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A Green Bank Telescope Search for Water Masers in Nearby Active Galactic Nuclei
Using the Green Bank Telescope, we have conducted a survey for 1.3 cmwater maser emission toward the nuclei of nearby active galaxies, themost sensitive large survey for H2O masers to date. Among 145galaxies observed, maser emission was newly detected in 11 sources andconfirmed in one other. Our survey targeted nearby (v<12,000 kms-1), mainly type 2 active galactic nuclei (AGNs) north ofδ=-20deg and includes a few additional sources as well.We find that more than one-third of Seyfert 2 galaxies have strong maseremission, although the detection rate declines beyond v~5000 kms-1 because of sensitivity limits. Two of the masersdiscovered during this survey are found in unexpected hosts: NGC 4151(Seyfert 1.5) and NGC 2782 (starburst). We discuss the possiblerelations between the large X-ray column to NGC 4151 and a possiblehidden AGN in NGC 2782 to the detected masers. Four of the masersdiscovered here, NGC 591, NGC 4388, NGC 5728, and NGC 6323, havehigh-velocity lines symmetrically spaced about the systemic velocity, alikely signature of molecular gas in a nuclear accretion disk. The masersource in NGC 6323, in particular, reveals the classic spectrum of a``disk maser'' represented by three distinct groups of Dopplercomponents. Future single-dish and VLBI observations of these fourgalaxies could provide a measurement of the distance to each galaxy andof the Hubble constant, independent of standard candle calibrations.
| Circumnuclear Structure and Black Hole Fueling: Hubble Space Telescope NICMOS Imaging of 250 Active and Normal Galaxies
Why are the nuclei of some galaxies more active than others? If mostgalaxies harbor a central massive black hole, the main difference isprobably in how well it is fueled by its surroundings. We investigatethe hypothesis that such a difference can be seen in the detailedcircumnuclear morphologies of galaxies using several quantitativelydefined features, including bars, isophotal twists, boxy and diskyisophotes, and strong nonaxisymmetric features in unsharp-masked images.These diagnostics are applied to 250 high-resolution images of galaxycenters obtained in the near-infrared with NICMOS on the Hubble SpaceTelescope. To guard against the influence of possible biases andselection effects, we have carefully matched samples of Seyfert 1,Seyfert 2, LINER, starburst, and normal galaxies in their basicproperties, taking particular care to ensure that each was observed witha similar average scale (10-15 pc pixel-1). Severalmorphological differences among our five different spectroscopicclassifications emerge from the analysis. The H II/starburst galaxiesshow the strongest deviations from smooth elliptical isophotes, whilethe normal galaxies and LINERs have the least disturbed morphology. TheSeyfert 2s have significantly more twisted isophotes than any othercategory, and the early-type Seyfert 2s are significantly more disturbedthan the early-type Seyfert 1s. The morphological differences betweenSeyfert 1s and Seyfert 2s suggest that more is at work than simply theviewing angle of the central engine. They may correspond to differentevolutionary stages.
| Properties of isolated disk galaxies
We present a new sample of northern isolated galaxies, which are definedby the physical criterion that they were not affected by other galaxiesin their evolution during the last few Gyr. To find them we used thelogarithmic ratio, f, between inner and tidal forces acting upon thecandidate galaxy by a possible perturber. The analysis of thedistribution of the f-values for the galaxies in the Coma cluster leadus to adopt the criterion f ≤ -4.5 for isolated galaxies. Thecandidates were chosen from the CfA catalog of galaxies within thevolume defined by cz ≤5000 km s-1, galactic latitudehigher than 40o and declination ≥-2.5o. Theselection of the sample, based on redshift values (when available),magnitudes and sizes of the candidate galaxies and possible perturberspresent in the same field is discussed. The final list of selectedisolated galaxies includes 203 objects from the initial 1706. The listcontains only truly isolated galaxies in the sense defined, but it is byno means complete, since all the galaxies with possible companions underthe f-criterion but with unknown redshift were discarded. We alsoselected a sample of perturbed galaxies comprised of all the diskgalaxies from the initial list with companions (with known redshift)satisfying f ≥ -2 and \Delta(cz) ≤500 km s-1; a totalof 130 objects. The statistical comparison of both samples showssignificant differences in morphology, sizes, masses, luminosities andcolor indices. Confirming previous results, we found that late spiral,Sc-type galaxies are, in particular, more frequent among isolatedgalaxies, whereas Lenticular galaxies are more abundant among perturbedgalaxies. Isolated systems appear to be smaller, less luminous and bluerthan interacting objects. We also found that bars are twice as frequentamong