目录
图像
上传图像
DSS Images Other Images
相关文章
Masses of the local group and of the M81 group estimated from distortions in the local velocity field
Based on high precision measurements of the distances to nearby galaxieswith the Hubble telescope, we have determined the radii of the zerovelocity spheres for the local group, R0 =0.96±0.03Mpc, and for the group of galaxies around M 81/M 82,0.89±0.05Mpc. These yield estimates of MT =(1.29±0.14)· 1012 Mȯ and(1.03±0.17)· 1012 Mȯ,respectively, for the total masses of these groups. The R0method allows us to determine the mass ratios for the two brightestmembers in both groups, as well. By varying the position of the centerof mass between the two principal members of a group to obtain minimalscatter in the galaxies on a Hubble diagram, we find mass ratios of0.8:1.0 for our galaxy and Andromeda and 0.54:1.00 for the M82 and M81galaxies, in good agreement with the observed ratios of the luminositiesof these galaxies.
| 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.
| 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).
| HIPASS High-Velocity Clouds: Properties of the Compact and Extended Populations
A catalog of southern anomalous-velocity H I clouds at decl. <+2° is presented. This catalog is based on data from the H I ParkesAll-Sky Survey (HIPASS) reprocessed with the MINMED5 procedure andsearched with a new high-velocity cloud-finding algorithm. The improvedsensitivity (5 σ: ΔTB= 0.04 K), resolution(15.5′), and velocity range (-500 kms-1
| 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.
| Line-of-sight velocity distributions of 53 early-type galaxies
55 long-slit spectra of 53 early-type galaxies were observed at LaSilla/ESO and reduced using standard methods. The line-of-sight velocitydistributions (LOSVDs) were measured using the fourier quotient methodand the fourier fitting method as described by van der Marel et al.(\cite{vdmarel93}). 32% of the examined galaxies contain kinematicallydecoupled stellar omponents, the size of these cores was 0.40 +/- 0.28kpc, in each case the core was smaller than 1 kpc. Analysis of thekinematics reveals in 49% of the sample galaxies the signature of astellar disk component, in 15% this is uncertain. There is evidence thatthe phenomenon of kinematically decoupled components is present in thewhole class of early-type galaxies. Several correlations betweenphotometric and kinematic parameters like the (v/sigma )* vs.epsilon diagram, the anisotropy - luminosity correlation or kappa -spacewere as well examined using measurement results for spectroscopic dataand photometric data out of literature. It is also shown that thosesample galaxies with kinematically decoupled components are more likelyto be found in groups of high density, strengthening the assumption thatsuch components are remnants of merging events. Full Fig. 6 is onlyavailable at http://www.edpsciences.org
| Optical counterparts to galaxies in the CEN A group discovered by HIPASS
We have completed a 21-cm survey of a 600 square degree region of theCentaurus A group of galaxies at a redshift of about 500 km per sec aspart of a larger survey of the entire southern sky. This group ofgalaxies was recently the subject of a separate and thorough opticalsurvey (Cote et al. 1997),and thus presented an ideal comparison for usto test the survey performance. We have identified 10 new group membersto add to the 21 already known in our survey area. Six of the newmembers are previously uncatalogued galaxies, while four were cataloguedbut assumed not to be group members. Including the 7 known membersoutside of our survey area, this brings the total known number of Cen Amembers to 38. All of the new HI detections have optical counterparts,most being intrinsically very faint, late-type low surface brightnessdwarfs. Most of the new members have HI masses only a few times oursurvey limit of 10^7 solar masses at an assumed distance for the groupof 3.5 Mpc, and are extremely gas-rich. Our limiting HI sensitivity wasactually slightly worse than the HI follow- up observations of the Coteet al. optical survey, yet we have already increased the known number ofgroup members by 50% using an HI survey technique. While we haveincreased the known number of members by about 50%, these new memberscontribute less than 4% to its light.
