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

# PGC 41587

Contents

### Images

DSS Images   Other Images

### Related articles

 Infrared Properties of Star-forming Dwarf Galaxies. II. Blue Compact Dwarf Galaxies in the Virgo ClusterA sample of 16 blue compact dwarf galaxies (BCDs) in the Virgo Clusterhas been imaged in the near-infrared (NIR) in J and Ks on the2.1 m telescope at the Observatorio Astronómico Nacional in theSierra San Pedro Mártir in Mexico. Isophotes as faint asμJ=24 mag arcsec-2 andμKs=23 mag arcsec-2 have beenreached in most of the targets. Surface brightness profiles can befitted across the whole range of radii by the sum of two components: ahyperbolic secant (sech) function, which is known to fit the lightprofiles of dwarf irregular galaxies (dIs), and a Gaussian component,which quantifies the starburst near the center. Isophotal and totalfitted NIR magnitudes have been calculated, along with semimajor axes atμJ=23 mag arcsec-2 andμKs=22 mag arcsec-2. The diffuseunderlying component and the young starburst have been quantified usingthe profile fitting. Most color profiles show a constant color, betweenJ-Ks=0.7 and 0.9 mag. The diffuse component represents theoverwhelming majority of the NIR light for most BCDs, with the starburstenhancing the flux by less than about 0.3 mag. Linear correlations werefound between the sech scale length and the sech magnitude and betweenthe sech semimajor axis and the sech magnitude. Overall, galaxies withmore luminous diffuse components are larger and brighter in the center.The central burst correlates with the diffuse component, with brighterBCDs having stronger starbursts, suggesting that more massive objectsare forming stars more efficiently. BCDs lie on the fundamentalplane'' defined by dIs in Paper I, following the same relation betweensech absolute magnitude, sech central surface brightness, and thehydrogen line width W20, although the scatter is larger thanfor the dIs. On the other hand, correlations between the sech absolutemagnitude and the sech central surface brightness in Ks forBCDs and dIs are equally good, indicating that BCD line widths may beenhanced by turbulence or winds.These data were acquired at the Observatorio Astronómico Nacionalin the Sierra San Pedro Mártir, Mexico. 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. Spectroscopy of Dwarf Galaxies in the Virgo Cluster. I. Data, Chemical Abundances, and Ionization StructureLong-slit spectroscopy has been obtained for a sample of 22 blue dwarfgalaxies selected in the direction of the Virgo Cluster, as part of alarger sample of Virgo blue dwarf galaxies for which deep Hαimaging has been collected. Most of the galaxies in the present sampleare classified as BCDs or dwarf Irregulars in the Virgo Cluster Catalog.Line fluxes, Hβ equivalent widths, extinction coefficients, spatialemission profiles, ionization structure, and physical conditions arepresented for each galaxy. Chemical abundances have been derived eitherusing a direct determination of the electron temperature or afterdetailed examination of the predictions of different abundancecalibrations. The oxygen abundances derived for the sample of Virgodwarf galaxies span the range 7.6<=12+log(O/H)<=8.9, and thecorresponding nitrogen-to-oxygen abundance ratio ranges from valuestypical of low-metallicity field BCD galaxies to near solar. Neutral Hydrogen Mapping of Virgo Cluster Blue Compact Dwarf GalaxiesA new installment of neutral hydrogen mappings of blue compact dwarf(BCD) galaxies, as defined by optical morphology, in and near the VirgoCluster is presented. The primary motivation was to search for outlyingclouds of H I as potential interactive triggers of enhanced starformation, and therefore the mapped galaxies were selected for large H Imass, large optical diameter, and large velocity profile width.Approximately half the sample proved to have one or more small, lowcolumn density, star-free companion clouds, either detached or appearingas an appendage in our maps, at a resolution on the order of 4 kpc.Comparison is made with a sample of similarly mapped field BCD galaxiesdrawn from the literature; however, the Virgo Cluster sample of mappedBCDs is still too small for conclusive comparisons to be made. We found,on the one hand, little or no evidence for ram-pressure stripping nor,on the other, for extremely extended low column density H I envelopes.The H I rotation curves in most cases rise approximately linearly andslowly, as far out as we can trace the gas. 