perturbed galaxies compared to isolated galaxies, in particularfor early Spirals and Lenticulars. The perturbed galaxies have higherLFIR/LB and Mmol/LB ratios,but the atomic gas content is similar for the two samples. The analysisof the luminosity-size and mass-luminosity relations shows similartrends for both families, the main difference being the almost totalabsence of big, bright and massive galaxies among the family of isolatedsystems, together with the almost total absence of small, faint and lowmass galaxies among the perturbed systems. All these aspects indicatethat the evolution induced by interactions with neighbors would proceedfrom late, small, faint and low mass Spirals to earlier, bigger, moreluminous and more massive spiral and lenticular galaxies, producing atthe same time a larger fraction of barred galaxies but preserving thesame relations between global parameters. The properties we found forour sample of isolated galaxies appear similar to those of high redshiftgalaxies, suggesting that the present-day isolated galaxies could bequietly evolved, unused building blocks surviving in low densityenvironments.Tables \ref{t1} and \ref{t2} are only available in electronic form athttp://www.edpsciences.org
| Radio emission from AGN detected by the VLA FIRST survey
Using the most recent (April 2003) version of the VLA FIRST survey radiocatalog, we have searched for radio emission from >2800 AGN takenfrom the most recent (2001) version of the Veron-Cetty and Veron AGNcatalog. These AGN lie in the 9033 square degrees of sky alreadycovered by the VLA FIRST survey. Our work has resulted in positivedetection of radio emission from 775 AGN of which 214 are new detectionsat radio wavelengths.Tables 3 and 4 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/416/35
| A Possible Signature of Connection between Blazars and Seyfert Galaxies
The accretion rates (dot{M}) and their correlation with cosmologicalredshifts for a sample of blazars and Seyfert galaxies are presented.The sample includes 77 blazars (28 FSRQs, 26 LBLs, and 23 HBLs) and 60Seyfert galaxies, of which the extended spectral energy distributioninformation and redshifts are available. Within the framework ofaccreting black holes, the accretion rates for these sources wereestimated based on their bolometric luminosities. The result shows thatthe accretion rates are significantly different for each subclass of theblazars and Seyfert galaxies. Their averages are, respectively, 50.2,17.0, 1.0, 0.1Modot yr-1 for the FSRQs, LBLs, HBLs, and theSeyfert galaxies, exhibiting a well descending sequence ofFSRQs-LBLs-HBLs-Seyfert galaxies. They are strongly correlated with theredshifts for both blazars and Seyfert galaxies. The linear correlationcoefficients are 0.81 and 0.68 with a chance probab ility of p <0.0001, respectively. A plot of dot{M} - z shows that the blazars andthe Seyfert galaxies distribute in a distinguishable regions with aconnection at z 0.7 and almost all the sources lie in a narrowregion of z1.40 ≤ dot{M} ≤ 250 z1.40,illustrating a strong correlation between the two quantities for thewhole sample. The regression line is dot{M} = (14.5 ± 1.2)z1.40±0.06 Modot yr-1 with a linearcoefficient of 0.93 and a chance probability of p < 0.0001,suggesting a connection between blazars and Seyfert galaxies. Thisconnection might imply that the two classes are on the same evolutionarysequence. Although the correlations of the data are formally solid, theconclusion may be affected by one source of considerable uncertainty atthe data level, which is also discussed.
| A Fundamental Plane of black hole activity
We examine the disc-jet connection in stellar mass and supermassiveblack holes by investigating the properties of their compact emission inthe X-ray and radio bands. We compile a sample of ~100 active galacticnuclei with measured masses, 5-GHz core emission, and 2-10 keVluminosities, together with eight galactic black holes with a total of~50 simultaneous observations in the radio and X-ray bands. Using thissample, we study the correlations between the radio (LR) andthe X-ray (LX) luminosity and the black hole mass (M). Wefind that the radio luminosity is correlated with bothM andLX, at a highly significant level. In particular, we showthat the sources define a `Fundamental Plane' in the three-dimensional(logLR, logLX, logM) space, given bylogLR= (0.60+0.11-0.11)logLX+ (0.78+0.11-0.09) logM+7.33+4.05-4.07, with a substantial scatter ofσR= 0.88. We compare our results to the theoreticalrelations between radio flux, black hole mass, and accretion ratederived by Heinz & Sunyaev. Such relations depend only on theassumed accretion model and on the observed radio spectral index.Therefore, we are able to show that the X-ray emission from black holesaccreting at less than a few per cent of the Eddington rate is unlikelyto be produced by radiatively efficient accretion, and is marginallyconsistent with optically thin synchrotron emission from the jet. On theother hand, models for radiatively inefficient accretion flows seem toagree well with the data.
