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On the origin of warps and the role of the intergalactic medium
There is still no consensus as to what causes galactic discs to becomewarped. Successful models should account for the frequent occurrence ofwarps in quite isolated galaxies, their amplitude as well as theobserved azimuthal and vertical distributions of the HI layer.Intergalactic accretion flows and intergalactic magnetic fields may bendthe outer parts of spiral galaxies. In this paper we consider theviability of these non-gravitational torques to take the gas off theplane. We show that magnetically generated warps are clearly flawedbecause they would wrap up into a spiral in less than two or threegalactic rotations. The inclusion of any magnetic diffusivity to dilutethe wrapping effect causes the amplitude of the warp to damp. We alsoconsider the observational consequences of the accretion of anintergalactic plane-parallel flow at infinity. We have computed theamplitude and warp asymmetry in the accretion model, for a disc embeddedin a flattened dark matter halo, including self-consistently thecontribution of the modes with azimuthal wavenumbers m= 0 and m= 1.Since the m= 0 component, giving a U-shaped profile, is not negligiblecompared to the m= 1 component, this model predicts quite asymmetricwarps, maximum gas displacements on the two sides in the ratio 3 : 2 forthe preferred Galactic parameters, and the presence of a fraction ~3.5per cent of U-shaped warps, at least. The azimuthal dependence of themoment transfer by the ram pressure would produce a strong asymmetry inthe thickness of the HI layer and asymmetric density distributions in z,in conflict with observational data for the warp in our Galaxy and inexternal galaxies. The amount of accretion that is required to explainthe Galactic warp would give gas scaleheights in the far outer disc thatare too small. We conclude that accretion of a flow with no net angularmomentum cannot be the main and only cause of warps.
| Low-Luminosity Active Galaxies and Their Central Black Holes
Central black hole masses for 117 spiral galaxies representingmorphological stages S0/a through Sc and taken from the largespectroscopic survey of Ho et al. are derived using Ks-banddata from the Two Micron All Sky Survey. Black hole masses are foundusing a calibrated black hole-Ks bulge luminosity relation,while bulge luminosities are measured by means of a two-dimensionalbulge-disk decomposition routine. The black hole masses are correlatedagainst a variety of parameters representing properties of the nucleusand host galaxy. Nuclear properties such as line width (FWHM [N II]), aswell as emission-line ratios (e.g., [O III]/Hβ, [O I]/Hα, [NII]/Hα, and [S II]/Hα), show a very high degree ofcorrelation with black hole mass. The excellent correlation with linewidth supports the view that the emission-line gas is in virialequilibrium with either the black hole or bulge potential. The very goodemission-line ratio correlations may indicate a change in ionizingcontinuum shape with black hole mass in the sense that more massiveblack holes generate harder spectra. Apart from theinclination-corrected rotational velocity, no excellent correlations arefound between black hole mass and host galaxy properties. Significantdifferences are found between the distributions of black hole masses inearly-, mid-, and late-type spiral galaxies (subsamples A, B, and C) inthe sense that early-type galaxies have preferentially larger centralblack holes, consistent with observations that Seyfert galaxies arefound preferentially in early-type systems. The line width distributionsshow a marked difference among subsamples A, B, and C in the sense thatearlier type galaxies have larger line widths. There are also cleardifferences in line ratios between subsamples A+B and C that likely arerelated to the level of ionization in the gas. Finally, aKs-band Simien & de Vaucouleurs diagram shows excellentagreement with the original B-band relation, although there is a largedispersion at a given morphological stage.
| 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*.
| A high-frequency radio survey of low-luminosity active galactic nuclei
We investigate the high-frequency radio spectra of 20 low-luminosityactive galactic nuclei (LLAGNs) with compact radio cores. Our millimetresurvey with the Nobeyama Millimetre Array (NMA) and analyses ofsubmillimetre archival data that had been obtained with theSubmillimetre Common User Bolometer Array (SCUBA) on the James ClerkMaxwell Telescope (JCMT) reveal the following properties. At least halfof the LLAGNs show inverted spectra between 15 and 96 GHz; we use thepublished data at 15 GHz with the Very Large Array (VLA) in a0.15-arcsec resolution and our measurements at 96 GHz with the NMA in a7-arcsec resolution. The inverted spectra are not artificially made dueto their unmatched beam sizes, because of little diffuse contaminationfrom dust, HII regions, or extended jets in these LLAGNs. Suchhigh-frequency inverted spectra are apparently consistent with a`submillimetre bump', which is predicted by an advection-dominatedaccretion flow (ADAF) model. We find a strong correlation between thehigh-frequency spectral index and low-frequency core power measured withvery-long-baseline-interferometry (VLBI) instruments. The invertedspectra are found exclusively in low-core-power sources, while steepspectra are in high-core-power ones with prominent pc-scale jets. Thissuggests that the ADAF and non-thermal jets may coexist. The flux ratiosbetween disc and jet seem to be different from LLAGN to LLAGN; disccomponents can be seen in nuclear radio spectra only if the jets arefaint.
