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Disturbed isolated galaxies: indicators of a dark galaxy population?
We report the results of our search for disturbed (interacting) objectsamong very isolated galaxies. The inspections of 1050 northern isolatedgalaxies from KIG and 500 nearby, very isolated galaxies situated in theLocal Supercluster yielded five and four strongly disturbed galaxies,respectively. We suggest that the existence of "dark" galaxies explainsthe observed signs of interaction. This assumption leads to a cosmicabundance of dark galaxies (with the typical masses for luminousgalaxies) that is less than ~1/20 the population of visible galaxies.
| 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.
| Optimization of Starburst99 for Intermediate-Age and Old Stellar Populations
We have incorporated the latest release of the Padova models into theevolutionary synthesis code Starburst99. The Padova tracks were extendedto include the full asymptotic giant branch (AGB) evolution until thefinal thermal pulse over the mass range 0.9-5 Msolar. Withthis addition, Starburst99 accounts for all stellar phases thatcontribute to the integrated light of a stellar population witharbitrary age from the extreme-ultraviolet to the near-infrared. AGBstars are important for ages between 0.1 and 2 Gyr, with theircontribution increasing at longer wavelengths. We investigatesimilarities and differences between the model predictions by the Genevaand the Padova tracks. The differences are particularly pronounced atages >1 Gyr, when incompleteness sets in for the Geneva models. Wealso perform detailed comparisons with the predictions of other majorsynthesis codes and find excellent agreement. Our synthesized opticalcolors are compared to observations of old, intermediate-age, and youngpopulations. Excellent agreement is found for the old globular clustersystem of NGC 5128 and for old and intermediate-age clusters in NGC4038/4039. In contrast, the models fail for red supergiant-dominatedpopulations with subsolar abundances. This failure can be traced back toincorrect red supergiant parameters in the stellar evolutionary tracks.Our models and the synthesis code are publicly available as version 5.0of Starburst99 at http://www.stsci.edu/science/starburst99.
| Star Formation Properties of a Large Sample of Irregular Galaxies
We present the results of Hα imaging of a large sample ofirregular galaxies. Our sample includes 94 galaxies with morphologicalclassifications of Im, 26 blue compact dwarfs (BCDs), and 20 Sm systems.The sample spans a large range in galactic parameters, includingintegrated absolute magnitude (MV of -9 to -19), averagesurface brightness (20-27 mag arcsec-2), current starformation activity (0-1.3 Msolar yr-1kpc-2), and relative gas content(0.02-5Msolar/LB). The Hα images were usedto measure the integrated star formation rates, determine the extents ofstar formation in the disks, and compare azimuthally averaged radialprofiles of current star formation to older starlight. The integratedstar formation rates of Im galaxies normalized to the physical size ofthe galaxy span a range of a factor of 104 with 10% Imgalaxies and one Sm system having no measurable star formation at thepresent time. The BCDs fall, on average, at the high star formation rateend of the range. We find no correlation between star formation activityand proximity to other cataloged galaxies. Two galaxies located in voidsare similar in properties to the Sm group in our sample. The H IIregions in these galaxies are most often found within the Holmbergradius RH, although in a few systems H II regions are tracedas far as 1.7RH. Similarly, most of the star formation isfound within three disk scale lengths RD, but in somegalaxies H II regions are traced as far as 6RD. A comparisonof Hα surface photometry with V-band surface photometry shows thatthe two approximately follow each other with radius in Sm galaxies, butin most BCDs there is an excess of Hα emission in the centers thatdrops with radius. In approximately half of the Im galaxies Hα andV correspond well, and in the rest there are small to large differencesin the relative rate of falloff with radius. The cases with stronggradients in the LHα/LV ratios and with highcentral star formation rate densities, which include most of the BCDs,require a significant fraction of their gas to migrate to the center inthe last gigayear. We discuss possible torques that could have causedthis without leaving an obvious signature, including dark matter barsand past interactions or mergers with small galaxies or H I clouds.There is now a substantial amount of evidence for these processes amongmany surveys of BCDs. We note that such gas migration will also increasethe local pressure and possibly enhance the formation of massive denseclusters but conclude that the star formation process itself does notappear to differ much among BCD, Im, and Sm types. In particular, thereis evidence in the distribution function for Hα surface brightnessthat the turbulent Mach numbers are all about the same in these systems.This follows from the Hα distribution functions corrected forexponential disk gradients, which are log-normal with a nearly constantdispersion. Thus, the influence of shock-triggered star formation isapparently no greater in BCDs than in Im and Sm types.
