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The dark matter halos of the bluest low surface brightness galaxies
We present BVI photometry and long-slit Hα rotation curve dataobtained with ESO VLT/FORS2 for six low surface brightness galaxies withextremely blue colours and very faint central regions. We find noevidence for a steep central density cusp of the type predicted by manyN-body simulations of cold dark matter (CDM) halos. Our observations areinstead consistent with dark matter halos characterized by cores ofroughly constant density, in agreement with previous investigations.While unremarkable in terms of the central density slope, these galaxiesappear unusually challenging for existing CDM halo models in terms ofaverage central halo density, as measured by the ΔV/2parameter. Since most of our target galaxies are bulgeless disks, ourobservations also disfavour a recently suggested mechanism for loweringthe central mass concentration of the halo by means of a fast collapsephase, as this scenario predicts that the original CDM profile shouldstill be detectable in bulgeless galaxies. Other potential ways ofreconciling the CDM predictions with these observations are discussed.
| The Dark Halo of NGC 5963 as a Constraint on Dark Matter Self-Interaction at the Low-Velocity Regime
Self-interacting dark matter has been proposed as a hypothesis toexplain the shallow central slopes of the density profiles of darkmatter halos in galaxies. In order to be consistent with observationalstudies at scales of galaxy clusters, the cross section should scaleinversely with the velocity of collision. In this paper we consider themass density profile of the halo of the low surface brightness (LSB)galaxy NGC 5963 to place an upper limit on the dark matter cross sectionfor collisions with velocities ~150 km s-1, i.e., at thelow-velocity regime. After calibrating against cosmological simulations,we found that the large inferred dark matter concentration and centraldark matter density in NGC 5963 are inconsistent with an effectivecollisional cross section per unit of mass >0.2 cm2g-1. Corrections were applied in order to account forreduction of the core by the adiabatic contraction caused by coolingbaryons. Our limits, which involve a number of simplifying, but alwaysconservative, assumptions, exclude the last permitted interval forvelocity-dependent cross sections to explain the flat density core inLSB galaxies. Implications for the nature of dark matter are alsodiscussed.
| The Molecular Interstellar Medium of Dwarf Galaxies on Kiloparsec Scales: A New Survey for CO in Northern, IRAS-detected Dwarf Galaxies
We present a new survey for CO in dwarf galaxies using the ARO Kitt Peak12 m telescope. This survey consists of observations of the centralregions of 121 northern dwarfs with IRAS detections and no known COemission. We detect CO in 28 of these galaxies and marginally detectanother 16, increasing by about 50% the number of such galaxies known tohave significant CO emission. The galaxies we detect are comparable instellar and dynamical mass to the Large Magellanic Cloud, althoughsomewhat brighter in CO and fainter in the far-IR. Within dwarfs, wefind that the CO luminosity LCO is most strongly correlatedwith the K-band and the far-infrared luminosities. There are also strongcorrelations with the radio continuum (RC) and B-band luminosities andlinear diameter. Conversely, we find that far-IR dust temperature is apoor predictor of CO emission within the dwarfs alone, although a goodpredictor of normalized CO content among a larger sample of galaxies. Wesuggest that LCO and LK correlate well because thestellar component of a galaxy dominates the midplane gravitational fieldand thus sets the pressure and density of the atomic gas, which controlthe formation of H2 from H I. We compare our sample with moremassive galaxies and find that dwarfs and large galaxies obey the samerelationship between CO and the 1.4 GHz RC surface brightness. Thisrelationship is well described by a Schmidt law withΣRC~Σ1.3CO. Therefore,dwarf galaxies and large spirals exhibit the same relationship betweenmolecular gas and star formation rate (SFR). We find that this result isrobust to moderate changes in the RC-to-SFR and CO-to-H2conversion factors. Our data appear to be inconsistent with large (orderof magnitude) variations in the CO-to-H2 conversion factor inthe star-forming molecular gas.
