 of the 57 objects.The quasar host galaxies are detected in all cases. The hosts are veryluminous, ranging in absolute magnitude MB from -19.0 to-23.8, with an average of MB,gal=-21.5, considerably above L*for field galaxies. For the luminous QSO subsample with MB< -23 the average host absolute magnitude is MB,gal=-23.0,while for the complementary low-luminosity AGN we obtainMB,gal=-21.2, roughly equal to L*.The luminous host galaxies in the sample are typically ~1 mag brighterthan expected when inferring B-band luminosities from studies of similarobjects at longer wavebands. We argue that this mismatch is not likelyto be explained by selection effects, but favours host galaxy colourssignificantly bluer than those of inactive galaxies. Although publishedB-band data are scant, this result and the findings of other authors arein good agreement.
| The Unified Model and Evolution of Active Galaxies: Implications from a Spectropolarimetric Study
We extend the analysis presented in Paper I of a spectropolarimetricsurvey of the CfA and 12 μm samples of Seyfert 2 galaxies (S2s). Weconfirm that polarized (hidden) broad-line region (HBLR) S2s tend tohave hotter circumnuclear dust temperatures, show mid-IR spectra morecharacteristic of Seyfert 1 galaxies (S1s), and are intrinsically moreluminous than non-HBLR S2s. The levels of obscuration and circumnuclearstar formation, however, appear to be similar between HBLR and non-HBLRS2 galaxies, based on an examination of various observationalindicators. HBLR S2s, on average, share many similar large-scale,presumably isotropic, characteristics with S1s, as would be expected ifthe unified model is correct, while non-HBLR S2s generally do not. Theactive nuclear engines of non-HBLR S2s, then, appear to be truly weakerthan HBLR S2s, which in turn are fully consistent with being S1s viewedfrom another direction. There is also evidence that the fraction ofdetected HBLRs increases with the radio power of the active galacticnucleus. Thus, all S2 galaxies may not be intrinsically similar innature, and we speculate that evolutionary processes may be at work.
| The Seyfert Population in the Local Universe
The magnitude-limited catalog of the Southern Sky Redshift Survey(SSRS2) is used to characterize the properties of galaxies hostingactive galactic nuclei (AGNs). Using emission-line ratios, we identify atotal of 162 (3%) Seyfert galaxies out of the parent sample with 5399galaxies. The sample contains 121 Seyfert 2 galaxies and 41 Seyfert 1galaxies. The SSRS2 Seyfert galaxies are predominantly in spirals oftypes Sb and earlier or in galaxies with perturbed appearance as theresult of strong interactions or mergers. Seyfert galaxies in thissample are twice as common in barred hosts as the non-Seyfert galaxies.By assigning galaxies to groups using a percolation algorithm, we findthat the Seyfert galaxies in the SSRS2 are more likely to be found inbinary systems when compared with galaxies in the SSRS2 parent sample.However, there is no statistically significant difference between theSeyfert and SSRS2 parent sample when systems with more than two galaxiesare considered. The analysis of the present sample suggests that thereis a stronger correlation between the presence of the AGN phenomenonwith internal properties of galaxies (morphology, presence of bar,luminosity) than with environmental effects (local galaxy density, groupvelocity dispersion, nearest neighbor distance).Partly based on observations at European Southern Observatory (ESO),under the ESO-ON agreement to operate the 1.52 m telescope.
| The Host Galaxies of Narrow-Line Seyfert 1 Galaxies: Evidence for Bar-Driven Fueling
We present a study of the host galaxy morphologies of narrow- andbroad-line Seyfert 1 galaxies (NLS1's and BLS1's) based on broadbandoptical images from the Hubble Space Telescope archives. We find thatlarge-scale stellar bars, starting at ~1 kpc from the nucleus, are muchmore common in NLS1's than BLS1's. Furthermore, the fraction of NLS1spirals that have bars increases with decreasing full width athalf-maximum of the broad component of Hβ. These results suggest alink between the large-scale bars, which can support high fueling ratesto the inner kiloparsecs, and the high mass accretion rates associatedwith the supermassive black holes in NLS1's.
