目录
图像
上传图像
DSS Images Other Images
相关文章
Associations of Dwarf Galaxies
The Hubble Space Telescope Advanced Camera for Surveys has been used todetermine accurate distances for 20 galaxies from measurements of theluminosity of the brightest red giant branch stars. Five associations ofdwarf galaxies that had originally been identified based on strongcorrelations on the plane of the sky and in velocity are shown to beequally well correlated in distance. Two more associations with similarproperties have been discovered. Another association is identified thatis suggested to be unbound through tidal disruption. The associationshave the spatial and kinematic properties expected of bound structureswith (1-10)×1011 Msolar. However, theseentities have little light, with the consequence that the mass-to-lightratios are in the range 100-1000 MsolarL-1solar. Within a well-surveyed volume extendingto a 3 Mpc radius, all but one known galaxy lie within one of the groupsor associations that have been identified.
| Stellar and Gas Properties of High H I Mass-to-Light Ratio Galaxies in the Local Universe
We present a multiwavelength study (BVRI-band photometry and H I lineinterferometry) of nine late-type galaxies selected from the HIPASSBright Galaxy Catalog on the basis of apparently high H I mass-to-lightratios (3Msolar/Lsolar,B5Msolar/Lsolar,B) galaxies are rare in thelocal universe. Extreme high-MHI/LB galaxiessuch as ESO 215-G?009 appear to have formed only the minimum number ofstars necessary to maintain the stability of their H I disks and couldpossibly be used to constrain galaxy formation models. They may alsohave been forming stars at a low, constant rate over their lifetimes.The best examples all have highly extended H I disks, are spatiallyisolated, and have normal baryonic content for their total masses butare deficient in stars. This suggests thathigh-MHI/LB galaxies are not lacking thebaryons to create stars but are underluminous, as they lack either theinternal or external stimulation for more extensive star formation.
| Advanced Camera for Surveys Imaging of 25 Galaxies in Nearby Groups and in the Field
We present Hubble Space Telescope Advanced Camera for Surveys images andcolor-magnitude diagrams for 25 nearby galaxies with radial velocitiesVLG<500 km s-1. Distances are determined basedon the luminosities of stars at the tip of the red giant branch thatrange from 2 to 12 Mpc. Two of the galaxies, NGC 4163 and IC 4662, arefound to be the nearest known representatives of blue compact dwarfobjects. Using high-quality data on distances and radial velocities of110 nearby field galaxies, we derive their mean Hubble ratio to be 68 kms-1 Mpc-1 with a standard deviation of 15 kms-1 Mpc-1. Peculiar velocities of most of thegalaxies, Vpec=VLG-68D, follow a Gaussiandistribution with σv=63 km s-1 but with atail toward high negative values. Our data display the known correlationbetween peculiar velocity and galaxy elevation above the LocalSupercluster plane. The small observed fraction of galaxies with highpeculiar velocities, Vpec<-500 km s-1, may beunderstood as objects associated with nearby groups (Coma I, Eridanus)outside the local volume.
| Dwarf galaxies.
Not Available
| Highlights from the Observatories
Not Available
| The Baryonic Tully-Fisher Relation of Galaxies with Extended Rotation Curves and the Stellar Mass of Rotating Galaxies
I investigate the baryonic Tully-Fisher relation for a sample ofgalaxies with extended 21 cm rotation curves spanning the range 20 kms-1<~Vf<=300 km s-1. A variety ofscalings of the stellar mass-to-light ratio Υ* areconsidered. For each prescription for Υ*, I give fitsof the form Md=AVxf.Presumably, the prescription that comes closest to the correct valuewill minimize the scatter in the relation. The fit with minimum scatterhas A=50 Msolar km-4 s4 andx=4. This relation holds over five decades in mass. Galaxy color,stellar fraction, and Υ* are correlated with eachother and with Md, in the sense that more massivegalaxies tend to be more evolved. There is a systematic dependence ofthe degree of maximality of disks on surface brightness. High surfacebrightness galaxies typically have Υ*~3/4 of themaximum disk value, while low surface brightness galaxies typicallyattain ~1/4 of this amount.
