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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.
| 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.
| Water-Vapor Maser Survey for Active Galactic Nuclei: A Megamaser in NGC 6926
We made a survey of water-vapor maser emission for 93 AGNs with theNobeyama 45-m and Mopra 22-m telescopes from 1999 to 2002. A megamaserwas detected in a Seyfert 2 galaxy, NGC 6926, at a distance of 80Mpc, in2002 June. [Greenhill et al. (2003a) have also reported a detection ofthe megamaser at the close date.] The peak flux density was 110mJy, andthe total isotropic luminosity was 340 Lȯ. The masershows triply peaked spectrum, suggesting an edge-on disk. A narrow-linefeature of the maser components at VLSR = 6001 kms-1 was strongly variable with a time scale of a few tens ofdays, and the variation should be of intrinsic origin. We also showed apossibility of variability of water-vapor maser emission of a megamaserpreviously detected in a Seyfert/ultraluminous FIR galaxy, NGC 6240.
| Kinematics of the local universe . XII. 21-cm line measurements of 586 galaxies with the new Nançay receiver
This paper presents 586 new 21-cm neutral hydrogen line measurementscarried out with the FORT receiver of the meridian transit Nançayradiotelescope in the period July 2000-March 2003. This observationalprogramme is part of a larger project aiming at collecting an exhaustiveand magnitude-complete HI extragalactic catalogue for Tully-Fisherapplications. It is associated with the building of the MIGALEspectroscopic archive and database.Tables 2, 3 and HI-profiles and corresponding comments are onlyavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/430/373, or directly atour web site http://klun.obs-nancay.fr
| Long slit spectroscopy of a sample of isolated spirals with and without an AGN
We present the kinematical data obtained for a sample of active(Seyfert) and non active isolated spiral galaxies, based on long slitspectra along several position angles in the Hα line region and,in some cases, in the Ca triplet region as well. Gas velocitydistributions are presented, together with a simple circular rotationmodel that allows us to determine the kinematical major axes. Stellarvelocity distributions are also shown. The main result is that activeand control galaxies seem to be equivalent in all kinematical aspects.For both subsamples, the departure from pure circular rotation in somegalaxies can be explained by the presence of a bar and/or of a spiralarm. They also present the same kind of peculiarities, in particular,S-shape structures are quite common near the nuclear regions. Theydefine very similar Tully-Fisher relations. Emission line ratios aregiven for all the detected HII regions; the analysis of the[NII]/Hα metallicity indicator shows that active and non-activegalaxies have indistinguishable disk metallicities. These results arguein favour of active and non-active isolated spiral galaxies havingessentially the same properties, in agreement with our previous resultsbased on the analysis of near infrared images. It appears now necessaryto confirm these results on a larger sample.Based on observations made with WHT operated on the island of La Palmaby ING in the Spanish Observatorio del Roque de Los Muchachos of theInstituto de Astrofísica de Canarias, the European SouthernObservatory (La Silla), Calar Alto Observatory (Almería, Spain)and Las Campanas Observatories (Chile).Table 3 and Figs. \ref{res_cen_u1395}, 5, 7, 9, 11, 13, 15, 17, 19, 21,23, 25, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50 and 52 are onlyavailable in electronic form at http://www.edpsciences.orgTable 5 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/416/475
| Extended gas in Seyfert 2 galaxies: implications for the nuclear source
We use long-slit spectroscopic optical data to derive the properties ofthe extended emitting gas and the nuclear luminosity of a sample of 18Seyfert 2 galaxies. From the emission-line luminosities and ratios wederive the density, reddening and mass of the ionized gas as a functionof distance up to 2-4 kpc from the nucleus. Taking into account thegeometric dilution of the nuclear radiation, we derive the radialdistribution of covering factors and the minimum rate of ionizingphotons emitted by the nuclear source. This number is an order ofmagnitude larger than that obtained from the rate of ionizing photons`intercepted' by the gas and measured from the Hα luminosity. Acalibration is proposed to recover this number from the observedluminosity. The HeIIλ4686/Hβ line ratio was used tocalculate the slope of the ionizing spectral energy distribution (SED),which in combination with the number of ionizing photons allows thecalculation of the hard X-ray luminosities. These luminosities areconsistent with those derived from X-ray spectra in the eight cases forwhich such data are available and recover the intrinsic X-ray emissionin Compton-thick cases. Our method can thus provide reliable estimatesof the X-ray fluxes in Seyfert 2 galaxies for the cases where it is notreadily available. We also use the ionizing SED and luminosity topredict the infrared luminosity under the assumption that it isdominated by reprocessed radiation from a dusty torus, and find a goodagreement with the observed IRAS luminosities.
