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The Local Group and Other Neighboring Galaxy Groups
Over the last few years, rapid progress has been made in distancemeasurements for nearby galaxies based on the magnitude of stars on thetip of the red giant branch. Current CCD surveys with the Hubble SpaceTelescope (HST) and large ground-based telescopes bring ~10% accuratedistances for roughly a hundred galaxies within 5 Mpc. The new data ondistances to galaxies situated in (and around) the nearest groups-theLocal Group, M81 Group, Cen A/M83 Group, IC 342/Maffei Group, Sculptorfilament, and Canes Venatici cloud-allowed us to determine their totalmass from the radius of the zero-velocity surface, R0, whichseparates a group as bound against the homogeneous cosmic expansion. Thevalues of R0 for the virialized groups turn out to be closeeach other, in the range of 0.9-1.3 Mpc. As a result, the total massesof the groups are close to each other, as well, yielding total mass toblue luminosity ratios of 10-40 MsolarL-1solar. The new total mass estimates are 3-5times lower than old virial mass estimates of these groups. Becauseabout half of galaxies in the Local volume belong to such loose groups,the revision of the amount of dark matter (DM) leads to a low localdensity of matter, Ωm~=0.04, which is comparable withthe global baryonic fraction Ωb but much lower than theglobal density of matter, Ωm=0.27. To remove thediscrepancy between the global and local quantities ofΩm, we assume the existence of two different DMcomponents: (1) compact dark halos around individual galaxies and (2) anonbaryonic dark matter ``ocean'' with ΩDM1~=0.07 andΩDM2~=0.20, respectively.Based in part on observations made with the NASA/ESA Hubble SpaceTelescope, obtained at the Space Telescope Science Institute, which isoperated by the Association of Universities for Research in Astronomy,Inc., under NASA contract NAS 5-26555.
| 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.
| FLASH redshift survey - I. Observations and catalogue
The FLAIR Shapley-Hydra (FLASH) redshift survey catalogue consists of4613 galaxies brighter than bJ= 16.7 (corrected for Galacticextinction) over a 700-deg2 region of sky in the generaldirection of the Local Group motion. The survey region is a70°× 10° strip spanning the sky from the ShapleySupercluster to the Hydra cluster, and contains 3141 galaxies withmeasured redshifts. Designed to explore the effect of the galaxyconcentrations in this direction (in particular the Supergalactic planeand the Shapley Supercluster) upon the Local Group motion, the 68 percent completeness allows us to sample the large-scale structure betterthan similar sparsely-sampled surveys. The survey region does notoverlap with the areas covered by ongoing wide-angle (Sloan or 2dF)complete redshift surveys. In this paper, the first in a series, wedescribe the observation and data reduction procedures, the analysis forthe redshift errors and survey completeness, and present the surveydata.
| 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
| The Southern Dwarf Hunt: Local Group Dwarf Candidates in the Southern Sky
We present observations of 82 Local Group dwarf galaxy candidates, ofwhich 62 were chosen visually from ESO-SRC survey plates of the southernsky (32 of which were not previously cataloged) and the rest suggestedby various sources in the literature. Two are the Local Group galaxiesAntlia and Cetus; nine are more distant galaxies, though still within afew megaparsecs; 45 are background galaxies; seven are planetary (orother emission) nebulae; 15 are reflection or other Galactic nebulae;two are galaxy clusters; one is a Galactic star cluster; and one is amisidentified star. We conclude that there is no large population offaint Local Group dwarf galaxies of any familiar type awaitingdiscovery. We point out the danger of relying on a single type of datato reach conclusions about an object. Based on observations made withthe Isaac Newton Telescope, operated on the island of La Palma by theIsaac Newton Group in the Spanish Observatorio del Roque de losMuchachos of the Instituto de Astrofísica de Canarias, and onobservations made at Cerro Tololo Interamerican Observatory (CTIO). CTIOis operated by the Association of Universities for Research inAstronomy, Inc. (AURA), under a cooperative agreement with the NationalScience Foundation as part of the National Optical Astronomy Observatory(NOAO).
| New distances to galaxies in the Centaurus A group
We present Hubble Space Telescope/WFPC2 images of seventeen dwarfgalaxies in the Centaurus A group. Their distances derived from themagnitudes of the tip of the red giant branch are 5.2 Mpc (KK112), 3.2Mpc (ESO 321-014), 3.5 Mpc (KK179), 3.4 Mpc (NGC 5102), 4.6 Mpc (KK200),3.7 Mpc (ESO 324-024), 4.7 Mpc (KK208), 4.6 Mpc (ESO 444-084), 4.4 Mpc(IC 4316), 4.5 Mpc (NGC 5264), 3.6 Mpc (KK211), 3.6 Mpc (KK213), 3.4 Mpc(ESO 325-011), 3.8 Mpc (KK217), 4.0 Mpc (KK221), 4.8 Mpc (NGC 5408), and3.6 Mpc (PGC 51659). The galaxies are concentrated in two spatiallyseparated groups around NGC 5128 = Cen A and NGC 5236 = M 83. The Cen Agroup itself has a mean distance of 3.63+/- 0.07 Mpc, a velocitydispersion of 89 km s-1, a mean projected radius of 263 kpc,an estimated orbital mass of 2.1x 1012 Msun, andan orbital mass-to-blue luminosity ratio of 64Msun/Lsun. For the M 83 group we derived a meandistance of 4.57+/- 0.05 Mpc, a velocity dispersion of 62 kms-1, a mean projected radius of 142 kpc, an estimated orbitalmass of 0.8x 1012 Msun, andMorb/LB = 37 Msun/Lsun. TheM 83 group moves away from the Cen A group, which yields a radius of thezero-velocity surface of the Cen A group of R0 < 1.26 Mpc.The total mass within R0, M0 < 2.7x1012 Msun, agrees with the orbital mass estimate.The centroids of both the groups have very small peculiar velocities,(+18+/- 24) km s-1 (Cen A) and (-17+/-27) km s-1(M 83) with respect to the local Hubble flow with H0 = 70 kms-1 Mpc-1. Based on observations made with theNASA/ESA Hubble Space Telescope. The Space Telescope Science Instituteis operated by the Association of Universities for Research inAstronomy, Inc. under NASA contract NAS 5-26555. Figure 3 is onlyavailable in electronic form at http://www.edpsciences.org
| The Mass of the Centaurus A Group of Galaxies
The mass M and the radius Rh of the Centaurus A group areestimated from the positions and radial velocities of 30 probablecluster members. For an assumed distance of 3.9 Mpc, it is found thatRh~640 kpc. The velocity dispersion in the Cen A group is114+/-21 km s-1. From this value and Rh=640 kpc,the virial theorem yields a total mass of 1.4x1013Msolar for the Cen A group. The projected mass method gives amass of 1.8x1013 Msolar. These values suggest thatthe Cen A group is about 7 times as massive as the Local Group. The CenA mass-to-light ratio is found to be M/LB=155-200(M/L)solar. The cluster has a zero-velocity radiusR0=2.3 Mpc.