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. A new catalogue of ISM content of normal galaxiesWe have compiled a catalogue of the gas content for a sample of 1916galaxies, considered to be a fair representation of normality''. Thedefinition of a normal'' galaxy adopted in this work implies that wehave purposely excluded from the catalogue galaxies having distortedmorphology (such as interaction bridges, tails or lopsidedness) and/orany signature of peculiar kinematics (such as polar rings,counterrotating disks or other decoupled components). In contrast, wehave included systems hosting active galactic nuclei (AGN) in thecatalogue. This catalogue revises previous compendia on the ISM contentof galaxies published by \citet{bregman} and \citet{casoli}, andcompiles data available in the literature from several small samples ofgalaxies. Masses for warm dust, atomic and molecular gas, as well asX-ray luminosities have been converted to a uniform distance scale takenfrom the Catalogue of Principal Galaxies (PGC). We have used twodifferent normalization factors to explore the variation of the gascontent along the Hubble sequence: the blue luminosity (LB)and the square of linear diameter (D225). Ourcatalogue significantly improves the statistics of previous referencecatalogues and can be used in future studies to define a template ISMcontent for normal'' galaxies along the Hubble sequence. The cataloguecan be accessed on-line and is also available at the Centre desDonnées Stellaires (CDS).The catalogue is available in electronic form athttp://dipastro.pd.astro.it/galletta/ismcat and at the CDS via anonymousftp to\ cdsarc.u-strasbg.fr (130.79.128.5) or via\http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/405/5 An H I Survey of Actively Star-forming Dwarf GalaxiesWe present the results of H I 21 cm observations of 139 activelystar-forming dwarf galaxies obtained with the 305 m radio telescope atArecibo Observatory. Our sample consists of all objects cataloged inobjective-prism surveys for UV-excess or emission-line galaxiespublished prior to the start of the survey that have luminosities belowMB=-17.0 and that are located within the declination limitsof the Arecibo telescope. Galaxies from the Markarian, Michigan, Case,Wasilewski, Haro, and Zwicky lists are included. The sample spans a widerange of both H I gas content and star formation levels. A total of 122objects (88%) were detected; 82 galaxies have been observed for thefirst time in H I. The median velocity width for our sample is 88 kms-1, and the median H I gas mass is 3.0×108Msolar. In general, the sample galaxies are gas-rich, with anaverage MHI/LB=1.3 after correcting for theluminosity enhancement due to the starburst. The progenitors of many ofthe star-forming dwarfs have higher MHI/LB thantypically seen in samples of nearby normal'' galaxies, emphasizingtheir distinct nature. The UZC-SSRS2 Group CatalogWe 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 galaxiesHα +[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, orbirthrate'' 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 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 The Morphologies of Dwarf Markarian GalaxiesThe morphologies of the 96 dwarf (M(B) -17m) galaxies in the Markariancatalog are determined from the digitized Schmidt plates obtained forthe construction of the Hubble Space Telescope Guide Star Catalog. Thefraction of double nucleus galaxies within the dwarf Markarian galaxiesis determined to be twice that found for all galaxies in the Markariancatalog. In addition to the 12 previously known cases, four definite andtwo probable galaxies with double nuclei are identified. The fraction ofdwarf Markarian galaxies with bright star forming regions is found to betwice that of Virgo cluster dwarf galaxies. No Elliptical galaxies arefound in the sample. Galaxies with blue compact dwarf and S0morphologies are more often found to contain unresolved regions of UVexcess emission. Dwarf Markarian galaxies with different morphologicalstructures and spectral classes are found to have similar FIRproperties. On the star-formation properties of emission-line galaxies in and around voidsWe present a study of the star formation properties of a sample ofemission line galaxies (ELGs) with respect to their environment. Thisstudy is part of a bigger project that aimed to find galaxies in voidsand to investigate the large scale structure of the ELGs. A survey forELGs was therefore conducted with the result that 16 galaxies have beenfound in very low density environments, of which 8 ELGs were found intwo very well defined nearby voids. The sample presented here containssome galaxies identified in voids, as well as in the field environmentthat delimited the voids. These ELGs are all Blue Compact Galaxies(BCGs), and all void galaxies are also dwarfs. Both void and fieldsample contain the same mixture of morphological subtypes of BCDs, fromthe extreme Searle-Sargent galaxies to the Dwarf-AmorphousNuclear-Starburst galaxies. The main result of this study is that fieldand void galaxies seem to have similar star formation rates (SFR),similar ratios between the current SFR and their average past SFR andsimilar mean SFR surface densities. There is no trend in metallicity, inthe sense that void galaxies would have lower metallicities than theirfield counterparts. The field-cluster dichotomy is also discussed usingavailable results from the literature, since our sample does not coverthe cluster environment. The implication of our findings are discussedin connection