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The environment of young massive clusters
We observed a sample of Blue Dwarf Galaxies in the Ks (2.2 μm) andLÕ (3.7 μm) IR bands at the ESO VLT with ISAAC. Thepurpose of the observations was to study the population of young massiveclusters and the conditions under which they are formed. The samplegalaxies included: Tol 1924-416, Tol 35, Pox 36, UM 462, He 2-10, II Zw40, Tol 3, NGC 1705, NGC 5408, IC 4662, NGC 5253. They were selected tohave evidence for star formation and firm detection by IRAS. Allgalaxies observed turned to be very rich of young massive clusters inKs. Only few clusters, about 8%, showed counterparts in LÕ.Most L' sources can be associated to radio thermal sources, with theonly exception of the NGC 1705's one. For two galaxies, NGC 5408 and IC4662, we derived the cluster luminosity functions finding themconsistent with a power law of index about -2. We compared the numbersand luminosities of the clusters with the star formation rate of thehost galaxy and could not find any evidence of a relation.
| Stellar clusters in dwarf galaxies
We present new observations in the Ks (2.2 μm) and L' (3.7μm) infrared bands of a sample of blue dwarf galaxies with the largeraim of studying the population of massive stellar clusters, theoccurrence of dust-embedded stellar clusters, and their properties. AllKs images show a rich population of clusters, but only asmall fraction of them is bright in L'. Most L' sources have radiocounterparts. We derived the luminosity function in Ks forthe galaxies IC 4661 and NGC 5408, finding both to be consistent withthose of similar galaxies. We also compared the number of clusters andtheir luminosities with the star-formation rate of the host galaxies andfound no compelling evidence of correlation. We conclude that youngclusters and embedded clusters are a common feature of blue dwarfgalaxies and possibly of galaxies in general, we suggest that theiroccurrence is due to purely statistical effects rather than a phenomenonrelated to specific physical conditions. In this sense we expect theseobjects to be abundant at high red-shift.
| Comparison of Star Clusters With and Without Wolf-Rayet Stars in Wolf-Rayet Galaxies
We compare the properties of young star clusters with and withoutWolf-Rayet (W-R) stars in W-R galaxies using optical, near-infraredimagery and optical spectroscopy. Our work identifies the clusters withW-R stars in these galaxies for the first time. With this information,comparisons of clusters with and without W-R stars are now possible,enabling us to understand the chemical and morphological impact ofmassive stars on their environment and to constrain the parameters formodeling these systems. We find that clusters with W-R stars (W-Rclusters) are systematically younger, bluer clusters. Knowing this agedifference between the two cluster sets, we use an evolutionary scenarioto interpret their other properties. Young clusters, typically W-Rclusters, have a Strömgren sphere-like gas configuration. They alsotend to have H-K colors redder than those of theoretical models. Weinterpret the H-K excess as a combination of thermal emission from hotdust, nebular emission, and molecular emission. Older clusters,typically clusters without W-R stars, have ionized gas in a superbubbleconfiguration caused by the prolonged influence of stellar winds andsupernovae. The H-K excess is generally absent for these clusters. Thenitrogen-to-oxygen abundance ratio (N/O) does not appear to increase asa function of age over the first 10 Myr. Systems without W-R stars doappear to have a significant, elevated N/O over systems with W-R starsin the metallicity range 12+log(O/H)=7.7-7.9. For the entire metallicityrange in our sample, this finding is only marginally significant. Weconcur with previous studies, which find no correlation between thesulfur-to-oxygen abundance ratio and metallicity.
