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The Host Galaxies of Narrow-Line Seyfert 1 Galaxies: Nuclear Dust Morphology and Starburst Rings
We present a study of the nuclear morphology of a sample of narrow- andbroad-line Seyfert 1 galaxies (NLS1s and BLS1s, respectively) based onbroadband images in the Hubble Space Telescope archives. In our previousstudy we found that large-scale stellar bars at >1 kpc from thenucleus are more common in NLS1s than BLS1s. In this paper we find thatNLS1s preferentially have grand-design dust spirals within ~1 kpc oftheir centers. We also find that NLS1s have a higher fraction of nuclearstar-forming rings than BLS1s. We find that many of the morphologicaldifferences are due to the presence or absence of a large-scale stellarbar within the spiral host galaxy. In general, barred Seyfert 1 galaxiestend to have grand-design dust spirals at their centers, confirming theresults of other researchers. The high fraction of grand-design nucleardust spirals and stellar nuclear rings observed in NLS1s' host galaxiessuggests a means for efficient fueling of their nuclei to support theirhigh Eddington ratios.
| 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.
| SWIFT/BAT Detections of Hard X-ray Sources III
We report on further detections of new high energy sources from theSwift Burst Alert Telescope (BAT) hard X-ray survey, and subsequentfollow-up observations with the X-ray Telescope (XRT). For previouslyreported sources and an explanation of the BAT survey observing campaignare given by Tueller et al. (ATEL #668, ATEL #669). In the tablebelow, the sources are identified by their Swift/BAT name and XRT localized position, followed by their likely identification and classification, where appropriate.
| Size and properties of AGN narrow-line regions from emission-line diagnostics.
Not Available
| Molecular gas properties of 12-μm Seyfert galaxies - I. The southern sample
We have used the 15-m Swedish European Southern Observatory (ESO)Submillimetre Telescope (SEST) to observe the J= 1 -> 0 and J= 2-> 1 transition lines of CO in 30 Southern hemisphere Seyfertgalaxies from the extended 12-μm sample of Rush, Malkan &Spinoglio. We detected CO J= 1 -> 0 in 16 out of the 30 Seyfertgalaxies and CO J= 2 -> 1 in 17 out of the 30 Seyfert galaxies. Fromthe observed spectra, various CO gas properties have been derivedincluding the luminosity of the CO gas and, using a standard conversionfactor, the H2 mass. The average H2 gas mass forSeyfert 1 galaxies was 3 × 109 Msolar for COJ= 1 -> 0 and 1 × 109 Msolar for CO J= 2-> 1, while in comparison the H2 gas mass for Seyfert 2type galaxies was 11 × 109 Msolar for CO J=1 -> 0 and 3 × 109 MsolarCO J= 2 -> 1.From this small sample of Seyfert galaxies, we tentatively support theconclusion that type 2 Seyfert galaxies contain more molecular gas thantheir type 1 counterparts.
| Stellar populations and dust extinction in non-active and Seyfert spiral galaxies
Metallicity and age gradients of the stellar populations and dustextinction are studied for a sample of 32 non-active, seven type 1Seyfert (S1) and 17 type 2 Seyfert (S2) spiral galaxies. The samplegalaxies cover the whole range from face-on to edge-on view, and thevariation of the optical and near-infrared colour gradients in the discas a function of the inclination angle is investigated in order toseparate colour changes caused by population gradients from those due todust effects.The measurements show that the observed colour gradients in the discs ofthe non-active galaxies are significantly larger than those found forthe S1 and S2 galaxies. In the near-infrared wavelengths, however, thesedifferences disappear, and the colour gradients are the same for allthree galaxy types. No systematic differences are found between thecolour gradients of the discs of the S1 galaxies and those of the S2galaxies.The data are compared to model images of dusty galaxies with a varietyof age and metallicity gradients in the disc. The radial variations ofthe optical and near-infrared colours of the model galaxies arecalculated from the radial changes of the ages and the metallicities ofthe stars, using broad-band colours of a single stellar population. Thestellar content at a given position in the disc is determined by theaverage age, the metallicity and the star formation history.For the non-active galaxies, the observed colour gradients arerepresented best by a model with a metallicity gradient, with the innerregions of the stellar disc being more metal-rich than the outerregions. However, the presence of an age gradient, with the innerregions of the stellar disc being older than the outer regions, cannotbe ruled out. For the S1 and S2 galaxies, the comparison between dataand models indicates that the age and metallicity gradients in thestellar disc are small. As far as the internal dust extinction isconcerned, the comparison between data and models indicates that boththe non-active and the S2 galaxies show significant dust extinction, butthey are not optically thick.
