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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.
| Globular Clusters in Dwarf Galaxies
Data are currently available on the luminosities and half-light radii of101 globular clusters associated with low-luminosity parent galaxies.The luminosity distribution of globular clusters embedded in dwarfgalaxies having Mv>-16 is found to differ dramaticallyfrom that for globular clusters surrounding giant host galaxies withMv<-16. The luminosity distribution of globular clustersin giant galaxies peaks at Mv~-7.5, whereas that for dwarfgalaxies is found to increase monotonically down to the completenesslimit of the cluster data at Mv~-5.0. Unexpectedly, thepower-law distribution of the luminosities of globular clusters hostedby dwarf galaxies is seen to be much flatter than that of the bright,unevolved part of the luminosity distribution of globular clustersassociated with giant galaxies. The specific frequency of globularclusters fainter than Mv=-7.5 is found to be particularlyhigh in dwarf galaxies. The luminosity distribution of the LMC globularclusters is similar to that found in giant galaxies and differs fromthose of globular clusters in dwarf galaxies. The present data appear toshow no strong dependence of globular cluster luminosity on themorphological type of their parent galaxies. No attempt is made toexplain the unexpected discovery that the luminosity distribution ofglobular clusters is critically dependent on parent galaxy luminosity(or mass) but insensitive to the morphological type of the host galaxy.
| 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.
| Hubble Space Telescope imaging of globular cluster candidates in low surface brightness dwarf galaxies
Fifty-seven nearby low surface brightness dwarf galaxies (-10MV -16) were searched for globular cluster candidates(GCCs) using Hubble Space Telescope WFPC2 imaging in V and I. The sampleconsists of 18 dwarf spheroidal (dSph), 36 irregular (dIrr), and 3"transition" type (dIrr/dSph) galaxies with angular sizes less than 3.7kpc situated at distances 2{-}6 Mpc in the field and in the nearbygroups: M 81, Centaurus A, Sculptor, Canes Venatici I cloud. We findthat 50% of dSph, dIrr/dSph, and dIrr galaxies contain GCCs. Thefraction of GCCs located near the center of dwarf spheroidal galaxies is2 times higher than for dIrrs. The mean integral color of GCCs indSphs, (V-I)_0=1.04±0.16 mag, coincides with the correspondingvalue for Galactic globular clusters and is similar to the blue globularcluster sub-populations in massive early-type galaxies. The colordistribution for GCCs in dIrrs shows a clear bimodality with peaks near(V-I)0 = 0.5 and 1.0 mag. Blue GCCs are presumably young withages t1 Gyr, while the red GCC population is likely to be older.The detected GCCs have absolute visual magnitudes betweenMV=-10 and -5 mag. We find indications for an excesspopulation of faint GCCs with MV-6.5 mag in both dSphand dIrr galaxies, reminiscent of excess populations of faint globularclusters in nearby Local Group spiral galaxies. The measurement ofstructural parameters using King-profile fitting reveals that most GCCshave structural parameters similar to extended outer halo globularclusters in the Milky Way and M 31, as well as the recently discoveredpopulation of "faint fuzzy" clusters in nearby lenticular galaxies.
| New distances of unresolved dwarf elliptical galaxies in the vicinity of the Local Group
We present Surface Brightness Fluctuation distances of nine early-typedwarf galaxies and the S0 galaxy NGC 4150 in the Local Volume based ondeep B- and R-band CCD images obtained with the 2.56 m Nordic OpticalTelescope. Typically, six stellar fields at various galactocentricdistances have been chosen for each galaxy as appropriately free offoreground stars and other contaminants, and Fourier analysed todetermine the distances, which are found to lie in the range of 3 to 16Mpc. The SBF method is thus demonstrated to efficiently measuredistances from the ground with mid-aperture telescopes for galaxies forwhich only the tip of the red giant branch method in combination withthe Hubble Space Telescope has been available until now. We obtained thefollowing distance moduli: 28.11 ± 0.15 mag (or 4.2 ± 0.3Mpc) for UGC 1703, 27.61 ± 0.17 mag (or 3.3 ± 0.3 Mpc) forKDG 61, 29.00 ± 0.27 mag (or 6.3 ± 0.8 Mpc) for UGCA 200,27.74 ± 0.18 mag (or 3.5 ± 0.3 Mpc) for UGC 5442, 30.22± 0.17 mag (or 11.1 ± 0.9 Mpc) for UGC 5944, 30.79± 0.11 mag (or 14.4 ± 0.7 Mpc) for NGC 4150, 31.02± 0.25 mag (or 16.0 ± 1.9 Mpc) for BTS 128, 29.27 ±0.16 mag (or 7.1 ± 0.6 Mpc) for UGC 7639, 30.19 ± 0.23 mag(or 10.9 ± 1.2 Mpc) for UGC 8799 with an alternative distance of30.61 ± 0.26 mag (or 13.2 ± 1.7 Mpc), and 29.60 ±0.20 mag (or 8.3 ± 0.8 Mpc) for UGC 8882.
