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A new method to determine the thickness of non-edge-on disk galaxies
Aims.We present a new method to determine the thickness of non-edge-ondisk galaxies. This method allows us to investigate the mass-to-lightratio of the disk. Methods: .Our method is based on the comparisonof observations and theory of the distribution of the vertical velocitydispersion, which is obtained from the solution of three dimensionalPoisson equations and the galactic dynamical equation. Results:.As examples, the thickness and mass-to-light ratio of two diskgalaxies, NGC 1566 and NGC 5247, which have been extensively studied byspectroscopy, have been calculated. The calculated results areconsistent with observations and support the use of this method.However, due to the small sample size available, the results should beconfirmed on other samples of 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.
| A Study of Edge-On Galaxies with the Hubble Space Telescope Advanced Camera for Surveys. II. Vertical Distribution of the Resolved Stellar Population
We analyze the vertical distribution of the resolved stellar populationsin six low-mass (Vmax=67-131 km s-1), edge-on,spiral galaxies observed with the Hubble Space Telescope Advanced Camerafor Surveys. In each galaxy we find evidence for an extraplanar stellarcomponent extending up to 15 scale heights (3.5 kpc) above the plane,with a scale height typically twice that of two-dimensional fits toKs-band Two Micron All Sky Survey images. We analyze thevertical distribution as a function of stellar age by tracking changesin the color-magnitude diagram. The young stellar component(<~108 yr) is found to have a scale height larger than theyoung component in the Milky Way, suggesting that stars in theselow-mass galaxies form in a thicker disk. We also find that the scaleheight of a stellar population increases with age, with youngmain-sequence stars, intermediate-age asymptotic giant branch stars, andold red giant branch (RGB) stars having successively larger scaleheights in each galaxy. This systematic trend indicates that diskheating must play some role in producing the extraplanar stars. Weconstrain the rate of disk heating using the observed trend betweenscale height and stellar age and find that the observed heating ratesare dramatically smaller than in the Milky Way. The color distributionsof the RGB stars well above the midplane indicate that the extendedstellar components we see are moderately metal-poor, with peakmetallicities around [Fe/H]=-1 and with little or no metallicitygradient with height. The lack of metallicity gradient can be explainedif a majority of extraplanar RGB stars were formed at early times andare not dominated by a younger heated population. Our observationssuggest that, like the Milky Way, low-mass disk galaxies also havemultiple stellar components. In its structure, mean metallicity, and oldage, the RGB component in these galaxies seems analogous to the MilkyWay thick disk. However, without additional kinematic and abundancemeasurements, this association is only circumstantial, particularly inlight of the clear existence of some disk heating at intermediate ages.Finally, we find that the vertical dust distribution has a scale heightsomewhat larger than that of the main-sequence stars.
| Detections of CO in Late-Type, Low Surface Brightness Spiral Galaxies
Using the IRAM 30 m telescope, we have obtained 12CO J=1-0and 2-1 spectral line observations toward the nuclear regions of 15edge-on, low surface brightness (LSB) spiral galaxies. Our samplecomprises extreme late-type LSB spirals with disk-dominated morphologiesand rotational velocities Vrot<~120 km s-1. Wereport detections of four galaxies in at least one transition (>~5σ) for the remainder of the sample we provide upper limits on thenuclear CO content. Adopting a standard GalacticICO-to-H2 conversion factor implies molecular gasmasses of (3.3-9.8)×106 Msolar in thenuclear regions (inner 1.1-1.8 kpc) of the detected galaxies. Combiningour new data with samples of late-type spirals from the literature, wefind that CO-detected LSB spirals adhere to the sameMH2-far-infrared correlation as more luminous andhigher surface brightness galaxies. The amount of CO in the centralregions of late-type spirals appears to depend more strongly on massthan on central optical surface brightness, and CO detectabilitydeclines significantly for moderate to low surface brightness spiralswith Vrot<~90 km s-1 no LSB spirals have so farbeen detected in CO below this threshold. Metallicity effects alone areunlikely to account for this trend, and we speculate that we are seeingthe effects of a decrease in the mean fraction of a galaxy disk able tosupport giant molecular cloud formation with decreasing galaxy mass.
