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Публикации по объекту
HI content in galaxies in loose groups
Gas deficiency in cluster spirals is well known and ram-pressurestripping is considered the main gas removal mechanism. In some compactgroups too gas deficiency is reported. However, gas deficiency in loosegroups is not yet well established. Lower dispersion of the membervelocities and the lower density of the intragroup medium in small loosegroups favour tidal stripping as the main gas removal process in them.Recent releases of data from the HI Parkes All-Sky Survey (HIPASS) andcatalogues of nearby loose groups with associated diffuse X-ray emissionhave allowed us to test this notion. In this paper, we address thefollowing questions: (i) do galaxies in groups with diffuse X-rayemission statistically have lower gas content compared to the ones ingroups without diffuse X-ray emission? (ii) does HI deficiency vary withthe X-ray luminosity, LX, of the loose group in a systematicway? We find that (i) galaxies in groups with diffuse X-ray emission, onaverage, are HI deficient, and have lost more gas compared to those ingroups without X-ray emission; the latter are found not to havesignificant HI deficiency; (ii) no systematic dependence of the HIdeficiency with LX is found. Ram-pressure-assisted tidalstripping and evaporation by thermal conduction are the two possiblemechanisms to account for this excess gas loss.
| Discovery of counter-rotating gas in the galaxies NGC 1596 and 3203 and the incidence of gas counter-rotation in S0 galaxies
We have identified two new galaxies with gas counter-rotation (NGC 1596and 3203) and have confirmed similar behaviour in another one (NGC 128),this using results from separate studies of the ionized-gas and stellarkinematics of a well-defined sample of 30 edge-on disc galaxies. Gascounter-rotators thus represent 10 +/- 5 per cent of our sample, but thefraction climbs to 21 +/- 11 per cent when only lenticular (S0) galaxiesare considered and to 27 +/- 13 per cent for S0 galaxies with detectedionized gas only. Those fractions are consistent with but slightlyhigher than previous studies. A compilation from well-defined studies ofS0 galaxies in the literature yields fractions of 15 +/- 4 and 23 +/- 5per cent, respectively. Although mainly based on circumstantialevidence, we argue that the counter-rotating gas originates primarilyfrom minor mergers and tidally induced transfer of material from nearbyobjects. Assuming isotropic accretion, twice those fractions of objectsmust have undergone similar processes, underlining the importance of(minor) accretion for galaxy evolution. Applications of gascounter-rotators to barred galaxy dynamics are also discussed.
| A radio census of nuclear activity in nearby galaxies
In order to determine the incidence of black hole accretion-drivennuclear activity in nearby galaxies, as manifested by their radioemission, we have carried out a high-resolution Multi-ElementRadio-Linked Interferometer Network (MERLIN) survey of LINERs andcomposite LINER/Hii galaxies from a complete magnitude-limited sample ofbright nearby galaxies (Palomar sample) with unknown arcsecond-scaleradio properties. There are fifteen radio detections, of which three arenew subarcsecond-scale radio core detections, all being candidate AGN.The detected galaxies supplement the already known low-luminosity AGN -low-luminosity Seyferts, LINERs and composite LINER/Hii galaxies - inthe Palomar sample. Combining all radio-detected Seyferts, LINERs andcomposite LINER/Hii galaxies (LTS sources), we obtain an overall radiodetection rate of 54% (22% of all bright nearby galaxies) and weestimate that at least ~50% (~20% of all bright nearby galaxies) aretrue AGN. The radio powers of the LTS galaxies allow the construction ofa local radio luminosity function. By comparing the luminosity functionwith those of selected moderate-redshift AGN, selected from the 2dF/NVSSsurvey, we find that LTS sources naturally extend the RLF of powerfulAGN down to powers of about 10 times that of Sgr A*.
| 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.
