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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.
| The AMIGA sample of isolated galaxies. II. Morphological refinement
We present a refinement of the optical morphologies for galaxies in theCatalog of Isolated Galaxies that forms the basis of the AMIGA (Analysisof the interstellar Medium of Isolated GAlaxies) project. Uniformreclassification using the digitized POSS II data benefited from thehigh resolution and dynamic range of that sky survey. Comparison withindependent classifications made for an SDSS overlap sample of more than200 galaxies confirms the reliability of the early vs. late-typediscrimination and the accuracy of spiral subtypes within Δ T =1-2. CCD images taken at the Observatorio de Sierra Nevada were alsoused to solve ambiguities in early versus late-type classifications. Aconsiderable number of galaxies in the catalog (n = 193) are flagged forthe presence of nearby companions or signs of distortion likely due tointeraction. This most isolated sample of galaxies in the local Universeis dominated by two populations: 1) 82% are spirals (Sa-Sd) with thebulk being luminous systems with small bulges (63% between types Sb-Sc)and 2) a significant population of early-type E-S0 galaxies (14%). Mostof the types later than Sd are low luminosity galaxies concentrated inthe local supercluster where isolation is difficult to evaluate. Thelate-type spiral majority of the sample spans a luminosity rangeMB-corr = -18 to -22 mag. Few of the E/S0 population are moreluminous than -21.0 marking the absence of the often-sought superL* merger (e.g. fossil elliptical) population. The rarity ofhigh luminosity systems results in a fainter derived M* forthis population compared to the spiral optical luminosity function(OLF). The E-S0 population is from 0.2 to 0.6 mag fainter depending onhow the sample is defined. This marks the AMIGA sample as unique amongsamples that compare early and late-type OLFs separately. In othersamples, which always involve galaxies in higher density environments,M^*_E/S0 is almost always 0.3-0.5 mag brighter than M^*_S, presumablyreflecting a stronger correlation between M* andenvironmental density for early-type galaxies.
| Ultraluminous X-Ray Sources in Nearby Galaxies from ROSAT High Resolution Imager Observations I. Data Analysis
X-ray observations have revealed in other galaxies a class ofextranuclear X-ray point sources with X-ray luminosities of1039-1041 ergs s-1, exceeding theEddington luminosity for stellar mass X-ray binaries. Theseultraluminous X-ray sources (ULXs) may be powered by intermediate-massblack holes of a few thousand Msolar or stellar mass blackholes with special radiation processes. In this paper, we present asurvey of ULXs in 313 nearby galaxies withD25>1' within 40 Mpc with 467 ROSAT HighResolution Imager (HRI) archival observations. The HRI observations arereduced with uniform procedures, refined by simulations that help definethe point source detection algorithm employed in this survey. A sampleof 562 extragalactic X-ray point sources withLX=1038-1043 ergs s-1 isextracted from 173 survey galaxies, including 106 ULX candidates withinthe D25 isophotes of 63 galaxies and 110 ULX candidatesbetween 1D25 and 2D25 of 64 galaxies, from which aclean sample of 109 ULXs is constructed to minimize the contaminationfrom foreground or background objects. The strong connection betweenULXs and star formation is confirmed based on the striking preference ofULXs to occur in late-type galaxies, especially in star-forming regionssuch as spiral arms. ULXs are variable on timescales over days to yearsand exhibit a variety of long term variability patterns. Theidentifications of ULXs in the clean sample show some ULXs identified assupernovae (remnants), H II regions/nebulae, or young massive stars instar-forming regions, and a few other ULXs identified as old globularclusters. In a subsequent paper, the statistic properties of the surveywill be studied to calculate the occurrence frequencies and luminosityfunctions for ULXs in different types of galaxies to shed light on thenature of these enigmatic sources.
| High-Resolution Measurements of the Halos of Four Dark Matter-Dominated Galaxies: Deviations from a Universal Density Profile
We derive rotation curves for four nearby, low-mass spiral galaxies anduse them to constrain the shapes of their dark matter density profiles.This analysis is based on high-resolution two-dimensional Hαvelocity fields of NGC 4605, NGC 5949, NGC 5963, and NGC 6689 and COvelocity fields of NGC 4605 and NGC 5963. In combination with ourprevious study of NGC 2976, the full sample of five galaxies containsdensity profiles that span the range from αDM=0 toαDM=1.20, where αDM is the power-lawindex describing the central density profile. The scatter inαDM from galaxy to galaxy is 0.44, 3 times as large asin cold dark matter (CDM) simulations, and the mean density profileslope is αDM=0.73, shallower than that predicted by thesimulations. These results call into question the hypothesis that allgalaxies share a universal dark matter density profile. We show that oneof the galaxies in our sample, NGC 5963, has a cuspy density profilethat closely resembles those seen in CDM simulations, demonstrating thatwhile galaxies with the steep central density cusps predicted by CDM doexist, they are in the minority. In spite of these differences betweenobservations and simulations, the relatively cuspy density profiles wefind do not suggest that this problem represents a crisis for CDM.Improving the resolution of the simulations and incorporating additionalphysics may resolve the remaining discrepancies. We also find that fourof the galaxies contain detectable radial motions in the plane of thegalaxy. We investigate the hypothesis that these motions are caused by atriaxial dark matter halo and place lower limits on the ellipticity ofthe orbits in the plane of the disk of 0.043-0.175.Based on observations carried out at the WIYN Observatory. The WIYNObservatory is a joint facility of the University of Wisconsin-Madison,Indiana University, Yale University, and the National Optical AstronomyObservatory.
