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|The structure of galactic disks. Studying late-type spiral galaxies using SDSS|
Using imaging data from the SDSS survey, we present the g' and r' radialstellar light distribution of a complete sample of ~90 face-on tointermediate inclined, nearby, late-type (Sb-Sdm) spiral galaxies. Thesurface brightness profiles are reliable (1 σ uncertainty lessthan 0.2 mag) down to μ27 mag/''. Only ~10% of all galaxies havea normal/standard purely exponential disk down to our noise limit. Thesurface brightness distribution of the rest of the galaxies is betterdescribed as a broken exponential. About 60% of the galaxies have abreak in the exponential profile between 1.5-4.5 times thescalelength followed by a downbending, steeper outer region. Another~30% shows also a clear break between 4.0-6.0 times thescalelength but followed by an upbending, shallower outer region. A fewgalaxies have even a more complex surface brightness distribution. Theshape of the profiles correlates with Hubble type. Downbending breaksare more frequent in later Hubble types while the fraction of upbendingbreaks rises towards earlier types. No clear relation is found betweenthe environment, as characterised by the number of neighbours, and theshape of the profiles of the galaxies.
|Radio Identifications of Markarian Galaxies and the Correlation between Radio and Far-Infrared Properties|
By checking DSS optical images and NVSS radio images, 782 Markariangalaxies were identified to be NVSS radio sources. A comparison of theradio luminosity at 1.4 GHz and the far-infrared (FIR) luminosity for468 ``normal" galaxies shows a tight correlation. Most of the Seyfertgalaxies and quasars follow the radio-FIR relation deduced from the``normal" galaxy sample, but with a somewhat larger scatter. A total 167Markarian galaxies, comprising 100 ``normal" galaxies, 66 Seyfertgalaxies and one quasar, have either excess radio emission or much lowerFIR spectral index α (25μm, 60μm). These galaxies may beclassified as ``AGN-powered". For ``normal" galaxies, the average qvalue (defined as the log ratio between FIR and radio luminosities) is2.3. There seems a trend for q to slightly decrease with increasingradio luminosity. This may imply that the ongoing active star formationin galaxies with higher radio luminosities is more efficient in heatingthe cosmic-ray electrons.
|The Structural Properties of Isolated Galaxies, Spiral-Spiral Pairs, and Mergers: The Robustness of Galaxy Morphology during Secular Evolution|
We present a structural analysis of nearby galaxies in spiral-spiralpairs in optical BVRI bands and compare them with the structures ofisolated spiral galaxies and galaxies in ongoing mergers. We use thesecomparisons to determine how galaxy structure changes during galaxyinteractions and mergers. We analyze light concentration (C), asymmetry(A), and clumpiness (S) parameters, and use the projections of CASparameter space to compare these samples. We find that the CASparameters of paired galaxies are correlated with the projectedseparations of the pair. For the widest and closest pairs, the CASparameters tend to be similar to those of isolated and ongoing majormergers (e.g., ultraluminous infrared galaxies), respectively. Ourresults imply that galaxy morphology is a robust property that onlychanges significantly during a strong interaction or major merger. Thetypical timescale for this change in our paired sample, based ondynamical friction arguments, is short, τ~0.1-0.5 Gyr. We findaverage enhancement factors for the spiral-pair asymmetries andclumpiness values of ~2.2 and 1.5. The S parameter, which is related tostar formation (SF) activity, has a moderate level of enhancement,suggesting that this activity in modern spirals depends more on internalprocesses than on external conditions. We further test the statisticalcriterion for picking up interacting galaxies in an automated way byusing the A-S projection plane. The diversity of our spiral-pair samplein the CAS space suggests that structural/SF/morphological properties ofinteracting galaxies change abruptly only when the interaction becomesvery strong and the criteria given previously by Conselice for findinggalaxies involved in major mergers are effective.
