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Objective Classification of Spiral Galaxies Having Extended Rotation Curves Beyond the Optical Radius
We carry out an objective classification of four samples of spiralgalaxies having extended rotation curves beyond the optical radius. Amultivariate statistical analysis (viz., principal component analysis[PCA]) shows that about 96% of the total variation is due to twocomponents, one being the combination of absolute blue magnitude andmaximum rotational velocity beyond the optical region and the otherbeing the central density of the halo. On the basis of PCA a fundamentalplane has been constructed that reduces the scatter in the Tully-Fisherrelation up to a maximum of 16%. A multiple stepwise regression analysisof the variation of the overall shape of the rotation curves shows thatit is mainly determined by the central surface brightness, while theshape purely in the outer part of the galaxy (beyond the optical radius)is mainly determined by the size of the galactic disk.
| GHASP: an Hα kinematic survey of spiral and irregular galaxies - IV. 44 new velocity fields. Extension, shape and asymmetry of Hα rotation curves
We present Fabry-Perot observations obtained in the frame of the GHASPsurvey (Gassendi HAlpha survey of SPirals). We have derived the Hαmap, the velocity field and the rotation curve for a new set of 44galaxies. The data presented in this paper are combined with the datapublished in the three previous papers providing a total number of 85 ofthe 96 galaxies observed up to now. This sample of kinematical data hasbeen divided into two groups: isolated (ISO) and softly interacting(SOFT) galaxies. In this paper, the extension of the Hα discs, theshape of the rotation curves, the kinematical asymmetry and theTully-Fisher relation have been investigated for both ISO and SOFTgalaxies. The Hα extension is roughly proportional toR25 for ISO as well as for SOFT galaxies. The smallestextensions of the ionized disc are found for ISO galaxies. The innerslope of the rotation curves is found to be correlated with the centralconcentration of light more clearly than with the type or thekinematical asymmetry, for ISO as well as for SOFT galaxies. The outerslope of the rotation curves increases with the type and with thekinematical asymmetry for ISO galaxies but shows no special trend forSOFT galaxies. No decreasing rotation curve is found for SOFT galaxies.The asymmetry of the rotation curves is correlated with themorphological type, the luminosity, the (B-V) colour and the maximalrotational velocity of galaxies. Our results show that the brightest,the most massive and the reddest galaxies, which are fast rotators, arethe least asymmetric, meaning that they are the most efficient withwhich to average the mass distribution on the whole disc. Asymmetry inthe rotation curves seems to be linked with local star formation,betraying disturbances of the gravitational potential. The Tully-Fisherrelation has a smaller slope for ISO than for SOFT galaxies.
| Halo Mass Profiles and Low Surface Brightness Galaxy Rotation Curves
A recent study has claimed that the rotation curve shapes and massdensities of low surface brightness (LSB) galaxies are largelyconsistent with ΛCDM predictions, in contrast to a large body ofobservational work. I demonstrate that the method used to derive thisconclusion is incapable of distinguishing the characteristic steep CDMmass-density distribution from the core-dominated mass-densitydistributions found observationally: even core-dominatedpseudoisothermal halos would be inferred to be consistent with CDM. Thismethod can therefore make no definitive statements regarding the(dis)agreement between the data and CDM simulations. After introducingan additional criterion that does take the slope of the massdistribution into account, I find that only about a quarter of the LSBgalaxies investigated are possibly consistent with CDM. However, formost of these, the fit parameters are so weakly constrained that this isnot a strong conclusion. Of the 20 galaxies with tightly constrained fitparameters, only 3 are consistent with ΛCDM. Two of thesegalaxies are likely dominated by stars, leaving only one possible darkmatter-dominated, CDM-consistent candidate. These conclusions are basedon comparison of data and simulations at identical radii and fits to theentire rotation curves. LSB galaxies that are consistent with CDMsimulations, if they exist, seem to be rare indeed.
