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Completing H I observations of galaxies in the Virgo cluster
High sensitivity (rms noise 0.5 mJy) 21-cm H I line observationswere made of 33 galaxies in the Virgo cluster, using the refurbishedArecibo telescope, which resulted in the detection of 12 objects. Thesedata, combined with the measurements available from the literature,provide the first set of H I data that is complete for all 355 late-type(Sa-Im-BCD) galaxies in the Virgo cluster with mp ≤ 18.0mag. The Virgo cluster H I mass function (HIMF) that was derived forthis optically selected galaxy sample is in agreement with the HIMFderived for the Virgo cluster from the blind HIJASS H I survey and isinconsistent with the Field HIMF. This indicates that both in this richcluster and in the general field, neutral hydrogen is primarilyassociated with late-type galaxies, with marginal contributions fromearly-type galaxies and isolated H I clouds. The inconsistency betweenthe cluster and the field HIMF derives primarily from the difference inthe optical luminosity function of late-type galaxies in the twoenvironments, combined with the HI deficiency that is known to occur ingalaxies in rich clusters.Tables \ref{t1, \ref{sample_dat} and Appendix A are only available inelectronic form at http://www.edpsciences.org
| Are interactions the primary triggers of star formation in dwarf galaxies?
We investigate the assumption that the trigger of star formation indwarf galaxies is interactions with other galaxies, in the context of asearch for a `primary' trigger of a first generation of stars. This iscosmologically relevant because the galaxy formation process consistsnot only of the accumulation of gas in a gravitational potential wellbut also of the triggering of star formation in this gas mass, and alsobecause some high-z potentially primeval galaxy blocks look like nearbystar-forming dwarf galaxies. We review theoretical ideas proposed toaccount for the tidal interaction triggering mechanism and present aseries of observational tests of this assumption using published data.We also show results of a search in the vicinity of a composite sampleof 96 dwarf late-type galaxies for interaction candidates showing starformation. The small number of possible perturbing galaxies identifiedin the neighbourhood of our sample galaxies, along with similar findingsfrom other studies, supports the view that tidal interactions may not berelevant as primary triggers of star formation. We conclude thatinteractions between galaxies may explain some forms of star formationtriggering, perhaps in central regions of large galaxies, but they donot seem to be significant for dwarf galaxies and, by inference, forfirst-time galaxies forming at high redshifts. Intuitive reasoning,based on an analogy with stellar dynamics, shows that conditions forprimary star formation triggering may occur in gas masses oscillating ina dark-matter gravitational potential. We propose this mechanism as aplausible primary trigger scenario, which would be worth investigatingtheoretically.
| UV to radio centimetric spectral energy distributions of optically-selected late-type galaxies in the Virgo cluster
We present a multifrequency dataset for an optically-selected,volume-limited, complete sample of 118 late-type galaxies (>=S0a) inthe Virgo cluster. The database includes UV, visible, near-IR, mid-IR,far-IR, radio continuum photometric data as well as spectroscopic dataof Hα , CO and HI lines, homogeneously reduced, obtained from ourown observations or compiled from the literature. Assuming the energybalance between the absorbed stellar light and that radiated in the IRby dust, we calibarte an empirical attenuation law suitable forcorrecting photometric and spectroscopic data of normal galaxies. Thedata, corrected for internal extinction, are used to construct thespectral energy distribution (SED) of each individual galaxy, andcombined to trace the median SED of galaxies in various classes ofmorphological type and luminosity. Low-luminosity, dwarf galaxies haveon average bluer stellar continua and higher far-IR luminosities perunit galaxy mass than giant, early-type spirals. If compared to nearbystarburst galaxies such as M 82 and Arp 220, normal spirals haverelatively similar observed stellar spectra but 10-100 times lower IRluminosities. The temperature of the cold dust component increases withthe far-IR luminosity, from giant spirals to dwarf irregulars. The SEDare used to separate the stellar emission from the dust emission in themid-IR regime. We show that the contribution of the stellar emission at6.75 mu m to the total emission of galaxies is generally important, from~ 80% in Sa to ~ 20% in Sc.Tables 2-5, 7, 8, and Fig. 2 are only available in electronic form athttp://www.edpsciences.orgTables 10-12 are 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/402/37
