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Публикации по объекту
Minivoids in the Local Volume
We consider a sphere of 7.5 Mpc radius, which contains 355 galaxies withaccurately measured distances, to detect the nearest empty volumes.Using a simple void detection algorithm, we found six large (mini)voidsin Aquila, Eridanus, Leo, Vela, Cepheus, and Octans, each of more than30 Mpc3. In addition, 24 middle-sized ``bubbles'' of morethan 5 Mpc3 volume are detected, as well as 52 small``pores.'' The six largest minivoids occupy 58% of the consideredvolume. The addition of the bubbles and pores to them increases thetotal empty volume up to 75% and 81%, respectively. The detected localvoids look like oblong potatoes with typical axial ratios b/a=0.75 andc/a=0.62 (in the triaxial ellipsoid approximation). Being arranged bythe size of their volume, local voids follow a power law for volume-rankdependence. A correlation Gamma function of the Local Volume galaxiesfollows a power law with a formally calculated fractal dimension D=1.5.We found that galaxies surrounding the local minivoids do not differsignificantly from other nearby galaxies in their luminosity, but haveappreciably higher hydrogen mass-to-luminosity ratios and also higherstar formation rates. We recognize an effect of the local expansion of atypical minivoid to be ΔH/H0~(25+/-15)%.
| 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.
| Oxygen and Nitrogen in Leo A and GR 8
We present elemental abundances for multiple H II regions in Leo A andGR 8 obtained from long-slit optical spectroscopy of these two nearbylow-luminosity dwarf irregular galaxies. As expected from theirluminosities, and in agreement with previous observations, the derivedoxygen abundances are extremely low in both galaxies. Highsignal-to-noise ratio (S/N) observations of a planetary nebula in Leo Ayield 12+log(O/H)=7.30+/-0.05 semiempirical calculations of the oxygenabundance in four H II regions in Leo A indicate12+log(O/H)=7.38+/-0.10. These results confirm that Leo A has one of thelowest ISM metal abundances of known nearby galaxies. Based on resultsfrom two H II regions with high S/N measurements of the weak [O III]λ4363 line, the mean oxygen abundance of GR 8 is12+log(O/H)=7.65+/-0.06 using ``empirical'' and ``semiempirical''methods, similar abundances are derived for six other GR 8 H II regions.Similar to previous results in other low-metallicity galaxies, the meanlog(N/O)=-1.53+/-0.09 for Leo A and -1.51+/-0.07 for GR 8. There is noevidence of significant variations in either O/H or N/O in the H IIregions. The metallicity-luminosity relation for nearby (D<5 Mpc)dwarf irregular galaxies with measured oxygen abundances has a meancorrelation of 12+log(O/H)=5.67MB-0.151MB, with adispersion in oxygen about the relationship of σ=0.21. Theseobservations confirm that gas-rich, low-luminosity galaxies haveextremely low elemental abundances in the ionized gas phase of theirinterstellar media. Although Leo A has one of the lowest metalabundances of known nearby galaxies, detection of tracers of an olderstellar population (RR Lyrae variable stars, horizontal branch stars,and a well-populated red giant branch) indicate that it is not a newlyformed galaxy, as has been proposed for some other similarlow-metallicity star-forming galaxies.
| 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.
| H I Distribution and Kinematics of UGCA 86
We present 21 cm H I line and 408 MHz and 1.4 GHz continuum observationsof the Magellanic dwarf galaxy UGCA 86, made with the Dominion RadioAstrophysical Observatory (DRAO) Synthesis Telescope. UGCA 86 isdetected in the continuum at both frequencies, with 408 MHz flux densityS408=120+/-30 mJy and 1.4 GHz flux densityS1400=79+/-3 mJy. The H I structure of UGCA 86 is complex,with two separate components: a rotating disk and a highly elongatedspur that is kinematically disjunct from the disk. The H I disk iscentered on the optical galaxy with similar axial ratio and orientationof the major axis. An area of the disk with a peculiar velocity of ~25km s-1 relative to the regular rotation of the disk is foundon the southern side, where most of the star formation is concentrated.The spur is seen along the minor axis of UGCA 86 and overlaps in partwith the disk. Toward the optical center of UGCA 86, the velocitydifference between the spur and the disk is 40 km s-1, aboutone-third of the rotation velocity of the H I disk at 6 kpc from thecenter. This implies a large radial component of the orbital velocity ofthe spur and therefore a significantly noncircular orbit. The median H Ivelocity dispersion of the disk is 8.8 km s-1, similar toother (dwarf) galaxies. The H I velocity dispersion of the spur variesfrom 10 to 30 km s-1. A possible tidal origin of the spur isconsidered in view of the proximity of the large Scd galaxy IC 342.However, the orientation of the spur along the minor axis and itsspatial overlap with the disk suggest that the spur is located faroutside the plane of the H I disk. No evidence is found that the outer HI disk is warped, which poses a problem for the interpretation of thespur as a tidal tail induced by IC 342. Detailed modeling of the IC342/UGCA 86 system will be required before a tidal origin of the spurcan be dismissed conclusively. The possibility that the spur is part ofthe nascent cloud of UGCA 86 or the remains of a small dwarf galaxy ispresented as an alternative interpretation.
