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Structure and kinematics of edge-on galaxy discs - V. The dynamics of stellar discs
In earlier papers in this series we determined the intrinsic stellardisc kinematics of 15 intermediate- to late-type edge-on spiral galaxiesusing a dynamical modelling technique. The sample covers a substantialrange in maximum rotation velocity and deprojected face-on surfacebrightness, and contains seven spirals with either a boxy orpeanut-shaped bulge. Here we discuss the structural, kinematical anddynamical properties. From the photometry we find that intrinsicallymore flattened discs tend to have a lower face-on central surfacebrightness and a larger dynamical mass-to-light ratio. This observationsuggests that, at a constant maximum rotational velocity, lower surfacebrightness discs have smaller vertical stellar velocity dispersions.Although the individual uncertainties are large, we find from thedynamical modelling that at least 12 discs are submaximal. The averagedisc contributes 53 +/- 4 per cent to the observed rotation at 2.2 discscalelengths (hR), with a 1σ scatter of 15 per cent.This percentage becomes somewhat lower when effects of finite discflattening and gravity by the dark halo and the gas are taken intoaccount. Since boxy and peanut-shaped bulges are probably associatedwith bars, the result suggests that at 2.2hR the submaximalnature of discs is independent of barredness. The possibility remainsthat very high surface brightness discs are maximal, as these discs areunderrepresented in our sample. We confirm that the radial stellar discvelocity dispersion is related to the galaxy maximum rotationalvelocity. The scatter in this σ versus vmax relationappears to correlate with the disc flattening, face-on central surfacebrightness and dynamical mass-to-light ratio. Low surface brightnessdiscs tend to be more flattened and have smaller stellar velocitydispersions. The findings are consistent with the observed correlationbetween disc flattening and dynamical mass-to-light ratio and cangenerally be reproduced by the simple collapse theory for disc galaxyformation. Finally, the disc mass Tully-Fisher relation is offset fromthe maximum-disc scaled stellar mass Tully-Fisher relation of the UrsaMajor cluster. This offset, -0.3 dex in mass, is naturally explained ifthe discs of the Ursa Major cluster spirals are submaximal.
| Structure and kinematics of edge-on galaxy discs - IV. The kinematics of the stellar discs
The stellar disc kinematics in a sample of 15 intermediate- to late-typeedge-on spiral galaxies are studied using a dynamical modellingtechnique. The sample covers a substantial range in maximum rotationvelocity and deprojected face-on surface brightness and contains sevenspirals with either a boxy- or peanut-shaped bulge. Dynamical models ofthe stellar discs are constructed using the disc structure from I-bandsurface photometry and rotation curves observed in the gas. Thedifferences in the line-of-sight stellar kinematics between the modelsand absorption-line spectroscopy are minimized using a least-squaresapproach. The modelling constrains the disc surface density and stellarradial velocity dispersion at a fiducial radius through the freeparameter (σz/σR)-1, whereσz/σR is the ratio of vertical andradial velocity dispersion and M/L is the disc mass-to-light ratio. For13 spirals a transparent model provides a good match to the meanline-of-sight stellar velocity dispersion. Models that include arealistic radiative transfer prescription confirm that the effect ofdust on the observable stellar kinematics is small at the observed slitpositions. We discuss possible sources of systematic error and concludethat most of these are likely to be small. The exception is the neglectof the dark halo gravity, which has probably caused an overestimate ofthe surface density in the case of low surface brightness discs.
| Structure and kinematics of edge-on galaxy discs - III. The rotation curves in the gas
A technique is introduced for deriving the gaseous rotation curves ofedge-on spiral galaxies. The entire major axis position-velocity (XV)diagram is modelled with a set of rings in a least-squares sense,allowing for the effects of beam-smearing and line-of-sight projection.The feasibility of the technique is demonstrated by applying it to goodquality HI XV diagrams of eight edge-on spirals. For seven additionalspirals the XV diagrams are of insufficient quality, and the HIrotational velocities derived earlier using the envelope-tracing methodare retained. The HI results are augmented with the optical emissionline (HII) kinematics to arrive at estimates of the full rotationcurves. A detailed comparison of the HI and HII kinematics shows thatthe discs in our sample are sufficiently transparent at the heightsabove the plane where we have taken our optical spectra to derive thestellar kinematics. In several of these spirals the HII is mainlyconfined to the spiral arms and does not extend out to the edge of theHI layer, which may have caused the HII velocity profiles to besignificantly narrower than those of HI.
