Contents
Images
Upload your image
DSS Images Other Images
Related articles
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.
| Spectrophotometry of galaxies in the Virgo cluster. II. The data
Drift-scan mode (3600-6800 Å) spectra with 500
| 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.
| Companions of Bright Barred Shapley-Ames Galaxies
Companion galaxy environment for a subset of 78 bright and nearby barredgalaxies from the Shapley-Ames Catalog is presented. Among the spiralbarred galaxies, there are Seyfert galaxies, galaxies with circumnuclearstructures, galaxies not associated with any large-scale galaxy cloudstructure, galaxies with peculiar disk morphology (crooked arms), andgalaxies with normal disk morphology; the list includes all Hubbletypes. The companion galaxy list includes the number of companiongalaxies within 20 diameters, their Hubble type, and projectedseparation distance. In addition, the companion environment was searchedfor four known active spiral galaxies, three of them are Seyfertgalaxies, namely, NGC 1068, NGC 1097, and NGC 5548, and one is astarburst galaxy, M82. Among the results obtained, it is noted that theonly spiral barred galaxy classified as Seyfert 1 in our list has nocompanions within a projected distance of 20 diameters; six out of 10Seyfert 2 bar galaxies have no companions within 10 diameters, six outof 10 Seyfert 2 galaxies have one or more companions at projectedseparation distances between 10 and 20 diameters; six out of 12 galaxieswith circumnuclear structures have two or more companions within 20diameters.
| 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.
| The Three-dimensional Structure of the Virgo Cluster Region from Tully-Fisher and H I Data
The distances and H I contents of 161 spiral galaxies in the region ofthe Virgo cluster are used to gain insight into the complicatedstructure of this galaxy system. Special attention has been paid to theinvestigation of the suggestion presented in an earlier work that someperipheral Virgo groups may contain strongly gas-deficient spiralgalaxies. The three-dimensional galaxy distribution has been inferredfrom quality distance estimates obtained by averaging distance modulibased on the Tully-Fisher relationship taken from eight published datasets previously homogenized, resulting in a relation with a dispersionof 0.41 mag. Previous findings that the spiral distribution issubstantially more elongated along the line of sight than in the planeof the sky are confirmed by the current data. In addition, an importanteast-west disparity in this effect has been detected. The overallwidth-to-depth ratio of the Virgo cluster region is about 1:4, with themost distant objects concentrated in the western half. The filamentarystructure of the spiral population and its orientation are alsoreflected by the H I-deficient objects alone. The H I deficiency patternshows a central enhancement extending from ~16 to 22 Mpc inline-of-sight distance; most of this enhancement arises from galaxiesthat belong to the Virgo cluster proper. However, significant gasdeficiencies are also detected outside the main body of the cluster in aprobable group of galaxies at line-of-sight distances ~25-30 Mpc, lyingin the region dominated by the southern edge of the M49 subcluster andclouds W' and W, as well as in various foreground galaxies. In the Virgoregion, the H I content of the galaxies then is not a straightforwardindicator of cluster membership.
| 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.
| 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
| Studies of galaxies in voids. I. H I observations of Blue Compact Galaxies
We present here results of studies of the properties of galaxies locatedin very low density environments. We observed 26 blue compact galaxies(BCGs) from the Second Byurakan (SBS) and Case surveys located in voidswith the radial velocities Vhel <~ 11 000 kms-1, two BCGs in the void behind the Virgo cluster and 11BCGs in denser environments. H I fluxes and profile widths, as well asestimates of total H I masses, are presented for the 27 detectedgalaxies (of which 6 are in three galaxy pairs and are not resolved bythe radiotelescope beam). Preliminary comparisons of void BCGs withsimilar objects from intermediate density regions - in the general fieldand the Local Supercluster (sub-samples of BCGs in the SBS zone) and inthe dense environment of the Virgo Cluster (a BCD sample) - areperformed using the hydrogen-to-blue-luminosity ratio M(ion{H}i)/LB. We find that for the same blue luminosity, forMB > -18.0m, BCGs in lower density environment have onaverage more H I. The slope beta of the M(ion {H}i)/LBvarpropto Lbeta for BCGs shows a trend of steepening withdecreasing bright galaxy density, being very close to zero for thedensest environment considered here and reaching beta = -0.4 for voids.