| A Study of Edge-On Galaxies with the Hubble Space Telescope Advanced Camera for Surveys. I. Initial Results
We present the initial results of a Hubble Space Telescope/AdvancedCamera for Surveys snapshot survey of 16 nearby, edge-on, late-typegalaxies covering a range in distance from 2 to 19 Mpc. The images ofthese galaxies show significant resolved stellar populations. We deriveF606W and F814W photometry for more than 1.2 million stars and presentcolor-magnitude diagrams that show a mixture of young, intermediate, andold stars in each galaxy. In one of the fields we serendipitously detectstars from the Large Magellanic Cloud. We also identify a candidateyoung dwarf galaxy lying ~2 kpc above the plane of NGC 4631. For thenearest six galaxies, we derive tip of the red giant branch distancesand demonstrate that these galaxies fall on the K-band Tully-Fisherrelation established in clusters. From the color of the red giantbranch, we also find evidence that these galaxies possess a metal-poorthick-disk or halo population.
| 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.
| Investigating the Origins of Dark Matter Halo Density Profiles
Although high-resolution N-body simulations make robust empiricalpredictions of the density distribution within cold dark matter halos,these studies have yielded little physical insight into the origins ofthe distribution. We therefore attempt to investigate the problem usinganalytic and semianalytic approaches. Simple analytic considerationssuggest that the inner slope of the central cusps in dark matter haloscannot be steeper than α=2 (where ρ~r-α),with α=1.5-1.7 being a more realistic upper limit. Moreover, ouranalysis suggests that any number of effects, whether real (e.g.,angular momentum imparted by tidal torques and secondary perturbations)or artificial (e.g., two-body interactions, the accuracy of thenumerical integrator, round-off errors) will result in shallower slopes.We also find that the halos should exhibit a well-defined relationshipbetween rperi/rapo andjθ/jr. We derive this relationshipanalytically and speculate that it may be ``universal.'' Using asemianalytic scheme based on Ryden & Gunn, we further explore therelationship between the specific angular momentum distribution in ahalo and its density profile. For present purposes, we restrictourselves to halos that form primarily via the nearly smooth accretionof matter, and consider only the specific angular momentum generated bysecondary perturbations associated with the cold dark matter spectrum ofdensity fluctuations. Compared to those formed in N-body simulations,our ``semianalytic'' halos are more extended, have flatter rotationcurves, and have a higher specific angular momentum, even though we havenot yet taken into account the effects of tidal torques. Whether thedensity profile of numerical halos is indeed the result of loss inangular momentum outside the central region, and whether this loss is afeature of hierarchical merging and major mergers in particular, isunder investigation.
| 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 KPNO International Spectroscopic Survey. IV. Hα-selected Survey List 2
The KPNO International Spectroscopic Survey (KISS) is an objective-prismsurvey for extragalactic emission-line objects. It combines many of thefeatures of previous slitless spectroscopic surveys with the advantagesof modern CCD detectors and is the first purely digital objective-prismsurvey for emission-line galaxies. Here we present the second list ofemission-line galaxy candidates selected from our red spectral data,which cover the wavelength range 6400 to 7200 Å. In most cases,the detected emission line is Hα. The current survey list covers a1.6d-wide strip located at δ=43°30' (B1950) and spans theright ascension range 11h55m to16h15m. The survey strip runs through the centerof the Bootes void and has enough depth to adequately sample the farside of the void. An area of 65.8 deg2 is covered. A total of1029 candidate emission-line objects have been selected for inclusion inthe survey list (15.6 deg-2). We tabulate accuratecoordinates and photometry for each source, as well as estimates of theredshift and emission-line flux and equivalent width based onmeasurements of the digital objective-prism spectra. The properties ofthe KISS emission-line galaxies are examined using the availableobservational data. Although the current survey covers only a modestfraction of the total volume of the Bootes void, we catalog at least 12objects that appear to be located within the void. Only one of theseobjects has been recognized previously as a void galaxy.