| 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 inner structure of ΛCDM haloes - II. Halo mass profiles and low surface brightness galaxy rotation curves
We use a set of high-resolution cosmological N-body simulations toinvestigate the inner mass profile of galaxy-sized cold dark matter(CDM) haloes. These simulations extend the numerical convergence studypresented in Paper I of this series, and demonstrate that the massprofile of CDM galaxy haloes can be robustly estimated beyond a minimumconverged radius of order rconv~ 1h-1 kpc in ourhighest-resolution runs. The density profiles of simulated haloes becomeprogressively shallower from the virial radius inwards, and show no signof approaching a well-defined power law near the centre. Atrconv, the density profile is steeper than expected from theformula proposed by Navarro, Frenk & White, which has aρ~r-1 cusp, but significantly shallower than the steeplydivergent ρ~r-1.5 cusp proposed by Moore et al. Weperform a direct comparison of the spherically averaged dark mattercircular velocity profiles with Hα rotation curves of a sample oflow surface brightness (LSB) galaxies. We find that most galaxies in thesample (about 70 per cent) have rotation curves that are consistent withthe structure of CDM haloes. Of the remainder, 20 per cent have rotationcurves which cannot be fit by any smooth fitting function with few freeparameters, and 10 per cent are inconsistent with CDM haloes. However,the latter consist mostly of rotation curves that do not extend to largeenough radii to accurately determine their shapes and maximumvelocities. We conclude that the inner structure of CDM haloes is notmanifestly inconsistent with the rotation curves of LSB galaxies.
| Cores of dark matter haloes correlate with stellar scalelengths
We investigate in detail the mass distribution obtained by means ofhigh-resolution rotation curves of 25 galaxies of differentmorphological types. The dark matter contribution to the circularrotation velocity is well-described by resorting to a dark component,the density of which shows an inner core, i.e. a central constantdensity region. We find a very strong correlation between the coreradius size RC and the stellar exponential scalelengthRD: RC~=13[RD/(5kpc)]1.05kpc, and between RCand the galaxy dynamical mass at this distance,Mdyn(RC). These relationships would not beexpected if the core radii were the product of an incorrectdecomposition procedure, or the biased result of wrong or misunderstoodobservational data. The very strong correlation between the dark andluminous scalelengths found here seems to hold also for different Hubbletypes and opens new scenarios for the nature of the dark matter ingalaxies.
| Dark Matter in Galaxies: Observational overview
I review the observational side of the present state of the debate aboutthe dark matter in galaxies, with emphasis on the core/cusp problem inlow surface brightness galaxies, and the question of maximum /sub-maximum disks in spiral galaxies. Some remarks are made about thedwarf spheroidals around the Milky Way, and about elliptical galaxies.
| A Catalog of Neighboring Galaxies
We present an all-sky catalog of 451 nearby galaxies, each having anindividual distance estimate D<~10 Mpc or a radial velocityVLG<550 km s-1. The catalog contains data onbasic optical and H I properties of the galaxies, in particular, theirdiameters, absolute magnitudes, morphological types, circumnuclearregion types, optical and H I surface brightnesses, rotationalvelocities, and indicative mass-to-luminosity and H I mass-to-luminosityratios, as well as a so-called tidal index, which quantifies the galaxyenvironment. We expect the catalog completeness to be roughly 70%-80%within 8 Mpc. About 85% of the Local Volume population are dwarf (dIr,dIm, and dSph) galaxies with MB>-17.0, which contributeabout 4% to the local luminosity density, and roughly 10%-15% to thelocal H I mass density. The H I mass-to-luminosity and the H Imass-to-total (indicative) mass ratios increase systematically fromgiant galaxies toward dwarfs, reaching maximum values about 5 in solarunits for the most tiny objects. For the Local Volume disklike galaxies,their H I masses and angular momentum follow Zasov's linear relation,expected for rotating gaseous disks being near the threshold ofgravitational instability, favorable for active star formation. We foundthat the mean local luminosity density exceeds 1.7-2.0 times the globaldensity, in spite of the presence of the Tully void and the absence ofrich clusters in the Local Volume. The mean local H I density is 1.4times its ``global'' value derived from the H I Parkes Sky Survey.However, the mean local baryon densityΩb(<8Mpc)=2.3% consists of only a half of the globalbaryon density, Ωb=(4.7+/-0.6)% (Spergel et al.,published in 2003). The mean-square pairwise difference of radialvelocities is about 100 km s-1 for spatial separations within1 Mpc, increasing to ~300 km s-1 on a scale of ~3 Mpc. alsoWe calculated the integral area of the sky occupied by the neighboringgalaxies. Assuming the H I size of spiral and irregular galaxies to be2.5 times their standard optical diameter and ignoring any evolutioneffect, we obtain the expected number of the line-of-sight intersectionswith the H I galaxy images to be dn/dz~0.4, which does not contradictthe observed number of absorptions in QSO spectra.