| The luminous and dark matter content of disk galaxies
We have compiled a sample of disk galaxies with available photometry inthe B and K bands, velocity line-widths and HI integral fluxes. Severalparameters that trace the luminous, baryonic and dark matter contentswere inferred. We investigated how these parameters vary with differentgalaxy properties, and compared the results with predictions of galaxyevolutionary models in the context of the Λ Cold Dark Matter(ΛCDM) cosmogony. The ratio of disk-to-total maximum circularvelocity, (Vd,m/Vt,m), depends mainly on thecentral disk surface density Σd,0 (or surfacebrightness, SB), increasing roughly asΣd,00.15. While a fraction of high SBgalaxies have a (Vd,m/Vt,m) ratio corresponding tothe maximum disk solution, the low SB are completely dark matterdominated. The trend is similar for the models, although they haveslightly smaller (Vd,m/Vt,m) ratios thanobservations, in particular at the highest SBs and when small baryonfractions are used. The scatter in the(Vd,m/Vt,m)- Σd,0 plot is large.An analysis of residuals shows that (Vd,m/Vt,m)tends to decrease as the galaxy is redder, more luminous (massive), andof earlier type. The models allow us to explain the physics of theseresults, which imply a connexion between halo structure and luminousproperties. The dynamical-to-baryon mass and dynamical mass-to-light (Band K) ratios at a given radius were also estimated. All these ratios,for observations and models, decrease with Σd,0; (orSB) and do not correlate significantly with the galaxy scale, contraryto what has been reported in previous works, based on the analysis ofrotation curve shapes. We discuss this difference and state theimportance of solving the controversy of whether the dark and luminouscontents in disk galaxies depend on SB or luminosity. The broadagreement between the models and observations presented here regardingthe trends of the dynamical-to-baryon matter and mass-to-light ratioswith several galaxy properties favors the ΛCDM scenario. However,the excess of dark matter inside the optical region of disk galaxiesremains the main difficulty.Appendices A and B are only available in electronic form athttp://www.edpsciences.org. Table 1 is only available at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/412/633
| Do bulges of early- and late-type spirals have different morphology?
We study HST/NICMOS H-band images of bulges of two equal-sized samplesof early- (TRC3 <= 3) and late-type spiral (mainly Sbc-Sc)galaxies matched in outer disk axis ratio. We find that bulges oflate-type spirals are more elongated than their counterparts inearly-type spirals. Using a KS-test we find that the two distributionsare different at the 98.4% confidence level. We conclude that the twodata sets are different, i.e. late-type galaxies have a broaderellipticity distribution and contain more elongated features in theinner regions. We discuss the possibility that these would correspond tobars at a later evolutionary stage, i.e. secularly evolved bars.Consequent implications are raised, and we discuss relevant questionsregarding the formation and structure of bulges. Are bulges ofearly-type and late-type spirals different? Are their formationscenarios different? Can we talk about bulges in the same way fordifferent types of galaxies?
| ``Hidden'' Seyfert 2 Galaxies and the X-Ray Background
Obscured active galactic nuclei, which are classified optically as type2 (narrow line) Seyfert galaxies in the local universe, are by far themost promising candidates for the origin of the hard (2-10 keV) X-raybackground radiation. However, optical follow-up observations of faintX-ray sources in deep Chandra images have revealed surprising numbers ofapparently normal galaxies at modest redshift. Such objects represent~40%-60% of the sources classified in deep Chandra surveys, raising thepossibility that the X-ray galaxy population has evolved with cosmictime. Alternatively, most of the faint X-ray galaxies in question are sodistant that their angular diameters are comparable to the slit widthsused in ground-based spectroscopic observations; thus, their nuclearspectral features may be overwhelmed (``hidden'') by host galaxy light.To test this hypothesis, we have obtained integrated spectra of a sampleof nearby, well-studied Seyfert 2 galaxies. The data, which accuratelysimulate observations of distant Chandra sources, demonstrateconvincingly that the defining spectral signatures of Seyfert 2s can behidden by light from their host galaxies. In fact, 60% of the observedobjects would not be classified as Seyfert 2s on the basis of theirintegrated spectra, similar to the fraction of faint X-ray sourcesidentified with ``normal'' galaxies. Thus, the numbers of narrow-lineactive galaxies in deep Chandra surveys (and perhaps all ground-basedspectroscopic surveys of distant galaxies) are likely to have beenunderestimated.
| Active Galactic Nucleus Black Hole Masses and Bolometric Luminosities
Black hole mass, along with mass accretion rate, is a fundamentalproperty of active galactic nuclei (AGNs). Black hole mass sets anapproximate upper limit to AGN energetics via the Eddington limit. Wecollect and compare all AGN black hole mass estimates from theliterature; these 177 masses are mostly based on the virial assumptionfor the broad emission lines, with the broad-line region size determinedfrom either reverberation mapping or optical luminosity. We introduce200 additional black hole mass estimates based on properties of the hostgalaxy bulges, using either the observed stellar velocity dispersion orthe fundamental plane relation to infer σ these methods assumethat AGN hosts are normal galaxies. We compare 36 cases for which blackhole mass has been generated by different methods and find, forindividual objects, a scatter as high as a couple of orders ofmagnitude. The less direct the method, the larger the discrepancy withother estimates, probably due to the large scatter in the underlyingcorrelations assumed. Using published fluxes, we calculate bolometricluminosities for 234 AGNs and investigate the relation between blackhole mass and luminosity. In contrast to other studies, we find nosignificant correlation of black hole mass with luminosity, other thanthose induced by circular reasoning in the estimation of black holemass. The Eddington limit defines an approximate upper envelope to thedistribution of luminosities, but the lower envelope depends entirely onthe sample of AGNs included. For any given black hole mass, there is arange in Eddington ratio of up to 3 orders of magnitude.