| Cores of dark matter haloes correlate with stellar scalelengths
We investigate in detail the mass distribution obtained by means ofhigh-resolution rotation curves of 25 galaxies of differentmorphological types. The dark matter contribution to the circularrotation velocity is well-described by resorting to a dark component,the density of which shows an inner core, i.e. a central constantdensity region. We find a very strong correlation between the coreradius size RC and the stellar exponential scalelengthRD: RC~=13[RD/(5kpc)]1.05kpc, and between RCand the galaxy dynamical mass at this distance,Mdyn(RC). These relationships would not beexpected if the core radii were the product of an incorrectdecomposition procedure, or the biased result of wrong or misunderstoodobservational data. The very strong correlation between the dark andluminous scalelengths found here seems to hold also for different Hubbletypes and opens new scenarios for the nature of the dark matter ingalaxies.
| Scaling Laws for Dark Matter Halos in Late-Type and Dwarf Spheroidal Galaxies
Published mass models fitted to galaxy rotation curves are used to studythe systematic properties of dark matter (DM) halos in late-type anddwarf spheroidal (dSph) galaxies. Halo parameters are derived by fittingnon-singular isothermals to (V^2 - Vvis^2)1/2,where V(r) is the observed rotation curve and Vvis is therotation curve of the visible matter. The latter is calculated from thesurface brightness assuming that the mass-to-light ratio M/L is constantwith radius. ``Maximum disk'' values of M/L are adjusted to fit as muchof the inner rotation curve as possible without making the halo have ahollow core. Rotation curve decomposition becomes impossible fainterthan absolute magnitude M_B ≃ -14, where V becomes comparable tothe velocity dispersion of the gas. To increase the luminosity rangefurther, we include dSph galaxies, which are physically related tospiral and irregular galaxies. Combining the data, we find that DM halossatisfy well defined scaling laws analogous to the ``fundamental plane''relations for elliptical galaxies. Halos in less luminous galaxies havesmaller core radii r_c, higher central densities ρ_0, and smallercentral velocity dispersions σ. Scaling laws provide new anddetailed constraints on the nature of DM and on galaxy formation andevolution. Some simple implications include:1 -- A single, continuous physical sequence of increasing mass extendsfrom dSph galaxies with M_B ≃ -7.6 to Sc I galaxies with M_B≃ -22.4.2 -- The high DM densities in dSph galaxies are normal for such tinygalaxies. Since virialised density depends on collapse redshiftzcoll, ρ_0 ∝ (1 + zcoll)^3, the smallestdwarfs formed at least Δ zcoll ≃ 7 earlier thanthe biggest spirals.3 -- The high DM densities of dSphs implies that they are real galaxiesformed from primordial density fluctuations. They are not tidalfragments. Tidal dwarfs cannot retain even the low DM densities of theirgiant-galaxy progenitors. In contrast, dSphs have higher DM densitiesthan do giant-galaxy progenitors.4 -- The fact that, as luminosity decreases, dwarf galaxies become muchmore numerous and also more nearly dominated by DM raises thepossibility that there exists a large population of objects that arecompletely dark. Such objects are a canonical prediction of cold DMtheory. If they exist, ``empty halos'' are likely to be small and dense-- that is, darker versions of Draco and UMi.5 -- The slopes of the DM parameter correlations provide a measure ongalactic mass scales of the slope n of the power spectrum|δk|2 ∝ k^n of primordial densityfluctuations. Our preliminary results, not yet corrected for baryoniccompression of DM, give n ≃ -1.9 ± 0.2. This is consistentwith cold DM theory.
| Dark Matter in Dwarf Galaxies: High Resolution Observations
We present observations and analysis of rotation curves and dark matterhalo density profiles in the central regions of four nearby dwarfgalaxies. This observing program has been designed to overcome some ofthe limitations of other rotation curve studies that rely mostly onlongslit spectra. We find that these objects exhibit the full range ofcentral density profiles between ρ∝ r^0 (constant density) andρ∝ r-1 (NFW halo). This result suggests that thereis a distribution of central density slopes rather than a unique halodensity profile.