| 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
| A Hubble Space Telescope Survey of Extended [O III] λ5007 Emission in a Far-Infrared Selected Sample of Seyfert Galaxies: Observations
We present a Hubble Space Telescope (HST) survey of extended [O III]emission for a sample of 60 Seyfert galaxies (22 Seyfert 1 galaxies and38 Seyfert 2 galaxies), selected based on their far-infrared properties.The observations for 42 of these galaxies were done in a snapshot surveywith WFPC2. The remaining 18 were obtained from the HST archive, most ofwhich were observed with the same configuration. These observationscover 68% of the objects in the sample defined by Kinney et al. andcreate a valuable data set for the study of the narrow-line region (NLR)properties of Seyfert galaxies. In this paper, we present the details ofthe observations, reductions, and measurements. We also discuss theextended structure of individual sources, and the relation of thisemission to the radio and host galaxy morphology. We also address howrepresentative the subsample of [O III]-imaged galaxies is of the entiresample, and possible selection effects that may affect this comparisonof the properties of Seyfert 1 and Seyfert 2 galaxies.Based on observations made with the NASA/ESA Hubble Space Telescope,which is operated by the Association of Universities for Research inAstronomy, Inc., under NASA contract NAS5-26555.
| 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 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.
| 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.
| Disc scalelengths of non-active and active spiral galaxies
Disc scalelengths rD are determined for a sample of 32non-active and 28 active spiral galaxies from optical CCD images. For 21of the 32 non-active galaxies and 20 of the 28 active galaxies B, V, Rand I data have been obtained, while for the remaining galaxies only Band I images have been taken. For 18 of the 21 non-active galaxies,which are measured in all four passbands, rD decreasessystematically from B to I, whereas such a decrease is found for onlyfour of the 20 active galaxies with BVRI data. For the non-activegalaxies, the ratios rD(B)/rD(I),rD(V)/rD(I) and rD(R)/rD(I)increase systematically with increasing apparent ellipticity ɛof the galaxies. For the active galaxies, no systematic variation of anyof the ratios with increasing ɛ is found. The variation ofrD(B)/rD(I) with ɛ is compared with modelcalculations. For the non-active galaxies, the data are represented bestby a model with a stellar disc that has an intrinsic colour gradient andwith a central optical depth in the B band for face-on view ofτ0B=3. For the active galaxies, the best agreement between data andmodels is found for models with a stellar disc with no intrinsic colourgradient and no dust. The best-fitting model for the non-active galaxiesdoes not reproduce the data of the active galaxies. The main conclusionof this work is that structural differences seem to exist between thediscs of non-active and active galaxies. The non-active galaxies showsignificant colour gradients within their discs, whereas the activegalaxies do not. These gradients are probably caused by a combination ofan intrinsic colour gradient within the stellar disc, and dustextinction. Furthermore, the measurements indicate that the non-activegalaxies show significant dust extinction in the centre, but they areoptically thin in the outer regions. The active galaxies do not seem tohave intrinsic colour gradients within the stellar disc and they areoptically thin throughout the disc.
| 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.
| 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.
