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Infrared Properties of Star-forming Dwarf Galaxies. II. Blue Compact Dwarf Galaxies in the Virgo Cluster
A 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 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.
| Spectroscopy of Dwarf Galaxies in the Virgo Cluster. I. Data, Chemical Abundances, and Ionization Structure
Long-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.
| A Catalog and Atlas of Cataclysmic Variables: The Living Edition
The Catalog and Atlas of Cataclysmic Variables (Edition 1: Downes &Shara; Edition 2: Downes, Webbink, & Shara) has been a valuablesource of information for the cataclysmic variable community. However,the goal of having a central location for all objects is slowly beinglost as each new edition is generated. There can also be a long timedelay between new information becoming available on an object and itspublication in the catalog. To eliminate these concerns, as well as tomake the catalog more accessible, we have created a Web site which willcontain a ``living'' edition of the catalog. We have also added orbitalperiod information, as well as finding charts for novae, to thecatalog.
| Total Magnitudes of Virgo Galaxies. I. Construction of a Self-Consistent Reference Dataset Spanning 8th to 18th Magnitude
The main objectives of this series of papers are: (1) to demonstrate theexistence of serious mutual disagreements between established total (andother integrated) magnitude scales for Virgo galaxies; (2) to attempt toquantify both the systematic and random errors present within thesemagnitude scales; (3) to investigate the origins of any large erroruncovered; and thereby (4) to encourage the general adoption of rigoroustotal-magnitude measurement procedures by the astronomical community.The ramifications of the findings presented in this series of paperswill be discussed in detail at a later date. In this paper, the first inthe series, a self-consistent dataset of trustworthy total-magnitudemeasurements is compiled for a sample of Virgo galaxies spanning a rangeof 10 000 in apparent brightness, based on only the most reliablemeasurements and photometry currently available. This reference dataset,which includes luminosity profile shape information, will be used insubsequent papers as one of the bases for assessing existing magnitudescales for Virgo galaxies. As most published magnitudes are based onB-band observations, this series of papers will also focus primarily onB-band measurements.
| A Catalog and Atlas of Cataclysmic Variables-Second Edition
We present a catalog of all 1020 known cataclysmic variables (CVs). Thispaper is a major update of the first edition of the catalog (Downes andShara 1993, PASP, 105, 127), which contained coordinates (measured inthe reference frame of the Hubble Space Telescope Guide Star Survey forthe non-novae, and obtained from the literature for the novae), thevariability type, the magnitude range, and references to both findingcharts and spectroscopy. Also included in the catalog were findingcharts for all dwarf novae, novalike variables, and objects classifiedonly as cataclysmic variables known as of 1993; a similar catalog andatlas for novae has been published by Duerbeck (1978a). This updatededition includes 195 new objects (172 CVs and 23 non-CVs), revisedidentifications for 57 objects, and revised information (classificationand spectral references) when available. We also now include plateidentification information for the coordinate measurements, a referenceto the classification, proper motion information where appropriate, anda table showing the CVs observed by space-based observatories. Thissecond edition is inclusive of the first edition, although only new orupdated charts are presented. (SECTION: Special Issue on CataclysmicVariable Stars)
| Optical structure and star formation in blue compact dwarf galaxies. II. Relations between photometric components and evolutionary implications.
In a preceding paper, we have derived the structural parameters of theyoung high-surface-brightness stellar component formed in starbursts andthat of the old underlying low-surface-brightness component, by applyinga 3-component decomposition scheme to the surface brightness profiles of12 blue compact dwarf galaxies (BCDs) and 2 starburst galaxies. Here wecompare the various properties of these two components. We find that thesize of the starburst component depends on the size and luminosity ofthe underlying component, as well as on the HI mass of the BCD.Furthermore, the fractional surface occupied by the star-forming regionsdecreases with increasing luminosity of the underlying host galaxy. Wecompare the structural properties of BCDs with those of other types ofdwarf galaxies. We find that, at equal B luminosity, the underlyingcomponent of a BCD has a central surface brightness brighter by ~1.5 magand an exponential scale length smaller by a factor of ~2 than that ofdwarf irregulars (dIs) and dwarf ellipticals (dEs). Thus there can beevolutionary connections between BCDs and dEs and dIs only if the BCDunderlying component can modify its structural properties. This mayoccur in response to changes in the global gravitational potential ofthe dwarf galaxy, caused by such events as mass infall from the outergas halo and/or mass loss in starburst-driven galactic winds.