| 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.
| Seyfert Galaxies with Circumnuclear/Nuclear Starbursts
In this paper, we present our preliminary results on Seyfert galaxieswith circumnuclear/nuclear starburst (SB) activity. We have searched therecent available literature and found 76 active galaxies with clearevidence of nuclear SB activity, among which 16 are Seyfert 1s, 51Seyfert 2s, and 9 LINERs. After studying the 51 Seyfert 2s, we find thatthose Seyfert 2s with hidden Seyfert 1 nuclei, have similarInfrared-Radio properties as Seyfert 1 galaxies, and are different from``real'' Seyfert 2s without a hidden Seyfert 1 nucleus. The later aresimilar to starburst galaxies.
| Circumnuclear Stellar Population, Morphology, and Environment of Seyfert 2 Galaxies: An Evolutionary Scenario
We investigate the relation between the characteristics of thecircumnuclear stellar population and both the galaxy morphology and thepresence of close companions for a sample of 35 Seyfert 2 nuclei.Fifteen galaxies present unambiguous signatures of recent episodes ofstar formation within ~300 pc of the nucleus. When we relate thisproperty to the Hubble type of the host galaxy, we find that theincidence of recent circumnuclear star formation increases along theHubble sequence; it seems to be greater than that in non-Seyfertgalaxies for the early Hubble types S0 and Sa but similar to that innon-Seyfert galaxies for later Hubble types. In both early-type andlate-type Seyfert galaxies, the presence of recent circumnuclear starformation is related to the galaxy morphology in the inner fewkiloparsecs, as observed in Hubble Space Telescope images through thefilter F606W by Malkan et al., who have assigned a late ``inner Hubbletype'' to most Seyfert 2 galaxies with recent circumnuclear starformation. This new classification is due to the presence of dust lanesand spiral structures in the inner region. The presence of recent starformation around Seyfert 2 nuclei is also related to interactions: amongthe 13 galaxies of the sample with close companions or in mergers, ninehave recent star formation in the nuclear region. These correlationsbetween the presence of companions, the inner morphology, and theincidence of recent star formation suggest an evolutionary scenario inwhich the interaction is responsible for sending gas inward, which bothfeeds the active galactic nucleus and triggers star formation. Thestarburst then fades with time and the composite Seyfert 2+starburstnucleus evolves to a ``pure'' Seyfert 2 nucleus with an old stellarpopulation. This scenario can reconcile the hypothesis that the activenucleus in Seyfert galaxies is triggered by interactions with theresults of previous studies, which find only a small excess ofinteracting galaxies in Seyfert samples when compared with non-Seyfertsamples. The large excess can only be found early after the interaction,in the phase in which a composite (Seyfert+starburst) nucleus isobserved.
| Empirical Diagnostics of the Starburst-AGN Connection
We examine a representative sample of 35 Seyfert 2 nuclei. Previous workhas shown that nearly half (15) of these nuclei show the direct (butdifficult to detect) spectroscopic signature at optical/near-UVwavelengths of the hot massive stars that power circumnuclearstarbursts. In the present paper we examine a variety of more easilymeasured quantities for this sample, such as the equivalent widths ofstrong absorption features, continuum colors, emission line equivalentwidths, emission line ratios and profiles, far-IR luminosities, andnear-UV surface brightness. We compare the composite starburst+Seyfert 2nuclei to ``pure'' Seyfert 2 nuclei, Starburst galaxies, and normalgalactic nuclei. Our goals are to verify whether the easily measuredproperties of the composite nuclei are consistent with the expectedimpact of a starburst and to investigate alternative less demandingmethods to infer the presence of starbursts in Seyfert 2 nuclei,applicable to larger or more distant samples. We show that starbursts doindeed leave clear and easily quantifiable imprints on the near-UV tooptical continuum and emission line properties of Seyfert 2's. Compositestarburst+Seyfert 2 systems can be recognized by: (1) a strong``featureless continuum'' (FC), which dilutes the Ca II K line from oldstars in the host's bulge to an equivalent width WK<10Å (2) emission lines whose equivalent widths are intermediatebetween starburst galaxies and ``pure'' Seyfert 2's (3) relatively lowexcitation line ratios, which indicate that part of the gas ionizationin these Seyfert 2's (typically ~50% of Hβ) is due tophotoionization by OB stars; (4) large far-IR luminosities(>~1010 Lsolar) (5) high near-UV surfacebrightness (~103 Lsolar pc-2). Thesecharacteristics are all consistent with the expected impact ofcircumnuclear starbursts on the observed properties of Seyfert 2's.Furthermore, they offer alternative empirical diagnostics of thepresence of circumnuclear starbursts from a few easily measuredquantities.