| Structure and kinematics of edge-on galaxy discs - II. Observations of the neutral hydrogen
We present Australia Telescope Compact Array and Westerbork SynthesisRadio Telescope HI observations of 15 edge-on spiral galaxies ofintermediate to late morphological type. The global properties and thedistribution and kinematics of the HI gas are analysed and discussed. Wedetermine the rotation curves using the envelope-tracing method. For 10spiral galaxies with a stellar disc truncation we find an average ratioof the HI radius to the truncation radius of the stellar disc of 1.1 +/-0.2 (1σ).
| Structure and kinematics of edge-on galaxy discs - I. Observations of the stellar kinematics
We present deep optical long-slit spectra of 17 edge-on spiral galaxiesof intermediate to late morphological type, mostly parallel to theirmajor axes and in a few cases parallel to the minor axes. Theline-of-sight stellar kinematics are obtained from the stellarabsorption lines using the improved cross-correlation technique. Ingeneral, the stellar kinematics are regular and can be traced well intothe disc-dominated region. The mean stellar velocity curves are far fromsolid-body, indicating that the effect of dust extinction is not large.The line-of-sight stellar disc velocity dispersion correlates with thegalaxy maximum rotational velocity, but detailed modelling is necessaryto establish whether this represents a physical relation. In fourspirals with a boxy- or peanut-shaped bulge we are able to detectasymmetric velocity distributions, having a common signature withprojected radius in the mean line-of-sight velocity and theh3 and h4 curves. In two cases this kinematicasymmetry probably represents the `figure-of-eight' pattern synonymouswith a barred potential. We emphasize, however, that the signatures seenin the h3 and h4 curves may also be due to thedisc seen in projection.
| Star Formation Properties of a Large Sample of Irregular Galaxies
We present the results of Hα imaging of a large sample ofirregular galaxies. Our sample includes 94 galaxies with morphologicalclassifications of Im, 26 blue compact dwarfs (BCDs), and 20 Sm systems.The sample spans a large range in galactic parameters, includingintegrated absolute magnitude (MV of -9 to -19), averagesurface brightness (20-27 mag arcsec-2), current starformation activity (0-1.3 Msolar yr-1kpc-2), and relative gas content(0.02-5Msolar/LB). The Hα images were usedto measure the integrated star formation rates, determine the extents ofstar formation in the disks, and compare azimuthally averaged radialprofiles of current star formation to older starlight. The integratedstar formation rates of Im galaxies normalized to the physical size ofthe galaxy span a range of a factor of 104 with 10% Imgalaxies and one Sm system having no measurable star formation at thepresent time. The BCDs fall, on average, at the high star formation rateend of the range. We find no correlation between star formation activityand proximity to other cataloged galaxies. Two galaxies located in voidsare similar in properties to the Sm group in our sample. The H IIregions in these galaxies are most often found within the Holmbergradius RH, although in a few systems H II regions are tracedas far as 1.7RH. Similarly, most of the star formation isfound within three disk scale lengths RD, but in somegalaxies H II regions are traced as far as 6RD. A comparisonof Hα surface photometry with V-band surface photometry shows thatthe two approximately follow each other with radius in Sm galaxies, butin most BCDs there is an excess of Hα emission in the centers thatdrops with radius. In approximately half of the Im galaxies Hα andV correspond well, and in the rest there are small to large differencesin the relative rate of falloff with radius. The cases with stronggradients in the LHα/LV ratios and with highcentral star formation rate densities, which include most of the BCDs,require a significant fraction of their gas to migrate to the center inthe last gigayear. We discuss possible torques that could have causedthis without leaving an obvious signature, including dark matter barsand past interactions or mergers with small galaxies or H I clouds.There is now a substantial amount of evidence for these processes amongmany surveys of BCDs. We note that such gas migration will also increasethe local pressure and possibly enhance the formation of massive denseclusters but conclude that the star formation process itself does notappear to differ much among BCD, Im, and Sm types. In particular, thereis evidence in the distribution function for Hα surface brightnessthat the turbulent Mach numbers are all about the same in these systems.This follows from the Hα distribution functions corrected forexponential disk gradients, which are log-normal with a nearly constantdispersion. Thus, the influence of shock-triggered star formation isapparently no greater in BCDs than in Im and Sm types.