| 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.
| First results from the HI Jodrell All Sky Survey: inclination-dependent selection effects in a 21-cm blind survey
Details are presented of the HI Jodrell All Sky Survey (HIJASS). HIJASSis a blind neutral hydrogen (HI) survey of the northern sky (δ> 22°), being conducted using the multibeam receiver on theLovell Telescope (full width at half-maximum beamwidth 12 arcmin) atJodrell Bank. HIJASS covers the velocity range -3500 to 10 000 kms-1, with a velocity resolution of 18.1 km s-1 andspatial positional accuracy of ~2.5 arcmin. Thus far about 1115deg2 of sky have been surveyed. The average rms noise duringthe early part of the survey was around 16 mJy beam-1.Following the first phase of the Lovell Telescope upgrade (in 2001), therms noise is now around 13 mJy beam-1. We describe themethods of detecting galaxies within the HIJASS data and of measuringtheir HI parameters. The properties of the resulting HI-selected sampleof galaxies are described. Of the 222 sources so far confirmed, 170 (77per cent) are clearly associated with a previously catalogued galaxy. Afurther 23 sources (10 per cent) lie close (within 6 arcmin) to apreviously catalogued galaxy for which no previous redshift exists. Afurther 29 sources (13 per cent) do not appear to be associated with anypreviously catalogued galaxy. The distributions of peak flux, integratedflux, HI mass and cz are discussed. We show, using the HIJASS data, thatHI self-absorption is a significant, but often overlooked, effect ingalaxies with large inclination angles to the line of sight. Properlyaccounting for it could increase the derived HI mass density of thelocal Universe by at least 25 per cent. The effect that this will haveon the shape of the HI mass function will depend on how self-absorptionaffects galaxies of different morphological types and HI masses. We alsoshow that galaxies with small inclinations to the line of sight may alsobe excluded from HI-selected samples, since many such galaxies will haveobserved velocity widths that are too narrow for them to bedistinguished from narrow-band radio-frequency interference. This effectwill become progressively more serious for galaxies with smallerintrinsic velocity widths. If, as we might expect, galaxies with smallerintrinsic velocity widths have smaller HI masses, then compensating forthis effect could significantly steepen the faint-end slope of thederived HI mass function.
| Evidence for a warm interstellar medium in the Fornax dwarf ellipticals FCC046 and FCC207
We present Hα+[NII] narrow-band imaging of FCC046 and FCC207, twodwarf ellipticals (dES) in the Fornax cluster. B-R and B-I colour mapsclearly show signs of dust absorption in FCC207. FCC046 has a verybright blue nucleus, offset by about 1.1 arcsec with respect to theouter isophotes. FCC046 was classified as a non-nucleated dE4 so thepresence of its nucleus came as a surprise. Moreover, FCC046 shows apronounced lopsided shape. Given that FCC046 is an isolated galaxy, itis unlikely that an encounter caused this asymmetry. The emittingregions differ considerably between the two galaxies. Whereas FCC207 hasonly one central emission region, FCC046 also contains fainter emissionregions. Based on broad-band colours, its disturbed shape and its verybright nucleus, FCC046 is akin to the class of amorphous dwarfs. Thecentral emission regions of both galaxies are barely resolved underseeing conditions of FWHM ~0.8 arcsec and we estimate their diameters atabout 60 pc. Their Hα luminosities can be explained asphotoionization by post asymptotic giant branch stars in an oldpopulation. Some of the fainter extended emission regions in FCC046 areresolved and have diameters of the order of 50-150 pc and Hαluminosities of the order of 1030 W, comparable to supernovaremnants or nebulae around Wolf-Rayet stars. Hence, FCC046 is clearlyundergoing star formation while for FCC207 the case is not as clear-cut.We estimate the mass of the HII gas in FCC046 at MHII= 40-150Msolar (for T= 104 K, Ne= 1000cm-3). The ionized-gas content of FCC207 is somewhat higher:MHII= 60-190 Msolar.
