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On the geometrical evolution of the ionized gas in HII galaxies
Aims.In this paper, we investigate the behaviour of the number of Lymancontinuum ionizing photons as compared to the actual number of hydrogenrecombinations in HII galaxies. Methods: .We evaluate the numberof ionizing photons from the population synthesis of spectra observed inthe visible, extrapolating the spectra to the extreme ultraviolet (EUV),beyond the Lyman limit. We check for possible systematic deviations ofthe predicted ionizing spectra in the EUV by comparing the ratio of thepredicted number of ionizing photons to the number of recombinations, asmeasured in Hβ, {Δ log Q(H^0)}, with the metallicity. We findthat, as far as the number of ionizing photons is concerned, nosystematic tendency can be detected. The Hβ equivalent width can beunderstood as a nebular age indicator, decreasing with age, although theobserved Hβ equivalent width can also be affected by thecontribution to the continuum by the accumulation of previous,non-ionizing stellar populations. Results: .We attribute theincrease of {Δ log Q(H^0)} with the age of the burst to the factthat more and more ionizing photons escape the nebulae when the nebulaeget older, because of their increasing, expansion-inducedsubfragmentation.
| 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.
| 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
| Stellar populations in Seyfert 2 galaxies. I. Atlas of near-UV spectra
We have carried out a uniform spectroscopic survey of Seyfert 2 galaxiesto study the stellar populations of the host galaxies. New spectra havebeen obtained for 79 Southern galaxies classified as Seyfert 2 galaxies,7 normal galaxies, and 73 stars at a resolution of 2.2 Å over thewavelength region 3500-5300 Å. Cross-correlation between thestellar spectra is performed to group the individual observations into44 synthesis standard spectra. The standard groups include a solarabundance sequence of spectral types from O5 to M3 for dwarfs, giants,and supergiants. Metal-rich and metal-weak F-K giants and dwarfs arealso included. A comparison of the stellar data with previouslypublished spectra is performed both with the individual spectra and thestandard groups. For each galaxy, two distinct spatial regions areconsidered: the nucleus and the external bulge. Spectroscopic variationsfrom one galaxy to another and from the central to the external regionare briefly discussed. It is found that the central region of a Seyfert2 galaxy, after subtracting the bulge stellar population, always shows anear-UV spectrum similar to one of three representative categories: a)many strong emission lines and only two visible absorption lines (Ca IiK and G band) (Sey2e); b) few emission lines, many absorption lines, anda redder continuum than the previous category (Sey2a); c) an almost flatcontinuum and high-order Balmer lines seen in absorption (Sey2b). Theproportion of Seyfert 2 galaxies belonging to each class is found to be22%, 28%, and 50% respectively. We find no significative differencesbetween morphology distributions of Seyfert 2 galaxies with Balmer linesdetected in absorption and the rest of the sample. This quick lookthrough the atlas indicates that half of Seyfert 2 galaxies harbour ayoung stellar population (about or less than 100 Myr) in their centralregion, clearly unveiled by the high order Balmer series seen inabsorption. Based on observations collected at the European SouthernObservatory, Chile (ESO 65.P-0014(A)). Tables 1-3 and 8 and Fig. A.1(Appendix A) are only available in electronic form athttp://www.edpsciences.org
| Surface photometry of binary galaxies.
