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The massive star population in the giant HII region Tol89 in NGC5398
We present new high spectral resolution Very Large Telescope(VLT)/UV-Visual Echelle Spectrograph (UVES) spectroscopy and archivalHubble Space Telescope (HST)/Space Telescope Imaging Spectrograph (STIS)imaging and spectroscopy of the giant HII region Tol89 in NGC5398. Fromoptical and ultraviolet (UV) HST images, we find that the star-formingcomplex as a whole contains at least seven young compact massiveclusters. We resolve the two brightest optical knots, A and B, into fiveindividual young massive clusters along our slit, A1-4 and B1,respectively. From UV spectral modelling using the STARBURST99 code ofLeitherer et al., and nebular Hβ equivalent widths in the optical,we derive ages that are consistent with the formation of two separateburst events, of ~4 +/- 1 Myr and <3 Myr for knots A (A1-4) and B(B1), respectively. A Large Magellanic Cloud (LMC) metallicity ismeasured for both knots from a nebular line analysis, while nebular HeII4686 is observed in knot B and perhaps in knot A. We detect underlyingbroad wings on the strongest nebular emission lines indicatingvelocities up to 600 km s-1. From UV and opticalspectroscopy, we estimate that there are ~95 early WN stars and ~35early WC stars in Tol89-A, using empirical template spectra of LMCWolf-Rayet (WR) stars from Crowther & Hadfield, with the WCpopulation confined to cluster A2. Remarkably, we also detect a smallnumber of approximately three mid WNs in the smallest (mass) cluster inTol89-A, A4, whose spectral energy output in the UV is entirelydominated by the WN stars. From the strength of nebular Hβ, weobtain N(O) ~ 690 and 2800 for knots A and B, respectively, whichimplies N(WR)/N(O) ~ 0.2 for knot A. We also employ a complementaryapproach using STARBURST99 models, in which the O star content isinferred from the stellar continuum, and the WR population is obtainedfrom spectral synthesis of optical WR features using the grids fromSmith et al. We find reasonable agreement between the two methods forthe O star content and the N(WR)/N(O) ratio but find that the WR subtypedistribution is in error in the STARBURST99 models, with far too few WNstars being predicted. We attribute this failure to the neglect ofrotational mixing in evolutionary models. Our various modellingapproaches allow us to measure the cluster masses. We identify A1 as asuper star cluster (SSC) candidate with a mass of ~1-2 ×105 Msolar. A total mass of ~6 ×105 Msolar is inferred for the ionizing sourceswithin Tol89-B.Based on observations collected at the European Southern Observatory,Chile, proposal ESO 73.B-0238(A) and with the NASA/ESA HST, obtainedfrom the ESO/ST-ECF Science Archive Facility.E-mail: fs@star.ucl.ac.uk
| Hαkinematics of the SINGS nearby galaxies survey - I*
This is the first part of an Hαkinematics follow-up survey of theSpitzer Infrared Nearby Galaxies Survey (SINGS) sample. The data for28galaxies are presented. The observations were done on three differenttelescopes with Fabry-Perot of New Technology for the Observatoire dumont Megantic (FaNTOmM), an integral field photon-counting spectrometer,installed in the respective focal reducer of each telescope. The datareduction was done through a newly built pipeline with the aim ofproducing the most homogenous data set possible. Adaptive spatialbinning was applied to the data cubes in order to get a constantsignal-to-noise ratio across the field of view. Radial velocity andmonochromatic maps were generated using a new algorithm, and thekinematical parameters were derived using tilted-ring models.
| ISO observations of the Wolf-Rayet galaxies NGC 5430, NGC 6764, Mrk 309 and VII Zw 19
Observations of four WR galaxies (NGC 5430, NGC 6764, Mrk 309 and VII Zw19) using the Infrared Space Observatory are presented here. ISOCAM mapsof NGC 5430, Mrk 309 and NGC 6764 revealed the location of starformation regions in each of these galaxies. ISOPHOT spectralobservations from 4 to 12 μm detected the ubiquitous PAH bands in thenuclei of the targets and several of the disk star forming regions,while LWS spectroscopy detected [O I] and [C II] emission lines from twogalaxies, NGC 5430 and NGC 6764. Using a combination of ISO and IRASflux densities, a dust model based on the sum of modified blackbodycomponents was successfully fitted to the available data. These modelswere then used to calculate new values for the total IR luminosities foreach galaxy, the size of the various dust populations, and the globalSFR. The derived flux ratios, the SFRs, the high L(PAH)/L(40-120 μm)and F(PAH 7.7 μm)/F(7.7 μm continuum) values suggest that most ofthese galaxies are home to only a compact burst of star formation. Theexception is NGC 6764, whose F(PAH 7.7 μm)/F(7.7 μm continuum)value of 1.22 is consistent with the presence of an AGN, yet theL(PAH)/L(40-120 μm) is more in line with a starburst, a finding inline with a compact low-luminosity AGN dominated by the starburst.