| The Arecibo Legacy Fast ALFA Survey. I. Science Goals, Survey Design, and Strategy
The recently initiated Arecibo Legacy Fast ALFA (ALFALFA) survey aims tomap ~7000 deg2 of the high Galactic latitude sky visible fromArecibo, providing a H I line spectral database covering the redshiftrange between -1600 and 18,000 km s-1 with ~5 kms-1 resolution. Exploiting Arecibo's large collecting areaand small beam size, ALFALFA is specifically designed to probe the faintend of the H I mass function in the local universe and will provide acensus of H I in the surveyed sky area to faint flux limits, making itespecially useful in synergy with wide-area surveys conducted at otherwavelengths. ALFALFA will also provide the basis for studies of thedynamics of galaxies within the Local Supercluster and nearbysuperclusters, allow measurement of the H I diameter function, andenable a first wide-area blind search for local H I tidal features, H Iabsorbers at z<0.06, and OH megamasers in the redshift range0.16
| Infrared Properties of Star-forming Dwarf Galaxies. I. Dwarf Irregular Galaxies in the Local Volume
A sample of 34 dwarf irregular galaxies (dIs) in the Local Volume, mostnearer than 5 Mpc, has been imaged in the near-infrared (NIR) in J andKs at the Canada-France-Hawaii Telescope (CFHT) in Hawaii andthe Observatorio Astronómico Nacional in the Sierra San PedroMártir, in Mexico. Absolute magnitudes in Ks rangefrom -14 to -18. In the CFHT images, stars brighter thanMKs~-7.5 were resolved. We show that the resolvedcomponent comprises more than 50% of the light from star formationbursts within the last 3 Gyr. In most cases, the resolved populationdown to MKs=-7.5 represents less than 5% of thetotal NIR flux in Ks, with fractions in J being 1.5-2 timeslarger. Thus, the NIR light of dIs can be considered to be predominantlycontributed by stars older than about 4 Gyr. Although exponential atlarge radii, surface brightness profiles for the unresolved componentflatten in the centers. They can be fitted across the whole range ofradii with a hyperbolic secant (sech) defined as a function of twoparameters: the central surface brightness and the scale length of theexponential. With respect to this model, only two galaxies (NGC 1569 andNGC 3738) show an excess of flux in the center, both of which arehosting starbursts. Isophotal, total, and fitted sech magnitudes havebeen calculated for all galaxies for which the unresolved component wasdetected, along with semimajor axes at μJ=23 magarcsec-2 and μKs=22 magarcsec-2. The scale length and the semimajor axes correlatelinearly with absolute isophotal magnitude. The same is true for colorsand the central brightness. More luminous dIs tend to be larger, redder,and brighter in the center. The fraction of light contributed by youngstars is independent of both luminosity and central surface brightness.The Tully-Fisher relation shows considerable scatter, but residuals aretied to surface brightness. The galaxies appear to lie in a``fundamental plane'' defined by the sech absolute magnitude, the sechcentral surface brightness, and the H I line width. The rms of residualsin MK is only 0.4 mag, which implies that the plane can beused to evaluate the distances of star-forming dwarfs. Corrections fortilt do not reduce the residuals, so line widths must be governedpredominantly by random motions. Color-magnitude diagrams (CMDs) arepresented for 29 galaxies in which stars were resolved. Most show afinger centered around J-Ks=1 mag. In some cases, there is ared tail extending to J-Ks=2.5 mag. Most color profilesconstructed for the unresolved component show a remarkably constantJ-Ks=0.8-1.0 mag, matching the color of the finger in theCMDs.Based on observations obtained at the Canada-France-Hawaii Telescope,which is operated by the National Research Council of Canada, the CentreNational de la Recherche Scientifique de France, and the University ofHawaii; also based on data acquired at OAN-SPM in Mexico.