| The ROSAT Bright Survey: II. Catalogue of all high-galactic latitude RASS sources with PSPC countrate CR > 0.2 s-1
We present a summary of an identification program of the more than 2000X-ray sources detected during the ROSAT All-Sky Survey (Voges et al.1999) at high galactic latitude, |b| > 30degr , with countrate above0.2 s-1. This program, termed the ROSAT Bright Survey RBS, isto more than 99.5% complete. A sub-sample of 931 sources with countrateabove 0.2 s-1 in the hard spectral band between 0.5 and 2.0keV is to 100% identified. The total survey area comprises 20391deg2 at a flux limit of 2.4 x 10-12 ergcm-2 s-1 in the 0.5 - 2.0 keV band. About 1500sources of the complete sample could be identified by correlating theRBS with SIMBAD and the NED. The remaining ~ 500 sources were identifiedby low-resolution optical spectroscopy and CCD imaging utilizingtelescopes at La Silla, Calar Alto, Zelenchukskaya and Mauna Kea. Apartfrom completely untouched sources, catalogued clusters and galaxieswithout published redshift as well as catalogued galaxies with unusualhigh X-ray luminosity were included in the spectroscopic identificationprogram. Details of the observations with an on-line presentation of thefinding charts and the optical spectra will be published separately.Here we summarize our identifications in a table which contains opticaland X-ray information for each source. As a result we present the mostmassive complete sample of X-ray selected AGNs with a total of 669members and a well populated X-ray selected sample of 302 clusters ofgalaxies with redshifts up to 0.70. Three fields studied by us remainwithout optical counterpart (RBS0378, RBS1223, RBS1556). While the firstis a possible X-ray transient, the two latter are isolated neutron starcandidates (Motch et al. 1999, Schwope et al. 1999).
| Luminous Infrared Galaxies. III. Multiple Merger, Extended Massive Star Formation, Galactic Wind, and Nuclear Inflow in NGC 3256
We report detailed evidence for multiple merger, extended massive starformation, galactic wind, and circular/noncircular motions in theluminous infrared galaxy NGC 3256, based on observations ofhigh-resolution imaging (Hubble Space Telescope, ESO NTT), and extensivespectroscopic data (more than 1000 spectra, collected at EstaciónAstrofísica de Bosque Alegre, Complejo Astronómico elLeoncito, Cerro Tololo InterAmerican Observatory, and IUEobservatories). We find in a detailed morphological study (resolution~15 pc) that the extended massive star formation process detectedpreviously in NGC 3256 shows extended triple asymmetrical spiral arms(r~5 kpc), emanating from three different nuclei. The main opticalnucleus shows a small spiral disk (r~500 pc), which is a continuation ofthe external one and reaches the very nucleus. The core shows blueelongated structure (50 pc×25 pc) and harbors a blue stellarcluster candidate (r~8 pc). We discuss this complex morphology in theframework of an extended massive star formation driven by a multiplemerger process (models of Hernquist et al. and Taniguchi et al.). Westudy the kinematics of this system and present a detailed Hαvelocity field for the central region(40''×40'' rmax~30''~5kpc), with a spatial resolution of 1" and errors of +/-15 kms-1. The color and isovelocity maps show mainly (1) akinematic center of circular motion with ``spider'' shape, locatedbetween the main optical nucleus and the close (5") mid-IR nucleus and(2) noncircular motions in the external parts. We obtained three``sinusoidal rotation curves'' (from the Hα velocity field) aroundposition angle (P.A.) ~55°, ~90°, and ~130°. In the mainoptical nucleus we found a clear ``outflow component'' associated withgalactic winds plus an ``inflow radial motion.'' The outflow componentwas also detected in the central and external regions (r<=5-6 kpc).The main axis of the inflow region (P.A.~80deg) ispractically perpendicular to the ouflow axis (atP.A.