| Stellar Kinematics of Boxy Bulges: Large-Scale Bars and Inner Disks
Long-slit stellar kinematic observations were obtained along the majoraxis of 30 edge-on spiral galaxies, 24 with a boxy or peanut-shaped(B/PS) bulge and six with other bulge types for comparison. Such B/PSbulges are identified in at least 45% of highly inclined systems, and agrowing body of theoretical and observational work suggests that theyare the edge-on projection of thickened bars. Profiles of the meanstellar velocity V, the velocity dispersion σ, as well as theasymmetric (h3) and symmetric (h4) deviations froma pure Gaussian are presented for all objects. Comparing these profileswith stellar kinematic bar diagnostics developed from N-bodysimulations, we find bar signatures in 24 of our sample galaxies (80%).Galaxies with a B/PS bulge typically show a double-humped rotation curvewith an intermediate dip or plateau. They also frequently show a ratherflat central velocity dispersion profile accompanied by a secondary peakor plateau, and numerous galaxies have a local central σ minimum(>~40%). The h3 profiles display up to three slopereversals. Most importantly, h3 is normally correlated with Vover the presumed bar length, contrary to expectations from axisymmetricdisks. These characteristic bar signatures strengthen the case for aclose relationship between B/PS bulges and bars and leave little roomfor other explanations of the bulges' shape. We also find thath3 is anticorrelated with V in the very center of mostgalaxies (>~60%), indicating that these objects additionally harborcold and dense decoupled (quasi-) axisymmetric central stellar disks,which may be related to the central light peaks. These central diskscoincide with previously identified star-forming ionized-gas disks(nuclear spirals) in gas-rich systems, and we argue that they formed outof gas accumulated by the bar at its center through inflow. As suggestedby N-body models, the asymmetry of the velocity profile (h3)appears to be a reliable tracer of asymmetries in disks, allowing us todiscriminate between axisymmetric and barred disks seen in projection.B/PS bulges (and thus a large fraction of all bulges) appear to be madeup mostly of disk material, which has acquired a large vertical extentthrough bar-driven vertical instabilities. Their formation is thusprobably dominated by secular evolution processes rather than merging.
| A new catalogue of ISM content of normal galaxies
We have compiled a catalogue of the gas content for a sample of 1916galaxies, considered to be a fair representation of ``normality''. Thedefinition of a ``normal'' galaxy adopted in this work implies that wehave purposely excluded from the catalogue galaxies having distortedmorphology (such as interaction bridges, tails or lopsidedness) and/orany signature of peculiar kinematics (such as polar rings,counterrotating disks or other decoupled components). In contrast, wehave included systems hosting active galactic nuclei (AGN) in thecatalogue. This catalogue revises previous compendia on the ISM contentof galaxies published by \citet{bregman} and \citet{casoli}, andcompiles data available in the literature from several small samples ofgalaxies. Masses for warm dust, atomic and molecular gas, as well asX-ray luminosities have been converted to a uniform distance scale takenfrom the Catalogue of Principal Galaxies (PGC). We have used twodifferent normalization factors to explore the variation of the gascontent along the Hubble sequence: the blue luminosity (LB)and the square of linear diameter (D225). Ourcatalogue significantly improves the statistics of previous referencecatalogues and can be used in future studies to define a template ISMcontent for ``normal'' galaxies along the Hubble sequence. The cataloguecan be accessed on-line and is also available at the Centre desDonnées Stellaires (CDS).The catalogue is available in electronic form athttp://dipastro.pd.astro.it/galletta/ismcat and at the CDS via anonymousftp to\ cdsarc.u-strasbg.fr (130.79.128.5) or via\http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/405/5
| A catalog of warps in spiral and lenticular galaxies in the Southern hemisphere
A catalog of optical warps of galaxies is presented. This can beconsidered complementary to that reported by Sánchez-Saavedra etal. (\cite{sanchez-saavedra}), with 42 galaxies in the northernhemisphere, and to that by Reshetnikov & Combes(\cite{reshetnikov99}), with 60 optical warps. The limits of the presentcatalog are: logr 25 > 0.60, B_t< 14.5, delta (2000) <0deg, -2.5 < t < 7. Therefore, lenticular galaxies havealso been considered. This catalog lists 150 warped galaxies out of asample of 276 edge-on galaxies and covers the whole southern hemisphere,except the Avoidance Zone. It is therefore very suitable for statisticalstudies of warps. It also provides a source guide for detailedparticular observations. We confirm the large frequency of warpedspirals: nearly all galaxies are warped. The frequency and warp angle donot present important differences for the different types of spirals.However, no lenticular warped galaxy has been found within the specifiedlimits. This finding constitutes an important restriction fortheoretical models.