| 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 Luminosity Distribution of Local Group Galaxies
From a rediscussion of Local Group membership and of distances toindividual galaxies, we obtain M_V values for 35 probable and possibleLocal Group members. The luminosity function of these objects is wellfitted by a Schechter function with faint-end slope alpha=-1.1+/-0.1.The probability that the luminosity distribution of the Local Group is asingle Schechter function with alpha steeper than -1.3 is less than 1%.However, more complicated luminosity functions, such as multicomponentSchechter functions with steep faint-end slopes, cannot be ruled out.There is some evidence that the luminosity distribution of dwarfspheroidal galaxies in the Local Group is steeper than that of dwarfirregular galaxies.
| The Solar Motion Relative to the Local Group
New data on the membership of the Local Group (LG) are used, inconjunction with new and improved radial velocity data, to refine thederivation of the motion of the Sun relative to the LG. The Sun is foundto be moving with a velocity of V=306+/-18 km s^-1 toward an apex atl=99 deg+/-5 deg and b=-4 deg+/-4 deg. This finding agrees very wellwith previous analyses, but we discuss the possibility of a bias if thephase-space distribution of LG galaxies is bimodal. The LG radialvelocity dispersion is 61+/-8 km s^-1. We use various mass estimators tocompute the mass of the LG and the Andromeda subgroup. We findM_LG=(2.3+/-0.6)x10^12 M_solar, from which M/L_V=44+/-12 (in solarunits). For an assumed LG age of 14+/-2 Gyr, the radius of an idealizedLG zero-velocity surface is r_0=1.18+/-0.15 Mpc. The LG is found to have35 likely members. Only three of these have (uncertain) distances>~1.0 Mpc from the LG barycenter. Barring new discoveries of lowsurface brightness dwarfs, this suggests that the LG is more compact andmore isolated from its surroundings than previously believed.
| 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
| Total magnitude, radius, colour indices, colour gradients and photometric type of galaxies
We present a catalogue of aperture photometry of galaxies, in UBVRI,assembled from three different origins: (i) an update of the catalogueof Buta et al. (1995) (ii) published photometric profiles and (iii)aperture photometry performed on CCD images. We explored different setsof growth curves to fit these data: (i) The Sersic law, (ii) The net ofgrowth curves used for the preparation of the RC3 and (iii) A linearinterpolation between the de Vaucouleurs (r(1/4) ) and exponential laws.Finally we adopted the latter solution. Fitting these growth curves, wederive (1) the total magnitude, (2) the effective radius, (3) the colourindices and (4) gradients and (5) the photometric type of 5169 galaxies.The photometric type is defined to statistically match the revisedmorphologic type and parametrizes the shape of the growth curve. It iscoded from -9, for very concentrated galaxies, to +10, for diffusegalaxies. Based in part on observations collected at the Haute-ProvenceObservatory.
| Discovery of Numerous Dwarf Galaxies in the Two Nearest Groups of Galaxies.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....114.1313C&db_key=AST
| HI halos of dwarf galaxies in the Centaurus Group.
Not Available
| Nearby galaxies. IV. The global Hubble parameter and the dispersion of the Hubble relation
Using a spherically symmetric model of the Virgo flow the global Hubbleparameter has been estimated from the observed radial velocities and thephotometrically measured distances of nearby galaxies. Adopting theobserved recession velocity of the Virgo Cluster to about 1000 km s(-1)and the infall velocity of the Local Group to 350 km s(-1) the globalHubble constant results to 73 +/- 10 km s(-1) Mpc(-) -1. This valuecorresponds with the distance of the Virgo Cluster of 18 +/- 2 Mpc. Thecosmic dispersion of the galaxies around the Hubble relation is of orderof 35 km s(-1) .
