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Gas distribution, kinematics and star formation in faint dwarf galaxies
We compare the gas distribution, kinematics and the current starformation in a sample of 10 very faint (-13.37 < MB <-9.55) dwarf galaxies. For five of these galaxies we present fresh,high-sensitivity, Giant Metrewave Radio Telescope HI 21-cm observations.We find that the large-scale HI distribution in the galaxies istypically irregular and clumpy, with the peak gas density rarelyoccurring at the geometric centre. We also find that the velocity fieldsfor all the galaxies have an ordered component, although in general, thepatterns seen do not fit that expected from a rotating disc. For all ourgalaxies we construct maps of the HI column density at a constant linearresolution of ~300 pc; this forms an excellent data set to check for thepresence of a threshold column density for star formation. We find thatwhile current star formation (as traced by Hα emission) isconfined to regions with relatively large [NHI > (0.4-1.7)× 1021cm-2] HI column density, themorphology of the Hα emission is in general not correlated withthat of the high HI column density gas. Thus, while high column densitygas may be necessary for star formation, in this sample at least, it isnot sufficient to ensure that star formation does in fact occur. Weexamine the line profiles of the HI emission, but do not find a simplerelation between regions with complex line profiles and those withongoing star formation. Our sample includes examples of regions wherethere is ongoing star formation, but the profiles are well fitted by asingle Gaussian, as well as regions where there is no star formation butthe line profiles are complex. Finally, we examine the very fine scale(~20-100 pc) distribution of the HI gas, and find that at these scalesthe emission exhibits a variety of shell-like, clumpy and filamentaryfeatures. The Hα emission is sometimes associated withhigh-density HI clumps, sometimes the Hα emission lies inside ahigh-density shell, and sometimes there is no correspondence between theHα emission and the HI clumps. In summary, the interplay betweenstar formation and gas density in these galaxies does not seem to showthe simple large-scale patterns observed in brighter galaxies.
| Broadband Imaging of a Large Sample of Irregular Galaxies
We present the results of UBV imaging of a large sample of irregulargalaxies: 94 Im systems, 24 blue compact dwarfs (BCDs), and 18 Smgalaxies. We also include JHK imaging of 42 of these galaxies. Thesample spans a large range in galactic parameters. Ellipse fit axialratios, inclinations, and position angles are derived, integratedphotometry and azimuthally averaged surface photometry profiles aredetermined, and exponential fits give the central surface brightnesses,scale lengths, and isophotal and half-power radii. These data are usedto address the shapes of Im galaxies, look for clues to pastinteractions in large-scale peculiarities, examine the nature andconsequences of bars, study color gradients and large-scale colorvariations, and compare the exponential disk profiles of the young andold stellar components. For example, color gradients exhibit a greatvariety and not all passbands are correlated. Bars are associated withhigher star formation rates. Many irregulars show a double-exponentialradial light profile that is steeper in the outer parts, and these arereproduced by a new model of star formation that is discussed in acompanion paper. Some galaxies, primarily BCDs, have double exponentialsthat are steeper (and bluer) in the inner parts, presumably fromcentralized star formation. Im-type galaxies have thicker, lessprominent dust layers than spiral galaxies because of their loweraverage surface densities and midplane extinctions.
| 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.
| DDO 43: A Prototypical Dwarf Irregular Galaxy?
We present sensitive and high-resolution 21 cm observations of the dwarfirregular (Im) galaxy DDO 43, in conjunction with optical broadband andnarrowband images in U, B, V, and Hα. The observations are used toexamine the relationship of its H I morphology and kinematics to pastand present star formation. Optically, it is a small (R25=990pc), faint (MB of -14.0) dwarf Im with a slightly boxy shape.In H I, DDO 43 has an extended (RHI/RH=2.8) gasenvelope. There is a high-density ridge associated with the optical bodyof the galaxy containing several higher density knots and lower densityholes. The largest hole is ~850×530 pc. No expansion is detected,so it must be relatively old. The largest and potentially oldest (7-70Myr) of the six identified star clusters is located at the western edgeof the hole. Four of the other clusters are located near high-densitypeaks. There are several H II regions, most (but not all) of which areassociated with peaks in the H I surface density. The overall starformation rate is average for its type. In many ways, DDO 43 is a verytypical dwarf Im galaxy. Its H I morphology is consistent with a historyof episodes of localized star formation that create holes and shells inthe interstellar medium, some of which can overlap. These features arelocated within the area of solid-body rotation in the galaxy; the lackof shear in these small systems allows such structures to persist forlong periods of time.
