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CO(1-0), CO(2-1), and Neutral Gas in NGC 6946: Molecular Gas in a Late-Type, Gas-Rich, Spiral Galaxy
We present on-the-fly maps of the CO(1-0) and CO(2-1) emission coveringa 10' × 10' region of NGC 6946. Using our CO maps and archival VLAH I observations we create a total gas surface density map,Σgas, for NGC 6946. The predominantly molecular innergas disk transitions smoothly into an atomic outer gas disk, withequivalent atomic and molecular gas surface densities at R = 3.5' (6kpc). We estimate that the total H2 mass is 3 ×109 Modot, roughly one-third of the interstellarhydrogen gas mass and about 2% of the dynamical mass of the galaxy atour assumed distance of 6 Mpc. The value of the CO(2-1)/CO(1-0) lineratio ranges from 0.35 to 2; 50% of the map is covered by very highratio gas (>1). The very high ratios are predominantly from interarmregions and appear to indicate the presence of wide-spread opticallythin gas. Star formation tracers are better correlated with the totalneutral gas disk than with the molecular gas by itself, implyingΣSFR ~ Σgas. Using the 100 μm and21 cm continua from NGC 6946 as star formation tracers, we arrive at agas consumption timescale of 2.8 Gyr, which is relatively uniform acrossthe disk. The high star formation rate at the nucleus appears to be dueto a large accumulation of molecular gas rather than a large increase inthe star formation efficiency. The midplane gas pressure in the outer (R> 10 kpc) H I arms of NGC 6946 is close to the value at the radiallimit (10 kpc) of our observed CO disk. If the midplane gas pressure isa factor for the formation of molecular clouds, these outer H I gas armsshould contain molecular gas, which we do not see because this gas isbeyond our detection limit.
| Modified Newtonian Dynamics Rotation Curves of Very Low Mass Spiral Galaxies
We present modified Newtonian dynamics (MOND) analysis for several ofthe lowest mass disk galaxies currently amenable to such analysis, with(baryonic) masses below 4×108 Msolar. Theagreement is good, extending the validity of MOND and its predicted massvelocity relation, to such low masses.
| High-Resolution Optical Velocity Fields of 11 Low Surface Brightness Galaxies
We present high-resolution two-dimensional velocity fields from integralfield spectroscopy, along with derived rotation curves for 11 lowsurface brightness galaxies. We fit NFW and pseudoisothermal halo modelsto the new data combined with previous long-slit and H I data. In mostcases, we find the pseudoisothermal halo to better represent the datathan the NFW halo, as the NFW concentrations are often lower thanexpected for a ΛCDM cosmology. We also compare our results toprevious studies and find that including the new two-dimensional opticaldata does not significantly alter the halo parameters but does decreasethe uncertainties by roughly a factor of 2.
| Halo Mass Profiles and Low Surface Brightness Galaxy Rotation Curves
A recent study has claimed that the rotation curve shapes and massdensities of low surface brightness (LSB) galaxies are largelyconsistent with ΛCDM predictions, in contrast to a large body ofobservational work. I demonstrate that the method used to derive thisconclusion is incapable of distinguishing the characteristic steep CDMmass-density distribution from the core-dominated mass-densitydistributions found observationally: even core-dominatedpseudoisothermal halos would be inferred to be consistent with CDM. Thismethod can therefore make no definitive statements regarding the(dis)agreement between the data and CDM simulations. After introducingan additional criterion that does take the slope of the massdistribution into account, I find that only about a quarter of the LSBgalaxies investigated are possibly consistent with CDM. However, formost of these, the fit parameters are so weakly constrained that this isnot a strong conclusion. Of the 20 galaxies with tightly constrained fitparameters, only 3 are consistent with ΛCDM. Two of thesegalaxies are likely dominated by stars, leaving only one possible darkmatter-dominated, CDM-consistent candidate. These conclusions are basedon comparison of data and simulations at identical radii and fits to theentire rotation curves. LSB galaxies that are consistent with CDMsimulations, if they exist, seem to be rare indeed.
| 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.
| Hα imaging of the local volume galaxies. I. The NGC 6946 galaxy group
We present new Hα imaging of all known dwarf irregular companionsto NGC 6946: UGC 11583, KK 251, KK 252, KKR 55, KKR 56, Cepheus 1, KKR59, and KKR 60. The galaxies span a range of blue absolute magnitudes of[ -13.6, -17.6] , relative gas content of [0.1, 2.5]Mȯ/Lȯ, current star formation activityof [0.2, ~5.2]× 10-2 ~Mȯyr-1, and timescale to exhaust the current gas supply of [6,86] Gyr.