| SINGS: The SIRTF Nearby Galaxies Survey
The SIRTF Nearby Galaxy Survey is a comprehensive infrared imaging andspectroscopic survey of 75 nearby galaxies. Its primary goal is tocharacterize the infrared emission of galaxies and their principalinfrared-emitting components, across a broad range of galaxy propertiesand star formation environments. SINGS will provide new insights intothe physical processes connecting star formation to the interstellarmedium properties of galaxies and provide a vital foundation forunderstanding infrared observations of the distant universe andultraluminous and active galaxies. The galaxy sample and observingstrategy have been designed to maximize the scientific and archivalvalue of the data set for the SIRTF user community at large. The SIRTFimages and spectra will be supplemented by a comprehensivemultiwavelength library of ancillary and complementary observations,including radio continuum, H I, CO, submillimeter, BVRIJHK, Hα,Paα, ultraviolet, and X-ray data. This paper describes the mainastrophysical issues to be addressed by SINGS, the galaxy sample and theobserving strategy, and the SIRTF and other ancillary data products.
| FLASH redshift survey - I. Observations and catalogue
The FLAIR Shapley-Hydra (FLASH) redshift survey catalogue consists of4613 galaxies brighter than bJ= 16.7 (corrected for Galacticextinction) over a 700-deg2 region of sky in the generaldirection of the Local Group motion. The survey region is a70°× 10° strip spanning the sky from the ShapleySupercluster to the Hydra cluster, and contains 3141 galaxies withmeasured redshifts. Designed to explore the effect of the galaxyconcentrations in this direction (in particular the Supergalactic planeand the Shapley Supercluster) upon the Local Group motion, the 68 percent completeness allows us to sample the large-scale structure betterthan similar sparsely-sampled surveys. The survey region does notoverlap with the areas covered by ongoing wide-angle (Sloan or 2dF)complete redshift surveys. In this paper, the first in a series, wedescribe the observation and data reduction procedures, the analysis forthe redshift errors and survey completeness, and present the surveydata.
| Searching for Embedded Super-Star Clusters in IC 4662, NGC 1705, and NGC 5398
Radio observations of IC 4662, NGC 5398, and NGC 1705 are used incombination with optical images to search for extremely young starclusters that are still embedded in their birth material. Radio datawere obtained at 3 and 6 cm using the Australia Telescope Compact Array,and optical data were retrieved from the Hubble Space Telescope (HST)archive. In IC 4662, three inverted spectrum thermal radio sources andone nonthermal source were detected. The thermal sources have Lymancontinuum fluxes ranging from ~20-200×1049s-1 (the equivalent of ~20-200 O7.5-type stars), modeled coreradii of r<~1 pc, and densitiesne>~103-104 cm-3. The HSTimages of this galaxy indicate a number of optical star clusters thatare <~10 Myr and have masses of ~103-104Msolar. The young optical clusters and radio clusters in IC4662 are spatially exclusive-supporting either large amounts ofextinction in the vicinity of the radio clusters or sequential starformation. No thermal sources are detected in NGC 1705 down to a 3σ level of ~5×1024 ergs s-1Hz-1 (0.17 mJy). At the distance of NGC 1705, the Galacticultracompact H II region complex W49A would have been a ~5 σdetection; therefore, the lack of detections of any thermal sources downto this detection threshold implies that star formation in NGC 1705 hasvery nearly ceased. NGC 5398 hosts an impressive thermal radio sourcethat is associated with the giant H II region Tol 89. This source has aLyman continuum flux of ~4500×1049 s-1 (theequivalent of ~4500 O7.5-type stars). At the distance to Tol 89 and theresolution of these radio data, we are only able to set an upper limiton its radius of r<~90 pc and a lower limit on its mean density ofne>50 cm-3.