| 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.
| Distances to nearby galaxies around IC 342
We present an analysis of Hubble Space Telescope/WFPC2 images of sixnearby galaxies in the projected vicinity of IC 342: Cas dSph, KK 35,UGCA 86, Cam A, NGC 1560, and Cam B. We derive distances to five of themfrom the luminosity of the tip of the red giant branch stars with atypical accuracy of ~ 10%. The galaxy distances are 0.79 Mpc (CasdSph), 3.16 Mpc (KK 35), 3.93 Mpc (Cam A), 3.45 Mpc (NGC 1560), and 3.34Mpc (Cam B). Two other observed galaxies, MB 2 and Cam C = KK 26, turnout to be Galactic cirrus and a Galactic H II region, respectively. CasdSph belongs to the Local Group and is a companion of M 31. Combiningour data with literature results, we find that there are seven dwarfgalaxies associated with the giant spiral galaxy IC 342. This group ischaracterized by an average distance of (3.28 +/- 0.15) Mpc, an averageradial velocity of (229 +/- 23) km s-1, a projected radius of322 kpc, a radial velocity dispersion of 60 km s-1, and atotal blue luminosity of 3.43x 1010 Lsun. Thederived virial and orbital mass-to-luminosity ratios are 20 and 28Msun/Lsun, respectively. The galaxy group aroundMaffei 1 has so far a less reliable distance of ~ 3.0 Mpc and anaverage radial velocity of (309 +/- 22) km s-1. This groupconsists of eight galaxies and is characterized by a projected radius of112 kpc, a radial velocity dispersion of 59 km s-1, and atotal blue luminosity of 2.97x 1010 Lsun. For theMaffei group we estimate mass-to-light ratios ofMvir/LB = 16 and Morb/LB = 5in solar units. The sum of the virial (119x 1010Msun) and orbital (109x 1010 Msun)masses of both groups agree well with their total mass, (107 +/- 33)1010 Msun, derived from the radius of the ``zerovelocity surface'', R0 = (0.9 +/- 0.1) Mpc, which separatesthe IC 342/Maffei complex from the Hubble flow.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.Figure A.1 is only available in electronic form athttp://www.edpsciences.org
| 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.
| 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
| 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 in the Neutral Hydrogen Disk of the Spiral Galaxy IC 342
We present 38"resolution Very Large Array 21 cm continuum and H I lineemission observations of the spiral galaxy IC 342, at an adopteddistance of 2 Mpc. Kinematic evidence exists for a m=2 spiral densitywave in the inner disk with a corotation radius located at 4 kpc and apossible four-arm pattern in the outer disk. On smaller scales, outsideof the central depression in H I column density, H I is organized into acomplex pattern of relatively short (~2-5 kpc), interconnected, spiralarm segments. Numerous ``holes'' are distributed throughout the H Idisk. By considering the effects of shear, structures that are notself-gravitating, such as holes and voids, cannot be long-termphenomena. The timescale, combined with the total energy required toevacuate holes, leads us to reject wind and supernovae origins for thelarge-scale pattern of H I holes in IC 342. Gravitational instabilitiesin the disk form on a timescale that is short compared with the rotationperiod of the disk. The pattern of H I spiral arm segments exists on ascale that is consistent with their being material arms that result fromgravitational instabilities. The H I cavities are a natural remnant ofthe process.
| 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).