| Advanced mergers of galaxies: luminosity profiles and dynamics
We have analyzed the near-IR Ks-band data from the 2MASS archivaldatabase for a large sample of twenty-seven galaxies that show signs ofinteraction but have a single nucleus. Surprisingly, half of theseadvanced mergers of galaxies show luminosity profiles which have anouter exponential fall-off with radius, as in a spiral galaxy (Chitreand Jog 2002). The kinematical data for two of these, Arp 224 and Arp214, available from the HYPERCAT database were used and these showkinematics similar to elliptical galaxies with the random motiondominating the rotation (Jog and Chitre 2002). The origin of the mixedproperties shown by these mergers is a puzzle. To understand thesesystems, we have recently studied the dynamics of mergers via N-bodysimulations for unequal-mass mergers covering a new range of galaxy massratios 4:1-10:1 (Bournaud, Combes, and Jog 2004). We show that suchmergers naturally result in remnants that have the mixed properties aswe have observed from the 2MASS data analysis. The transition betweenelliptical and disk-like remnants is found to occur over a narrow rangeof galaxy mass ratios 3:1-4.5:1 (Bournaud, Jog and Combes 2005).
| The Link between Star Formation and Accretion in LINERs: A Comparison with Other Active Galactic Nucleus Subclasses
We present archival high-resolution X-ray imaging observations of 25nearby LINERs observed by ACIS on board Chandra. This sample builds onour previously published proprietary and archival X-ray observations andincludes the complete set of LINERs with published black hole masses andFIR luminosities that have been observed by Chandra. Of the 82 LINERsobserved by Chandra, 41 (50%) display hard nuclear cores consistent withan AGN. The nuclear 2-10 keV luminosities of these AGN-LINERs range from~2×1038 to ~1×1044 ergss-1. Reinforcing our previous work, we find a significantcorrelation between the Eddington ratio,Lbol/LEdd, and the FIR luminosity,LFIR, as well as the IR brightness ratio,LFIR/LB, in the host galaxy of AGN-LINERs thatextends over 7 orders of magnitude in Lbol/LEdd.Combining our AGN-LINER sample with galaxies from other AGN subclasses,we find that this correlation is reinforced in a sample of 129 AGNs,extending over almost 9 orders of magnitude inLbol/LEdd. Using archival and previously publishedobservations of the 6.2 μm PAH feature from ISO, we find that it isunlikely that dust heating by the AGN dominates the FIR luminosity inour sample of AGNs. Our results may therefore imply a fundamental linkbetween the mass accretion rate (M˙), as measured by the Eddingtonratio, and the star formation rate (SFR), as measured by the FIRluminosity. Apart from the overall correlation, we find that thedifferent AGN subclasses occupy distinct regions in the LFIRand Lbol/LEdd plane. Assuming a constant radiativeefficiency for accretion, our results may imply a variation in theSFR/M˙ ratio as a function of AGN activity level, a result that mayhave significant consequences for our understanding of galaxy formationand black hole growth.
| The Hubble Space Telescope View of LINER Nuclei: Evidence for a Dual Population?