| Red Thick Disks of Nearby Galaxies
Edge-on systems reveal the properties of disk galaxies as a function ofheight, z, above the plane. Four local edge-on galaxies that are closeenough to have been resolved into stars by the Hubble Space Telescopeshow thick disks composed of a red stellar population that is old andrelatively metal rich. Color gradients, Δ(V-I)/Δz, are zeroor slightly positive. Favored models may have an explicit thick diskformation phase.
| The inner structure of ΛCDM haloes - II. Halo mass profiles and low surface brightness galaxy rotation curves
We use a set of high-resolution cosmological N-body simulations toinvestigate the inner mass profile of galaxy-sized cold dark matter(CDM) haloes. These simulations extend the numerical convergence studypresented in Paper I of this series, and demonstrate that the massprofile of CDM galaxy haloes can be robustly estimated beyond a minimumconverged radius of order rconv~ 1h-1 kpc in ourhighest-resolution runs. The density profiles of simulated haloes becomeprogressively shallower from the virial radius inwards, and show no signof approaching a well-defined power law near the centre. Atrconv, the density profile is steeper than expected from theformula proposed by Navarro, Frenk & White, which has aρ~r-1 cusp, but significantly shallower than the steeplydivergent ρ~r-1.5 cusp proposed by Moore et al. Weperform a direct comparison of the spherically averaged dark mattercircular velocity profiles with Hα rotation curves of a sample oflow surface brightness (LSB) galaxies. We find that most galaxies in thesample (about 70 per cent) have rotation curves that are consistent withthe structure of CDM haloes. Of the remainder, 20 per cent have rotationcurves which cannot be fit by any smooth fitting function with few freeparameters, and 10 per cent are inconsistent with CDM haloes. However,the latter consist mostly of rotation curves that do not extend to largeenough radii to accurately determine their shapes and maximumvelocities. We conclude that the inner structure of CDM haloes is notmanifestly inconsistent with the rotation curves of LSB galaxies.
| Kinematics of two dwarf galaxies in the NGC 6946 group
We present high velocity resolution (˜1.6 km s-1) GiantMeterwave Radio Telescope (GMRT) HI 21 cm synthesis images of the dwarfgalaxies KK98 250 and KK98 251, as well as optical broad band images ofKK98 250. We find that, despite being faint (MB ⪉ -14),both galaxies have regular velocity fields. In both cases the velocityfields are consistent with rigid body rotation. We derive rotationcurves for the galaxies and fit mass models to them. For both galaxies,we find acceptable fits using isothermal halos while NFW halos provide apoor fit. Finally, we compile from literature a sample of galaxies withHI synthesis observations and I band magnitudes. From this sample wefind, in agreement with earlier studies (which used single dish HIdata), that dwarf galaxies tend to lie below the I band Tully-Fisherrelation defined by brighter galaxies.
| The ISOPHOT 170 μm Serendipity Survey II. The catalog of optically identified galaxies%
The ISOPHOT Serendipity Sky Survey strip-scanning measurements covering≈15% of the far-infrared (FIR) sky at 170 μm were searched forcompact sources associated with optically identified galaxies. CompactSerendipity Survey sources with a high signal-to-noise ratio in at leasttwo ISOPHOT C200 detector pixels were selected that have a positionalassociation with a galaxy identification in the NED and/or Simbaddatabases and a galaxy counterpart visible on the Digitized Sky Surveyplates. A catalog with 170 μm fluxes for more than 1900 galaxies hasbeen established, 200 of which were measured several times. The faintest170 μm fluxes reach values just below 0.5 Jy, while the brightest,already somewhat extended galaxies have fluxes up to ≈600 Jy. For thevast majority of listed galaxies, the 170 μm fluxes were measured forthe first time. While most of the galaxies are spirals, about 70 of thesources are classified as ellipticals or lenticulars. This is the onlycurrently available large-scale galaxy catalog containing a sufficientnumber of sources with 170 μm fluxes to allow further statisticalstudies of various FIR properties.Based on observations with ISO, an ESA project with instruments fundedby ESA Member States (especially the PI countries: France, Germany, TheNetherlands and the UK) and with the participation of ISAS and NASA.Members of the Consortium on the ISOPHOT Serendipity Survey (CISS) areMPIA Heidelberg, ESA ISO SOC Villafranca, AIP Potsdam, IPAC Pasadena,Imperial College London.Full Table 4 and Table 6 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/422/39
| 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.
| New optical velocities of nearby dwarf LSB galaxies
We present radial velocities for nearby dwarf galaxy candidates found byKarachentseva & Karachentsev (\cite{Karachentseva1998}) on thePOSS-II films. Out of 118 observed objects, 88 have been detected in theHalpha line. Their median radial velocity is 1750 kms-1. A quarter of the galaxies belong to the Local Volume,having corrected radial velocities V_LG < 500 km s-1. Someof them are members of the nearby groups around Maffei/IC 342, M 81, andNGC 6946.