|Strong Emission Line H II Galaxies in the Sloan Digital Sky Survey. I. Catalog of DR1 Objects with Oxygen Abundances from Te Measurements|
We present the first edition of the SDSS H II galaxies with Oxygenabundances Catalog (SHOC), which is a listing of strong emission-linegalaxies (ELGs) from the Sloan Digital Sky Survey (SDSS). Oxygenabundances have been obtained with the classic Te method. Wedescribe the method exploiting the SDSS database to construct thissample. The selection procedures are described and discussed in detail,as well as some problems encountered in the process of deriving reliableemission line parameters. The method was applied to the SDSS DataRelease 1 (DR1). We present 612 SDSS emission-line galaxies (624separate SDSS targets in total), for which the oxygen abundances12+log(O/H) have rms uncertainties <=0.20 dex. The subsample of 263ELGs (272 separate SDSS targets) have an uncertainty <=0.10 dex,while 459 ELGs (470 separate SDSS targets) have an uncertainty <=0.15dex. The catalog includes the main parameters of all selected ELGs, theintensities and equivalent widths of hydrogen and oxygen emission lines,as well as oxygen abundances with their uncertainties. The informationon the presence of Wolf-Rayet blue and/or red bumps in 109 galaxies isalso included. With the use of combined g, r, i SDSS images we performedvisual morphological classification of all SHOC galaxies. Four hundredsixty-one galaxies (~75%) are classified as confident or probable bluecompact galaxies (BCG/BCG?), 78 as irregular ones, 20 as low surfacebrightness galaxies (LSBG), 10 as obviously interacting, and 43 asspiral galaxies. In creating the catalog, 30 narrow-line active galacticnuclei and 69 LINERs were also identified; these are also presentedapart of the main catalog. We outline briefly the content of thecatalog, and the prospects of its use for statistical studies of thestar formation and chemical evolution issues. Some of these studies willbe presented in the forthcoming paper. Finally, we show that the methodpresented by Kniazev et al. for calculating O+/H+using intensities of the [O II] λλ7320, 7330 lines forSDSS emission-line spectra in the absence of [O II] λ3727 lineappears to yield reliable results over a wide range of studied oxygenabundances: 7.10<12+log(O/H)<8.5.
|The UZC-SSRS2 Group Catalog|
We apply a friends-of-friends algorithm to the combined Updated ZwickyCatalog and Southern Sky Redshift Survey to construct a catalog of 1168groups of galaxies; 411 of these groups have five or more members withinthe redshift survey. The group catalog covers 4.69 sr, and all groupsexceed the number density contrast threshold, δρ/ρ=80. Wedemonstrate that the groups catalog is homogeneous across the twounderlying redshift surveys; the catalog of groups and their membersthus provides a basis for other statistical studies of the large-scaledistribution of groups and their physical properties. The medianphysical properties of the groups are similar to those for groupsderived from independent surveys, including the ESO Key Programme andthe Las Campanas Redshift Survey. We include tables of groups and theirmembers.
|BVRI surface photometry of (S+S) binary galaxies I. The data|
We present multicolour broad band (BVRI) photometry for a sample of 33spiral-spiral (S+S) binary galaxies drawn from the KarachentsevCatalogue of Isolated Pairs of Galaxies (KPG). The data is part of ajoint observational programme devoted to systematic photometric study ofone of the most complete and homogeneous pair samples available in theliterature. We present azimuthally averaged colour and surfacebrightness profiles, colour index (B-I) maps, B band and sharp/filteredB band images as well as integrated magnitudes, magnitudes at differentcircular apertures and integrated colours for each pair. Internal andexternal data comparisons show consistency within the estimated errors.Two thirds of the sample have total aperture parameters homogeneouslyderived for the first time. After reevaluating morphology for all thepairs, we find a change in Hubble type for 24 galaxies compared to theoriginal POSS classifications. More than half of our pairs showmorphological concordance which could explain, in part, the strongcorrelation in the (B-V) colour indices (Holmberg Effect) between paircomponents. We find a tendency for barred galaxies to show grand designmorphologies and flat colour profiles. The measurements will be used ina series of forthcoming papers where we try to identify and isolate themain structural and photometric properties of disk galaxies at differentstages of interaction. Table A.1 is only available in electronic form atthe CDS via anonymous ftp cdsarc.u-strasbg.fr (188.8.131.52) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/379/54 and Tables 2-4 arealso available in electronic form at the CDS. Full Fig. 5 is onlyavailable in electronic form at the http://www.edpsciences.org Based ondata obtained at the 2.1 m telescope of the Observatorio Guillermo Haroat Cananea, Sonora, México, operated by the Instituto Nacional deAstrofísica, Optica y Electrónica.