| A Survey for H2O Megamasers. III. Monitoring Water Vapor Masers in Active Galaxies
We present single-dish monitoring of the spectra of 13 extragalacticwater megamasers taken over a period of 9 years and a single epoch ofsensitive spectra for seven others. The primary motivation is a searchfor drifting line velocities analogous to those of the systemic featuresin NGC 4258, which are known to result from centripetal acceleration ofgas in an edge-on, subparsec molecular disk. We detect a velocity driftanalogous to that in NGC 4258 in only one source, NGC 2639. Another, themaser source in NGC 1052, exhibits erratic changes in its broad maserprofile over time. Narrow maser features in all of the other diskgalaxies discussed here either remain essentially constant in velocityover the monitoring period or are sufficiently weak or variable inintensity that individual features cannot be traced reliably from oneepoch to the next. In the context of a circumnuclear, molecular diskmodel, our results suggest that either (a) the maser lines seen aresystemic features subject to a much smaller acceleration than present inNGC 4258, presumably because the gas is farther from the nuclear blackhole, or (b) we are detecting ``satellite'' lines for which theacceleration is in the plane of the sky.Our data include the first K-band science observations taken with thenew 100 m Green Bank Telescope (GBT). The GBT data were taken duringtesting and commissioning of several new components and so are subjectto some limitations; nevertheless, they are in most cases the mostsensitive H2O spectra ever taken for each source and cover800 MHz (~=10,800 km s-1) of bandwidth. Many new maserfeatures are detected in these observations. Our data also include atentative and a clear detection of the megamaser in NGC 6240 at epochs ayear and a few months, respectively, prior to the detections reported byHagiwara et al. and Nakai et al.We also report a search for water vapor masers toward the nuclei of 58highly inclined (i>80deg), nearby galaxies. These sourceswere selected to investigate the tendency that H2O megamasersfavor inclined galaxies. None were detected, confirming that megamasersare associated exclusively with active galactic nuclei.
| 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 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
| Local galaxy flows within 5 Mpc
We present Hubble Space Telescope/WFPC2 images of sixteen dwarf galaxiesas part of our snapshot survey of nearby galaxy candidates. We derivetheir distances from the luminosity of the tip of the red giant branchstars with a typical accuracy of ~ 12%. The resulting distances are4.26 Mpc (KKH 5), 4.74 Mpc (KK 16), 4.72 Mpc (KK 17), 4.66 Mpc (ESO115-021), 4.43 Mpc (KKH 18), 3.98 Mpc (KK 27), 4.61 Mpc (KKH 34), 4.99Mpc (KK 54), 4.23 Mpc (ESO 490-017), 4.90 Mpc (FG 202), 5.22 Mpc (UGC3755), 5.18 Mpc (UGC 3974), 4.51 Mpc (KK 65), 5.49 Mpc (UGC 4115), 3.78Mpc (NGC 2915), and 5.27 Mpc (NGC 6503). Based on distances and radialvelocities of 156 nearby galaxies, we plot the local velocity-distancerelation, which has a slope of H0 = 73 km s-1Mpc-1 and a radial velocity dispersion of 85 kms-1. When members of the M81 and Cen A groups are removed,and distance errors are taken into account, the radial velocitydispersion drops to sigmav = 41 km s-1. The localHubble flow within 5 Mpc exhibits a significant anisotropy, with twoinfall peculiar velocity regions directed towards the Supergalacticpoles. However, two observed regions of outflow peculiar velocity,situated on the Supergalactic equator, are far away ( ~ 50degr ) fromthe Virgo/anti-Virgo direction, which disagrees with a sphericallysymmetric Virgo-centric flow. About 63% of galaxies within 5 Mpc belongto known compact and loose groups. Apart from them, we found six newprobable groups, consisting entirely of dwarf galaxies.Based on observations made with the NASA/ESA Hubble Space Telescope. TheSpace Telescope Science Institute is operated by the Association ofUniversities for Research in Astronomy, Inc. under NASA contract NAS5-26555.}\fnmsep\thanks{Table 2, and Figs. 1 and 2, are only availablein electronic form at http://www.edpsciences.org
| Galaxy flow in the Canes Venatici I cloud