with the theories for the formation and evolution of BCDs.Based on observations obtained at the German-Spanish Observatory atCalar Alto, Almeria, Spain 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 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. A multifrequency radio continuum and IRAS faint source survey of markarian galaxiesResults are presented from a multifrequency radio continumm survey ofMarkarian galaxies (MRKs) and are supplemented by IRAS infrared datafrom the Faint Source Survey. Radio data are presented for 899 MRKsobserved at nu = 4.755 GHz with the National Radio Astronomy Observatory(NRAO)-Green Bank 300 foot (91 m) telescope, including nearly 88% ofthose objects in Markarian lists VI-XIV. In addition, 1.415 GHzmeasurements of 258 MRKs, over 30% of the MRKs accessible from theNational Aeronomy and Ionosphere Center (NAIC)-Arecibo, are reported.Radio continuum observations of smaller numbers of MRKs were made at10.63 GHz and at 23.1 GHz and are also presented. Infrared data from theIRAS Faint Source Survey (Ver. 2) are presented for 944 MRKs, withreasonably secure identifications extracted from the NASA/IPACExtragalactic Database. MRKs exhibit the same canonical infraredcharacteristics as those reported for various other galaxy samples, thatis well-known enhancement of the 25 micrometer/60 micrometer color ratioamong Seyfert MRKs, and a clear tendency for MRKs with warmer 60micrometer/100 micrometer colors to also possess cooler 12 micrometer/25micrometer colors. In addition, non-Seyfert are found to obey thewell-documented infrared/radio luminosity correlation, with the tightestcorrelation seen for starburst MRKs. On the Spectroscopic Properties of Star-Forming Dwarf Galaxies in Different EnvironmentsA study is presented on the spectroscopic properties of a sample ofstar- forming dwarf galaxies in extreme density environments, as part ofan ongoing project intended to evaluate the influence of the environmenton the evolution of dwarf galaxies. Subsets of dwarf galaxies in nearbyvoids, and in the field of the local supercluster have been selected tocharacterize lower density regions. Conversely, higher densityenvironments have been characterized choosing a subset of galaxies inthe direction of the core of the Virgo Cluster, as well as an isolatedclump of galaxies. Our findings indicate that, overall, the spectra ofthose star-forming dwarf galaxies located in low-density regions tend topresent higher excitations and ionization parameters, higher Hβequivalent widths, and larger total Hβ luminosities than similarobjects located in higher density environments. At the same time, onlymarginal evidence may be found supporting a trend between the gasmetallicity and the density of the environment. The general metallicityluminosity relation for dwarf galaxies appears to be followed by mostgalaxies in the sample. An analysis of the spectroscopic ratios of thegalaxies using recent evolutionary models of giant H II regions suggestsa mixed star-formation history for most of the Virgo star- formingdwarfs, requiring continuous star formation in addition to somecurrently observable bursts. 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. 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. The Virgo cluster as a test for quantization of extragalactic redshiftsTifft'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. Vacuum ultraviolet imagery of the Virgo Cluster region. II - Total far-ultraviolet flux of galaxiesThe total flux in the far-ultraviolet region around 150 nm was measuredfor more than 40 galaxies in the central region of the Virgo Cluster,using two imaging telescopes on board a sounding rocket. The observedfar-ultraviolet flux shows positive correlations with the H I 21 cm fluxand the far-infrared flux for spiral galaxies, and with the X-ray fluxand the radio continuum flux for elliptical galaxies. The formercorrelations of spiral galaxies are interpreted in terms of starformation activity, which indicates substantial depletion in the Virgogalaxies in accordance with the H I stripping. The latter correlationsof elliptical galaxies indicate possible far-ultraviolet sources ofyoung population, in addition to evolved hot stars. Far-ultravioletfluxes from two dwarf elliptical galaxies were obtained tentatively,indicating star formation activity in elliptical galaxies. Ahigh-resolution UV imagery by HST would be effective to distinguish theyoung population and the old population in elliptical galaxies. Spectrophotometrical study of the blue compact dwarf galaxies in the Virgo cluster.Not Available IRAS observations of galaxies in the Virgo cluster areaIRAS data on 196 galaxies in the area of the Virgo Cluster arepresented. The data derive from combining all available surveyobservations for each object and therefore achieve greater sensitivitythan the IRAS Point Source Catalog (PSC). The enhanced sensitivityallows 78 galaxies to be detected at 12 microns, 82 at 25 microns, 139at 60 microns, and 135 at 100 microns, compared to 16, 23, 88, and 