| Palomar/Las Campanas Imaging Atlas of Blue Compact Dwarf Galaxies. II. Surface Photometry and the Properties of the Underlying Stellar Population
We present the results from an analysis of surface photometry of B, R,and Hα images of a total of 114 nearby galaxies(vhelio<4000 km s-1) drawn from the Palomar/LasCampanas Imaging Atlas of blue compact dwarf (BCD) galaxies. Surfacebrightness and color profiles for the complete sample have beenobtained. We determine the exponential and Sérsic profiles thatbest fit the surface brightness distribution of the underlying stellarpopulation detected in these galaxies. We also compute the (B-R) colorand total absolute magnitude of the underlying stellar population andcompared them to the integrated properties of the galaxies in thesample. Our analysis shows that the (B-R) color of the underlyingpopulation is systematically redder than the integrated color, except inthose galaxies where the integrated colors are strongly contaminated byline and nebular-continuum emission. We also find that galaxies withrelatively red underlying stellar populations [typically (B-R)>=1mag] show structural properties compatible with those of dwarfelliptical galaxies (i.e., a smooth light distribution, fainterextrapolated central surface brightness, and larger scale lengths thanBCD galaxies with blue underlying stellar populations). At least ~15% ofthe galaxies in the sample are compatible with being dwarf elliptical(dE) galaxies experiencing a burst of star formation. For the remainingBCD galaxies in the sample we do not find any correlation between therecent star formation activity and their structural differences withrespect to other types of dwarf galaxies.
| Metal Abundances of KISS Galaxies. III. Nebular Abundances for Fourteen Galaxies and the Luminosity-Metallicity Relationship for H II Galaxies
We report results from the third in a series of nebular abundancestudies of emission-line galaxies from the KPNO InternationalSpectroscopic Survey (KISS). Galaxies with coarse metallicity estimatesof 12+log(O/H) less than 8.2 dex were selected for observation. Spectraof 14 galaxies, which cover the full optical region from [O II]λλ3727, 3729 to beyond [S II] λλ6717, 6731,are presented, and abundance ratios of N, O, Ne, S, and Ar are computed.The auroral [O III] λ4363 line is detected in all 14 galaxies.Oxygen abundances determined through the direct electron temperature(Te) method confirm that the sample is metal-poor with7.61<=12+log(O/H)<=8.32. By using these abundances in conjunctionwith other Te-based measurements from the literature, wedemonstrate that H II galaxies and more quiescent dwarf irregulargalaxies follow similar metallicity-luminosity (L-Z) relationships. Theprimary difference is a zero-point shift between the correlations suchthat H II galaxies are brighter by an average of 0.8 B magnitudes at agiven metallicity. This offset can be used as evidence to argue thatlow-luminosity H II galaxies typically undergo factor of 2 luminosityenhancements, and starbursts that elevate the luminosities of their hostgalaxies by 2-3 mag are not as common. We also demonstrate that theinclusion of interacting galaxies can increase the scatter in the L-Zrelation and may force the observed correlation toward lowermetallicities and/or larger luminosities. This must be taken intoaccount when attempting to infer metal abundance evolution by comparinglocal L-Z relations with ones based on higher redshift samples, sincethe fraction of interacting galaxies should increase with look-backtime.
| 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.
| Palomar/Las Campanas Imaging Atlas of Blue Compact Dwarf Galaxies. I. Images and Integrated Photometry
We present B, R, and Hα images for a total of 114 nearby galaxies(vhelio<4000 km s-1) that, with exception ofnine objects, are classified as blue compact dwarfs (BCDs). BRintegrated magnitudes, Hα fluxes and Hα equivalent widthsfor all the objects in the sample are presented. A new set ofquantitative, observational criteria for a galaxy to be classified as aBCD is proposed. These criteria include a limit on the K-band luminosity(i.e., stellar mass; MK>-21 mag), peak surface brightness(μB,peak<22 mag arcsec-2), and color at thepeak surface brightness(μB,peak-μR,peak<~1). Hα emissionis detected in all but three sample galaxies. Typical color, absolutemagnitude, and Hα luminosity are (B-R)=0.7+/-0.3 mag,MB=-16.1+/-1.4 mag, and log (LHα)=40.0+/-0.6(ergs s-1). Galaxies morphologically classified as nE and iEBCDs within our sample show lower Hα equivalent widths and reddercolors, on average, than the iI- and i0-type BCDs. For most of thegalaxies the presence of an evolved stellar population is required toexplain their observed properties; only the most metal-poor BCDs (e.g.,I Zw 18, Tol 65) are still compatible with a pure, young burst. Theflux-calibrated and WCS-compliant images in this Atlas are individuallyavailable through the NASA/IPAC Extragalactic Database (NED) imageserver and collectively through a dedicated Web page.