| Inner-truncated Disks in Galaxies
We present an analysis of the disk brightness profiles of 218 spiral andlenticular galaxies. At least 28% of disk galaxies exhibit innertruncations in these profiles. There are no significant trends oftruncation incidence with Hubble type, but the incidence among barredsystems is 49%, more than 4 times that for nonbarred galaxies. However,not all barred systems have inner truncations, and not allinner-truncated systems are currently barred. Truncations represent areal dearth of disk stars in the inner regions and are not an artifactof our selection or fitting procedures nor the result of obscuration bydust. Disk surface brightness profiles in the outer regions are wellrepresented by simple exponentials for both truncated and nontruncateddisks. However, truncated and nontruncated systems have systematicallydifferent slopes and central surface brightness parameters for theirdisk brightness distributions. Truncation radii do not appear tocorrelate well with the sizes or brightnesses of the bulges. Thissuggests that the low angular momentum material apparently missing fromthe inner disk was not simply consumed in forming the bulge population.Disk parameters and the statistics of bar orientations in our sampleindicate that the missing stars of the inner disk have not simply beenredistributed azimuthally into bar structures. The sharpness of thebrightness truncations and their locations with respect to othergalactic structures suggest that resonances associated with diskkinematics, or tidal interactions with the mass of bulge stars, might beresponsible for this phenomenon.
| Ionized gas and stellar kinematics of seventeen nearby spiral galaxies
Ionized gas and stellar kinematics have been measured along the majoraxes of seventeen nearby spiral galaxies of intermediate to latemorphological type. We discuss the properties of each sample galaxy,distinguishing between those characterized by regular or peculiarkinematics. In most of the observed galaxies, ionized gas rotates morerapidly than stars and has a lower velocity dispersion, as is to beexpected if the gas is confined in the disc and supported by rotationwhile the stars are mostly supported by dynamical pressure. In a fewobjects, gas and stars show almost the same rotational velocity and lowvelocity dispersion, suggesting that their motion is dominated byrotation. Incorporating the spiral galaxies studied by Bertola et al.(\cite{Bertola1996}), Corsini et al. (\cite{Corsini1999},\cite{Corsini2003}) and Vega Beltrán et al. (\cite{Vega2001}) wehave compiled a sample of 50 S0/a-Scd galaxies, for which the major-axiskinematics of the ionized gas and stars have been obtained with the samespatial (≈1'') and spectral (≈50 km;s-1) resolution,and measured with the same analysis techniques. This allowed us toaddress the frequency of counter-rotation in spiral galaxies. It turnsout that less than 12% and less than 8% (at the 95% confidence level) ofthe sample galaxies host a counter-rotating gaseous and stellar disc,respectively. The comparison with S0 galaxies suggests that theretrograde acquisition of small amounts of external gas gives rise tocounter-rotating gaseous discs only in gas-poor S0s, while in gas-richspirals the newly acquired gas is swept away by the pre-existing gas.Counter-rotating gaseous and stellar discs in spirals are formed onlyfrom the retrograde acquisition of large amounts of gas exceeding thatof pre-existing gas, and subsequent star formation, respectively.Based on observations carried out at the European Southern Observatory,La Silla (Chile) (ESO 56.A-0684 and 57.A-0569).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/424/447Full Fig. \ref{fig:kinematics} and Figs. \ref{fig:gascomparison} and\ref{fig:starcomparison} are only available in electronic form athttp://www.edpsciences.org
| 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
| The Contribution of H I-rich Galaxies to the Damped Lyα Absorber Population at z = 0
We present a study of the expected properties of the low-redshift dampedLyα absorber population determined from a sample of H I-selectedgalaxies in the local universe. Because of a tight correlation betweenthe H I mass and H I cross section, which we demonstrate spans allgalaxy types, we can use our H I-selected sample to predict theproperties of the absorption-line systems. We use measurements of thenumber density and H I cross section of galaxies to show that the totalH I cross section at column densities sufficient to produce dampedLyα absorption is consistent with no evolution of the absorberpopulation. We also find that the dN/dz distribution is dominated bygalaxies with H I masses near 109 Msolar. However,because of the large dispersion in the correlation between H I mass andstellar luminosity, we find that the distribution of dN/dz as a functionof LJ is fairly flat. In addition, we examine the line widthsof the H I-selected galaxies and show that there may be evolution in thekinematics of H I-rich galaxies, but it is not necessary for the higherredshift population to contain a greater proportion of high-massgalaxies than we find locally.