| 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.
| Jet Directions in Seyfert Galaxies: B and I Imaging Data
We present the results of broadband B and I imaging observations for asample of 88 Seyfert galaxies (29 Seyfert 1s and 59 Seyfert 2s),selected from a mostly isotropic property, the flux at 60 μm. We alsopresent the B and I imaging results for an additional sample of 20Seyfert galaxies (7 Seyfert 1s and 13 Seyfert 2s), selected from theliterature and known to have extended radio emission. The I-band imagesare fitted with ellipses to determine the position angle and ellipticityof the host galaxy major axis. This information will be used in a futurepaper, combined with information from radio observations, to study theorientation of radio jets relative to the planes of their host galaxies.Here we present surface brightness profiles and magnitudes in the B andI bands, as well as mean ellipticities and major axis position angles.
| The Frequency of Nuclear Star Formation in Seyfert 2 Galaxies
We investigate the detectability of starburst signatures in the nuclearspectrum of Seyfert 2 galaxies by constructing spectral models in thewavelength range λλ3500-4100, combining the spectrum of abulge population (of age ~10 Gyr) with that of younger stellarpopulations, spanning ages from ~3 Myr to 1 Gyr. The major constraintsin the analysis are (1) the continuum ratio λλ3660/4020,which efficiently discriminates between models combining a bulgespectrum with a stellar population younger than ~50 Myr and those witholder stellar populations; (2) the presence of the Balmer lines H8, H9,and H10 in absorption, which are unambiguous signatures of stellarpopulations with ages in the range 10 Myr-1 Gyr for the relevantmetallicities. Their detectability depends both on the age of the youngcomponent and on its contribution to the total flux relative to that ofthe bulge. We also construct models combining the bulge template with apower-law (PL) continuum, which is observed in some Seyfert 2 galaxiesin polarized light, contributing with typically 10%-40% of the flux at4020 Å. We conclude that such continuum cannot be distinguishedfrom that of a very young stellar population (age<=10 Myr),contributing with less than ~0.02% of the mass of the bulge. The modelsare compared with nuclear spectra-corresponding to a radius of 200-300pc at the galaxy-of 20 Seyfert 2 galaxies, in which we specifically lookfor the signatures above of young- to intermediate-aged stellarpopulations. We find them in 10 galaxies, thus 50% of the sample. Butonly in six cases (30% of the sample) can they be attributed to youngstars (age<500 Myr): Mrk 1210, ESO 362-G8, NGC 5135, NGC 5643, NGC7130, and NGC 7582. In the remaining four cases, the signatures arecaused by intermediate-aged stars (~1 Gyr). We find a tendency for theyoung stars to be found more frequently among the late-type Seyfertgalaxies, a well-known effect in the nuclei of normal galaxies. Thistendency is supported by a comparison between the equivalent widths (W)of absorption lines of the nuclear spectra of the Seyfert 2 galaxieswith those of normal galaxies of the same Hubble type. For the late-typegalaxies, the W values of the Seyfert galaxies are within the observedrange of the normal galaxies, suggesting a similar stellar population.On the other hand, the W values are lower than those of the normalgalaxies for seven out of the 11 Seyferts in early-type galaxies.
| Nearby Optical Galaxies: Selection of the Sample and Identification of Groups
In this paper we describe the Nearby Optical Galaxy (NOG) sample, whichis a complete, distance-limited (cz<=6000 km s-1) andmagnitude-limited (B<=14) sample of ~7000 optical galaxies. Thesample covers 2/3 (8.27 sr) of the sky (|b|>20deg) andappears to have a good completeness in redshift (97%). We select thesample on the basis of homogenized corrected total blue magnitudes inorder to minimize systematic effects in galaxy sampling. We identify thegroups in this sample by means of both the hierarchical and thepercolation ``friends-of-friends'' methods. The resulting catalogs ofloose groups appear to be similar and are among the largest catalogs ofgroups currently available. Most of the NOG galaxies (~60%) are found tobe members of galaxy pairs (~580 pairs for a total of ~15% of objects)or groups with at least three members (~500 groups for a total of ~45%of objects). About 40% of galaxies are left ungrouped (field galaxies).We illustrate the main features of the NOG galaxy distribution. Comparedto previous optical and IRAS galaxy samples, the NOG provides a densersampling of the galaxy distribution in the nearby universe. Given itslarge sky coverage, the identification of groups, and its high-densitysampling, the NOG is suited to the analysis of the galaxy density fieldof the nearby universe, especially on small scales.
