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K-band observations of boxy bulges - I. Morphology and surface brightness profiles
In this first paper of a series on the structure of boxy andpeanut-shaped (B/PS) bulges, Kn-band observations of a sample of 30edge-on spiral galaxies are described and discussed. Kn-bandobservations best trace the dominant luminous galactic mass and areminimally affected by dust. Images, unsharp-masked images, as well asmajor-axis and vertically summed surface brightness profiles arepresented and discussed. Galaxies with a B/PS bulge tend to have a morecomplex morphology than galaxies with other bulge types, more oftenshowing centred or off-centred X structures, secondary maxima along themajor-axis and spiral-like structures. While probably not uniquelyrelated to bars, those features are observed in three-dimensional N-bodysimulations of barred discs and may trace the main bar orbit families.The surface brightness profiles of galaxies with a B/PS bulge are alsomore complex, typically containing three or more clearly separatedregions, including a shallow or flat intermediate region (Freeman TypeII profiles). The breaks in the profiles offer evidence for bar-driventransfer of angular momentum and radial redistribution of material. Theprofiles further suggest a rapid variation of the scaleheight of thedisc material, contrary to conventional wisdom but again as expectedfrom the vertical resonances and instabilities present in barred discs.Interestingly, the steep inner region of the surface brightness profilesis often shorter than the isophotally thick part of the galaxies, itselfalways shorter than the flat intermediate region of the profiles. Thesteep inner region is also much more prominent along the major-axis thanin the vertically summed profiles. Similarly to other recent work butcontrary to the standard `bulge + disc' model (where the bulge is boththick and steep), we thus propose that galaxies with a B/PS bulge arecomposed of a thin concentrated disc (a disc-like bulge) containedwithin a partially thick bar (the B/PS bulge), itself contained within athin outer disc. The inner disc likely formed secularly throughbar-driven processes and is responsible for the steep inner region ofthe surface brightness profiles, traditionally associated with a classicbulge, while the bar is responsible for the flat intermediate region ofthe surface brightness profiles and the thick complex morphologicalstructures observed. Those components are strongly coupled dynamicallyand are formed mostly of the same (disc) material, shaped by the weakbut relentless action of the bar resonances. Any competing formationscenario for galaxies with a B/PS bulge, which represent at least 45 percent of the local disc galaxy population, must explain equally well andself-consistently the above morphological and photometric properties,the complex gas and stellar kinematics observed, and the correlationsbetween them.
| Boxy/peanut `bulges': comparing the structure of galaxies with the underlying families of periodic orbits
The vertical profiles of disc galaxies are built by the material trappedaround stable periodic orbits, which form their `skeletons'. Therefore,knowledge of the stability of the main families of periodic orbits inappropriate 3D models enables one to predict possible morphologies foredge-on disc galaxies. In a pilot survey we compare the orbitalstructures that lead to the appearance of `peanut'- and `X'-likefeatures with the edge-on profiles of three disc galaxies (IC 2531, NGC4013 and UGC 2048). The subtraction from the images of a modelrepresenting the axisymmetric component of the galaxies reveals thecontribution of the non-axisymmetric terms. We find a directcorrespondence between the orbital profiles of 3D bars in models and theobserved main morphological features of the residuals. We also apply asimple unsharp masking technique in order to study the sharpest featuresof the images. Our basic conclusion is that the morphology of the boxy`bulges' of these galaxies can be explained by considering disc materialtrapped around stable 3D periodic orbits. In most models, thesebuilding-block periodic orbits are bifurcated from the planar centralfamily of a non-axisymmetric component, usually a bar, at low-ordervertical resonances. In such a case, the boxy `bulges' are parts of barsseen edge-on. For the three galaxies we study, the families associatedwith the `peanut' or `X'-shape morphology are probably bifurcations atthe vertical 2/1 or 4/1 resonance.