| High-Resolution Measurements of the Halos of Four Dark Matter-Dominated Galaxies: Deviations from a Universal Density Profile
We derive rotation curves for four nearby, low-mass spiral galaxies anduse them to constrain the shapes of their dark matter density profiles.This analysis is based on high-resolution two-dimensional Hαvelocity fields of NGC 4605, NGC 5949, NGC 5963, and NGC 6689 and COvelocity fields of NGC 4605 and NGC 5963. In combination with ourprevious study of NGC 2976, the full sample of five galaxies containsdensity profiles that span the range from αDM=0 toαDM=1.20, where αDM is the power-lawindex describing the central density profile. The scatter inαDM from galaxy to galaxy is 0.44, 3 times as large asin cold dark matter (CDM) simulations, and the mean density profileslope is αDM=0.73, shallower than that predicted by thesimulations. These results call into question the hypothesis that allgalaxies share a universal dark matter density profile. We show that oneof the galaxies in our sample, NGC 5963, has a cuspy density profilethat closely resembles those seen in CDM simulations, demonstrating thatwhile galaxies with the steep central density cusps predicted by CDM doexist, they are in the minority. In spite of these differences betweenobservations and simulations, the relatively cuspy density profiles wefind do not suggest that this problem represents a crisis for CDM.Improving the resolution of the simulations and incorporating additionalphysics may resolve the remaining discrepancies. We also find that fourof the galaxies contain detectable radial motions in the plane of thegalaxy. We investigate the hypothesis that these motions are caused by atriaxial dark matter halo and place lower limits on the ellipticity ofthe orbits in the plane of the disk of 0.043-0.175.Based on observations carried out at the WIYN Observatory. The WIYNObservatory is a joint facility of the University of Wisconsin-Madison,Indiana University, Yale University, and the National Optical AstronomyObservatory.
| Dark Matter in Dwarf Galaxies: High Resolution Observations
We present observations and analysis of rotation curves and dark matterhalo density profiles in the central regions of four nearby dwarfgalaxies. This observing program has been designed to overcome some ofthe limitations of other rotation curve studies that rely mostly onlongslit spectra. We find that these objects exhibit the full range ofcentral density profiles between ρ∝ r^0 (constant density) andρ∝ r-1 (NFW halo). This result suggests that thereis a distribution of central density slopes rather than a unique halodensity profile.
| The visible matter -- dark matter coupling
In the inner parts of spiral galaxies, of high or low surfacebrightness, there is a close correlation between rotation curve shapeand light distribution. For any feature in the luminosity profile thereis a corresponding feature in the rotation curve and vice versa. Thisimplies that the gravitational potential is strongly correlated with thedistribution of luminosity: either the luminous mass dominates or thereis a close coupling between luminous and dark matter. In a similar way,the declining rotation curves observed in the outer parts of highluminosity systems are a clear signature of the stellar disk whicheither dominates or traces the distribution of mass.The notion that the baryons are dynamically important in the centres ofgalaxies, including LSBs, undermines the whole controversy over thecusps in CDM halos and the comparison with the observations. If thebaryons dominate in the central regions of all spirals, including LSBs,how can the CDM profiles be compared with the observations?Alternatively, if the baryons do not dominate but simply trace the DMdistribution, why, in systems of comparable luminosity, are some DMhalos cuspy (like the light) and others (also like the light) are not?
| 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
| The Hα galaxy survey. I. The galaxy sample, Hα narrow-band observations and star formation parameters for 334 galaxies
We discuss the selection and observations of a large sample of nearbygalaxies, which we are using to quantify the star formation activity inthe local Universe. The sample consists of 334 galaxies across allHubble types from S0/a to Im and with recession velocities of between 0and 3000 km s-1. The basic data for each galaxy are narrowband H\alpha +[NII] and R-band imaging, from which we derive starformation rates, H\alpha +[NII] equivalent widths and surfacebrightnesses, and R-band total magnitudes. A strong correlation is foundbetween total star formation rate and Hubble type, with the strongeststar formation in isolated galaxies occurring in Sc and Sbc types. Moresurprisingly, no significant trend is found between H\alpha +[NII]equivalent width and galaxy R-band luminosity. More detailed analyses ofthe data set presented here will be described in subsequent papers.Based on observations made with the Jacobus Kapteyn Telescope operatedon the island of La Palma by the Isaac Newton Group in the SpanishObservatorio del Roque de los Muchachos of the Instituto deAstrofísica de Canarias.The full version of Table \ref{tab3} is available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/414/23 Reduced image datafor this survey can be downloaded fromhttp://www.astro.livjm.ac.uk/HaGS/
| Formalism and quality of a proper motion link with extragalactic objects for astrometric satellite missions
The accuracy of the link of the proper motion system of astrometricsatellite missions like AMEX and GAIA is discussed. Monte-Carlo methodswere used to simulate catalogues of positions and proper motions ofquasars and galaxies to test the link. The main conclusion is, thatfuture satellite missions like GAIA may be ``self-calibrated'' by theirmeasurements of QSOs, while additional measurements from radio stars orHST-data are needed to calibrate the less deep reaching astrometricsatellite missions of AMEX type.