| Redshift-Distance Survey of Early-Type Galaxies: Spectroscopic Data
We present central velocity dispersions and Mg2 line indicesfor an all-sky sample of ~1178 elliptical and S0 galaxies, of which 984had no previous measures. This sample contains the largest set ofhomogeneous spectroscopic data for a uniform sample of ellipticalgalaxies in the nearby universe. These galaxies were observed as part ofthe ENEAR project, designed to study the peculiar motions and internalproperties of the local early-type galaxies. Using 523 repeatedobservations of 317 galaxies obtained during different runs, the dataare brought to a common zero point. These multiple observations, takenduring the many runs and different instrumental setups employed for thisproject, are used to derive statistical corrections to the data and arefound to be relatively small, typically <~5% of the velocitydispersion and 0.01 mag in the Mg2 line strength. Typicalerrors are about 8% in velocity dispersion and 0.01 mag inMg2, in good agreement with values published elsewhere.
| The Role of Interactions in the Evolution of Highly Star-forming Early-Type (Sa-Sab) Spiral Galaxies
We present a search for the signatures of galaxy-galaxy interactions inthe neutral gas of early-type spirals. New neutral hydrogen observationsfor four highly star-forming early-type spirals are presented here,along with H I data for three additional galaxies from other sources. HI maps of six of seven galaxies reveal unambiguous signs of a recentencounter, via tidal tails and H I bridges. Most of these galaxiesappear undisturbed in the optical, and these interactions probably wouldhave gone unnoticed without H I mapping. Such high rates of interactionsuggest that galactic encounters may play an important role in theevolution of early-type spiral galaxies.
| Redshift-Distance Survey of Early-Type Galaxies: Circular-Aperture Photometry
We present R-band CCD photometry for 1332 early-type galaxies, observedas part of the ENEAR survey of peculiar motions using early-typegalaxies in the nearby universe. Circular apertures are used to tracethe surface brightness profiles, which are then fitted by atwo-component bulge-disk model. From the fits, we obtain the structuralparameters required to estimate galaxy distances using theDn-σ and fundamental plane relations. We find thatabout 12% of the galaxies are well represented by a pure r1/4law, while 87% are best fitted by a two-component model. There are 356repeated observations of 257 galaxies obtained during different runsthat are used to derive statistical corrections and bring the data to acommon system. We also use these repeated observations to estimate ourinternal errors. The accuracy of our measurements are tested by thecomparison of 354 galaxies in common with other authors. Typical errorsin our measurements are 0.011 dex for logDn, 0.064 dex forlogre, 0.086 mag arcsec-2 for<μe>, and 0.09 for mRC,comparable to those estimated by other authors. The photometric datareported here represent one of the largest high-quality and uniformall-sky samples currently available for early-type galaxies in thenearby universe, especially suitable for peculiar motion studies.Based on observations at Cerro Tololo Inter-American Observatory (CTIO),National Optical Astronomy Observatory, which is operated by theAssociation of Universities for Research in Astronomy, Inc., undercooperative agreement with the National Science Foundation (NSF);European Southern Observatory (ESO); Fred Lawrence Whipple Observatory(FLWO); and the MDM Observatory on Kitt Peak.