| 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/
| Simulating observations of dark matter dominated galaxies: towards the optimal halo profile
Low surface brightness galaxies are dominated by dark matter, and theirrotation curves thus reflect their dark matter distribution. Recenthigh-resolution rotation curves suggest that their dark mattermass-density distributions are dominated by a constant-density core.This seems inconsistent with the predictions of cold dark matter (CDM)models which produce haloes with compact density cusps and steepmass-density profiles. However, the observationally determined massprofiles may be affected by non-circular motions, asymmetries andoffsets between optical and dynamical centres, all of which tend tolower the observed slopes. Here we determine the impact of each of theseeffects on a variety of halo models, and we compare the results withobserved mass-density profiles. Our simulations suggest that no singlesystematic effect can reconcile the data with the cuspy CDM haloes. Thedata are best described by a model with a soft core with an innerpower-law mass-density slope α=-0.2 +/- 0.2. However, no singleuniversal halo profile provides a completely adequate description of thedata.
| Unstable Cold Dark Matter and the Cuspy Halo Problem in Dwarf Galaxies
We speculate that the dark halos of dwarf galaxies and low surfacebrightness galaxies soften their central cusps by the decay of afraction of cold dark matter (CDM) particles to stable particles with arecoiling velocity of a few tens of kilometers per second, after theyhave driven the formation of galactic halos. This process, however, doesnot necessarily produce a significant reduction of the central darkmatter density of satellite dwarf spheroidals such as Draco or Fornax.It is shown that the recovered distribution of concentration parametersc for the initial (before decay) Navarro-Frenk-White halos is in goodagreement with CDM predictions. Other interesting potentials of unstableCDM are highlighted.
| The Kinematic State of the Local Volume
The kinematics of galaxies within 10 Mpc of the Milky Way isinvestigated using published distances and radial velocities. Withrespect to the average Hubble flow (isotropic or simple anisotropic),there is no systematic relation between peculiar velocity dispersion andabsolute magnitude over a range of 10 mag; neither is there any apparentvariation with galaxy type or between field and cluster members. Thereare several possible explanations for the lack of variation, though allhave difficulties: either there is no relationship between light andmass on these scales, the peculiar velocities are not produced bygravitational interaction, or the background dynamical picture is wrongin some systematic way. The extremely cold local flow of 40-60 kms-1 dispersion reported by some authors is shown to be anartifact of sparse data, a velocity dispersion of over 100 kms-1 being closer to the actual value. Galaxies with a high(positive) radial velocity have been selected against in studies of thisvolume, biasing numerical results.
| The Central Mass Distribution in Dwarf and Low Surface Brightness Galaxies
We present high-resolution Hα rotation curves for a sample of 15dwarf and low surface brightness galaxies. From these we derive limitson the slopes of the central mass distributions, using both a directinversion of the rotation curves and detailed mass models. Assuming thatthe density distributions of dark matter halos follow a power law atsmall radii, ρ(r)~r-α, we find inner slopes in therange 0<~α<~1 for most galaxies. Thus, even with therelatively high spatial resolution of the Hα rotation curvespresented here, the inner slopes are poorly constrained. In generalhalos with constant density cores (α=0) provide somewhat betterfits, but the majority of our galaxies (~75%) are also consistent withα=1, as long as the R-band stellar mass-to-light ratios aresmaller than about 2. Halos with α=1.5, however, are ruled out invirtually every case. In order to investigate the robustness of theseresults we discuss and model several possible causes of systematicerrors, including noncircular motions, galaxy inclination, slit width,seeing, and slit alignment errors. Taking the associated uncertaintiesinto account, we conclude that even for the ~25% of the cases whereα=1 seems inconsistent with the rotation curves, we cannot ruleout cusp slopes this steep. Inclusion of literature samples similar tothe one presented here leads to the same conclusion when the possibilityof systematic errors is taken into account. In the ongoing debate onwhether the rotation curves of dwarf and low surface brightness galaxiesare consistent with predictions for a cold dark matter universe, weargue that our sample and the literature samples discussed in this paperprovide insufficient evidence to rule out halos with α=1. At thesame time, we note that none of the galaxies in these samples requirehalos with steep cusps, as most are equally well or better explained byhalos with constant density cores.