| 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.
| 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
| Age and metallicity of a globular cluster in the dwarf spheroidal galaxy DDO 78
We present the results of moderate resolution spectroscopy for aglobular cluster in the M81 group dwarf spheroidal galaxy DDO 78. TheDDO 78 globular cluster, 4 Milky Way globular clusters, spectroscopicand radial velocity standards were observed with the Long-slitspectrograph of the 6-m telescope (SAO RAS, Russia). Lickspectrophotometric indices were determined in the bandpasses adopted byBurstein et al. (\cite{Bur84}). We have derived the mean metallicity ofthe globular cluster in DDO78 to be [Fe/H] =-1.6 +/- 0.1 dex by takingthe weighted mean of metallicities obtained from the strength of severalabsorption features. We have estimated an age for the globular clusterof 9-12 Gyr similar to that found for the Galactic globular cluster NGC362, which resembles the DDO 78 cluster in its chemical abundance andintegrated spectrophotometric properties.
| A Blind H I Survey of the M81 Group
Results are presented of the first blind H I survey of the M81 Group ofgalaxies. The data were taken as part of the H I Jodrell All-Sky Survey(HIJASS). The survey reveals several new aspects to the complexmorphology of the H I distribution in the group. All four of the knowndwarf irregular (dIrr) galaxies close to M81 can be unambiguously seenin the HIJASS data. Each forms part of the complex tidal structure inthe area. We suggest that at least three of these galaxies may haveformed recently from the tidal debris in which they are embedded. Thestructure connecting M81 to NGC 2976 is revealed as a single tidalbridge of mass ~=2.1×108 Msolar andprojected spatial extent ~=80 kpc. Two ``spurs'' of H I projecting fromthe M81 complex to lower declinations are traced over a considerablylarger spatial and velocity extent than by previous surveys. The dwarfelliptical (dE) galaxies BK5N and Kar 64 lie at the spatial extremity ofone of these features and appear to be associated with it. We suggestthat these may be the remnants of dIrr's that have been stripped of gasand transmuted into dE's by close gravitational encounters with NGC3077. The nucleated dE galaxy Kar 61 is unambiguously detected in H Ifor the first time and has an H I mass of ~108Msolar, further confirming it as a dE/dIrr transitionalobject. HIJASS has revealed one new possible group member, HIJASSJ1021+6842. This object contains ~=2×107Msolar of H I and lies ~=105' from IC 2574. It has no opticalcounterpart on the Digital Sky Survey.
| 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.
| Radial velocities of dwarf spheroidal galaxies in the M 81 group
Long-slit observations of 4 dwarf spheroidal galaxies in the M 81 groupare presented. We have obtained the heliocentric velocity of a globularcluster candidate located near the center of DDO 78 to be 55 +/- 10 kms-1 by cross-correlation with template stars. We estimated aheliocentric radial velocity of -116 +/- 21 km s-1 for an HIIregion seen in K 61. A red diffuse object near the K 64 center is foundto be a remote galaxy with a heliocentric velocity of +46 530 kms-1. Based on observations collected with the 6 m telescopeof the Special Astrophysical Observatory (SAO) of the Russian Academy ofSciences (RAS), operated under the financial support of the ScienceDepartment of Russia (registration number 01-43).
