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Multicomponent decompositions for a sample of S0 galaxies
We have estimated the bulge-to-total (B/T) light ratios in theKs band for a sample of 24 S0, S0/a and Sa galaxies byapplying a two-dimensional multicomponent decomposition method. For thedisc an exponential function is used, the bulges are fitted by aSérsic R1/n function and the bars and ovals aredescribed either by a Sérsic or a Ferrers function. In order toavoid non-physical solutions, preliminary characterization of thestructural components is made by inspecting the radial profiles of theorientation parameters and the low azimuthal wavenumber Fourieramplitudes and phases. In order to identify also the inner structures,unsharp masks were created: previously undetected inner spiral arms werefound in NGC 1415 and marginally in NGC 3941. Most importantly, we foundthat S0s have a mean K ratio of 0.24 +/- 0.11,which is significantly smaller than the mean R=0.6 generally reported in the literature. Also, the surface brightnessprofiles of the bulges in S0s were found to be more exponential-likethan generally assumed, the mean shape parameter of the bulge being= 2.1 +/- 0.7. We did not find examples of barred S0s lackingthe disc component, but we found some galaxies (NGC 718, 1452 and 4608)having a non-exponential disc in the bar region. To our knowledge, ourstudy is the first attempt to apply a multicomponent decompositionmethod for a moderately sized sample of early-type disc galaxies.
| Secular evolution of galactic discs: constraints on phase-space density
It has been argued in the past that bulges of galaxies could not beformed through collisionless secular evolution because that wouldviolate constraints on the phase-space density: the phase-space densityin bulges is several times larger than in the inner parts of discs. Weshow that these arguments against secular evolution are incorrect.Observations give estimates of the coarsely grained phase-spacedensities of galaxies,f'=ρs/σRσφσz,where ρs is the stellar density and σR,σφ and σz are the radial,tangential and vertical rms velocities of stars, respectively. Usinghigh-resolution N-body simulations, we study the evolution of f' instellar discs of Galaxy-size models. During the secular evolution, thediscs, which are embedded in live cold dark matter haloes, form a barand then a thick, dynamically hot, central mass concentration. Duringthe course of evolution f' declines at all radii. However, the declineis different in different parts of the disc. In the inner disc, f'(R)develops a valley with a minimum around the end of the central massconcentration. The final result is that the values of f' in the centralregions are significantly larger than those in the inner disc. Theminimum, which becomes deeper with time, seems to be due to a largephase mixing produced by the outer bar. We find that the shape and theamplitude of f'(R) for different simulations agree qualitatively withthe observed f'(R) in our Galaxy. Curiously enough, the fact that thecoarsely grained phase-space density of the bulge is significantlylarger than that of the inner disc turns out to be an argument in favourof secular formation of bulges, not against it.
| Structure and kinematics of edge-on galaxy discs - V. The dynamics of stellar discs
In earlier papers in this series we determined the intrinsic stellardisc kinematics of 15 intermediate- to late-type edge-on spiral galaxiesusing a dynamical modelling technique. The sample covers a substantialrange in maximum rotation velocity and deprojected face-on surfacebrightness, and contains seven spirals with either a boxy orpeanut-shaped bulge. Here we discuss the structural, kinematical anddynamical properties. From the photometry we find that intrinsicallymore flattened discs tend to have a lower face-on central surfacebrightness and a larger dynamical mass-to-light ratio. This observationsuggests that, at a constant maximum rotational velocity, lower surfacebrightness discs have smaller vertical stellar velocity dispersions.Although the individual uncertainties are large, we find from thedynamical modelling that at least 12 discs are submaximal. The averagedisc contributes 53 +/- 4 per cent to the observed rotation at 2.2 discscalelengths (hR), with a 1σ scatter of 15 per cent.This percentage becomes somewhat lower when effects of finite discflattening and gravity by the dark halo and the gas are taken intoaccount. Since boxy and peanut-shaped bulges are probably associatedwith bars, the result suggests that at 2.2hR the submaximalnature of discs is independent of barredness. The possibility remainsthat very high surface brightness discs are maximal, as these discs areunderrepresented in our sample. We confirm that the radial stellar discvelocity dispersion is related to the galaxy maximum rotationalvelocity. The scatter in this σ versus vmax relationappears to correlate with the disc flattening, face-on central surfacebrightness and dynamical mass-to-light ratio. Low surface brightnessdiscs tend to be more flattened and have smaller stellar velocitydispersions. The findings are consistent with the observed correlationbetween disc flattening and dynamical mass-to-light ratio and cangenerally be reproduced by the simple collapse theory for disc galaxyformation. Finally, the disc mass Tully-Fisher relation is offset fromthe maximum-disc scaled stellar mass Tully-Fisher relation of the UrsaMajor cluster. This offset, -0.3 dex in mass, is naturally explained ifthe discs of the Ursa Major cluster spirals are submaximal.