| Simulating observations of dark matter dominated galaxies: towards the optimal halo profile
Low surface brightness galaxies are dominated by dark matter, and theirrotation curves thus reflect their dark matter distribution. Recenthigh-resolution rotation curves suggest that their dark mattermass-density distributions are dominated by a constant-density core.This seems inconsistent with the predictions of cold dark matter (CDM)models which produce haloes with compact density cusps and steepmass-density profiles. However, the observationally determined massprofiles may be affected by non-circular motions, asymmetries andoffsets between optical and dynamical centres, all of which tend tolower the observed slopes. Here we determine the impact of each of theseeffects on a variety of halo models, and we compare the results withobserved mass-density profiles. Our simulations suggest that no singlesystematic effect can reconcile the data with the cuspy CDM haloes. Thedata are best described by a model with a soft core with an innerpower-law mass-density slope α=-0.2 +/- 0.2. However, no singleuniversal halo profile provides a completely adequate description of thedata.
| 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.
| High-Resolution Rotation Curves of Low Surface Brightness Galaxies. II. Mass Models
We present mass models for a sample of 30 high-resolution rotationcurves of low surface brightness galaxies. We fit both pseudoisothermal(core dominated) and cold dark matter (CDM; cusp dominated) halos for awide variety of assumptions about the stellar mass-to-light ratio. Wefind that the pseudoisothermal model provides superior fits. CDM fitsshow systematic deviations from the data and often have a smallstatistical likelihood of being the appropriate model. The distributionof concentration parameters is too broad, and has too low a mean, to beexplained by low-density, flat CDM (ΛCDM). This failing becomesmore severe as increasing allowance is made for stellar mass: Navarro,Frenk, & White (NFW) model fits require uncomfortably lowmass-to-light ratios. In contrast, the maximum disk procedure does oftensucceed in predicting the inner shape of the rotation curves, but itrequires uncomfortably large stellar mass-to-light ratios. The data doadmit reasonable stellar population mass-to-light ratios if halos havecores rather than cusps.
| High-Resolution Rotation Curves of Low Surface Brightness Galaxies. I. Data
We present long-slit Hα observations of 50 low surface brightnessgalaxies. Of these, 36 are of sufficient quality to form rotationcurves. These data provide a large increase in the number of low surfacebrightness galaxies for which accurate rotation curves are available.They also represent an order-of-magnitude improvement in spatialresolution over previous 21 cm studies (1"-2" instead of 13"-45"). Theimproved resolution and accuracy of the data extend and strengthen thescientific conclusions previously inferred from 21 cm data. Based onobservations using the 4 m telescope, Kitt Peak National Observatory,National Optical Astronomy Observatory, which is operated by theAssociation of Universities for Research in Astronomy, Inc., undercooperative agreement with the National Science Foundation, and the duPont Telescope of the Las Campanas Observatory, Carnegie Institution ofWashington.
| Mass Density Profiles of Low Surface Brightness Galaxies
We derive the mass density profiles of dark matter halos that areimplied by high spatial resolution rotation curves of low surfacebrightness galaxies. We find that, at small radii, the mass densitydistribution is dominated by a nearly constant density core with a coreradius of a few kiloparsecs. For ρ(r)~rα, thedistribution of inner slopes α is strongly peaked aroundα=-0.2. This is significantly shallower than the cuspyα<=-1 halos found in cold dark matter simulations. While theobserved distribution of α does have a tail toward such extremevalues, the derived value of α is found to depend on the spatialresolution of the rotation curves: α~-1 is found only for theleast well resolved galaxies. Even for these galaxies, our data are alsoconsistent with constant-density cores (α=0) of modest (~1 kpc)core radius, which can give the illusion of steep cusps wheninsufficiently resolved. Consequently, there is no clear evidence for acuspy halo in any of the low surface brightness galaxies observed.
| Companions and interactions in the NGC 6946 system
We report the results of a survey of the Hi environment of NGC 6946 in asearch for gas-rich companions to the galaxy. Such gas-rich companionscould include material left over from the galaxy assembly process whichcould persist into the current day around an isolated galaxy such as NGC6946. NGC 6946 is prolifically forming stars, has a nuclear starburst,and has widespread high-velocity clouds associated with the disc. All ofthese features could be explained by the accretion of low-mass Hi cloudsby NGC 6946. Our survey recovered two previously detected dwarf galaxiesassociated with NGC 6946, but otherwise found no signatures ofinteractions in the NGC 6946 system. The companions are small enough,and distant enough from NGC 6946 that they should have minimal effect onthe main galaxy. Some tidal debris may be expected due to interactionbetween the two dwarf galaxies, but none is observed. This could bebecause it is at low column densities, or because the dwarf galaxies aremore separated than they appear on the sky. This study of the systemsuggests that NGC 6946 is a gravitationally bound system with two dwarfgalaxies in stable orbits about the larger primary galaxy.