| WFPC2 observations of two dwarf spheroidal galaxies in the M 81 group
We have obtained HST WFPC2 and ground-based images of two low surfacebrightness dwarf spheroidal galaxies in the M 81 group, FM1 and KKH57.Their colour-magnitude diagrams show red giant branches with tips at I =23.77 +/- 0.14 and I = 23.97 +/-0.17, respectively. The derived truedistance moduli, 27.66 +/- 0.16 and 27.96 +/- 0.19, agree well with themean distance modulus of the M 81 group, 27.84 +/- 0.05. Absolute Vmagnitudes of the galaxies (-11.46 and -10.85), their colours ((B-V) =0.88 and 0.80), and central surface brightnesses (Sigma 0,V =24.8 and 24.4 mag/sq arcsec ) are in the range of other dSph companionsof M 81, M 31, and Milky Way. With two new objects the maximum projectedradius of the dwarf spheroidal subsystem around M 81 is 380 kpc. Basedon observations made with the NASA/ESA Hubble Space Telescope. The SpaceTelescope Science Institute is operated by the Association ofUniversities for Research in Astronomy, Inc. under NASA contract NAS5-26555. Based in part on observations obtained with the Apache PointObservatory 3.5-meter telescope, which is owned and operated by theAstrophysical Research Consortium.
| Multiwavelength study of the nuclei of a volume-limited sample of galaxies - I. X-ray observations
We discuss ROSAT HRI X-ray observations of 33 very nearby galaxies,sensitive to X-ray sources down to a luminosity of approximately1038ergs-1. The galaxies are selected from acomplete, volume-limited sample of 46 galaxies with LX ∝L1.5host d < 7 MPc for which we have extensivemultiwavelength data. For an almost complete subsample withMB < -14 MB (29/31 objects) we have HRI images.Contour maps and source lists are presented within the central region ofeach galaxy, together with nuclear upper limits where no nuclear sourcewas detected. Nuclear X-ray sources are found to be very common,occurring in ~35per cent of the sample. Nuclear X-ray luminosity isstatistically connected to host galaxy luminosity - there is not a tightcorrelation, but the probability of a nuclear source being detectedincreases strongly with galaxy luminosity, and the distribution ofnuclear luminosities seems to show an upper envelope that is roughlyproportional to galaxy luminosity. While these sources do seem to be agenuinely nuclear phenomenon rather than nuclear examples of the generalX-ray source population, it is far from obvious that they are miniatureSeyfert nuclei. The more luminous nuclei are very often spatiallyextended, and Hii region nuclei are detected just as often as LINERs.Finally, we also note the presence of fairly common superluminous X-raysources in the off-nuclear population - out of 29 galaxies we find ninesources with a luminosity greater than 1039ergs-1.These show no particular preference for more luminous galaxies. One isalready known to be a multiple SNR system, but most have no obviousoptical counterpart and their nature remains a mystery.
| A search for LSB dwarf galaxies in the M 81 group on digitally stacked Schmidt plates
We present a search for low surface brightness (LSB) dwarf galaxies in aregion of 10 square degrees around M 81. The survey is based on thedigital co-addition of Schmidt plates where algorithms for sub-arcsecondco-centering, quality-weighting and sigma-clipping ``bad pixel''rejection are applied. The 3 sigma surface brightness limit is mu_lim =25.6 mag/Box arcsec . In a substantial fraction of the surveyed area,the detection of LSB objects is limited by ``Galactic cirrus'' ratherthan by the limiting magnitude of the stacked image. Optimum searchparameters for an automated detection of dwarf galaxies are derived fromsimulations. The final selection of LSB dwarf candidates relies on acombination of automated detection and visual inspection. We present sixnew dwarf galaxy candidates with mu B(0) >= 23 mag/Boxarcsec . Photometric data and best fitting parameters for theexponential model are derived both for the new candidates and for somepreviously known LSB dwarf galaxies in the field. For the most likelynew dwarf member of the M 81 group, a central surface brightness of muB(0) = 25.4 mag/Box arcsec and a scale-length of 0.3 kpc arederived. Based on observations made with the 2 m telescope of theThüringer Landessternwarte Tautenburg, Germany.