| Inclination of Broad Line Region in Narrow Line and Broad Line Seyfert 1 Galaxies
The sizes of the Broad Line Region (BLR) of some Seyfert 1 galaxies andnearby quasars can be determined by the reverberation mapping method.Combining with the observed FWHM of Hβ emission line and assumingthat the motion of BLR clouds is virialized, the black hole masses ofthese objects have been estimated. However, this method stronglydepends on the poorly-understood geometry and inclination of the BLR. On the other hand, a tight correlation between the black hole mass andthe bulge velocity dispersion was recently found for both active andnearby inactive galaxies. This may provide another method, independentof the BLR geometry, for estimating the black hole mass. Using thismethod for estimating the black hole mass and combining with themeasured BLR size and FWHM of Hβ emission line, we derived the BLRinclination angles for 20 Seyfert 1 galaxies under the assumption thatthe BLR is disk-like. The derived inclination angles agree well withthose derived previously by fitting the UV continuum and Hβemission line profiles. Adopting a relation between the FWHMs of[OIII]λ5007 forbidden line and the stellar velocity dispersion,we also estimated the BLR inclinations for 50 narrow line Seyfert 1galaxies (NLS1s). We found that the inclinations of broad Line Seyfert 1galaxies (BLS1s) are systematically greater than those of NLS1s, whichseldom exceed 30 deg. This may be an important factor that leads to thedifferences between NLS1s and BLS1s if the BLR of NLS1s is reallydisk-like.
| Gas Metallicity of Narrow-Line Regions in Narrow-Line Seyfert 1 Galaxies and Broad-Line Seyfert 1 Galaxies
We investigate gas metallicity of narrow-line regions in narrow-lineSeyfert 1 galaxies (NLS1's) and broad-line ones (BLS1's) in order toexamine whether or not there is a difference in the gas metallicitybetween the two populations of Seyfert 1 galaxies. We apply two methodsto study this issue. One is to use the emission-line flux ratio [N II]λ6583/Hαnarrow in combination with some otheroptical emission line flux ratios. This method, which has been oftenapplied to Seyfert 2 galaxies, suggests that the gas metallicity ofnarrow-line regions is indistinguishable, or possibly higher in BLS1'sthan in NLS1's. On the contrary, the other method, in which onlyforbidden emission line fluxes are used, results in that NLS1's tend topossess metal-richer gas in the narrow-line regions than BLS1's. Wepoint out that this inconsistency may be owing to the contamination ofthe narrow component of permitted lines by the broad component in thefirst method. Since the results derived by using only forbidden emissionline fluxes do not suffer from any uncertainty of the fitting functionfor the broad component of Balmer lines, the results from this methodare more reliable than those derived by using permitted lines. We thusconclude that the gas metallicity of narrow-line regions tends to behigher in NLS1's than in BLS1's.
| High-resolution radio observations of Seyfert galaxies in the extended 12-μm sample - II. The properties of compact radio components
We discuss the properties of compact nuclear radio components in Seyfertgalaxies from the extended 12-μm AGN sample of Rush et al. Our mainresults can be summarized as follows. Type 1 and type 2 Seyferts producecompact radio components which are indistinguishable in strength andaspect, indicating that their central engines are alike, as proposed bythe unification model. Infrared IRAS fluxes are more closely correlatedwith low-resolution radio fluxes than high-resolution radio fluxes,suggesting that they are dominated by kiloparsec-scale, extranuclearemission regions; extranuclear emission may be stronger in type 2Seyferts. Early-type Seyfert galaxies tend to have stronger nuclearradio emission than late-type Seyfert galaxies. V-shaped extendedemission-line regions, indicative of `ionization cones', are usuallyfound in sources with large, collimated radio outflows. Hidden broadlines are most likely to be found in sources with powerful nuclear radiosources. Type 1 and type 2 Seyferts selected by their IRAS 12-μm fluxdensities have well-matched properties.
| Jet Directions in Seyfert Galaxies: Radio Continuum Imaging Data
We present the results of VLA A-array 8.46 GHz continuum imaging of 55Seyfert galaxies (19 Seyfert 1's and 36 Seyfert 2's). These galaxies arepart of a larger sample of 88 Seyfert galaxies, selected from mostlyisotropic properties, the flux at 60 μm, and warm infrared 25-60μm colors. These images are used to study the structure of the radiocontinuum emission of these galaxies and their position angles, in thecase of extended sources. These data, combined with information frombroadband B and I observations, have been used to study the orientationof radio jets relative to the plane of their host galaxies (Kinney etal.).