| Structural Parameters of Thin and Thick Disks in Edge-on Disk Galaxies
We analyze the global structure of 34 late-type, edge-on, undisturbed,disk galaxies spanning a wide range of mass. We measure structuralparameters for the galaxies using two-dimensional least-squares fittingto our R-band photometry. The fits require both a thick and a thin diskto adequately fit the data. The thick disks have larger scale heightsand longer scale lengths than the embedded thin disks by factors of ~2and ~1.25, respectively. The observed structural parameters agree wellwith the properties of thick and thin disks derived from star counts inthe Milky Way and from resolved stellar populations in nearby galaxies.We find that massive galaxies' luminosities are dominated by the thindisk. However, in low-mass galaxies (Vc<~120 kms-1) thick disk stars contribute nearly half the luminosityand dominate the stellar mass. Thus, although low-mass dwarf galaxiesappear blue, the majority of their stars are probably quite old.Our data are most easily explained by a formation scenario in which thethick disk is assembled through direct accretion of stellar materialfrom merging satellites while the thin disk is formed from accreted gas.The baryonic fraction in the thin disk therefore constrains the gasrichness of the merging pregalactic fragments. If we include the mass inH I as part of the thin disk, the thick disk contains <~10% of thebaryons in high-mass galaxies and ~25%-30% of the baryons in low-massgalaxies. Our data, therefore, indicate that the fragments were quitegas rich at the time of merging (fgas=75%-90%). However,because low-mass galaxies have a smaller fraction of baryons in theirthin disks, the pregalactic fragments from which they assembled musthave been systematically more gas poor. We believe this trend resultsfrom increased outflow due to supernova-driven winds in the lower masspregalactic fragments. We estimate that ~60% of the total baryonic massin these systems was lost due to outflows. Pushing the episode ofsignificant winds to early times allows the mass-metallicityrelationship for disks to be established early, before the main disk isassembled, and obviates the difficulty in driving winds from diffusedisks with low star formation efficiencies. We discuss otherimplications of this scenario for solving the G dwarf problem, forpredicting abundance trends in thick disks, and for removingdiscrepancies between semianalytic galaxy formation models and theobserved colors of low-mass galaxies.
| 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.
| The Interacting Galaxy Pair NGC 5394/95: Near-Infrared Photometry, Structure, and Morphology
We present near-infrared observations in the J, H, and K' passbands ofthe interacting pair of galaxies NGC 5394/95 (KPG 404). The totalmagnitudes, colors, surface brightnesses, and color profiles arecalculated. In addition, aperture magnitudes are compared againstprevious determinations. We also perform a structural (disk + bulge)analysis, as well as a two-dimensional Fourier analysis, to gain insightinto the morphology of the pair. The disk + bulge fit shows that NGC5394 (KPG 404A) is more compact than normal galaxies, while NGC 5395(KPG 404B) is less concentrated. The two-dimensional Fourier analysisshows that NGC 5394 is an H2β galaxy in the dust-penetrated (DP)classification by Block & Puerari. NGC 5395, in contrast, displays avery complex structure that needs a number of Fourier coefficients to beexplained. A tightly wound m=1 coefficient (DP class H1α) is themain structure, but other m=1 and m=2 coefficients (suggestingmodulation) are also present in the Fourier spectra. The m=1coefficients represent a pseudo-ring-type structure, indicative of acollision rather than a passage. Based on our results we are able toassert that the scenario of the interaction between the galaxy membersof KPG 404 should take into account a crossing of NGC 5394 through thedisk of NGC 5395 in a Cartwheel-like encounter rather than a passage asin M51-type pairs. Numerical simulations could help to unravel thestructural and morphological evolution of this interacting pair.
| 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.
| Optical Imaging and Spectroscopy of the Edge-on Sbc Galaxy UGC 10043: Evidence for a Galactic Wind and a Peculiar Triaxial Bulge
We present new optical imaging and spectroscopy of the peculiar, edge-onSbc galaxy UGC 10043. Using the WIYN telescope, we have obtained B, R,and Hα+[NII] images, together with DensePak integral fieldspectroscopic measurements of the stellar Ca II infrared triplet and theHα and [N II] lines from the ionized gas. The imaging observationsshow that the inner bulge of UGC 10043 (a<=7.5") is elongatedperpendicular to the galaxy major axis. At larger r the bulge isophotestwist to become oblate and nearly circular, suggesting the bulge istriaxial. The bulge shows no clear evidence for rotation about eitherits major or minor axis. The inner, southwestern quadrant of the bulgeis girdled by a narrow dust lane parallel to the minor axis; unsharpmasking reveals that this minor-axis dust lane may be part of an innerpolar ring, although we find no unambiguous kinematic evidence oforthogonally rotating material. The stellar disk of UGC 10043 has arather low optical surface brightness [μ(0)R,i~23.2 magarcsec-2], a small scale height (hz=395 pc forD=33.4 Mpc), and a mild integral sign warp. A dusty, inner diskcomponent that appears tilted relative to the outlying disk is alsoseen. The Hα and [N II] emission lines in UGC 10043 resolve intomultiple velocity components, indicating the presence of a large-scalegalactic wind with an outflow velocity of Vout>~104 kms-1. Hα+[NII] imaging reaffirms this picture byrevealing ionized gas extended to |z|~3.5 kpc in the form of a roughlybiconical structure. The [N II]/Hα line intensity ratio increaseswith increasing distance from the plane, reaching values as high as 1.7.Unlike most galaxies with large-scale winds, UGC 10043 has only a modestglobal star formation rate (<~1 Msolar yr-1),implying the wind is powered by a rather feeble central starburst. Wediscuss evolutionary scenarios that could account for both thestructural complexities of UGC 10043 and its large-scale wind. The mostplausible scenarios require a major accretion or merger event at least afew gigayears ago.