| A search for Low Surface Brightness galaxies in the near-infrared. I. Selection of the sample
A sample of about 3800 Low Surface Brightness (LSB) galaxies wasselected using the all-sky near-infrared (J, H and Ks-band)2MASS survey. The selected objects have a mean central surfacebrightness within a 5'' radius around their centre fainter than 18 magarcsec-2 in the Ks band, making them the lowestsurface brightness galaxies detected by 2MASS. A description is given ofthe relevant properties of the 2MASS survey and the LSB galaxy selectionprocedure, as well as of basic photometric properties of the selectedobjects. The latter properties are compared to those of other samples ofgalaxies, of both LSBs and ``classical'' high surface brightness (HSB)objects, which were selected in the optical. The 2MASS LSBs have aBT_c-KT colour which is on average 0.9 mag bluerthan that of HSBs from the NGC. The 2MASS sample does not appear tocontain a significant population of red objects.All tables and Figs. 2a-c are only available in electronic form athttp://www.edpsciences.org
| Searching for Embedded Super Star Clusters in IC4662, NGC1705, and NGC5398
Radio observations of IC4662, NGC5398, and NGC1705 are used incombination with optical images to search for extremely young starclusters which are still embedded in their birth material. Radio datawere obtained at 3cm and 6cm using ATCA, and optical data were obtainedat SSO and retrieved from the HST archive. In IC4662, three invertedspectrum thermal radio sources and one non-thermal source were detected.These sources have Lyman continuum fluxes ranging from ~ 20-200 x1049s-1 (the equivalent of ~ 20-200 O7-typestars), modeled core radii of r < 1pc, and densities ne> 103 - 104cm-3. The HST images ofthis galaxy indicate a number of optical star clusters which are <10Myr which have masses of ~ 103 - 104Msun. The young optical clusters and radio clusters in IC4662are spatially exclusive --- supporting either large amounts ofextinction in the vicinity of the radio clusters or sequential starformation. No thermal sources are detected in NGC1705 down to a 3σlevel of ~ 5 x 1024erg s-1 Hz-1. At thedistance of NGC1705, the Galactic ultracompact HII region complex W49Awould have been a >5σ detection; therefore the lack ofdetections of any thermal sources implies that star formation in NGC1705has very nearly shut off. NGC5398 hosts an extremely impressive thermalradio source which is associated with the giant HII region Tol 89. Thissource has a Lyman continuum flux of ~ 4500 x1049s-1 (the equivalent of ~ 4500 O7-type stars).At the distance to Tololo 89 and the resolution of these radio data, weare only able to put an upper limit on its radius of r ~ 90pc and alower limit on its density of ne > 50cm-3. Wegratefully acknowledge support for this work from the National ScienceFoundation.
| Deep optical imaging and spectroscopy of a sample of Wolf-Rayet galaxies
We present results of narrow-band (Hα and adjacent continuum) andbroad-band (U, B and V) optical CCD imaging together with high- andintermediate-resolution optical spectroscopy for a sample dwarf and/orirregular Wolf-Rayet (WR) galaxies with absolute B magnitudes in therange -14 to -22 mag, taken from the catalogue of Conti (1991). We findthat the recent star formation processes in the galaxies of the sampleare distributed in different knots. These knots are H ii regionsprobably ionized by so-called super star clusters (or aggregates ofthem) found in space observations of WR and interacting galaxies. Acomparative study of the U-B colour and the -W(Hα ) of thedifferent star-forming knots of the galaxies indicates that these twomagnitudes give consistent age estimates. However, the B-V colour givecomparatively greater ages, which can be explained by the presence ofunderlying stellar populations in many of the objects. This is confirmedby the presence of a much more extended and diffuse morphology (in somecases with a disc shape) in broad-band compared to Hα images. Ourstudy has also revealed that a substantial fraction of irregular anddwarf WR galaxies at first classified as isolated objects, may in factbe interacting or merging with other low surface brightness companionsthat escaped detection in previous studies. These interaction processescould be the cause of the triggering of the strong star formation we arenow seeing in many of the objects. The Hα morphology of thegalaxies indicates that the presence of bubble-like and low surfacebrightness filamentary structures is a rather common characteristic ofthese kinds of objects. Spectroscopic observations reported in this andprevious papers confirm the presence of high-velocity asymmetric flowsthat extend to the outer zones in several galaxies. Figures 1--18 areonly available electronically with the On-Line publication athttp://link.springer.de/link/service/00230/
| New catalogue of Wolf-Rayet galaxies and high-excitation extra-galactic HII regions
