Thierry Contini

New catalogue of Wolf-Rayet galaxies and high-excitation extra-galactic Hii regions

We present a new compilation of Wolf-Rayet (WR) galaxies and extra-galactic Hii regions showing broad He ii 4686 emission drawn from the literature. Relevant information on the presence of other broad emis- sion lines (N iii 4640, C iv 5808 and others) from WR stars of WN and WC subtypes, and other existing broad nebular lines is provided. In total we include 139 known WR galaxies. Among these, 57 objects show both broad He ii 4686 and C iv 5808 features. In addition to the broad (stellar) He ii 4686 emission, a nebular He ii component is well es- tablished (suspected) in 44 (54) objects. We nd 19 extra-galatic Hii regions without WR detections showing nebular He ii 4686 emission. The present sample can be used for a variety of studies on massive stars, interactions of massive stars with the ISM, stellar populations, starburst galaxies etc. The data is accessible electronically and will be updated periodically.

Starbursts in barred spiral galaxies - III. Definition of a homogeneous sample of starburst nucleus galaxies

This paper presents optical long-slit spectro- scopic observations of 105 barred Markarian IRAS galax- ies. These observations are used to determine the spectral type (starburst or Seyfert) of emission-line regions in the nucleus and along the bar of the galaxies, in order to de- ne a homogeneous sample of Starburst Nucleus Galaxies (SBNGs). Our selection criteria (ultraviolet excess, far infrared emission and barred morphology) have been very ecient for selecting star-forming galaxies, since our sample of 221 emission-line regions includes 82% nuclear or extranuclear starbursts. The contamination by Seyferts is low (9%). The remaining galaxies (9%) are objects with ambiguous classication (Hii or LINER). The dust content and H luminosity increase towards the nuclei of the galaxies. No signicant variation of the electron density is found between nuclear and bar Hii re- gions. However, the mean H luminosity and electron den- sity in the bar are higher than in typical disk Hii regions. We investigate dierent mechanisms for explaining the excess of nitrogen emission observed in our starburst nu- clei. There is no evidence for the presence of a weak hidden active galactic nucleus in our starburst galaxies. The cause of this excess is probably a selective enrichment of nitro- gen in the nuclei of the galaxies, following a succession of short and intense bursts of star formation. Our sample of SBNGs, located at a mean redshift of 0.015, has moderate H ( 10 41 erg s 1 ) and far in- frared (10 10 L) luminosities. The types are distributed equally among early- and late-type giant spirals with a

Detection of Wolf-Rayet Stars of WN and WC Subtypes in Super-Star Clusters of NGC 5253*

We present spectroscopic observations of the central star clusters in NGC 5253, the aim of which is to search for WC stars. Our observations show the presence of Wolf-Rayet (W-R) stars not only of WN but also of WC subtype in two star-forming regions corresponding to the maximum optical and UV emission. The massive star population that we derive is consistent with young bursts of ~3 and ~4 Myr. The region of maximum optical emission is found to provide the dominant contribution to the ionizing flux, as opposed to the less extinguished region of maximum UV brightness. The presence of W-R stars near the N-enriched regions found by Walsh & Roy and Kobulnicky et al. suggests that they are a possible source of nitrogen. It is presently unclear whether our detection of WC stars is compatible with the normal observed He/O and C/O abundance ratios.

The Pico dos Dias Survey Starburst Galaxies

We discuss the nature of the galaxies found in the Pico dos Dias Survey (PDS) for young stellar objects. The PDS galaxies were selected from the IRAS Point Source catalog. They have flux density of moderate or high quality at 12, 25, and 60 ?m and spectral indices in the ranges -3.00 ? ?(25, 12) ? + 0.35 and -2.50 ? ?(60, 25) ? +0.85. These criteria allowed the detection of 382 galaxies, which are a mixture of starburst and Seyfert galaxies. Most of the PDS Seyfert galaxies are included in the catalog of warm IRAS sources by de Grijp et al. The remaining galaxies constitute a homogeneous sample of luminous [log F (LB/L?) = 9.9 ? 0.4] starburst galaxies, 67% of which were not recognized as such before. The starburst nature of the PDS galaxies is established by comparing their LIR/LB ratios and IRAS colors with a sample of emission-line galaxies from the literature already classified as starburst galaxies. The starburst galaxies show an excess of FIR luminosity, and their IRAS colors are significantly different from those of Seyfert galaxies-99% of the starburst galaxies in our sample have a spectral index ?(60, 25) -2.5. This color cutoff also marks a change in the dominant morphologies of the galaxies: the normal IRAS galaxies are preferentially late-type spirals (Sb and later), while the starbursts are more numerous among early-type spirals (earlier than Sbc). This preference of starbursts for early-type spirals is not new, but a trait of the massive starburst nucleus galaxies (Coziol et al.). As in other starburst nucleus galaxy samples, the PDS starbursts show no preference for barred galaxies. No difference is found between the starbursts detected in the FIR and those detected on the basis of UV excess. The PDS starburst galaxies represent the FIR luminous branch of the UV-bright starburst nucleus galaxies, with mean FIR luminosity log (LIR/L?) = 10.3 ? 0.5 and redshifts smaller than 0.1. They form a complete sample limited in flux in the FIR at 2 ? 10-10 ergs cm-2 s-1.

The Chemical Evolution of Starburst Nucleus Galaxies

The metallicities derived from spectroscopic observations of a sample of starburst nucleus galaxies (SBNGs) are compared with those of several other types of galaxies (normal giant, irregular, and H II galaxies) drawn from the literature. The SBNGs are deficient in metals with respect to normal galaxies of same morphological type, suggesting that SBNGs are galaxies still in the process of formation. Breaking the SBNGs into early types (Sb and earlier) and late types reveals that the former seem to follow the same linear luminosity-metallicity relation as the irregular and elliptical galaxies, whereas the latter and the giant spirals show comparable (0.2 and 0.3 dex) excess abundances with respect to the linear relation. This difference between the two types of SBNGs is consistent with the predictions of the model of hierarchical formation of galaxies: the early-type SBNGs are building their bulges by successive mergers of small stellar and gaseous systems, while the late-type SBNGs are mostly accreting gas to form a disk.