We present an analysis of Hubble Space Telescope/WFPC2 images ofeighteen galaxies in the Canes Venatici I cloud. We derive theirdistances from the luminosity of the tip of the red giant branch starswith a typical accuracy of ~ 12%. The resulting distances are 3.9 Mpc(UGC 6541), 4.9 Mpc (NGC 3738), 3.0 Mpc (NGC 3741), 4.5 Mpc (KK 109),>6.3 Mpc (NGC 4150), 4.2 Mpc (UGC 7298), 4.5 Mpc (NGC 4244), 4.6 Mpc(NGC 4395), 4.9 Mpc (UGC 7559), 4.2 Mpc (NGC 4449), 4.4 Mpc (UGC 7605),4.6 Mpc (IC 3687), 4.7 Mpc (KK 166), 4.7 Mpc (NGC 4736), 4.2 Mpc (UGC8308), 4.3 Mpc (UGC 8320), 4.6 Mpc (NGC 5204), and 3.2 Mpc (UGC 8833).The CVn I cloud has a mean radial velocity of 286 +/- 9 kms-1, a mean distance of 4.1 +/- 0.2 Mpc, a radial velocitydispersion of 50 km s-1, a mean projected radius of 760 kpc,and a total blue luminosity of 2.2 x 1010 Lsun .Assuming virial or closed orbital motions for the galaxies, we estimatedtheir virial and their orbital mass-to-luminosity ratio to be 176 and 88Msun /Lsun , respectively. However, the CVn Icloud is characterized by a crossing time of 15 Gyr, and is thus farfrom a state of dynamical equilibrium. The large crossing time for thecloud, its low content of dSph galaxies (<6%), and the almost``primordial'' shape of its luminosity function show that the CVn Icomplex is in a transient dynamical state, driven rather by the freeHubble expansion than by galaxy interactions.Based on observations made with the NASA/ESA Hubble Space Telescope. TheSpace Telescope Science Institute is operated by the Association ofUniversities for Research in Astronomy, Inc. under NASA contract NAS5-26555.Figures 1 and 2 are only available in electronic form athttp://www.edpsciences.org
| Disk Boundaries in Spiral Galaxies
We explore the hypothesis that the outer boundaries(“cutoffs”) of the stellar disks observed in many galaxiesare determined by the condition of local gravitational (Jeans) stabilityfor the gaseous protodisks at large galactocentric distances. The ratioof the surface density of the disk Σdisk to the critical value forJeans instability Σcrit is computed for a number of galaxies,assuming that the gas velocity dispersion in the forming diskcorresponded to its current thickness and that the disk itself is in aquasi-equilibrium state. The mean estimated stellar velocity dispersionin the vicinity of the cutoff (12 km/s) is close to the typical velocitydispersions of gaseous clouds in disk galaxies. At greater distances,such velocity dispersions should ensure gravitational stability of thedisk both at the present epoch and in the past. The cutoff radius of thedisk R cut is correlated with other disk parameters, and the ratioΣdisk/Σcrit at R cut is close to unity in most cases. Weconclude that the available observational data agree well with thehypothesis that stellar disk cutoffs are due to a rapid decrease in thestar-formation rate beyond R cut, where the gaseous disk has always beenstable.
| The Dwarf Irregular/Wolf-Rayet Galaxy NGC 4214. I. A New Distance, Stellar Content, and Global Parameters
We present the results of a detailed optical and near-IR study of thenearby star-forming dwarf galaxy NGC 4214. We discuss the stellarcontent, drawing particular attention to the intermediate-age and/or oldfield stars, which are used as a distance indicator. On images obtainedwith the Hubble Space Telescope Wide Field Planetary Camera 2 andNear-Infrared Camera and Multi-Object Spectrometer (NICMOS) instrumentsin the equivalents of the V, R, I, J and H bands, the galaxy is wellresolved into stars. We achieve limiting magnitudes of F814W~27 in theWF chips and F110W~25 in the NICMOS 2 camera. The optical andnear-infrared color-magnitude diagrams confirm a core-halo galaxymorphology: an inner, high surface brightness, young population within~1.5′ (~1 kpc) from the center of the galaxy, where the stars areconcentrated in bright complexes along a barlike structure, and arelatively low surface brightness, field star population extending outto at least 8' (7 kpc). The color-magnitude diagrams of the core regionshow evidence of blue and red supergiants, main-sequence stars,asymptotic giant branch stars, and blue loop stars. We identify somecandidate carbon stars from their extreme near-IR color. The field-starpopulation is dominated by the ``red tangle,'' which contains the redgiant branch. We use the I-band luminosity function to determine thedistance based on the tip of the red giant branch method: 2.7+/-0.3 Mpc.This is much closer than the values usually assumed in the literature,and we provide revised distance-dependent parameters such as physicalsize, luminosity, H I mass, and star formation rate. From the mean colorof the red giant branch in V and I, we estimate the mean metal abundanceof this population to be [Fe/H]~=-1.7 dex, with a large internalabundance spread characterized by σint([Fe/H])~1 dex.Based on observations made with the NASA/ESA Hubble Space Telescope,obtained at the Space Telescope Science Institute, which is operated bythe Association of Universities for Research in Astronomy, Inc., underNASA contract NAS 5-26555.