We present a new compilation of Wolf-Rayet (WR) galaxies andextra-galactic Hii regions showing broad He ii lambda 4686 emissiondrawn from the literature. Relevant information on the presence of otherbroad emission lines ([N i] lambda 5199ii, C iv lambda 5808 and others)from WR stars of WN and WC subtypes, and other existing broad nebularlines is provided. In total we include 139 known WR galaxies. Amongthese, 57 objects show both broad He ii lambda 4686 and C iv lambda 5808features. In addition to the broad (stellar) He ii lambda 4686 emission,a nebular He ii component is well established (suspected) in 44 (54)objects. We find 19 extra-galatic Hii regions without WR detectionsshowing nebular He ii lambda 4686 emission. The present sample can beused for a variety of studies on massive stars, interactions of massivestars with the ISM, stellar populations, starburst galaxies etc. Thedata is accessible electronically and will be updated periodically. Thecatalogue is available at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Ultraviolet spectral properties of magellanic and non-magellanic irregulars, H BT II and starburst galaxies
This paper presents the results of a stellar population analysisperformed on nearby (V_R<=5 000 km s^{-1}) star-forming galaxies,comprising magellanic and non-magellanic irregulars, H Ii and starburstgalaxies observed with the IUE satellite. Before any comparison ofgalaxy spectra, we have formed subsets according to absolute magnitudeand morphological classification. Subsequently, we have coadded thespectra within each subset into groups of similar spectral properties inthe UV. As a consequence, high signal-to-noise ratio templates have beenobtained, and information on spectral features can now be extracted andanalysed. Seven groups resulted from this procedure: the magellanicirregulars (including H Ii galaxies) produced two different bluespectral groups; the non-magellanic irregulars could be grouped into twospectral groups with rather peculiar properties; and the luminousstarbursts produced one flat and two blue template spectra. Theirstellar populations are analysed by means of a population synthesisalgorithm based on star cluster spectral components. The syntheticspectra reproduce the observed ones successfully (except thenon-magellanic irregular groups) both in terms of continuum distributionand spectral features. The synthesis flux fractions of different agegroups were transformed into mass fractions, allowing inferences on thestar formation histories. Young stellar populations (age <500 Myrs)are the main flux contributors; in a few cases the intermediate agepopulation (age~1 M_B-2 Myrs) is important, while the old bulgepopulation contributes at most with ~2 % of the lambda2646 Angstromsflux in the case of starburst galaxies, and is negligible in themagellanic irregulars. We also study the reddening values and theextinction law: an SMC-like extinction law is appropriate for all cases.Based upon data collected with the International Ultraviolet Explorer(IUE) Satellite, supported by NASA, SERC and ESA.
| Populations of WC and WN stars in Wolf-Rayet galaxies
We report the detection of WC stars in five Wolf-Rayet (W-R) galaxies:He 2-10, NGC 3049, NGC 3125, NGC 5253 and Tol 89. The faint broad C ivlambda5808 line requires sufficiently high S/N (>~ 40) to be detectedexplaining the non-detection of this WC feature in previousobservations. From the measurement of W-R emission lines (N iiilambda4640+C iii lambda4650, He ii lambda4686, and C iv lambda5808), weconclude that all W-R regions contain a mixed population of WNL, andearly WC stars. The exception is the high-metallicity region NGC 3049where late WC stars prevail. A spatial offset between the multiple peaksof the nebular emission and the stellar light in He 2-10 and Tol 89 isobserved. These nebular emission structures are likely due to theexistence of bubbles and loops, owing to the injection of mechanicalenergy in the ISM through the W-R winds and/or supernovae. Due to agedifferences and likely smaller energy deposition the structures aroundthe W-R regions are possibly smaller than the ones predominantlyenergized by SNe. The spatial distribution of W-R stars closely followsthe stellar continuum with no significant distinction between WN and WCstars. From the luminosity of the W-R signatures we have estimated theabsolute number of W-R stars of the different subtypes. The WC/WN numberratios have typical values between 0.2-0.4, and show no clear trend withmetallicity. For low-metallicity objects (Z ~ 1/5 Zsun),these values are larger than the observed WC/WN ratios in Local Groupobjects, but are compatible with expectations for star forming eventswith short duration if stellar evolution models with high mass loss areused. We derive ages for the starburst regions in the range of 3 to 6Myr and confirm that the burst duration must not exceed ~ 2-4 Myr toaccount for the high population of W-R stars observed in starburstregions, even if emission line stars similar to those observed in R136and NGC 3603 are common in starbursts. Within the uncertainties themajority of the observed quantities is reasonably reproduced by modelswith a Salpeter IMF. Although some W-R lines in few regions are strongerthan predicted by the models no clear case requiring a significantlyflatter IMF is found. IMF slopes much steeper than Salpeter may,however, not be compatible with our data. Based on observations obtainedat the European Southern Observatory (ESO), Chile
| 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.
| The I band Tully-Fisher relation for cluster galaxies: data presentation.