| Dark Matter in Galaxies: Observational overview
I review the observational side of the present state of the debate aboutthe dark matter in galaxies, with emphasis on the core/cusp problem inlow surface brightness galaxies, and the question of maximum /sub-maximum disks in spiral galaxies. Some remarks are made about thedwarf spheroidals around the Milky Way, and about elliptical galaxies.
| A Catalog of Neighboring Galaxies
We present an all-sky catalog of 451 nearby galaxies, each having anindividual distance estimate D<~10 Mpc or a radial velocityVLG<550 km s-1. The catalog contains data onbasic optical and H I properties of the galaxies, in particular, theirdiameters, absolute magnitudes, morphological types, circumnuclearregion types, optical and H I surface brightnesses, rotationalvelocities, and indicative mass-to-luminosity and H I mass-to-luminosityratios, as well as a so-called tidal index, which quantifies the galaxyenvironment. We expect the catalog completeness to be roughly 70%-80%within 8 Mpc. About 85% of the Local Volume population are dwarf (dIr,dIm, and dSph) galaxies with MB>-17.0, which contributeabout 4% to the local luminosity density, and roughly 10%-15% to thelocal H I mass density. The H I mass-to-luminosity and the H Imass-to-total (indicative) mass ratios increase systematically fromgiant galaxies toward dwarfs, reaching maximum values about 5 in solarunits for the most tiny objects. For the Local Volume disklike galaxies,their H I masses and angular momentum follow Zasov's linear relation,expected for rotating gaseous disks being near the threshold ofgravitational instability, favorable for active star formation. We foundthat the mean local luminosity density exceeds 1.7-2.0 times the globaldensity, in spite of the presence of the Tully void and the absence ofrich clusters in the Local Volume. The mean local H I density is 1.4times its ``global'' value derived from the H I Parkes Sky Survey.However, the mean local baryon densityΩb(<8Mpc)=2.3% consists of only a half of the globalbaryon density, Ωb=(4.7+/-0.6)% (Spergel et al.,published in 2003). The mean-square pairwise difference of radialvelocities is about 100 km s-1 for spatial separations within1 Mpc, increasing to ~300 km s-1 on a scale of ~3 Mpc. alsoWe calculated the integral area of the sky occupied by the neighboringgalaxies. Assuming the H I size of spiral and irregular galaxies to be2.5 times their standard optical diameter and ignoring any evolutioneffect, we obtain the expected number of the line-of-sight intersectionswith the H I galaxy images to be dn/dz~0.4, which does not contradictthe observed number of absorptions in QSO spectra.
| The Dark Matter Of Galactic Halos
We focus on the problem of representing only the dark matter presentlyassociated with the halos of isolated galaxies. This manifests itself ingravitational lenses and as the unexplained source of the extended flatportion of the rotation curves Vrot(r) ≈ const. of theMilky Way and other galaxies. For example,any halo fluid with a simpleequation of state must have finite density at the origin and beisothermal in those regions for which Vrot is flat. Suchfluids are represented by Bonnor-Ebert models; these are gravitationallyunstable for halos extending beyond 20 kpc. We also note a halo ofexotic non-interacting particles satisfying the collisionless Boltzmanequation cannot be restored to even approximate spherical symmetry inregions where galaxy-galaxy collisions have occured. Provisionally, wesuggest that the halos arose as very small amplitude unstablefluctuation in a classical scalar field of the generic formc-2∂ 2ttφ -∇2φ = m2φ (1-φ 2) where1/m 3 kpc; the growth of spacial fluctuations is limited to finiteamplitude by the non-linear term. From an initial value δ φ 10-4 it takes 105 yrs to develop tofinite amplitude; they could not have been important in the early daysof the universe. These disturbances today play the role of `dark' halosaround galaxies.The gravitational fields the produce can well representthe observed rotation curves of the Milky Way, NGC4605, F583-1, &DDO 154, with 1/m 2-5 kpc determining the onset of the flatfortion of Vrot. When galaxies are clustered, the boundariesbetween halos is described by discontinuities in the second derivativesof the φ -field and a Λ -term appears naturally inrepresenting the field's energy density. The universe's present energydensity associated with these halo fields is Ω 1/2 -2/3. Ifthe universe were modeled as an enormous cluster of equally spacedgalactic halos, the resulting cosmological fluid's energy density wouldscale with the cosmic scale factor as R}(t)-2. Using this, apossible scenario in which R}(t) would have experienced a recentacceleration, representing a `quintessence' effect.