| Dwarf spheroidal galaxies in the M81 group imaged with WFPC2
We obtained HST/WFPC2 images of the dwarf spheroidal (dSph) galaxiesK61, K63, K64, DDO78, BK6N, and kk77 in the M81 group. Ourcolor-magnitude diagrams show red giant branches with tips (TRGB)falling within the range of I = [23.8 -24.0] mag. The derived truedistance moduli (DM) of the 6 dSphs ranging from 27.71 to 27.93 mag areconsistent with their membership in the group. Given accurate distancesof 5 other group members, which have been derived via TRGB or cepheids,the mean DM of the M81 group is (27.84+/-0.05) mag. We find thedifference of the mean distances to the M81 and NGC 2403 groups to beD_M81 - D_NGC2403 =(0.5+/-0.2) Mpc, which yields a deprojectedseparation of 0.9 Mpc. With respect to the Local group, M81 and NGC 2403have radial velocities of 106 and 267 km s-1 respectively,while the velocities of the group centroids are 142 and 281 kms-1. The higher velocity of the closer system may indicatethat these groups are moving towards each other, similar to the MilkyWay and M31 in the Local group. Several globular cluster candidates havebeen identified in the galaxies. 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.
| Galaxy coordinates. II. Accurate equatorial coordinates for 17298 galaxies
Using images of the Digitized Sky Survey we measured coodinates for17298 galaxies having poorly defined coordinates. As a control, wemeasured with the same method 1522 galaxies having accurate coordinates.The comparison with our own measurements shows that the accuracy of themethod is about 6 arcsec on each axis (RA and DEC).
| 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
| Astrophysics in 1997
Martian marvels, a gamma-ray burster with a redshift, Galileo converseswith Ganymede, a record galactic redshift of 4.92, and much else. Fiscal1997 was definitely an exciting year for astronomers. We have tried hardto hit all the obvious highlights, but also to report more gradualprogress on traditional problems of understanding planets, stars,galaxies, and the universe. Though the year was saddened by the loss ofmany valued colleagues, we nevertheless indulge in occasionalsoupçons of frivolity.
| Dwarf elliptical galaxies in the M81 Group - The structure and stellar populations of BK5N and F8D1
We have carried out a CCD survey of the M81 Group to search for analogsto Local Group dwarf elliptical (dE) galaxies. All the M81 dwarfspreviously identified in photographic surveys were recovered, and wealso discovered several new systems whose surface brightnesses fallwithin the range found for Local Group dE's. We have obtained HubbleSpace Telescope Wide Field Planetary Camera 2 images through the F555Wand F814W filters of two M81 Group dE's, BK5N and a new system,designated F8D1. The resulting color-magnitude diagrams show the upper 2mag of the red giant branch. The I magnitudes of the red giant branchtip in both galaxies yield distances that are consistent with membershipin the M81 Group. Surface brightness and total magnitude measurementsindicate that BK5N and F8D1 have similar central surface brightnesses,but F8D1's larger length scale results in its being 3 mag more luminousthan BK5N. BK5N lies on the relation between central surface brightnessand absolute magnitude defined by Local Group dwarf elliptical galaxies,but F8D1 does not. F8D1 is more luminous for its central surfacebrightness than the relation predicts, similar to the large low surfacebrightness dwarf galaxies found in, for example, Virgo. The mean colorof the giant branch is used to establish the mean abundance of eachgalaxy. F8D1, the more luminous galaxy, is significantly more metal-richthan BK5N.
| Structure and stellar content of dwarf galaxies. I. B and R photometry of dwarf galaxies in the M 81 group
We have carried out CCD photometry in the Cousins B and R bands of 25dwarf galaxy members and suspected members of the M81 group of galaxies. Based on azimuthally averaged brightnessprofiles we have derived total magnitudes, effective radii, effectivesurface brightnesses, as well as galaxy diameters at various isophotallevels in both photometric bands. Best-fitting exponential parametersand B - R colour gradients are also given for these galaxies. The datawill be interpreted, along with those of another supplementary paper, inPaper III of this series (to appear in the main journal). In twoappendices we discuss the nature of a clustering of unusual low-surfacebrightness objects in the south-east corner of the M81 group and show the luminosity function of its presentlyknown members. Based on observations made at Observatoire de HauteProvence (CNRS), France.