| Stellar Velocity Dispersion and Mass Estimation for Galactic Disks
Available velocity dispersion estimates for the old stellar populationof galactic disks at galactocentric distances r=2L (where L is thephotometric radial scale length of the disk) are used to determine thethreshold local surface density of disks that are stable againstgravitational perturbations. The mass of the disk Mdcalculated under the assumption of its marginal stability is comparedwith the total mass Mt and luminosity LB of thegalaxy within r=4L. We corroborate the conclusion that a substantialfraction of the mass in galaxies is probably located in their darkhalos. The ratio of the radial velocity dispersion to the circularvelocity increases along the sequence of galactic color indices anddecreases from the early to late morphological types. For most of thegalaxies with large color indices (B-V)0 > 0.75, whichmainly belong to the S0 type, the velocity dispersion exceedssignificantly the threshold value required for the disk to be stable.The reverse situation is true for spiral galaxies: the ratiosMd/LB for these agree well with those expected forevolving stellar systems with the observed color indices. This suggeststhat the disks of spiral galaxies underwent no significant dynamicalheating after they reached a quasi-equilibrium stable state.
| 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.
| Minor-axis velocity gradients in disk galaxies
We present the ionized-gas kinematics and photometry of a sample of 4spiral galaxies which are characterized by a zero-velocity plateau alongthe major axis and a velocity gradient along the minor axis,respectively. By combining these new kinematical data with thoseavailable in the literature for the ionized-gas component of the S0s andspirals listed in the Revised Shapley-Ames Catalog of Bright Galaxies werealized that about 50% of unbarred galaxies show a remarkable gasvelocity gradient along the optical minor axis. This fraction rises toabout 60% if we include unbarred galaxies with an irregular velocityprofile along the minor axis. This phenomenon is observed all along theHubble sequence of disk galaxies, and it is particularly frequent inearly-type spirals. Since minor-axis velocity gradients are unexpectedif the gas is moving onto circular orbits in a disk coplanar to thestellar one, we conclude that non-circular and off-plane gas motions arenot rare in the inner regions of disk galaxies.Based on observations carried out at the European Southern Observatoryin La Silla (Chile) (ESO 69.B-0706 and 70.B-0338), with the MultipleMirror Telescope which is a joint facility of the SmithsonianInstitution and the University of Arizona, and with the ItalianTelescopio Nazionale Galileo (AOT-5, 3-18) at the Observatorio del Roquede los Muchachos in La Palma (Spain).Table 1 is only available in electronic form athttp://www.edpsciences.org. Table 5 is only available in electronic format the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) orvia http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/416/507
| Disk-bulge decompositions of spiral galaxies in UBVRI
A sample of 26 bright spiral galaxies (Btot < 12.7) withlow to medium inclination and without a bar was observed with UBVRIfilters. The CAFOS focal reducer camera at the Calar Alto 2.2 mtelescope was used. The surface-brightness distributions were fittedusing a 2-dimensional algorithm with corresponding functions for thedisk- and bulge-structure. For the disks an exponential function wasused, for the bulges a Sérsic Rβ law, was appliedwith the concentration parameter β = 1/n as another fit variable.Correlations of the resulting structural parameters of disks and bulgesin UBVRI are investigated, giving clues to the formation history of thebulges.We confirm that the large and bright bulges of early-type spirals aresimilar to elliptical galaxies. They were probably formed prior to thedisks in a monolithic collapse or via early mergers. Late-type spiralshave tiny and faint bulges with disk-like profiles. These bulges wereprobably formed after the disk in secular evolution processes, e.g. froma disk instability. The comparison of the color indices of correspondingspirals and bulges with population synthesis computations support aboveformation scenarios.Tables 2-4 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/415/63