| 1.65-μm (H -band) surface photometry of galaxies - VIII. The near-IR κ space at z =0
We present the distribution of a statistical sample of nearby galaxiesin the κ -space (κ 1 ~logM , κ 2~logI e 3 M /L , κ 3 ~logM /L ).Our study is based on near-IR (H -band: λ =1.65μm)observations, for the first time comprising early- and late-typesystems. Our data confirm that the mean effective dynamicalmass-to-light ratio M /L of the E+S0+S0a galaxies increases withincreasing effective dynamical mass M , as expected from the existenceof the Fundamental Plane relation. Conversely, spiral and Im/BCDgalaxies show a broad distribution in M /L with no detected trend of M/L with M , the former galaxies having M /L values about twice largerthan the latter, on average. For all the late-type galaxies, the M /Lincreases with decreasing effective surface intensity I e ,consistent with the existence of the Tully-Fisher relation. Theseresults are discussed on the basis of the assumptions behind theconstruction of the κ -space and their limitations. Our study iscomplementary to a previous investigation in the optical (B -band:λ =0.44μm) and allows us to study wavelength dependences ofthe galaxy distribution in the κ -space. As a first result, wefind that the galaxy distribution in the κ 1 -κ2 plane reproduces the transition from bulgeless tobulge-dominated systems in galaxies of increasing dynamical mass.Conversely, it appears that the M /L of late-types is higher (lower)than that of early-types with the same M in the near-IR (optical). Theorigins of this behaviour are discussed in terms of dust attenuation andstar formation history.
| Far-Infrared Photometry of a Statistical Sample of Late-Type Virgo Cluster Galaxies
We present deep diffraction-limited far-infrared (FIR) strip maps of asample of 63 galaxies later than S0 and brighter thanBT=16.8, selected from the Virgo Cluster Catalogue ofBinggeli, Sandage, & Tammann. The ISOPHOT instrument on board theInfrared Space Observatory was used to achieve sensitivities typicallyan order of magnitude deeper than IRAS in the 60 and 100 μm bands andto reach the confusion limit at 170 μm. The averaged 3 σ upperlimits for integrated flux densities of point sources at 60, 100, and170 μm are 43, 33, and 58 mJy, respectively. A total of 63.5% aredetected at all three wavelengths. The highest detection rate (85.7%) isin the 170 μm band. In many cases the galaxies are resolved, allowingthe scale length of the infrared disks to be derived from theoversampled brightness profiles in addition to the spatially integratedemission. The data presented should provide the basis for a variety ofstatistical investigations of the FIR spectral energy distributions ofgas-rich galaxies in the local universe spanning a broad range in starformation activity and morphological types, including dwarf systems andgalaxies with rather quiescent star formation activity. Based onobservations with the Infrared Space Observatory (ISO), an ESA projectwith instruments funded by ESA member states (especially the PIcountries: France, Germany, the Netherlands, and the United Kingdom) andwith the participation of ISAS and NASA.
| Hα surface photometry of galaxies in the Virgo cluster. IV. The current star formation in nearby clusters of galaxies
Hα +[NII] imaging observations of 369 late-type (spiral) galaxiesin the Virgo cluster and in the Coma/A1367 supercluster are analyzed,covering 3 rich nearby clusters (A1367, Coma and Virgo) and nearlyisolated galaxies in the Great-Wall. They constitute an opticallyselected sample (mp<16.0) observed with ~ 60 %completeness. These observations provide us with the current(T<107 yrs) star formation properties of galaxies that westudy as a function of the clustercentric projected distances (Theta ).The expected decrease of the star formation rate (SFR), as traced by theHα EW, with decreasing Theta is found only when galaxies brighterthan Mp ~ -19.5 are considered. Fainter objects show no orreverse trends. We also include in our analysis Near Infrared data,providing information on the old (T>109 yrs) stars. Puttogether, the young and the old stellar indicators give the ratio ofcurrently formed stars over the stars formed in the past, or``birthrate'' parameter b. For the considered galaxies we also determinethe ``global gas content'' combining HI with CO observations. We definethe ``gas