| The ISOPHOT 170 μm Serendipity Survey II. The catalog of optically identified galaxies%
The ISOPHOT Serendipity Sky Survey strip-scanning measurements covering≈15% of the far-infrared (FIR) sky at 170 μm were searched forcompact sources associated with optically identified galaxies. CompactSerendipity Survey sources with a high signal-to-noise ratio in at leasttwo ISOPHOT C200 detector pixels were selected that have a positionalassociation with a galaxy identification in the NED and/or Simbaddatabases and a galaxy counterpart visible on the Digitized Sky Surveyplates. A catalog with 170 μm fluxes for more than 1900 galaxies hasbeen established, 200 of which were measured several times. The faintest170 μm fluxes reach values just below 0.5 Jy, while the brightest,already somewhat extended galaxies have fluxes up to ≈600 Jy. For thevast majority of listed galaxies, the 170 μm fluxes were measured forthe first time. While most of the galaxies are spirals, about 70 of thesources are classified as ellipticals or lenticulars. This is the onlycurrently available large-scale galaxy catalog containing a sufficientnumber of sources with 170 μm fluxes to allow further statisticalstudies of various FIR properties.Based on observations with ISO, an ESA project with instruments fundedby ESA Member States (especially the PI countries: France, Germany, TheNetherlands and the UK) and with the participation of ISAS and NASA.Members of the Consortium on the ISOPHOT Serendipity Survey (CISS) areMPIA Heidelberg, ESA ISO SOC Villafranca, AIP Potsdam, IPAC Pasadena,Imperial College London.Full Table 4 and Table 6 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/422/39
| 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 insights to the photometric structure of Blue Compact Dwarf galaxies from deep Near-Infrared studies. I. Observations, surface photometry and decomposition of surface brightness profiles
We have analyzed deep Near Infrared (NIR) broad band images for a sampleof Blue Compact Dwarf Galaxies (BCDs), observed with the ESO NTT andCalar Alto 3.6 m telescopes. The data presented here allows for thedetection and quantitative study of the extended stellar low-surfacebrightness (LSB) host galaxy in all sample BCDs. NIR surface brightnessprofiles (SBPs) of the LSB host galaxies agree at large galactocentricradii with those from optical studies, showing also an exponentialintensity decrease and compatible scale lengths. At small tointermediate radii (within 1-3 exponential scale lengths), however, theNIR data reveals for more than one half of our sample BCDs evidence fora significant flattening of the exponential profile of the LSBcomponent. Such profiles (type V SBPs, Binggeli & Cameron\cite{binggeli91}) have rarely been detected in the LSB component ofBCDs at optical wavelengths, where the relative flux contribution of thestarburst, being stronger than in the NIR, can readily hide a possiblecentral intensity depression in the underlying LSB host. The structuralproperties, frequency and physical origin of type V LSB profiles in BCDsand dwarf galaxies in general have not yet been subject to systematicstudies. Nevertheless, the occurrence of such profiles in an appreciablefraction of BCDs would impose important new observational constraints tothe radial mass distribution of the stellar LSB component, as well as tothe photometric fading of these systems after the termination ofstar-forming activities. We test the suitability of two empiricalfitting functions, a modified exponential distribution (Papaderos et al.\cite{papaderos96a}) and the Sérsic law, for the systematizationof the structural properties of BCD host galaxies which show a type Vintensity distribution. Either function has been found to satisfactorilyfit a type V distribution. However, it is argued that the practicalapplicability of Sérsic fits to the LSB emission of BCDs islimited by the extreme sensitivity of the achieved solutions to, e.g.,small uncertainties in the sky subtraction and SBP derivation. We findthat most of the sample BCDs show in their stellar LSB host galaxyoptical-NIR colors indicative of an evolved stellar population withsubsolar metallicity. Unsharp-masked NIR maps reveal numerousmorphological details and indicate in some cases, in combination withoptical data, appreciable non-uniform dust absorption on a spatial scaleas large as ~ 1 kpc.European Southern Observatory, program ID 65.N-0318(A).German-Spanish Astronomical Center, Calar Alto, operated by theMax-Planck-Institute for Astronomy, Heidelberg, jointly with the SpanishNational Commission for Astronomy.