| The Hα galaxy survey. I. The galaxy sample, Hα narrow-band observations and star formation parameters for 334 galaxies
We discuss the selection and observations of a large sample of nearbygalaxies, which we are using to quantify the star formation activity inthe local Universe. The sample consists of 334 galaxies across allHubble types from S0/a to Im and with recession velocities of between 0and 3000 km s-1. The basic data for each galaxy are narrowband H\alpha +[NII] and R-band imaging, from which we derive starformation rates, H\alpha +[NII] equivalent widths and surfacebrightnesses, and R-band total magnitudes. A strong correlation is foundbetween total star formation rate and Hubble type, with the strongeststar formation in isolated galaxies occurring in Sc and Sbc types. Moresurprisingly, no significant trend is found between H\alpha +[NII]equivalent width and galaxy R-band luminosity. More detailed analyses ofthe data set presented here will be described in subsequent papers.Based on observations made with the Jacobus Kapteyn Telescope operatedon the island of La Palma by the Isaac Newton Group in the SpanishObservatorio del Roque de los Muchachos of the Instituto deAstrofísica de Canarias.The full version of Table \ref{tab3} is available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/414/23 Reduced image datafor this survey can be downloaded fromhttp://www.astro.livjm.ac.uk/HaGS/
| Circumnuclear Dust in Nearby Active and Inactive Galaxies. II. Bars, Nuclear Spirals, and the Fueling of Active Galactic Nuclei
We present a detailed study of the relation between circumnuclear dustmorphology, host-galaxy properties, and nuclear activity in nearbygalaxies. We use our sample of 123 nearby galaxies withvisible-near-infrared color maps from the Hubble Space Telescope tocreate well-matched, ``paired'' samples of 28 active and 28 inactivegalaxies, as well as 19 barred and 19 unbarred galaxies, that have thesame host-galaxy properties. Comparison of the barred and unbarredgalaxies shows that grand-design nuclear dust spirals are found only ingalaxies with a large-scale bar. These nuclear dust spirals, which arepresent in approximately one-third of all barred galaxies, also appearto be connected to the dust lanes along the leading edges of thelarge-scale bars. Grand-design nuclear spirals are more common thaninner rings, which are present in only a small minority of the barredgalaxies. Tightly wound nuclear dust spirals, in contrast, show a strongtendency to avoid galaxies with large-scale bars. Comparison of theactive galactic nuclei (AGNs)and inactive samples shows that nucleardust spirals, which may trace shocks and angular momentum dissipation inthe interstellar medium, occur with comparable frequency in both activeand inactive galaxies. The only difference between the active andinactive galaxies is that several inactive galaxies appear to completelylack dust structure in their circumnuclear region, while none of theAGNs lack this structure. The comparable frequency of nuclear spirals inactive and inactive galaxies, combined with previous work that finds nosignificant difference in the frequency of bars or interactions betweenwell-matched active and inactive galaxies, suggests that no universalfueling mechanism for low-luminosity AGNs operates at spatial scalesgreater than a ~100 pc radius from the galactic nuclei. The similaritiesof the circumnuclear environments of active and inactive galaxiessuggest that the lifetime of nuclear activity is less than thecharacteristic inflow time from these spatial scales. Anorder-of-magnitude estimate of this inflow time is the dynamicaltimescale. This sets an upper limit of several million years to thelifetime of an individual episode of nuclear activity.Based on observations with the NASA/ESA Hubble Space Telescope obtainedat the Space Telescope Science Institute, which is operated by theAssociation of Universities for Research in Astronomy, Inc., under NASAcontract NAS5-26555.