| Power Spectra in V band and Hα of Nine Irregular Galaxies
Fourier transform power spectra of major axis cuts in V and Hαimages were made for a sample of nine irregular galaxies. These powerspectra reveal structure over a wide range of scales. For six of thegalaxies the power spectrum slopes at intermediate scales (10-400 pc) inthe V-band images range from -1.3 to -1.5. The similarity of slopessuggests that the same processes are structuring these systems. Theseslopes are slightly shallower than those observed in other galaxies in HI, molecular emission, dust extinction, and optical light. Three of thegalaxies have flat power spectra like sky noise; these three galaxiesare relatively indistinct in the direct images. The power spectrum slopefor Hα steepens with increasing star formation rate, ranging froma shallow value comparable to the noise at low rates to a steep valuewith a slope of ~-1.5 at high rates. This change reflects the increasingareal filling factor of Hα emission with increasing star formationrate and an apparently universal slope inside the Hα regions thatis comparable to that for Kolmogorov turbulence. The power spectrum of HI in one galaxy has a steeper power law, with a slope of ~-2.9. The factthat the power laws of star formation are about the same for dwarfgalaxies and giant spiral galaxies suggests the microscopic processesare the same, independent of spiral density waves and galaxy size.
| Gas and Stars in an H I-Selected Galaxy Sample
We present the results of a J-band study of the H I-selected AreciboDual-Beam Survey and Arecibo Slice Survey galaxy samples using TwoMicron All Sky Survey data. We find that these galaxies span a widerange of stellar and gas properties. However, despite the diversitywithin the samples, we find a very tight correlation between luminosityand size in the J band, similar to that found in a previous paper byRosenberg & Schneider between the H I mass and size. We also findthat the correlation between the baryonic mass and the J-band diameteris even tighter than that between the baryonic mass and the rotationalvelocity.
| DDO 88: A Galaxy-sized Hole in the Interstellar Medium
We present an H I and optical study of the gas-rich dwarf irregulargalaxy DDO 88. Although the global optical and H I parameters of DDO 88are normal for its morphological type, it hosts a large (3 kpc diameter)and unusually complete ring of enhanced H I emission. The normalappearance of this galaxy in the optical and the outer regions of the HI give no hint of the presence of the striking H I ring in the innerregions. The gas ring is located at approximately one-third of the totalH I radius and one-half the optically defined Holmberg radius, andcontains 30% of the total H I of the galaxy. The ring surrounds acentral depression in the H I distribution. If the H I ring and centraldepression in the gas were formed by the energy input from winds andsupernova explosions of massive stars formed in a starburst, as isthought often to be the case, the star-forming event would have formed0.1%-1% of the total stellar mass of the galaxy. However, the UBV colorsin the H I hole are not bluer than the rest of the galaxy, as would beexpected if an unusual star-forming event had taken place thererecently, although there is an old (~1-3 Gyr), red cluster near thecenter of the hole that is massive enough to have produced the hole inthe H I. An age estimate for the ring is uncertain, however, because itis not observed to be expanding. An expansion model produces a lowerestimate of 0.5 Gyr, but the presence of faint star formation regionsassociated with the ring indicates a much younger age. We also estimatethat the ring could have dispersed by now if it is older than 0.5 Gyr.This implies that the ring is younger than 0.5 Gyr. A younger age wouldindicate that the red cluster did not produce the hole and ring.Therefore, uncertainties prevent us from concluding that the cluster andthe H I hole are definitely related. If this ring and the depression inthe gas that it surrounds were not formed by stellar winds andsupernovae, this would indicate that some other, currently unidentified,mechanism is operating.