| On the Metallicity of Star-forming Dwarf Galaxies
We construct three extremely different scenarios of the star formationhistories applicable to a sample of dwarf galaxies, based on eithertheir present metallicity or their luminosity. The three possiblescenarios imply different mechanical energy input rates, and these wecompare with the theoretical lower limits established for the ejectionof processed matter out of dwarf galaxies. The comparison stronglypoints to the existence of extended gaseous halos in these galaxiesacting as the barrier that allows galaxies to retain their metals andenhance their abundance. At the same time, our findings strongly pointto a continuous star-forming process, rather than to coeval bursts, asthe main contributor to the overall metallicity in our galaxy sample.
| The 1 to 2.5 mu broad band emission of Blue Compact Dwarf Galaxies
We present J, H and K surface photometry of 12 Blue Compact DwarfGalaxies (BCDGs) selected from the southern sample (Doublier et al.\cite{doublieretal99a}). A systematic excess of light in the K band withrespect to the other bands in the visible and the near infrared isobserved, indicating, since nebular emission is negligible, that astellar population of red giants dominates the global flux from thegalaxy. Moreover, comparisons of the metallicity-color relations ofBCDGs and globular clusters show very little differences, indicatingthat BCDGs are most probably old, in the cosmological sense, systems.Local colors of the star forming regions show that these regions areindeed very young and possibly coeval across the galaxy when severalstarburst locations exist. At least 4 BCDGs (UM 465A and B, Haro 14 andTololo 0610-378) show evidence of the presence of young red supergiantstars. The light distributions in the J, H and K bands are generallyconsistent with those in the optical, the differences are discussed. Weconfirm that our optical photometric classification remains valid in thenear infrared. Thus, the global light distribution in the galaxy is anintrinsic property of the host galaxy independent of the presence of thestarburst. Based on observations made at 2.2~m Danish telescope in LaSilla, operated by the European Southern Observatory.
| The Taxonomy of Blue Amorphous Galaxies. II. Structure and Evolution
Dwarf galaxies play an important role in our understanding of galaxyformation and evolution, and starbursts are believed to affect thestructure and evolution of dwarf galaxies strongly. We have thereforeembarked on a systematic study of 12 of the nearest dwarf galaxiesthought to be undergoing bursts of star formation. These were selectedprimarily by their morphological type (blue ``amorphous'' galaxies). Weshow that these blue amorphous galaxies are not physicallydistinguishable from dwarfs selected as starbursting by other methods,such as blue compact dwarfs (BCDs) and H II galaxies. All these classesexhibit surface brightness profiles that are exponential in the outerregions (r>~1.5r_e) but often have a predominantly central blueexcess, suggesting a young burst in an older, redder galaxy. Typically,the starbursting ``cores'' are young (~10^7-10^8 yr) events compared tothe older (~10^9-10^10 yr) underlying galaxy (the ``envelope''). Theratio of the core to envelope in blue light ranges from essentially zeroto about 2. These starbursts are therefore modest events involving onlya few percent of the stellar mass. The envelopes have surfacebrightnesses that are much higher than typical dwarf irregular (dI)galaxies, so it is unlikely that there is a straightforward evolutionaryrelation between typical dIs and dwarf starburst galaxies. Instead wesuggest that amorphous galaxies may repeatedly cycle through starburstand quiescent phases, corresponding to the galaxies with strong andweak/absent cores, respectively. Once amorphous galaxies use up theavailable gas (either through star formation or galactic winds) so thatstar formation is shut off, the faded remnants would strongly resembledwarf elliptical galaxies. However, in the current cosmological epoch,this is evidently a slow process that is the aftermath of a series ofmany weak, recurring bursts. Present-day dE's must have experienced morerapid and intense evolution than this in the distant past.