| Molecular Gas in NUclei of GAlaxies (NUGA). I. The counter-rotating LINER NGC 4826
We present new high-resolution observations of the nucleus of thecounter-rotating LINER NGC 4826, made in the J=1-0 and J=2-1 lines of12CO with the IRAM Plateau de Buremm-interferometer(PdBI).The CO maps, which achieve 0.8arcsec (16 pc)resolution in the 2-1 line, fully resolve an inner molecular gas diskwhich is truncated at an outer radius of 700 pc. The total molecular gasmass (3.1*E8 Msun) is distributed in a lopsidednuclear disk of 40 pc radius, containing 15% of the total gas mass, andtwo one-arm spirals, which develop at different radii in the disk. Thedistribution and kinematics of molecular gas in the inner 1 kpc of NGC4826 show the prevalence of different types of m=1 perturbations in thegas. Although dominated by rotation, the gas kinematics are perturbed bystreaming motions related to the m=1 instabilities. The non-circularmotions associated with the inner m=1 perturbations (lopsidedinstability and inner one-arm spiral) agree qualitatively with thepattern expected for a trailing wave developed outside corotation(``fast'' wave). In contrast, the streaming motions in the outer m=1spiral are better explained by a ``slow'' wave. A paradoxicalconsequence is that the inner m=1 perturbations would not favour AGNfeeding. An independent confirmation that the AGN is not beinggenerously fueled at present is found in the low values of thegravitational torques exerted by the stellar potential for R<530 pc.The distribution of star formation in the disk of NGC 4826 is alsostrongly asymmetrical. The observed asymmetries, revealed by HST imagesof the inner disk, follow the scales of the various m=1 perturbationsidentified in the molecular gas disk. Massive star formation is stillvigorous, fed by the significant molecular gas reservoir at R<700 pc.There is supporting evidence for a recent large mass inflow episode inNGC 4826. The onset of m=1 instabilities of the type observed in NGC4826 may be a consequence of secular evolution of disks with high gasmass contents.These observations have been made in the context of the NUclei ofGAlaxies (NUGA) project, aimed at the study of the different mechanismsfor gas fueling of Active Galactic Nuclei (AGN).Based on observations carried out with the IRAM Plateau de BureInterferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany)and IGN (Spain).
| Inner Molecular Rings in Barred Galaxies: BIMA Survey of Nearby Galaxies CO Observations
Although inner star-forming rings are common in optical images of barredspiral galaxies, observational evidence for the accompanying moleculargas has been scarce. In this paper we present images of molecular innerrings, traced using the CO (1-0) emission line, from theBerkeley-Illinois-Maryland-Association Survey of Nearby Galaxies (BIMASONG). We detect inner-ring CO emission from all five SONG barredgalaxies classified as inner ring [type (r)]. We also examine the sevenSONG barred galaxies classified as inner spiral [type (s)]; in one ofthese, NGC 3627, we find morphological and kinematic evidence for amolecular inner ring. Inner-ring galaxies have been classified as suchbased on optical images, which emphasize recent star formation. Weconsider the possibility that there may exist inner rings in which starformation efficiency is not enhanced. However, we find that in NGC 3627the inner-ring star formation efficiency is enhanced relative to mostother regions in that galaxy. We note that the SONG (r) galaxies have apaucity of CO and Hα emission interior to the inner ring (exceptnear the nucleus), while NGC 3627 has relatively bright bar CO andHα emission; we suggest that galaxies with inner rings such as NGC3627 may be misclassified if there are significant amounts of gas andstar formation in the bar.
| 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.
| 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.