| The 1000 Brightest HIPASS Galaxies: H I Properties
We present the HIPASS Bright Galaxy Catalog (BGC), which contains the1000 H I brightest galaxies in the southern sky as obtained from the H IParkes All-Sky Survey (HIPASS). The selection of the brightest sourcesis based on their H I peak flux density (Speak>~116 mJy)as measured from the spatially integrated HIPASS spectrum. The derived HI masses range from ~107 to 4×1010Msolar. While the BGC (z<0.03) is complete inSpeak, only a subset of ~500 sources can be consideredcomplete in integrated H I flux density (FHI>~25 Jy kms-1). The HIPASS BGC contains a total of 158 new redshifts.These belong to 91 new sources for which no optical or infraredcounterparts have previously been cataloged, an additional 51 galaxiesfor which no redshifts were previously known, and 16 galaxies for whichthe cataloged optical velocities disagree. Of the 91 newly cataloged BGCsources, only four are definite H I clouds: while three are likelyMagellanic debris with velocities around 400 km s-1, one is atidal cloud associated with the NGC 2442 galaxy group. The remaining 87new BGC sources, the majority of which lie in the zone of avoidance,appear to be galaxies. We identified optical counterparts to all but oneof the 30 new galaxies at Galactic latitudes |b|>10deg.Therefore, the BGC yields no evidence for a population of``free-floating'' intergalactic H I clouds without associated opticalcounterparts. HIPASS provides a clear view of the local large-scalestructure. The dominant features in the sky distribution of the BGC arethe Supergalactic Plane and the Local Void. In addition, one can clearlysee the Centaurus Wall, which connects via the Hydra and Antlia Clustersto the Puppis Filament. Some previously hardly noticable galaxy groupsstand out quite distinctly in the H I sky distribution. Several newstructures, including some not behind the Milky Way, are seen for thefirst time.
| 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.
| The gas content of peculiar galaxies: Strongly interacting systems
A study of the gas content in 1038 interacting galaxies, essentiallyselected from Arp, Arp & Madore, Vorontsov-Velyaminov catalogues andsome of the published literature, is presented here. The data on theinterstellar medium have been extracted from a number of sources in theliterature and compared with a sample of 1916 normal galaxies. The meanvalues for each of the different ISM tracers (FIR, 21 cm, CO lines,X-ray) have been estimated by means of survival analysis techniques, inorder to take into account the presence of upper limits. From the datait appears that interacting galaxies have a higher gas content thannormal ones. Galaxies classified as ellipticals have both a dust and gascontent one order of magnitude higher than normal. Spirals have in mostpart a normal dust and HI content but an higher molecular gas mass. TheX-ray luminosity also appears higher than that of normal galaxies ofsame morphological type, both including or excluding AGNs. We consideredthe alternative possibilities that the molecular gas excess may derivefrom the existence of tidal torques which produce gas infall from thesurrounding regions or from a different metallicity which affects the Xconversion factor between the observed CO line luminosity and the H_2calculated mass. According to our tests, it appears that interactinggalaxies possess a higher molecular mass than normal galaxies but with asimilar star formation efficiency.Table 1 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/422/941
| Thick disks of lenticular galaxies. 3D-photometric thin/thick disk decomposition of eight edge-on s0 galaxies
Thick disks are faint and extended stellar components found aroundseveral disk galaxies including our Milky Way. The Milky Way thick disk,the only one studied in detail, contains mostly old disk stars (≈10Gyr), so that thick disks are likely to trace the early stages of diskevolution. Previous detections of thick disk stellar light in externalgalaxies have been originally made for early-type, edge-on galaxies butdetailed 2D thick/thin disk decompositions have been reported for only ascant handful of mostly late-type disk galaxies. We present in thispaper for the first time explicit 3D thick/thin disk decompositionscharacterising the presence and properties (e.g. scalelength andscaleheight) for a sample of eight lenticular galaxies by fitting 3Ddisk models to the data. For six out of the eight galaxies we were ableto derive a consistent thin/thick disk model. The mean scaleheight ofthe thick disk is 3.6 times larger than that of the thin disk. Thescalelength of the thick disk is about twice, and its central luminositydensity between 3-10% of, the thin disk value. Both thin and thick diskare truncated at similar radii. This implies that thick disks extendover fewer scalelengths than thin disks, and turning a thin disk into athick one requires therefore vertical but little radial heating. Allthese structural parameters are similar to thick disk parameters forlater Hubble-type galaxies previously studied. We discuss our data inrespect to present models for the origin of thick disks, either as pre-or post-thin-disk structures, providing new observational constraints.Based on observations obtained at the European Southern Observatory,Chile.Full appendices are only available in electronic form athttp://www.edpsciences.org
| An Hα survey aiming at the detection of extraplanar diffuse ionized gas in halos of edge-on spiral galaxies. I. How common are gaseous halos among non-starburst galaxies?