| Rotation curves and metallicity gradients from HII regions in spiral galaxies
In this paper we study long slit spectra in the region of Hαemission line of a sample of 111 spiral galaxies with recognizable andwell defined spiral morphology and with a well determined environmentalstatus, ranging from isolation to non-disruptive interaction withsatellites or companions. The form and properties of the rotation curvesare considered as a function of the isolation degree, morphological typeand luminosity. The line ratios are used to estimate the metallicity ofall the detected HII regions, thus producing a composite metallicityprofile for different types of spirals. We have found that isolatedgalaxies tend to be of later types and lower luminosity than theinteracting galaxies. The outer parts of the rotation curves of isolatedgalaxies tend to be flatter than in interacting galaxies, but they showsimilar relations between global parameters. The scatter of theTully-Fisher relation defined by isolated galaxies is significantlylower than that of interacting galaxies. The [NII]/Hα ratios, usedas a metallicity indicator, show a clear trend between Z andmorphological type, t, with earlier spirals showing higher ratios; thistrend is tighter when instead of t the gradient of the inner rotationcurve, G, is used; no trend is found with the change in interactionstatus. The Z-gradient of the disks depends on the type, being almostflat for early spirals, and increasing for later types. The[NII]/Hα ratios measured for disk HII regions of interactinggalaxies are higher than for normal/isolated objects, even if all thegalaxy families present similar distributions of Hα EquivalentWidth. Tables 3 and 4 and Figs. 6, 7 and 21 are only available inelectronic form at http://www.edpsciences.org. Table 5 is only availablein electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/393/389 Based on dataobtained Asiago/Ekar Observatory. Also based on observations made withINT operated on the island of La Palma by ING in the SpanishObservatorio del Roque de Los Muchachos of the Instituto deAstrofísica de Canarias.
| The Westerbork HI survey of spiral and irregular galaxies. II. R-band surface photometry of late-type dwarf galaxies
R-band surface photometry is presented for 171 late-type dwarf andirregular galaxies. For a subsample of 46 galaxies B-band photometry ispresented as well. We present surface brightness profiles as well asisophotal and photometric parameters including magnitudes, diameters andcentral surface brightnesses. Absolute photometry is accurate to 0.1 magor better for 77% of the sample. For over 85% of the galaxies the radialsurface brightness profiles are consistent with published data withinthe measured photometric uncertainty. For most of the galaxies in thesample H I data have been obtained with the Westerbork Synthesis RadioTelescope. The galaxies in our sample are part of the WHISP project(Westerbork H I Survey of Spiral and Irregular Galaxies), which aims atmapping about 500 nearby spiral and irregular galaxies in H I. Theavailability of H I data makes this data set useful for a wide range ofstudies of the structure, dark matter content and kinematics oflate-type dwarf galaxies. Based on observations made with INT operatedon the island of La Palma by the Isaac Newton Group in the SpanishObservatorio del Roque de los Muchachos of the Instituto de Astrofisicade Canarias. The tables in Appendix A are only available in electronicform at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/390/863. Thefigures in Appendix B are only available in electronic formhttp://www.edpsciences.org
| Environment status of blue compact galaxies and trigger of star formation
The work studies of the environment of low-mass galaxies with activestar formation (SF) and a possible trigger of SF bursts due togravitational interaction. Following the study by Taylor et al. (1995),we extend the search for possible disturbing galaxies of various massesto a much larger sample of 86 BCGs from the sky region of the SecondByurakan survey (SBS). The BCG magnitudes and radial velocities arerevised and up-dated. The sample under study is separated by thecriteria: EW([O III]λ5007) > 45 Å andVh < 6,000 kms and should be representative of alllow-mass galaxies which experience SF bursts. We argue that the moderatetidal disturbers should be taken into account, and incorporate therespective range of distances in the search for disturbing neighbours.The majority of the neighbours in the vicinity of the studied BCGs arefound through the study of their environment among UZC (Falco et al.