| A dwarf galaxy with a giant HI disk
We present Giant Meterwave Radio Telescope (GMRT) HI 21 cm images of anearby dwarf irregular galaxy NGC 3741 (MB -13.13)which show it to have a gas disk that extends to ~8.3 times its Holmbergradius. This makes it probably the most extended gas disk known. Ourobservations allow us to derive the rotation curve (which is flat in theouter regions) out to ~38 optical scale lengths. NGC 3741 has adynamical mass to light ratio of ~107 and is one of the“darkest” irregular galaxies known. However, the bulk of thebaryonic mass in NGC 3741 is in the form of gas and the ratio of thedynamic mass to the baryonic mass (~8), falls within the range that istypical for galaxies. Thus the dark matter halo of NGC 3741 has acquiredits fair share of baryons, but for some reason, these baryons have beenunable to collapse to form stars. A comparison of NGC 3741's dark haloproperties with those of a sample of galaxies with well measuredrotation curves suggests that if one has to reconcile the observationswith the expectation that low mass galaxies suffer fractionally greaterbaryon loss then baryon loss from halos occurs in such a way that, inthe net, the remaining baryons occupy a fractionally smaller volume ofthe total halo.
| 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/
| 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.
| Distribution of star-forming complexes in dwarf irregular galaxies
We study the distribution of bright star-forming complexes in ahomogeneous sample of 72 late-type (``irregular'') dwarf galaxieslocated within the 10 Mpc volume. Star-forming complexes are identifiedas bright lumps in B-band galaxy images and isolated by means of theunsharp-masking method. For the sample as a whole the radial numberdistribution of bright lumps largely traces the underlyingexponential-disk light profiles, but peaks at a 10 percent smaller scalelength. Moreover, the presence of a tail of star forming regions out toat least six optical scale lengths provides evidence against asystematic star formation truncation within that galaxy extension.Considering these findings, we apply a scale length-independentconcentration index, taking into account the implied non-uniform randomspread of star formation regions throughout the disk. The numberprofiles frequently manifest a second, minor peak at about two scalelengths. Relying on a two-dimensional stochastic self-propagating starformation model, we show these secondary peaks to be consistent withtriggered star formation; for a few of the brighter galaxies a peculiarpeak distribution is observed that is conceivably due to the onset ofshear provided by differential rotation. On scales between 100 and 1000pc, and by taking into account exponential-disk structure, bright lumpsreveal cluster dimensions between 1.3 and 2, with a weak trend to higherdimensions for brighter galaxies. Cluster dimension weaklyanticorrelates with the lumpiness index (the fraction of the totalgalaxy light due to the light contributed by the lumps), the latterindex showing no dependence on luminosity. Lump spreading within thedisk, as measured by the concentration index, and lump clustering, asgiven by the cluster dimension, are not linked to each other.Interpreting cluster dimension in terms of porosity of a self-similarintragalactic medium, we derive a relation between current starformation rate, scale length, and porosity.