| A survey for OB associations in the Sculptor Group spiral galaxy NGC 7793
We report on the results from application of an objective algorithm(PLC) to find OB associations, to B and V images of the Sculptor spiralgalaxy NGC 7793, which were obtained with the ESO VLT and FORSinstrument and basically cover the entire spatial extent of the galaxy.We detected 148 associations. Statistical tests show that less than 6 ofthese detections are caused by randomly concentrated blue stars. In thesize distribution, a sharp peak is observed at a value of about 35microradians, which corresponds to a linear diameter of 135 pc, assuminga distance of 3.91 Mpc to the galaxy. We also find 25 much largerobjects. A second application of the PLC technique shows that 20 of themare stellar complexes consisting of multiple sub-associations withtypical sizes on the order of 130 pc. A comparison of the sizedistribution of the detected OB associations in NGC 7793 with observeddistributions in other galaxies suggests that the conditions in twoSculptor Group galaxies (NGC 300 and NGC 7793) favour the formation oflarge associations. We provide a catalog giving coordinates and physicalparameters for all the associations and stellar complexes we have foundin our survey.
| The star formation history of the LSB galaxy UGC 5889
We present HST photometry of the LSB galaxy UGC 889 and derive itsrecent star formation history. In the last 200 Myr the star formationproceeded in modest bursts at a rate of the order of10-2-10-3 Mȯ/yr, with periods ofextremely low SFR or even quiescence. The rate derived from the presentstudy for the last 20 Myr is in agreement with the Hα emissionfrom the galaxy. The presence of a consistent population older than 200Myr is suggested by the data. However, observational errors andcompleteness correction prevent any firm conclusion on the oldest age.The total mass of stars is of the order of 5.5 × 107Mȯ. Even if the recent episodes of star formation haveheated the gas and carved a hole in the disk, blow-away of the gas isunlikely to occur.
| Dwarf and Normal Spiral Galaxies: are they Self-Similar?
The investigation presented here was focused on clarifying the existenceof dwarf spiral galaxies as a separate group from classical spirals.First, a list of spiral galaxies with small sizes was obtained.Information on colors, luminosities, morphologies and chemical contentwas searched for in the literature for these galaxies. Using thisinformation, it can be concluded that dwarf spirals are not likely to bethe tail of the distribution of classical galaxies. On the contrary,significant differences in some of the most important properties ofspiral galaxies, such as the metallicity gradient and the bar frecuency,were found. In any case, further and more accurate observations areneeded for a definitive answer.
| New Dwarf Galaxy Candidates in the Leo-I Group
We have carried out a search for low-surface-brightness dwarf galaxiesin the region of the Leo-I Group (M96) in images of the second PalomarSky Survey. We found a total of 36 likely dwarf members of the groupwith typical magnitudes B t 18m 19m in an area of sky covering 120square degrees. Half of these galaxies are absent from known catalogsand lists of galaxies. The radial-velocity dispersion calculated for 19galaxies is 130 km/s. The Leo-I Group has a mean distance from the Sunof 10.4 Mpc, a mean projected radius of 352 kpc, an integratedluminosity of 6.7 × 1010 L ȯ, a virial mass-to-luminosityratio of 107 M ȯ/L ȯ, and a mean crossing time of 2.7 Gyr. Thegroup shows evidence for a radial segregation of the galaxies accordingto morphological type and luminosity, suggesting that the group is in astate of dynamical relaxation. The subsystem of bright galaxies in theLeo-I Group is smaller in size (250 kpc) and has a lower velocitydispersion (92 km/s), resulting in a lower virial mass-to-luminosityratio (34 M ȯ/L ȯ), as is typical of the Local Group and othernearby groups of galaxies.