\cite{Falco99}) galaxies, and the follow-up careful search of thefainter galaxies in the NED database. For the remaining BCGs, theneighbouring galaxies are found based on the results of the SAO 6mtelescope spectroscopy. By studing the data on the radial velocities ofgalaxies in the vicinity of BCGs we found: 1) 33 of the studied BCGs(~38.5%) are associated with significantly brighter galaxies (Δ B>= 1.5m); 2) 23 BCGs (~26.5%) have neighbours either ofcomparable or significantly lower brightness; 3) 14 of the studied BCGs(16\%) with no evident associated galaxy are either certain, orprobable, mergers. Summarizing, we conclude that in ~80% (or more) BCGsfrom the studied sample, the SF bursts are triggered either by tidalaction of various strengths from other galaxies, or due to mergers oflow-mass galaxies. We briefly discuss the implications of our mainconclusion for evolutionary links of BCGs to other types of low-massgalaxies. Part of our sample falls into the volume belonging to theLocal Supercluster. Therefore we formulate the results separately on the``Local Supercluster volume'' and ``general field region''. The totalfractions of BCGs likely triggered by interaction with other galaxy arerespectively, ~84.5% and 80% for the nearby volume and for the generalfield. The fractions of BCGs with significantly brighter disturbers inthese two groups are seemingly different (~54±14% vs.~31.5±7%, respectively). Among the so called ``isolated'' BCGs(that is, without a bright neighbouring galaxy) in both the LocalSupercluster volume and in general field, ~43±10% are probablydisturbed by dwarf galaxies and ~26±8% have a merger morphology.In the Appendix we present the results of the spectroscopy with the SAO6m telescope of 27 galaxies in an attempt to find possible disturbinggalaxies in the vicinity of some of the sample BCGs. Tables 2, 3 and A.1with their notes and Figs. A.1-A.3 are only available in electronic format http://www.edpsciences.org
| 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.
| Arcsecond Positions of UGC Galaxies
We present accurate B1950 and J2000 positions for all confirmed galaxiesin the Uppsala General Catalog (UGC). The positions were measuredvisually from Digitized Sky Survey images with rms uncertaintiesσ<=[(1.2")2+(θ/100)2]1/2,where θ is the major-axis diameter. We compared each galaxymeasured with the original UGC description to ensure high reliability.The full position list is available in the electronic version only.
| Lopsidedness in Early-Type Disk Galaxies
We quantify the mean asymmetry of 54 face-on, early-type disk galaxies(S0 to Sab) using the amplitude of the m = 1 azimuthal Fourier componentof the R-band surface brightness. We find that the median lopsidedness,, of our sample is 0.11 and that the most lopsided 20% ofour galaxies have >= 0.19. Asymmetries in early-typedisks appear to be of similar frequency and strength as in late-typedisk galaxies. We have observed our early-type disks in a bandpass (Rband) in which the light is dominated by stars with ages greater than10^9 yr and therefore are seeing azimuthal asymmetries in the stellarmass distribution. The similar degree of lopsidedness seen in disks ofvery different star formation rates indicates that the lopsidedness inall galactic disks is primarily due to azimuthal mass asymmetries.Hence, 20% of all disk galaxies (regardless of Hubble type) haveazimuthal asymmetries, >= 0.19, in their stellar diskmass distribution, confirming lopsidedness as a dynamical phenomenon.
| Catalogue of HI maps of galaxies. I.
A catalogue is presented of galaxies having large-scale observations inthe HI line. This catalogue collects from the literature the informationthat characterizes the observations in the 21-cm line and the way thatthese data were presented by means of maps, graphics and tables, forshowing the distribution and kinematics of the gas. It containsfurthermore a measure of the HI extension that is detected at the levelof the maximum sensitivity reached in the observations. This catalogueis intended as a guide for references on the HI maps published in theliterature from 1953 to 1995 and is the basis for the analysis of thedata presented in Paper II. The catalogue is only available inelectronic form at the CDS via anonymous ftp 130.79.128.5 orhttp://cdsweb.u-strasbg.fr/Abstract.html
| 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.