| High-Resolution Measurements of the Dark Matter Halo of NGC 2976: Evidence for a Shallow Density Profile
We have obtained two-dimensional velocity fields of the dwarf spiralgalaxy NGC 2976 in Hα and CO. The high spatial (~75 pc) andspectral (13 and 2 km s-1, respectively) resolution of theseobservations, along with our multicolor optical and near-infraredimaging, allows us to measure the shape of the density profile of thedark matter halo with good precision. We find that the total (baryonicplus dark matter) mass distribution of NGC 2976 follows aρtot~r-0.27+/-0.09 power law out to a radiusof 1.8 kpc, assuming that the observed radial motions provide nosupport. The density profile attributed to the dark halo is evenshallower, consistent with a nearly constant density of dark matter overthe entire observed region. A maximal disk fit yields an upper limit tothe K-band stellar mass-to-light ratio (M*/LK) of0.09+0.15-0.08Msolar/LsolarK(including systematic uncertainties), with the caveat that forM*/LK>0.19Msolar/LsolarKthe dark matter density increases with radius, which is unphysical.Assuming0.10Msolar/LsolarK<~M*/LK<=0.19Msolar/LsolarK,the dark matter density profile lies betweenρDM~r-0.17 andρDM~r-0.01. Therefore, independent of anyassumptions about the stellar disk or the functional form of the densityprofile, NGC 2976 does not contain a cuspy dark matter halo. We alsoinvestigate some of the systematic effects that can hamper rotationcurve studies and show that (1) long-slit rotation curves are far morevulnerable to systematic errors than two-dimensional velocity fields,(2) NGC 2976 contains radial motions that are as large as 90% of therotational velocities at small radii, and (3) the Hα and COvelocity fields of NGC 2976 agree within their uncertainties, with atypical scatter between the two velocities of 5.3 km s-1 atany position in the galaxy.Based on observations carried out at the WIYN Observatory. The WIYNObservatory is a joint facility of the University of Wisconsin-Madison,Indiana University, Yale University, and the National Optical AstronomyObservatory.
| 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.
| The IRAS Revised Bright Galaxy Sample
IRAS flux densities, redshifts, and infrared luminosities are reportedfor all sources identified in the IRAS Revised Bright Galaxy Sample(RBGS), a complete flux-limited survey of all extragalactic objects withtotal 60 μm flux density greater than 5.24 Jy, covering the entiresky surveyed by IRAS at Galactic latitudes |b|>5°. The RBGS includes629 objects, with median and mean sample redshifts of 0.0082 and 0.0126,respectively, and a maximum redshift of 0.0876. The RBGS supersedes theprevious two-part IRAS Bright Galaxy Samples(BGS1+BGS2), which were compiled before the final(Pass 3) calibration of the IRAS Level 1 Archive in 1990 May. The RBGSalso makes use of more accurate and consistent automated methods tomeasure the flux of objects with extended emission. The RBGS contains 39objects that were not present in the BGS1+BGS2,and 28 objects from the BGS1+BGS2 have beendropped from RBGS because their revised 60 μm flux densities are notgreater than 5.24 Jy. Comparison of revised flux measurements forsources in both surveys shows that most flux differences are in therange ~5%-25%, although some faint sources at 12 and 25 μm differ byas much as a factor of 2. Basic properties of the RBGS sources aresummarized, including estimated total infrared luminosities, as well asupdates to cross identifications with sources from optical galaxycatalogs established using the NASA/IPAC Extragalactic Database. Inaddition, an atlas of images from the Digitized Sky Survey with overlaysof the IRAS position uncertainty ellipse and annotated scale bars isprovided for ease in visualizing the optical morphology in context withthe angular and metric size of each object. The revised bolometricinfrared luminosity function, φ(Lir), forinfrared-bright galaxies in the local universe remains best fit by adouble power law, φ(L)~Lα, withα=-0.6(+/-0.1) and α=-2.2(+/-0.1) below and above the``characteristic'' infrared luminosityL*ir~1010.5Lsolar,respectively. A companion paper provides IRAS High Resolution (HIRES)processing of over 100 RBGS sources where improved spatial resolutionoften provides better IRAS source positions or allows for deconvolutionof close galaxy pairs.