| Jet Directions in Seyfert Galaxies
Here we present the study of the relative angle between the accretiondisk (or radio jet) and the galaxy disk for a sample of Seyfert galaxiesselected from a mostly isotropic property, the 60 μm flux, and warminfrared colors. We used VLA A-array 3.6 cm continuum data andground-based optical imaging, homogeneously observed and reduced tominimize selection effects. For parts of the analysis we enlarged thesample by including galaxies serendipitously selected from theliterature. For each galaxy we have a pair of points (i, δ), whichare the inclination of the galaxy relative to the line of sight and theangle between the jet projected into the plane of the sky and the hostgalaxy major axis, respectively. For some galaxies we also hadinformation about which side of the minor axis is closer to Earth. Thisdata is combined with a statistical technique, developed by us, todetermine the distribution of β angles in three dimensions, theangle between the jet and the host galaxy plane axis. We found from aninitial analysis of the data of the 60 μm sample, where Seyfert 1 and2 galaxies were not differentiated, that the observed distribution of iand δ values can be well represented either by a homogeneoussinβ distribution in the range0deg<=β<=90deg or in0deg<=β<=65deg, but not by anequatorial ring. A more general model, which tested β-distributionsin the range β1<=β<=β2, fordifferent ranges of β1 and β2 values,required β2 to be larger than 65° and gavepreference for β1 smaller than 40°-50°. Animportant result from our analysis was obtained when we determinedwhether the jet was projected against the near or the far side of thegalaxy and differentiated between Seyfert 1 and Seyfert 2 galaxies,which showed that the model could not represent Seyfert 1 galaxiesadequately. We found that the inclusion of viewing angle restrictionsfor Seyfert 1 galaxies, namely, that a galaxy can be recognized as aSeyfert 1 only if the angle between the jet and the line of sight(|φ|) is smaller than a given angle φc and that thegalaxy inclination i is smaller than an angle ic, gave riseto statistically acceptable models. This indication that there is adifference in viewing angle to the central engine between Seyfert 1galaxies and Seyfert 2 galaxies is a direct and independent confirmationof the underlying concepts of the unified model. We discuss possibleexplanations for the misalignment between the accretion disk and thehost galaxy disk: warping of the accretion disk by self-irradiationinstability, by the Bardeen-Petterson effect, or by a misalignedgravitational potential of a nuclear star cluster surrounding the blackhole, as well as feeding of the accretion disk by a misaligned inflow ofgas from minor mergers, capture of individual stars or gas from thenuclear star cluster, and the capture of individual molecular cloudsfrom the host galaxy.
| Spectral synthesis of the nuclear regions of Seyfert 2 and radio galaxies
We present the results of an optical spectral synthesis analysis for thenuclei of 20 Seyfert 2 and four radio galaxies, using a base of stellarpopulation templates of different ages and metallicities and a power-lawcontinuum. Compared with the stellar population of elliptical galaxies,we find that Seyfert 2s usually have a smaller contribution from oldmetal-rich stars (age 10 Gyr, Z >= Z_solar), and a largercontribution from stars with ages of 100 Myr. We also find that thecontributions from stars with ages <= 10 Myr and from a power-lawcontinuum are small, rarely exceeding 5 per cent. These results showthat the general assumption of elliptical galaxies as stellar populationtemplates for these objects is incorrect, also implying that the excessblue continuum frequently found in their nuclear spectra is probably dueto this template mismatch. We find a considerable contribution from100-Myr-old stars (~ 5 per cent), which can be interpreted from thepoint of view of models where the fuelling of the AGN is carried out byinteractions/mergers.