deficiency'' parameter as the logarithmic difference betweenthe gas content of isolated galaxies of a given Hubble type and themeasured gas content. For the isolated objects we find that b decreaseswith increasing NIR luminosity. In other words less massive galaxies arecurrently forming stars at a higher rate than their giant counterpartswhich experienced most of their star formation activity at earliercosmological epochs. The gas-deficient objects, primarily members of theVirgo cluster, have a birthrate significantly lower than the isolatedobjects with normal gas content and of similar NIR luminosity. Thisindicates that the current star formation is regulated by the gaseouscontent of spirals. Whatever mechanism (most plausibly ram-pressurestripping) is responsible for the pattern of gas deficiency observed inspiral galaxies members of rich clusters, it also produces the observedquenching of the current star formation. A significant fraction of gas``healthy'' (i.e. with a gas deficiency parameter less than 0.4) andcurrently star forming galaxies is unexpectedly found projected near thecenter of the Virgo cluster. Their average Tully-Fisher distance isfound approximately one magnitude further away (muo = 31.77)than the distance of their gas-deficient counterparts (muo =30.85), suggesting that the gas healthy objects belong to a cloudprojected onto the cluster center, but in fact lying a few Mpc behindVirgo, thus unaffected by the dense IGM of the cluster. Based onobservations taken at the Observatorio Astronómico Nacional(Mexico), the OHP (France), Calar Alto and NOT (Spain) observatories.Table \ref{tab4} is only available in electronic form athttp://www.edpsciences.org
| Broad-band colours of Virgo cluster low surface brightness dwarf irregular galaxies
We present UBVRI images and surface photometry of a complete sample of29 low-luminosity dwarf irregular galaxies in the Virgo cluster, forwhich we derive central surface brightnesses, scalelengths, integratedmagnitudes and median colours. The colour distributions are discussed interms of radial surface brightness profiles, and colour gradients areinterpreted and compared with corresponding ones for lowsurface-brightness (LSB) spiral galaxies. By combining broad-band andnarrow-band filter observations, the past and current influences of thecluster environment on the evolution of LSB dwarf irregular galaxies isevaluated.
| Lopsidedness in dwarf irregular galaxies
We quantify the amplitude of the lopsidedness, the azimuthal angularasymmetry index and the concentration of star-forming regions, asrepresented by the distribution of the Hα emission, in a sample of78 late-type irregular galaxies. We bin the observed galaxies into twogroups representing blue compact galaxies (BCDs) andlow-surface-brightness dwarf galaxies (LSBs). The light distribution isanalysed with a novel algorithm, which allows detection of details inthe light distribution pattern. We find that while the asymmetry of theunderlying continuum light, representing the older stellar generations,is relatively small, the Hα emission is very asymmetric and iscorrelated in position angle with the continuum light. We show that theconcentration of continuum light is correlated with the Hαconcentration; this implies that the young star formation has the samespatial properties as the older stellar populations, but that theseproperties are more strongly expressed by the young stars. We test amodel of random star formation over the extent of a galaxy by simulatingHii regions in artificial dwarf galaxies. A galaxy is traced by assumingred star clusters distributed on an underlying exponential disc ofradius twice the scalelength. The disc is allowed to change in apparentmagnitude, scaleradius, position angle and ellipticity. We compare theasymmetry-concentration distribution predicted by the simulations withthe real observed distribution; we find that only LSBs match thedistribution predicted by the model. The reason is that, independentlyof the number of Hii regions, LSBs show no particular location of Hiiregions, whereas BCDs show current star formation activity restrictedvery much to the central parts of the galaxies. A consideration of theproperties of the continuum light leads to the conclusion that most ofLSBs can be approximated by exponential discs of radius twice theirscalelength; BCDs call, however, for much more concentrated underlyingsystems, with smaller scalelengths than assumed in the simulations. Theimplication is that random star formation over the full extent of agalaxy may be generated in LSB dwarf irregular galaxies but not in BCDgalaxies.