| Revised positions for CIG galaxies
We present revised positions for the 1051 galaxies belonging to theKarachentseva Catalog of Isolated Galaxies (CIG). New positions werecalculated by applying SExtractor to the Digitized Sky Survey CIG fieldswith a spatial resolution of 1 arcsper 2. We visually checked theresults and for 118 galaxies had to recompute the assigned positions dueto complex morphologies (e.g. distorted isophotes, undefined nuclei,knotty galaxies) or the presence of bright stars. We found differencesbetween older and newer positions of up to 38 arcsec with a mean valueof 2 arcsper 96 relative to SIMBAD and up to 38 arcsec and 2 arcsper 42respectively relative to UZC. Based on star positions from the APMcatalog we determined that the DSS astrometry of five CIG fields has amean offset in (alpha , delta ) of (-0 arcsper 90, 0 arcsper 93) with adispersion of 0 arcsper 4. These results have been confirmed using the2MASS All-Sky Catalog of Point Sources. The intrinsic errors of ourmethod combined with the astrometric ones are of the order of 0 arcsper5.Full Table 1 is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/411/391
| A new catalogue of ISM content of normal galaxies
We have compiled a catalogue of the gas content for a sample of 1916galaxies, considered to be a fair representation of ``normality''. Thedefinition of a ``normal'' galaxy adopted in this work implies that wehave purposely excluded from the catalogue galaxies having distortedmorphology (such as interaction bridges, tails or lopsidedness) and/orany signature of peculiar kinematics (such as polar rings,counterrotating disks or other decoupled components). In contrast, wehave included systems hosting active galactic nuclei (AGN) in thecatalogue. This catalogue revises previous compendia on the ISM contentof galaxies published by \citet{bregman} and \citet{casoli}, andcompiles data available in the literature from several small samples ofgalaxies. Masses for warm dust, atomic and molecular gas, as well asX-ray luminosities have been converted to a uniform distance scale takenfrom the Catalogue of Principal Galaxies (PGC). We have used twodifferent normalization factors to explore the variation of the gascontent along the Hubble sequence: the blue luminosity (LB)and the square of linear diameter (D225). Ourcatalogue significantly improves the statistics of previous referencecatalogues and can be used in future studies to define a template ISMcontent for ``normal'' galaxies along the Hubble sequence. The cataloguecan be accessed on-line and is also available at the Centre desDonnées Stellaires (CDS).The catalogue is available in electronic form athttp://dipastro.pd.astro.it/galletta/ismcat and at the CDS via anonymousftp to\ cdsarc.u-strasbg.fr (130.79.128.5) or via\http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/405/5
| 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
| A Search for Active Galactic Nuclei in Sc Galaxies with H II Spectra
We have searched for nuclear radio emission from a statisticallycomplete sample of 40 Sc galaxies within 30 Mpc that are opticallyclassified as star-forming objects, in order to determine whether weakactive galactic nuclei might be present. Only three nuclear radiosources were detected, in NGC 864, NGC 4123, and NGC 4535. Thesegalaxies have peak 6 cm radio powers of ~1020 WHz-1 at arcsecond resolution, while upper limits of thenondetected galaxies typically range from 1018.4 to1020 W Hz-1. The three nuclear radio sources areall resolved and appear to have diffuse morphologies, with linear sizesof ~300 pc. This strongly indicates that circumnuclear star formationhas been detected in these three H II galaxies. Comparisons withprevious 20 cm Very Large Array (VLA) results for the detected galaxiesshow that the extended nuclear radio emission has a flat spectrum in twoobjects and is almost certainly generated by thermal emission from gasionized by young stars in the centers of those galaxies. The 6 cm radiopowers are comparable to predictions for thermal emission that are basedon the nuclear Hα luminosities and imply nuclear star formationrates of 0.08-0.8 Msolar yr-1, while thelow-resolution NRAO VLA Sky Survey implies galaxy-wide star formationrates of 0.3-1.0 Msolar yr-1 in stars above 5Msolar. In a few of the undetected galaxies, the upper limitsto the radio power are lower than predicted from the Hαluminosity, possibly because of overresolution of central star-formingregions. Although the presence of active nuclei powered by massive blackholes cannot be definitively ruled out, the present results suggest thatthey are likely to be rare in these late-type galaxies with H IIspectra.
| Dust-induced Systematic Errors in Ultraviolet-derived Star Formation Rates
Rest-frame far-ultraviolet (FUV) luminosities form the ``backbone'' ofour understanding of star formation (SF) at all cosmic epochs. Theseluminosities are typically corrected for dust by assuming that the tightrelationship between the UV spectral slopes (β) and the FUVattenuations (AFUV) of starburst galaxies applies to allstar-forming galaxies. Data from seven independent UV experimentsdemonstrate that quiescent, ``normal'' star-forming galaxies deviatesubstantially from the starburst galaxy β-AFUVcorrelation in the sense that normal galaxies are redder thanstarbursts. Spatially resolved data for the Large Magellanic Cloudsuggest that dust geometry and properties, coupled with a smallcontribution from older stellar populations, cause deviations from thestarburst galaxy β-AFUV correlation. Folding in data forstarbursts and ultraluminous infrared galaxies, it is clear that neitherrest-frame UV/optical colors nor UV/Hα colors help significantlyin constraining the UV attenuation. These results argue that theestimation of SF rates from rest-frame UV and optical data alone issubject to large (factors of at least a few) systematic uncertaintiesbecause of dust, which cannot be reliably corrected for using onlyUV/optical diagnostics.