| Flattening and truncation of stellar discs in edge-on spiral galaxies
We analyse the global structure of the old stellar discs in 34 edge-onspiral galaxies. The radial and vertical exponential scale parameters ofthe discs are obtained by applying an improved two-dimensionaldecomposition technique to our I-band photometry. We find a clearincrease in the disc scaleheight with maximum rotational velocity, inaccordance with observations of the stellar velocity dispersions ingalaxy discs. The range and maximum of the intrinsic flattening of thedisc light seem to increase with both maximum rotational velocity andtotal HI mass. We use the disc flattening to estimate the disccontribution to the maximum rotational velocity, resulting in an averageof 57 +/- 22 per cent. The disc light distributions are furtherinvestigated for the presence of radial truncations. We find that theradial light distributions of at least 20 spirals are truncated,corresponding to 60 per cent of the sample. For small scalelengthspirals, which are the most numerous in the local Universe, the resultssuggest that the average ratio of disc truncation radius to discscalelength is at least four.
| Warps and correlations with intrinsic parameters of galaxies in the visible and radio
From a comparison of the different parameters of warped galaxies in theradio, and especially in the visible, we find that: a) No large galaxy(large mass or radius) has been found to have high amplitude in thewarp, and there is no correlation of size/mass with the degree ofasymmetry of the warp. b) The disc density and the ratio of dark toluminous mass show an opposing trend: smaller values give moreasymmetric warps in the inner radii (optical warps) but show nocorrelation with the amplitude of the warp; however, in the externalradii is there no correlation with asymmetry. c) A third anticorrelationappears in a comparison of the amplitude and degree of asymmetry in thewarped galaxies. Hence, it seems that very massive dark matter haloeshave nothing to do with the formation of warps but only with the degreeof symmetry in the inner radii, and are unrelated to the warp shape forthe outermost radii. Denser discs show the same dependence.
| Homogenization of the Stellar Population along Late-Type Spiral Galaxies
We present a study of the broadband UBV color profiles for 257 Sbcbarred and nonbarred galaxies, using photoelectric aperture photometrydata from the literature. Using robust statistical methods, we haveestimated the color gradients of the galaxies, as well as the total andbulge mean colors. A comparative photometric study using CCD images wasdone. In our sample, the color gradients are negative (reddish inward)in approximately 59% of the objects, are almost null in 27%, and arepositive in 14%, considering only the face-on galaxies, which representapproximately 51% of the sample. The results do not change, essentially,when we include the edge-on galaxies. As a consequence of this study wehave also found that barred galaxies are overrepresented among theobjects having null or positive gradients, indicating that bars act as amechanism of homogenization of the stellar population. This effect ismore evident in the U-B color index, although it can also be detected inthe B-V color. A correlation between the total and bulge colors wasfound that is a consequence of an underlying correlation between thecolors of bulges and disks found by other authors. Moreover, the meantotal color is the same irrespective of the gradient regime, whilebulges are bluer in galaxies with null or positive gradients, whichindicates an increase of the star formation rate in the central regionsof these objects. We have also made a quantitative evaluation of theamount of extinction in the center of these galaxies. This was doneusing the Wide Field Planetary Camera 2 (WFPC2) and the Near InfraredCamera and Multi-Object Spectrometer (NICMOS) Hubble Space Telescope(HST) archival data, as well as CCD B, V, and I images. We show thatalthough the extinction in the V-band can reach values up to 2 mag inthe central region, it is unlikely that dust plays a fundamental role inglobal color gradients. We found no correlation between color and O/Habundance gradients. This result could suggest that the color gradientsare more sensitive to the age rather than to the metallicity of thestellar population. However, the absence of this correlation may becaused by dust extinction. We discuss this result by considering apicture in which bars are a relatively fast, recurrent phenomenon. Theseresults are not compatible with a pure classical monolithic scenario forbulge and disk formation. On the contrary, they favor a scenario inwhich both these components are evolving in a correlated process inwhich stellar bars play a crucial role. Based partly on observationsmade at the Pico dos Dias Observatory (PDO/LNA-CNPq), Brazil.