| 1.65 μm (H-band) surface photometry of galaxies. V. Profile decomposition of 1157 galaxies
We present near-infrared H-band (1.65 μm) surface brightness profiledecomposition for 1157 galaxies in five nearby clusters of galaxies:Coma, A1367, Virgo, A262 and Cancer, and in the bridge between Coma andA1367 in the ``Great Wall". The optically selected (mpg≤16.0) sample is representative of all Hubble types, from E to Irr+BCD,except dE and of significantly different environments, spanning fromisolated regions to rich clusters of galaxies. We model the surfacebrightness profiles with a de Vaucouleurs r1/4 law (dV), withan exponential disk law (E), or with a combination of the two (B+D).From the fitted quantities we derive the H band effective surfacebrightness (μe) and radius (re) of each component, theasymptotic magnitude HT and the light concentration indexC31. We find that: i) Less than 50% of the Ellipticalgalaxies have pure dV profiles. The majority of E to Sb galaxies is bestrepresented by a B+D profile. All Scd to BCD galaxies have pureexponential profiles. ii) The type of decomposition is a strong functionof the total H band luminosity (mass), independent of the Hubbleclassification: the fraction of pure exponential decompositionsdecreases with increasing luminosity, that of B+D increases withluminosity. Pure dV profiles are absent in the low luminosity rangeLH<1010 L\odot and become dominantabove 1011 L\odot . Based on observations taken atTIRGO, Gornergrat, Switzerland (operated by CAISMI-CNR, Arcetri,Firenze, Italy) and at the Calar Alto Observatory (operated by theMax-Planck-Institut für Astronomie (Heidelberg) jointly with theSpanish National Commission for Astronomy). Table 2 and Figs. 2, 3, 4are available in their entirety only in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Late-type dwarf irregular galaxies in the Virgo cluster - I. H alpha and red continuum data
We present H alpha and red continuum observations for a sample oflate-type low surface brightness (LSB) dwarf irregular galaxies,consisting of all the ImIV and V galaxies with m_B<= 17.2 in theVirgo cluster, and compare them with similar data for a representativesample of high surface brightness (HSB) dwarf irregular galaxies, alsoin the Virgo cluster. Line fluxes and equivalent widths are listed forindividual HII regions, and total H alpha emission is measured for theentire galaxy. Although significant line emission originates in the HIIregions that we have identified, it does not make up the entire H alphaoutput of all galaxies. For those objects in the LSB sample withHα emission, we find typical star formation rates (SFRs) from6.9x10^-3 to as high as 4.3x10^-2 M_solar yr^-1. This is, on average,one order of magnitude weaker than for HSB objects, although the SFRsoverlap. On average, ~2 HII regions are detected per LSB galaxy, for atotal of 38 HII regions among 17 galaxies with Hα emission. TheHII regions are smaller and fainter than in HSB galaxies in the sameVirgo cluster environment, have Hα line equivalent widths about 50per cent of those in HSBs, and cover similar fractions of the galaxies.When more than one HII region is present in a galaxy, we observe astrong intensity difference between the brightest and the secondbrightest HII regions. The line-emitting regions of LSB galaxies arepreferentially located at the periphery of the galaxy, while in HSBsthey tend to be central. The Hα line strength of an HII region iscorrelated with the red continuum light underneath the region; thisholds for both LSBs and HSBs. We do not identify fundamental differencesin the star formation properties of the LSB and HSB dwarf galaxies thatwe have studied, and we infer that these galaxies must be similar, withthe difference being the intensity of the present star formation burst.
| 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.
| A linear near-IR Tully-Fisher relation for giant and dwarf late-type galaxies
We present the near-IR (K(') -band, i.e.: lambda = 2.1 ^mu m)Tully-Fisher (TF) relation for a sample of 50 giant and dwarf late-typegalaxies, selected from the Virgo Cluster Catalogue. We find that L ~VMax(4) along a range of 8 K(') -mag for galaxies withdifferent Hubble types (from Sa to Im-BCD), phenomenologies, structures,star-formation histories, masses, dark-to-luminous mass ratios,metallicities and, perhaps, ages. The linearity of the near-IR TFrelation is in contrast with recent determinations of the optical TFrelations for samples of extreme late-type and dwarf galaxies. Thenear-IR TF law is in agreement both with the expectation from theFundamental Plane for disk systems and with the scenario ofself-regulating star-formation in disks. The previous results suggestthat the TF relation reflects the connection between thestructural/dynamical properties and the star-formation process of bothgiant and dwarf late-type galaxies, through a gas supply forstar-formation regulated by the gravitational potential of the galaxy.
| Morphology of star formation regions in irregular galaxies
The location of HII regions, which indicates the locus of present starformation in galaxies, is analysed for a large collection of 110irregular galaxies (Irr) imaged in Hα and nearby continuum. Theanalysis is primarily by visual inspection, although a two-dimensionalquantitative measure is also employed. The two different analyses yieldessentially identical results. HII regions appear preferentially at theedges of the light distribution, predominantly on one side of thegalaxy, contrary to what is expected from stochastic self-propagatingstar formation scenarios. This peculiar distribution of star-formingregions cannot be explained by a scenario of star formation triggered byan interaction with extragalactic gas, or by a strong one-armed spiralpattern.