| 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
| Structure and stellar content of dwarf galaxies. VII. B and R photometry of 25 southern field dwarfs and a disk parameter analysis of the complete sample of nearby irregulars
We present B and R band surface photometry of 25 Southern field dwarfgalaxies within a distance of 10 Mpc. For each galaxy we give theessential model-free photometric parameters and, by fitting exponentialsto the surface brightness profiles, the central extrapolated surfacebrightness and the exponential scale length, in both colour bands.Surface brightness and colour profiles are shown. One of the objects, avery faint dwarf elliptical in the vicinity of NGC 2784, has beendiscovered in the course of this work. Drawing on the data from this andall previous papers of this series, we construct a complete sample of 72late-type (``irregular'') dwarf galaxies in nearby groups and the fieldwithin the 10 Mpc volume, to study the exponential-disk parameterrelations of these galaxies with respect to galaxy environment. Weconfirm our previous finding of statistically lower scale lengths/highercentral surface brightnesses for field and group galaxies as compared tocluster galaxies. However, using a clear-cut definition of ``group''versus ``field'' environment, we find no significant difference in thephotometric structure of group and field irregulars. A difference in thestar formation history may partly account for this structure-environmentrelation: for a given luminosity cluster dwarfs are on average redderthan field and group galaxies. We also report evidence for the colourgradients of dwarf irregulars being roughly inversely proportional tothe disk scale lengths. Supplementing our photometric data withkinematic data from the literature, we study possible relations withkinematic properties of the inner disk. Applying the dark matter scalingrelations for a Burkert halo we show that for field and group galaxiesof a given luminosity faster-than-mean disk rotational velocities at aradius of about two scale lengths are correlated with larger-than-meandisk scale lengths. Based on observations collected at the EuropeanSouthern Observatory, La Silla, Chile. Table 3 containing ``BRphotometry and kinematic data for the 72 irregular dwarf galaxies of ourcomplete sample'' is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/388/29
| The M 81 group of galaxies: New distances, kinematics and structure
We present Hubble Space Telescope/WFPC2 images of the galaxies NGC 2366,NGC 2976, NGC 4236, IC 2574, DDO 53, DDO 82, DDO 165, Holmberg I,Holmberg II, Holmberg IX, K52, K73, BK3N, Garland, and A0952+69 in the M81 complex. Their true distance moduli, derived from the brightness ofthe tip of the red giant branch, lie in the range of 27fm 52 (NGC 2366)to 28fm 30 (DDO 165), with a median of 27fm 91, which is typical forother known M 81 group members. Using distances and radial velocities ofabout 50 galaxies in and around the M 81/NGC 2403 complex, we find theradius of the zero-velocity surface of the M 81 group to be R_0 =(1.05+/-0.07) Mpc, which yields a total mass M(R_0) = (1.6+/-0.3)x1012 Msun and a total mass-to-luminosity ratioM(R_0)/L_B = (38+/-7) Msun/Lsun. The total masswithin R_0 agrees well with the sum of masses estimated via the virialtheorem (1.2x 1012 Msun) and from orbital motions(2.0x 1012 Msun) of companions around M 81 and NGC2403. We suggest that most of the dark matter in the group isconcentrated around the luminous matter, allowing us to explain theobserved asymmetry of the peculiar motions of the M 81 companions. M 81itself has a peculiar velocity of about 130 km s-1 withrespect to the local Hubble flow, but the centroid of the M 81/NGC 2403complex is almost at rest with respect to Hubble flow (v_pec < 35 kms-1). Based on observations made with the NASA/ESA HubbleSpace Telescope. The Space Telescope Science Institute is operated bythe Association of Universities for Research in Astronomy, Inc. underNASA contract NAS 5-26555. Figures 2 to 5 are only available inelectronic form at http://www.edpsciences.org
| 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.
| Structure and stellar content of dwarf galaxies. IV. B and R photometry of dwarf galaxies in the CVnI cloud
We have carried out CCD photometry in the Cousins B and R bands of 15galaxies in the Canes Venatici I cloud. Total magnitudes, effectiveradii, effective surface brightnesses, as well as galaxy radii atvarious isophotal levels in both colors were determined. Best-fittingexponential parameters and color gradients are also given for thesegalaxies. The photometric parameters presented here will be analyzed ina forthcoming paper, together with previously published data for nearbydwarf galaxies. Based on observations made at Observatoire de HauteProvence (CNRS), 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.