| Emission-Line Spectroscopy of H II Regions in Irregular and Blue Compact Dwarf Galaxies
We present reddenings and abundances of 189 H II regions measured from203 emission-line spectra in a sample of 65 irregular (Im), blue compactdwarf (BCD), and Sm galaxies. In most of these spectra we measure [OIII] lambda5007, Hβ, [N II] lambda6584, and [S II]lambdalambda6717, 6731; in 24 spectra we measure [O II] lambda3727 andin five we measure [O III] lambda4363. The internal reddenings of thegalaxies are used to determine whether redder irregular galaxies arealso dustier than bluer irregulars. We find that the range in opticalbroadband colors among Im galaxies is most likely dominated bydifferences in the contributions of the massive star population or theeffects of abundances, while the range in colors of BCDs does showevidence consistent with a contribution from dustiness. We use theabundances to confirm that our sample of BCD galaxies, selected to becomparable to Im systems in other global properties, are also comparablein abundances and, hence, evolutionary status. Finally, we explorerelationships between abundances and other global galactic propertiesand find few convincing correlations. However, bluer galaxies tend to bemore metal-poor. There is a slight trend of higher relative gas contentwith lower abundances among the BCD sample, but not in the Im sample.The difference could be due to a difference in gas distributions and thefraction of total gas that is actively participating in the chemicalevolution of the galaxy. In addition, our BCD, but not our Im, sample ofgalaxies are consistent by themselves with the galacticluminosity-metallicity relationship determined by others, but the Imsample is consistent with the general trend seen over a large baselinewhen combined with spiral galaxies. However, the scatter is large.
| Multi-spectral study of a new sample of Blue Compact Dwarf Galaxies. II. B and R surface photometry of 22 southern objects
We present the results of surface photometry on a new sample of BlueCompact Dwarf galaxies (BCDGs), in continuation to a previous paper(Doublier et al. 1997, hereafter Paper I). The 22 galaxies (plus twocompanions) discussed in the present paper have been selected in theSouthern Hemisphere, from several lists. An atlas containing isophotalmaps, surface brightnesses and B-R color profiles of the sample isgiven, together with the tables containing the photometric parameters.The results are consistent with those obtained in Paper I for objectsselected from the Byurakan Surveys in the Northern hemisphere.Similarly, we find about one fourth of the BCDGs showing a dominantr(1/4) brightness distribution component, one fourth of the BCDG showinga dominant exponential surface brightness profile, and about half ofthem show composite brightness distributions. Integrated properties,colors, mean surface brightnesses and luminosity-radius relations areinvestigated and discussed for the objects presented in this paper andPaper I. We found that r(1/4) BCDGs tend to show a different behaviourcompared to the exponential BCDGs, with respect to colors, compactnessand luminosity-radius relations. We also include a brief study of thesurroundings of the galaxies, where we find several candidatecompanions. Based on observations collected at the 1.54 m DanishTelscope at the European Southern observatory (La Silla, Chile).
| Morphology of star formation regions in irregular galaxies
The location of HII regions, which indicates the locus of present starformation in galaxies, is analysed for a large collection of 110irregular galaxies (Irr) imaged in Hα and nearby continuum. Theanalysis is primarily by visual inspection, although a two-dimensionalquantitative measure is also employed. The two different analyses yieldessentially identical results. HII regions appear preferentially at theedges of the light distribution, predominantly on one side of thegalaxy, contrary to what is expected from stochastic self-propagatingstar formation scenarios. This peculiar distribution of star-formingregions cannot be explained by a scenario of star formation triggered byan interaction with extragalactic gas, or by a strong one-armed spiralpattern.
| 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 Southern Sky Redshift Survey
We report redshifts, magnitudes, and morphological classifications for5369 galaxies with m_B <= 15.5 and for 57 galaxies fainter than thislimit, in two regions covering a total of 1.70 sr in the southerncelestial hemisphere. The galaxy catalog is drawn primarily from thelist of nonstellar objects identified in the Hubble Space TelescopeGuide Star Catalog (GSC). The galaxies have positions accurate to ~1"and magnitudes with an rms scatter of ~0.3 mag. We compute magnitudes(m_SSRS2) from the relation between instrumental GSC magnitudes and thephotometry by Lauberts & Valentijn. From a comparison with CCDphotometry, we find that our system is homogeneous across the sky andcorresponds to magnitudes measured at the isophotal level ~26 magarcsec^-2. The precision of the radial velocities is ~40 km s^-1, andthe redshift survey is more than 99% complete to the m_SSRS2 = 15.5 maglimit. This sample is in the direction opposite that of the CfA2; incombination the two surveys provide an important database for studies ofthe properties of galaxies and their large-scale distribution in thenearby universe. Based on observations obtained at Cerro TololoInter-American Observatory, National Optical Astronomy Observatories,operated by the Association of Universities for Research in Astronomy,Inc., under cooperative agreement with the National Science Foundation;Complejo Astronomico El Leoncito, operated under agreement between theConsejo Nacional de Investigaciones Científicas de laRepública Argentina and the National Universities of La Plata,Córdoba, and San Juan; the European Southern Observatory, LaSilla, Chile, partially under the bilateral ESO-ObservatórioNacional agreement; Fred Lawrence Whipple Observatory;Laboratório Nacional de Astrofísica, Brazil; and the SouthAfrican Astronomical Observatory.