| The Galaxy Motion Relative to Nearby Galaxies and the Local Velocity Field
We consider a sample of 103 galaxies with radial velocities V_0_ <500 km s^-1^ and distances obtained by means of photometric distanceindicators: Cepheids (n = 17), brightest stars (n = 69), and galaxymembership in the nearby bound groups (n = 17). Ranking the galaxieswith their distance R we determine a running apex for the Sun, theGalaxy, and the Local Group as a function of R. For the solar apex withrespect to the LG galaxies we obtain the parameters: {l_sun_ =93^deg^+/-2^deg^, b_sun_ = -4^deg^+/- 2^deg^, V_sun_ = 316+/-5 kms^-1^}. That corresponds to a Galaxy center apex {l = 107^deg^, b =-18^deg^, v = 90 km s^-1^}, pointing at ~14^deg^ from M31. When theconsidered volume depth increases from 1.0-1.5 Mpc up to 4-8 Mpc, thesolar apex drifts to {l_sun_ = 91^deg^, b_sun_ = 0^deg^, V_sun_ = 334 kms^-1^}, while the LG centroid apex shows a complicate wandering in aregion {l = [40^deg^, 100^deg^], b = [0^deg^, +60^deg^]) with velocityincreasing from 0 up to 40 km s^-1^, The running value for the localHubble parameter, H(R), reaches the maximum (90+/-5) km s^-1^ Mpc^-1^ atR ~ 2 Mpc, and then decreases down to (70-65) km s^-1^ Mpc^- 1^. Whenboth the Hubble component and the apex velocity are removed, theresidual velocity field shows clear signs of anisotropy. Within theLocal Supergalactic plane there is a prevalence of negative peculiarvelocities towards the "+SGY" direction. This feature perhaps has thesame origin as the "Local Velocity Anomaly" (LVA) known to exist over ascale of 10-30 Mpc. Besides the LVA, an excess of negative peculiarvelocities is seen also along the SGZ axis and can be interpreted as ifthe expansion of the local pancake proceeds about 30% slower in thedirection perpendicular to the symmetry plane than in the plane itself.Inside the Local Volume, galaxies possess a peculiar velocity dispersionof (72+/-2) km s^-1^ independent on the assumed volume depth. This valueis almost the same for dwarf and giant galaxies: a behavior which has nosimple explanations. The use of more precise solar apex parameters andthe correction for the local anisotropy improves the use of radialvelocities of nearby galaxies as distance indicators and allows to builda more accurate 3D map of the LV which reveals more "fine grain"structure details than Tully's catalog data.
| The Local Group in comparison with other nearby groups of galaxies.
Ensembles of probable physical companions around nearby massive galaxieswith V_0_<500km/s and M>3x10^11^Msun_ are derived.Recent estimates of distances for galaxies, a new criterion ofmembership, and also special searches for diffuse ("spheroidal") dwarfobjects have been used for this purpose. Under such an approach theMilky Way has thirteen companions, M31 eleven, M81 fifteen, NGC5128 ten,NGC5236 five, and M101 has seven. According to linear dimension(140kpc), radial velocity dispersion (68km/s), and morphological content(62 percent of E+Sph) the Local Group appears a common one among othersystems. Some properties of structure and kinematics of the nearbygroups are noted in relation to the luminosity ratio of their twobrightest members. The dynamical status of the 6 nearby groups can beexplained also without invoking significant amounts of Dark Matterbeyond 2-3 standard radii of the principal galaxies.
| Candidates for a southern extension of the Karachentsev catalogue of isolated pairs of galaxies.
Not Available
| Spectroscopic studies of emission line galaxies.
Not Available
| The outer fringes of the local group
The distances of all galaxies that have recently been suggested aspossible members of the Local Group are discussed. Among 22 Local Groupsuspects only IC 10, Aquarius (=DD 0210) and Sagittarius (=SagDIG) havea high probability of being physical Group members. This brings thetotal number of certain or probable Local Group members to 29. AmongLocal Group dwarfs stellar population type appears to correlate withlocation. Faint DSph galaxies are mostly close satellites of M31 or theGalaxy. On the other hand the majority of DIr galaxies are situated morethan 0.4 Mpc from the Andromeda nebula and the Milky Way system.
| General study of group membership. II - Determination of nearby groups
We present a whole sky catalog of nearby groups of galaxies taken fromthe Lyon-Meudon Extragalactic Database. From the 78,000 objects in thedatabase, we extracted a sample of 6392 galaxies, complete up to thelimiting apparent magnitude B0 = 14.0. Moreover, in order to considersolely the galaxies of the local universe, all the selected galaxieshave a known recession velocity smaller than 5500 km/s. Two methods wereused in group construction: a Huchra-Geller (1982) derived percolationmethod and a Tully (1980) derived hierarchical method. Each method gaveus one catalog. These were then compared and synthesized to obtain asingle catalog containing the most reliable groups. There are 485 groupsof a least three members in the final catalog.