|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.
|Arcsecond Positions of UGC Galaxies|
We present accurate B1950 and J2000 positions for all confirmed galaxiesin the Uppsala General Catalog (UGC). The positions were measuredvisually from Digitized Sky Survey images with rms uncertaintiesσ<=[(1.2")2+(θ/100)2]1/2,where θ is the major-axis diameter. We compared each galaxymeasured with the original UGC description to ensure high reliability.The full position list is available in the electronic version only.
|Molecular Gas in Strongly Interacting Galaxies. I. CO (1-0) Observations|
We present observations of the CO (1-0) line in 80 interacting galaxiesas part of a program to study the role of interactions and mergers intriggering starbursts. The sample, which only includes obviouslyinteracting pairs of galaxies, is the largest such sample observed inCO. The observations were carried out at the NRAO 12 m and IRAM 30 mtelescopes. CO emission was detected in 56 galaxies (of which 32 are newdetections), corresponding to a detection rate of 70%. Because mostgalaxies are slightly larger than the telescope beam, correction factorswere applied to include CO emission outside the beam. The correctionfactors were derived by fitting a Gaussian function or an exponential CObrightness distribution to galaxies with multiple pointings and byassuming an exponential model for galaxies with single pointing. Wecompared the global CO fluxes of 10 galaxies observed by us at bothtelescopes. We also compared the measured fluxes for another 10 galaxiesobserved by us with those by other authors using the NRAO 12 m and FCRAO14 m telescopes. These comparisons provide an estimate of the accuracyof our derived global fluxes, which is ~40%. Mapping observations of twoclose pairs of galaxies, UGC 594 (NGC 317) and UGC 11175 (NGC 6621), arealso presented. In subsequent papers we will report the statisticalanalyses of the molecular properties in our sample galaxies and makecomparisons between isolated spirals and interacting galaxies.
|Catalogue of HI maps of galaxies. I.|
A catalogue is presented of galaxies having large-scale observations inthe HI line. This catalogue collects from the literature the informationthat characterizes the observations in the 21-cm line and the way thatthese data were presented by means of maps, graphics and tables, forshowing the distribution and kinematics of the gas. It containsfurthermore a measure of the HI extension that is detected at the levelof the maximum sensitivity reached in the observations. This catalogueis intended as a guide for references on the HI maps published in theliterature from 1953 to 1995 and is the basis for the analysis of thedata presented in Paper II. The catalogue is only available inelectronic form at the CDS via anonymous ftp 184.108.40.206 orhttp://cdsweb.u-strasbg.fr/Abstract.html
|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.
|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.
|A multifrequency radio continuum and IRAS faint source survey of markarian galaxies|
Results are presented from a multifrequency radio continumm survey ofMarkarian galaxies (MRKs) and are supplemented by IRAS infrared datafrom the Faint Source Survey. Radio data are presented for 899 MRKsobserved at nu = 4.755 GHz with the National Radio Astronomy Observatory(NRAO)-Green Bank 300 foot (91 m) telescope, including nearly 88% ofthose objects in Markarian lists VI-XIV. In addition, 1.415 GHzmeasurements of 258 MRKs, over 30% of the MRKs accessible from theNational Aeronomy and Ionosphere Center (NAIC)-Arecibo, are reported.Radio continuum observations of smaller numbers of MRKs were made at10.63 GHz and at 23.1 GHz and are also presented. Infrared data from theIRAS Faint Source Survey (Ver. 2) are presented for 944 MRKs, withreasonably secure identifications extracted from the NASA/IPACExtragalactic Database. MRKs exhibit the same canonical infraredcharacteristics as those reported for various other galaxy samples, thatis well-known enhancement of the 25 micrometer/60 micrometer color ratioamong Seyfert MRKs, and a clear tendency for MRKs with warmer 60micrometer/100 micrometer colors to also possess cooler 12 micrometer/25micrometer colors. In addition, non-Seyfert are found to obey thewell-documented infrared/radio luminosity correlation, with the tightestcorrelation seen for starburst MRKs.