| A catalogue of spatially resolved kinematics of galaxies: Bibliography
We present a catalogue of galaxies for which spatially resolved data ontheir internal kinematics have been published; there is no a priorirestriction regarding their morphological type. The catalogue lists thereferences to the articles where the data are published, as well as acoded description of these data: observed emission or absorption lines,velocity or velocity dispersion, radial profile or 2D field, positionangle. Tables 1, 2, and 3 are proposed in electronic form only, and areavailable from the CDS, via anonymous ftp to cdsarc.u-strasbg.fr (to130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html
| The Giant, Gas-Rich, Low-Surface-Brightness Galaxy NGC 289
Using Australia Telescope Compact Array neutral hydrogen andAnglo-Australian Telescope optical observations, we investigate thedistribution of luminous and dark matter in the giant, gas-rich,low-surface-brightness galaxy NGC 289. The observations show NGC 289 tohave a high H 1-to-stellar mass ratio (M_HI/M_* ~ 0.4), and an extremelylarge H 1 radius (70 kpc, or ~ 13 disk scale-lengths), making the H 1velocity field an excellent probe of a galaxy dark halo to an unusuallylarge radius. Between ~ 10 kpc and 30 kpc the rotation curve dips by 14%of the maximum velocity. Warped disk and spiral density wave models areinvestigated to explain this dip and to determine the cause ofsignificant velocity deviations in the vicinity of the H 1 spiral arms.The best-fit kinematic model has M / L_I = 2.1Msun/Lsun for the stellar disk, only slightlylower than the maximum disk value of 2.3. A dark matter halo of 3.5x10(11) Msun is present, which is ~ 3.5 times as massive asthe combined stellar and gaseous components at the last measured pointon the rotation curve.
| Optical and I-band surface photometry of spiral galaxies. I. The data.
We present V- and I-band CCD surface photometry on 234 inclined Sa-Sdgalaxies, completed by similar data in B and R for a reduced subsample.In this first paper of a series, the reduction of the data is discussed,and several comparisons are made with other recent works. Radialprofiles are presented for the surface brightness and thecharacteristics of ellipses fitted to isophotes; global, effective, andisophotal parameters are listed. All the results are available inelectronic form.
| An image database. II. Catalogue between δ=-30deg and δ=70deg.
A preliminary list of 68.040 galaxies was built from extraction of35.841 digitized images of the Palomar Sky Survey (Paper I). For eachgalaxy, the basic parameters are obtained: coordinates, diameter, axisratio, total magnitude, position angle. On this preliminary list, weapply severe selection rules to get a catalog of 28.000 galaxies, wellidentified and well documented. For each parameter, a comparison is madewith standard measurements. The accuracy of the raw photometricparameters is quite good despite of the simplicity of the method.Without any local correction, the standard error on the total magnitudeis about 0.5 magnitude up to a total magnitude of B_T_=17. Significantsecondary effects are detected concerning the magnitudes: distance toplate center effect and air-mass effect.
| A very large array survey of neutral hydrogen in Virgo Cluster spirals. 3: Surface density profiles of the gas
In this paper we analyze the radial profiles of the neutral hydrogensurface density distribution of 17 bright spirals in the Virgo Cluster.The profiles were derived from images, which were obtained with the VeryLarge Array (VLA) and which have been presented in a previous paper(Cayatte et al., (1990)). Although the sample is still small, we can forthe first time show, that different galaxies are affected differently bythe cluster environment. We make a quantitative estimate of theimportance of the different gas removal mechanisms for selectedindividual galaxies and compare these estimates with the observed H Imorphology. In some galaxies ram-pressure stripping has done seriousdamage to the H I disks, while in other galaxies turbulent viscousstripping and thermal conductivity have caused a mild, but global H Ideficiency across the entire disk. For our analysis we divide thegalaxies into three groups according to the ration of H I to opticaldiameter, a fourth group contains the anemic galaxies. As it turns out aclassification according to relative H I diameter helps to elucidatewhich gas removal processes play a role. Galaxies in different groupshave many other properties in common, most importantly the projecteddistance from the cluster center. A comparison of the radial H I surfacedensity profiles with those of field spirals of the same morphologicaltype shows, that spirals in different groups are affected verydifferently by the environment. Galaxies with the smallest H I sizeshave normal central surface densities and we suggest that these are thegalaxies that are currently undergoing ram-pressure sweeping. Thegalaxies with only slightly smaller than usual H I diameters have adepressed H I surface density across the entire face of the galaxy. Thisis quite likely due to viscous stripping. One group is only very mildlyaffected, this could be caused by gravitational effects due to distantencounters.
| A revised catalog of CfA1 galaxy groups in the Virgo/Great Attractor flow field
A new identification of groups and clusters in the CfA1 Catalog ofHuchra et al. is presented, using a percolation algorithm to identifydensity enhancements. It is shown that in the resulting catalog,contamination by interlopers is significantly reduced. The Schechterluminosity function is redetermined, including the Malmquist bias.