| Late-type dwarf galaxies in the Virgo cluster - II. Star formation properties
We study star-formation-inducing mechanisms in galaxies throughmultiwavelength measurements of a sample of dwarf galaxies in the Virgocluster described in Paper I. Our main goal is to test howstar-formation-inducing mechanisms depend on several parameters of thegalaxies, such as morphological type and hydrogen content. We derive thestar formation rate and star formation histories of the galaxies, andcheck their dependence on other parameters. Comparison of the samplegalaxies with population synthesis models shows that these objects havesignificantly lower metallicity than the solar value. The colours cangenerally be explained as a combination of two different stellarpopulations: a young (3-20 Myr) metal-poor population which representsthe stars currently forming presumably in a starburst, and an older(0.1-1 Gyr) population of previous stellar generations. There isevidence that the older stellar population was also formed in astarburst. This is consistent with the explanation that star formationin this type of objects takes place in short bursts followed by longquiescent periods. No significant correlation is found between the starformation properties of the sample galaxies and their hydrogen content.Apparently, when star formation occurs in bursts, other parametersinfluence the star formation properties more significantly than theamount of atomic hydrogen. No correlation is found between the projectedVirgocentric distance and the rate of star formation in the galaxies,suggesting that tidal interactions are not significant in triggeringstar formation in cluster dwarf galaxies.
| Late-type dwarf galaxies in the Virgo cluster - I. The samples
We selected samples of late-type dwarf galaxies in the Virgo clusterwith HI information. The galaxies were observed at the Wise Observatoryusing several broad-band and Hα bandpasses. UV measurements werecarried out with the IUE Observatory from VILSPA, and with the FAUSTshuttle-borne UV telescope. We describe the observations in detail,paying particular attention to the determination of measurement errors,and present the observational results together with published data andfar-infrared information from IRAS. The sample will be analysed insubsequent papers, in order to study star formation mechanisms ingalaxies.
| Catalogue of HI maps of galaxies. I.
A catalogue is presented of galaxies having large-scale observations inthe HI line. This catalogue collects from the literature the informationthat characterizes the observations in the 21-cm line and the way thatthese data were presented by means of maps, graphics and tables, forshowing the distribution and kinematics of the gas. It containsfurthermore a measure of the HI extension that is detected at the levelof the maximum sensitivity reached in the observations. This catalogueis intended as a guide for references on the HI maps published in theliterature from 1953 to 1995 and is the basis for the analysis of thedata presented in Paper II. The catalogue is only available inelectronic form at the CDS via anonymous ftp 130.79.128.5 orhttp://cdsweb.u-strasbg.fr/Abstract.html
| 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.
| Near infrared surface photometry of late-type Virgo cluster galaxies
Near Infrared (K' band) surface photometry has been obtained for 102 (88late-type) Virgo cluster galaxies. A subset of 20 galaxies was alsoimaged in the H band. Magnitudes and diameters within the 21.5 and 22.0mag arcsec$^{-2}$ isophote, concentration indices and total H and K'magnitudes are derived. Basic statistical properties of a completesample of spiral galaxies spanning the range 6.3 < K'_T < 13.5 aregiven. Tables 3, 5 and 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/Abstract.html} Based on observations taken atthe Calar Alto Observatory, operated by the Max-Planck-Institut furAstronomie (Heidelberg) jointly with the Spanish National Commission forAstronomy.
| Arecibo H i Mapping of a Large Sample of Dwarf Irregular Galaxies
Neutral hydrogen mapping of 70 dwarf irregular (Sm, Im, and BCD)galaxies is reported, with position-velocity contour maps (and a fewcontour maps in R.A. and decl.) presented for those resolved by theArecibo beam. The galaxies were selected either from the Virgo ClusterCatalog, from similarly identified field galaxies, or from a distance-limited sample within the Arecibo declination range. We do not find anyisolated dwarfs with a larger H I to optical radius ratio than DDO 154;the "protogalaxy" H I 1225+01 of Giovanelli & Haynes continues to bea unique object among dwarfs that have been mapped in H I. For alldwarfs with significant rotation, we are able to determine the sense ofthe spin. For a number of better resolved dwarfs, we are able todetermine rotation curves, in most cases extending well beyond the lastmeasured point in available synthesis array maps. Correlations among theseveral measures of galaxy size and mass are studied; in a companionpaper we combine these data with those for the set of all availablemapped dwarf irregular galaxies and for mapped spirals spanning asimilar range of redshifts to investigate variations in Tully-Fisherrelations and in surface densities as functions of galaxy size andluminosity or mass.
| An image database. II. Catalogue between δ=-30deg and δ=70deg.