In a series of two papers we present results of a new Hα imagingsurvey, aiming at the detection of extraplanar diffuse ionized gas inhalos of late-type spiral galaxies. We have investigated a sample of 74nearby edge-on spirals, covering the northern and southern hemisphere.In 30 galaxies we detected extraplanar diffuse emission at meandistances of |z| ~ 1-2 kpc. Individual filaments can be traced out to|z|<=6 kpc in a few cases. We find a good correlation between the FIRflux ratio (S60/S100) and the SFR per unit area(LFIR/D225), based on thedetections/non-detections. This is actually valid for starburst, normaland for quiescent galaxies. A minimal SFR per unit area for the lowestS60/S100 values, at which extended emission hasbeen detected, was derived, which amounts to dotEA25thres = (3.2+/-0.5)*E40ergs-1 kpc-2. There are galaxies where extraplanaremission was detected at smaller values ofLFIR/D225, however, only in combinationwith a significantly enhanced dust temperature. The results corroboratethe general view that the gaseous halos are a direct consequence of SFactivity in the underlying galactic disk.Based on observations collected at the European Southern Observatory,Chile (ESO No. 63.N-0070, ESO No. 64.N-0034, ESO No. 65.N.-0002).
| 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.
| Flat Galaxies of the RFGC Catalog Detected in the HIPASS Survey
Data from the H I Parkes All-Sky Survey (HIPASS) of the southern sky inthe neutral hydrogen line are used to determine the radial velocitiesand widths of the H I line for flat spiral galaxies of the RevisedFlat-Galaxy Catalog (RFGC) seen edge-on. The sample of 103 flat galaxiesdetected in HIPASS is characterized by a median radial velocity of +2037km/sec and a median width of the H I line at the level of 50% of maximumof 242 km/sec. For RFGC galaxies the 50% detection level in HIPASScorresponds to an apparent magnitude B t = 14 m .5 or an angulardiameter a = 2.9. The relative number of detected galaxies increasesfrom 2% for the morphological types Sbc and Sc to 41% for the type Sm.The median value of the ratio of hydrogen mass to total mass for RFGCgalaxies is 0.079. With allowance for the average internal extinctionfor edge-on galaxies, B t m .75, the median ratio of hydrogen mass toluminosity, M H I/L B = 0.74 M ȯ/L ȯ, is typical for late-typespirals. Because of its small depth, HIPASS reveals only a few RFGCgalaxies with previously unknown velocities and line widths.
| 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.
| A Dust-penetrated Classification Scheme for Bars as Inferred from Their Gravitational Force Fields
The division of galaxies into ``barred'' (SB) and ``normal'' (S) spiralsis a fundamental aspect of the Hubble galaxy classification system. This``tuning fork'' view was revised by de Vaucouleurs, whose classificationvolume recognized apparent ``bar strength'' (SA, SAB, SB) as acontinuous property of galaxies called the ``family.'' However, the SA,SAB, and SB families are purely visual judgments that can have littlebearing on the actual bar strength in a given galaxy. Until veryrecently, published bar judgments were based exclusively on blue lightimages, where internal extinction or star formation can either mask abar completely or give the false impression of a bar in a nonbarredgalaxy. Near-infrared camera arrays, which principally trace the oldstellar population in both normal and barred galaxies, now facilitate aquantification of bar strength in terms of their gravitationalpotentials and force fields. In this paper, we show that the maximumvalue, Qb, of the ratio of the tangential force to the meanaxisymmetric radial force in a barred disk galaxy is a quantitativemeasure of the strength of a bar. Qb does not measure barellipticity or bar shape but rather depends on the actual forcing due tothe bar embedded in its disk. We show that a wide range of true barstrengths characterizes the category ``SB,'' while the de Vaucouleurscategory ``SAB'' corresponds to a narrower range of bar strengths. Wepresent Qb values for 36 galaxies, and we incorporate our barclasses into a dust-penetrated classification system for spiralgalaxies.