| Observational Constraints on Disk Heating as a Function of Hubble Type
Current understanding of the secular evolution of galactic diskssuggests that this process is dominated by two or more ``heating''mechanisms, which increase the random motions of stars in the disk. Inparticular, the gravitational influence of giant molecular clouds andirregularities in the spiral potential have been proposed to explain theobserved velocity dispersions in the solar neighborhood. Each of thesemechanisms acts on different components of the stellar velocity, whichaffects the ratio σz/σR of thevertical and radial components differently. Since the relative strengthsof giant molecular clouds and spiral irregularities vary with Hubbletype, a study of σz/σR as function ofHubble type has the potential to provide strong constraints on diskheating mechanisms. We present major- and minor-axis stellar kinematicsfor four spiral galaxies of Hubble type from Sa to Sbc and use the datato infer the ratios σz/σR in thegalaxy disks. We combine the results with those for two galaxies studiedpreviously with the same technique, with Milky Way data, and withestimates obtained using photometric techniques. The results show thatσz/σR is generally in the range0.5-0.8. There is a marginally significant trend of decreasingσz/σR with advancing Hubble type,consistent with the predictions of disk heating theories. However, theerrors on individual measurements are large, and the absence of anytrend is consistent with the data at the 1 σ level. As aby-product of our study, we find that three of the four galaxies in oursample have a central drop in their stellar line-of-sight velocitydispersion, a phenomenon that is increasingly observed in spiralgalaxies.
| 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?
| 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.
| Bar Galaxies and Their Environments
The prints of the Palomar Sky Survey, luminosity classifications, andradial velocities were used to assign all northern Shapley-Ames galaxiesto either (1) field, (2) group, or (3) cluster environments. Thisinformation for 930 galaxies shows no evidence for a dependence of barfrequency on galaxy environment. This suggests that the formation of abar in a disk galaxy is mainly determined by the properties of theparent galaxy, rather than by the characteristics of its environment.
| Detailed Structural Decomposition of Galaxy Images
We present a two-dimensional fitting algorithm (GALFIT) designed toextract structural components from galaxy images, with emphasis onclosely modeling light profiles of spatially well-resolved, nearbygalaxies observed with the Hubble Space Telescope. Our algorithmimproves on previous techniques in two areas: by being able tosimultaneously fit a galaxy with an arbitrary number of components andwith optimization in computation speed, suited for working on largegalaxy images. We use two-dimensional models such as the ``Nuker'' law,the Sérsic (de Vaucouleurs) profile, an exponential disk, andGaussian or Moffat functions. The azimuthal shapes are generalizedellipses that can fit disky and boxy components. Some potentialapplications of our program include: standard modeling of global galaxyprofiles; extracting bars, stellar disks, double nuclei, and compactnuclear sources; and measuring absolute dust extinction or surfacebrightness fluctuations after removing the galaxy model. When examinedin detail, we find that even simple looking galaxies generally requireat least three components to be modeled accurately, rather than the oneor two components more often employed. Many galaxies with complexisophotes, ellipticity changes, and position angle twists can be modeledaccurately in two dimensions. We illustrate this by way of 11 casestudies, which include regular and barred spiral galaxies, highly diskylenticular galaxies, and elliptical galaxies displaying various levelsof complexities. A useful extension of this algorithm is to accuratelyextract nuclear point sources in galaxies. We compare two-dimensionaland one-dimensional extraction techniques on simulated images ofgalaxies having nuclear slopes with different degrees of cuspiness, andwe then illustrate the application of the program to several examples ofnearby galaxies with weak nuclei. Based on observations with theNASA/ESA Hubble Space Telescope, obtained at the Space Telescope ScienceInstitute, which is operated by the Association of Universities forResearch in Astronomy (AURA), Inc., under NASA contract NAS 5-26555.