| The Density Profile of the Dark Matter Halo of NGC 4605
We have obtained ~100 pc resolution CO and ~60 pc resolution Hαobservations of the dwarf spiral galaxy NGC 4605. We use them to derivea high-resolution rotation curve and study the central density profileof NGC 4605's dark matter halo. We find that these observations do notagree with the predictions of most high-resolution cold dark mattercalculations. We investigate two extreme cases: (1) NGC 4605 has amaximal exponential disk, which we model using K-band observations andremove to study the structure of its dark matter halo, and (2) NGC 4605is dark matter-dominated, and its disk is dynamically negligible.Because the mass-to-light ratio of the maximal disk is already very low,we favor the first solution, which indicates the halo has one componentwith a density profile ρ~r-0.65 out to R~2.8 kpc. In thesecond case, the rotation curve requires the presence of two components:a small (~600 pc) core surrounded by a much steeperρ~r-1.1 halo. Removal of intermediate (submaximal) disksdoes not ameliorate the discrepancy between the predictions and theobservations.
| Bar Galaxies and Their Environments
The prints of the Palomar Sky Survey, luminosity classifications, andradial velocities were used to assign all northern Shapley-Ames galaxiesto either (1) field, (2) group, or (3) cluster environments. Thisinformation for 930 galaxies shows no evidence for a dependence of barfrequency on galaxy environment. This suggests that the formation of abar in a disk galaxy is mainly determined by the properties of theparent galaxy, rather than by the characteristics of its environment.
| An Infrared Space Observatory Atlas of Bright Spiral Galaxies
In this first paper in a series we present an atlas of infrared imagesand photometry from 1.2 to 180 μm for a sample of bright spiralgalaxies. The atlas galaxies are an optically selected,magnitude-limited sample of 77 spiral and S0 galaxies chosen from theRevised Shapley-Ames Catalog (RSA). The sample is a representativesample of spiral galaxies and includes Seyfert galaxies, LINERs,interacting galaxies, and peculiar galaxies. Using the Infrared SpaceObservatory (ISO), we have obtained 12 μm images and photometry at60, 100, and 180 μm for the galaxies. In addition to its imagingcapabilities, ISO provides substantially better angular resolution thanis available in the IRAS survey, and this permits discrimination betweeninfrared activity in the central regions and global infrared emission inthe disks of these galaxies. These ISO data have been supplemented withJHK imaging using ground-based telescopes. The atlas includes 2 and 12μm images. Following an analysis of the properties of the galaxies,we have compared the mid-infrared and far-infrared ISO photometry withIRAS photometry. The systematic differences we find between the IRASFaint Source Catalog and ISO measurements are directly related to thespatial extent of the ISO fluxes, and we discuss the reliability of IRASFaint Source Catalog total flux densities and flux ratios for nearbygalaxies. In our analysis of the 12 μm morphological features we findthat most but not all galaxies have bright nuclear emission. We find 12μm structures such as rings, spiral arm fragments, knotted spiralarms, and bright sources in the disks that are sometimes brighter thanthe nuclei at mid-infrared wavelengths. These features, which arepresumably associated with extranuclear star formation, are common inthe disks of Sb and later galaxies but are relatively unimportant inS0-Sab galaxies. Based on observations with the Infrared SpaceObservatory (ISO), an ESA project with instruments funded by ESA MemberStates (especially the PI countries: France, Germany, Netherlands, andUnited Kingdom) and with the participation of ISAS and NASA.
| The Westerbork HI survey of spiral and irregular galaxies. II. R-band surface photometry of late-type dwarf galaxies
R-band surface photometry is presented for 171 late-type dwarf andirregular galaxies. For a subsample of 46 galaxies B-band photometry ispresented as well. We present surface brightness profiles as well asisophotal and photometric parameters including magnitudes, diameters andcentral surface brightnesses. Absolute photometry is accurate to 0.1 magor better for 77% of the sample. For over 85% of the galaxies the radialsurface brightness profiles are consistent with published data withinthe measured photometric uncertainty. For most of the galaxies in thesample H I data have been obtained with the Westerbork Synthesis RadioTelescope. The galaxies in our sample are part of the WHISP project(Westerbork H I Survey of Spiral and Irregular Galaxies), which aims atmapping about 500 nearby spiral and irregular galaxies in H I. Theavailability of H I data makes this data set useful for a wide range ofstudies of the structure, dark matter content and kinematics oflate-type dwarf galaxies. Based on observations made with INT operatedon the island of La Palma by the Isaac Newton Group in the SpanishObservatorio del Roque de los Muchachos of the Instituto de Astrofisicade Canarias. The tables in Appendix A are only available in electronicform at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/390/863. Thefigures in Appendix B are only available in electronic formhttp://www.edpsciences.org
| Neutral hydrogen in dwarf galaxies. I. The spatial distribution of HI
This paper is the first in a series presenting a sample of 30 late-typedwarf galaxies, observed with the Westerbork Synthesis Radio Telescope(WSRT) in the 21-cm line of neutral atomic hydrogen (HI). The sampleitself, the HI content of and the HI distribution in the sample galaxiesare briefly discussed. Four sample galaxies were also detected in thecontinuum.