|Large-Scale Structures in the Zone of Avoidance: The Galactic Anticenter Region|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...449..527L&db_key=AST
|Wolf-Rayet population syntheses for starburst galaxies.|
We present new evolutionary population synthesis models based on themost recent grids of stellar models computed at the Geneva Observatory.We study the effects on the massive star populations born in astarburst, of the star formation rate (SFR), of the initial massfunction (IMF), of the age, of the metallicity (Z) and of a change ofthe mass loss rates by stellar winds (˙(M)). We obtain that the moreintense and shorter is the burst of star formation, the higher are theratios of WR to O-type stars reached after the burst. The same trend isexpected when the IMF's slope becomes flatter, the upper mass cut off,the metallicity, and/or the mass loss rates increase. At a given age andmetallicity, the way the WR are distributed among the different WRsubtypes depends sensitively on the rate of mass loss experienced by thestars. For metallicities Z=0.004 and Z=0.008, we have that only the high˙(M) models do predict the existence of a long WC-dominated phase.Moreover, only the high ˙(M) models might account for the presenceof a significant number of WC stars at very low metallicity (Z=0.001).We estimate the percentage of young starbursts, (i.e. with O and/or WRstars), whose massive star population is dominated by O-type stars,Wolf-Rayet, WNL, WNE and WC stars respectively. We find that thefraction of starbursts with a WNL-dominated population varies between 6and 33% depending on the metallicity. We study the supernova ratesexpected in recent and powerful star formation regions and find that themaximum rate occurs when the most massive stars explode. One obtainsthat for the most powerful starburst region observed by Vacca &Conti (1992, NGC 1614), one can expect, at the maximum, a supernova rateof about 12 supernovae per century. The present evolutionary populationsynthesis models can account for the very high ratios of WNL to O-typestars observed in some starburst galaxies. If the presence of asignificant WC star population is confirmed in the low metallicstarburst regions He 2-10 A and NGC 4214, this will be an indicationthat the mass loss rates experienced by the stars, at least during thepre-WR phases, are higher than previously thought, in agreement with theconclusions of Maeder & Meynet (1994).
|The nuclear 10 micron emission of spiral galaxies|
We examine the 10 micrometer(s) emission of the central regions of 281spiral galaxies, after having compiled all ground-based, small-aperture(approximately 5 sec) broad-band photometric observations at lambdaapproximately 10 micrometer(s) (N magnitudes) published in theliterature. We evaluate the compactness of the approximately 10micrometer(s) emission of galaxy nuclei by comparing these small-beammeasures with the large-beam IRAS 12 micrometer(s) fluxes. In theanalysis of different subsets of objects, we apply survival analysistechniques in order to exploit the information contained in 'censored'data (i.e., upper limits on the fluxes). Seyfert galaxies are found tocontain the most powerful nuclear sources of mid-infrared emission,which in approximately one-third of the cases provide the bulk of theemission of the entire galaxy; thus, mid-infrared emission in the outerdisk regions is not uncommon in Seyfert galaxies. The 10 micrometer(s)emission of Seyfert galaxies appears to be unrelated to their X-rayemission. H II region-like nuclei are stronger mid-infrared sources thannormal nuclei and LINER nuclei (whose level of emission is notdistinguishable form that of normal nuclei). Interacting objects have,on average, greater 10 micrometer(s) luminosities than noninteractingones and exhibit more compact emission. Early-type spirals have strongerand more compact 10 micrometer(s) emisison than late-type ones. Barredspirals are brighter at approximately 10 micrometer(s) than unbarredsystems, essentially because they more frequently contain H IIretion-like nuclei. The results of our detailed comparison between thebehavior of various categories of objects stress that the 10micrometer(s) emission of spiral nuclei is closely linked to the(predominantly nonthermal synchrotron) radio emission.
