Spectrophotometry of Star-forming Regions in H II Galaxies
We present spectrophotometric observations of 111 H II galaxies selectedfrom various surveys. Apart from the integrated spectra, we presentemission-line fluxes and equivalent widths of different star-formingknots for 33 galaxies for which the spatial distribution of physicalproperties can be assessed. Most of the objects have been observedpreviously. We reobserved these galaxies with uniform instrumentation,and data reduction was performed with homogeneous methods. Our analysisof the quality of the data indicates that our observations reach goodsignal-to-noise ratio over the whole spectral range, allowing themeasurement of-and the inclusion of additional-low-intensity emissionlines.Based on observations collected at the European Southern Observatory,Chile, under an agreement between the Observatório Nacional,Brazil, and the ESO.
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Stellar populations in HII galaxies
We analyse the stellar content of a large number of HII galaxies fromthe continua and absorption features of their spectra using populationsynthesis methods, in order to gain information about the star formationhistories of these objects.We find that all galaxies of our sample contain an old stellarpopulation (≥1 Gyr) that dominates the stellar mass, and in amajority of these we also found evidence for an intermediate-agepopulation ≥50 Myr apart from the presently bursting, ionizing younggeneration ≤107 yr.Appendix A is only available in electronic form athttp://www.edpsciences.org
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Formalism and quality of a proper motion link with extragalactic objects for astrometric satellite missions
The accuracy of the link of the proper motion system of astrometricsatellite missions like AMEX and GAIA is discussed. Monte-Carlo methodswere used to simulate catalogues of positions and proper motions ofquasars and galaxies to test the link. The main conclusion is, thatfuture satellite missions like GAIA may be ``self-calibrated'' by theirmeasurements of QSOs, while additional measurements from radio stars orHST-data are needed to calibrate the less deep reaching astrometricsatellite missions of AMEX type.
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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
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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.
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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
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Asymmetry in high-precision global H I profiles of isolated spiral galaxies
New high-SNR 21 cm H I line profiles have been obtained for 104 galaxieswith the Green Bank 43 m telescope. The primary sample is composed ofisolated spirals with no known optical companions within a 1 radius anda median ratio of optical diameter to beamwidth of 0.17. An effort wasmade to ensure linearity of baseline fitting and precise flux densitycalibration to better than 5 percent. Two quantitative measures ofasymmetry are applied to assess the occurrence of lopsidedness in theglobal H I profiles. In agreement with previous estimates, half thegalaxies show significant H I profile asymmetries. The lopsidednesscannot be explained by pointing offsets but, rather, must result fromnoncircular motions, confusion with unidentified companions within thetelescope beam, or true distortions in the H I distribution.
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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 130.79.128.5 orhttp://cdsweb.u-strasbg.fr/Abstract.html
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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
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Element abundances in H II galaxies
Data for 121 H II systems from the spectrophotometric catalog of H IIgalaxies (Terlevich et al. 1991) have been analyzed to determine theabundances of the most common chemical elements. The range of O/Hspanned by the data is from 0.5 to 0.03 the solar value. The rarity ofobjects in the sample with metallicities similar to that of I Zw 18could correspond to the claimed increasing probability to findlow-metallicity objects among intrinsically fainter systems. It isargued that the correction for ionization for Ne could be inadequate dueto the transformation of part of the O(2+) into O(+) in thehigh-ionization zone through charge transfer reactions. The apparentover-abundance of Ne found in low-excitation objects would then be justan artifact. When the analysis is restricted to high-excitation nebulae(O(2+)/O is greater than or equal to 0.9), we find a constant Ne/O =0.17 ratio, in agreement with the current ideas about thenucleosynthesis of those two elements. The N/O ratio, once the systemswith detected traces of the presence of shocks were discarded, was foundto be constant at the level 0.032. Thus, for those objects, N isessentially primary in origin. On the other hand, the greater Nabundances in higher metallicity systems would indicate that secondaryproduction is at work in them. Those mechanisms, however, are operativeonly when the metallicity is greater than some threshold value. The lastelement we have considered is helium. It is argued that none of theproposed ionization correction schemes works correctly, so only objectsfor which the amount of neutral He is seemingly negligible can beretained to determine He abundances. It is remarked that the selectionby effective temperature corresponds in fact to a selection bymetallicity. The lower envelope of the He abundances we find is about22%. We do not find any trend between the He content and the abundancesof other elements like O or N.
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Corrections and additions to the third reference catalogue of bright galaxies
List of corrections and additions to the Third Reference Catalogue ofBright Galaxies (RC3) are given. The corrected version of the catalogue(RC3.9b), dated April 1994, is currently available through the nationaldata centers.
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A survey of H II galaxies to detect H I companion objects
Results are presented from a nine-galaxy sample survey of H II galaxiesfor neutral hydrogen companion objects; nearby H I companions aredetected for four. The probability of an H II galaxy having a companionis at least 0.17. This detection of companions around apparentlyisolated H II galaxies supports the hypothesis that galaxiesexperiencing a burst of star formation are good places to search forsmall, H I-rich companions which span the same mass and column densityranges as the population of Lyman-alpha absorbers seen in QSO spectra,constituting a low-z analog to that population.