We study a complete, distance-limited sample of 25 LINERs, 21 of whichhave been imaged with the Hubble Space Telescope. In nine objects wedetect an unresolved nucleus. To study their physical properties, wecompare the radio and optical properties of the nuclei of LINERs withthose of other samples of local active galactic nuclei (AGNs), namely,Seyfert galaxies and low-luminosity radio galaxies (LLRGs). Our resultsshow that the LINER population is not homogeneous, as there are twosubclasses: (1) the first class is similar to the LLRG class, as itextends the population of radio-loud nuclei to lower luminosities; (2)the second is similar to Seyfert galaxies and extends the properties ofradio-quiet nuclei toward the lowest luminosities. The objects areoptimally discriminated in the plane formed by the black hole massversus nuclear radio loudness: all radio-loud LINERs haveMBH>~108Msolar, while Seyfertgalaxies and radio-quiet LINERs haveMBH<~108Msolar. The different natureof the various classes of local AGNs are best understood when thefraction of the Eddington luminosity they irradiate,Lo/LEdd, is plotted against the nuclearradio-loudness parameter: Seyfert galaxies are associated withrelatively high radiative efficienciesLo/LEdd>~10-4 (and high accretionrates onto low-mass black holes); LLRGs are associated with lowradiative efficiencies (and low accretion rates onto high-mass blackholes); all LINERs have low radiative efficiency (and accretion rates)and can be radio-loud or radio-quiet, depending on their black holemass.Based on observations obtained at the Space Telescope Science Institute,which is operated by the Association of Universities for Research inAstronomy, Inc., under NASA contract NAS5-26555.
| Hα Imaging of Early-Type Sa-Sab Spiral Galaxies. II. Global Properties
New results, based on one of the most comprehensive Hα imagingsurveys of nearby Sa-Sab spirals completed to date, reveals early-typespirals to be a diverse group of galaxies that span a wide range inmassive star formation rates. While the majority of Sa-Sab galaxies inour sample are forming stars at a modest rate, a significant fraction(~29%) exhibit star formation rates greater than 1 Msolaryr-1, rivaling the most prolifically star-forming late-typespirals. A similar diversity is apparent in the star formation historyof Sa-Sab spirals as measured by their Hα equivalent widths.Consistent with our preliminary results presented in the first paper inthis series, we find giant H II regions [L(Hα)>=1039ergs s-1] in the disks of ~37% of early-type spirals. Wesuspect that recent minor mergers or past interactions are responsiblefor the elevated levels of Hα emission and, perhaps, for thepresence of giant H II regions in these galaxies. Our results, however,are not in total agreement with the Hα study of Kennicutt &Kent, who did not find any early-type spirals with Hα equivalentwidths >14 Å. A close examination of the morphologicalclassification of galaxies, however, suggests that systematicdifferences between the Revised Shapley-Ames Catalog and the SecondReference Catalogue may be responsible for the contrasting results.Based on observations obtained with the 3.5 m telescope at Apache PointObservatory (APO) and the 0.9 m telescope at Kitt Peak NationalObservatory (KPNO). The APO 3.5 m telescope is owned and operated by theAstrophysical Research Consortium.
| Molecular gas in NUclei of GAlaxies (NUGA). III. The warped LINER NGC 3718
We present the first interferometric observations of CO(1-0) and CO(2-1)line emission from the warped LINER NGC 3718,obtained with the IRAM Plateau de Bure Interferometer (PdBI). This L1.9galaxy has a prominent dust lane and on kiloparsec scales, a stronglywarped atomic and molecular gas disk. The molecular gas is closelyassociated with the dust lane across the nucleus and its kinematiccenter is consistent with the millimeter continuum AGN. A comparison ofour interferometric mosaic data, which fully cover the ~ 9 kpc warpeddisk, with a previously obtained IRAM 30 m single dish CO(1-0) map showsthat the molecular gas distribution in the disk is heavily resolved bythe PdBI map. On the nucleus the interferometric maps alone contain lessthan one half of the single dish line flux, and the overall mosaicaccounts for about a tenth of the total molecular gas mass of ~2.4× 108 Mȯ. After applying ashort-spacing correction with the IRAM 30 m data to recover the missingextended flux, we find in total six main source components within thedust lane: one associated with the nucleus, four symmetricallypositioned on either side at galactocentric distances of about 1.3 kpcand 4.0 kpc from the center, and a sixth on the western side at ~ 3 kpcwith only a very weak eastern counterpart. In the framework of akinematic model using tilted rings, we interpret the five symmetricsource components as locations of strong orbital crowding. We furtherfind indications that the warp appears not only on kpc scales, butcontinues down to ~ 250 pc. Besides the sixth feature on the westernside, the lower flux (a factor of ~2) of the eastern components comparedto the western ones indicates an intrinsic large scale asymmetry in NGC3718 that cannot be explained by the warp. Indications for a small scaleasymmetry are also seen in the central 600 pc. These asymmetries mightbe evidence for a tidal interaction with a companion galaxy (largescales) and gas accretion onto the nucleus (small scales). Our study ofNGC 3718 is part of the NUclei of GAlaxies (NUGA) project that aims atinvestigating the different processes of gas accretion onto ActiveGalactic Nuclei (AGN).