| New light on the search for low-metallicity galaxies - I. The N2 calibrator
We present a simple metallicity estimator based on the logarithmic [Nii]ratio, hereafter N2, which we envisage will become very useful forranking galaxies in a metallicity sequence from redshift survey-qualitydata even for moderately low spectral resolution. We have calibrated theN2 estimator using a compilation of Hii galaxies having accurate oxygenabundances, plus photoionization models covering a wide range ofabundances. The comparison of models and observations indicates thatboth primary and secondary nitrogen are important for the relevant rangeof metallicities. The N2 estimator follows a linear relation withlog(O/H) that holds for the whole abundance range covered by the sample,from approximately to twice the Solar value . We suggest that the ([Sii]ratio (hereafter S2) can also be used as a rough metallicity indicator.Because of its large scatter the S2 estimator will be useful only insystems with very low metallicity, where [Nii] λ 6584 is notdetected or in low-resolution spectra where [Nii] λ 6584 isblended with Hα .
| Near-infrared properties of Blue Compact Dwarf Galaxies: The link between solar and low metallicity
We have obtained near-infrared images and spectra of three blue compactdwarf galaxies of intermediate sub-solar metallicity Tol 35, Tol 3 andUM 462. This work is part of a larger project aimed to study the starformation and the stellar populations of low metallicity galaxies in thenear-infrared. In this frame work galaxies of intermediate metallicityrepresent an important step in understanding the most extreme casesfilling the gap between solar and very low metallicity galaxies. We haveobserved HII region like spectra in all three galaxies; in all cases thestar formation episodes are only a few Myr old. Consistently with ayoung age our spectra show no evidence for stellar absorption featurestypical of supergiants, nor of [FeII] emission typical of supernovae.The K-band gas fraction ranges from 20 to 40% showing that gas emissioncan significantly contaminate broadband near-infrared colors in youngmetal-poor starbursts. We have detected molecular hydrogen in emissionin all three objects. All sources show bright knots superimposed on alower surface brighness envelope. The knots are identified with SuperStar Clusters; six of them are present in UM 462. In all galaxies wedetect the presence of an old stellar population. Based on observationsobtained at the ESO-NTT in La Silla.
| Population synthesis of Hii galaxies
We study the stellar population of galaxies with active star formation,determining ages of the stellar components by means of spectralpopulation synthesis of their absorption spectra. The data consist ofoptical spectra of 185 nearby (z<=0.075) emission-line galaxies. Theyare mostly Hii galaxies, but we also include some starbursts and Seyfert2s, for comparison purposes. They were grouped into 19 highsignal-to-noise ratio template spectra, according to their continuumdistribution, absorption- and emission-line characteristics. Thetemplates were then synthesized with a star cluster spectral base. Thesynthesis results indicate that Hii galaxies are typically age-compositestellar systems, presenting important contributions from generations upto as old as 500Myr. We detect a significant contribution of populationswith ages older than 1Gyr in two groups of Hii galaxies. The agedistributions of stellar populations among starbursts can varyconsiderably despite similarities in the emission-line spectra. In thecase of Seyfert 2 groups we obtain important contributions from the oldpopulation, consistent with a bulge. From the diversity of starformation histories, we conclude that typical Hii galaxies in the localUniverse are not systems presently forming their first stellargeneration.
| Nearby Optical Galaxies: Selection of the Sample and Identification of Groups
In this paper we describe the Nearby Optical Galaxy (NOG) sample, whichis a complete, distance-limited (cz<=6000 km s-1) andmagnitude-limited (B<=14) sample of ~7000 optical galaxies. Thesample covers 2/3 (8.27 sr) of the sky (|b|>20deg) andappears to have a good completeness in redshift (97%). We select thesample on the basis of homogenized corrected total blue magnitudes inorder to minimize systematic effects in galaxy sampling. We identify thegroups in this sample by means of both the hierarchical and thepercolation ``friends-of-friends'' methods. The resulting catalogs ofloose groups appear to be similar and are among the largest catalogs ofgroups currently available. Most of the NOG galaxies (~60%) are found tobe members of galaxy pairs (~580 pairs for a total of ~15% of objects)or groups with at least three members (~500 groups for a total of ~45%of objects). About 40% of galaxies are left ungrouped (field galaxies).We illustrate the main features of the NOG galaxy distribution. Comparedto previous optical and IRAS galaxy samples, the NOG provides a densersampling of the galaxy distribution in the nearby universe. Given itslarge sky coverage, the identification of groups, and its high-densitysampling, the NOG is suited to the analysis of the galaxy density fieldof the nearby universe, especially on small scales.