| Seyfert 2 Galaxies with Spectropolarimetric Observations
We present a compilation of radio, infrared, optical, and hard X-ray(2-10 keV) data for a sample of 90 Seyfert 2 galaxies (Sy2s) withspectropolarimetric observations (41 Sy2s with detection of polarizedbroad lines [PBLs] and 49 without PBLs). Compared to Sy2s without PBLs,Sy2s with PBLs tend to be earlier type spirals and show warmermidinfrared color and significant excess of emissions (including thehard X-ray [2-10 keV], [O III] λ5007, infrared [25 μm], andradio). Our analyses indicate that the majority of Sy2s without PBLs arethose sources having less powerful active galactic nucleus (AGN)activities, most likely caused by a low accretion rate. It implies thatthe detectability of the polarized broad emission lines in Sy2s maydepend on their central AGN activities in most cases. Based on theavailable data, we find no compelling evidence for the presence of twotypes of Sy2s; one of which has been proposed to be intrinsicallydifferent from Sy2s claimed in the unification model.
| Nested and Single Bars in Seyfert and Non-Seyfert Galaxies
We analyze the observed properties of nested and single stellar barsystems in disk galaxies. The 112 galaxies in our sample comprise thelargest matched Seyfert versus non-Seyfert galaxy sample of nearbygalaxies with complete near-infrared or optical imaging sensitive tolength scales ranging from tens of parsecs to tens of kiloparsecs. Thepresence of bars is deduced by fitting ellipses to isophotes in HubbleSpace Telescope (HST) H-band images up to 10" radius and in ground-basednear-infrared and optical images outside the H-band images. This is aconservative approach that is likely to result in an underestimate ofthe true bar fraction. We find that a significant fraction of the samplegalaxies, 17%+/-4%, have more than one bar, and that 28%+/-5% of barredgalaxies have nested bars. The bar fractions appear to be stableaccording to reasonable changes in our adopted bar criteria. For thenested bars, we detect a clear division in length between thelarge-scale (primary) bars and small-scale (secondary) bars, in bothabsolute and normalized (to the size of the galaxy) length. We arguethat this bimodal distribution can be understood within the framework ofdisk resonances, specifically the inner Lindblad resonances (ILRs),which are located where the gravitational potential of the innermostgalaxy switches effectively from three-dimensional to two-dimensional.This conclusion is further strengthened by the observed distribution ofthe sizes of nuclear rings which are dynamically associated with theILRs. While primary bar sizes are found to correlate with the hostgalaxy sizes, no such correlation is observed for the secondary bars.Moreover, we find that secondary bars differ morphologically from singlebars. Our matched Seyfert and non-Seyfert samples show a statisticallysignificant excess of bars among the Seyfert galaxies at practically alllength scales. We confirm our previous results that bars are moreabundant in Seyfert hosts than in non-Seyfert galaxies and that Seyfertgalaxies always show a preponderance of ``thick'' bars compared to thebars in non-Seyfert galaxies. Finally, no correlation is observedbetween the presence of a bar and that of companion galaxies, evenrelatively bright ones. Overall, since star formation and dustextinction can be significant even in the H band, the stellar dynamicsof the central kiloparsec cannot always be revealed reliably by the useof near-infrared surface photometry alone.
| The UZC-SSRS2 Group Catalog
We apply a friends-of-friends algorithm to the combined Updated ZwickyCatalog and Southern Sky Redshift Survey to construct a catalog of 1168groups of galaxies; 411 of these groups have five or more members withinthe redshift survey. The group catalog covers 4.69 sr, and all groupsexceed the number density contrast threshold, δρ/ρ=80. Wedemonstrate that the groups catalog is homogeneous across the twounderlying redshift surveys; the catalog of groups and their membersthus provides a basis for other statistical studies of the large-scaledistribution of groups and their physical properties. The medianphysical properties of the groups are similar to those for groupsderived from independent surveys, including the ESO Key Programme andthe Las Campanas Redshift Survey. We include tables of groups and theirmembers.