| Radio sources in low-luminosity active galactic nuclei. IV. Radio luminosity function, importance of jet power, and radio properties of the complete Palomar sample
We present the completed results of a high resolution radio imagingsurvey of all ( 200) low-luminosity active galactic nuclei (LLAGNs) andAGNs in the Palomar Spectroscopic Sample of all ( 488) bright northerngalaxies. The high incidences of pc-scale radio nuclei, with impliedbrightness temperatures ≳107 K, and sub-parsec jetsargue for accreting black holes in ≳50% of all LINERs andlow-luminosity Seyferts; there is no evidence against all LLAGNs beingmini-AGNs. The detected parsec-scale radio nuclei are preferentiallyfound in massive ellipticals and in type 1 nuclei (i.e. nuclei withbroad Hα emission). The radio luminosity function (RLF) of PalomarSample LLAGNs and AGNs extends three orders of magnitude below, and iscontinuous with, that of “classical” AGNs. We find marginalevidence for a low-luminosity turnover in the RLF; nevertheless LLAGNsare responsible for a significant fraction of present day massaccretion. Adopting a model of a relativistic jet from Falcke &Biermann, we show that the accretion power output in LLAGNs is dominatedby the kinetic power in the observed jets rather than the radiatedbolometric luminosity. The Palomar LLAGNs and AGNs follow the samescaling between jet kinetic power and narrow line region (NLR)luminosity as the parsec to kilo-parsec jets in powerful radio galaxies.Eddington ratios {l_Edd} (=L_Emitted/L_Eddington) of≤10-1{-}10-5 are implied in jet models of theradio emission. We find evidence that, in analogy to Galactic black holecandidates, LINERs are in a “low/hard” state (gas poornuclei, low Eddington ratio, ability to launch collimated jets) whilelow-luminosity Seyferts are in a “high” state (gas richnuclei, higher Eddington ratio, less likely to launch collimated jets).In addition to dominating the radiated bolometric luminosity of thenucleus, the radio jets are energetically more significant thansupernovae in the host galaxies, and are potentially able to depositsufficient energy into the innermost parsecs to significantly slow thegas supply to the accretion disk.
| Bar-induced perturbation strengths of the galaxies in the Ohio State University Bright Galaxy Survey - I
Bar-induced perturbation strengths are calculated for a well-definedmagnitude-limited sample of 180 spiral galaxies, based on the Ohio StateUniversity Bright Galaxy Survey. We use a gravitational torque method,the ratio of the maximal tangential force to the mean axisymmetricradial force, as a quantitative measure of the bar strength. Thegravitational potential is inferred from an H-band light distribution byassuming that the M/L ratio is constant throughout the disc. Galaxiesare deprojected using orientation parameters based on B-band images. Inorder to eliminate artificial stretching of the bulge, two-dimensionalbar-bulge-disc decomposition has been used to derive a reliable bulgemodel. This bulge model is subtracted from an image, the disc isdeprojected assuming it is thin, and then the bulge is added back byassuming that its mass distribution is spherically symmetric. We findthat removing the artificial bulge stretch is important especially forgalaxies having bars inside large bulges. We also find that the massesof the bulges can be significantly overestimated if bars are not takeninto account in the decomposition.Bars are identified using Fourier methods by requiring that the phasesof the main modes (m= 2, m= 4) are maintained nearly constant in the barregion. With such methods, bars are found in 65 per cent of the galaxiesin our sample, most of them being classified as SB-type systems in thenear-infrared by Eskridge and co-workers. We also suggest that as muchas ~70 per cent of the galaxies classified as SAB-types in thenear-infrared might actually be non-barred systems, many of them havingcentral ovals. It is also possible that a small fraction of the SAB-typegalaxies have weak non-classical bars with spiral-like morphologies.