| High-Resolution Radio Maps of Wolf-Rayet Galaxies: Optically Thick H II Regions?
We present 20, 6, 3.6, and 2 cm Very Large Array maps and continuum-freeHα images of nine Wolf-Rayet galaxies. The radio maps were madewith high spatial resolution to reject extended emission and toemphasize the star formation regions. The ratio of Hα to radio isat least a factor of 10 lower than predicted, indicating that the radioemission is from highly obscured sources. We map the radio spectralindex, α (Sν~να), across eachgalaxy. In all the sample galaxies except one, the radio spectrum ismuch flatter than in spiral starburst galaxies, suggesting thatfree-free emission is more dominant in the dwarfs and that these arevery young starbursts that have produced few supernovae. In many of thegalaxies, there are regions where the spectrum rises from 6 to 2 cm.This requires that the radio emission be optically thick at wavelengthsas short as 2 cm. In these optically thick regions, the emissionmeasure, electron density, and ionizing fluxes must be very high, andthey are probably the youngest parts of the starburst. The deducedionization of these sources implies stellar content of hundreds to manythousands of O stars, which means that they may be responsible for asignificant fraction of the total infrared luminosities of the galaxies.We discuss what these sources imply for the history and evolution of thestarburst in each galaxy. Wise Observatory preprint 99/2.
| 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/
| Spectral classification of emission-line galaxies
The main goal of this work is to further investigate the classificationof emission-line galaxies from the ``Spectrophotometric Catalogue of HII galaxies'' by Terlevich et al. (1991) in a homogeneous and objectiveway, using the three line-ratio diagrams, called diagnostic diagrams, ofVeilleux & Osterbrock (1987). On the basis of the resultingcatalogue, we critically discuss the classification methods in theoptical range. In particular we compare our classification scheme to theone done by Rola et al. (1997) which is efficient for the classificationof redshifted galaxies. We also propose a new diagnostic diagraminvolving the known intensity ratio R23=([O II],l 3727+[OIII] l 4959+{[O III] l 5007)/Hb which appears to be a very goodcriterion allowing to discriminate the Seyfert 2 from H ii galaxies. Therevised catalogue including 314 narrow-emission-line galaxies contains HII galaxies, Seyfert 2 galaxies, Low Ionization Nuclear Emission-LineRegions (hereafter LINERs) galaxies and some particular types ofgalaxies with the most intriguing ones, called ``ambiguous'', due to theambiguity of their location in the diagnostic diagrams. These galaxiesappear as H II galaxies and as active galactic nuclei (hereafter AGNs)in different diagrams of Veilleux & Osterbrock and constitutecertainly a sample of particularly interesting candidates for a thoroughstudy of connections between starbursts and AGNs. Available inelectronic form only via anonymous ftp 130.79.128.5 orhttp://cdsweb.u-strasbg.fr/Abstract.html
| On Measuring Nebular Chemical Abundances in Distant Galaxies Using Global Emission-Line Spectra
The advent of 8-10 m class telescopes enables direct measurement of thechemical properties in the ionized gas of cosmologically distantgalaxies with the same nebular analysis techniques used in local H IIregions. We show that spatially unresolved (i.e., global) emission-linespectra can reliably indicate the chemical properties of distantstar-forming galaxies. However, standard nebular chemical abundancemeasurement methods (those with a measured electron temperature from [OIII] lambda4363) may be subject to small systematic errors when theobserved volume includes a mixture of gas with diverse temperatures,ionization parameters, and metallicities. To characterize thesesystematic effects, we compare physical conditions derived fromspectroscopy of individual H II regions with results from global galaxyspectroscopy. We consider both low-mass, metal-poor galaxies withuniform abundances and larger galaxies with internal chemical gradients.For low-mass galaxies, standard chemical analyses using global spectraproduce small systematic errors in that the derived electrontemperatures are 1000-3000 K too high due to nonuniform electrontemperatures and large variations in the ionization parameter. As aresult, the oxygen abundances derived from direct measurements of theelectron temperatures are too low, but it is possible to compensate forthis effect by applying a correction of Delta(O/H)<=+0.1 dex to theoxygen abundances derived from global spectra. For more massivemetal-rich galaxies like local spiral galaxies, direct measurements ofelectron temperatures are seldom possible from global spectra.Well-established empirical calibrations using strong-line ratios canserve as reliable (+/-0.2 dex) indicators of the overall systemic oxygenabundance even when the signal to noise of the Hβ and [O III]emission lines is as low as 8:1. We present prescriptions, directedtoward high-redshift observers, for using global emission-line spectrato trace the chemical properties of star-forming galaxies in the distantuniverse.