~160deg). We analyze in detail the physical conditions inthe giant H II regions located in the asymmetric spiral arms, the twomain optical nuclei, and the outflow component (using long-slitspectroscopy, plus standard models of photoionization, shocks, andstarbursts). We present four detailed emission-line ratios (NII/Hα, S II/Hα, S II/S II), and FWHM (Hα) maps for thecentral region (30''×30''rmax~22''~4 kpc), with a spatial resolution of 1".In the central region (r~5-6 kpc) we detected that the nuclear starburstand the extended giant H II regions (in the spiral arms) have verysimilar properties, i.e., high metallicity and low-ionization spectra,with Teff=35,000 K, solar abundance, a range ofTe~6000-7000 K, and Ne~100-1000 cm-3.The nuclear and extended outflow shows properties typical of galacticwind/shocks, associated with the nuclear starburst. We suggest that theinteraction between dynamical effects, the galactic wind (outflow),low-energy cosmic rays, and the molecular+ionized gas (probably in theinflow phase) could be the possible mechanism that generate the``similar extended properties in the massive star formation, at a scaleof 5-6 kpc!'' We have also studied the presence of the closemerger/interacting systems NGC 3256C (at ~150 kpc, ΔV=-100 kms-1) and the possible association between the NGC 3256 and3263 groups of galaxies. In conclusion, these results suggest that NGC3256 is the product of a multiple merger, which generated an extendedmassive star formation process with an associated galactic wind plus anuclear inflow. Therefore, NGC 3256 is another example in which therelation between mergers and extreme starburst (and the powerfulgalactic wind, ``multiple'' Type II supernova explosions) play animportant role in the evolution of galaxies (the hypothesis of Rieke etal., Joseph et al., Terlevich et al., Heckman et al., and Lípariet al.). Based on observations obtained at the Hubble Space Telescope(HST; Wide Field Planetary Camera 2 [WFPC2] and NICMOS) satellite;International Ultraviolet Explorer (IUE) satellite; European SouthernObservatory (ESO, NTT); Chile, Cerro Tololo Inter-American Observatory(CTIO), Chile; Complejo Astronómico el Leoncito (CASLEO),Argentina; Estación Astrofísica de Bosque Alegre(BALEGRE), Argentina.
| Morphology of the 12 Micron Seyfert Galaxies. II. Optical and Near-Infrared Image Atlas
We present 263 optical and near-infrared (NIR) images for 42 1s and 48Seyfert 2s, selected from the Extended 12 μm Galaxy Sample.Elliptically averaged profiles are derived from the images, andisophotal radii and magnitudes are calculated from these. We also reportvirtual aperture photometry that, judging from comparison with previouswork, is accurate to roughly 0.05 mag in the optical, and 0.07 mag inthe NIR. Our B-band isophotal magnitude and radii, obtained from ellipsefitting, are in good agreement with those of Third Reference Catalogueof Bright Galaxies. When compared with the B band, V, I, J, and Kisophotal diameters show that the colors in the outer regions of Seyfertgalaxies are consistent with the colors of normal spirals. Differencesin the integrated isophotal colors and comparison with a simple modelshow that the active nucleus+bulge are stronger and redder in the NIRthan in the optical. Finally, roughly estimated Seyfert disk surfacebrightnesses are significantly brighter in B and K than those in normalspirals of similar morphological type.
| 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
| 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 Difference between the Narrow-Line Regions of Seyfert 1 and Seyfert 2 Galaxies
This paper presents a comparative study of emission-line ratios of thenarrow-line regions (NLRs) of Seyfert 1 and Seyfert 2 galaxies. Itincludes a literature compilation of the emission-line fluxes [O II]lambda3727, [Ne III] lambda3869, [O III] lambda5007, and [Ne V]lambda3426 as well as 60 μm continuum flux, for a sample of 52Seyfert 1 and 68 Seyfert 2 galaxies. The distribution of theemission-line ratios [O II]/[Ne III] and [O II]/[Ne V] shows thatSeyfert 1 and Seyfert 2 galaxies are statistically different: Seyfert 1galaxies have smaller values than Seyfert 2 galaxies, indicating ahigher excitation spectrum. These and other emission-line ratios arecompared with sequences of models that combine different proportions ofmatter and ionization-bounded clouds and also with sequences of modelsthat vary only the ionization parameter. This comparison shows that theformer models better reproduce the overall distribution of emission-lineratios, indicating that Seyfert 1 galaxies have a smaller number ofionization-bounded clouds than Seyfert 2 galaxies. This difference,together with other results available in the literature, are interpretedfrom the point of view of four different scenarios. The most likelyscenario assumes that Seyfert 1 galaxies have smaller NLRs than Seyfert2 galaxies, possibly due to a preferential alignment of the torus axisclose to the host galaxy plane axis in Seyfert 1 galaxies.