| On the Spectroscopic Properties of Star-Forming Dwarf Galaxies in Different Environments
A 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.
| Near Infrared Imaging of Dwarf Ellipticals Irregulars and Blue Compact Galaxies in the Virgo Cluster
New near-IR images are presented for 13 dwarf galaxies in the Virgocluster. Together with previous data these provide a data base of JHKimaging for 26 dwarf ellipticals (dEs), dwarf irregulars (dIs) and bluecompact dwarfs (BCDs). These images show the dIs to be highly asymmetricand unrelaxed, implying that they are dynamically young and unevolved.This is consistent with their blue near-IR and optical-IR colours whichare most easily explained by young stellar populations. The dEs aresymmetrical and apparently relaxed, with very uniform colours indicatingthat they are dominated by old stars. They generally have exponentiallight profiles, but the brighter galaxies tend to exhibit more cuspedlight distributions, similar to the de Vaucouleurs profiles of brightellipticals. The BCDs have moderately asymmetric light profiles, andparadoxically red colours, possibly indicating an intermediate-agestellar population. They are probably dEs which have undergone bursts ofstar formation in the last few X 10^9^ years, whilst the dIs are afundamentally distinct population. Colour gradients are present in manyof the galaxies, invariably in the sense that the nuclei are redder thanthe surrounding galaxy light.
| Dwarf galaxies in the Virgo cluster. II - Photometric techniques and basic data
Results 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.
| Extreme blue compact dwarf galaxies in the Virgo Cluster
CCD images and surface photometry are presented for six extreme(especially compact) blue compact dwarf (BCD) galaxies in the VirgoCluster. The photometric parameters of the galaxies are used to studytheir possible fate once star formation has ended. It is found that theymay fade to form dwarf elliptical galaxies, as has previously beensuggested, but the dE galaxies formed from these BCDs would lie amongthe most compact in existing samples. Two of the BCDs studied have nosurrounding low-surface-brightness envelopes detected to a limit ofmu(v) = 27 mag/sq arcsec.
| The Virgo cluster as a test for quantization of extragalactic redshifts
Tifft's (1972, 1977) hypothesis that redshifts are partially quantizedwith a periodicity in the range 70-75 km/s is tested for samples ofbright spiral and dwarf irregular galaxies with accurate H I redshiftsin the region of the Virgo cluster. The heliocentric redshifts arecorrected for solar motion, first by adopting an estimate of the sun'smotion with respect to the centroid of the Local Group, and then byallowing the solar velocity vector to vary in direction over the wholesky. Power spectrum analyses of the corrected redshifts are used tosearch for a significant periodicity in the prescribed range 70-75 km/s.No such periodicity is found for the dwarf irregulars, but there is apossible periodicity of about 71.1 km/s for the bright spirals. In afurther exploratory study, the sample of 112 spirals is divided upaccording to environment. The spirals in high-density regions of thecluster show no quantization, whereas those in low-density regionsappear to be partially quantized in intervals of about 71.0 km/s.
| KISO survey for ultraviolet-excess galaxies. IX
A set of identification charts is presented for UV-excess galaxiesdetected on multicolor plates for ten survey fields. The charts are partof the Kiso UV galaxy catalog (Takase and Miyauchi-Isobe, 1988). Thisset of charts brings the total number of objects in the catalog to 583,covering a 300-sq deg sky area down to a photographic magnitude of about18. The parameters presented include morphological classifications,image sizes, and degree of UV-excess.