| Star Formation Properties of a Large Sample of Irregular Galaxies
We present the results of Hα imaging of a large sample ofirregular galaxies. Our sample includes 94 galaxies with morphologicalclassifications of Im, 26 blue compact dwarfs (BCDs), and 20 Sm systems.The sample spans a large range in galactic parameters, includingintegrated absolute magnitude (MV of -9 to -19), averagesurface brightness (20-27 mag arcsec-2), current starformation activity (0-1.3 Msolar yr-1kpc-2), and relative gas content(0.02-5Msolar/LB). The Hα images were usedto measure the integrated star formation rates, determine the extents ofstar formation in the disks, and compare azimuthally averaged radialprofiles of current star formation to older starlight. The integratedstar formation rates of Im galaxies normalized to the physical size ofthe galaxy span a range of a factor of 104 with 10% Imgalaxies and one Sm system having no measurable star formation at thepresent time. The BCDs fall, on average, at the high star formation rateend of the range. We find no correlation between star formation activityand proximity to other cataloged galaxies. Two galaxies located in voidsare similar in properties to the Sm group in our sample. The H IIregions in these galaxies are most often found within the Holmbergradius RH, although in a few systems H II regions are tracedas far as 1.7RH. Similarly, most of the star formation isfound within three disk scale lengths RD, but in somegalaxies H II regions are traced as far as 6RD. A comparisonof Hα surface photometry with V-band surface photometry shows thatthe two approximately follow each other with radius in Sm galaxies, butin most BCDs there is an excess of Hα emission in the centers thatdrops with radius. In approximately half of the Im galaxies Hα andV correspond well, and in the rest there are small to large differencesin the relative rate of falloff with radius. The cases with stronggradients in the LHα/LV ratios and with highcentral star formation rate densities, which include most of the BCDs,require a significant fraction of their gas to migrate to the center inthe last gigayear. We discuss possible torques that could have causedthis without leaving an obvious signature, including dark matter barsand past interactions or mergers with small galaxies or H I clouds.There is now a substantial amount of evidence for these processes amongmany surveys of BCDs. We note that such gas migration will also increasethe local pressure and possibly enhance the formation of massive denseclusters but conclude that the star formation process itself does notappear to differ much among BCD, Im, and Sm types. In particular, thereis evidence in the distribution function for Hα surface brightnessthat the turbulent Mach numbers are all about the same in these systems.This follows from the Hα distribution functions corrected forexponential disk gradients, which are log-normal with a nearly constantdispersion. Thus, the influence of shock-triggered star formation isapparently no greater in BCDs than in Im and Sm types.
| A Catalog of Neighboring Galaxies
We present an all-sky catalog of 451 nearby galaxies, each having anindividual distance estimate D<~10 Mpc or a radial velocityVLG<550 km s-1. The catalog contains data onbasic optical and H I properties of the galaxies, in particular, theirdiameters, absolute magnitudes, morphological types, circumnuclearregion types, optical and H I surface brightnesses, rotationalvelocities, and indicative mass-to-luminosity and H I mass-to-luminosityratios, as well as a so-called tidal index, which quantifies the galaxyenvironment. We expect the catalog completeness to be roughly 70%-80%within 8 Mpc. About 85% of the Local Volume population are dwarf (dIr,dIm, and dSph) galaxies with MB>-17.0, which contributeabout 4% to the local luminosity density, and roughly 10%-15% to thelocal H I mass density. The H I mass-to-luminosity and the H Imass-to-total (indicative) mass ratios increase systematically fromgiant galaxies toward dwarfs, reaching maximum values about 5 in solarunits for the most tiny objects. For the Local Volume disklike galaxies,their H I masses and angular momentum follow Zasov's linear relation,expected for rotating gaseous disks being near the threshold ofgravitational instability, favorable for active star formation. We foundthat the mean local luminosity density exceeds 1.7-2.0 times the globaldensity, in spite of the presence of the Tully void and the absence ofrich clusters in the Local Volume. The mean local H I density is 1.4times its ``global'' value derived from the H I Parkes Sky Survey.However, the mean local baryon densityΩb(<8Mpc)=2.3% consists of only a half of the globalbaryon density, Ωb=(4.7+/-0.6)% (Spergel et al.,published in 2003). The mean-square pairwise difference of radialvelocities is about 100 km s-1 for spatial separations within1 Mpc, increasing to ~300 km s-1 on a scale of ~3 Mpc. alsoWe calculated the integral area of the sky occupied by the neighboringgalaxies. Assuming the H I size of spiral and irregular galaxies to be2.5 times their standard optical diameter and ignoring any evolutioneffect, we obtain the expected number of the line-of-sight intersectionswith the H I galaxy images to be dn/dz~0.4, which does not contradictthe observed number of absorptions in QSO spectra.