| Physical Sources of Scatter in the Tully-Fisher Relation
We analyze residuals from the Tully-Fisher relation for theemission-line galaxies in the Nearby Field Galaxy Survey, a broadlyrepresentative survey designed to fairly sample the variety of galaxymorphologies and environments in the local universe for luminositiesfrom MB=-15 to -23. For a subsample consisting of the spiralgalaxies brighter than MiR=-18, we find strongcorrelations between Tully-Fisher residuals and both B-R color andEW(Hα). The extremes of the correlations are populated by Sagalaxies, which show consistently red colors, and spiral galaxies withmorphological peculiarities, which are often blue. If we apply anEW(Hα)-dependent or B-R color-dependent correction term to theTully-Fisher relation, the scatter in the relation no longer increasesfrom R to B to U but instead drops to a nearly constant level in allbands, close to the scatter we expect from measurement errors. We arguethat these results probably reflect correlated offsets in luminosity andcolor as a function of star formation history. Broadening the sample inmorphology and luminosity, we find that most nonspiral galaxies brighterthan MiR=-18 follow the same correlations betweenTully-Fisher residuals and B-R color and EW(Hα) as do spirals,albeit with greater scatter. However, the color and EW(Hα)correlations do not apply to galaxies fainter thanMiR=-18 or to emission-line S0 galaxies withanomalous gas kinematics. For the dwarf galaxy population, theparameters controlling Tully-Fisher residuals are instead related to thedegree of recent evolutionary disturbance: overluminous dwarfs havehigher rotation curve asymmetries, brighter U-band effective surfacebrightnesses, and shorter gas consumption timescales than theirunderluminous counterparts. As a result, sample selection stronglyaffects the measured faint-end slope of the Tully-Fisher relation, and asample limited to include only passively evolving, rotationallysupported galaxies displays a break toward steeper slope at lowluminosities.
| Neutral hydrogen and optical observations of edge-on galaxies: Hunting for warps
We present 21-cm HI line and optical R-band observations for a sample of26 edge-on galaxies. The HI observations were obtained with theWesterbork Synthesis Radio Telescope, and are part of the WHISP database(Westerbork HI Survey of Spiral and Irregular Galaxies). We present HImaps, optical images, and radial HI density profiles. We have alsoderived the rotation curves and studied the warping and lopsidedness ofthe HI disks. 20 out of the 26 galaxies of our sample are warped,confirming that warping of the HI disks is a very common phenomenon indisk galaxies. Indeed, we find that all galaxies that have an extendedHI disk with respect to the optical are warped. The warping usuallystarts around the edge of the optical disk. The degree of warping variesconsiderably from galaxy to galaxy. Furthermore, many warps areasymmetric, as they show up in only one side of the disk or exhibitlarge differences in amplitude in the approaching and receding sides ofthe galaxy. These asymmetries are more pronounced in rich environments,which may indicate that tidal interactions are a source of warpasymmetry. A rich environment tends to produce larger warps as well. Thepresence of lopsidedness seems to be related to the presence of nearbycompanions. Full Fig. 13 is only available in electronic form athttp://www.edpsciences.org
| The infrared luminosity of the torus and the visibility of scattered broad line emission in Seyfert 2 galaxies
A number of studies have shown that the visibility of scattered broademission lines in Seyfert 2 galaxies is strongly dependent on the IRASf60/f25 flux ratio, where those Seyfert 2 galaxieswith `warm' IRAS colours show polarized broad line emission. It is nowclear that this effect is owing to the increasing dominance of thegalactic rather than the active galactic nucleus (AGN) emission at60μm in less-luminous `cool' Seyfert 2 galaxies. However, we presentevidence that the 25-μm emission is a good measure of the AGNluminosity for most Seyfert 2 galaxies. Using this result, we show thatthe visibility of scattered broad line emission has a dependence on theAGN luminosity. The observations can be interpreted self-consistently ifthe scaleheight of the scattering zone varies with central sourceluminosity whilst the scaleheight of the obscuring torus isapproximately constant.