| A search for Low Surface Brightness galaxies in the near-infrared. I. Selection of the sample
A sample of about 3800 Low Surface Brightness (LSB) galaxies wasselected using the all-sky near-infrared (J, H and Ks-band)2MASS survey. The selected objects have a mean central surfacebrightness within a 5'' radius around their centre fainter than 18 magarcsec-2 in the Ks band, making them the lowestsurface brightness galaxies detected by 2MASS. A description is given ofthe relevant properties of the 2MASS survey and the LSB galaxy selectionprocedure, as well as of basic photometric properties of the selectedobjects. The latter properties are compared to those of other samples ofgalaxies, of both LSBs and ``classical'' high surface brightness (HSB)objects, which were selected in the optical. The 2MASS LSBs have aBT_c-KT colour which is on average 0.9 mag bluerthan that of HSBs from the NGC. The 2MASS sample does not appear tocontain a significant population of red objects.All tables and Figs. 2a-c are only available in electronic form athttp://www.edpsciences.org
| 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
| GHASP: A 3-D Survey of Spiral and Irregular Galaxies at Hα
Not Available
| Bar Galaxies and Their Environments
The prints of the Palomar Sky Survey, luminosity classifications, andradial velocities were used to assign all northern Shapley-Ames galaxiesto either (1) field, (2) group, or (3) cluster environments. Thisinformation for 930 galaxies shows no evidence for a dependence of barfrequency on galaxy environment. This suggests that the formation of abar in a disk galaxy is mainly determined by the properties of theparent galaxy, rather than by the characteristics of its environment.
| An H I Survey of Actively Star-forming Dwarf Galaxies
We present the results of H I 21 cm observations of 139 activelystar-forming dwarf galaxies obtained with the 305 m radio telescope atArecibo Observatory. Our sample consists of all objects cataloged inobjective-prism surveys for UV-excess or emission-line galaxiespublished prior to the start of the survey that have luminosities belowMB=-17.0 and that are located within the declination limitsof the Arecibo telescope. Galaxies from the Markarian, Michigan, Case,Wasilewski, Haro, and Zwicky lists are included. The sample spans a widerange of both H I gas content and star formation levels. A total of 122objects (88%) were detected; 82 galaxies have been observed for thefirst time in H I. The median velocity width for our sample is 88 kms-1, and the median H I gas mass is 3.0×108Msolar. In general, the sample galaxies are gas-rich, with anaverage MHI/LB=1.3 after correcting for theluminosity enhancement due to the starburst. The progenitors of many ofthe star-forming dwarfs have higher MHI/LB thantypically seen in samples of nearby ``normal'' galaxies, emphasizingtheir distinct nature.
| 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
| The Westerbork HI survey of spiral and irregular galaxies. I. HI imaging of late-type dwarf galaxies
Neutral hydrogen observations with the Westerbork Synthesis RadioTelescope are presented for a sample of 73 late-type dwarf galaxies.These observations are part of the WHISP project (Westerbork H I Surveyof Spiral and Irregular Galaxies). Here we present H I maps, velocityfields, global profiles and radial surface density profiles of H I, aswell as H I masses, H I radii and line widths. For the late-typegalaxies in our sample, we find that the ratio of H I extent to opticaldiameter, defined as 6.4 disk scale lengths, is on average 1.8 +/- 0.8,similar to that seen in spiral galaxies. Most of the dwarf galaxies inthis sample are rich in H I, with a typical Mion {Hi}/L_B of1.5. The relative H I content M_ion {HI}/L_R increases towards fainterabsolute magnitudes and towards fainter surface brightnesses. Dwarfgalaxies with lower average H I column densities also have lower averageoptical surface brightnesses. We find that lopsidedness is as commonamong dwarf galaxies as it is in spiral galaxies. About half of thedwarf galaxies in our sample have asymmetric global profiles, a thirdhas a lopsided H I distribution, and about half shows signs of kinematiclopsidedness.
| Neutral hydrogen in dwarf galaxies. I. The spatial distribution of HI
This paper is the first in a series presenting a sample of 30 late-typedwarf galaxies, observed with the Westerbork Synthesis Radio Telescope(WSRT) in the 21-cm line of neutral atomic hydrogen (HI). The sampleitself, the HI content of and the HI distribution in the sample galaxiesare briefly discussed. Four sample galaxies were also detected in thecontinuum.