| POX 4 and Tol 35: Two Peculiar Wolf-Rayet Dwarf Galaxies
We present results of narrowband (Hα and adjacent continuum) andbroadband (U, B, and V) optical CCD imaging together withhigh-resolution Hα spectroscopy of the blue compact Wolf-Rayetdwarf galaxies POX 4 and Tol 35. POX 4 has a fainter, irregular, anddiffuse companion located 20.5" (4.7 kpc) along the minor axis of thegalaxy, which is visible also in the Hα emission. The differencein recession velocity between the galaxy and the companion is about 130km s-1. The observational results lead us to propose that POX4 could be interpreted as a low-mass ring galaxy, produced by a head-onintrusion of the fainter companion. Regarding the other object, aspectrum taken along the major axis of Tol 35 shows the coexistence ofsystems of motion with a velocity difference of about 50 kms-1. Moreover, the deep continuum-subtracted Hα imageof the galaxy shows very faint features that resemble the beginning ofcrossed tidal tails or gaseous filaments powered by the mechanicalaction of the young stellar population. In this sense, Tol 35 could beinterpreted either as an object in an intermediate-stage merging processbetween two gas-rich dwarf galaxies or as an object suffering the effectof a galactic wind.
| 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
| The interacting Wolf-Rayet galaxy MKN 8
We present results of narrow-band and broad-band optical CCD imagingtogether with intermediate-resolution spectroscopy of the Wolf-Rayetgalaxy Mkn 8. Analysis of the morphology and kinematics of the objectindicates that the strong star formation episode we are witnessing inMkn 8 is the product of the interaction of two (or three) disk galaxies.The chemical abundances and abundance ratios measured in the brightestknots suggest that the interacting galaxies are chemically evolvedgas-rich objects, perhaps late-type spirals.
| A Comparison of the Intrinsic Shapes of Two Different Types of Dwarf Galaxies: Blue Compact Dwarfs and Dwarf Ellipticals
We measure the apparent shapes for a sample of 62 blue compact dwarfgalaxies (BCDs) and compare them with the apparent shapes for a sampleof 80 dwarf elliptical galaxies (dEs). The BCDs are flatter, on average,than the dEs, but the difference is only marginally significant. We thenuse both nonparametric and parametric techniques to determine possibledistributions of intrinsic shapes for the BCDs. The hypothesis that BCDsare oblate spheroids can be ruled out with a high confidence level(>99%), but the hypothesis that they are prolate spheroids cannot beexcluded. The apparent shapes of BCDs are totally consistent with thehypothesis that they are triaxial ellipsoids. If the intrinsic axisratios beta and gamma are distributed according to a Gaussian with meansbeta 0 and gamma 0 and standard deviation sigma , we find that thebest-fitting distribution for BCDs has ( beta 0, gamma 0, sigma ) =(0.66, 0.55, 0.16), while that for dEs has ( beta 0, gamma 0, sigma ) =(0.85, 0.64, 0.24). Our results are consistent with the hypothesis thatBCDs have a close evolutionary relation with dEs.