| On the central surface brightness problem in disk galaxies
We have measured the diameters of a large number of disk galaxies onvarious Sky Surveys in order to examine the problem of the apparentuniformity of the central surface brightness in disk galaxies. From theratio of diameters on the various surveys we find that at least 55percent of the disk galaxies follow this rule. Another 26 percent of thegalaxies have only a very modest increase in diameters on the SRC-Jsurvey when compared to the Palomar survey prints, indicating thepresence of a cutoff in the outer disk. Nineteen percent of the galaxiesmeasured have a large increase in diameter. From their integrated H Iprofiles, these turn out to be mostly dynamically giant galaxies.Several examples are shown. The phenomenon of low surface brightnessextensions is greatly reduced for galaxies in the Virgo cluster. Fromfollow-up observations we conclude that the low surface brightnessgiants contain only about half the amount of luminous material as do'normal' spiral galaxies following the 21.65 law.
| Groups of galaxies within 80 Mpc. II - The catalogue of groups and group members
This paper gives a catalog of the groups and associations obtained bymeans of a revised hierarchical algorithm applied to a sample of 4143galaxies with diameters larger than 100 arcsec and redshifts smallerthan 6000 km/s. The 264 groups of galaxies obtained in this way (andwhich contain at least three sample galaxies) are listed, with the looseassociations surrounding them and the individual members of eachaggregate as well; moreover, the location of every entity among 13regions corresponding roughly to superclusters is specified. Finally,1729 galaxies belong to the groups, and 466 to the associations, i.e.,the total fraction of galaxies within the various aggregates amounts to53 percent.
| The far-infrared properties of the CfA galaxy sample. I - The catalog
IRAS flux densities are presented for all galaxies in the Center forAstrophysics magnitude-limited sample (mB not greater than 14.5)detected in the IRAS Faint Source Survey (FSS), a total of 1544galaxies. The detection rate in the FSS is slightly larger than in thePSC for the long-wavelength 60- and 100-micron bands, but improves by afactor of about 3 or more for the short wavelength 12- and 25-micronbands. This optically selected sample consists of galaxies which are, onaverage, much less IR-active than galaxies in IR-selected samples. Itpossesses accurate and complete redshift, morphological, and magnitudeinformation, along with observations at other wavelengths.
| Arm classification and velocity gradients in spiral galaxies
On the basis of published rotation curves, velocity gradients arecompiled for 94 galaxies. A significant correlation is found in thissample of galaxies between their gradients and arm classes (as given byElmegreen and Elmegreen, 1982); galaxies with steeper curves tend tohave a flocculent arm structure, and galaxies with flatter curves tendto have a grand design morphology. The correlation is true, since it isnot induced by other correlations. The present result is in agreementwith previous suggestions by Whitmore (1984) and with the recent resultby Elmegreen and Elmegreen; it is also consistent with the predictionsof density wave theory for the formation of the spiral structure.
| Kinematical observations of ordinary spiral galaxies - A bibliographical compilation
Data extracted from 280 papers reporting observations of the kinematicsof 245 nonbarred spiral galaxies are presented. Information is providedon the type of observations (instruments, spectral lines used, etc.) andthe derived geometrical and kinematical parameters of the galaxies(major axis position angle, inclination, heliocentric systemic velocity,maximum extension of the kinematical measurements, etc.). In addition,whenever possible, a 'mean' rotation curve has been considered, fromwhich the maximum rotational velocity of the galaxy and a parameterdescribing the essential shape of the rotation curve within r25 havebeen derived. Histograms illustrating the distribution of morphologicaltypes, inclinations, extensions of the kinematical measurements, andmaximum rotational velocities account for the statistical properties ofthis sample of spiral galaxies.
| On the behaviour of the IR CA II triplet in normal and active galaxies
The strength of the Ca II triplet in absorption at 8498/8542/8662 A hasbeen found to serve as a good luminosity indicator for metal-richstellar populations; high S/N near-IR spectroscopic data are presentedfor the nuclear regions of 42 normal and active galaxies. The normalgalaxies' Ca II triplet strengths exhibit a small spread around a meanvalue of 7 A. The large equivalent width of the IR Ca II triplet inSeyfert nuclei furnishes a unique means for probing the gravitationalpotential close to the central engine. Nuclear velocity dispersions in'active' galaxies are comparable to those in normal ones of similarluminosity.
| Properties of the redshift. I - Data and calibrations
Data at 21 cm are presented for 100 galaxies intended to be used forsystem comparisons between the NRAO 140 and 300 foot telescope and the100 m Effelsberg telescope. Data from the 300 foot telescope are alsogiven for galaxies selected for overlap comparisons with older studies.Flux calibrations and measurement uncertainties in flux, redshifts,profile width, and profile shape are discussed.
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