| The orthogonal gaseous kinematical decoupling in the Sa spiral NGC 2855
We present major and minor-axis kinematics of stars and ionized gas aswell as narrow and broad-band surface photometry of the Sa spiral NGC2855. In the nuclear regions of this unbarred and apparently undisturbedspiral galaxy the gas is rotating perpendicularly to the galaxy disk. Wesuggest that this kinematically-decoupled component is the signature ofan acquisition process in the history of this galaxy. Based onobservations carried out at the Observatorio del Roque de los Muchachos,La Palma (Spain) with the Italian Telescopio Nazionale Galileo and atthe European Southern Observatory, La Silla (Chile) (ESO 62.N-0463 and67.B-0230). Tables 3 and 4 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/382/488
| The SBF Survey of Galaxy Distances. IV. SBF Magnitudes, Colors, and Distances
We report data for I-band surface brightness fluctuation (SBF)magnitudes, (V-I) colors, and distance moduli for 300 galaxies. Thesurvey contains E, S0, and early-type spiral galaxies in the proportionsof 49:42:9 and is essentially complete for E galaxies to Hubblevelocities of 2000 km s-1, with a substantial sampling of Egalaxies out to 4000 km s-1. The median error in distancemodulus is 0.22 mag. We also present two new results from the survey.(1) We compare the mean peculiar flow velocity (bulk flow) implied byour distances with predictions of typical cold dark matter transferfunctions as a function of scale, and we find very good agreement withcold, dark matter cosmologies if the transfer function scale parameterΓ and the power spectrum normalization σ8 arerelated by σ8Γ-0.5~2+/-0.5. Deriveddirectly from velocities, this result is independent of the distributionof galaxies or models for biasing. This modest bulk flow contradictsreports of large-scale, large-amplitude flows in the ~200 Mpc diametervolume surrounding our survey volume. (2) We present adistance-independent measure of absolute galaxy luminosity, N and showhow it correlates with galaxy properties such as color and velocitydispersion, demonstrating its utility for measuring galaxy distancesthrough large and unknown extinction. Observations in part from theMichigan-Dartmouth-MIT (MDM) Observatory.
| Asymmetry in Isolated, Morphologically Normal SA Galaxies
We have examined the morphological and dynamical H I symmetry propertiesof a sample of moderately inclined Sa galaxies classified asmorphologically normal. The sample galaxies were known a priori toexhibit kinematic peculiarities ranging from warps to independent,wholly decoupled disks and are possibly the remnants of minor mergers.We compare the asymmetry of the rotation curves to global kinematicasymmetry and find a relationship between rotation curve asymmetry andthe kinematic n=2 mode. We have also examined the kinematics of thesegalaxies following the discussion of Briggs and find that the warpsobserved in the H I disks of these galaxies deviate significantly fromthe simple rules for warps that commonly apply.
| The gas content of peculiar galaxies: Counterrotators and polar rings
This paper studies the global ISM content in a sample of 104 accretinggalaxies, including counterrotators and polar rings, which spans theentire Hubble sequence. The molecular, atomic and hot gas content ofaccretors is compared to a newly compiled sample of normal galaxies. Wepresent results of a small survey of the J=1-0 line of 12COwith the 15 m SEST telescope on a sample of 11 accretors (10counterrotators and 1 polar ring). The SEST sample is enlarged withpublished data from 48 galaxies, for which observational evidence ofcounterrotation in the gas and/or the stars has been found. Furthermore,the available data on a sample of 46 polar ring galaxies has beencompiled. In order to explore the existence of an evolutionary pathlinking the two families of accretors, the gas content ofcounterrotators and polar rings is compared. It was found that thenormalized content of cold gas (Mgas/LB) in polarrings is ~ 1 order of magnitude higher than the reference value derivedfor normal galaxies. The inferred gas masses are sufficient to stabilizepolar rings through self-gravity. In contrast, it was found that thecold gas content of counterrotators is close to normal for all galaxytypes. Although counterrotators and polar rings probably share a commonorigin, the gas masses estimated here confirm that light gas ringsaccreted by future counterrotators may have evolved faster than theself-gravitating structures of polar rings. In this scenario, thetransformation of atomic into molecular gas could be enhanced near thetransition region between the prograde and the retrograde disks,especially in late-type accretors characterized by a high content ofprimordial gas. This is tentatively confirmed in this work: the measuredH2/HI ratio seems larger in counterrotators than in normal orpolar ring galaxies for types later than S0s. Based on observationscollected at SEST telescope, European Southern Observatory, La Silla,Chile. Table 1 is only available in electronic form athttp://www.edpsciences.org