| Neutral hydrogen and optical observations of edge-on galaxies: Hunting for warps
We present 21-cm HI line and optical R-band observations for a sample of26 edge-on galaxies. The HI observations were obtained with theWesterbork Synthesis Radio Telescope, and are part of the WHISP database(Westerbork HI Survey of Spiral and Irregular Galaxies). We present HImaps, optical images, and radial HI density profiles. We have alsoderived the rotation curves and studied the warping and lopsidedness ofthe HI disks. 20 out of the 26 galaxies of our sample are warped,confirming that warping of the HI disks is a very common phenomenon indisk galaxies. Indeed, we find that all galaxies that have an extendedHI disk with respect to the optical are warped. The warping usuallystarts around the edge of the optical disk. The degree of warping variesconsiderably from galaxy to galaxy. Furthermore, many warps areasymmetric, as they show up in only one side of the disk or exhibitlarge differences in amplitude in the approaching and receding sides ofthe galaxy. These asymmetries are more pronounced in rich environments,which may indicate that tidal interactions are a source of warpasymmetry. A rich environment tends to produce larger warps as well. Thepresence of lopsidedness seems to be related to the presence of nearbycompanions. Full Fig. 13 is only available in electronic form athttp://www.edpsciences.org
| 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.
| 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.
| 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.
| Detection of a Corrugated Velocity Pattern in the Spiral Galaxy NGC 5427
Here we report the detection, in Hα emission, of a radialcorrugation in the velocity field of the spiral galaxy NGC 5427. Thecentral velocity of the Hα line displays coherent, wavy-likevariations in the vicinity of the spiral arms. The spectra along threedifferent arm segments show that the maximum amplitude of the sinusoidalline variations are displaced some 500 pc from the central part of thespiral arms. The peak blueshifted velocities appear some 500 pc upstreamof the arm, whereas the peak redshifted velocities are located some 500pc downstream of the arm. This kinematical behavior is similar to theone expected in a galactic bore generated by the interaction of a spiraldensity wave with a thick gaseous disk, as recently modeled by Martos& Cox. Based on observations made with the William HerschelTelescope operated on the island of La Palma by the Isaac Newton Groupin the Spanish Observatorio del Roque de Los Muchachos of the Institutode Astrofísica de Canarias.
| 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.
| 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 Pressure Anomaly for H II Regions in Irregular Galaxies
The pressures of giant H II regions in six dwarf irregular galaxies arefound to be a factor of ~10 larger than the average pressures of thecorresponding galaxy disks, obtained from the stellar and gaseous columndensities. This is unlike the situation for spiral galaxies, where thesetwo pressures are approximately equal. Either the H II regions in thesedwarfs are all so young that they are still expanding, or there is anunexpected source of disk self-gravity that increases the backgroundpressure. We consider first whether any additional self-gravity mightcome from disk dark matter that either is cold H2 gas indiffuse or self-gravitating clouds with weak CO emission, or is the samematerial as the halo dark matter inferred from rotation curves. TheH2 solution is possible because cold molecular clouds wouldbe virtually invisible in existing surveys if they were also CO-weakfrom the low metal abundances in these galaxies. Cosmological darkmatter might be possible too because of the relatively large volumefraction occupied by the disk within the overall galaxy potential. Thereis a problem with both of these solutions, however: the vertical scaleheights inferred for irregular galaxies are consistent with the luminousmatter alone. The amount of disk dark matter that is required to explainthe high H II region pressures would give gas and stellar scale heightsthat are too small. The anomalous pressures in star-forming regions aremore likely the result of local peaks in the gravitational field thatcome from large gas concentrations. These peaks also explain theanomalously low average column density thresholds for star formationthat were found earlier for irregular galaxies, and they permit theexistence of a cool H I phase as the first step toward dense molecularcores. The evidence for concentrations of H I in regions of starformation is summarized; the peak column densities are shown to beconsistent with local pressure equilibrium for the H II regions.Strongly self-gravitating star-forming regions should also limit thedispersal of metals into the intergalactic medium. The third possibilityis that all of the visible H II regions in these dwarf galaxies arestrongly overpressured and still expanding. The mean time to pressureequilibrium is ~15 times their current age, which implies that theobserved population is only 7% of the total if they live that long; therest are presumably too faint to see. The expansion model also impliesthat the volume-filling factor can reach ~100 times the current factor,in which case faint and aging H II regions should merge and occupynearly the entire dwarf galaxy volume. This would explain the origin ofthe giant H I shells seen in these galaxies as the result of old,expanded H II regions that were formerly driven by OB associations. Theexciting clusters would now be so old and dispersed that they would notbe recognized easily. The shells are still round because of a lack ofshear.
