WIKISKY.ORG
 Home Getting Started To Survive in the Universe News@Sky Astro Photo The Collection Forum Blog New! FAQ Press Login

# PGC 42378

Contents

### Images

DSS Images   Other Images

### Related articles

 Completing H I observations of galaxies in the Virgo clusterHigh 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. Companions of Bright Barred Shapley-Ames GalaxiesCompanion 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 clusterWe 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 Hα surface photometry of galaxies in the Virgo cluster III. Observations with INT and NOT 2.5 m telescopesWe present Hα line imaging observations of 30 galaxies obtained atthe 2.5 m INT and NOT telescopes. The observed galaxies are mostly BCDVirgo cluster galaxies. Hα +[NII] fluxes and equivalent widths, aswell as images of all the detected targets are presented. With theseobservations, Hα data are available for =~ 50% of the BCD galaxieslisted in the VCC. Based on observations taken at the INT and NOTtelescopes, operated on the island of La Palma by the ING and NOT teamsin the Spanish Observatorio del Roque de Los Muchachos of the Institutode AstrofÃ­sica de Canarias. Figure 1 is only available inelectronic form at http://www.edpsciences.org 1.65 μm (H-band) surface photometry of galaxies. V. Profile decomposition of 1157 galaxiesWe 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 A linear near-IR Tully-Fisher relation for giant and dwarf late-type galaxiesWe 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. Mid-IR emission of galaxies in the Virgo cluster. II. Integrated propertiesWe 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 Near infrared surface photometry of late-type Virgo cluster galaxiesNear 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. 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. General study of group membership. II - Determination of nearby groupsWe 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. Dwarf galaxies in the Virgo cluster. II - Photometric techniques and basic dataResults are presented of photographic surface photometry carried out for305 (mostly dwarf) galaxies in the Virgo cluster, in which the galaxyimages were digitized on 14 of the 67 du Pont plates used for the Virgocluster survey. Azimuthally averaged surface brightness profiles areshown for all galaxies. The following model-free photometric parametersare derived and listed for each galaxy: total apparent blue magnitude,mean effective radius and surface brightness, and various isophotalradii, ellipticity, and position angle. Most galaxies were fitted by anexponential form and/or a King model profile. The best-fittingparameters, including the 'nuclear' (central residual) magnitudes fordE+dS0 galaxies, are listed. The kinematics of the Virgo cluster revisitedThe 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. 21 centimeter line width distances of cluster galaxies and the value of H0Locally 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 areaNew 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). UBV colors of Virgo cluster irregular galaxiesPhotoelectric 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. Studies of the Virgo Cluster. II - A catalog of 2096 galaxies in the Virgo Cluster area.The present catalog of 2096 galaxies within an area of about 140 sq degapproximately centered on the Virgo cluster should be an essentiallycomplete listing of all certain and possible cluster members,independent of morphological type. Cluster membership is essentiallydecided by galaxy morphology; for giants and the rare class of highsurface brightness dwarfs, membership rests on velocity data. While 1277of the catalog entries are considered members of the Virgo cluster, 574are possible members and 245 appear to be background Zwicky galaxies.Major-to-minor axis ratios are given for all galaxies brighter than B(T)= 18, as well as for many fainter ones. A catalog of dwarf galaxies in VirgoA catalog listing the location, apparent angular diameter, type,estimated central light concentration, and estimated brightness of 846dwarf galaxies in a 200-deg-sq region in Virgo is presented. Thegalaxies comprise 634 ellipticals, 137 IC-3475-type galaxies, 73 dwarfspirals and irregulars, and two objects which are jets of normalgalaxies, and were found on nine long-exposure IIIa-J-emulsion platesmade with the 1.2-m-Schmidt telescope at Palomar Observatory from 1971to 1976. Concordances to other catalogs, tables of additionalparameters, maps, graphs, and photographs are provided. The projecteddistributions of normal and dwarf galaxies and the dependence ofapparent luminosity on central light concentration are discussed. It isfound that dwarf ellipticals and IC-3475-type galaxies are probablemembers of the Virgo cluster, while dwarf spirals and possibly dwarfirregulars are not.
Submit a new article