A preliminary list of 68.040 galaxies was built from extraction of35.841 digitized images of the Palomar Sky Survey (Paper I). For eachgalaxy, the basic parameters are obtained: coordinates, diameter, axisratio, total magnitude, position angle. On this preliminary list, weapply severe selection rules to get a catalog of 28.000 galaxies, wellidentified and well documented. For each parameter, a comparison is madewith standard measurements. The accuracy of the raw photometricparameters is quite good despite of the simplicity of the method.Without any local correction, the standard error on the total magnitudeis about 0.5 magnitude up to a total magnitude of B_T_=17. Significantsecondary effects are detected concerning the magnitudes: distance toplate center effect and air-mass effect.
| Distribution of the spin vectors of the disk galaxies of the Virgo cluster. I. The catalogue of 310 disk galaxies in the Virgo area.
Not Available
| General study of group membership. II - Determination of nearby groups
We present a whole sky catalog of nearby groups of galaxies taken fromthe Lyon-Meudon Extragalactic Database. From the 78,000 objects in thedatabase, we extracted a sample of 6392 galaxies, complete up to thelimiting apparent magnitude B0 = 14.0. Moreover, in order to considersolely the galaxies of the local universe, all the selected galaxieshave a known recession velocity smaller than 5500 km/s. Two methods wereused in group construction: a Huchra-Geller (1982) derived percolationmethod and a Tully (1980) derived hierarchical method. Each method gaveus one catalog. These were then compared and synthesized to obtain asingle catalog containing the most reliable groups. There are 485 groupsof a least three members in the final catalog.
| The kinematics of the Virgo cluster revisited
The paper updates the velocity data of Virgo cluster galaxies andreconsiders the kinematic structure of the Virgo cluster. New velocitiesare given for 144 galaxies listed in the Virgo Cluster Catalog (VCC).Improved velocities are given for another 131 VCC galaxies. The Virgocluster is disentangled from its surrounding clouds of galaxies, and thelikely members of each of these clouds are listed. The velocitydistribution of dwarf elliptical cluster members is found to be highlyasymmetric. This phenomenon is interpreted as evidence for the imminentmerging of two subclusters in the core region, which points to thedynamical youth of the Virgo cluster. The mean heliocentric velocity ofthe Virgo cluster is estimated at 1050 +/- 35 km/s.
| The Virgo cluster as a test for quantization of extragalactic redshifts
Tifft's (1972, 1977) hypothesis that redshifts are partially quantizedwith a periodicity in the range 70-75 km/s is tested for samples ofbright spiral and dwarf irregular galaxies with accurate H I redshiftsin the region of the Virgo cluster. The heliocentric redshifts arecorrected for solar motion, first by adopting an estimate of the sun'smotion with respect to the centroid of the Local Group, and then byallowing the solar velocity vector to vary in direction over the wholesky. Power spectrum analyses of the corrected redshifts are used tosearch for a significant periodicity in the prescribed range 70-75 km/s.No such periodicity is found for the dwarf irregulars, but there is apossible periodicity of about 71.1 km/s for the bright spirals. In afurther exploratory study, the sample of 112 spirals is divided upaccording to environment. The spirals in high-density regions of thecluster show no quantization, whereas those in low-density regionsappear to be partially quantized in intervals of about 71.0 km/s.
| 21 centimeter line width distances of cluster galaxies and the value of H0
Locally calibrated blue and infrared Tully-Fisher (TF) relations areapplied to an 82 percent complete sample of 81 Sab-Sm galaxies which arebona fide members of the Virgo Cluster. A nearly unbiased Virgo modulusof 31.60 + or - 0.15 can be derived in perfect agreement withindependent recent determinations. It is shown that the blue TF andinfrared TF relations give almost identical distance moduli from anyselected Virgo subsample. The intrinsic scatter about the two TFrelations is 0.7 mag, considerably larger than the observed scatter inthe UMa Cluster and in 10 more distant clusters. Distance determinationof these clusters therefore can be achieved only by fitting the upperenvelopes of their TF relations onto the blue and infrared upperenvelopes of the Virgo Cluster. The resulting distances define a linearexpansion law with a small scatter. The present cluster data require H0= 56.6 + or - 0.9 km/s/Mpc.