| Hα surface photometry of galaxies in the Virgo cluster I. Observations with the San Pedro Martir 2.1 m telescope
Hα imaging observations of 125 galaxies obtained with the 2.1 mtelescope of the San Pedro Martir Observatory (SPM) (Baja California,Mexico) are presented. The observed galaxies are mostly Virgo clustermembers (77), with 36 objects in the Coma/A1367 supercluster and 12 inthe clusters A2197 and A2199 taken as fillers. Hα +[NII] fluxesand equivalent widths, as well as images of the detected targets arepresented. The observatory of San Pedro Martir (Mexico) belongs to theObservatorio Astronómico Nacional, UNAM. Figure 4 is onlyavailable in electronic form at http://www.edpsciences.org
| 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.
| Nearby Optical Galaxies: Selection of the Sample and Identification of Groups
In this paper we describe the Nearby Optical Galaxy (NOG) sample, whichis a complete, distance-limited (cz<=6000 km s-1) andmagnitude-limited (B<=14) sample of ~7000 optical galaxies. Thesample covers 2/3 (8.27 sr) of the sky (|b|>20deg) andappears to have a good completeness in redshift (97%). We select thesample on the basis of homogenized corrected total blue magnitudes inorder to minimize systematic effects in galaxy sampling. We identify thegroups in this sample by means of both the hierarchical and thepercolation ``friends-of-friends'' methods. The resulting catalogs ofloose groups appear to be similar and are among the largest catalogs ofgroups currently available. Most of the NOG galaxies (~60%) are found tobe members of galaxy pairs (~580 pairs for a total of ~15% of objects)or groups with at least three members (~500 groups for a total of ~45%of objects). About 40% of galaxies are left ungrouped (field galaxies).We illustrate the main features of the NOG galaxy distribution. Comparedto previous optical and IRAS galaxy samples, the NOG provides a densersampling of the galaxy distribution in the nearby universe. Given itslarge sky coverage, the identification of groups, and its high-densitysampling, the NOG is suited to the analysis of the galaxy density fieldof the nearby universe, especially on small scales.
| 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.
| Internal extinction, population incompleteness bias and the faint-end of the B-band Tully-Fisher relation
We analyse the distribution of three different samples of spiralgalaxies of the Local Universe in the B-band luminosity-maximumrotational velocity (L_B-VMax) plane, i.e. the B-magnitudeTully-Fisher (TF) relation. The first sample comprises 25+31 late-type(from Sa to Im-BCD) galaxies, selected from, respectively, the Virgo andthe Ursa Major clusters. In addition, a sample of 20 group extremelate-type (ELT) spiral (from Sd to Sm) galaxies and a sample of 13 dwarflate-type galaxies are selected. First, we analyse the influence ofthree different corrections for internal extinction (IE) on both theslope and the zero-point of the relation. These recipes reflect eitheri) the morphological type dependence of the IE or ii) the assumption ofa ``sandwich-model'' for the distribution of the dust and the stellarcomponents within the disk or iii) the existence of the metallicity-massrelation. As a first result we find that the latter recipe of IEcorrection systematically makes Sa-Sc galaxies brighter than laterspirals. Since the former galaxies mainly populate the region of thebright, fast rotators, the slope of the corresponding TF relationbecomes much steeper than in the other two cases. Under the hypothesisthat the ELT spiral galaxies in clusters and in groups share the sameLF, we show that the claimed skew of the group ELT spiral galaxies withrespect to the extrapolated TF relation of more luminous systems (i.e.the local TF calibrators) is due both to the population incompletenessbias affecting such a template and to the type segregation. Finally, weconfirm that the distribution of dwarf galaxies with comparablerotational and random velocities in the L_B-VMax plane isconsistent with the relation of more luminous systems, while therotationally supported dwarf galaxies are underluminous with respect tothe ELT galaxies of the same VMax. However, the latterresults may suffer from the heterogeneous methods of measurement ofdwarf galaxy distances that were adopted.
| 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.