| The Hα galaxy survey. I. The galaxy sample, Hα narrow-band observations and star formation parameters for 334 galaxies
We discuss the selection and observations of a large sample of nearbygalaxies, which we are using to quantify the star formation activity inthe local Universe. The sample consists of 334 galaxies across allHubble types from S0/a to Im and with recession velocities of between 0and 3000 km s-1. The basic data for each galaxy are narrowband H\alpha +[NII] and R-band imaging, from which we derive starformation rates, H\alpha +[NII] equivalent widths and surfacebrightnesses, and R-band total magnitudes. A strong correlation is foundbetween total star formation rate and Hubble type, with the strongeststar formation in isolated galaxies occurring in Sc and Sbc types. Moresurprisingly, no significant trend is found between H\alpha +[NII]equivalent width and galaxy R-band luminosity. More detailed analyses ofthe data set presented here will be described in subsequent papers.Based on observations made with the Jacobus Kapteyn Telescope operatedon the island of La Palma by the Isaac Newton Group in the SpanishObservatorio del Roque de los Muchachos of the Instituto deAstrofísica de Canarias.The full version of Table \ref{tab3} is available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/414/23 Reduced image datafor this survey can be downloaded fromhttp://www.astro.livjm.ac.uk/HaGS/
| The Outer Edges of Dwarf Irregular Galaxies: Stars and Gas
Workshop held in Flagstaff, AZ, on 2002 October 10-11. Proceedings areavailable on-line at http://www.lowell.edu/Workshops/Lowell02.
| Globular Clusters as Candidates for Gravitational Lenses to Explain Quasar-Galaxy Associations
We argue that globular clusters (GCs) are good candidates forgravitational lenses in explaining quasar-galaxy associations. Thecatalog of associations (Bukhmastova 2001) compiled from the LEDAcatalog of galaxies (Paturel 1997) and from the catalog of quasars(Veron-Cetty and Veron 1998) is used. Based on the new catalog, we showthat one might expect an increased number of GCs around irregulargalaxies of types 9 and 10 from the hypothesis that distant compactsources are gravitationally lensed by GCs in the halos of foregroundgalaxies. The King model is used to determine the central surfacedensities of 135 GCs in the Milky Way. The distribution of GCs incentral surface density was found to be lognormal.
| The Contribution of H I-rich Galaxies to the Damped Lyα Absorber Population at z = 0
We present a study of the expected properties of the low-redshift dampedLyα absorber population determined from a sample of H I-selectedgalaxies in the local universe. Because of a tight correlation betweenthe H I mass and H I cross section, which we demonstrate spans allgalaxy types, we can use our H I-selected sample to predict theproperties of the absorption-line systems. We use measurements of thenumber density and H I cross section of galaxies to show that the totalH I cross section at column densities sufficient to produce dampedLyα absorption is consistent with no evolution of the absorberpopulation. We also find that the dN/dz distribution is dominated bygalaxies with H I masses near 109 Msolar. However,because of the large dispersion in the correlation between H I mass andstellar luminosity, we find that the distribution of dN/dz as a functionof LJ is fairly flat. In addition, we examine the line widthsof the H I-selected galaxies and show that there may be evolution in thekinematics of H I-rich galaxies, but it is not necessary for the higherredshift population to contain a greater proportion of high-massgalaxies than we find locally.