| The Ursa Major cluster of galaxies - III. Optical observations of dwarf galaxies and the luminosity function down to MR=-11
Results are presented of a deep optical survey of the Ursa Majorcluster, a spiral-rich cluster of galaxies at a distance of 18.6Mpcwhich contains about 30 per cent of the light but only 5 per cent of themass of the nearby Virgo cluster. Fields around known cluster membersand a pattern of blind fields along the major and minor axes of thecluster were studied with mosaic CCD cameras on the Canada-France-HawaiiTelescope. The dynamical crossing time for the Ursa Major cluster isonly slightly less than a Hubble time. Most galaxies in the localUniverse exist in similar moderate-density environments. The Ursa Majorcluster is therefore a good place to study the statistical properties ofdwarf galaxies, since this structure is at an evolutionary stagerepresentative of typical environments, yet has enough galaxies thatreasonable counting statistics can be accumulated. The mainobservational results of our survey are as follows. (i) The galaxyluminosity function is flat, with a logarithmic slope α=-1.1 for-17
| The Ursa Major Cluster of Galaxies. V. H I Rotation Curve Shapes and the Tully-Fisher Relations
This paper investigates the statistical properties of the Tully-Fisher(TF) relations for a volume-limited complete sample of spiral galaxiesin the nearby Ursa Major Cluster. The merits of B, R, I, and K' surfacephotometry and the availability of detailed kinematic information from HI synthesis imaging have been exploited. In addition to the corrected HI global profile widths WiR,I, the available H Irotation curves allow direct measurements of the observed maximumrotational velocities Vmax and the amplitudesVflat of the outer flat parts. The dynamical state of the gasdisks could also be determined in detail from the radio observations.The four luminosity and three kinematic measures allowed theconstruction of 12 correlations for various subsamples. For large galaxysamples, the Mb,iR-logWiR,Icorrelation in conjunction with strict selection criteria is preferredfor distance determinations with a 7% accuracy. Galaxies with rotationcurves that are still rising at the last measured point liesystematically on the low-velocity side of the TF relation. Galaxieswith a partly declining rotation curve(Vmax>Vflat) tend to lie systematically on thehigh-velocity side of the relation when usingWiR,I or Vmax. However, systematicoffsets are eliminated when Vflat is used. Residuals of theMb,iB-log(2Vflat) relation correlateconsistently with global galaxy properties along the Hubble sequencelike morphological type, color, surface brightness, and gas massfraction. These correlations are absent for the near-infraredMb,iK'-log(2Vflat)residuals. The tightest correlation(χ2red=1.1) is found for theMb,iK'-log(2Vflat) relation,which has a slope of -11.3+/-0.5 and a total observed scatter of 0.26mag with a most likely intrinsic scatter of zero. The tightness of thenear-infrared correlation is preserved when converting it into abaryonic TF relation that has a slope of -10.0 in the case(Mgas/LK')=1.6 while a zerointrinsic scatter remains most likely. Based on the tightness of thenear-infrared and baryonic correlations, it is concluded that the TFrelation reflects a fundamental correlation between the mass of the darkmatter halo, measured through its induced maximum rotational velocityVflat, and the total baryonic mass Mbar of agalaxy where Mbar~V4flat. Althoughthe actual distribution of the baryonic matter inside halos of similarmass can vary significantly, it does not affect this relation.
| A Composite Seyfert 2 X-Ray Spectrum: Implications for the Origin of the Cosmic X-Ray Background
We present a composite 1-10 keV Seyfert 2 X-ray spectrum derived fromASCA observations of a distance-limited sample of nearby galaxies. All29 observed objects were detected. Above ~3 keV, the composite spectrumis inverted, confirming that Seyfert 2 galaxies as a class have thespectral properties necessary to explain the flat shape of the cosmicX-ray background spectrum. Integrating the composite spectrum overredshift, we find that the total emission from Seyfert 2 galaxies,combined with the expected contribution from unabsorbed type 1 objects,provides an excellent match to the spectrum and intensity of the hardX-ray background. The principal uncertainty in this procedure is thecosmic evolution of the Seyfert 2 X-ray luminosity function. Separatecomposite spectra for objects in our sample with and without polarizedbroad optical emission lines are also presented.
| The Multitude of Unresolved Continuum Sources at 1.6 Microns in Hubble Space Telescope Images of Seyfert Galaxies
We examine 112 Seyfert galaxies observed by the Hubble Space Telescopeat 1.6 μm. We find that ~50% of the Seyfert 2.0 galaxies which arepart of the Revised Shapely-Ames (RSA) Catalog or the CfA redshiftsample contain unresolved continuum sources at 1.6 μm. All but acouple of the Seyfert 1.0-1.9 galaxies display unresolved continuumsources. The unresolved sources have fluxes of order 1 mJy,near-infrared luminosities of order 1041 ergs s-1,and absolute magnitudes MH~-16. Comparison non-Seyfertgalaxies from the RSA Catalog display significantly fewer (~20%),somewhat lower luminosity nuclear sources, which could be due to compactstar clusters. We find that the luminosities of the unresolved Seyfert1.0-1.9 sources at 1.6 μm are correlated with [O III] λ5007and hard X-ray luminosities, implying that these sources are nonstellar.Assuming a spectral energy distribution similar to that of a Seyfert 2galaxy, we estimate that a few percent of local spiral galaxies containblack holes emitting as Seyferts at a moderate fraction,~10-1-10-4, of their Eddington luminosities. Wefind no strong correlation between 1.6 μm fluxes and hard X-ray or [OIII] λ5007 fluxes for the pure Seyfert 2.0 galaxies. Thesegalaxies also tend to have lower 1.6 μm luminosities compared to theSeyfert 1.0-1.9 galaxies of similar [O III] luminosity. Either largeextinctions (AV~20-40) are present toward theircontinuum-emitting regions or some fraction of the unresolved sources at1.6 μm are compact star clusters. With increasing Seyfert type thefraction of unresolved sources detected at 1.6 μm and the ratio of1.6 μm to [O III] fluxes tend to decrease. These trends areconsistent with the unification model for Seyfert 1 and 2 galaxies.