| The Marseille Schmidt survey. I. Data on 92 emission line objects in two fields
We present data from a moderately deep spectroscopic Schmidt survey(B_lim = 17.5) of ``active galaxies'' selected by the presence ofemission lines in their spectra and/or their UV excess. The redshift,magnitudes, color and diameter reduction methods have been discussed ina previous paper. Here we explain the emission line equivalent widthdetermination method. 92 emission line objects have been found in twoadjacent fields (approximately 50 deg(2) ) in the direction of thesouthern extension of the Virgo cluster. We give a catalog containingpositions, photographic R and B magnitudes, U{- }R colors, effectivediameters, redshifts, equivalent widths and intensity ratios of the[OIII]<~mbda<~mbda 4959,5007, H_beta and [OII]<~mbda 3727emission lines. On these fields, we evaluate the completeness limit ofthe survey at a pseudo B magnitude value of 15.7. A more elaborateastrophysical analysis will appear in a forthcoming paper. The table isalso available in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html} for active star-forminggalaxies. Finding charts, including information on star formationlocation is available in electronic form via http://www.edpsciences.com
| 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.
| Broad Low-Intensity Wings in the Emission-Line Profiles of Four Wolf-Rayet Galaxies
High-resolution spectroscopic observations have been obtained for theWolf-Rayet galaxies He 2-10, II Zw 40, POX 4, and Tol 35. Severalsubregions have been selected in each slit position in order toinvestigate possible spatial variations in the line profiles, radialvelocities, and ionization conditions of the gas. The most remarkablefeature of the spectra is the presence of asymmetric broad low-intensitywings in the profiles of the brightest emission lines. These spectralfeatures are detected farther out from the star-forming knots, showinglinear dimensions between 300 pc and 4.1 kpc. The maximum expansionvelocity measured for this gas is between 120 and 340 km s-1 and appearsto be quite constant along the slit for all the objects. Additionalgeneral properties of the spectra are (1) the quoted emission-lineratios are similar in the narrow and broad components, (2) no systematicdifferences of the behavior of the broad and narrow components have beenfound along the major and minor axis of the galaxies, and (3) thespatial distribution of the ionized gas is peaked centrally. Differentmechanisms capable of producing the observed broad spectral features arediscussed: cloud-cloud collisions in virialized gas, "academic"superbubbles, champagne flows, and superbubble blowout. It is concludedthat superbubble blowout expanding over a cloudy medium can explain theobservational properties in a reasonable manner.
| Recent progress in the research of big bang nucleosynthesis.
Not Available
| H II Galaxies versus Photoionization Models for Evolving Starbursts
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJS..107..661S&db_key=AST
| Elemental Abundance Variations and Chemical Enrichment from Massive Stars in Starbursts. I. NGC 4214
This spectroscopic study of NGC 4214 is part of a project to determinethe extent to which the winds and supernovae from massive starscontribute to the short-term, localized chemical enrichment of theinterstellar medium (ISM) in low-metallicity galaxies. Long-slit opticalspectroscopy at 82 distinct spatial locations covering multiplestarburst knots reveals no significant localized O, N, or He abundancedifferences that might be attributed to the winds of massive stars. Wedo find large- scale (200 pc) variations in the oxygen abundance. Thesouthernmost, and probably youngest, starburst region exhibits higher Oabundances by 0.095 +/- 0.019 dex and correspondingly lower N/O (0.108+/- 0.038 dex) than the rest of the bright emission-line regions. Thisdifference is consistent with O pollution at the locations of the youngstarburst, possibly from recent supernovae. The surveyed regions exhibitan anticorrelation between N/O and O/H consistent with O pollution, butno significant correlations between Ne/O and O/H. If as expected fromnucleosynthesis models, O and Ne are produced predominantly in the sameshort-lived massive stars, and N is produced predominantly in lessmassive, longer lived stars, then these trends are both consistent withthe O pollution hypothesis. We show that observed internal N/O and Ovariations within NGC 4214, NGC 5253, and NGC 3125 are consistent withtheoretical chemical evolution predictions during a phase of Oproduction associated with massive stars early in a starburst. Whileuncertainties in the electron temperature, T(O^++^) are the dominantsource of error, we show that the observed abundance trends are notconsistent with those expected from temperature uncertainty effects. TheN/O and He/H ratios are relatively insensitive to temperature errors andshould serve as good indicators of abundance inhomogeneities whereverthey may exist. We also present a sell-consistent recomputation andtabulation of O, N/O, and He/H measurements in 60 metal-poor H IIgalaxies from the literature. Analysis of these data indicates thatgalaxies with strong Wolf-Rayet (W-R) features in their integratedspectrum exhibit identical N/O and He abundances to those galaxieslacking such features. Although abundance pollution from massive starsmust occur on long timescales and global spatial scales, we take theabsence of significant differences between W-R and non-W-R galaxies asevidence that W-R stars are not a significant contributor to abundancefluctuations on timescales comparable to the lifetimes of the H IIregions. Thus, W-R galaxies need not be treated differently than non-W-Rgalaxies in studies of galactic chemical evolution and primordialabundance studies.