| Spiral Galaxies with HST/NICMOS. II. Isophotal Fits and Nuclear Cusp Slopes
We present surface brightness profiles for 56 of the 78 spiral galaxiesobserved in the HST/NICMOS2 F160W snapshot survey introduced in Paper Iof this series, as well as surface brightness profiles for 23 objectsout of the 41 that were also observed in the F110W filter. We fit thesesurface brightness profiles with the Nuker law of Lauer et al. and usethe smooth analytical descriptions of the data to compute the averagenuclear stellar cusp slopes <γ> in the 0.1"-0.5" radialrange. Our main result is the startling similarity between the nuclearstellar cusp slopes <γ> in the near-infrared compared withthose derived in the visual passband. This similarity has severalimplications: (1) Despite the significant local color variations thatare found in the nuclear regions of spirals and that are documented inPaper I, there are typically little or no optical-NIR global colorgradients, and thus no global stellar population variations, inside~50-100 pc from the nucleus in nearby spirals. (2) The large observedrange of the strength of the nuclear stellar cusps seen in the HSToptical study of spiral galaxies reflects a physical difference betweengalaxies and is not an artifact caused by nuclear dust and/or recentstar formation. (3) The dichotomy between R1/4 bulges, withsteep nuclear stellar cusps <γ>~1, and exponential bulges,with shallow nuclear stellar cusps <γ><0.3, is also notan artifact of the effects of dust or recent star formation. (4) Thepresence of a surrounding massive disk appears to have no effect on therise of the stellar density distribution within the innermost hundredparsecs of the R1/4 spheroids. These results imply abreakdown within the family of exponential bulges of the nuclear versusglobal relationships that have been found for the R1/4spheroids. Such a breakdown is likely to have significant implicationsconcerning the formation of exponential bulges and their connection withthe R1/4 spheroids. Based on observations with the NASA/ESAHubble Space Telescope, obtained at the Space Telescope ScienceInstitute, which is operated by the Association of Universities forResearch in Astronomy, Inc., under NASA contract NAS 5-26555.
| Spiral Galaxies with HST/NICMOS. I. Nuclear Morphologies, Color Maps, and Distinct Nuclei
This is the first of two papers where we present the analysis of anHST/NICMOS2 near-infrared (NIR) snapshot survey in the F160W (H) filterfor a sample of 78 spiral galaxies selected from the UGC and ESOLVcatalogs. For 69 of these objects we provide nuclear color informationderived by combining the H data either with additional NICMOS F110W (J)images or with V WFPC2/HST data. Here we present the NIR images and theoptical-NIR color maps. We focus our attention on the properties of thephotometrically distinct ``nuclei'' which are found embedded in most ofthe galaxies and provide measurements of their half-light radii andmagnitudes in the H (and when available in the J) band. We find that (1)in the NIR the nuclei embedded in the bright early- to intermediate-typegalaxies span a much larger range in brightness than the nuclei whichare typically found embedded in bulgeless late-type disks: the nucleiembedded in the early- to intermediate-type galaxies reach, on thebright end, values up to HAB~-17.7 mag; (2) nuclei are foundin both nonbarred and barred hosts, in large-scale (>~1 kpc) as wellas in nuclear (up to a few 100 pc) bars; (3) there is a significantincrease in half-light radius with increasing luminosity of the nucleusin the early/intermediate types (a decade in radius for ~8 magbrightening), a correlation which was found in the V band and which isalso seen in the NIR data; (4) the nuclei of early/intermediate-typespirals cover a large range of optical-NIR colors, from V-H~-0.5 to 3.Some nuclei are bluer and others redder than the surroundinggalaxy,indicating the presence of activity or reddening by dust in many ofthese systems; (5) someearly/intermediate nuclei are elongated and/orslightly offset from the isophotal center of the host galaxy. Onaverage, however, these nuclei appear as centered, star-cluster-likestructures similar to those whichare found in the late-type disks. Basedon observations with the NASA/ESA Hubble Space Telescope, obtained atthe Space Telescope Science Institute, which is operated by Associationof Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.