| The visible environment of galaxies with counterrotation
In this paper we present a statistical study of the environments of 49galaxies in which there is gas- or stellar-counterrotation. The numberof possible companions in the field (to apparent magnitude 22), theirsize and concentration were considered. All the statistical parameterswere analysed by means of Kolgomorov-Smirnov tests, using a controlsample of 43 galaxies without counterrotation. From our data, nosignificant differences between the counter-rotating and control samplesappear. This is different to Seyfert or radio-loud galaxies which lie inenvironments with a higher density of companions. On the contrary, if aweak tendency exists, for galaxies with gas counterrotation only, it isdiscovered in regions of space where the large scale density of galaxiesis smaller. Our results tend to disprove the hypothesis thatcounterrotation and polar rings derive from a recent interaction with asmall satellite or a galaxy of similar size. To a first approximation,they seem to follow the idea that all galaxies are born through a mergerprocess of smaller objects occurring very early in their life, or thatthey derive from a continuous, non-traumatic infall of gas that formedstars later. Whatever the special machinery is which producescounterrotation or polar rings instead of a co-planar, co-rotatingdistribution of gas and stars, it seems not to be connected to thepresent galaxy density of their environments.
| Surface photometry of spiral galaxies in NIR: Structural parameters of disks and bulges
A sample of 40 bright spiral galaxies (BT < 12) with lowinclination and without bar was observed with JHK filters. For thispurpose the MAGIC NICMOS3 camera at the 2.2 m telescope of the CalarAlto observatory, Spain was used. With a newly developed 2-dimensionalalgorithm the distribution of the surface brightness was fittedsimultaneously by corresponding functions for the disk- andbulge-structure. While the disk was fitted with an exponential function,the bulge profile was fitted with a generalized de VaucouleursRbeta law, with the concentration parameter beta = 1/n as afurther fit variable. The correlation of the resulting structuralparameters of disks and bulges lead to some interesting relations: 1.The use of a variable exponent beta is necessary for a realisticdescription of the bulge structure; 2. Disks and bulges show similarcorrelations between effective radius, effective surface brightness andluminosity; 3. They populate a common strip in the fundamental plane; 4.From the correlations between beta and Hubble type some conclusionsabout the formation and evolution of spiral galaxies can be drawn.
| 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.
| Kinematic Evidence of Minor Mergers in Normal SA Galaxies: NGC 3626, NGC 3900, NGC 4772, and NGC 5854
BVRI and Hα imaging and long-slit optical spectroscopic data arepresented for four morphologically normal and relatively isolated Sagalaxies, NGC 3626, NGC 3900, NGC 4772, and NGC 5854. VLA H I synthesisimaging is presented for the first three objects. In all four galaxies,evidence of kinematic decoupling of ionized gas components is found inthe long-slit spectroscopic data; the degree and circumstances of thedistinct kinematics vary from complete counterrotation of all of the gasfrom all of the stars (NGC 3626) to nuclear gas disks decoupled from thestars (NGC 5854) to anomalous velocity central gas components (NGC 3900and NGC 4772). In the three objects mapped in H I, the neutral gasextends far beyond the optical radius, RHI/R25>=2. In general, the H I surface density isvery low, and the outer H I is patchy and asymmetric (NGC 3900) or foundin a distinct ring, exterior to the optical edge (NGC 3626 and NGC4772). While the overall H I velocity fields are dominated by circularmotions, strong warps are suggested in the outer regions by bending ofthe minor axis isovelocity contours (NGC 3900) and/or systematic shiftsin position angle between inner and outer rings (NGC 3626 and NGC 4772).In the interior, coincidence is found between the Hα and H I inrings, sometimes partial and crisscrossed by dust lanes. Optical imagingis also presented for NGC 4138 previously reported by Jore et al. toshow counterrotating stellar components. The multiwavelength evidence isinterpreted in terms of the kinematic ``memory'' of past minor mergersin objects that otherwise exhibit no morphological signs of interaction.