| About the Initial Mass Function and He II Emission in Young Starbursts
We demonstrate that it is crucial to account for the evolution of thestarburst population in order to derive reliable numbers of O stars fromintegrated spectra for burst ages t > 2--3 Myr. In these cases, themethod of Vacca & Conti and Vacca systematically underestimates thenumber of O stars. Therefore, the current WR/O number ratios inWolf-Rayet (WR) galaxies are overestimated. This questions recent claimsabout flat initial mass function (IMF) slopes ( alpha ~ 1--2) in theseobjects. If the evolution of the burst is properly treated, we find thatthe observations are indeed compatible with a Salpeter IMF, in agreementwith earlier studies. Including recent predictions from non-LTE,line-blanketed model atmospheres that account for stellar winds, wesynthesize the nebular and WR He II lambda 4686 emission in youngstarbursts. For metallicities 1/5Zsolar <= Z <= Zsolar, we predicta strong nebular He II emission due to a significant fraction of WCstars in early WR phases of the burst. For other metallicities, broad WRemission will always dominate the He II emission. Our predictions of thenebular He II intensity agree well with the observations in WR galaxies,and an important fraction of the giant H II regions where nebular He IIis detected. We propose further observational tests of our result.
| The environment of HII galaxies
Recent morphological studies by Telles & Terlevich of HII galaxies,i.e. dwarf galaxies dominated by a very luminous starburst, haveindicated that luminous HII galaxies tend to show disturbed morphologysuggestive of tidal interactions triggering the present starburst, whilelow-luminosity HII galaxies tend, instead, to be symmetric and regular.To check the tidal origin of the starburst in HII galaxies, we havesearched for companions in the neighbourhood of a sample of 51 HIIgalaxies. We found that only 12 HII galaxies have a neighbour within aprojected distance of 1Mpc and 250 km s^-1 in velocity difference and,of these 12, only four have a luminous (M_B<-19)neighbour. Surprisingly, isolated HII galaxies tend to be of highluminosity and disturbed morphology, while HII galaxies with neighbourstend to be low-luminosity regular HII galaxies. Furthermore, the metalabundance and the equivalent width of the emission lines in HII galaxiesdo not depend on the presence of a companion. These results are opposedto what is expected if interaction with a bright companion is the mainmechanism triggering the starbursts. We have also found a loose group ofHII galaxies with no luminous companion. For this, there is theadditional difficulty of understanding how these starbursts aresynchronized on time-scales of less than 10^7 yr in systems separated by~1-2 Mpc.