| GHASP: An Hα kinematic survey of spiral and irregular galaxies. I. Velocity fields and rotation curves of 23 galaxies
GHASP (Gassendi Hα survey of SPirals) is a survey of Hαvelocities in spiral and irregular galaxies. The observations began in1998, with a scanning Fabry-Perot and a focal reducer attached at theCassegrain focus of the 1.93 m telescope at the Observatoire deHaute-Provence. This paper presents the Hα maps, the 2D velocityfields and the rotation curves obtained for a set of 23 galaxiesobserved in October 1998 and April 1999. Most of them have already beenobserved in HI in the frame of the WHISP survey led at Westerbork, forwhich GHASP brings an interesting complement. The aim is to provide areference sample of 2D velocity fields for about 200 nearby spiralgalaxies at Hα wavelength. Based on observations collected at theObservatoire de Haute de Provence. All the figures are only available inelectronic form at http://www.edpsciences.org
| High-resolution rotation curves of low surface brightness galaxies
We present high-resolution rotation curves of a sample of 26 low surfacebrightness galaxies. From these curves we derive mass distributionsusing a variety of assumptions for the stellar mass-to-light ratio. Weshow that the predictions of current Cold Dark Matter models for thedensity profiles of dark matter halos are inconsistent with the observedcurves. The latter indicate a core-dominated structure, rather than thetheoretically preferred cuspy structure. based on observations at theObservatoire de Haute Provence.
| Local Field of Galaxy Velocities
A sample of 145 galaxies having radial velocities relative to thecentroid of the Local Group V LG D H ij , with principal values of81:62:48 in km/sec·Mpc, which have a standard error of 4km/sec·Mpc. The minor axis of the Hubble ellipsoid is orientedalmost along the polar axis of the Local Supercluster, while the majoraxis forms an angle = (29 ± 5)° with the direction toward thecenter of the Virgo Cluster. Such a configuration of thepeculiar-velocity field shows unsatisfactory agreement with the model ofa spherically symmetric flow of galaxies toward the Virgo Cluster.Rotation of the Local Supercluster may be one reason for thisdifference. The peculiar velocities of galaxies within a volume with D V= 74 km/sec, a considerable part of which is due to the virial motionsof galaxies in groups and to distance errors. For field galaxies,located in a layer of 1 < D < 3 Mpc around the Local Group, theradial-velocity dispersion does not exceed 25 km/sec. Thevelocitydistance relation, constructed from the 20 closestgalaxies around the Local Group with D < 3 Mpc and with errorsσ(D) < 0.2 Mpc, exhibits the expected effect of gravitationaldeceleration. Using the estimate of R 0 = (0.96 ± 0.05) Mpc forthe observed radius of the zero-velocity sphere, we determined the totalmass of the Local Group to be (1.2 ± 0.2)·1012 M ȯ,which agrees well with the sum of the virial masses of the subgroups ofgalaxies around the Local Group and M31. The ratio of the Local Group'stotal mass (within R 0) to its luminosity is M/L = (23 ± 4) Mȯ/L ȯ, which does not require the existence of supermassivedark halos around our Galaxy and M31.
| 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.
| A detailed study of the ringed galaxy NGC 3344
We study the relatively isolated galaxy NGC 3344, classified as SABbc,as part of our study of ringed isolated non-barred galaxies. This galaxyshows an inner and an outer ring, together with a small bar inside theinner ring. This bar is too small to relate it directly to the formationof the outer ring and we explore here its origin through HI (WSRT) linedata together with broad band BR CCD-photometry and opticalspectroscopy. We show that the bar is exponential and dominates thecentral parts, while the bulge component is small. This suggests amorphological type later than Sbc for NGC 3344, further supported by thestrong abundance gradient reported in the literature for this galaxy.The inner ring defines the beginning of the spiral structure whichpartially wraps around this ring at small radii. Less than 1% of the HIis located in this ring which is mostly composed by a young stellarpopulation. The outer ring shows colours similar to those of the innerring, indicating that is actively forming stars. It is not locatedsymmetrically with respect to the center of the galaxy, its center beingshifted by about 18\arcs. Twenty percent of the HI emission isconcentrated in this ring. The atomic gas is distributed asymmetricallyin NGC 3344, extending 20% farther to the SE than in the oppositedirection. The outer parts of the velocity field also deviate from thatof a disk in circular rotation, with a pronounced warp especially abruptto the SE. We derive a mass model for this galaxy, but the deviationsfrom axisymmetry prohibit a good determination of a single pattern speedexplaining the location of the rings. based partially on data collectedat the Observatoire de Haute Provence, France
| 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.