| Multi-colour photometry of nearby dwarf galaxies
Observations of 39 nearby, mostly dwarf galaxies are presented. Theobservations were carried out at the 1.2-m telescope of Observatoire deHaute-Provence (France) with B, V and I Cousins filters. Based onsurface and integrated photometry of the obtained images we derivedtotal B, V and I magnitudes and integrated B-V, V-I colours as well asradii and magnitudes at the 25 m isophotal level. Azimuthally averagedsurface brightness profiles were derived for 33 galaxies in eachphotometric band. Most of the profiles can be well fitted by anexponential intensity law of brightness distribution. The best-fittingexponential parameters are also given for the galaxies. Based onobservations made at Observatoire de Haute Provence (CNRS), France.Table 3 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| 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
| The IC 342/Maffei Group Revealed
Deep wide-field CCD images in the optical and near-infrared have beenacquired for 14 of the 16 known or suspected members of the IC342/Maffei Group of galaxies, one of the closest groups to the MilkyWay, and probably the closest group to M31. Because of their lowGalactic latitude, all galaxies are heavily extinguished, and myriads offoreground stars are superimposed. A sophisticated algorithm builtaround DAOPHOT has been developed which successfully removes theforeground stars, making possible comprehensive morphological andphotometric studies. The cleaned near-infrared images reveal the truemorphology and extent of many of the galaxies for the first time, threeof which are among the largest in the northern sky. Besides surfacebrightness profiles, precise total magnitudes and colors have beenmeasured. Many of the results represent substantial revisions toprevious estimates. The data will make possible new determinations ofthe distances and masses of the galaxies, which are crucial forevaluating the impact the group may have had upon the dynamicalevolution of the Local Group.
| 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.
| Surface Brightness Fluctuation Distances to Dwarf Elliptical Galaxies in the Sculptor Group
As part of an ongoing search for dwarf elliptical galaxies (dE's) in thevicinity of the Local Group (Jerjen et al.), we acquired deep B- andR-band images for five dE candidates identified on morphologicalcriteria in the Sculptor (Scl) group region. We carried out a surfacebrightness fluctuation (SBF) analysis on the R-band images to measurethe apparent fluctuation magnitude m_R for each dE. Using predictionsfrom stellar population synthesis models (Worthey) giving M_R values inthe narrow range between -1.17 and -1.13, the galaxy distances weredetermined. All of these dE candidates turned out to be satellites ofScl group major members. A redshift measurement of the dE candidate ESO294-010 yielded an independent confirmation of its group membership: the[O III] and Hα emission lines from a small H II region gave aheliocentric velocity of 117 (+/-5) km s^-1, in close agreement with thevelocity of its parent galaxy NGC 55 (v_ȯ = 125 km s^-1). Theprecision of the SBF distances (5%-10%) contributes to delineating thecigar-like distribution of the Scl group members, which extend overdistances from 1.7 to 4.4 Mpc and are concentrated in three, possiblyfour subclumps. The Hubble diagram for nine Scl galaxies, including twoof our dE's, exhibits a tight linear velocity-distance relation with asteep slope of 119 km s^-1 Mpc^-1. The results indicate thatgravitational interaction among the Scl group members plays only a minorrole in the dynamics of the group. However, the Hubble flow of theentire system appears strongly disturbed by the large masses of ourGalaxy and M31, which leads to the observed shearing motion. From thedistances and velocities of 49 galaxies located in the Local Group andtoward the Scl group, we illustrate the continuity of the galaxydistribution, which strongly supports the view that the two groups forma single supergalactic structure.
| Automatic Determination of Unbiased Luminosity Functions for H II Regions. II. Four Nearby Dwarf Galaxies
Luminosity functions in Hα have been measured for H II regions inthe four dwarf galaxies UGCA 86, UGCA 92, UGCA 105, and UGC 4115 usingboth the traditional flux measurement method of fixed-thresholdphotometry (FTP) and the new method, percentage-of-peak photometry(PPP). The UGCA galaxies are members of the IC 342-Maffei 1 group. Thesetwo methods give significantly different results in galaxies in whichsignificant numbers of peaks are associated with H II region complexes.The work demonstrates that fluxes from FTP can lead to biased luminosityfunctions and that PPP should, in general, be preferred. It is alsoshown that PPP luminosity functions are not very sensitive toatmospheric transparency, whereas those constructed from FTP can be,based on data taken under different atmospheric conditions. Results todate for six galaxies show that spirals and dwarfs have luminosityfunctions of similar shape, which implies that the distribution of themasses of star formation sites is largely independent of the mass, andby implication, the metallicity, of the host galaxy. As measured by PPP,the mean surface brightness of the lower luminosity H II regions growsas the one-third power of the flux grows, exactly as predicted for anensemble in which the gas density does not vary systematically with themass of the star cluster. For the brightest H II regions, however, therelation steepens, which implies that the most massive star clusters areformed out of the densest clouds.