| On the local radio luminosity function of galaxies. I. The Virgo cluster
We cross-correlate the galaxies brighter than m_B=18 in the Virgocluster with the radio sources in the NVSS survey (1.4 GHz), resultingin 180 radio-optical identifications. We determine the radio luminosityfunction of the Virgo galaxies, separately for the early- andlate-types. Late-type galaxies develop radio sources with a probabilityproportional to their optical luminosity. In fact their radio/optical(R_B) distribution is gaussian, centered at log R_B ~ -0.5, i.e. theradio luminosity is ~ 0.3 of the optical one. The probability oflate-type galaxies to develop radio sources is almost independent oftheir detailed Hubble type, except for Sa (and S0+S0a) which are afactor of ~ 5 less frequent than later types at any R_B. Giantelliptical galaxies feed ``monster" radio sources with a probabilitystrongly increasing with mass. However the frequency of fainter radiosources is progressively less sensitive on the system mass. The faintestgiant E galaxies (M_B=-17) have a probability of feeding low power radiosources similar to that of dwarf E galaxies as faint as M_B=-13. Table~1is only available in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| 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.
| A Complete Redshift Survey to the Zwicky Catalog Limit in a 2^h X 15 deg Region around 3C 273
We compile 1113 redshifts (648 new measurements, 465 from theliterature) for Zwicky catalog galaxies in the region (-3.5d <= delta<= 8.5d, 11h5 <= alpha <= 13h5). We include redshifts for 114component objects in 78 Zwicky catalog multiplets. The redshift surveyin this region is 99.5% complete to the Zwicky catalog limit, m_Zw =15.7. It is 99.9% complete to m_Zw = 15.5, the CfA Redshift Survey(CfA2) magnitude limit. The survey region is adjacent to the northernportion of CfA2, overlaps the northernmost slice of the Las CampanasRedshift Survey, includes the southern extent of the Virgo Cluster, andis roughly centered on the QSO 3C 273. As in other portions of theZwicky catalog, bright and faint galaxies trace the same large-scalestructure.
| 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.
| Mid-IR emission of galaxies in the Virgo cluster. II. Integrated properties
We analyse the integrated properties of the Mid-IR emission of acomplete, optically selected sample of galaxies in the Virgo clusterobserved with the ISOCAM instrument on board the ISO satellite. TheISOCAM data allows us to construct the luminosity distribution at 6.75and 15 mu m of galaxies for different morphological classes. These dataare used to study the spectral energy distribution of galaxies ofdifferent type and luminosity in the wavelength range 2000 Angstroms -100 mu m. The analysis shows that the Mid-IR emission up to 15 mu m ofoptically-selected, normal early-type galaxies (E, S0 and S0a) isdominated by the Rayleigh-Jeans tail of the cold stellar component. TheMid-IR emission of late-type galaxies is instead dominated by thethermal emission from dust. As in the Milky Way, the small dust grainsemitting in the Mid-IR have an excess of emission if compared to biggrains emitting in the Far-IR. While the Far-IR emission of galaxiesincreases with the intensity of the interstellar radiation field, theirMid-IR emission is non-linearly related to the UV radiation field. Thespectral energy distributions of the target galaxies indicate that thereis a linear relationship between the UV radiation field and the Mid-IRemission of galaxies for low or intermediate activities of starformation, while the emission from the hot dust seems to drop for strongUV fields. The Mid-IR colour of late-type galaxies is not related totheir activity of star formation. The properties of the dust emission inthe Mid-IR seem more related to the mass than to the morphological typeof the target galaxy. Since the activity of star formation isanticorrelated to the mass of galaxies, this reflects a relationshipbetween the emission of dust in the Mid-IR and the UV radiation field:galaxies with the lowest Mid-IR emission for a given UV field are lowmass, dwarf galaxies. These observational evidences are easily explainedif the carriers of the Unidentified Infrared Bands that dominate the6.75 mu m emission are destroyed by the intense UV radiation field ofdwarf galaxies, although abundance effects can also play a role. Basedon observations with ISO, an ESA project with instruments founded by ESAmember states (especially the PI countries: France, Germany, theNetherlands and the United Kingdom) and with participation of ISAS andNASA
| FAUST Observations of Ultraviolet Sources toward the Virgo Cluster
We analyze three UV images covering a ~100 square degree field towardthe Virgo cluster, obtained by the FAUST space experiment. We detect 191sources to a signal-to-noise ratio of 4.4 and identify 94% of them. Mostsources have optical counterparts in existing catalogs, and about halfare identified as galaxies. Some sources with no listed counterpart wereobserved at the Wise Observatory. We present the results oflow-resolution visible spectrophotometry and discuss the foreground 101stellar sources and the 76 detected galaxies, both in the cluster and inthe foreground or background. We derive conclusions on star formationproperties of galaxies and on the total UV flux from discrete anddiffuse sources in the cluster. We test for the presence of intraclusterdust, determine the clustering properties of UV emitting galaxies, andderive the UV luminosity function of Virgo galaxies.