| A new H I catalog of Low Surface Brightness galaxies out to z = 0.1. Tripling the number of massive LSB galaxies known
Using both the Arecibo 305 m and the Nançay decimetric 100-mclass radio telescopes, we have observed the H I line of 116 Low SurfaceBrightness (LSB) galaxies from the Bothun et al. (1985) subset of LSBgalaxies in the Uppsala General Catalog. The observations had adetection rate of 70%, resulting in the new determination of H Iproperties for 81 galaxies. Surprisingly, roughly half of the detectedobjects (38) have MHI ≥1010Mȯ, placing them into the category of massive LSBgalaxies. As previously only 18 of these ``Malin 1 cousins'' wereknown, our results have more than tripled the number of thesefascinating and enigmatic systems known. Combining our results withprevious studies done on the Bothun et al. catalog results in awell-defined catalog of H I properties of 526 LSB galaxies ranging inredshift space from 0 ≤z ≤0.1. With this catalog in hand, wehave been able to explore the parameter space occupied by LSB galaxiesmore completely than has been previously possible. In agreement withprevious studies, our results show LSB galaxies with some of the mostextreme properties of disk galaxies, includingMHI/LB ratios often exceeding 10Mȯ/Lȯ,B.Tables 1-3 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/428/823Appendix is only available in electronic form athttp://www.edpsciences.org
| The ISOPHOT 170 μm Serendipity Survey II. The catalog of optically identified galaxies%
The ISOPHOT Serendipity Sky Survey strip-scanning measurements covering≈15% of the far-infrared (FIR) sky at 170 μm were searched forcompact sources associated with optically identified galaxies. CompactSerendipity Survey sources with a high signal-to-noise ratio in at leasttwo ISOPHOT C200 detector pixels were selected that have a positionalassociation with a galaxy identification in the NED and/or Simbaddatabases and a galaxy counterpart visible on the Digitized Sky Surveyplates. A catalog with 170 μm fluxes for more than 1900 galaxies hasbeen established, 200 of which were measured several times. The faintest170 μm fluxes reach values just below 0.5 Jy, while the brightest,already somewhat extended galaxies have fluxes up to ≈600 Jy. For thevast majority of listed galaxies, the 170 μm fluxes were measured forthe first time. While most of the galaxies are spirals, about 70 of thesources are classified as ellipticals or lenticulars. This is the onlycurrently available large-scale galaxy catalog containing a sufficientnumber of sources with 170 μm fluxes to allow further statisticalstudies of various FIR properties.Based on observations with ISO, an ESA project with instruments fundedby ESA Member States (especially the PI countries: France, Germany, TheNetherlands and the UK) and with the participation of ISAS and NASA.Members of the Consortium on the ISOPHOT Serendipity Survey (CISS) areMPIA Heidelberg, ESA ISO SOC Villafranca, AIP Potsdam, IPAC Pasadena,Imperial College London.Full Table 4 and Table 6 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/422/39
| 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
| Photometric structure of polar-ring galaxies
The results of B, V, R surface photometry of three polar-ring galaxies(PRGs) - A 0017+2212, UGC 1198, UGC 4385 - are presented. The data wereacquired at the 6-m telescope of the Special Astrophysical Observatoryof the Russian Academy of Sciences. It was shown that all three galaxiesare peculiar late-type spirals in the state of ongoing interaction ormerging. We discuss available photometric properties of the PRGs withspiral hosts and consider the Tully-Fisher relation for different typesof PRGs. In agreement with Iodice et al. (\cite{Iodice03}), we haveshown that true PRGs demonstrate 1/3 larger maximum rotationvelocities than spiral galaxies of the same luminosity. Peculiar objectswith forming polar structures satisfy, on average, the Tully-Fisherrelation for disk galaxies but with large scatter.
| 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
| Warped molecular gas disk in NGC 3718
We present the first observations of the CO(1-0), CO(2-1) and HCN(1-0)rotational line emission of NGC 3718, conducted withthe IRAM 30 m telescope. The results of the data analysis show a thinstrongly warped molecular gas disk harboring the active galactic nucleus(AGN). The ratio of the total molecular gas mass (2×108\msun) to the dynamical mass, enclosed within the same region, is foundto be rather low (0.17%), but still typical for spiral galaxies.The found molecular gas disk is well associated with the dust lane,visible at optical wavelengths. We traced the warped CO structure downto the central 20''. In its outer region the molecular disk is wellcorrelated with the HI distribution. The CO data is used to improve thekinematic modelling in the inner part of the galaxy (10''≤r≤120'') employing a tilted ring-model. Furthermore the propertiesof NGC 3718 are compared with those of its northernsky ``twin'' NGC 5128 (Centaurus A).