| Catalogue of HI maps of galaxies. II. Analysis of the data
We use some of the maps of the catalogue presented in Paper I to providesome evidence for global conditions that must be fulfilled by thegalaxies to have extended hydrogen. For this purpose, we tried to findpossible connections between the HI gas extension and other propertiesof the galaxies (morphological type, surface brightness, gas density,etc.). With isophotal hydrogen diameters of a large sample, we couldobserve that optically smaller galaxies seem to have greater relative HIextensions. By means of the relation with the apparent HI surfacedensity, we found an expression that should provide a rough estimate ofthe gas extension. With respect to the dependence on morphological type,we could not find any significant correlation either for the real HIsurface density or the relative gas extension. Nevertheless, whereas forspiral and irregular galaxies the real HI surface density exhibits abroad range of values, the values are rather lower for elliptical and S0galaxies. Table 1 is also available in electronic form at the CDS viaanonymous ftp 130.79.128.5 or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Catalogue of HI maps of galaxies. I.
A catalogue is presented of galaxies having large-scale observations inthe HI line. This catalogue collects from the literature the informationthat characterizes the observations in the 21-cm line and the way thatthese data were presented by means of maps, graphics and tables, forshowing the distribution and kinematics of the gas. It containsfurthermore a measure of the HI extension that is detected at the levelof the maximum sensitivity reached in the observations. This catalogueis intended as a guide for references on the HI maps published in theliterature from 1953 to 1995 and is the basis for the analysis of thedata presented in Paper II. The catalogue is only available inelectronic form at the CDS via anonymous ftp 130.79.128.5 orhttp://cdsweb.u-strasbg.fr/Abstract.html
| Three new low velocity irregular galaxies undetected in HI
We have detected in Hα three very nearby (D < 3 Mpc) irregulardwarf galaxies, which have been observed but undetected in HI. Theirheliocentric radial velocities are: -64 km/s (Cam C), +445 km/s (Arp211), and -141 km/s (NGC 6789) with the standard error +/-8 km/s.
| Search and Redshift Survey for IRAS Galaxies behind the Milky Way and Structure of the Local Void
This is the third and final paper of our systematic visual search forIRAS galaxies behind the Milky Way at |b| <= 15 deg. This paperpresents a catalog of 950 IRAS galaxies with 60 mu m flux densitieslarger than 0.6 Jy located between l = 0 deg and 150 deg, of which 293are newly identified by this search. We made a redshift survey for theidentified galaxies and obtained new redshift data of 171 galaxies. Wealso present newly measured redshifts of 27 IRAS galaxies between l =150 deg and 225 deg at |b| <= 15 deg. In this paper we studied thestructure of the Local void using IRAS galaxies and galaxies from theThird Reference Catalogue of Bright Galaxies in the region l = 30deg--120 deg and b = -50 deg to +30 deg. The center of the Local voidturned out to be located at l ~ 60 deg, b ~ -15 deg, and cz ~ 2500 kms-1, and the size is about 2500 km s-1 along the direction toward thecenter.
| Revised photometric distances to nearby dwarf galaxies in the IC 342/Maffei complex
The results of DAOPHOT photometry of several hundred stars in fiveirregular galaxies are presented using V and I CCD frames, obtained withthe Nordic Optical Telescope under a 0.6 arcsec seeing. Based on thebrightest blue and red stars we estimate the following distances to thegalaxies: 3.2 Mpc for UGCA 105, 2.6 Mpc for UGCA 86, 1.8 Mpc for UGCA92, 1.7 Mpc for NGC 1569, and 1.7 Mpc for Cas 1. The problem ofmembership of the galaxies to the IC 342/Maffei complex is brieflydiscussed Tables 2 to 6 are only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Calibration of the luminosity function of bright blue stars as a distance indicator for late-type 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) .
| 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.
| H II Regions in Four Galaxies in and near the Local Group
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...451..176H&db_key=AST
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Наблюдательные данные и астрометрия
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