| Near-infrared photometry of isolated spirals with and without an AGN. I. The data
We present infrared imaging data in the J and K' bands obtained for 18active spiral galaxies, together with 11 non active galaxies taken as acontrol sample. All of them were chosen to satisfy well definedisolation criteria so that the observed properties are not related togravitational interaction. For each object we give: the image in the K'band, the sharp-divided image (obtained by dividing the observed imageby a filtered one), the difference image (obtained by subtracting amodel to the observed one), the color J-K' image, the ellipticity andposition angle profiles, the surface brightness profiles in J and K',their fits by bulge+disk models and the color gradient. We have foundthat four (one) active (control) galaxies previously classified asnon-barred turn out to have bars when observed in the near-infrared. Oneof these four galaxies (UGC 1395) also harbours a secondary bar. For 15(9 active, 6 control) out of 24 (14 active, 10 control) of the opticallyclassified barred galaxies (SB or SX) we find that a secondary bar (or adisk, a lense or an elongated ring) is present. The work presented hereis part of a large program (DEGAS) aimed at finding out whether thereare differences between active and non active galaxies in the propertiesof their central regions that could be connected with the onset ofnuclear activity. Based on data obtained at: the European SouthernObservatory, La Silla, Chile, the Télescope Bernard Lyot, CalarAlto Observatory, Las Campanas Observatory. Also based on observationsmade with the NASA/ESA Hubble Space Telescope, obtained from the dataarchive at the Space Telescope Institute. Figures 1-35 are onlyavailable in electronic form at the http://www.edpsciences.org
| Seyfert galaxies and the radio-far-infrared correlation
We have observed a sample of 149 Seyfert galaxies and radio-quietquasars at 13 cm with both a 275-km radio interferometer and the 6-kmcompact array of the Australia Telescope. The high-resolutionobservations searched for the presence of compact,high-brightness-temperature radio emission from the active nucleus. Thelow-resolution observations measured the total radio emission from thegalaxy disc and Seyfert core and lobes. From these we draw the followingconclusions. (i) Seyfert galaxies that lack compact radio cores displaya correlation between radio and far-infrared (FIR) emission similar tothe correlation displayed by normal spirals, albeit with greaterscatter. The correlation is found to be intrinsic and is not an artefactof the richness effect. (ii) A very different radio-FIR correlation isdisplayed by those Seyferts that harbour compact radio cores. These tendto be more radio-loud than either normal spirals or the Seyferts thatlack compact cores. The compact core emission thus seems to beresponsible for the generally poor radio-FIR correlation displayed bySeyfert galaxies. (iii) The radio-FIR correlation is not significantlyimproved by subtracting off the 0.1-arcsec (20- to 200-pc) compact radioemission from the total radio emission. This suggests that the emissionfrom the active galactic nucleus has significant structure on scaleslarger than 0.1 arcsec. Perhaps these structures are the `linear' radiofeatures that have been seen previously in Seyfert nuclei.
| The Stellar Content of Active Galaxies
We present the results of a long-slit spectroscopic study of 38 activeand four normal galaxies. Stellar absorption features, continuum coloursand their radial variations are analysed in an effort to characterizethe stellar population in these galaxies and detect the presence of afeatureless continuum underlying the starlight spectral component.Spatial variations of the equivalent widths of conspicuous absorptionlines and continuum colours are detected in most galaxies. Star-formingrings, in particular, leave clear fingerprints in the equivalent widthsand colour profiles. We find that the stellar populations in the innerregions of active galaxies present a variety of characteristics, andcannot be represented by a single starlight template. Dilution of thestellar lines by an underlying featureless continuum is detected in mostbroad-lined objects, but little or no dilution is found for most of the20 type 2 Seyferts in the sample. Colour gradients are also ubiquitous.In particular, all but one of the observed Seyfert 2s are redder at thenucleus than in its immediate vicinity. Possible consequences of thesefindings are briefly outlined.
| A Hubble Space Telescope Imaging Survey of Nearby Active Galactic Nuclei
We have obtained WFPC2 images of 256 of the nearest (z <= 0.035)Seyfert 1, Seyfert 2, and starburst galaxies. Our 500 s broadband(F606W) exposures reveal much fine-scale structure in the centers ofthese galaxies, including dust lanes and patches, bars, rings, wisps,and filaments, and tidal features such as warps and tails. Most of thisfine structure cannot be detected in ground-based images. We haveassigned qualitative classifications for these morphological featuresand a Hubble type for the inner region of each galaxy, and we have alsomeasured quantitative information such as 0."18 and 0."92 aperturemagnitudes, position angles, and ellipticities, where possible. There islittle direct evidence for unusually high rates of interaction in theSeyfert galaxies. Slightly less than 10% of all the galaxies show tidalfeatures or multiple nuclei. The incidence of inner starburst rings isabout 10% in both classes of Seyfert galaxies. In contrast, galaxieswith H II region emission-line spectra appear substantially moreirregular and clumpy because of their much higher rates of current starformation per unit of galactic mass. The presence of an unresolvedcentral continuum source in our Hubble Space Telescope images is avirtually perfect indicator of a Seyfert 1 nucleus as seen byground-based spectroscopy. Fifty-two percent of these Seyfert 1 pointsources are saturated in our images; we use their wings to estimatemagnitudes ranging from 15.8 to 18.5. The converse is not universallytrue, however, as over one-third of Seyferts with direct spectroscopicevidence for broad Balmer wings show no nuclear point source. These 34resolved Seyfert 1's have fainter nonstellar nuclei, which appear to bemore extinguished by dust absorption. Like the Seyfert 2's, they havecentral surface brightnesses consistent with those expected for thebulges of normal galaxies. The rates for the occurrences of bars inSeyfert 1's and 2's and non-Seyferts are the same. We found onesignificant morphological difference between the host galaxies ofSeyfert 1 and Seyfert 2 nuclei. The Seyfert 2 galaxies are significantlymore likely to show nuclear dust absorption, especially in lanes andpatches that are irregular or reach close to the nucleus. A few simpletests show that the difference cannot be explained by different averageredshifts or selection techniques. It is confirmed by our galaxymorphology classifications, which show that Seyfert 1 nuclei reside inearlier type galaxies than Seyfert 2 nuclei. If, as we believe, this isan intrinsic difference in host galaxy properties, it undermines one ofthe postulates of the strong unification hypothesis for Seyfertgalaxies, that they merely appear different because of the orientationof their central engine. The excess galactic dust we see in Seyfert 2'smay cause substantial absorption that obscures their hypothesized broademission line regions and central nonstellar continua. This galacticdust could produce much of the absorption in Seyfert 2 nuclei that hadinstead been attributed to a thick dusty accretion torus forming theouter part of the central engine.