| A group of galaxies around the giant spiral NGC 6946
We present large-scale CCD images of a dozen low surface brightnessobjects in the vicinity of giant Sc galaxy NGC 6946, which have beenfound recently on POSS-II copies. Six of them: UGC 11583, kk251, kk252,kkr55, kkr56, and kkr59 are dwarf irregular galaxies resolved intostars. We determined their distances from the luminosity of thebrightest blue stars. The mean estimated distance to the NGC 6946 groupis 5.9+/-0.4 Mpc. Together with Cepheus 1, discovered before, the groupconsist of 8 late type galaxies. Almost all of them are detected ormarginally detected in the HI line. The group is characterized by alinear projected diameter of 420 kpc, a radial velocity dispersion of 95km s-1, and a virial mass-to-luminosity ratio about 56Msun /Lsun .
| HI observations of nearby galaxies . I. The first list of the Karachentsev catalog
We present HI observations of the galaxies in the first list of theKarachentsev catalog of previously unknown nearby dwarf galaxies(Karachentseva & Karachentsev 1998). This survey covers all knownnearby galaxy groups within the Local Volume (i.e. within 10 Mpc) andtheir environment, that is about 25% of the total sky. A total of 257galaxies have been observed with a detection rate of 60%. We searched afrequency band corresponding to heliocentric radial velocities from -470km s-1 to ~ +4000 km s-1. Non-detections areeither due to limited coverage in radial velocity, confusion with LocalHI (mainly in the velocity range -140 km s-1 to +20 kms-1), or lack of sensitivity for very weak emission. 25% ofthe detected galaxies are located within the Local Volume. Thosegalaxies are dwarf galaxies judged by their optical linear diameter (1.4+/- 0.2 kpc on the average), their mean total HI mass (4.6107 Msun), and their observed linewidths (39 kms-1).
| 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
| Galaxies detected by the Dwingeloo Obscured Galaxies Survey
The Dwingeloo Obscured Galaxies Survey (DOGS) is a 21-cm blind surveyfor galaxies hidden in the northern Zone of Avoidance (ZOA): the portionof the optical extragalactic sky which is obscured by dust in the MilkyWay. Like the Parkes southern hemisphere ZOA survey, the DOGS project isdesigned to reveal hidden dynamically important nearby galaxies and tohelp "fill in the blanks" in the local large scale structure. To date,36 galaxies have been detected by the Dwingeloo survey; 23 of these werepreviously unknown (no corresponding sources recorded in the NASAExtragalactic Database). Among the interesting detections are threenearby galaxies in the vicinity of NGC 6946 and 11 detections in theSupergalactic plane crossing region. VLA follow-up observations havebeen conducted for several of the DOGS detections.
| Discovery of a Nearby Low Surface Brightness Spiral Galaxy
During the course of a search for compact, isolated gas clouds movingwith anomalous velocities in or near our own Galaxy, we have discoveredin the data of the Leiden/Dwingeloo survey of Galactic hydrogen the H Isignature of a large galaxy moving at a recession velocity of 282 kms^-1 with respect to our Galaxy. Deep multicolor and spectroscopicoptical observations show the presence of star formation in scattered HII regions; radio H I synthesis interferometry confirms that the galaxyis rich in H I and has the rotation signature of a spiral galaxy; asubmillimeter observation failed to detect the CO molecule. The radioand optical evidence combined suggest its classification as a lowsurface brightness (LSB) spiral galaxy. It is located in close spatialand kinematic proximity to the galaxy NGC 6946. The newly discoveredgalaxy, which we call Cep 1, is at a distance of about 6 Mpc. It isprobably to be numbered among the nearest few LSB spiral galaxies.
| 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
| HI-search for nearby dwarf galaxies.
We present 26 new candidates (mainly from the POSS II) for nearby dwarfgalaxies of which 17 have been detected in the 21-cm line from neutralhydrogen with the 100-m radiotelescope at Effelsberg. There is one newdwarf member of the IC342/Maffei group (Camelopardalis B), three newmembers each of the NGC6946 and the NGC672/IC1727 group. These sevengalaxies (~25% of our search list) are within the range of theKraan-Korteweg-Tammann sample (i.e. v_0_<=500km/s).
| Photometric distance to the galaxy NGC 6946 and its companion.
Not Available
| 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.
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