| Discrete dynamical classes for galaxy discs and the implication of a second generation of Tully-Fisher methods
In Roscoe (\cite{RoscoeA}), it was described how the modelling of asmall sample of optical rotation curves (ORCs) given by Rubin et al.(\cite{Rubin}) with the power-law Vrot=ARα,where where the parameters (A,alpha ) vary between galaxies, raised thehypothesis that the parameter A (considered in the form ln A) had apreference for certain discrete values. This specific hypothesis wastested in that paper against a sample of 900 spiral galaxy rotationcurves measured by Mathewson et al. (\cite{Mathewson1992}), but foldedby Persic & Salucci (\cite{Persic1995}), and was confirmed on thislarge sample with a conservatively estimated upper bound probability of10-7 against it being a chance effect. In this paper, webegin by reviewing the earlier work, and then describe the analyses ofthree additional samples; the first of these, of 1200+ Southern skyORCs, was published by Mathewson & Ford (\cite{Mathewson1996}), thesecond, of 497 Northern sky ORCs, is a composite sample provided by kindpermission of Giovanelli & Haynes published in the sequence ofpapers Dale et al. (\cite{Dale1997}, \cite{Dale1998}, \cite{Dale1999})and Dale & Uson (\cite{Dale2000}), whilst the third, of 305 Northernsky ORCs, was published by Courteau (\cite{Courteau}). These analysesprovide overwhelmingly compelling confirmation of what was already apowerful result. Apart from other considerations, the results leaddirectly to what can be described as a ``second generation ofTully-Fisher methods''. We give a brief discussion of the furtherimplications of the result.
| The M 81 group of galaxies: New distances, kinematics and structure
We present Hubble Space Telescope/WFPC2 images of the galaxies NGC 2366,NGC 2976, NGC 4236, IC 2574, DDO 53, DDO 82, DDO 165, Holmberg I,Holmberg II, Holmberg IX, K52, K73, BK3N, Garland, and A0952+69 in the M81 complex. Their true distance moduli, derived from the brightness ofthe tip of the red giant branch, lie in the range of 27fm 52 (NGC 2366)to 28fm 30 (DDO 165), with a median of 27fm 91, which is typical forother known M 81 group members. Using distances and radial velocities ofabout 50 galaxies in and around the M 81/NGC 2403 complex, we find theradius of the zero-velocity surface of the M 81 group to be R_0 =(1.05+/-0.07) Mpc, which yields a total mass M(R_0) = (1.6+/-0.3)x1012 Msun and a total mass-to-luminosity ratioM(R_0)/L_B = (38+/-7) Msun/Lsun. The total masswithin R_0 agrees well with the sum of masses estimated via the virialtheorem (1.2x 1012 Msun) and from orbital motions(2.0x 1012 Msun) of companions around M 81 and NGC2403. We suggest that most of the dark matter in the group isconcentrated around the luminous matter, allowing us to explain theobserved asymmetry of the peculiar motions of the M 81 companions. M 81itself has a peculiar velocity of about 130 km s-1 withrespect to the local Hubble flow, but the centroid of the M 81/NGC 2403complex is almost at rest with respect to Hubble flow (v_pec < 35 kms-1). Based on observations made with the NASA/ESA HubbleSpace Telescope. The Space Telescope Science Institute is operated bythe Association of Universities for Research in Astronomy, Inc. underNASA contract NAS 5-26555. Figures 2 to 5 are only available inelectronic form at http://www.edpsciences.org
| Predicting the peculiar velocities of nearby PSCz galaxies using the Least Action Principle
We use the Least Action Principle to predict the peculiar velocities ofPSCz galaxies inside cz=2000kms-1. Linear theory is used toaccount for tidal effects to cz=15000kms-1, and we iterategalaxy positions to account for redshift distortions. As the LeastAction Principle is valid beyond linear theory, we can predict reliablepeculiar velocities even for very nearby galaxies (i.e.,cz<=500kms-1). These predicted peculiar velocities arethen compared with the observed velocities of 12 galaxies with Cepheiddistances. The combination of the PSCz galaxy survey (with its large skycoverage and uniform selection) with the accurate Cepheid distancesmakes this comparison relatively free from systematic effects. We findthat galaxies are good tracers of the mass, even at small(<=10h-1Mpc) scales; under the assumption of no biasing,0.25<=β<=0.75 (at 90 per cent confidence). We use thereliable predicted peculiar velocities to estimate the Hubble constantH0 from the local volume without `stepping up' the distanceladder, finding a confidence range of65-75kms-1Mpc-1 (at 90 per cent confidence).