|Spectroscopic evolutionary synthesis models of Wolf-Rayet galaxies|
We present spectroscopic evolutionary synthesis calculations forstarburst galaxies of various metallicities in order to model the broademission lines He II 4686 and C III 4650 produced by WR stars in thespectra of WR galaxies. The strengths of both lines strongly decreasewith decreasing metallicity. The presence of WR emission features is aclear indicator of very recent star formation less than 4 to 7 x 10 exp6 yr ago. Bursts of duration 1 to 5 x 10 exp 6 yr which lead to anincrease in the total stellar mass in the galaxy by 0.1 to 10 percentare compatible with the equivalent width of He II 4686 observed in WRgalaxies.
|General study of group membership. II - Determination of nearby groups|
We present a whole sky catalog of nearby groups of galaxies taken fromthe Lyon-Meudon Extragalactic Database. From the 78,000 objects in thedatabase, we extracted a sample of 6392 galaxies, complete up to thelimiting apparent magnitude B0 = 14.0. Moreover, in order to considersolely the galaxies of the local universe, all the selected galaxieshave a known recession velocity smaller than 5500 km/s. Two methods wereused in group construction: a Huchra-Geller (1982) derived percolationmethod and a Tully (1980) derived hierarchical method. Each method gaveus one catalog. These were then compared and synthesized to obtain asingle catalog containing the most reliable groups. There are 485 groupsof a least three members in the final catalog.
|Radio and infrared emission from Markarian starburst galaxies|
Radio and infrared emission were compared for a sample of 58 Markarianstarburst galaxies, chosen to cover a wide range of 60-micron luminositydensity. New radio observations were from the VLA at 6 and 20 cm in theB and A configurations. IRAS data were reanalyzed for 25 of thestarbursts that were previously undetected at either 25 or 100 microns.The correlation between the global radio and IR emission for thestarbursts in the sample is strongest at 25 and 60 microns, wavelengthsin which the warm dust dominates. The radio spectral index steepens awayfrom the center. This indicates that nonthermal emission leaks out ofthe starburst region. The change in the spectral index implies thatwhile nonthermal sources dominate in the entire region, the bulk of theinterior emission at 6 cm is thermal. The radio spectral index does notappear to vary as a function of the infrared luminosity or the infraredcolors, which indicates that the slope of the initial mass function doesnot appear to be a function of either the mass or temperature of thestarburst.
|Optical spectrophotometry of Wolf-Rayet galaxies|
We have obtained long-slit optical spectra of 10 Wolf-Rayet galaxies andfour other starburst galaxies. Using the nebular emission lines we havedetermined the electron temperatures, electron densities, extinctions,oxygen abundances, mass of ionized hydrogen, and numbers of ionizingphotons due to hot stars in these galaxies. The various forbidden lineratios clearly indicate a stellar origin for the emission-line spectrum.From the flux of the broad He II 4686 A emission feature we haveestimated the number of Wolf-Rayet stars present. We have accounted forthe contribution of these stars to the total ionizing flux and havecalculated the ratio of the number of these stars to the number of Ostars. Wolf-Rayet galaxies are among the youngest examples of thestarburst phenomenon, which we observed at a propitious moment.
|Groups of galaxies within 80 Mpc. II - The catalogue of groups and group members|
This paper gives a catalog of the groups and associations obtained bymeans of a revised hierarchical algorithm applied to a sample of 4143galaxies with diameters larger than 100 arcsec and redshifts smallerthan 6000 km/s. The 264 groups of galaxies obtained in this way (andwhich contain at least three sample galaxies) are listed, with the looseassociations surrounding them and the individual members of eachaggregate as well; moreover, the location of every entity among 13regions corresponding roughly to superclusters is specified. Finally,1729 galaxies belong to the groups, and 466 to the associations, i.e.,the total fraction of galaxies within the various aggregates amounts to53 percent.
|Spectroscopic evolutionary synthesis of the emission lines He II 4686 A and C III 4650 A in Wolf-Rayet galaxies|
Spectroscopic evolutionary synthesis calculations for starburst galaxiesof various metallicities are presented for the broadened emission linesHe II 4686 A and C III 4650 A produced by WR stars in the spectra of WRgalaxies. The strengths of both lines strongly decrease with decreasingmetallicity. While a strong C III 4650 A line caused by WC stars is onlyprominent in the spectra of model galaxies with solar metallicity, He II4686 A emission mainly due to WN stars can be expected down to Z = 1/10Z (solar). Bursts of duration 1 to 5 x 10 exp 6 yr which lead to anincrease in the total stellar mass in the galaxy by 0.1 to 10 percentare compatible with the equivalent width of He II 4686 A observed in WRgalaxies.