Observational parameters which can be used for redshift-independentdistance determination using the Tully-Fisher (TF) technique are givenfor \ntot spiral galaxies in the fields of 24 clusters or groups. I bandphotometry for the full sample was either obtained by us or compiledfrom published literature. Rotational velocities are derived either from21 cm spectra or optical emission line long-slit spectra, and convertedto a homogeneous scale. In addition to presenting the data, a discussionof the various sources of error on TF parameters is introduced, and thecriteria for the assignment of membership to each cluster are given.
| Parameters of 2447 Southern Spiral Galaxies for Use in the Tully-Fisher Relation
I-band luminosities, rotational velocities, and redshifts of 1092 spiralgalaxies have been measured by CCD photometry and Hα spectroscopyusing the 1 m and 2.3 m telescopes at Siding Spring Observatory,respectively. The results are tabulated. Luminosity profiles andHα rotation curves are given for the galaxies. When these resultsare combined with similar data for 1355 spiral galaxies publishedpreviously (Mathewson, Ford, & Buchhorn, hereafter Paper I), itprovides a large, uniform, and unique data set with which to measure,via the Tully-Fisher relation, the peculiar velocities of galaxies inthe local universe to a distance of 11,000 km s^-1^ (Mathewson &Ford). Taking advantage of the opportunity for publishing this data inmachine-readable form, in the CD-ROM, we have also included similar datafor the 1355 galaxies in Paper I.
| The Catalog of Southern Ringed Galaxies
The Catalog of Southern Ringed Galaxies (CSRG) is a comprehensivecompilation of diameters, axis ratios, relative bar position angles, andmorphologies of inner and outer rings, pseudorings, and lenses in 3692galaxies south of declination -17 deg. The purpose of the catalog is toevaluate the idea that these ring phenomena are related to orbitalresonances with a bar or oval in galaxy potentials. The catalog is basedon visual inspection of most of the 606 fields of the Science ResearchCouncil (SRC) IIIa-J southern sky survey, with the ESO-B, ESO-R, andPalomar Sky surveys used as auxiliaries when needed for overexposed coreregions. The catalog is most complete for SRC fields 1-303 (mostly southof declination -42 deg). In addition to ringed galaxies, a list of 859mostly nonringed galaxies intended for comparison with other catalogs isprovided. Other findings from the CSRG that are not based on statisticsare the identification of intrinsic bar/ring misalignment; bars whichunderfill inner rings; dimpling of R'1pseudorings; pointy, rectangular, or hexagonal inner or outer ringshapes; a peculiar polar-ring-related system; and other extreme examplesof spiral structure and ring morphology.
| A Preliminary Classification Scheme for the Central Regions of Late-Type Galaxies
The large-scale prints in The Carnegie Atlas of Galaxies have been usedto formulate a classification scheme for the central regions oflate-type galaxies. Systems that exhibit small bright central bulges ordisks (type CB) are found to be of earlier Hubble type and of higherluminosity than galaxies that do not contain nuclei (type NN). Galaxiescontaining nuclear bars, or exhibiting central regions that are resolvedinto individual stars and knots, and galaxies with semistellar nuclei,are seen to have characteristics that are intermediate between those oftypes CB and NN. The presence or absence of a nucleus appears to be auseful criterion for distinguishing between spiral galaxies andmagellanic irregulars.