| 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 Taxonomy of Blue Amorphous Galaxies. I. H alpha and UBVI Data
Dwarf galaxies play an important role in our understanding of galaxyformation and evolution. We have embarked on a systematic study of 12nearby dwarf galaxies (most of which have been classified as amorphous)selected preferentially by their blue colors. The properties of thegalaxies in the sample suggest that they are in a burst or postburststate. It seems likely that these amorphous galaxies are closely relatedto other "starburst" dwarfs such as blue compact dwarfs (BCDs) and H IIgalaxies but are considerably closer and therefore easier to study. Ifso, these galaxies may offer important insights into dwarf galaxyevolution. In an effort to clarify the role of starbursts inevolutionary scenarios for dwarf galaxies, we present H alpha and UBVIdata for our sample. Blue amorphous galaxies, like BCDs and H IIgalaxies, have surface brightness profiles that are exponential in theouter regions (r >~ 1.5re) but have a predominantly blue centralexcess, which suggests a young burst in an older, redder galaxy. Sevenof the galaxies have the bubble or filamentary H alpha morphology anddouble-peaked emission lines that are the signature of superbubbles orsuperwind activity. These galaxies are typically the ones with thestrongest central excesses. The underlying exponential galaxies are verysimilar to those found in BCDs and H II galaxies. How amorphous galaxiesfit into the dwarf irregular--"starburst dwarf"--dwarf ellipticalevolutionary debate is less clear. In this paper, we present our dataand make some preliminary comparisons between amorphous galaxies andother classes of dwarf galaxies. In a future companion paper, we willcompare this sample more quantitatively with other dwarf galaxy samplesin an effort to determine if amorphous galaxies are a physicallydifferent class of object from other starburst dwarfs such as BCDs and HII galaxies and also investigate their place in dwarf galaxy evolutionscenarios.
| The Absence of X-Ray Flashes from Nearby Galaxies and the Gamma-Ray Burst Distance Scale
If typical gamma-ray bursts (GRBs) have X-ray counterparts similar tothose detected by Ginga, then sensitive-focusing X-ray telescopes willbe able to detect GRBs 3 orders of magnitude fainter than the detectionlimit of the Burst and Transient Source Experiment (BATSE). If asubstantial portion of the burst population detected by BATSE originatesin a Galactic halo at distances greater than or equal to 150 kpc,existing X-ray telescopes will be able to detect GRBs in externalgalaxies out to a distance of at least 4.5 Mpc. As reported in Gotthelf,Hamilton, & Helfand, the imaging proportional counter (IPC) on boardthe Einstein Observatory detected 42 transient events with pointlikespatial characteristics and timescales of less than 10 s. These eventsare distributed isotropically on the sky; in particular, they are notconcentrated in the directions of nearby external galaxies. For halomodels of the BATSE bursts with radii of 150 kpc or greater, we wouldexpect to see several burst events in observations pointed toward nearbygalaxies. We see none. We therefore conclude that if the Gingadetections are representative of the population of GRBs sampled byBATSE, GRBs cannot originate in a Galactic halo population with limitingradii between 150 and 400 kpc. Inasmuch as halos with limiting radiioutside of this range have been excluded by the BATSE isotropymeasurements, our result indicates that all halo models are excluded.This result is independent of whether the flashes we do detect have anastronomical origin.
| Ultraviolet properties of early-type galaxies.