| On position angle errors in the Tremaine-Weinberg method
I show that Tremaine-Weinberg (TW) measurements of bar pattern speedsare sensitive to errors in the position angle of the disc,PAdisc. I use an N-body experiment to measure these errors;for typical random PAdisc errors, the resulting scatter inthe measured values of the dimensionless bar speed parameter (defined asthe ratio of the corotation radius to the bar semi-major axis) is of theorder of the scatter in the observed values.I also consider how the systematic PAdisc errors produced bydisc ellipticities affect TW measurements. The scatter produced by theseerrors may be significant, depending on the ellipticity distribution.Conversely, by using the sample of TW observations, I find that an upperlimit of the typical disc (density) ellipticity is 0.07 at the 90 percent confidence level, which is in good agreement with previousmeasurements.Taken together, the random and systematic scatter suggest that theintrinsic distribution of of gas-poor early-type barred galaxies may beas narrow as that of the gas-rich later types.
| The size of the broad-line regions in dwarf active galaxies
Using the empirical relation between black hole mass and bulge velocitydispersion established for active and quiescent galaxies, we derive thesizes of the broad-line regions (BLRs) for 22 dwarf active galaxies.These sizes are compared with those of Seyfert 1 galaxies and quasars.We find that the size of the BLRs of Seyfert 1s and quasars is wellscaled with the luminosity of the Hα line with a slope of ~=0.5,and dwarf active galaxies show larger BLRs than the values predicted bythe BLR size-luminosity relation for Seyfert 1 galaxies andquasi-stellar objects (QSOs). The results suggest that the BLRs of dwarfactive galactic nuclei (AGN) have lower ionization or/and lower densitythan those of Seyfert 1 galaxies and QSOs. Photoionization calculationsshow that the large BLRs are consistent with observed emission linespectra.
| A Search for ``Dwarf'' Seyfert Nuclei. VI. Properties of Emission-Line Nuclei in Nearby Galaxies
We use the database from Paper III to quantify the global and nuclearproperties of emission-line nuclei in the Palomar spectroscopic surveyof nearby galaxies. We show that the host galaxies of Seyferts, LINERs,and transition objects share remarkably similar large-scale propertiesand local environments. The distinguishing traits emerge on nuclearscales. Compared with LINERs, Seyfert nuclei are an order of magnitudemore luminous and exhibit higher electron densities and internalextinction. We suggest that Seyfert galaxies possess characteristicallymore gas-rich circumnuclear regions and hence a more abundant fuelreservoir and plausibly higher accretion rates. The differences betweenthe ionization states of the narrow emission-line regions of Seyfertsand LINERs can be partly explained by the differences in their nebularproperties. Transition-type objects are consistent with being composite(LINER/H II) systems. With very few exceptions, the stellar populationwithin the central few hundred parsecs of the host galaxies is uniformlyold, a finding that presents a serious challenge to starburst orpost-starburst models for these objects. Seyferts and LINERs havevirtually indistinguishable velocity fields as inferred from their linewidths and line asymmetries. Transition nuclei tend to have narrowerlines and more ambiguous evidence for line asymmetries. All threeclasses of objects obey a strong correlation between line width and lineluminosity. We argue that the angular momentum content of circumnucleargas may be an important factor in determining whether a nucleus becomesactive. Finally, we discuss some possible complications for theunification model of Seyfert galaxies posed by our observations.
| Companions of Bright Barred Shapley-Ames Galaxies
Companion galaxy environment for a subset of 78 bright and nearby barredgalaxies from the Shapley-Ames Catalog is presented. Among the spiralbarred galaxies, there are Seyfert galaxies, galaxies with circumnuclearstructures, galaxies not associated with any large-scale galaxy cloudstructure, galaxies with peculiar disk morphology (crooked arms), andgalaxies with normal disk morphology; the list includes all Hubbletypes. The companion galaxy list includes the number of companiongalaxies within 20 diameters, their Hubble type, and projectedseparation distance. In addition, the companion environment was searchedfor four known active spiral galaxies, three of them are Seyfertgalaxies, namely, NGC 1068, NGC 1097, and NGC 5548, and one is astarburst galaxy, M82. Among the results obtained, it is noted that theonly spiral barred galaxy classified as Seyfert 1 in our list has nocompanions within a projected distance of 20 diameters; six out of 10Seyfert 2 bar galaxies have no companions within 10 diameters, six outof 10 Seyfert 2 galaxies have one or more companions at projectedseparation distances between 10 and 20 diameters; six out of 12 galaxieswith circumnuclear structures have two or more companions within 20diameters.