| H I detection survey of a complete magnitude-limited sample of dwarf irregular galaxies in the Virgo Cluster area
New single-beam Arecibo H I observations of 298 late-type galaxies inthe Virgo Cluster drawn mostly from the new catalog of Binggeli,Sandage, and Tammann (1985) are presented. Two hundred seventeen ofthese constitute a magnitude-limited 'complete sample' of such galaxies,types Sdm through Im and BCD. Sixty-one percent of this 'completesample' was detected, greatly enhancing the store of redshifts and H Imasses for such galaxies in the Virgo Cluster. For detected galaxies,heliocentric velocities, 50 percent profile widths, and single-beamfluxes are presented. For those that escaped detection, upper limits arecomputed to the flux appropriate to the redshift range (-600 to +3000km/s).
| Neutral hydrogen observations of four dwarf irregular galaxies in the Virgo Cluster
High-resolution H I observations of IC 3522, IC 3365, UGC 7902, and 6deg 18, obtained with the C configuration of the VLA on August 2 and 4,1985, are reported. The data are presented in extensive tables, graphs,and maps along with the V-band surface photometry of Bothun et al.(1986) and analyzed in detail. IC 3365 is found to be falling into theVirgo cluster core, with the small H I disk and sharp cutoff indicativeof ram-pressure stripping by the interstellar medium; three galaxiesgive evidence of dark matter in small gravitational systems, withluminous masses of about 10 to the 8th solar masses and mass/luminosityratios of 5-10.
| UGC 8508 - A dwarf galaxy associated with the M 101 group
Two-color CCD photometry of UGC 8508 has resolved the system into stars.The color-magnitude diagram shows blue and red supergiants, the apparentmagnitudes of the brightest stars indicate that UGC 8508 lies within 2Mpc of the adopted 6 Mpc distance of the M 101 group. The galaxycontains a significant color gradient; star formation is confined to thecentral 1.5 scale lengths (0.8 kpc). UGC 8508 has a central surfacebrightness intermediate between bursting and quiescent dwarf irregulargalaxies.
| Comparative photometric parameters of dwarf irregular and elliptical galaxies in the Virgo Cluster - Two different classes of dwarf galaxies?
The possible evolutionary relationships of dwarf irregular (dI) anddwarf elliptical (dE) galaxies is explored with a data base thatconsists of 21 cm data, infrared photometry, and CCD multicolor surfacephotometry of both dIs and dEs in the Virgo cluster. In general, dIs areat or slightly below the same surface-brightness level as dEs, yet theyare significantly bluer. To have the same optical and IR colordistribution as the dEs requires that dIs fade by 1.5 mag in the blue.This will in turn produce a population of dwarf galaxies that will haveaverage surface brightness below the detection threshold of conventionalphotographic plates. It is concluded that the progenitors of thebrighter dE galaxies in the Virgo cluster are not to be found among thecurrent generation of dIs with the exception that some of the largerblue compact dwarf galaxies are probably gas-rich analogs to dEs.Furthermore, it is probable that dIs form a parallel sequence of dwarfgalaxies with surface mass densities significantly lower than the dEs.
| UBV colors of Virgo cluster irregular galaxies
Photoelectric UBV aperture photometry is presented for 65 dwarfirregular and morphologically related types of galaxies that areprobable Virgo cluster members. Virgo cluster Irr galaxies cover a widerrange in color than typical samples of field Irr systems, primarily dueto the presence of unusually red Im galaxies in Virgo. The extremelyblue 'blue compact dwarf' and the red amorphous galaxies in Virgo alsostand out on a UBV color-color plot, but the majority of Virgo Irrs areundistinguished in terms of UBV colors. Statistical correlations arefound between colors and location within the cluster. Red Irrs often arein elliptical galaxy rich, dense areas of the cluster, while the blueIrrs roughly follow the spiral distribution pattern. Thus a connectionexists between environment and the properties of Irrs. Simplestatistical tests for ongoing stripping as the source of red Irrs,however, yields null results.
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