We analyse the UV properties of early-type galaxies from their UVspectra in the IUE library, including both normal and active nuclei. Weco-added the spectra, and hence the objects into groups of similarspectral properties in the UV, also taking into account their propertiesin the visible/near-infrared ranges. Although, owing to the presence ofa residual fixed pattern noise, IUE data cannot be improved byco-addition as expected for spectra containing only random noise, thisprocedure still provided spectra of higher signal/noise ratio than inprevious studies, often based on individual spectra and therefromderived colour indices. Thanks to the co-adding procedure, informationon spectral features can now be assessed. The red stellar populationgroups exhibit a far-UV flux at different levels. The higher ones denotethe presence of the UV turnup, which possibly exhibits absorptionfeatures, at least as detected through the IUE aperture. As to the bluestellar population groups and/or AGNs, we have carried out simplesyntheses with UV star cluster templates and galaxy spectra in order toinfer the properties such as burst ages and contamination by an activenucleus. It has been possible to derive information on the extinctionlaw affecting some internally reddened galaxies; there are cases wherethe presence of the λ2200 A absorption feature suggests areddening law similar to the Galactic one, and others without theλ2200A feature, suggesting that it is rather an SMC type lawwhich applies, then.
| An image database. II. Catalogue between δ=-30deg and δ=70deg.
A preliminary list of 68.040 galaxies was built from extraction of35.841 digitized images of the Palomar Sky Survey (Paper I). For eachgalaxy, the basic parameters are obtained: coordinates, diameter, axisratio, total magnitude, position angle. On this preliminary list, weapply severe selection rules to get a catalog of 28.000 galaxies, wellidentified and well documented. For each parameter, a comparison is madewith standard measurements. The accuracy of the raw photometricparameters is quite good despite of the simplicity of the method.Without any local correction, the standard error on the total magnitudeis about 0.5 magnitude up to a total magnitude of B_T_=17. Significantsecondary effects are detected concerning the magnitudes: distance toplate center effect and air-mass effect.
| The morphological catalogue of galaxies equatorial survey
We present 865 redshifts of galaxies located in the equatorial stripdelta between -17.5 deg and -2.5 deg in the right ascension rangebetween 20 h and 5 h. Redshifts have been obtained for the completesample of all 833 galaxies in the Morphological Catalog of Galaxies withmagnitudes brighter than m = 14.5 (corresponding approximately tom(Zwicky) = 15.0). This sample also includes three galaxies from othersources with more reliable magnitudes, satisfying this limit, and 29fainter galaxies, usually companions of the galaxies in the magnitudelimited sample. Our maps of a very large volume of nearby spacedemonstrate a variety of coherent large scale structures which includelarge voids, 20-50/h Mpc in diameter and large walls at least 70/h Mpcacross.
| Imaging of the Wolf-Rayet galaxy He 2-10
We present B, V, and emission-line CCD images of the Wolf-Rayet galaxyHe 2-10. The broad band images reveal the galaxy to consist of twostarburst regions at the center of an elliptical stellar envelope about10 times their size, with a major axis diameter of approximately 3.8kpc. Previous imaging detected only the starburst regions, leading tothe erroneous description of the object as an interacting pair.Morphologically, He 2-10 resembles the majority of blue compact dwarfgalaxies (BCDGs), some of which also show Wolf-Rayet features in theirspectra. The lack of nearby neighbors to He 2-10 suggests that its starformation is proceeding stochastically, rather than as the result ofinteraction, and its morphological similarity to other BCDGs suggeststhat all such galaxies may pass through a Wolf-Rayet phase. Thesimilarity of the outer regions of He 2-10 and other BCDGs to normaldwarf ellipticals also supports models in which the former evolve intothe latter.
| Molecular gas in elliptical galaxies
C-12O(2-1) observations of 24 FIR-bright ellipticals, as well as fiveother early-type galaxies, including one FIR-faint elliptical, IC 2006,are reported. The detected ellipticals are found to have typicalmolecular gas masses of about 10 to the 7th - 10 to the 8th solarmasses, similar to their H I masses, and an approximately power-lawdistribution of M(H2)/L(B), extending to much lower values than for thespirals. The lenticular galaxies have CO properties intermediate betweenthe elliptical and spiral systems. It is concluded that theseellipticals have global interstellar medium properties similar to thosein late-type galaxies, but on a much smaller scale. A comparison of theproperties of those ellipticals which have been detected in CO with theundetected galaxies indicates that the molecular gas may occurpreferentially in the bluer, lower luminosity dwarf ellipticals, whichhave more than twice the detection rate of the brighter galaxies.