| Rotation curves and metallicity gradients from HII regions in spiral galaxies
In this paper we study long slit spectra in the region of Hαemission line of a sample of 111 spiral galaxies with recognizable andwell defined spiral morphology and with a well determined environmentalstatus, ranging from isolation to non-disruptive interaction withsatellites or companions. The form and properties of the rotation curvesare considered as a function of the isolation degree, morphological typeand luminosity. The line ratios are used to estimate the metallicity ofall the detected HII regions, thus producing a composite metallicityprofile for different types of spirals. We have found that isolatedgalaxies tend to be of later types and lower luminosity than theinteracting galaxies. The outer parts of the rotation curves of isolatedgalaxies tend to be flatter than in interacting galaxies, but they showsimilar relations between global parameters. The scatter of theTully-Fisher relation defined by isolated galaxies is significantlylower than that of interacting galaxies. The [NII]/Hα ratios, usedas a metallicity indicator, show a clear trend between Z andmorphological type, t, with earlier spirals showing higher ratios; thistrend is tighter when instead of t the gradient of the inner rotationcurve, G, is used; no trend is found with the change in interactionstatus. The Z-gradient of the disks depends on the type, being almostflat for early spirals, and increasing for later types. The[NII]/Hα ratios measured for disk HII regions of interactinggalaxies are higher than for normal/isolated objects, even if all thegalaxy families present similar distributions of Hα EquivalentWidth. Tables 3 and 4 and Figs. 6, 7 and 21 are only available inelectronic form at http://www.edpsciences.org. Table 5 is only availablein electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/393/389 Based on dataobtained Asiago/Ekar Observatory. Also based on observations made withINT operated on the island of La Palma by ING in the SpanishObservatorio del Roque de Los Muchachos of the Instituto deAstrofísica de Canarias.
| Local velocity field from sosie galaxies. I. The Peebles' model
Pratton et al. (1997) showed that the velocity field around clusterscould generate an apparent distortion that appears as tangentialstructures or radial filaments. In the present paper we determine theparameters of the Peebles' model (1976) describing infall of galaxiesonto clusters with the aim of testing quantitatively the amplitude ofthis distortion. The distances are determined from the concept of sosiegalaxies (Paturel 1984) using 21 calibrators for which the distanceswere recently calculated from two independent Cepheid calibrations. Weuse both B and I-band magnitudes. The Spaenhauer diagram method is usedto correct for the Malmquist bias. We give the equations for theconstruction of this diagram. We analyze the apparent Hubble constant indifferent regions around Virgo and obtain simultaneously the Local Groupinfall and the unperturbed Hubble constant. We found:[VLG-infall = 208 ± 9 km s-1] [\log H =1.82 ± 0.04 (H ≈ 66 ± 6 km s-1Mpc-1).] The front side and backside infalls can be seenaround Virgo and Fornax. In the direction of Virgo the comparison ismade with the Peebles' model. We obtain: [vinfall} =CVirgo/r0.9 ± 0.2] withCVirgo=2800 for Virgo and CFornax=1350 for Fornax,with the adopted units (km s-1 and Mpc). We obtain thefollowing mean distance moduli: [μVirgo=31.3 ± 0.2(r=18 Mpc )] [μFornax=31.7 ± 0.3 (r=22 Mpc). ] Allthese quantities form an accurate and coherent system. Full Table 2 isonly available in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/393/57
| Neutral hydrogen in dwarf galaxies. I. The spatial distribution of HI
This paper is the first in a series presenting a sample of 30 late-typedwarf galaxies, observed with the Westerbork Synthesis Radio Telescope(WSRT) in the 21-cm line of neutral atomic hydrogen (HI). The sampleitself, the HI content of and the HI distribution in the sample galaxiesare briefly discussed. Four sample galaxies were also detected in thecontinuum.