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The age and size of the universe
Distance determinations of galaxies are reviewed and placed on auniform, self-consistent scale. It is shown that abundance ratios ofradioactive elements may be used to determine the age of the Milky WayGalaxy which probably lies in the range of 10 x 10 exp 9 to 20 x 10 exp9 years. Galactic ages in the range of 12 x 10 exp 9 to 17 x 10 exp 9years are obtained by fitting stellar evolutionary tracks to thecolor-magnitude diagrams of stars in the oldest globular clusters. Anage of the universe in the range of 13 x 10 exp 9 to 18 x 10 exp 9 yearsis obtained allowing about 1 x 10 exp 9 years for the proto-Galaxy toaccumulate and for globular clusters to form. Using standardcosmological models with a density parameter equal to 1 and acosmological constant equal to 0, the corresponding values of the Hubbleparameter are found to be greater than or equal to 36 but less than orequal to 50 km/s/Mpc.
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A spectrophotometric catalogue of HII galaxies
A spectrophotometric catalog is presented of 425 emission-line galaxiesdiscovered in objective prism surveys for which redshifts, emission-lineintensities, equivalent widths, and absolute fluxes are derived. Thevast majority of objects in the catalog are H II region-like galaxies (HII galaxies). In more than 80 H II galaxies the forbidden line O III4363 was measured with accuracy good enough to permit precise electrontemperature determinations. The observational parameters that define theproperties of H II galaxies as a class are characterized and discussed.
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Environmental properties of violently star-forming galaxies
A sample of 71 objects from the Spectrophotometric Catalogue of H IIgalaxies (Terlevich et al., 1990) has been searched for neighboringobjects. According to the metallicity, IRAS colors, morphology, andenvironmental circumstances, the objects have been classified in sixdifferent groups. Specific denominations are proposed for each class,from nuclear starburst galaxies to irregular blue galaxies and bluecompact dwarf galaxies. Blue irregular and blue compact objects havelower metallicities and higher f25 microns/f100 microns color indicesthan nuclear starburst objects, indicating different evolutionaryhistories. All the nuclear starbursts and blue irregulars have massivecompanions, but only 2/3 of the blue compacts do have. The hypothesis ofcloud-cloud collisions or galaxy-galaxy interactions to understand thetriggering mechanism for the violent star formation is brieflydiscussed.
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Michigan 160 - Internal kinematics and the cosmic distance scale
The kinematics and mass distribution of the emission-line irregulargalaxy Michigan 160 have been studied, and the results are reported. Thevelocity field is adequately fitted by a rotating, tilted disk model inwhich velocities are solid body to about 50 arcsec and constant at 51 +or - 2 km/s thereafter. Central asymmetries are present and may beexplained either by barlike or by warp distortions. The physical basisof these distortions appears to be the overall ringlike massdistribution. The kinematics and mass distribution are consistent withlittle or no dark matter content and an absolute distance of 41.8 + or -4.0 Mpc. This distance is based on a direct fit of the observed H I andoptical brightness distributions to the observed velocity field. It isproposed that the present method will make a substantial contribution tothe measurement of distances over cosmologically significant scales.
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Comparisons between 21 CM data from Effelsberg and Greenbank
Comparison of 21-cm data from the Effelsberg 100-m and NRAO Greenbank91-m telescopes are used to find the limiting precision for redshiftmeasurement. At SNR levels of 10 or above, the random uncertaintyactually achieved in a single redshift measurement is demonstrated to be0.85 km/s at a bandwidth of 6.25 MHz. Uncertainty in other bands scalesas the square root of the bandwidth relative to 6.25 MHz. Random erroris also found to be independent of which telescope or software is usedas long as the SNR is large. At low SNR the choice of software affectsprecision. Substantial systematic errors are shown to be present in someexisting systems or software, due to errors in specifying the locationof the center frequency. Such errors can easily be eliminated withstandardized intercomparisons.
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Spectrophotometric and neutral hydrogen observations of Michigan 160
Spectrophotometry, deep optical imagery and neutral hydrogenobservations of the emission-line galaxy Michigan 160 are presented. Itis identified as a young, gas-rich system dominated by four massive H IIregions. The galaxy has a disturbed optical structure suggestive ofrecent interaction, and it is probable that its neutral gas content(which exceeds 50 per cent of its total mass) is truly primordial. Themetallicities and neutral gas fractions for Michigan 160 and a sample ofsimilar emission-line and late-type galaxies are adequately explained bya chemical evolution model in which (1) the heavy element yield isconstant (p=0.004) and (2) the enrichment process is modified by inflow.
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Uncertainties in 21 centimeter redshifts. I - Data
High-precision data on the 21-cm redshifts, profile widths, and shapesfor 625 galaxies are presented. Each galaxy is listed in across-identification and morphology table. High-resolution spectra arealso given for each galaxy. Internal redshift consistency is roughly 1km/s for galaxies for which the S/N is above 15. No systematic effectshave been found which might influence the observed redshift quantizationat 72.5 km/s or its submultiples.
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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.
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Atlas of interacting galaxies, Part. II and the concept of fragmentation of galaxies.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1977A&AS...28....1V&db_key=AST
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