| Study of the Virgo Cluster Using the B-Band Tully-Fisher Relation
The distances to spiral galaxies of the Virgo cluster are estimatedusing the B-band Tully-Fisher (TF) relation, and the three-dimensionalstructure of the cluster is studied. The analysis is made for a completespiral sample taken from the Virgo Cluster catalog of Binggeli, Sandage,& Tammann. The sample contains virtually all spiral galaxies down toM_{BT}=-15 mag at 40 Mpc. A careful examination is made ofthe selection effect and errors of the data. We estimate distance to 181galaxies, among which distances to 89 galaxies are reasonably accurate.We compare these distances to those obtained by other authors on agalaxy-by-galaxy basis. We find reasonable consistency of theTully-Fisher distance among various authors. In particular, it is foundthat the discrepancy in the distance among the different analyses withdifferent data is about 15%, when good H I and photometric data areavailable. We clarify that the different results on the Virgo distanceamong authors arise from the choice of the sample and interpretation ofthe data. We confirm that the Tully-Fisher relation for the Virgocluster shows an unusually large scatter sigma = 0.67 mag, compared tothat for other clusters. We conclude that this scatter is not due to theintrinsic dispersion of the Tully-Fisher relation, but due to a largedepth effect of the Virgo cluster, which we estimate to be extended from12 Mpc to 30 Mpc. The distribution of H I--deficient galaxies isconcentrated at around 14--20 Mpc, indicating the presence of a core atthis distance, and this agrees with the distance estimated for M87 andother elliptical galaxies with other methods. We show also that thespatial number density of spiral galaxies takes a peak at this distance,while a simple average of all spiral galaxy distances gives 20 Mpc. Thefact that the velocity dispersion of galaxies takes a maximum at 14--18Mpc lends an additional support for the distance to the core. Thesefeatures cannot be understood if the large scatter of the TF relation ismerely due to the intrinsic dispersion. The structure of the VirgoCluster we infer from the Tully-Fisher analysis looks like a filamentwhich is familiar to us in a late phase of structure formation in thepancake collapse in hierarchical clustering simulations. This Virgofilament lies almost along the line of sight, and this is the originthat has led a number of authors to much confusion in the Virgo distancedeterminations. We show that the M87 subcluster is located around 15--18Mpc, and it consists mainly of early-type type spiral galaxies inaddition to elliptical and S0 galaxies. There are very few late-typespiral galaxies in this subcluster. The spiral rich M49 subclusterconsists of a mixture of all types of spiral galaxies and is located atabout 22 Mpc. The two other known clouds, W and M, are located at about30--40 Mpc and undergo infall toward the core. The M cloud contains fewearly type spirals. We cannot discriminate, however, whether thesesubclusters or clouds are isolated aggregates or merely parts offilamentary structure. Finally, we infer the Hubble constant to be 82+/- 10 km s-1 Mpc-1.
| 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.
| Influence of a partial incompleteness of the sample on the determination of the Hubble constant.
This paper presents a study of the Malmquist bias effect in thedetermination of the Hubble constant from the method of "sosies"(look-alike) galaxies. It is shown that a bias appears when a partialincompleteness exists in the sample. A new method, based on the use ofthe completeness curve, is proposed to correct for such a bias. Afterthis correction, the Hubble constant drops of about 20% just because ofthe existence of the partial incompleteness. From the present resultsand on the acceptance of the distance modulus of primary calibrators,the value of the Hubble constant would be: H_0_=~60km/s/Mpc with aninternal statistical error of about 2km/s/Mpc.
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
Catalogs and designations:
|