| The Southern Sky Redshift Survey
We report redshifts, magnitudes, and morphological classifications for5369 galaxies with m_B <= 15.5 and for 57 galaxies fainter than thislimit, in two regions covering a total of 1.70 sr in the southerncelestial hemisphere. The galaxy catalog is drawn primarily from thelist of nonstellar objects identified in the Hubble Space TelescopeGuide Star Catalog (GSC). The galaxies have positions accurate to ~1"and magnitudes with an rms scatter of ~0.3 mag. We compute magnitudes(m_SSRS2) from the relation between instrumental GSC magnitudes and thephotometry by Lauberts & Valentijn. From a comparison with CCDphotometry, we find that our system is homogeneous across the sky andcorresponds to magnitudes measured at the isophotal level ~26 magarcsec^-2. The precision of the radial velocities is ~40 km s^-1, andthe redshift survey is more than 99% complete to the m_SSRS2 = 15.5 maglimit. This sample is in the direction opposite that of the CfA2; incombination the two surveys provide an important database for studies ofthe properties of galaxies and their large-scale distribution in thenearby universe. Based on observations obtained at Cerro TololoInter-American Observatory, National Optical Astronomy Observatories,operated by the Association of Universities for Research in Astronomy,Inc., under cooperative agreement with the National Science Foundation;Complejo Astronomico El Leoncito, operated under agreement between theConsejo Nacional de Investigaciones Científicas de laRepública Argentina and the National Universities of La Plata,Córdoba, and San Juan; the European Southern Observatory, LaSilla, Chile, partially under the bilateral ESO-ObservatórioNacional agreement; Fred Lawrence Whipple Observatory;Laboratório Nacional de Astrofísica, Brazil; and the SouthAfrican Astronomical Observatory.
| Chemical Abundance Calibrations for the Narrow-Line Region of Active Galaxies
We investigate two chemical abundance calibrations for the narrow-lineregion (NLR) of active galaxies in terms of three easily observableoptical emission-line ratios, namely, [O iii] lambdalambda4959,5007/Hβ [N ii] lambdalambda6548, 6584/Hα and [O ii]lambda3727/[O iii] lambdalambda4959, 5007. The calibrations are obtainedfrom a grid of models on the assumption that the main processresponsible for the production of these lines is photoionization by a``typical'' active galactic nucleus continuum. The elemental abundancesvary with oxygen, except nitrogen, which is assumed to be a product ofsecondary nucleosynthesis. The calibrations are calculated for the range8.4 <= 12 + log (O/H) <= 9.4 and tested using NLR data for asample of Seyfert galaxies and LINERs that have H ii regions in thevicinity of the nucleus. The gaseous abundances of these H ii regionshave been determined in previous works, and the NLR abundances areobtained on the assumption that they can be extrapolated from those ofthe H ii regions. The calibrations work very well for the Seyfertgalaxies, yielding abundance values that agree with those obtained fromthe H ii regions, and can thus be used for quick estimates of thechemical abundances of the NLRs. For the LINERs, the calibrations yieldlower values than those derived from the corresponding H ii regions,suggesting that the assumptions of the models do not apply for them andthat there are different physical processes at work in the NLR of theLINERs.