| New Galaxies Discovered in the First Blind H I Survey of the Centaurus A Group
We have commenced a 21 cm survey of the entire southern sky(δ<0^deg, -1200 km s^-1-13.0), low surface brightness dwarf galaxies with H I profileline-widths suggestive of dynamics dominated by dark matter. The newgroup members add approximately 6% to the H I mass of the group and 4%to its light. The H I mass function, derived from all the known groupgalaxies in the interval 10^7 M_solar
| The Shapley Supercluster. I. Spectroscopic Observations in the Central Region
We present a new analysis of the kinematics of the Shapley superclusterbased on radial velocities for 1087 galaxies in the clusters A3558(Shapley 8), A3528 (Klemola 21), A3532 (Klemola 22), A3530, A3556 (SC1321-314), A3559 (CE 1327-292), A3560, A3562, SC 1329-314 and in theintercluster region of the core of the supercluster, of which 367 arenew measurements. We also present accurate positions from APM and MAMAscans of the ESO/SERC Southern Sky Survey photographic plates. We obtainnew velocity dispersions and estimate the masses of the member clusters,evaluating dynamical models of the supercluster. The supercluster isfound to be significantly flattened. We find that for {OMEGA}_0_ = 0.3,H_0_= 75 km s^-1^ Mpc^-1^, the gravitational pull of the superclustermay account for up to 25% of the peculiar velocity of the Local Grouprequired to explain the dipole anisotropy of the Cosmic MicrowaveBackground radiation, in which case the mass of the supercluster wouldbe dominated by intercluster dark matter. This fractional contributionwould be considerably higher for combinations of significantly lowervalues of {OMEGA}_0_ and higher values of H_0_.
| Nearby galaxies. I - The catalogue
The data of 289 nearby galaxies have been compiled. The inclusion of agalaxy into the catalog depends on its redshift as in the catalogue ofKraan-Korteweg and Tammann (1979) or on the fact that the objects areknown to be certain or probable members of nearby groups. The galaxiesin the sample form the Local Group with 51 certain and probable membersand several additional groups. One third of the galaxies in the catalog(96 objects) does not seem to belong to any group. The main emphasis isto get a distance-limited sample of galaxies, especially of dwarfobjects.
| The Centaurus-Hydra supercluster region. II
In this paper, 139 redshifts obtained in the region of theCentaurus-Hydra supercluster are presented. These data, combined withthe radial velocities reported in an earlier paper, are used in apreliminary investigation of the spatial distribution of galaxies in thesurroundings of the Centaurus cluster. Attention is focused on twoparticular regions of the sky for which we have nearly complete redshiftsamples of galaxies brighter than blue magnitude 15.0. From the analysisof the spatial distribution of galaxies in these two regions, it isfound that the system of galaxies associated with the Centaurus clusterextends northeastward, and that the complexes of Centaurus and Hydra maywell be considered as separate superclusters.
| Static properties of galaxies in the Shapley-Centaurus cluster. I - The catalogue
A catalogue of the positions, sizes, orientations, ellipticities, andmorphological descriptions of 127 galaxies measured in the Southern SkySurvey Field 444 is given. The measurement errors, both internal andexternal, are discussed.
| A comparison of distance scales for early-type galaxies
The distance scales of elliptical and lenticular galaxies areintercompared, based on the velocity dispersion indicator derived from arevised Faber-Jackson relation. The scales are found to be in nearperfect agreement with scales derived from the luminosity index and fromthe 21 cm line width indicator. The scales are also in excellentagreement with the distance scale derived by Michard (1979). Additionsare offered for the general catalog of 424 early-type galaxies, and aseries of reduction equations is presented which reduces the externalerrors in the distance moduli.
| Redshifts in Klemola 27
Observational data for galaxies in the galaxy cluster Klemola 27gathered over the last few years are presented. These are mostly newredshifts and further, accurate coordinates and morphological types fora large number of 'prominent' galaxies in the ESO/SRC-Survey fields 444and 445. A few preliminary H I radial velocities are also reported. Thedata available for this cluster are briefly discussed.
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