| 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
| HI observations of nearby galaxies V. Narrow (HI) line galaxies
In this paper we present new HI observations with high velocityresolution for 104 nearby narrow-line galaxies with half power linewidths smaller than 50 km s-1 most of which are wellapproximated by a Gaussian. The FWHM line width of 30 of theseintegrated HI profiles is less than 25 km s-1. We presentglobal parameters of these nearby galaxies and discuss the sizedependence, the luminosity dependence, and the dependence of theseparameters with the observed line width. Our sample essentially is asubsample of the Local Volume (i.e. galaxies within 10 Mpc) withdeclinations ge -30o and only a few galaxies at greaterdistances. It is described by the following median values of globalphysical parameters: total absolute blue magnitude MB_t =-12.85; linear diameter A0 = 1.63 kpc (this corresponds tothe de Vaucouleurs diameter D25); half power line widthWc = 29 km s-1; total HI mass MHI = 2x107 Msun; distance D = 5.1 Mpc; HImass-to-luminosity ratio MHI/LB = 0.9Msun/Lsun; total mass-to luminosity ratioMt/LB = 2.9 Msun/Lsun.Table 1 is only available in electronic form athttp://www.edpsciences.org
| The faint end of the galaxy luminosity function
We present and discuss optical measurements of the faint end of thegalaxy luminosity function down to MR=-10 in five differentlocal environments of varying galaxy density and morphological content.The environments we studied, in order of decreasing galaxy density, arethe Virgo Cluster, the NGC 1407 Group, the Coma I Group, the Leo Groupand the NGC 1023 Group. Our results come from a deep wide-angle surveywith the National Astronomical Observatories of Japan Subaru 8-mTelescope on Mauna Kea and are sensitive down to very faintsurface-brightness levels. Galaxies were identified as group or clustermembers on the basis of their surface brightness and morphology. Thefaintest galaxies in our sample have R~ 22.5. There were thousands offainter galaxies but we cannot distinguish cluster members frombackground galaxies at these faint limits so do not attempt to determinea luminosity function fainter than MR=-1010. In all cases,there are far fewer dwarfs than the numbers of low-mass haloesanticipated by cold dark matter theory. The mean logarithmic slope ofthe luminosity function between MR=-1018 andMR=-1010 is α~=-1.2, far shallower than the cold darkmatter mass function slope of α~=-1.8. We would therefore need tobe missing about 90 per cent of the dwarfs at the faint end of oursample in all the environments we study to achieve consistency with CDMtheory. It is unlikely that such large numbers of dwarfs are missedbecause (i) the data are deep enough that we are sensitive to very lowsurface brightness galaxies, and (ii) the seeing is good enough that wecan have some confidence in our ability to distinguish high surfacebrightness dwarfs from background galaxies brighter than R= 22.5. Onecaveat is that we miss compact members taken to be background galaxies,but such objects (like M32) are thought to be rare.
| The UZC-SSRS2 Group Catalog
We apply a friends-of-friends algorithm to the combined Updated ZwickyCatalog and Southern Sky Redshift Survey to construct a catalog of 1168groups of galaxies; 411 of these groups have five or more members withinthe redshift survey. The group catalog covers 4.69 sr, and all groupsexceed the number density contrast threshold, δρ/ρ=80. Wedemonstrate that the groups catalog is homogeneous across the twounderlying redshift surveys; the catalog of groups and their membersthus provides a basis for other statistical studies of the large-scaledistribution of groups and their physical properties. The medianphysical properties of the groups are similar to those for groupsderived from independent surveys, including the ESO Key Programme andthe Las Campanas Redshift Survey. We include tables of groups and theirmembers.
| Large-scale star formation in galaxies. II. The spirals NGC 3377A, NGC 3507 and NGC 4394. Young star groupings in spirals
The identification of young star groupings (YSG) in the three spiralgalaxies NGC 3377A, NGC 3507, NGC 4394 is obtained by mean of thestatistical method described in Paper I. We find 83, 90, 185 YSGs,respectively. An identification map of YSGs, as well as their sizedistribution, their B-luminosity function and their surface luminositydensity radial behaviour are presented and compared. These data, inaddition to those in Paper I, constitute a first sample suitable forseeking correlations among properties of galaxies and their YSGs, whichwe briefly discuss here.