| A Survey for H 2O Megamasers in Active Galactic Nuclei. II. A Comparison of Detected and Undetected Galaxies
A survey for H2O megamaser emission from 354 active galaxies hasresulted in the detection of 10 new sources, making 16 known altogether.The galaxies surveyed include a distance-limited sample (coveringSeyferts and LINERs with recession velocities less than 7000 km s-1) anda magnitude-limited sample (covering Seyferts and LINERs with mB <=14.5). In order to determine whether the H2O-detected galaxies are"typical" active galactic nuclei (AGNs) or have special properties thatfacilitate the production of powerful masers, we have accumulated adatabase of physical, morphological, and spectroscopic properties of theobserved galaxies. The most significant finding is that H2O megamasersare detected only in Seyfert 2 and LINER galaxies, not Seyfert 1's. Thislack of detection in Seyfert 1's indicates either that they do not havemolecular gas in their nuclei with physical conditions appropriate toproduce 1.3 cm H2O masers or that the masers are beamed away from Earth,presumably in the plane of the putative molecular torus that hides theSeyfert 1 nucleus in Seyfert 2's. LINERs are detected at a similar rateto Seyfert 2's, which constitutes a strong argument that at least somenuclear LINERs are AGNs rather than starbursts, since starbursts havenot been detected as H2O megamasers. We preferentially detect H2Oemission from the nearer galaxies and from those that are apparentlybrighter at mid- and far-infrared and centimeter radio wavelengths.There is also a possible trend for the H2O-detected galaxies to be moreintrinsically luminous in nuclear 6 cm radio emission than theundetected ones, though these data are incomplete. We find evidence thatSeyfert 2's with very high (NH > 1024 cm-2) X-ray--absorbing columnsof gas are more often detected as H2O maser emitters than Seyfert 2'swith lower columns. It may be that the probability of detecting H2Omaser emission in Seyfert galaxies increases with increasing column ofcool gas to the nucleus, from Seyfert 1's through narrow-line X-raygalaxies to Seyfert 2's.
| Optical and Far-Infrared Emission of IRAS Seyfert Galaxies
This paper presents an analysis of moderately large samples of type 1and 2 Seyfert galaxies through optical observations and far-infraredIRAS data, also taking into account theoretical color indices derivedfrom dust emission models. The galaxies in the samples cover a ratherlarge interval in far-infrared luminosity, i.e., 7.6 <= log(LIR/Lȯ) <= 12.6. We show that both types of Seyferts haveapproximately the same distribution of number of objects with a givenLIR. Galaxies with similar far-infrared color indices alpha (100, 60)are grouped together, and the corresponding average color indices areinterpreted in terms of a simple model in which the observed colorsresult from the combination of dust directly heated by the activegalactic nucleus with a component from the host galaxy represented bythe emission of cool dust. On the basis of the average IRAS colors ofthe derived groups, we show that type 1 and 2 Seyfert galaxies areundistinguishable from each other. From the luminosity ratios LIR/LHalpha and LIR/L[O III], we show that basically the same model can beapplied to both types of Seyfert, only allowing for the variation ofmodel conditions: type 2 Seyferts would be like type 1 Seyferts but withthe Seyfert nucleus and broad line region more effectively "hidden" bydust.
| A Survey for H 2O Megamasers in Active Galactic Nuclei. I. Observations
We report an extensive search for 22 GHz H_2_O maser emission fromnearby active galaxies. Our sample includes all Seyfert and LINERgalaxies listed in the Huchra catalog or the Veron-Cetty & Veroncatalog with recessional velocities less than 7000 km s^-1^, and allSeyfert galaxies and LINERs in Huchra's catalog with m_b_ <= 14. Inaddition to these distance- and magnitude-limited samples, we have alsoobserved a number of active galaxies, including radio galaxies, athigher redshift; In all, some 354 galaxies have been surveyed. Ten newH_2_O megamaser sources have been detected, resulting in 16 galaxiesthat are currently known to contain H_2_O masers with isotropicluminosities greater than 20 L_sun_. Of the observed active galaxieswith cz < 7000 km s^-1^, 5.4% have detectable H_2_O megamaseremission. This fraction increases to 11% for those sources with cz <2000 km s^-1^. The newly discovered megamaser sources were monitored onsubsequent observing runs. The strength of the maser features varies forthese sources, as they do for Galactic masers. Three of the galaxieshave sufficient data to test for velocity changes of narrow masercomponents comparable in magnitude to those of the well-studied systemicfeatures in NGC 4258. The maser line in one of these galaxies-NGC2639-is found to have a systematic redward velocity drift of 6.6 +/- 0.4km s^-1^ yr^-1^. No systematic velocity drifts are found for the othertwo sources. We also report large apparent velocity changes in theunusual broad H_2_O emission feature in NGC 1052.