| Distribution and motions of atomic hydrogen in lenticular galaxies. X - The blue S0 galaxy NGC 5102
Results of the mapping of the blue gas-rich S0 galaxy NGC 5102 in the21-cm H I line with a spatial resolution of 34 x 37 arcsec (delta(alpha)x Delta(delta)) and a velocity resolution of 12 km/s are presented. TheH I distribution has a pronounced central depression of 1.9 kpc radius,and most of the H I is concentrated in a 3.6 kpc wide ring with anaverage radius of 3.7 kpc, assuming a distance of 4 Mpc for NGC 5102.The maximum azimuthally averaged H I surface density in the ring is 1.4solar mass/sq pc, comparable to that found in other S0 galaxies. The HIvelocity field is quite regular, showing no evidence for large-scaledeviations from circular rotation, and the H I is found to rotate in theplane of the stellar disk. Both the H I mass/blue luminosity ratio andthe radial H I distribution are similar to those in early-type spirals.The H I may be an old disk or it may have been acquired through captureof a gas-rich smaller galaxy. The recent starburst in the nuclearregion, which gave the galaxy its blue color, may have been caused bypartial radial collapse of the gas disk, or by infall of a gas-richdwarf galaxy.
| Galaxy shredding. I - Centaurus A, NGC 5237, and the Fourcade-Figueroa shred
Numerical simulations of galaxy shredding are presented together with acase study of the nearby active galaxy Centaurus A. It is suggested thata shred-forming encounter with a spiral galaxy (about the same size asthe Milky Way) took place some 5 x 10 exp 8 yr ago. The captured diskmaterial now forms the conspicuous ring of gas and dust which girdlesCentaurus A, and probably provides the fuel that powers the radioemission seen today. The present shredding model provides a consistentpicture of many aspects of the Centaurus A system, including: therelative positions and velocities of Centaurus A, NGC 5237, and theFourcade-Figueroa shred; the orientation and sense of rotation of thedust lane in Centaurus A; the peculiar nature of the interacting dwarfelliptical galaxy NGC 5237; and the orientation and observed nonrotationof the Fourcade-Figueroa shred.
| 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.
| Groups of galaxies within 80 Mpc. II - The catalogue of groups and group members
This paper gives a catalog of the groups and associations obtained bymeans of a revised hierarchical algorithm applied to a sample of 4143galaxies with diameters larger than 100 arcsec and redshifts smallerthan 6000 km/s. The 264 groups of galaxies obtained in this way (andwhich contain at least three sample galaxies) are listed, with the looseassociations surrounding them and the individual members of eachaggregate as well; moreover, the location of every entity among 13regions corresponding roughly to superclusters is specified. Finally,1729 galaxies belong to the groups, and 466 to the associations, i.e.,the total fraction of galaxies within the various aggregates amounts to53 percent.
| The supergalactic plane redshift survey
Redshift measurements, about 1000 of which are new, are presented for1314 galaxies in a survey toward the apex of the large-scale streamingflow for ellipticals. The velocity histogram shows that the excess ingalaxy number counts in this area is due to a substantial concentrationof galaxies with discrete peaks at V about 3000 km/s and V about 4500km/s. After correction for the sampling function, the centroid of thedensity distribution is found to be near V about 4500 km/s.Normalization to the more extensive SSRS survey, which was selected bythe same criteria, shows that the region studied contains a considerableoverdensity of galaxies from 2000 to 6000 km/s. This result is in goodagreement with the 'great attractor' model suggested by Lynden-Bell etal. (1988) which attributes the peculiar motions of elliptical galaxiesover a large region of space to an extensive mass overdensity whichincludes the Hydra-Centaurus and Pavo-Indus superclusters. The centroidof the density enhancement is also consistent with new data by Dresslerand Faber (1990) of peculiar motions of elliptical and spiral galaxies,both of which show a zero crossing of the Hubble line at approximately4500-5000 km/s.
|
提交文章
相关链接
提交链接
下列团体成员
|
观测天体数据
目录:
|