| ROSAT All-Sky Survey observations of IRAS galaxies. I. Soft X-ray and far-infrared properties
The 120 000 X-ray sources detected in the RASS II processing of theROSAT All-Sky Survey are correlated with the 14 315 IRAS galaxiesselected from the IRAS Point Source Catalogue: 372 IRAS galaxies showX-ray emission within a distance of 100 arcsec from the infraredposition. By inspecting the structure of the X-ray emission in overlayson optical images we quantify the likelihood that the X-rays originatefrom the IRAS galaxy. For 197 objects the soft X-ray emission is verylikely associated with the IRAS galaxy. Their soft X-ray properties aredetermined and compared with their far-infrared emission. X-ray contourplots overlaid on Palomar Digitized Sky Survey images are given for eachof the 372 potential identifications. All images and tables displayedhere are also available in electronic form.
| The extinction, flux distribution and luminosity of Seyfert 1 nuclei derived from UBV(RI)C aperture photometry
UBV(RI)C aperture photometry was carried out over a four-yrperiod for 92 broad-line Seyfert galaxies. Where possible, theobservations were repeated at different epochs in order to try to detectbrightness variations. Significant variations were found in the majorityof the objects observed at more than one epoch. Plots of the fluxmeasurements through different bands against each other closely resemblelinear relationships. Error contours of the data points in these plotsare shown to be covariant ellipses. A statistical method is developedthat enables one to obtain the best linear fit taking into account theerror geometry peculiar to these data. The nuclear colors are determinedfor 50 significantly variable objects by calculating the beststraight-line fits according to this statistical method. Chi-squaredtests are used to show that, contrary to claims made in some recentstudies, there is no significant deviation of the data from thestraight-line fit in the vast majority of cases. The relationshipbetween galaxy inclination and nuclear extinction is found to be verypoorly defined, showing that the extinction largely depends on theamount of dust in in the circumnuclear region rather than interstellardust in the galaxy itself.
| The circumnuclear region in the Seyfert 1 galaxy NGC 3227
This article presents Hα and [O iii] narrow-band images andlong-slit optical and near-infrared spectroscopy at position angles 65.5deg and 25 deg through the circumnuclear region in the Seyfert 1 galaxyNGC 3227. After subtraction of a bulge+disc model, the continuum imageat lambda5900A shows an excess of emission aligned with the companiongalaxy NGC 3226. We attribute this emission to a stellar bar induced bythe interaction. Along the leading parts of the bar, we find dust lanesand 70 per cent of the H ii regions detected in the disc. The Hαand [O iii] images show extended emission in the circumnuclear regionwith very different morphologies. [O iii] is elongated to the north andnearly aligned with the bar. This emission is formed by two kinematicalcomponents, a broad component blueshifted with respect to a narrowercomponent. The blue component could be photoionized by radiation fromthe active nucleus, but the red component might be associated with thestarburst detected to the west. The Hα image is aligned alongPA=65 deg, and shows a bright knot at 4arcsec south-west of the nucleusand a shell-like structure; there the line ratios can be fitted byphotoionization by a stellar source. To the north-east, the spectrumshows characteristics of a high-excitation low-ionization nuclearemission region (LINER), and the line ratios can be explained asphotoionization by a blackbody with a temperature of 140 000K,ionization parameter 0.001, and solar chemical composition with anoverabundance of N and S. Even though Hα and [O iii] presentdifferent morphologies, both are extended 500pc from the nucleus, insidethe inner Lindblad resonance; this suggests that gravitational torques,associated with the non-axisymmetric potential produced by the bar andby interaction with the companion galaxy, transport the gas to the innerLindblad resonance (ILR), from where it fuels the circumnuclear regionin NGC 3227.
| 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.
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