| Statistical Properties of Circumnuclear H II Regions in Nearby Galaxies
We analyze the statistical properties of the circumnuclear H II regionsof a sample of 52 nearby galaxies (v<1000 km s-1) fromarchival HST/NICMOS H-band and Paα (1.87 μm) observations atunprecedented spatial resolutions of between 1 and 30 pc. We catalog HII regions from the continuum-subtracted Paα images and find H IIregions in the central regions of most galaxies, and more than a hundredin each of eight galaxies. In contrast to disk H II regions, thephysical properties (luminosity and size) of individual circumnuclear HII regions do not vary strongly with the morphological type of the hostgalaxy, nor does the number of circumnuclear H II regions per unit area.The Hα luminosity within the central kiloparsec, as derived from HII region emission, is significantly enhanced in early-type (S0/a-Sb)galaxies. We find evidence that bars increase the circumnuclear starformation, presumably by funneling gas from the disk toward the nucleus.Barred galaxies exhibit enhanced luminosities of the brightest H IIregion, the central kiloparsec Hα luminosities (an effect mostlydue to the early-type galaxies in our sample), and the star formationrates per unit stellar mass (which could also be understood as theintegral equivalent widths of Paα) over the central kiloparsecwith respect to nonbarred galaxies. We fit the luminosity functions(LFs) and diameter distributions of the circumnuclear H II regions ineight galaxies where we can catalog enough H II regions to do so in ameaningful way. We use power laws and find that the fitted slopes of theH II region LF are exactly in the previously found ranges and evenconfirm a trend with steeper slopes in galaxies of earlier morphologicaltype. This implies that the physical processes giving rise to enhancedstar formation in the circumnuclear regions of galaxies must be similarto those in disks. Based on observations with the NASA/ESA Hubble SpaceTelescope, obtained from the data archive at the Space Telescope ScienceInstitute, which is operated by the Association of Universities forResearch in Astronomy, Inc., under NASA contract NAS 5-26555.
| Statistical Properties of the Emission in Mixed-Morphology (E+S) Pairs. II. MIR/FIR Results
We present a statistical analysis of mid/far-IR emission properties fora mixed morphology (E/S0+S/I) sample of galaxy pairs based on a newco-addition of the IRAS database. The sample is large and diverse enough(~130 pairs) to permit discrimination of pairs by component morphologiesand interaction classes. It samples a large enough volume of space toenable a nonparametric estimate of the far-infrared luminosity function(FIRLF). We find average factors of 3 and 5 enhancement in FIR and 25μm luminosities, respectively, for the late-type components relativeto an isolated galaxy control sample. This is interpreted as the MIR/FIRsignature of interaction induced star formation. A more detailed studyreveals (1) a strong correlation between the IR luminosity andinteraction class, (2) a poor anticorrelation between IR luminosity andprojected separation in pairs where 25 μm seems to be more sensitivethan FIR, (3) an increase in the ratio of present to past star formation(IR luminosities scaled to LB luminosity) from early to latetype spiral pair components, and (4) a high-mass (M>=10Msolar) star formation rate (SFR) higher in paired Sc spiralsthan that in isolated Sc galaxies by a factor ~2-3.
| 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 Dynamical Study of Galaxies in the Hickson Compact Groups
To investigate dynamical properties of spiral galaxies in the Hicksoncompact groups (HCGs), we present rotation curves of 30 galaxies in 20HCGs. We found as follows: (1) There is no significant relation betweendynamical peculiarity and morphological peculiarity in HCG spiralgalaxies. (2) There is no significant relation between the dynamicalproperties and the frequency distribution of nuclear activities in HCGspiral galaxies. (3) There are no significant correlations between thedynamical properties of HCG spiral galaxies and any group properties(i.e., size, velocity dispersion, galaxy number density, and crossingtime). (4) Asymmetric and peculiar rotation curves are more frequentlyseen in the HCG spiral galaxies than in field spiral galaxies or incluster ones. However, this tendency is more obviously seen in late-typeHCG spiral galaxies. These results suggest that the dynamical propertiesof HCG spiral galaxies do not strongly correlate with the morphology,the nuclear activity, and the group properties. Our results also suggestthat more frequent galaxy collisions occur in the HCGs than in the fieldand in the clusters.
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