| The Frequency of Active and Quiescent Galaxies with Companions: Implications for the Feeding of the Nucleus
We analyze the idea that nuclear activity, either active galactic nuclei(AGNs) or star formation, can be triggered by interactions by studyingthe percentage of active, H II, and quiescent galaxies with companions.Our sample was selected from the Palomar survey and avoids selectionbiases faced by previous studies. This sample was split into fivedifferent groups, Seyfert galaxies, LINERs, transition galaxies, H IIgalaxies, and absorption-line galaxies. The comparison between the localgalaxy density distributions of the different groups showed that in mostcases there is no statistically significant difference among galaxies ofdifferent activity types, with the exception that absorption-linegalaxies are seen in higher density environments, since most of them arein the Virgo Cluster. The comparison of the percentage of galaxies withnearby companions showed that there is a higher percentage of LINERs,transition galaxies, and absorption-line galaxies with companions thanSeyfert and H II galaxies. However, we find that when we consider onlygalaxies of similar morphological types (elliptical or spiral), there isno difference in the percentage of galaxies with companions amongdifferent activity types, indicating that the former result was due tothe morphology-density effect. In addition, only small differences arefound when we consider galaxies with similar Hα luminosities. Thecomparison between H II galaxies of different Hα luminositiesshows that there is a significantly higher percentage of galaxies withcompanions among H II galaxies with L(Hα)>1039 ergss-1 than among those with L(Hα)<=1039ergs s-1, indicating that interactions increase the amount ofcircumnuclear star formation, in agreement with previous results. Thefact that we find that galaxies of different activity types have thesame percentage of companions suggests that interactions betweengalaxies is not a necessary condition to trigger the nuclear activity inAGNs. We compare our results with previous ones and discuss theirimplications.
| The Ursa Major cluster of galaxies. IV. HI synthesis observations
In this data paper we present the results of an extensive 21 cm-linesynthesis imaging survey of 43 spiral galaxies in the nearby Ursa Majorcluster using the Westerbork Synthesis Radio Telescope. Detailedkinematic information in the form of position-velocity diagrams androtation curves is presented in an atlas together with HI channel maps,21 cm continuum maps, global HI profiles, radial HI surface densityprofiles, integrated HI column density maps, and HI velocity fields. Therelation between the corrected global HI linewidth and the rotationalvelocities Vmax and Vflat as derived from therotation curves is investigated. Inclination angles obtained from theoptical axis ratios are compared to those derived from the inclined HIdisks and the HI velocity fields. The galaxies were not selected on thebasis of their HI content but solely on the basis of their clustermembership and inclination which should be suitable for a kinematicanalysis. The observed galaxies provide a well-defined, volume limitedand equidistant sample, useful to investigate in detail the statisticalproperties of the Tully-Fisher relation and the dark matter halos aroundthem.
| 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.
| Hubble Space Telescope WFPC2 Imaging of a Sample of Early-Type Seyfert Galaxies
We have defined a complete sample comprising all 14 Seyfert galaxies inearly-type (E, S0, Sa) host galaxies with apparent magnitudemv<14.5 mag and recessional velocity cz<3000 kms-1. This paper presents Hubble Space Telescope (HST) imagingobservations of 12 of them, the other two having been observedpreviously with HST. The observations are of the [O III] λ5007and [N II] λλ6548, 6583+Hα emission lines and theiradjacent continua (centered near 5500 and 8000 Å). We find thatall the galaxies in our sample display prominent nuclear dust features.In some objects, the dust strongly influences the morphology of thestarlight and ionized gas. Despite the restriction to early-typegalaxies, five (possibly six) galaxies of the 14 have a significant (ifnot dominant) part of their [N II]+Hα emission originating in H IIregions. This result supports the notion that the Seyfert phenomenontends to be associated with ongoing star formation. Based onobservations with the NASA/ESA Hubble Space Telescope obtained at theSpace Telescope Science Institute, which is operated by the Associationof Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.