| Galaxies possibly resembling M82-type galaxies
A list of 298 galaxies with possible features of M82 galaxies ispresented. This list contains those Irr II candidates whose images onPalomar photographs shown no trace of dust although the objects are redand suspected to be peculiar.
| The nuclear activity of interacting galaxies
A search for active galactic nuclei among interacting galaxies isreported. A sample of 167 systems of interacting and asymmetric galaxieswas observed spectrophotometrically in the spectral range 4700-7100 A.The results are compared with a sample of isolated galaxies. It is foundthat (1) there are no Seyfert nuclei in elliptical or dwarf irregulargalaxies of the sample; (2) there is an excess of Seyfert nuclei amonginteracting spirals, but it is only at the 90 percent confidence level;(3) this excess becomes statistically significant (98 percent) when onlystrongly interacting spirals are included (four new Seyfert nuclei arepresented); (4) in the subgroup of galaxies with extreme tidaldistortions, no Seyfert nuclei were found.
| Catalog of CO observations of galaxies
A series of tables summarizes all observations of CO isotopes inexternal galaxies up to spring 1984. Entries include the morphologicaltype, apparent magnitude, diameter, recession velocity, and H I contentof the galaxies, and lists for the CO observations the telescope used,the features examined, the portion of the galaxy observed, the antennatemperatures of detections and their upper limits, the detected andextrapolated integrated emission, the uncertainties in the data, and thedistribution of emission in mapped galaxies. Differences in thecalibration conventions employed by observers and notations appearing inthe literature are explained, and conversion factors are derived.
| Infrared colors of blue irregular galaxies
JHK photometry are presented for a sample of blue irregular galaxies,including nearby giant systems and more distant luminous compactgalaxies. Four giant H II regions were also observed for comparison. TheH II regions exhibit a considerable range in JHK and V-K colors, whichare attributed to variations in the massive blue and red stellarpopulations and in the amount of dust. The irregular galaxies, on theother hand, have rather homogeneous colors which are similar to those ofspiral and elliptical galaxies. From the infrared colors alone, it wasnot possible to distinguish between giant stars, asymptotic giants, andsupergiants as the dominant source of infrared light in irregulars.However, the uniformity of JHK colors from galaxy to galaxy as comparedwith individual young stellar systems suggests that young populationsare not major contributors to the infrared light. Also, no correlationwas found between metallicity and infrared colors in irregular galaxies.
| Photoelectric Observations of Interacting and Compact Galaxies
Not Available
| H I line studies of galaxies. III - Distance moduli of 822 disk galaxies
The distance scale established on the basis of a distance moduli catalog(for 822 galaxies) that was derived from 21-cm line widths via theB-band Tully-Fisher relation is compared with several independent scaleshaving a common zero point, that are based on the indicators forluminosity index, redshift, ring diameters, brightest superassociations,and effective diameters. These are in excellent systematic agreement,and confirm the linearity of the H I scale in the 24-35 modulusinterval, but indicate a small systematic zero point difference of about0.2 mag, which must be added to the H I moduli to place them on the same'short' distance scale defined by the others.
| Radio continuum observations of blue compact dwarf galaxies
A sample of 52 blue compact dwarf and low surface brightness galaxieshas been observed at a wavelength of 6.3 cm using the Effelsberg 100-mradio telescope. The flux densities which have been derived for thesample are compared with global properties in other spectral domains. Onaverage, blue compact dwarf galaxies exhibit about 10 times higherradio-to-optical luminosity than normal spirals. There is evidence thatthe relation between the radio and the optical luminosity of bluecompact dwarf galaxies is different from that found for normal spirals.The average radio continuum spectra of blue compact dwarf galaxiesappears to be significantly flatter, suggesting a low fraction ofsynchrotron radiation. Since these blue galaxies show clear evidence forviolent star formation taking place at present, nonthermal emission isexpected to be present due to supernova events. It is suggested thatweak magnetic fields in blue compact dwarf galaxies are the reason forthis weak synchrotron emission.
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