| Modelling the Dust Content of Spiral Galaxies
We compare optical and near-infrared surface photometry of seven edge-onspiral galaxies with corresponding surface photometry calculated from arealistic model of spiral galaxies which takes into account bothabsorption and scattering by the interstellar dust. For the stars andthe dust in the disc we use exponential distributions in bothdirections, radially and perpendicular to the plane of the disc, whilethe de Vaucouleurs (R^1/4) profile is used for the description of thebulge. The effect of the spiral structure in the galactic discs is alsoexamined and it is found that the simple exponential disc model is ableto describe quite accurately the real galaxy. From this analysis we wereable to obtain some general conclusions, the most significant of whichare: 1) The face-on central optical depth is less than unity in alloptical bands, indicating that typical spiral galaxies like those wehave modelled would be completely transparent if they were to be seenface on. 2) The dust scale height is about half that of the stars, whichmeans that dust is more concentrated near the plane of the disc. 3) Thedust scale length is about 1.4 times larger than that of the stars anddust is more radially extended than the stars. 4) The gas-to-dust massratio calculated, with the dust mass derived from the model, is close tothe value derived for our Galaxy. 5) The derived extinction law matchesthe Galactic extinction law quite well, indicating a universal dustbehaviour.
| 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.
| A list of peculiar velocities of RFGC galaxies
A list of radial velocities, HI line widths and peculiar velocities of1327 galaxies from the RFGC catalogue has been compiled using actualobservations and literature data. The list can be used for studying bulkmotions of galaxies, construction of the field of peculiar velocitiesand other tasks.
| The Extraordinary ``Superthin'' Spiral Galaxy UGC 7321. II. The Vertical Disk Structure
We explore the vertical light distribution as a function ofgalactocentric radius in the edge-on (i=88deg) Sd``superthin'' galaxy UGC 7321. UGC 7321 is a low-luminosity spiral(MB,i=-17.0) with a diffuse, low surface brightness stellardisk and no discernible bulge component. Within ~0.25′ (~725 pc)of the disk center the global luminosity profile of UGC 7321 can bereasonably characterized by an exponential function with a scale heighthz~2.9" (~140 pc) in H and hz~3.1" (~150 pc) in R,making this among the thinnest galaxy disks known. Near the disk centerwe derive a ratio of disk scale length to global disk scale heighthr/hz~14 in both H and R; near the edge of thedisk, hr/hz~10. At intermediate galactocentricradii (0.25′<=|r|<=1.5′), the disk of UGC 7321becomes less peaked than an exponential near the galactic plane. Atthese radii the vertical luminosity profiles can be well reproduced by alinear combination of two isothermal disk components of differing scaleheights. These fits, together with the strong disk color gradients byMatthews, Gallagher, & van Driel, suggest that UGC 7321 has multipledisk subcomponents comprised of stellar populations with different agesand velocity dispersions. Thus even examples of the thinnest pure diskgalaxies exhibit complex structure and signatures of dynamical heating.
| 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.}
| Spectroscopy of diffuse ionized gas in halos of selected edge-on galaxies
In order to examine the excitation and ionization mechanism ofextraplanar diffuse ionized gas (DIG) we have obtained optical longslitspectra of seven edge-on spiral galaxies. In four objects the brightestemission lines can be traced out to distances of typically 1.5 kpc abovethe disk. For NGC 1963 and NGC 3044 line ratios such as [N Ii]lambda6583 /Hα or [S Ii] lambda6717 /Hα as well as [ion{O{iii}] lambda5007 }/Hβ could be measured for the halo DIG. Thisallows us to discuss the DIG in the halo of these objects in theframework of diagnostic diagrams. For these two objects, the line ratiosof [ion {O{iii}] lambda5007 }/Hβ decrease with increasing |z|,different from the recently reported trend in NGC 891 (Rand\cite{rand}). We find that emission lines from the DIG in the disks arein good agreement with photoionization models using a dilute radiationfield. However, with increasing |z| these models fail to predict themeasured [ion {Oi] lambda 6300}/Hα \ and ion {Hei lambda5876}/Hα line ratios for NGC 1963. Diagnostic diagrams reveal forNGC 1963 the need for a second ionization mechanism of the halo DIG(besides photoionization). This additional source could be shockionization. The same diagrams demonstrate an intermediate classificationfor NGC 3044. Plots of [ion {S}{ii}]/[ion {N}{ii}] vs. emission measurereveal significant changes towards the halo and seem to trace localsmall scale density fluctuations of the extraplanar DIG. Based onobservations obtained at ESO/La Silla (Chile)
| 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).
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