| 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
| Bar strengths in spiral galaxies estimated from 2MASS images
Non-axisymmetric forces are presented for a sample of 107 spiralgalaxies, of which 31 are barred (SB) and 53 show nuclear activity. As adata base we use JHK images from the 2 Micron All-sky Survey, and thenon-axisymmetries are characterized by the ratio of the tangential forceto the mean axisymmetric radial force field, following Buta & Block.Bar strengths have an important role in many extragalactic problems andtherefore it is important to verify that the different numerical methodsapplied for calculating the forces give mutually consistent results. Weapply both direct Cartesian integration and a polar grid integrationutilizing a limited number of azimuthal Fourier components of density.We find that the bar strength is independent of the method used toevaluate the gravitational potential. However, because of thedistance-dependent smoothing by Fourier decomposition, the polar methodis more suitable for weak and noisy images. The largest source ofuncertainty in the derived bar strength appears to be the uncertainty inthe vertical scaleheight, which is difficult to measure directly formost galaxies. On the other hand, the derived bar strength is ratherinsensitive to the possible gradient in the vertical scaleheight of thedisc or to the exact model of the vertical density distribution,provided that the same effective vertical dispersion is assumed in allmodels. In comparison with the pioneering study by Buta & Block, thebar strength estimate is improved here by taking into account thedependence of the vertical scaleheight on the Hubble type: we find thatfor thin discs bar strengths are stronger than for thick discs by anamount that may correspond to as much as one bar strength class. Weconfirm the previous result by Buta and co-workers showing that thedispersion in bar strength is large among all the de Vaucouleurs opticalbar classes. In the near-infrared 40 per cent of the galaxies in oursample have bars (showing constant phases in the m= 2 Fourier amplitudesin the bar region), while in the optical band one-third of these barsare obscured by dust. Significant non-axisymmetric forces can also beinduced by the spiral arms, generally in the outer parts of the galacticdiscs, which may have important implications on galaxy evolution.Possible biases of the selected sample are also studied: we find thatthe number of bars identified drops rapidly when the inclination of thegalactic disc is larger than 50°. A similar bias is found in theThird Reference Catalogue of Bright Galaxies, which might be of interestwhen comparing bar frequencies at high and low redshifts.
| 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.
| Arm Structure in Anemic Spiral Galaxies
Anemic galaxies have less prominent star formation than normal galaxiesof the same Hubble type. Previous studies showed they are deficient intotal atomic hydrogen but not in molecular hydrogen. Here we compare thecombined surface densities of H I and H2 at mid-disk radiiwith the Kennicutt threshold for star formation. The anemic galaxies arebelow the threshold, which explains their lack of prominent starformation, but they are not much different than other early-typegalaxies, which also tend to be below threshold. The spiral waveamplitudes of anemic and normal galaxies were also compared, usingimages in B and J passbands from the OSU Bright Spiral Galaxy Survey.Anemic galaxies have normal spiral wave properties too, with the sameamplitudes and radial dependencies as other galaxies of the same armclass. Because of the lack of gas, spiral waves in early-type galaxiesand anemics do not have a continuous supply of stars with low velocitydispersions to maintain a marginally stable disk. As a result, they areeither short lived, evolving toward lenticulars and S0 types in only afew rotations at mid-disk, or they are driven by the asymmetriesassociated with gas removal in the cluster environment.
| Spiral-like light profiles but elliptical-like kinematics in mergers of galaxies
It is commonly accepted that a merger of two spiral galaxies results ina remnant with an elliptical-like surface-brightness profile.Surprisingly, our recent study (Chitre & Jog \cite{Chitre}) of the2MASS data for twenty-seven advanced mergers of galaxies has shown thathalf of these have a light distribution that decreases exponentiallywith radius. Such a distribution normally characterizes a rotationallysupported disk in a spiral galaxy. Here we show from kinematic data fortwo of these mergers, Arp 224 and Arp 214, that the main support againstgravitational collapse comes from pressure due to random motion of starsas seen in an elliptical galaxy rather than from rotation. The origin ofthe unusual combination of properties seen here is a puzzle. Thestandard theoretical N-body models in the literature cannot account forthese systems. Further observational and dynamical studies of this newclass of merger remnants are needed, and would be important forunderstanding merger dynamics and galaxy evolution.