| Anatomy of the counterrotating molecular disk in the spiral NGC 3593. 12CO(1-0) interferometer observations and numerical simulations
This paper presents high-resolution (4arcsec x3arcsec ) interferometerobservations of the inner disk of the starburst spiral NGC 3593, made inthe (1-0) line of 12CO. NGC 3593 is an early-type systemknown to possess two counterrotating stellar disks of markedly differentscale lengths and masses. The CO emission comes from a highly structuredmolecular gas disk of Mgas ~ 3x108Msun,and total radial extent r ~ 35arcsec . The observed CO kinematicsindicates that the molecular gas is counterrotating at all radii withrespect to the most massive stellar disk (disk I). The bulk of the COemission arises from a ringed circumnuclear disk (CND) of radius r ~10arcsec and mass Mgas ~ 1.5x108Msun,which hosts a nuclear starburst. The link between the starburst and theCND is corroborated by high-resolution observations of other starformation tracers (Hα , Paalpha and J-K color index maps). Thestarburst episode is fueling the less massive counterrotating stellardisk (disk II). We find extinctions A_V of ~ 1 mag in the CND based onoptical and near-infrared recombination lines, but find >5 mag fromthe CO and 100 mu m fluxes. Out of the CND, molecular gas is distributedin a one-arm spiral feature which winds up tightly from the edges of theCND (r ~ 10arcsec ) up to r ~ 35arcsec . The CO one-arm spiral isleading with respect to the gas flow in the southern half of the disk.There is a secondary trailing spiral arc in the northern half. Theanalysis of streaming motions linked with the passage of the CO one-armspiral indicates that the southern feature would be a stationary m=1instability (pattern speed Omega_p ~ 0). To account for the observed gasresponse in the disk of NGC 3593, we have run self-consistent numericalsimulations, including the stellar and the gaseous components, in aphysical scenario which approximates this case of study. We discuss therapidly changing response of the disk, which evolves from a transitoryregime, in which all instabilities are m=1 waves leading with respect tothe counterrotating gas, towards a stationary regime, in which m=1 aremixed with m=2 features, trailing with respect to the gas flow at allradii. In the light of the present simulations, NGC 3593 might bestarting to change from the transitory towards the stationary regime.Based on observations carried out with the IRAM Plateau de BureInterferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany)and IGN (Spain).
| A new HI ring: LGG 138
A complete ring of neutral hydrogen gas (HI) in the LGG 138 group ofgalaxies has been found. The HI mass of the ring is greater than 10^9solar masses, and the gas appears to be rotating with a projectedcircular speed of about 200 km per sec. Two bright galaxies are enclosedby the ring, both having radial velocities consistent with membership ofthe group. Faint stellar emission extends to the radial distance of theHI ring, where a small but distinct colour discontinuity of between 0.05and 0.20 magnitudes is detected. Three simple models for the formationof the system are briefly described, the most likely appearing to be apast gas-sweeping collision between one of the two bright galaxies andan outside intruder, with the colour break being partly due to anexpanding density wave that is triggering star formation, and partly toa different stellar population that has been collected from theoutskirts of the intruder.
| 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.