| Emission-Line Spectroscopy of H II Regions in Irregular and Blue Compact Dwarf Galaxies
We present reddenings and abundances of 189 H II regions measured from203 emission-line spectra in a sample of 65 irregular (Im), blue compactdwarf (BCD), and Sm galaxies. In most of these spectra we measure [OIII] lambda5007, Hβ, [N II] lambda6584, and [S II]lambdalambda6717, 6731; in 24 spectra we measure [O II] lambda3727 andin five we measure [O III] lambda4363. The internal reddenings of thegalaxies are used to determine whether redder irregular galaxies arealso dustier than bluer irregulars. We find that the range in opticalbroadband colors among Im galaxies is most likely dominated bydifferences in the contributions of the massive star population or theeffects of abundances, while the range in colors of BCDs does showevidence consistent with a contribution from dustiness. We use theabundances to confirm that our sample of BCD galaxies, selected to becomparable to Im systems in other global properties, are also comparablein abundances and, hence, evolutionary status. Finally, we explorerelationships between abundances and other global galactic propertiesand find few convincing correlations. However, bluer galaxies tend to bemore metal-poor. There is a slight trend of higher relative gas contentwith lower abundances among the BCD sample, but not in the Im sample.The difference could be due to a difference in gas distributions and thefraction of total gas that is actively participating in the chemicalevolution of the galaxy. In addition, our BCD, but not our Im, sample ofgalaxies are consistent by themselves with the galacticluminosity-metallicity relationship determined by others, but the Imsample is consistent with the general trend seen over a large baselinewhen combined with spiral galaxies. However, the scatter is large.
| HI properties of nearby galaxies from a volume-limited sample
We consider global HI and optical properties of about three hundrednearby galaxies with V_0 < 500 km s(-1) . The majority of them haveindividual photometric distance estimates. The galaxy sample parametersshow some known and some new correlations implying a meaningful dynamicexplanation: 1) In the whole range of diameters, 1 - 40 Kpc, the galaxystandard diameter and rotational velocity follows a nearly linearTully-Fisher relation, lg A25~(0.99+/-0.06)lg V_m. 2) The HImass-to-luminosity ratio and the HI mass-to-``total" mass (inside thestandard optical diameter) ratio increase systematically from giantgalaxies towards dwarfs, reaching maximum values 5 ;M_ȯ/L_ȯand 3, respectively. 3) For all the Local Volume galaxies their totalmass-to-luminosity ratio lies within a range of [0.2-16]M_ȯ/L_ȯ with a median of 3.0 ;M_ȯ/L_ȯ. TheM25/L ratio decreases slightly from giant towards dwarfgalaxies. 4) The M_HI/L and M25/L ratios for the samplegalaxies correlate with their mean optical surface brightness, which maybe caused by star formation activity in the galaxies. 5) The M_HI/L andM25/L ratios are practically independent of the local massdensity of surrounding galaxies within the range of densities of aboutsix orders of magnitude. 6) For the LV galaxies their HI mass andangular momentum follow a nearly linear relation: lgM_HI~(0.99+/-0.04)lg (V_m* A25), expected for rotatinggaseous disks being near the threshold of gravitational instability,favourable for active star formation. Table in the Appendix is availableonly in electronic form at the CDS via anonymous ftp 130.79.128.5 orhttp//cdsweb.u-strasbg.fr/Abstract.html
| Infrared Observations of Galaxies in the Local Universe. I. The Survey and Some Representative Results
This paper introduces a continuing survey of galaxies in the localuniverse. Consistent deep images are being acquired for a representativesample of 321 galaxies in the Uppsala General Catalogue down to 21.7 magarcsec-2 at Ks (2.16 mu m) and 22.4 mag arcsec-2 at J (1.25 mu m) usinga NICMOS camera with a 3.'8 x 3.'8 field of view attached to the 61 inch(1.5 m) telescope on Mount Bigelow. We provide some examples of theresults being obtained by employing 64 deep images of a subset of 44galaxies. Bulge-to-disk ratios are tabulated for 30 galaxies. Thebrightness of the central region of 44 galaxies declines approximately 5mag from Hubble type S0 to Sm. An exponential vertical scale height atKs is found to be 500 pc for the disk of UGC 5173. Arm amplitudes offour nearly face-on spiral galaxies are found to range between 11% and88% compared to the interarm region. There is some evidence that the armamplitude is larger at Ks than it is at J. Color gradients are measuredfor 15 galaxies with only one showing a significant nonzero result. Ameasurement of galactic symmetry applied to 64 deep images reveals anaverage asymmetry of 7.6% ( sigma = 4.6%) for these galaxies.
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