| Testing the Unified Model with an Infrared-selected Sample of Seyfert Galaxies
We present a series of statistical tests done to a sample of 29 Seyfert1 and 59 Seyfert 2 galaxies selected from mostly isotropic properties,their far-infrared fluxes and warm infrared colors. Such selectioncriteria provide a profound advantage over the criteria used by mostinvestigators in the past, such as ultraviolet excess. These tests weredone using ground-based high-resolution Very Large Array A-configuration3.6 cm radio and optical B and I imaging data. From the relative numberof Seyfert 1's and Seyfert 2's, we calculate that the torus half-openingangle is 48°. We show that, as seen in previous papers, there is alack of edge-on Seyfert 1 galaxies, suggesting that dust and gas alongthe host galaxy disk probably play an important role in hiding somenuclei from direct view. We find that there is no statisticallysignificant difference in the distribution of host galaxy morphologicaltypes and radio luminosities of Seyfert 1's and Seyfert 2's, suggestingthat previous results showing the opposite may have been due toselection effects. The average extension of the radio emission ofSeyfert 1's is smaller than that of Seyfert 2's by a factor of ~2-3, aspredicted by the unified model. A search for galaxies around ourSeyferts allows us to put a lower and an upper limit on the possiblenumber of companions around these galaxies of 19% and 28%, respectively,with no significant difference in the number of companion galaxiesbetween Seyfert 1's and Seyfert 2's. We also show that there is nopreference for the radio jets to be aligned closer to the host galaxydisk axis in late-type Seyferts, unlike results claimed by previouspapers. These results, taken together, provide strong support for aunified model in which type 2 Seyferts contain a torus seen more edge-onthan the torus in type 1 Seyferts.
| Where is the[O III] λ4363 Emitting Region in Active Galactic Nuclei?
The emission-line flux ratio of [O III] λ4363/[O III]λ5007 (RO III) is a useful diagnostic for theionization mechanism and physical properties of emission-line regions inactive galactic nuclei (AGNs). However, it is known that simplephotoionization models underpredict the [O III] λ4363 intensity,being inconsistent with observations. In this paper we report on severalpieces of evidence that a large fraction of the [O III] λ4363emission arises from the dense gas obscured by putative tori: (1) thevisibility of high-RO III regions is correlated to that ofbroad-line regions, (2) higher RO III objects show hottermid-infrared colors, (3) higher RO III objects show strongerhighly ionized emission lines such as [Fe VII] λ6087 and [Fe X]λ6374, and (4) higher RO III objects have broader linewidth of [O III] λ4363 normalized by that of [O III]λ5007. To estimate how such a dense component contributes to thetotal emission-line flux, dual-component photoionization modelcalculations are performed. It is shown that the observed values ofRO III of type 1 AGNs may be explained by introducing a5%-20% contribution from the dense component, while those of type 2 AGNsmay be explained by introducing a 0%-2% contribution. We also discussthe [O III] λ4363 emitting regions in LINERs in the framework ofour dual-component model.
| The Narrow-Line Region of Seyfert Galaxies: Narrow-Line Seyfert 1 Galaxies versus Broad-Line Seyfert 1 Galaxies
It is known that the spectral energy distribution (SED) of the nuclearradiation of narrow-line Seyfert 1 galaxies (NLS1's) has differentshapes with respect to that of ordinary broad-line Seyfert 1 galaxies(BLS1's) particularly in X-ray wavelengths. This may cause somedifferences in the ionization degree and the temperature of gas innarrow-line regions (NLRs) between NLS1's and BLS1's This paper aims toexamine whether or not there are such differences in the physicalconditions of NLR gas between them. For this purpose, we have compiledthe emission-line ratios of 36 NLS1's and 83 BLS1's from the literature.Comparing these two samples, we have found that the line ratios of [O I]λ6300/[O III] λ5007 and [O III] λ4363/[O III]λ5007, which represent the ionization degree and the gastemperature respectively, are statistically indistinguishable betweenNLS1's and BLS1's. Based on new photoionization model calculations, weshow that these results are not inconsistent with the difference of theSED between them. The influence of the difference of SEDs on the highlyionized emission lines is also briefly discussed.
| Black hole mass and velocity dispersion of narrow line region in active galactic nuclei and narrow line Seyfert 1 galaxies
Controversy regarding whether Narrow Line Seyfert 1 galaxies (NLS1s)follow the same black hole - galactic bulge relation as normal galaxieshas been raised by Mathur et al. (\cite{Mathur01}) and Ferrarese et al.(\cite{Ferrarese01}). In this paper, the correlation between the blackhole mass and the velocity dispersion of the narrow line region,indicated by the [OIII] line width for a heterogeneous sample of NLS1s,is examined. We show that the non-virial component subtracted [OIII]width, which may well represent the stellar velocity dispersion (sigma), correlates with the estimated black hole mass MBH, madeusing the empirical law for the size of the broad line region from thereverberation mapping measurements. Considering measurement errors, wefind that the relation between MBH and the [OIII] width inactive galactic nuclei (both NLS1s in this paper and normal Seyferts inNelson \cite{Nelson00}) is consistent with that defined in nearby hotgalaxies (ellipticals and spiral bulge) but with more scatter. It seemsthat there is no clear difference in the relation between MBHand sigma (represented by the [OIII] width for AGN) in both NLS1s andnormal broad line active galactic nuclei from the same relation definedby nearby hot galaxies.