| Spectrophotometry of Nearby Field Galaxies: The Data
We have obtained integrated and nuclear spectra as well as U, B, Rsurface photometry for a representative sample of 196 nearby galaxies.These galaxies span the entire Hubble sequence in morphological type, aswell as a wide range of luminosities (MB=-14 to -22). Here wepresent the spectrophotometry for these galaxies. The selection of thesample and the U, B, R surface photometry is described in a companionpaper. Our goals for the project include measuring the current starformation rates and metallicities of these galaxies, and elucidatingtheir star formation histories, as a function of luminosity andmorphology. We thereby extend the work of Kennicutt to lower luminositysystems. We anticipate that our study will be useful as a benchmark forstudies of galaxies at high redshift. We describe the observing, datareduction, and calibration techniques and demonstrate that ourspectrophotometry agrees well with that of Kennicutt. The spectra spanthe range 3550-7250 Å at a resolution (FWHM) of ~6 Å andhave an overall relative spectrophotometric accuracy of ~+/-6%. Wepresent a spectrophotometric atlas of integrated and nuclear rest-framespectra as well as tables of equivalent widths and synthetic colors. Theatlas and tables of measurements will be made available electronically.We study the correlations of galaxy properties determined from thespectra and images. Our findings include: (1) galaxies of a givenmorphological class display a wide range of continuum shapes andemission-line strengths if a broad range of luminosities are considered,(2) emission-line strengths tend to increase and continua tend to getbluer as the luminosity decreases, and (3) the scatter on the generalcorrelation between nuclear and integrated Hα emission-linestrengths is large.
| Surface Photometry of Nearby Field Galaxies: The Data
We have obtained integrated spectra and multifilter photometry for arepresentative sample of ~200 nearby galaxies. These galaxies span theentire Hubble sequence in morphological type, as well as a wide range ofluminosities (MB=-14 to -22) and colors (B-R=0.4-1.8). Herewe describe the sample selection criteria and the U, B, R surfacephotometry for these galaxies. The spectrophotometric results will bepresented in a companion paper. Our goals for the project includemeasuring the current star formation rates and metallicity of thesegalaxies, and elucidating their star formation histories, as a functionof luminosity and morphology. We thereby extend the work of Kennicutt tolower luminosity systems. We anticipate that our study will be useful asa benchmark for studies of galaxies at high redshift. We discuss theobserving, data reduction, and calibration techniques and show that ourphotometry agrees well with previous work in those cases in whichearlier data are available. We present an atlas of images, radialsurface brightness profiles, and color profiles as well as tables ofderived parameters. The atlas and tables of measurements will be madeavailable electronically. We study the correlations of galaxy propertiesdetermined from the galaxy images. Our findings include the following:(1) colors determined within the effective radius correlate better withmorphological type than with MB and (2) 50% of thelow-luminosity galaxies are bluest in their centers.
| 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.
| ASCA Observations of ``Type 2'' LINERs: Evidence for a Stellar Source of Ionization
We present ASCA observations of low-ionization nuclear emission-lineregions (LINERs) without broad Hα emission in their opticalspectra. The sample of ``type 2'' LINERs consists of NGC 404, 4111,4192, 4457, and 4569. We have detected X-ray emission from all theobjects except for NGC 404; among the detected objects are two so-calledtransition objects (NGC 4192 and NGC 4569), which have been postulatedto be composite nuclei having both an H II region and a LINER component.The images of NGC 4111 and NGC 4569 in the soft (0.5-2 keV) and hard(2-7 keV) X-ray bands are extended on scales of several kiloparsecs. TheX-ray spectra of NGC 4111, NGC 4457, and NGC 4569 are well fitted by atwo-component model that consists of soft thermal emission with kT~0.65keV and a hard component represented by a power law (photon index ~2) orby thermal bremsstrahlung emission (kT~several keV). The extended hardX-rays probably come from discrete sources, while the soft emission mostlikely originates from hot gas produced by active star formation in thehost galaxy. We have found no clear evidence for the presence of activegalactic nuclei (AGNs) in the sample. Using black hole masses estimatedfrom host galaxy bulge luminosities, we obtain an upper limit on theimplied Eddington ratios less than 5×10-5. If an AGNcomponent is the primary ionization source of the optical emissionlines, then it must be heavily obscured with a column densitysignificantly larger than 1023 cm-2, since theobserved X-ray luminosity is insufficient to drive the luminosities ofthe optical emission lines. Alternatively, the optical emission could beionized by a population of exceptionally hot stars. This interpretationis consistent with the small [O I] λ6300/Hα ratios observedin these sources, the ultraviolet spectral characteristics in the caseswhere such information exists, and the X-ray results reported here. Wealso analyze the X-ray properties of NGC 4117, a low-luminosity Seyfert2 galaxy serendipitously observed in the field of NGC 4111.
| Arcsecond Positions of UGC Galaxies
We present accurate B1950 and J2000 positions for all confirmed galaxiesin the Uppsala General Catalog (UGC). The positions were measuredvisually from Digitized Sky Survey images with rms uncertaintiesσ<=[(1.2")2+(θ/100)2]1/2,where θ is the major-axis diameter. We compared each galaxymeasured with the original UGC description to ensure high reliability.The full position list is available in the electronic version only.
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