| 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.
| The Arecibo Dual-Beam Survey: Arecibo and VLA Observations
The Arecibo Dual-Beam Survey is a ``blind'' 21 cm search for galaxiescovering ~430 deg2 of sky. We present the data from thedetection survey as well as from the follow-up observations to confirmdetections and improve positions and flux measurements. We find 265galaxies, many of which are extremely low surface brightness. Some ofthese previously uncataloged galaxies lie within the zone of avoidance,where they are obscured by the gas and dust in our Galaxy. Eighty-one ofthese sources are not previously cataloged optically, and there are 11galaxies that have no associated optical counterpart or are onlytentatively associated with faint wisps of nebulosity on the DigitizedSky Survey images. We discuss the properties of the survey, and inparticular we make direct determinations of the completeness andreliability of the sample. The behavior of the completeness and itsdependencies is essential for determining the H I mass function. Weleave the discussion of the mass function for a later paper, but do notethat we find many low surface brightness galaxies and seven sources withMHI<108 Msolar. The AreciboObservatory is part of the National Astronomy and Ionosphere Center,which is operated by Cornell University under cooperative agreement withthe National Science Foundation. in Puerto Rico.
| A Comparative Study of Star-forming and Quiescent Dwarf Galaxies
We present the results from a comparative study of the atomic hydrogen(H I) and optical properties of a sample of 16 dwarf galaxies, chosen toinvestigate the effects of star formation on the properties of low-masssystems. The violent star formation bursts believed to occur in theselow-mass systems suggest a possible connection between the activelystar-forming blue compact dwarfs (BCDs), and the quiescent low surfacebrightness dwarfs (LSBDs). It has been suggested that LSBDs, uponundergoing a burst of star formation, will evolve into BCDs and thenback into LSBDs when the star formation slows or stops as the H I columndensity falls below the critical threshold necessary to support it. Wehave examined the location and kinematics of H I in eight BCDs and eightLSBDs of similar H I masses and a range of color indices to investigatethis ``evolutionary'' sequence. The starburst episodes in these low-massgalaxies should lead to (1) a dispersal/depletion of the H I seen in theeight LSB dwarfs and (2) more centrally concentrated and agitated H I inthe eight BCDs. The results of this project indicate that the quiescentLSBD galaxies have more diffuse H I distributions and often show aringlike structure, while the active galaxies have more highly centrallyconcentrated H I reservoirs. The bluer, more recently active systems ofboth types also have higher internal H I velocity dispersions,indicating that energy has been pumped into the interstellar medium ofthese galaxies. These observations are consistent with an evolutionaryscheme wherein the H I reservoirs in these galaxies take on differentcharacteristics depending upon their star formation histories.
| 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.
| Evolutionary Status of Dwarf ``Transition'' Galaxies
We present deep B-band, R-band, and Hα imaging of three dwarfgalaxies: NGC 3377A, NGC 4286, and IC 3475. Based on previous broadbandimaging and H I studies, these mixed morphology galaxies have beenproposed to be, respectively, a gas-rich low surface brightness Imdwarf, a nucleated dwarf that has lost most of its gas and is intransition from Im to dS0, N, and the prototypical example of a gas-poor``huge low surface brightness'' early-type galaxy. From the combinationof our broadband and Hα imaging with the published information onthe neutral gas content of these three galaxies, we find that (1) NGC3377A is a dwarf spiral, similar to those found by Schombert andcoworkers and Matthews & Gallagher; (2) both NGC 3377A and NGC 4286have comparable amounts of ongoing star formation, as indicated by theirHα emission, while IC 3475 has no detected H II regions to a verylow limit; (3) the global star formation rates are at least a factor of20 below those of 30 Doradus for NGC 3377A and NGC 4286; (4) while theamount of star formation is comparable, the distribution of star-formingregions is very different between NGC 3377A and NGC 4286, with Hαemission scattered over most of the optical face of NGC 3377A and allcontained within the inner half of the optical disk of NGC 4286; (5)given their current star formation rates and gas contents, both NGC3377A and NGC 4286 can continue to form stars for more than a Hubbletime; (6) both NGC 3377A and NGC 4286 have integrated total B-R colorsthat are redder than the integrated total B-R color for IC 3475 and thusit is unlikely that either galaxy will ever evolve into an IC 3475counterpart; and (7) IC 3475 is too blue to be a dE. We thus concludethat we have not identified potential precursors to galaxies such as IC3475, and unless significant changes occur in the star formation rates,neither NGC 3377A nor NGC 4286 will evolve into a dwarf elliptical ordwarf spheroidal within a Hubble time. Furthermore, optical morphology,even when coupled with the knowledge of the neutral gas content of adwarf galaxy, is not sufficient to determine its evolutionary phase. Theevolutionary states of NGC 3377A and NGC 4286 are thus unclear and morecomplicated than might be inferred from either previous broadbandimaging or H I content alone.