| Circumnuclear Star Formation in Active Galaxies
We study the gas kinematics and chemical abundances in the inner regionsof six galaxies with active galactic nuclei. The galaxies were selectedfor having star-forming regions in rings or spirals within a fewkiloparsecs of the nucleus. The goal of the project is to search for anyconnections between the gas-dynamics, the chemical abundances, and thenuclear activity. Narrowband images have been obtained to map out theionized gas. Medium-dispersion long-slit spectroscopy at severalpositions over the nuclear region has been used to obtain the gaseousvelocity field and distribution of excitation. The H II regions in therings are located near the turnover point of the rotation curves,suggesting association with the inner Lindblad resonance. The nuclearring in the LINER NGC 1326 may be located between the two inner Lindbladresonances, and the inner rings in the Seyfert 2 galaxy NGC 3081 and theLINER/Seyfert 1 NGC 7213 may be associated with the {OMEGA} - κ/4resonance. A warm ionized medium (WIM) is found to pervade the innerregion in all galaxies. There is a correlation between the [NII]/Hα and [S II/Hα ratios and the FWHM of the [N II]λ 6584 emission line in this WIM, indicating that shockscontribute to the ionization of the gas. We show that contamination bythis diffuse emission increases the measured [N II]/Hα and [SII]]Hα ratios at H II regions close to the nuclei and thus mayaccount, in part, for the systematically higher [N II]/Hα and [SII]/Hα found in the present work and by previous authors for near-nuclear H II regions compared with H II regions farther out in the diskof the galaxy. In the present paper, we correct for this contaminationby interpolating the contribution of the WIM at the H II regions andsubtracting it off. Oxygen and nitrogen abundances are obtained for 18 HII regions and are extrapolated to obtain the abundance of the nucleargas, which is found to range from solar to 2 times solar for oxygen andfrom 2 to 4 times solar for nitrogen. Such values are similar to thoseobserved in nonactive galaxies with the same luminosity andmorphological type and do not support the idea that the central regionsof active galaxies have undergone unusual chemical processing.
| The Catalog of Southern Ringed Galaxies
The Catalog of Southern Ringed Galaxies (CSRG) is a comprehensivecompilation of diameters, axis ratios, relative bar position angles, andmorphologies of inner and outer rings, pseudorings, and lenses in 3692galaxies south of declination -17 deg. The purpose of the catalog is toevaluate the idea that these ring phenomena are related to orbitalresonances with a bar or oval in galaxy potentials. The catalog is basedon visual inspection of most of the 606 fields of the Science ResearchCouncil (SRC) IIIa-J southern sky survey, with the ESO-B, ESO-R, andPalomar Sky surveys used as auxiliaries when needed for overexposed coreregions. The catalog is most complete for SRC fields 1-303 (mostly southof declination -42 deg). In addition to ringed galaxies, a list of 859mostly nonringed galaxies intended for comparison with other catalogs isprovided. Other findings from the CSRG that are not based on statisticsare the identification of intrinsic bar/ring misalignment; bars whichunderfill inner rings; dimpling of R'1pseudorings; pointy, rectangular, or hexagonal inner or outer ringshapes; a peculiar polar-ring-related system; and other extreme examplesof spiral structure and ring morphology.
| Warm IRAS sources from the point source catalog. IV. Extended optical line emission.
We present a list of objects observed to have extended line emission inour spectroscopic survey of infrared-warm AGN. Slit spectroscopic datawere obtained for 225 galaxies identified with objects in our compendiumof warm sources from the IRAS Point Source Catalog. Of these, 44 havespatially-resolved emission-line regions along the (arbitrarily placed)slit direction. Measured (projected) linear sizes of the ionized gasregions extend to >10kpc. In the case of the IRAS Seyfert galaxiesthe spatially extended line emission appears to have a lower ionizationstate than the nuclear emission. This contrasts with the warm IRASstarbust galaxies for which there is no significant difference betweenthe ionization states of the nuclear and extended emission. For thestarburst galaxies, there is a relation between the extent of starformation as seen at Hα and the far-IR colors, with more compactbursts having "warmer" colors.
| Variability studies of Seyfert galaxies. II - Spectroscopy
Results of spectroscopic observations of 35 southern Seyfert galaxiesare reported. The objects are classified, line fluxes and widths aremeasured, and peculiarities of the spectra are discussed. Many of theobjects were observed more than once, and changes in the line strengthsand profiles are examined. Comparisons with the spectra published byother investigators are also made. Attention is given to the activityclass, the redshift on which the estimate of the luminosity depends, theBalmer decrement, the width of the broad lines, the luminosity of thebroad-line region, the luminosity of the narrow-line region, and therelative strength of the F II emission features.
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