| A spectrophotometric atlas of Narrow-Line Seyfert 1 galaxies
We have compiled a list of 83 objects classified as Narrow-Line Seyfert1 galaxies (NLS1s) or known to have a broad Balmer component narrowerthan 2 000 km s-1. Of these, 19 turned out to have beenspectroscopically misidentified in previous studies; only 64 of theselected objects are genuine NLS1s. We have spectroscopically observed59 of them and tried to characterize their Narrow and Broad-Line Regions(NLR and BLR) by fitting the emission-lines with Gaussian and/orLorentzian profiles. In most cases, the broad Balmer components are wellfitted by a single Lorentzian profile, confirming previous claims thatLorentzian rather than Gaussian profiles are better suited to reproducethe shape of the NLS1s broad emission lines. This has consequencesconcerning their FWHMs and line ratios: when the broad Balmer componentsare fitted with a Lorentzian, most narrow line regions have line ratiostypical of Seyfert 2s while, when a Gaussian profile is used for fittingthe broad Balmer components, the line ratios are widely scattered in theusual diagnostic diagrams (Veilleux & Osterbrock \cite{vei87});moreover, the FWHM of the best fitting Lorentzian is systematicallysmaller than the FWHM of the Gaussian. We find that, in general, the [OIII] lines have a relatively narrow Gaussian profile ( ~ 200-500 kms-1 FWHM) with often, in addition, a second broad ( ~ 500-1800 km s-1 FWHM), blueshifted Gaussian component. We do notconfirm that the [O III] lines are weak in NLS1s. As previouslysuggested, there is a continuous transition of all properties betweenNLS1s and classical Broad-Line Seyfert 1 Galaxies (BLS1s) and the limitof 2000 km s-1 used to separate the two species is arbitrary;R4570, the ratio of the Fe II to the Hβ fluxes, could bea physically more meaningful parameter to distinguish them.
| Soft X-ray properties of a spectroscopically selected sample of interacting and isolated Seyfert galaxies
We present a catalogue of ROSAT detected sources in the sample ofspectroscopically selected Seyfert 1 and Seyfert 2 galaxies of Rafanelliet al. (\cite{Rafanelli95}). The catalogue contains 102 Seyfert 1 and 36Seyfert 2 galaxies. The identification is based on X-ray contour mapsoverlaid on optical images taken from the Digitized Sky Survey. We havederived the basic spectral and timing properties of the X-ray detectedSeyfert galaxies. For Seyfert 1 galaxies a strong correlation betweenphoton index and X-ray luminosity is detected. We confirm the presenceof generally steeper X-ray continua in narrow-line Seyfert 1 galaxies(NLS1s) compared to broad-line Seyfert 1 galaxies. Seyfert 2 galaxiesshow photon indices similar to those of NLS1s. Whereas a tendency for anincreasing X-ray luminosity with increasing interaction strength isfound for Seyfert 1 galaxies, such a correlation is not found forSeyfert 2 galaxies. For Seyfert 1 galaxies we found also a strongcorrelation for increasing far-infrared luminosity with increasinginteraction strength. Both NLS1s and Seyfert 2 galaxies show the highestvalues of far-infrared luminosity compared to Seyfert 1 galaxies,suggesting that NLS1s and Seyfert 2 galaxies host strong (circumnuclear)star formation. For variable Seyfert galaxies we present the X-ray lightcurves obtained from the ROSAT All-Sky Survey and from ROSAT PSPC andHRI pointed observations. Besides the expected strong short- andlong-term X-ray variability in Seyfert 1 galaxies, we find indicationsfor X-ray flux variations in Seyfert 2 galaxies. All overlays can beretrieved via CDS anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)}or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/368/797
| Narrow-Line Seyfert 1 Galaxies: The O IIIλ5007/Hβ Ratio and Photoionization Models for the NLR
We study optical profiles and the physical conditions of the narrow lineregion (NLR) of narrow-line Seyfert 1 galaxies (NLS1s). Our results showthat the flux carried out by the narrow component of Hβ can be upto 10 times higher than the value usually adopted in the literature. Asa result, the O IIIλ5007/Hβ ratio emitted in the NLR variesfrom 1 to 5, instead of the universally adopted value of 10. We testphotoionization models that consider a NLR composed of a combination ofmatter-bounded and ionization-bounded clouds and show that this scenarioreproduces with very good agreement the observed emission lines ratiosof NLS1s. We propose that the peculiar properties of the NLR of NLS1scan be explained by a steep continuum of power-law form in the EUV-softX-ray region, with spectral index α ~ -2.2, consistent with ROSATobservations of this class of objects.
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