| Properties of tidally-triggered vertical disk perturbations
We present a detailed analysis of the properties of warps andtidally-triggered perturbations perpendicular to the plane of 47interacting/merging edge-on spiral galaxies. The derived parameters arecompared with those obtained for a sample of 61 non-interacting edge-onspirals. The entire optical (R-band) sample used for this study waspresented in two previous papers. We find that the scale height of disksin the interacting/merging sample is characterized by perturbations onboth large ( =~ disk cut-off radius) and short ( =~ z0)scales, with amplitudes of the order of 280 pc and 130 pc on average,respectively. The size of these large (short) -scale instabilitiescorresponds to 14% (6%) of the mean disk scale height. This is a factorof 2 (1.5) larger than the value found for non-interacting galaxies. Ahallmark of nearly all tidally distorted disks is a scale height thatincreases systematically with radial distance. The frequent occurrenceand the significantly larger size of these gradients indicate that diskasymmetries on large scales are a common and persistent phenomenon,while local disturbances and bending instabilities decline on shortertimescales. Nearly all (93%) of the interacting/merging and 45% of thenon-interacting galaxies studied are noticeably warped. Warps ofinteracting/merging galaxies are ~ 2.5 times larger on average thanthose observed in the non-interacting sample, with sizes of the order of340 pc and 140 pc, respectively. This indicates that tidal distortionsdo considerably contribute to the formation and size of warps. However,they cannot entirely explain the frequent occurrence of warped disks.Based on observations obtained at the European Southern Observatory(ESO, La Silla, Chile), Calar Alto Observatory operated by the MPIA(DSAZ, Spain), Lowell Observatory (Flagstaff,AZ, USA), and Hoher ListObservatory (Germany).
| Tracing the vertical composition of disc galaxies through colour gradients
Optical observations of a statistically complete sample of edge-ondisc-dominated galaxies are used to study the intrinsic vertical colourgradients in the galactic discs, in order to constrain the effects ofpopulation gradients, residual dust extinction and gradients in themetal abundance of the galaxies. For the majority of our samplegalaxies, the colours and colour gradients in the range1.0hz<=|z|<=3.0hz most likely reflect theintrinsic galactic properties (where hz is the verticalscaleheight). It appears that the intrinsic vertical colour gradientsare either non-existent, or small and relatively constant as a functionof position along the major axes of the galaxies. On average, theearlier-type galaxies exhibit smaller vertical (B-I) gradients than thelater types; our results are consistent with the absence of any verticalcolour gradient in the discs of the early-type sample galaxies. In mostgalaxies small-scale variations in the magnitude and even the directionof the vertical gradient are observed: at larger galactocentricdistances they generally display redder colours with increasing zheight, whereas the opposite is often observed in and near the galacticcentres. For a significant fraction of our sample galaxies anothermechanism in addition to the effects of stellar population gradients isrequired to explain the magnitude of the observed gradients. Thenon-zero colour gradients in a significant fraction of our samplegalaxies are likely to be (at least) partially due to residual dustextinction at these z heights, as is also evidenced from the sometimessignificant differences between the vertical colour gradients measuredon either side of the galactic planes. We suggest that initial verticalmetallicity gradients, if any, have probably not been accentuated byaccretion or merging events over the lifetimes of our sample galaxies.On the other hand, they may have weakened any existing verticalmetallicity gradients, although they also may have left the existingcorrelations unchanged.
| 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.
| Box- and peanut-shaped bulges. I. Statistics
We present a classification for bulges of a complete sample of ~ 1350edge-on disk galaxies derived from the RC3 (Third Reference Catalogue ofBright Galaxies, de Vaucouleurs et al. \cite{rc3}). A visualclassification of the bulges using the Digitized Sky Survey (DSS) inthree types of b/p bulges or as an elliptical type is presented andsupported by CCD images. NIR observations reveal that dust extinctiondoes almost not influence the shape of bulges. There is no substantialdifference between the shape of bulges in the optical and in the NIR.Our analysis reveals that 45% of all bulges are box- and peanut-shaped(b/p). The frequency of b/p bulges for all morphological types from S0to Sd is > 40%. In particular, this is for the first time that such alarge frequency of b/p bulges is reported for galaxies as late as Sd.The fraction of the observed b/p bulges is large enough to explain theb/p bulges by bars. Partly based on observations collected at ESO/LaSilla (Chile), DSAZ/Calar Alto (Spain), and Lowell Observatory/Flagstaff(AZ/U.S.A.). Tables 6 and 7 are only available in electronic form at CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| The influence of interactions and minor mergers on the structure of galactic disks I. Observations and disk models
This paper is the first part in our series on the influence of tidalinteractions and minor mergers on the radial and vertical disk structureof spiral galaxies. We report on the sample selection, our observations,and data reduction. Surface photometry of the optical and near infrareddata of a sample of 110 highly-inclined/edge-on disk galaxies arepresented. This sample consists of two subsamples of 61 non-interactinggalaxies (control sample) and of 49 interacting galaxies/minor mergingcandidates. Additionally, 41 of these galaxies were observed in the nearinfrared. We show that the distribution of morphological types of bothsubsamples is almost indistinguishable, covering the range between 0<= T <= 9. An improved, 3-dimensional disk modelling- and fittingprocedure is described in order to analyze and to compare the diskstructure of our sample galaxies by using characteristic parameters. Wefind that the vertical brightness profiles of galactic disks respondvery sensitive even to small deviations from the perfect edge-onorientation. Hence, projection effects of slightly inclined disks maycause substantial changes in the value of the disk scale height and musttherefore be considered in the subsequent study. Based on observationsobtained at the European Southern Observatory (ESO, La Silla, Chile),Calar Alto Observatory operated by the MPIA (DSAZ, Spain), LowellObservatory (Flagstaff/AZ, USA), and Hoher List Observatory (Germany).