| Star Formation in Extragalactic HII Regions. Determination of Parameters of the Initial Mass Function
A method for using the colors of star-forming complexes to derive theslope and upper mass limit of the initial mass function (IMF) and theage of the complex is proposed in the framework of syntheticevolutionary models of star-cluster populations. The star-formationparameters of 105 complexes in 20 spiral and irregular galaxies aredetermined. The IMF slopes in different star-forming complexes differappreciably, and their dependence on the luminosities and masses of thecomplexes is derived. The duration of the star-formation periodincreases with the luminosity of the complex, and complexes with longerstar-formation periods are richer in metals. The slope of the integratedIMF in a Galaxy depends on the mass spectrum of its complexes, and theupper mass limit of the IMF is lower in early-type spirals.
| 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.
| Hubble Space Telescope Optical-Near-Infrared Colors of Nearby R1/4 and Exponential Bulges
We have analyzed V, H, and J Hubble Space Telescope (HST) images for asample of early- to late-type spiral galaxies and have reportedelsewhere the statistical frequency of R1/4-law andexponential bulges in our sample as a function of Hubble type and thefrequency of occurrence and structural properties of the resolvedcentral nuclei hosted by intermediate- to late-type bulges and disks(see references in the text). Here we use these data to show thefollowing:1.The V-H color distribution of the R1/4 bulge peaksaround ~1.3, with a sigma Δ(V-H)~0.1 mag. Assuming asolar metallicity, these values correspond to stellar ages of ~6+/-3Gyr. In contrast, the V-H color distribution of the exponential bulgespeaks at and has a sigma Δ(V-H)~0.4 mag. Thislikely implies significantly smaller ages and/or lower metallicities for(a significant fraction of the stars in) the exponential bulges comparedto the R1/4-law spheroids. 2.Most of the central nuclei hosted by the exponential bulges haveV-H and J-H colors that are compatible with relatively unobscuredstellar populations. Assuming no or little dust effects, ages >~1 Gyrare suggested for these nuclei, which in turn imply masses of about afew 106 to a few 107 Msolar, i.e.,sufficient to dissolve progenitor bars with masses consistent with thoseinferred for the exponential bulges by their luminosities.3. While different bulge-nucleus pairscover a large range of V-H colors, each bulge-nucleus pair has quitesimilar V-H colors and thus possibly similar stellar populations.The HST photometric analysis suggests thatexponential-type bulge formation is taking place in the local universeand that this process is consistent with being the outcome of secularevolution processes within the disks. The structures that are currentlyformed inside the disks are quite dissimilar from the oldelliptical-like spheroids that are hosted by the early-type disks. Basedon observations with the NASA/ESA Hubble Space Telescope, obtained atthe Space Telescope Science Institute, which is operated by Associationof Universities for Research in Astronomy, Inc. (AURA), under NASAcontract NAS 5-26555.
| 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.
| The O/H Distribution in NGC 7479: Evidence for a Minor Merger Event
Results of emission-line spectrophotometry of 68 H II regions in thestrongly barred spiral galaxy NGC 7479 obtained with the Multi-ObjectSpectrograph at the Canada-France-Hawaii Telescope are presented. Theaverage nebular extinction across the galaxy disk is Av~1.1mag. There is a radial trend (-0.042+/-0.010 mag kpc-1) inthe values of reddening suggesting a global difference of about 1.1 magbetween the inner and outer parts of the galaxy. All the H II regionsfall within the well-defined sequences of normal H II regions in thestandard diagnostic diagrams [O III]/Hβ versus[N II]/Hα, and [O III]/Hβ versus[O I]/Hα. The values of excitation ([OIII]/Hβ) of the regions located in the western arm are higher byabout 0.4 dex compared to those of the eastern arm and central regions.There is evidence that the ionization parameter is higher and theelectronic density lower in these regions. The global O/H abundancegradient is shallow (~-0.025+/-0.005 dex kpc-1), in agreementwith what is found for galaxies with a strong bar. No break is seen inthe O/H radial gradient. The azimuthal O/H variations in the disk aresmall at less than 0.3 dex. These results are discussed in the frameworkof a merger in which NGC 7479 captured a small galaxy about3×108 yr ago.