| 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
| Detailed images and distance measurements for eighteen dwarf irregular galaxies in the Canes Venatici cloud
In the Canes Venatici cloud, eighteen dwarf irregular galaxies wereobserved in B, V bands at the Nordic Optical Telescope under a seeing ofone arcsec. Most of the galaxies having radial velocities V_0 < 500km/s have been resolved into stars for the first time. The galaxydistances were derived based on photometry of their brightest bluestars. Distances to some of the galaxies: UGC 6782, UGC 7131 and,probably, K 215, which are located at the CVn southern edge, wereestimated to be about 15 Mpc, which is typical of the Virgo clusteroutskirts. For two LSB galaxies, K 200 and K 215, the distances may beoverestimated, probably because of a lack of young massive stars. Forthe remaining galaxies: UGC 7559, UGC 7599, UGC 7605, UGC 7639, UGC7698, UGCA 290, UGCA 292, UGC 7866, UGC 8024, UGC 8638, UGC 8651, UGC8760, and UGC 8833 the estimated distances range from 2.3 to 8.0 Mpc,indicating their actual membership in the CVn cloud. Several objectsstudied here (UGC 7605, UGC 7639, UGC 8638, UGC 8833) have awell-resolved bluish core and regular yellow outer parts, which maypoint to composite (new and old) populations. The galaxy UGCA 292 = CVndwA has unusual global parameters: (B-V)_T=+0.08, M_T=-11.4, M(HI)/L_B =6\ M_sun/L_sun and M(HI)/M_T =0.7, being, perhaps, one of the youngestknown objects in the Local Universe. Table 2 to 19 are only available atthe CDS via anonymous ftp 130.79.128.5 or viahttp://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.
| Calibration of the luminosity function of bright blue stars as a distance indicator for late-type galaxies.
Not Available
| Distance moduli for thirteen nearby isolated dwarf galaxies.
Not Available
| CCD stellar photometry in 13 dwarf irregular galaxies.
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) .
| Global properties of dwarf galaxies. I. Galaxy sample and IRAS infrared flux-densities
We have selected a sample of 278 dwarf galaxies for which at least Bmagnitudes and preferably also optical colour information are available.For those galaxies that have no previously published IRAS fluxes, wehave used the IRAS database to extract fluxes or upper limits tosensitivity levels significantly better than those of the IRAS PointSource Catalog. New IRAS data include 79 galaxies detected in at leastone band, and 66 galaxies with good upper limits. In total, about 60% ofall dwarf galaxies in the sample now have been detected at 60/100μm.
| Global properties of dwarf galaxies II. Colours and luminosities
We have used a previously determined sample of 278 dwarf galaxies formost of which B magnitudes, optical colours, HI fluxes and IRASflux-densities are known, in order to derive luminosities, colours andsurface brightnesses. Dwarf galaxy properties are compared to those of acontrol sample of 228 larger spiral galaxies. The dwarf galaxies have onaverage higher 60/100μm flux ratios and lower 12/25μm flux ratiosthan the spiral galaxies, indicating that the contribution of `cirrus'to the infrared emission from dwarf galaxies is relativelyinsignificant. In the dwarf galaxies, the 60/100μm flux ratioincreases with increasing optical blueness; spiral galaxies show theopposite. Dwarf galaxies with a low optical surface brightness have low100μm/HI ratios, but the converse is not true. Galaxies with high100μm/HI ratios (indicative of high dust-to-gas ratios) also havehigh FIR/B ratios as well as high 60/100μm flux-density ratios.Although this is true for both spiral and dwarf galaxies, at given100μm/HI ratios the dwarf galaxies have both a lower FIR/B ratio anda higher 60/100μm flux-density ratio. This result is of importance inthe interpretation of FIR/B - 60/100μm diagrams in terms of starformation activity.
| A revised catalog of CfA1 galaxy groups in the Virgo/Great Attractor flow field
A new identification of groups and clusters in the CfA1 Catalog ofHuchra et al. is presented, using a percolation algorithm to identifydensity enhancements. It is shown that in the resulting catalog,contamination by interlopers is significantly reduced. The Schechterluminosity function is redetermined, including the Malmquist bias.
|
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:
|