| Box- and peanut-shaped bulges. II. NIR observations
We have observed 60 edge-on galaxies in the NIR in order to study thestellar distribution in galaxies with box/peanut-shaped bulges. The muchsmaller amount of dust extinction at these wavelengths allows us toidentify in almost all target galaxies with box/peanut-shaped bulges anadditional thin, central component in cuts parallel to the major axis.This structure can be identified with a bar. The length of thisstructure scaled by the length of the bulge correlates with themorphologically classified shape of the bulge. This newly establishedcorrelation is therefore mainly interpreted as the projection of the barat different aspect angles. Galaxies with peanut bulges have a bar seennearly edge-on and the ratio of bar length to thickness, 14 +/- 4, canbe directly measured for the first time. In addition, the correlation ofthe boxiness of bulges with the bar strength indicates that the barcharacteristic could partly explain differences in the bulge shape.Furthermore, a new size relation between the box/peanut structure andthe central bulge is found. Our observations are discussed in comparisonto a N-body simulation for barred galaxies (Pfenniger & Friedli\cite{pfe}). We conclude that the inner region of barred disk galaxiesare build up by three distinct components: the spheroidal bulge, a thinbar, and a b/p structure most likely representing the thick part of thebar. Based on observations collected at ESO/La Silla (61.A-0143),DSAZ/Calar Alto, and TIRGO/Gornergrat.}
| The influence of interactions and minor mergers on the structure of galactic disks. II. Results and interpretations
We present the second part of a detailed statistical study focussed onthe effects of tidal interactions and minor mergers on the radial andvertical disk structure of spiral galaxies. In the first part wereported on the sample selection, observations, and applied disk models.In this paper the results are presented, based on disk parametersderived from a sample of 110 highly-inclined/edge-on galaxies. Thissample consists of two subsamples of 49 interacting/merging and 61non-interacting galaxies. Additionally, 41 of these galaxies wereobserved in the NIR. We find significant changes of the disk structurein vertical direction, resulting in ~ 1.5 times larger scale heights andthus vertical velocity dispersions. The radial disk structure,characterized by the cut-off radius and the scale length, shows nostatistically significant changes. Thus, the ratio of radial to verticalscale parameters, h/z0, is ~ 1.7 times smaller for the sampleof interacting/merging galaxies. The total lack of typical flat diskratios h/z0 > 7 in the latter sample implies that verticaldisk heating is most efficient for (extremely) thin disks. Statisticallynearly all galactic disks in the sample (93%) possess non-isothermalvertical luminosity profiles like the sech (60%) and exp (33%)distribution, independent of the sample and passband investigated. Thisindicates that, in spite of tidal perturbations and disk thickening, theinitial vertical distribution of disk stars is not destroyed byinteractions or minor mergers. Based on observations obtained at theEuropean Southern Observatory (ESO, La Silla, Chile), Calar AltoObservatory operated by the MPIA (DSAZ, Spain), Lowell Observatory(Flagstaff/AZ, USA), and Hoher List Observatory (Germany).