95detections listed in the PSC. From the blue compact dwarf galaxy sample,23 and 19 objects are detected at 60 and 100 microns, compared to threeand two detections listed in the PSC. The emission in three close pairsof galaxies which are reported as single sources in the PSC areseparated here. These statistics demonstrate the importance andpotential of a detailed examination of IRAS data, especially forpossibly resolved sources and, in particular, for galaxies out toredshifts of 0.008 or galaxies with D(25) of 3 arcmin or greater. A catalog of Markarian galaxiesA catalog of Markarian galaxies is presented which tabulates redshifts,spectral and morphological classifications, magnitudes, infrared andradio flux densities, and over 600 references to available datapublished before January 1, 1986. Redshifts are now available for 1228objects with strong ultraviolet continua, and follow-up spectroscopicand photometric observations of Markarian galaxies have providedclassifications of 115 Seyfert 1, 43 Seyfert 2, and 137 starburst and HII-type galaxies. After a description of the Markarian survey and thecurrent catalog, a summary of the general results obtained from the datais presented. A preliminary study of the infrared properties ofMarkarian galaxies as measured by IRAS reveals a number of interestingresults, including the existence of a sample of elliptical andlenticular galaxies with appreciable infrared emission. 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. HI-observations of galaxies in the Virgo cluster of galaxies. I - The dataNew H I-data for a large number of bright galaxies inside the 10 degradius area of the Virgo cluster of galaxies have been obtained with the100 m radiotelescope at Effelsberg. A total of 234 galaxies was observedfor the first time. Among them, 53 have been detected providing newaccurate radial velocities. Data from the literature have been compiled.Together with the new data, they form a (nearly homogeneous) set of H Iobservations for more than 450 galaxies. The structure of the Virgo cluster of galaxiesA new detailed analysis of galaxies in the Virgo area shows that theconventional Virgo cluster comprises two different clouds of galaxies:the Virgo cluster I and the Southern cloud II by the definition proposedhere. Excluding the galaxies in the Southern cloud II, the Virgo clusterI centered at 12 h 27.6 m, +13 deg 07 arcmin (1950), has a mean radialvelocity of 980 + or - 60 km/s and there is no significant velocitydifference between elliptical-lenticular and spiral-irregular galaxiesin the Virgo cluster I. The Southern cloud II is centered at about 12 h25 m, +7 deg 30 arcmin (1950) and all types of galaxies in the cloud arediffusely distributed, while elliptical galaxies in the Virgo cluster Iare concentrated to the center. The mean radial velocity within a radiusof 3.5 deg of the Southern cloud II is +1240 + or - 80 km/s, which issignificantly higher than the mean velocity of the Virgo cluster I. The statistical distribution of the neutral-hydrogen content of elliptical galaxiesAn examination has been conducted of the form of the distributionfunction for the relative H I content, MH I/LB, of elliptical galaxies,using a data set derived from all recent H I observations of ellipticalsin the literature. The characteristics of this combined data set arepoorly defined, but upon examination it appears to be reassuringly freeof built-in biases and correlations. The data set contains 152 galaxies;23 of these have been detected in the H I line. The detected galaxiesare shown to be more H I rich on average than the galaxies in the wholesample. A method for recovering the intrinsic distribution of MH I/LB,using both detection and upper-limit data, is described, and the dataare shown to be consistent with a shallow power-law differentialdistribution N approximately (MH I/LB) to the -1.5th. This distributionis quite different from that for spirals, where N(MH I/LB) has awell-defined mean value and a small dispersion. This result stronglysuggests that the gas and star contents of ellipticals are decoupled,i.e., the gas has an external origin. A successful survey of H I in low-luminosity elliptical galaxiesA neutral hydrogen survey of 28 faint elliptical galaxies was made usingthe 305 m antenna of the Arecibo Observatory in order to explorevariations in gas content that are related to size, stellar velocitydispersion, and rotation. Eleven out of 28 galaxies were detected, and acorrelation of the H I line width with blue luminosity, similar to theFaber-Jackson relation, was found. The larger gas content of faintelliptical galaxies is attributed to a combination of much shortercooling times and the possible change in the structure in the wind dueto the angular momentum of the gas shed from a more rapidly rotatingstellar system. Studies of the Virgo cluster. III - A classification system and an illustrated atlas of Virgo cluster dwarf galaxiesAbstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1984AJ.....89..919S&db_key=AST
Submit a new article