| 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.
| A list of new nearby dwarf galaxy candidates
To increase completeness of the distance limited sample of nearbygalaxies from the \cite[Kraan-Korteweg & Tammann (1979)]{Kra79}catalogue we undertook a search for small companions of larger knowngalaxies which have corrected radial velocities within 500 km/s. Basedprimarily on the POSS-II and ESO/SERC films we found 260 nearby dwarfgalaxy candidates with angular diameters aga0 .5 arcmin. More than 50%of the objects were revealed for the first time. As we suppose, asignificant part of them (about 30%) may really belong to the LocalVolume sample. Tables 1 and 2 also available in electronic form at CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via\breakftp://cdsweb.u-strasbg.fr/Abstract.html
| An H i line search for optically identified dwarf galaxy candidates in the M 81 group
Sensitive 21cm Hi line observations were performed for 23 dwarf membersand possible members of the nearby M 81 group of galaxies, includingfive objects of a clustering of extremely low-surface brightness objectsof unknown nature. With the Nancay decimetric radio telescope the radialvelocity range of -529 to 1826 \mboxkms(-1) was searched to an rms noiseof ~ 2-4\ mJy. Only three objects were detected. However, their highradial velocities (between 600 and 1150 \mboxkms(-1) ) show them to liebehind the M 81 group. These three objects, classified as dS0: (UGC4998) and Im (Kar 1N and UGC 5658), have Hi masses of 0.4, 1.6 and 2.0\10(8) {cal M_sun}, for the assumed distance of 4 Mpc, and Himass-to-blue light ratios of 0.04, 0.73 and 0.18 {cal M_sun}LBsun,respectively. Considering that half of the observed objects areclassified as irregular dwarfs, hence expected to be relativelygas-rich, the resulting detection rate of about 1/3 is quite low.However, the mean redshift and velocity dispersion of the M 81 group( = 101 \mboxkms(-1) , sigma =114 \mboxkms(-1) ) suggest thatthe Hi emission of low velocity Hi-rich members of the M 81 group maystill remain hidden within the strong Galactic Hi emission (typically-150< V < 115 \mboxkms(-1) ) or, for the 6 dwarf candidates in theimmediate vicinity of M 81, overshadowed by the very extended Hienvelope encompassing M 81, M 82, NGC 3077, and NGC 2976 (-280< V< 355 \mboxkms(-1) ).
| A High-Excitation HII Region in the faint dwarf elliptical galaxy A0951+68
We present the results of BVRI imaging and optical spectroscopy of thedwarf galaxy A0951+68. The images reveal that, although this galaxy isclassified as a dwarf elliptical, it has some properties that aresimilar to dwarf irregular galaxies. It contains two bright knots ofemission, one of which is red and unresolved, and the other blue andunresolved. The blue knot also shows a high-excitation emission-linespectrum. The observed line ratios indicate that this is an H II region,though with some line ratios that are border-line with those in AGM. Theemission-line luminosity is consistent with ionization by a single, veryluminous O star, or several smaller O stars, but the extended blue lightin the knot shows that this has occurred as part of a substantial recentstar formation event. We find that the metal abundance, while lowcompared to typical large galaxies, actually seems to be high for such alow-luminosity dwarf. The position of A0951 in the literature isincorrect, and we provide the correct value.
| 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.
| Revised sizes and positions for the Mailyan dwarf galaxy catalog
New positions (good to +/- 15 arcsec), revised sizes, and samplecross-identifications are presented for dwarf galaxies discovered andpublished by Mailyan (1973, Astrofizika, 9, 33). Of the 104 originallycataloged galaxies we were able to recover only 100, despite anextensive search of the red and blue Palomar Observatory Sky Survey(POSS) prints. Over half of the recovered objects were found tocorrespond to previously cataloged galaxies; few if any of these aredwarf spheriodal galaxies, but rather mostly dwarf irregulars of lowsurface brightness.
| 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.
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