| Imaging and spectrophotometry of Virgo cluster irregular galaxies
Large-aperture spectrophotometric observations and CCD images in theH-alpha and R bands have been obtained for Virgo cluster Magellanic,dwarf, and amorphous irregular galaxies. Although a small number ofVirgo cluster irregulars have optical and H I properties consistent withrecent gas loss, the rate of production of gas-poor irregulars is toolow to account for the large population of Virgo cluster dE galaxies orto explain the deficiency in the number of irregulars relative tospirals. Radial brightness profiles reveal that only NGC 4641 followsthe r exp 1/4 law of classical ellipticals, that four of the galaxieshave exponential brightness distributions, and that one system has anindeterminant profile form. It is shown that the properties of Virgocluster irregular galaxies can be best understood in terms ofenvironmental modifications of normal systems in the circumclusterenvironment and in the cluster core.
| IRAS observations of galaxies in the Virgo cluster area
IRAS 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.
| H I detection survey of a complete magnitude-limited sample of dwarf irregular galaxies in the Virgo Cluster area
New single-beam Arecibo H I observations of 298 late-type galaxies inthe Virgo Cluster drawn mostly from the new catalog of Binggeli,Sandage, and Tammann (1985) are presented. Two hundred seventeen ofthese constitute a magnitude-limited 'complete sample' of such galaxies,types Sdm through Im and BCD. Sixty-one percent of this 'completesample' was detected, greatly enhancing the store of redshifts and H Imasses for such galaxies in the Virgo Cluster. For detected galaxies,heliocentric velocities, 50 percent profile widths, and single-beamfluxes are presented. For those that escaped detection, upper limits arecomputed to the flux appropriate to the redshift range (-600 to +3000km/s).
| Comparative photometric parameters of dwarf irregular and elliptical galaxies in the Virgo Cluster - Two different classes of dwarf galaxies?
The possible evolutionary relationships of dwarf irregular (dI) anddwarf elliptical (dE) galaxies is explored with a data base thatconsists of 21 cm data, infrared photometry, and CCD multicolor surfacephotometry of both dIs and dEs in the Virgo cluster. In general, dIs areat or slightly below the same surface-brightness level as dEs, yet theyare significantly bluer. To have the same optical and IR colordistribution as the dEs requires that dIs fade by 1.5 mag in the blue.This will in turn produce a population of dwarf galaxies that will haveaverage surface brightness below the detection threshold of conventionalphotographic plates. It is concluded that the progenitors of thebrighter dE galaxies in the Virgo cluster are not to be found among thecurrent generation of dIs with the exception that some of the largerblue compact dwarf galaxies are probably gas-rich analogs to dEs.Furthermore, it is probable that dIs form a parallel sequence of dwarfgalaxies with surface mass densities significantly lower than the dEs.
| UBV colors of Virgo cluster irregular galaxies
Photoelectric UBV aperture photometry is presented for 65 dwarfirregular and morphologically related types of galaxies that areprobable Virgo cluster members. Virgo cluster Irr galaxies cover a widerrange in color than typical samples of field Irr systems, primarily dueto the presence of unusually red Im galaxies in Virgo. The extremelyblue 'blue compact dwarf' and the red amorphous galaxies in Virgo alsostand out on a UBV color-color plot, but the majority of Virgo Irrs areundistinguished in terms of UBV colors. Statistical correlations arefound between colors and location within the cluster. Red Irrs often arein elliptical galaxy rich, dense areas of the cluster, while the blueIrrs roughly follow the spiral distribution pattern. Thus a connectionexists between environment and the properties of Irrs. Simplestatistical tests for ongoing stripping as the source of red Irrs,however, yields null results.
| HI-observations of galaxies in the Virgo cluster of galaxies. I - The data
New 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.
| HI-observations of galaxies in the Kraan-Korteweg - Tammann catalogue of nearby galaxies. I - The data
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1986A&AS...63..323H&db_key=AST
| 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.
| On the Largescale Distribution of Faint Blue Galaxies
Not Available
| Radial Velocities of Galaxies in the Virgo Cluster
Not Available
| Faint blue objects in the Virgo cluster region.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1967AJ.....72...59R&db_key=AST
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