| Quantitative Morphology of Bars in Spiral Galaxies
As suggested by numerical simulations, the axis ratio of the bar is afundamental parameter to describe the dynamical evolution of a barredgalaxy. In a first-order approximation considering bars as ellipticalfeatures, visual measurements of bar axis ratios and lengths of 136spiral galaxies were performed on photographs of good linear scale.Despite the limitations affecting such measurements, morphologicalproperties of bars in spirals along the Hubble sequence as well as therelationship between the bar axis ratio and nuclear star formationactivity are studied. It is found that the relative length of bars inearly-type galaxies is, on average, about a factor of 3 larger than thelength observed in late-type spirals. Also, a relation between barlengths and bulge diameters is observed for both early-type andlate-type spirals, confirming results from previous works. Furthermore,although the number of objects is small, there is an apparentcorrelation between the presence of nuclear star formation activity andthe bar axis ratio: about 71% of the starburst galaxies included in thesample have a strong bar (b/a < 0.6). The introduction of thesequantitative parameters in galaxy classification schemes is discussed.
| On the size and formation mechanism of the largest star-forming complexes in spiral and irregular galaxies
The average diameters of the largest star complexes in most of thespiral and irregular galaxies in the Sandage and Bedke Atlas of Galaxieswere measured from the Atlas photographs. The complex diametersDc correlate with galaxy magnitude as Dc = 0.18 -0.14MB, which has about the same slope as the correlation forthe largest H II regions studied by Kennicutt. There is no obviouscorrelation between Dc and either Hubble type or spiral armclass at a given magnitude. The variation of Dc withMB closely matches the expected variation in thecharacteristic length of the gaseous gravitational instabilityconsidering that the rotation curve varies with MB and thatthe stability parameter Q is about 1 in the outer regions of the disk.This match corresponds to an effective velocity dispersion of 6.1 km/sthat is about the same for all spiral and irregular galaxies.
| Mean galaxy luminosity classifications
To prepare a catalog of weighted means on the classification system ofvan den Bergh, we have combined eight independent lists of luminosityclass estimates, L. Luminosity class values from each set weretransformed to the standard system and weighted according to the errorsderived through a statistical comparison of L differences betweencatalog pairs. Relations were derived for predicting accidental errorsassociated with galaxy diameter and inclination. In addition, we presentformulas for correcting systematic errors associated with diameter andinclination. Finally, we tabulate a high weight subsample of the meanluminosity classes usable as standards. Most values are tabulated in theThird Reference Catalog of Bright Galaxies.
| A southern sky survey of the peculiar velocities of 1355 spiral galaxies
The paper presents data from photometric and spectroscopic observationsof 1355 southern spiral galaxies and uses them to determine theirdistances and peculiar velocities via the Tully-Fisher (TF) relation.I-band CCD surface photometry was carried out using the 1-m and 3.9-mtelescopes at Siding Spring Observatory. H-alpha rotation curves for 965galaxies and 551 H I profiles are presented. The physical parameters,photometric and velocity data, distances, and peculiar velocities of thegalaxies are presented in tabular form. The mean distance, systemicvelocity, and average peculiar velocity of 24 clusters in the sample aregiven. TF diagrams are presented for each cluster.
| I-band CCD surface photometry of spiral galaxies in 16 nearby clusters
Results of I-band CCD surface photometry for 284 spiral galaxies in 16clusters in the redshift range from 3000 to 11,000 km/s are presented.Various effects on surface photometry are discussed, and the relevantcorrections are outlined.
| The supergalactic plane redshift survey
Redshift measurements, about 1000 of which are new, are presented for1314 galaxies in a survey toward the apex of the large-scale streamingflow for ellipticals. The velocity histogram shows that the excess ingalaxy number counts in this area is due to a substantial concentrationof galaxies with discrete peaks at V about 3000 km/s and V about 4500km/s. After correction for the sampling function, the centroid of thedensity distribution is found to be near V about 4500 km/s.Normalization to the more extensive SSRS survey, which was selected bythe same criteria, shows that the region studied contains a considerableoverdensity of galaxies from 2000 to 6000 km/s. This result is in goodagreement with the 'great attractor' model suggested by Lynden-Bell etal. (1988) which attributes the peculiar motions of elliptical galaxiesover a large region of space to an extensive mass overdensity whichincludes the Hydra-Centaurus and Pavo-Indus superclusters. The centroidof the density enhancement is also consistent with new data by Dresslerand Faber (1990) of peculiar motions of elliptical and spiral galaxies,both of which show a zero crossing of the Hubble line at approximately4500-5000 km/s.