| 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
| Dust outflows from quiescent spiral disks.
We have conducted a search for ``dust chimneys'' in a sample of 10highly-inclined spiral galaxies (i=86-90deg) which we hadpreviously observed in the Hα emission line (Rand 1996). We haveprocured B-band CCD images for this purpose and employed unsharp-maskingtechniques to accentuate the structure of the dust lane. Ascattering+absorption radiation transfer model enabled us to separate 5galaxies from the sample which are sufficiently inclined(i>87deg) for us to reliably identify and quantify dustclouds residing at over 2 scale-heights above the disk. Three of thesegalaxies possess numerous curvi-linear chimney structures stretching upto 2 kpc from the midplane and the fraction of total galactic dustcontained in such structures is of order 1%. Optical extinction offers alower limit to the amount of dust contained in the extraplanar layerbut, by examining the transparent submm thermal emission from NGC 891,we fix an upper limit of 5%. Our results are consistent with a similarrecent study by Howk & Savage (1999) which indicates that about halfof quiescent spiral disks possess detectable dust chimneys. We havecompared our optical images with the corresponding Hαemission-line radiation. We do not find a detailed spatialcorrespondance between dust chimneys and either sites of recentstar-formation or the extraplanar diffuse ionized gas. This is somewhatsurprising given that FIR-bright galaxies, such as M 82, are known toentrain dust at the working surface of the starburst-driven outflow(traced in Hα ). It is possible a global correlation exists, withdisks experiencing overall higher rates of star-formation alsopossessing the greatest number of chimneys. This may indicate atimescale difference between the two phenomena with the Hα phaselasting ~ 106 yr but chimneys requiring ~ 107 yrto form. Additionally, we have investigated the edge-on disk NGC 55which, being ten times closer than galaxies in our main sample, allowsus to examine in greater spatial detail the relationship betweenchimneys and recent star-formation. Our discussion touches upon highlatitude dust and supershells observed in the Milky Way. We rule outquiescent disks as prolific sources of intergalactic grains and metalsbut note that the rate at which dust is expelled from the main dustlayer is comparable to the rate at which it is produced by disk stars(suggesting that it may be an important regulatory process).
| The Revised Flat Galaxy Catalogue.
We present a new improved and completed version of the Flat GalaxyCatalogue (FGC) named the Revised Flat Galaxy Catalogue (RFGC)containing 4236 thin edge-on spiral galaxies and covering the whole sky.The Catalogue is intended to study large-scale cosmic streamings as wellas other problems of observational cosmology. The dipole moment ofdistribution of the RFGC galaxies (l = 273 degr; b =+19 degr) lieswithin statistical errors (+/-10 degr) in the direction of the LocalGroup motion towards the Microwave Background Radiation (MBR).
| Distances to eight nearby isolated low-luminosity galaxies
Eight isolated dwarf galaxies with radial velocities between 350 and 500km/s have been resolved into stars for the first time. Based onphotometry of the brightest blue and red stars, we obtained thefollowing distance estimates (in Mpc) for these galaxies: 6.5 (UGC2684), 6.9 (NGC 2537), 6.8 (UGC 5288), 5.3 (UGC 5423), 6.2 (UGC 5672),7.4 (UGC 5918), 5.4 (NGC 5023), and 5.1 (NGC 5229). A wide variety ofmorphological features is noted in the isolated galaxies underconsideration, which is clearly attributable to a difference in theirstar-formation activity. The median value of individual estimates of theHubble parameter H = V_0/D for these galaxies is 68 km/s per Mpc.
| 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.
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