| Smoothed Particle Hydrodynamics Simulations of Counterrotating Disk Formation in Spiral Galaxies
We present the results of smoothed particle hydrodynamics (SPH)simulations of the formation of a massive counterrotating disk in aspiral galaxy. The current study revisits and extends (with SPH)previous work carried out with sticky particle gas dynamics, in whichadiabatic gas infall and a retrograde gas-rich dwarf merger were testedas the two most likely processes for producing such a counterrotatingdisk. We report on experiments with a cold primary similar to ourGalaxy, as well as a hot, compact primary modeled after NGC 4138. Wehave also conducted numerical experiments with varying amounts ofprograde gas in the primary disk and an alternative infall model (aspherical shell with retrograde angular momentum). The structure of theresulting counterrotating disks is dramatically different with SPH. Thedisks we produce are considerably thinner than the primary disks andthose produced with sticky particles. The timescales for counterrotatingdisk formation are shorter with SPH, because the gas loses kineticenergy and angular momentum more rapidly. Spiral structure is evident inmost of the disks, but an exponential radial profile is not a naturalby-product of these processes. The infalling gas shells that we testedproduce counterrotating bulges and rings rather than disks. The presenceof a considerable amount of preexisting prograde gas in the primarycauses, at least in the absence of star formation, a rapid inflow of gasto the center and a subsequent hole in the counterrotating disk. For anormal counterrotating disk to form, there must be either little or nopreexisting prograde gas in the primary, or its dissipative influencemust be offset by significant star formation activity. The latterscenario, along with the associated feedback to the interstellar medium,may be necessary to produce a counterrotating disk similar in scalelength and scale height to the primary disk. In general, our SPHexperiments yield stronger evidence to suggest that the accretion ofmassive counterrotating disks drives the evolution of the host galaxiestoward earlier (S0/Sa) Hubble types.
| First Detection of a Counterrotating Molecular Gas Disk in a Spiral Galaxy: NGC 3626
In this paper we report the detection of a massive counterrotatingmolecular gas disk in the early-type spiral NGC 3626, observed in the1-0 and 2-1 lines of 12CO, mapped with the 30 m telescope and Bureinterferometer. 12CO emission is concentrated in a compact nuclear diskof average radius r ~ 12" (1.2 kpc). In the outer disk, from r = 20" tor = 100" (2-10 kpc), 12CO is not detected, and the neutral gas contentis largely dominated by H I. The observed 12CO velocity field patterncorresponds to a gaseous disk with a sense of rotation opposite to thatof the stars. Counterrotation is shared by molecular and ionized gas inthe center. There is no strong evidence of 12CO emission from gas indirect rotation. The estimated molecular mass in the 12CO nuclear diskis M(H2) ~ 0.3 x 109 Mȯ, 3 times lower than the mass of the H Idisk. Within the nuclear disk, 12CO is distributed in a central sourceof ~1" (100 pc) radius, where the derived 12CO rotation curve reaches~240 km s-1, surrounded by a pseudoring of average radius ~6" (600 pc)characterized by strong noncircular motions. The dynamics of moleculargas, characterized by a regular counterrotating pattern and streamingmotions typical of a steady density-wave driven flow and normal 12COline widths, preclude the occurrence of violent large-scale shocks or ofa nonequilibrium dynamical state for the gas. The available optical (Halpha , N [II] and S [II]) and radio continuum data (at 12.6 cm and 21cm) indicate that no violent burst of star formation is associated withthe nuclear molecular gas. This is confirmed by the lack of IRAS fluxrecord for the nucleus of NGC 3626. The present 12CO observationssuggest that we are probably seeing a late stage of a merger happened inNGC 3626.
| Groups of galaxies. III. Some empirical characteristics.
Not Available
| Bulge-Disk Decomposition of 659 Spiral and Lenticular Galaxy Brightness Profiles
We present one of the largest homogeneous sets of spiral and lenticulargalaxy brightness profile decompositions completed to date. The 659galaxies in our sample have been fitted with a de Vaucouleurs law forthe bulge component and an inner-truncated exponential for the diskcomponent. Of the 659 galaxies in the sample, 620 were successfullyfitted with the chosen fitting functions. The fits are generally welldefined, with more than 90% having rms deviations from the observedprofile of less than 0.35 mag. We find no correlations of fittingquality, as measured by these rms residuals, with either morphologicaltype or inclination. Similarly, the estimated errors of the fittedcoefficients show no significant trends with type or inclination. Thesedecompositions form a useful basis for the study of the lightdistributions of spiral and lenticular galaxies. The object base issufficiently large that well-defined samples of galaxies can be selectedfrom it.
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