| Spiral galaxy distance indicators based on near-infrared photometry
We compare two methods of distance determination to spiral galaxiesusing optical/near-infrared (NIR) observations, the (I-K) versusMK colour-absolute magnitude (CM) relation and the I- andK-band Tully-Fisher relation (TFR). Dust-free colours and NIR absolutemagnitudes greatly enhance the usefulness of the NIR CM relation as adistance indicator for moderately to highly inclined spiral galaxies inthe field (inclinations between ~80 deg and 90 deg) by avoidingcontamination by dust the scatter in the CM relation is significantlyreduced, compared with similar galaxy samples published previously. TheCM relation can be used to determine distances to field spiral galaxieswith MK>-25.5, to at least MK~-20. Our results,supplemented with previously published observations for which we can -to some degree - control the effects of extinction, are consistent witha universal nature of the CM relation for field spiral galaxies.High-resolution observations made with the Hubble Space Telescope canprovide a powerful tool to calibrate the relation and extend the usefuldistance range by more than a factor of 2 compared with ground-basedobservations. The intrinsic scatter in the NIR CM relation in theabsolute K-band magnitudes is ~0.5mag, yielding a lower limit to theaccuracy of distance determinations of the order of 25per cent. Althoughwe find an unusually low scatter in the TFR (probably a statisticalaccident), a typical scatter in the TFR would yield distances to oursample galaxies with uncertainties of only ~15per cent. However, one ofthe main advantages of the use of the NIR CM relation is that we needonly photometric data to obtain distance estimates; use of the TFRrequires additional kinematic data, although it can be used tosignificantly greater distances.
| The Nature of Boxy/Peanut-Shaped Bulges in Spiral Galaxies
We present a systematic observational study of the relationship betweenbars and boxy/peanut-shaped (B/PS) bulges. We first review and discussproposed mechanisms for their formation, focusing on accretion andbar-buckling scenarios. Using new methods relying on the kinematics ofedge-on disks, we then look for bars in a large sample of edge-on spiralgalaxies with a B/PS bulge and in a smaller control sample of edge-onspirals with more spheroidal bulges. We present position-velocitydiagrams of the ionized gas obtained from optical long-slitspectroscopy. We show that almost all B/PS bulges are due to a thick barviewed edge-on, while only a few extreme cases may be due to theaccretion of external material. This strongly supports the bar-bucklingmechanism for the formation of B/PS bulges. None of the galaxies in thecontrol sample show evidence for a bar, which suggests conversely thatbars are generally B/PS.We consider the effects of dust in the disk ofthe galaxies but conclude that it does not significantly affect ourresults. Unusual emission-line ratios correlating with kinematicalstructures are observed in many objects, and we argue that this isconsistent with the presence of strong bars in the disk of the galaxies.As expected from N-body simulations, the boxy-peanut transition appearsto be related to the viewing angle, but more work is required to derivethe precise orientation of the bars in the bulges. The reliableidentification of bars in edge-on spiral galaxies opens up for the firsttime the possibility of studying observationally the vertical structureof bars.
| The global structure of galactic discs
A statistical study of global galaxy parameters can help to improve ourunderstanding of galaxy formation processes. In this paper we presentthe analysis of global galaxy parameters based on optical andnear-infrared observations of a large sample of edge-on disc galaxies.We found a correlation between the ratio of the radial to vertical scaleparameter and galaxy type: galaxies become systematically thinner whengoing from type S0 to type Sc, whereas the distribution seems to leveloff for later types. The observed scalelength ratios (and thus theradial colour gradients) largely represent the dust content of thegalaxies. On average, the colour gradients indicated by the scalelengthratios increase from type Sa to at least type Sc. For galaxy types laterthan Sc, the average colour gradient seems to decrease again. Thedistribution of K-band (edge-on) disc central surface brightnesses israther flat, although with a large scatter. However, the latest-typesample galaxies (T>6) show an indication that their average disccentral surface brightnesses may be fainter than those of the earliertypes. This effect is probably not the result of dust extinction.
| 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.
| Attenuation Effects in Spiral Galaxies: Multiwavelength Photometry and Disk Radiative Transfer Models
We present a quantitative investigation of the optical depth throughspiral disks using BVRIJHK colors of 15 highly inclined Sab-Sc spiralsand new models for radiative transfer in stellar disks. The modelsinclude exponential stellar and dust disks, exponential stellar bulgecomponents, multiple scattering, and both homogeneous and clumpy dustdistributions. Preliminary comparisons of the observed optical andnear-infrared (NIR) color gradients across galaxy dust lanes withpredictions from radiative transfer models with slab and sphericalshapes underscore the need for these realistic exponential diskgeometries. When compared with the extent of reddening predicted by thedisk models, the maximum optical and NIR color excesses in galaxy dustlanes imply central face-on optical depths of 0.5-2.0 in the V band. Forthese highly inclined systems, we find this inferred optical depth to belargely insensitive to the difference between clumpy and homogeneousdust distributions. Comparisons of galaxy color gradients to models withhigh central optical depths contradict the often-stated claim thatspiral disks are opaque out to D_25. Our derived optical depths showthat the predicted radial color changes caused by attenuation in face-ongalaxies are much smaller than the observed color gradients in suchsystems, which suggests that the observed changes are the result ofvariations in stellar content. The face-on optical depths also implythat, when viewed edge-on, galaxy dust lanes have optical depths greaterthan 1.0 even in the K band and, thus, the NIR mass-to-light ratiochanges across dust features.