| 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
| CCD imaging of twenty nearby isolated irregular galaxies
We present B, V and I CCD stellar photometry for a sample of 20 fieldirregular dwarf galaxies. Their corrected radial velocity is V_0 <500 km s(-1) . Most of them have been resolved into stars for the firsttime. Based on photometry of their brightest blue stars we have derivedthe following distances: 5.9 Mpc (UGC 685), 5.4 Mpc (UGC 1281), 7.2 Mpc(UGC 3303), 7.0 Mpc (UGC 3476), 7.3: Mpc (UGC 3600), 7.2: Mpc (UGC3698), 7.9 Mpc (NGC 2337), 8.6 Mpc (UGC 3817), 5.7 Mpc (UGC 3860), 5.6Mpc (UGC 4426), >=7.9 Mpc (F 565-v1), 7.4: Mpc (UGC 5086), 7.1 Mpc(UGC 5272), 5.9 Mpc (UGC 5340), 7.1 Mpc (UGC 5427), 2.7: Mpc (UGC 5456),6.6 Mpc (NGC 3274), 9.3 Mpc (UGC 5889), 5.2 Mpc (NGC 5238), and 8.0 Mpc(UGC 9405). Our sample exhibits diverse morphological propertiesevidently caused by their different starburst activity. The galaxysample has a median integral absolute magnitude M_B = -14.6 and a medianintegral colour (B-V)_T = +0.47. One dwarf, UGC 5340, stands out by itsvery blue colour, (B-V)_T = +0.18, and by its high M(HI)/L ratio, asexpected for young galaxies. Four objects of the sample are IRASsources. Being well isolated systems, the considered galaxies may beused to estimate a local value of the Hubble parameter, H = V_0/D. Forhalf of the sample galaxies their individual H- values are concentratedwithin [58-68] km s(-1) /Mpc with a median of 65 km s(-1) /Mpc. Tables2--17 are only available in electronic form at the CDS via anonymous ftpto cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Total magnitude, radius, colour indices, colour gradients and photometric type of galaxies
We present a catalogue of aperture photometry of galaxies, in UBVRI,assembled from three different origins: (i) an update of the catalogueof Buta et al. (1995) (ii) published photometric profiles and (iii)aperture photometry performed on CCD images. We explored different setsof growth curves to fit these data: (i) The Sersic law, (ii) The net ofgrowth curves used for the preparation of the RC3 and (iii) A linearinterpolation between the de Vaucouleurs (r(1/4) ) and exponential laws.Finally we adopted the latter solution. Fitting these growth curves, wederive (1) the total magnitude, (2) the effective radius, (3) the colourindices and (4) gradients and (5) the photometric type of 5169 galaxies.The photometric type is defined to statistically match the revisedmorphologic type and parametrizes the shape of the growth curve. It iscoded from -9, for very concentrated galaxies, to +10, for diffusegalaxies. Based in part on observations collected at the Haute-ProvenceObservatory.
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