| Wolf-Rayet galaxies - an introduction and a catalog
The first catalog of Wolf-Rayet galaxies is presented and discussed.These are a subset of emission-line galaxies in which a broad 4686 He IIemission feature due to WR stars is observed in the integrated spectrum.About one-quarter of these galaxies also show a broad line at 4640 A dueto N III which is prominent in the latest type WN stars. The number ofLyman-continuum photons emitted by WR galaxies scales roughly with theirintegrated magnitudes, similar to emission-line galaxies. Both WRgalaxies and emission-line galaxies form an overlap with and luminousextension of giant H II regions in these properties. The fraction of WRstars to O stars in some of these galaxies appears to be large, which ifconfirmed by more detailed quantitative work would imply that theinitial mass function was relatively 'flat'.
| Studies of nearby poor clusters - A3574 and S753
Photometric and spectroscopic data are presented for two clusters, A3574and S753, belonging to the Centaurus concentration of galaxies. Themasses of the clusters are estimated at 1.5 x 10 to the 14th solarmasses; no evidence of substructure has been detected in either cluster.The solution of a two-body linear orbit suggests that the clusters donot form a bound system, although the result is marginal.
| A spectrophotometric catalogue of HII galaxies
A spectrophotometric catalog is presented of 425 emission-line galaxiesdiscovered in objective prism surveys for which redshifts, emission-lineintensities, equivalent widths, and absolute fluxes are derived. Thevast majority of objects in the catalog are H II region-like galaxies (HII galaxies). In more than 80 H II galaxies the forbidden line O III4363 was measured with accuracy good enough to permit precise electrontemperature determinations. The observational parameters that define theproperties of H II galaxies as a class are characterized and discussed.
| Revised supernova rates in Shapley-Ames galaxies
Observations of 855 Shapley Ames galaxies made from November 1, 1980 toOctober 31, 1988, together with improved supernova luminosities, havebeen used to derive the frequency of supernovae of different types, andthe results are presented in tables. From a uniform database of 24supernovae discovered, the following SN rates are found, expressed in SNper century per 10 to the 10th L(B)(solar): SN Ia, 0.3; SN Ib, 0.3; andSN II, 1.0. The present data confirm the relatively high frequency of SNII in late-type galaxies that has been found by many previousinvestigators.
| The detection of Wolf-Rayet stars in a very powerful far-infrared galaxy - Direct evidence for a starburst
Spectra covering the wavelength range 4476-7610 A are presented for thepowerful far-infrared galaxy IRAS 01003-2238. The broad emission bandcentered at a rest wavelength of roughly 4660 A, and other broad weakerfeatures are interpreted, as arising from the combined effect ofapproximately 100,000 late Wolf-Rayet stars of the WN subtype. Thisrepresents perhaps the most direct evidence to date for the presence ofa large number of hot massive stars in the nucleus of a very powerfulfar-infrared galaxy. The high number of Wolf-Rayet stars in relation tothe number of O-type stars may be interpreted as arguing againstcontinuous steady state star formation in 01003-2238, in favor of arecent burst of star formation occurring approximately 100 million yrsago.
| A new supergiant H II region in galaxy HS 1227 + 4758
The discovery of a supergiant H II region (H2R) of luminosity greaterthan or equal to that of H2R-like dwarf galaxies at about 8 pc fromnucleus of HS 1227 + 4758 is reported. Data obtained at Calar Altoobservatory (objective-prism plates made with the 80-cm Schmidttelescope and long-slit spectra made with the Boller and Chivensspectrograph and CCD detector on the 3.5-m telescope) are presented intables, spectra, and sample images and characterized in detail. Thesupergiant H2R is found to have redshift z = 0.025, H-beta luminosity 1x 10 to the 40th erg/s, emission lines 2-3 times brighter than theparent-galaxy nucleus, and N and O abundances 10 and 20 times lower(respectively) than solar values and 3 times lower than in theparent-galaxy nucleus. It is suggested that the present system may bethe result of a merger between a galaxy and an H2R-like galaxy, asproposed by Arkhipova et al. (1987) for MCG 1-6-57.
| Latel-type galaxies - Star formation rates
A simple method for determining star formation rates (SFRs) in externalgalaxies is presented which is based on surface photometry in one coloronly. The intensity distributions of 59 late-type spiral and irregulargalaxies were divided into two components each, one containing the lightof the smoothly distributed old disk population, the other containingthe light of the clumped extreme Population I. This makes it possible todetermine the ratios of the 'present' SFRs (for stars with ages lessthan 50 million yr) to the average SFRs. Among other results, this ratiois found to be higher in asymmetric galaxies than in symmetric ones.
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