| The Variability of Seyfert 1.8 and 1.9 Galaxies at 1.6 Microns
We present a study of Seyfert 1.5-2.0 galaxies observed at two epochswith the Hubble Space Telescope (HST) at 1.6 μm. We find thatunresolved nuclear emission from nine of 14 nuclei varies at the levelof 10%-40% on timescales of 0.7-14 months, depending upon the galaxy. Acontrol sample of Seyfert galaxies lacking unresolved sources andgalaxies lacking Seyfert nuclei show less than 3% instrumental variationin equivalent aperture measurements. This proves that the unresolvedsources are nonstellar and associated with the central parsecs of activegalactic nuclei. Unresolved sources in Seyfert 1.8 and 1.9 galaxies arenot usually detected in HST optical surveys; however, high angularresolution infrared observations will provide a way to measure timedelays in these galaxies.
| A Subarcsecond Resolution Near-Infrared Study of Seyfert and ``Normal'' Galaxies. II. Morphology
We present a detailed study of the bar fraction in the CfA sample ofSeyfert galaxies and in a carefully selected control sample of nonactivegalaxies to investigate the relation between the presence of bars and ofnuclear activity. To avoid the problems related to bar classification inthe Third Reference Catalogue (RC3), e.g., subjectivity, low resolution,and contamination by dust, we have developed an objective barclassification method, which we conservatively apply to our newsubarcsecond resolution near-infrared (NIR) imaging data set discussedin the first paper in this series. We are able to use stringent criteriabased on radial profiles of ellipticity and major axis position angle todetermine the presence of a bar and its axial ratio. Concentrating onnoninteracting galaxies in our sample for which morphologicalinformation can be obtained, we find that Seyfert hosts are barred moreoften (79%+/-7.5%) than the nonactive galaxies in our control sample(59%+/-9%), a result which is at the ~2.5 σ significance level.The fraction of nonaxisymmetric hosts becomes even larger wheninteracting galaxies are taken into account. We discuss the implicationsof this result for the fueling of central activity by large-scale bars.This paper improves on previous work by means of imaging at higherspatial resolution and by the use of a set of stringent criteria for barpresence and confirms that the use of NIR is superior to optical imagingfor detection of bars in disk galaxies.
| The Milky Way as a galaxy.
Not Available
| La transformation des galaxies spirales
Not Available
| 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.
| A Subarcsecond-Resolution Near-Infrared Study of Seyfert and ``Normal'' Galaxies. I. Imaging Data
We present new high-resolution near-infrared observations in the J, H,and K bands, obtained to study the properties of Seyfert host galaxies.The data set consists of images in the three bands of practically theentire CfA sample of Seyfert galaxies, and K-band images of a controlsample of nonactive, ``normal,'' galaxies, matched to the Seyfert samplein the distribution of type and inclination. The spatial resolution andsampling of the new images is a factor of 2 better than previouslypublished K-band data. In this paper, we present the data in the form ofprofiles of surface brightness and color, ellipticity and major axisposition angle, as well as gray-scale maps of surface brightness in H orK and both J-H and H-K colors. We compare our surface brightness andcolor profiles with the literature and find good agreement. Our data arediscussed in detail in three subsequent publications, where we analyzethe morphologies of Seyfert and normal hosts, quantify the strength ofnonaxisymmetric features in disks and their relationship to nuclearactivity, address the question of bar fraction in Seyferts and normalgalaxies, and analyze the color information in the framework of emissionmechanisms in Seyfert 1's and 2's and in nonactive galaxies.
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