| On the abundance of primordial helium
We have used recent observations of helium-4, nitrogen, and oxygen fromsome four dozen, low-metallicity, extragalactic H II regions to definemean N vs. O, He-4 vs. N, and He-4 vs. O relations which areextrapolated to zero metallicity to determine the primordial He-4 massfraction YP. The data and various subsets of the data,selected on the basis of nitrogen and oxygen, are all consistent withYP = 0.232 +/- 0.003. For the 2 sigma (statistical) upperbound we find YP2 sigma less than or equal to0.238. Estimating a 2% systematic uncertainity (sigmasyst =+/- 0.005) leads to a maximum upper bound to the primordial helium massfraction: YPMAX = YP2 sigma+ sigmasyst less than or equal to 0.243. We compare theseupper bounds to YP with recent calculations of the predictedyield from big bang nucleosynthesis to derive upper bounds to thenucleon-to-photon ratio eta (eta10 defined as 1010eta) and the number of equivalent light (less than or approximatelyequal to 10 MeV) neutrino species. For YP less than or equalto 0.238 (0.243), we find eta10 less than or equal to 2.5(3.9) and Nnu less than or equal to 2.7 (3.1). If indeedYP less than or equal to 0.238, then big bang nucleosynthesis(BBN) predicts enhanced production of deuterium and helium-3 which maybe in conflict with the primordial abundances inferred frommodel-dependent (chemical evolution) extrapolations of solar system andinterstellar observations. Better chemical evolution models and moredata -- especially D-absorption in the QSO Lyman-alpha -- will becrucial to resolve this potential crisis for BBN. The larger upperbound, YP less than or equal to 0.243, is completelyconsistent with BBN which now, bounds the universal density of nucleons(for Hubble parameter H0 greater than or equal to 40 and lessthan or equal to 100 km/((s)(Mpc)) and cosmic background radiationtemperature T = 2.726 +/- 0.010) to lie in the range OmegaBBNgreater than or equal to 0.01 and less than or equal to 0.09 (forH0 = (50) h50 km/((s)(Mpc)),(OmegaBBN)(h50 exp 2) greater than or equal to0.04 and less than or equal to 0.06).
| The chemical enrichment by massive stars in Wolf-Rayet galaxies.
We present stellar population models for starbursts in a sample ofeleven Wolf-Rayet galaxies. Taking into account the observational dataavailable, we try to reconstruct the number of Wolf-Rayet stars observedand estimate the number of type II supernovae that have exploded in theionizing cluster. Using the stellar yields of the most recent stellarevolutionary models for massive stars, we derive the expected chemicalenrichment in helium, oxygen and nitrogen produced by the burst on thesurrounding ionized gas. The results of this modelling indicate thatsince the helium and nitrogen production accounts for a fraction of thetotal content of the H II regions in these elements - implying theoccurrence of previous star formation events in the history of theparent galaxies -, the oxygen appears strongly overproduced in most ofthe objects. This fact and the correlation between the supernova ratesderived for the bursts and their corresponding oxygen overproduction aswell as the large volume filling factors expected for the hot gas thatfills the supernova remnants, suggest the action of differential massloss from the H II regions that could lead to galactic winds. We findthat the chemical evolution of WR galaxies in the Y vs. N/H diagramappears to run parallel to the fit of the observational data for"normal" H II galaxies obtained by Pagel et al. (1992). Moreover, thepollution by the present-day population of Wolf-Rayet stars is unable toexplain the apparently abnormal position of some Wolf-Rayet galaxies onthat diagram. We find that the effect of temperature fluctuations in thedetermination of the electron temperature of the ionized gas probablydue to the presence of shocks could be an alternative explanation forthis problem.
| Element Abundances in Blue Compact Galaxies
Models of the chemical evolution of blue compact galaxies, where thestar formation is assumed to proceed in short, intense bursts ofactivity, have been computed, with special attention to the evolution ofhelium, nitrogen, oxygen and iron. The contribution to the chemicalenrichment by supernovae (SNe) of the various types (Ia, lb, II) istaken into account, following the most up-to-date prescriptions.Galactic winds powered by SNe are also considered and confirmed as beingable to explain the observed element distributions. In particular, windsreleasing metals in different proportions can explain the high ratio of{DELTA}(He/H)/{DELTA}(O/H) and the distribution of N/O with O/H observedin extragalactic HII regions. No anomalous assumption on the initialmass function (IMF) slope and/or mass cut-offs seems to be required toobtain model predictions in agreement with the data. In particular,Salpeter`s initial mass function is applicable to all these galaxies,although some slight differences cannot be excluded. The [O/Fe] ratiosresulting from these models are always positive, except when many starformation episodes and differential galactic winds are assumed, thussuggesting the latter scenario for systems like the Magellanic Clouds,where the observed [O/Fe] ratios are negative.
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