| Kinematics of the local universe. VII. New 21-cm line measurements of 2112 galaxies
This paper presents 2112 new 21-cm neutral hydrogen line measurementscarried out with the meridian transit Nan\c cay radiotelescope. Amongthese data we give also 213 new radial velocities which complement thoselisted in three previous papers of this series. These new measurements,together with the HI data collected in LEDA, put to 6 700 the number ofgalaxies with 21-cm line width, radial velocity, and apparent diameterin the so-called KLUN sample. Figure 5 and Appendices A and B forcorresponding comments are available in electronic form at thehttp://www.edpsciences.com
| Total magnitude, radius, colour indices, colour gradients and photometric type of galaxies
We present a catalogue of aperture photometry of galaxies, in UBVRI,assembled from three different origins: (i) an update of the catalogueof Buta et al. (1995) (ii) published photometric profiles and (iii)aperture photometry performed on CCD images. We explored different setsof growth curves to fit these data: (i) The Sersic law, (ii) The net ofgrowth curves used for the preparation of the RC3 and (iii) A linearinterpolation between the de Vaucouleurs (r(1/4) ) and exponential laws.Finally we adopted the latter solution. Fitting these growth curves, wederive (1) the total magnitude, (2) the effective radius, (3) the colourindices and (4) gradients and (5) the photometric type of 5169 galaxies.The photometric type is defined to statistically match the revisedmorphologic type and parametrizes the shape of the growth curve. It iscoded from -9, for very concentrated galaxies, to +10, for diffusegalaxies. Based in part on observations collected at the Haute-ProvenceObservatory.
| The z-structure of disk galaxies towards the galaxy planes
We present a detailed study of a statistically complete sample of highlyinclined disk galaxies in the near-infrared K' band. Since the K'-bandlight is relatively insensitive to contamination by galactic dust, wehave been able to follow the vertical light distributions all the waydown to the galaxy planes. The mean levels for the sharpness of theK'-band luminosity peaks indicate that the vertical luminositydistributions are more peaked than expected for the intermediate sech(z)distribution, but rounder than exponential. After fitting a generalizedfamily of fitting functions characterised by an exponent 2/n (n = inftyfor exponential, n = 2 for sech and n = 1 for sech(2) ; van der Kruit1988) we find that the mean value for 2/n in the K' band equals<2/n>_{K'} = 0.538, sigma_ {K'} = 0.198. Since projection of notcompletely edge-on galaxies onto the plane of the sky causes verticalluminosity profiles to become rounder, we have performed simulationsthat show that it is possible that all our galaxies can haveintrinsically exponential vertical surface brightness distributions. Wefind that the profile shape is independent of galaxy type, and varieslittle with position along the major axis. The fact that we observe thisin all our sample galaxies indicates that the formation process of thegalaxy disks perpendicular to the galaxy planes is a process intrinsicto the disks themselves. Based on observations obtained at the EuropeanSouthern Observatory, La Silla, Chile
| Infrared Photometry and Dust Absorption in Highly Inclined Spiral Galaxies
We present JHK surface photometry of 15 highly inclined, late-type (Sab-Sc) spirals and investigate the quantitative effects of dust extinction.Using the J- H, H- K two-color diagram, we compare the color changesalong the minor axis of each galaxy to the predictions from differentmodels of radiative transfer. Models in which scattering effects aresignificant and those with more than a small fraction of the lightsources located near the edge of the dust distribution do not produceenough extinction to explain the observed color gradients across diskabsorption features. The optical depth in dust near the plane as deducedfrom the color excess depends sensitively on the adopted dust geometry,ranging from τ = 4 to 15 in the visual band. This suggests that arealistic model of the dust distribution is required, even for infraredphotometry, to correct for dust extinction in the bulges of nearly edge-on systems.
| Candidates for a southern extension of the Karachentsev catalogue of isolated pairs of galaxies.
Not Available
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