|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'.
|The radio-far-infrared relation of interacting and non-interacting spiral galaxies. I - Observations and data collection|
Data from 6.3-cm radio continuum, H I, and far-infrared (FIR)observations are presented for a sample of isolated pairs of spiralgalaxies, and for a comparison sample of noninteracting ones. H I dataare used to separate the FIR emission of the cold and warm dustcomponent, employing a modification of the model presented by Buat andDeharveng (1988). The FIR flux of the warm dust component is used toestimate the thermal radio emission for some galaxies. A comparisonbetween the calculated thermal 6.3-cm flux densities and those derivedfrom radio observations show good agreement. It is concluded that themodel for the separation of the cold and warm dust component can be usedfor a further examination of the radio-FIR correlation.
|Nearby starburst galaxies|
New multiaperture 1.65 and 2.2 micron photometry has been obtained forthe central region of 132 spirals exhibiting 2 orders of magnitude rangein central 10-micron luminosity. This multiaperture photometry alongwith optical spectroscopy indicated that the high central 10-micronluminosity (about 1 billion solar luminosities) is powered by massivestar formation for the majority of the sample objects. The large database has led to the definition of a complete sample of nearby M82-typestarburst galaxies, the majority of which have not previously beenrecognized as such. Observation results and comparison with starburstmodels support the interpretation that, as in the case of M82, redsupergiants dominate the central 2.2-micron luminosity of the starburstsin this sample. The starburst galaxy M82 is anomalous in comparison withthe starburst galaxies identified in this study, by virtue of a rarehigh central 2.2-micron luminosity.
|IRAS observations of an optically selected sample of interacting galaxies|
IRAS observations of a large, morphologically selected sample ofstrongly interacting disk-type galaxies have demonstrated thatgalaxy-galaxy collisions can lead to enhanced infrared emission, but notin all cases. Infrared luminosities of the interacting galaxies span alarge range, but are about a factor of 2 higher, on average, than thoseof isolated disk galaxies. The data suggest the existence of a cutoff inblue luminosity, below which no galaxies show markedly enhanced infraredemission. Only the most strongly interacting systems in the sample showextreme values of infrared excess, suggesting that deep,interpenetrating collisions are necessary to drive infrared emission toextreme levels. Comparisons with optical indicators of star formationshow that infrared excess and color temperatures correlate with thelevel of star-formation activity in the interacting galaxies. Allinteracting galaxies in our sample that exhibit an infrared excess andhave higher than normal color temperatures also have optical indicatorsof high levels of star formation. It is not necessary to invokeprocesses other than star formation to account for the enhanced infraredluminosity in this sample of interacting galaxies.
|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.
|Optical and far-IR luminosity functions of Markarian galaxies|
A new optical luminosity function of Markarian galaxies is presentedwhich improves on earlier determinations. The importance of clusteringof Markarian galaxies is checked by applying an alternative methodproposed by Turner (1979) which allows the shape of the luminosityfunction to be derived for an arbitrary space distribution provided thatthe shape is the same in clusters and in the field. A fractionalbivariate function is constructed using IRAS data, and survival analysistechniques are used to exploit the information content of IR upperlimits. The resulting far-IR luminosity function is presented andcompared with previous estimates.
|The spatial distribution of 10 micron luminosity in spiral galaxies|
The present ground-based 10-micron observations of 133 nearby luminous,noninteracting IR galaxies indicate that about 40 percent of theearly-type barred spirals are associated with enhanced 10-micronluminosity in the central (about 1-kpc diameter) region. The luminositysource may be either Seyfert activity or star formation, or both. Thedifference in bar-central luminosity association in early- and late-typespirals indicates that the bulge/disk ratio may be an importantparameter in the determination of central IR luminosity in barredspirals.
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