| Radio sources in low-luminosity active galactic nuclei. III. ``AGNs'' in a distance-limited sample of ``LLAGNs''
This paper presents the results of a high resolution radio imagingsurvey of all known (96) low-luminosity active galactic nuclei (LLAGNs)at D <= 19 Mpc. We first report new 2 cm (150 mas resolution usingthe VLA) and 6 cm (2 mas resolution using the VLBA) radio observationsof the previously unobserved nuclei in our samples and then presentresults on the complete survey. We find that almost half of all LINERsand low-luminosity Seyferts have flat-spectrum radio cores when observedat 150 mas resolution. Higher (2 mas) resolution observations of aflux-limited subsample have provided a 100% (16 of 16) detection rate ofpc-scale radio cores, with implied brightness temperatures gtrsim108 K. The five LLAGNs with the highest core radio fluxesalso have pc-scale ``jets''. Compact radio cores are almost exclusivelyfound in massive ellipticals and in type 1 nuclei (i.e. nuclei withbroad Hα emission). Only a few ``transition'' nuclei have compactradio cores; those detected in the radio have optical emission-linediagnostic ratios close to those of LINERs/Seyferts. This indicates thatsome transition nuclei are truly composite Seyfert/LINER+H II regionnuclei, with the radio core power depending on the strength of theformer component. The core radio power is correlated with the nuclearoptical ``broad'' Hα luminosity, the nuclear optical ``narrow''emission-line luminosity and width, and with the galaxy luminosity. Inthese correlations LLAGNs fall close to the low-luminosityextrapolations of more powerful AGNs. The scalings suggest that many ofthe radio-non-detected LLAGNs are simply lower power versions of theradio-detected LLAGNs. The ratio of core radio power to nuclear opticalemission-line luminosity increases with increasing bulge luminosity forall LLAGNs. Also, there is evidence that the luminosity of the diskcomponent of the galaxy is correlated with the nuclear emission-lineluminosity (but not the core radio power). About half of all LLAGNs withmultiple epoch data show significant inter-year radio variability.Investigation of a sample of ~ 150 nearby bright galaxies, most of themLLAGNs, shows that the nuclear (<=150 mas size) radio power isstrongly correlated with both the black hole mass and the galaxy bulgeluminosity; linear regression fits to all ~ 150 galaxies give: logP2 cm = 1.31(+/-0.16) log {MMDO} + 8.77 and logP2 cm = 1.89(+/-0.21) log LB(bulge) -0.17. Lowaccretion rates (<=10-2-10-3 of the Eddingtonrate) are implied in both advection- and jet-type models. In brief, allevidence points towards the presence of accreting massive black holes ina large fraction, perhaps all, of LLAGNs, with the nuclear radioemission originating in either the accretion inflow onto the massiveblack hole or from jets launched by this black hole-accretion disksystem.
| Luminosity profiles of advanced mergers of galaxies using 2MASS data
A sample of 27 disturbed galaxies that show signs of interaction buthave a single nucleus were selected from the Arp and the Arp-Madorecatalogues. For these, the Ks band images from the Two MicronAll Sky Survey (2MASS) are analysed to obtain their radial luminosityprofiles and other structural parameters. We find that in spite of theirsimilar optical appearance, the sample galaxies vary in their dynamicalproperties, and fall into two distinct classes. The first class consistsof galaxies which can be described by a single r1/4 law andthe second class consists of galaxies that show an outer exponentialdisk. A few galaxies that have disturbed profiles cannot be fit intoeither of the above classes. However, all the galaxies are similar inall other parameters such as the far-infrared colours, the molecularhydrogen content and the central velocity dispersion. Thus, thedynamical parameters of these sets seem to be determined by the ratio ofthe initial masses of the colliding galaxies. We propose that thegalaxies in the first class result from a merger of spiral galaxies ofequal masses whereas the second class of galaxies results from a mergerof unequal mass galaxies. The few objects that do not fall into eithercategory show a disturbed luminosity profile and a wandering centre,which is indicative of these being unrelaxed mergers. Of the 27 galaxiesin our sample, 9 show elliptical-like profiles and 13 show an outerexponential. Interestingly, Arp 224, the second oldest merger remnant ofthe Toomre sequence shows an exponential disk in the outer parts.
| 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.
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