Not Available
| 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
| A Survey for H 2O Megamasers in Active Galactic Nuclei. II. A Comparison of Detected and Undetected Galaxies
A survey for H2O megamaser emission from 354 active galaxies hasresulted in the detection of 10 new sources, making 16 known altogether.The galaxies surveyed include a distance-limited sample (coveringSeyferts and LINERs with recession velocities less than 7000 km s-1) anda magnitude-limited sample (covering Seyferts and LINERs with mB <=14.5). In order to determine whether the H2O-detected galaxies are"typical" active galactic nuclei (AGNs) or have special properties thatfacilitate the production of powerful masers, we have accumulated adatabase of physical, morphological, and spectroscopic properties of theobserved galaxies. The most significant finding is that H2O megamasersare detected only in Seyfert 2 and LINER galaxies, not Seyfert 1's. Thislack of detection in Seyfert 1's indicates either that they do not havemolecular gas in their nuclei with physical conditions appropriate toproduce 1.3 cm H2O masers or that the masers are beamed away from Earth,presumably in the plane of the putative molecular torus that hides theSeyfert 1 nucleus in Seyfert 2's. LINERs are detected at a similar rateto Seyfert 2's, which constitutes a strong argument that at least somenuclear LINERs are AGNs rather than starbursts, since starbursts havenot been detected as H2O megamasers. We preferentially detect H2Oemission from the nearer galaxies and from those that are apparentlybrighter at mid- and far-infrared and centimeter radio wavelengths.There is also a possible trend for the H2O-detected galaxies to be moreintrinsically luminous in nuclear 6 cm radio emission than theundetected ones, though these data are incomplete. We find evidence thatSeyfert 2's with very high (NH > 1024 cm-2) X-ray--absorbing columnsof gas are more often detected as H2O maser emitters than Seyfert 2'swith lower columns. It may be that the probability of detecting H2Omaser emission in Seyfert galaxies increases with increasing column ofcool gas to the nucleus, from Seyfert 1's through narrow-line X-raygalaxies to Seyfert 2's.
| A Survey for H 2O Megamasers in Active Galactic Nuclei. I. Observations
We report an extensive search for 22 GHz H_2_O maser emission fromnearby active galaxies. Our sample includes all Seyfert and LINERgalaxies listed in the Huchra catalog or the Veron-Cetty & Veroncatalog with recessional velocities less than 7000 km s^-1^, and allSeyfert galaxies and LINERs in Huchra's catalog with m_b_ <= 14. Inaddition to these distance- and magnitude-limited samples, we have alsoobserved a number of active galaxies, including radio galaxies, athigher redshift; In all, some 354 galaxies have been surveyed. Ten newH_2_O megamaser sources have been detected, resulting in 16 galaxiesthat are currently known to contain H_2_O masers with isotropicluminosities greater than 20 L_sun_. Of the observed active galaxieswith cz < 7000 km s^-1^, 5.4% have detectable H_2_O megamaseremission. This fraction increases to 11% for those sources with cz <2000 km s^-1^. The newly discovered megamaser sources were monitored onsubsequent observing runs. The strength of the maser features varies forthese sources, as they do for Galactic masers. Three of the galaxieshave sufficient data to test for velocity changes of narrow masercomponents comparable in magnitude to those of the well-studied systemicfeatures in NGC 4258. The maser line in one of these galaxies-NGC2639-is found to have a systematic redward velocity drift of 6.6 +/- 0.4km s^-1^ yr^-1^. No systematic velocity drifts are found for the othertwo sources. We also report large apparent velocity changes in theunusual broad H_2_O emission feature in NGC 1052.
| Candidates for a southern extension of the Karachentsev catalogue of isolated pairs of galaxies.
Not Available
| A large sample of southern IRAS galaxies - Spectral classes and superclustering
Results are presented of an extensive spectroscopic survey of IRASgalaxies, in three Southern-Hemisphere fields totaling about 0.5 sr.Spectroscopic observations have been made of 527 galaxies which arecandidates for 474 IRAS sources. Together with published data, there arenow measured redshifts for almost 850 of the 1178 selected IRAS galaxiesin these fields. This measured sample includes nearly all galaxies athigh redshifts, and hense high infrared luminosities, within thesefields. Classification of more than 350 of these galaxies usingemission-line ratios and line widths shows that about 90 percent havestarburst characteristics. Two distinct groups of starburst galaxies inthe sample display forbidden O III-line intensities which significantlyexceed those observed in optically selected starburst galaxies. One ofthese groups, with strong N II forbidden lines, may be related to linersand/or Seyfert galaxies. The other, with weak N II forbidden-lineemission, displays unusually narrow lines; this group is interpreted interms of the youngest phase of starburst activity.
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