Broad Low‐Intensity Wings in the Emission‐Line Profiles of Four Wolf‐Rayet Galaxies

Méndez, David I.; Esteban, C.

doi:10.1086/304745

Cited by 36 publications

(36 citation statements)

References 44 publications

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“…Lack of sufficient spectral resolution will derive a blending of both lines and a probable over-estimation of the [N ii] λ5683 flux, that would be even higher if broad low-intensity wings in the Hα profile exist, which are actually rather common in WR galaxies (e.g. Méndez & Esteban 1997). On the other hand, as explained by Izotov et al (2006), the bright doublet [O ii] λλ3726,3729 is not observed in the SDSS spectra for nearby galaxies, and hence the estimate of the total oxygen abundance has to be done via the [O ii] λλ7319,7330, which is much fainter, very dependent on the electron density and severely affected by sky emission features.…”

Section: Nitrogen Enrichment In Wr Galaxiesmentioning

confidence: 99%

Massive star formation in Wolf-Rayet galaxies

López-Sánchez

Esteban

2010

A&A

124

121

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Aims. We have performed a comprehensive multiwavelength analysis of a sample of 20 starburst galaxies that show a substantial population of very young massive stars, most of them classified as Wolf-Rayet (WR) galaxies. In this paper, the forth of the series, we present the global analysis of the derived photometric and chemical properties. Methods. We compare optical/NIR colours and the physical properties (reddening coefficient, equivalent widths of the emission and underlying absorption lines, ionization degree, electron density, and electron temperature) and chemical properties (oxygen abundances and N/O, S/O, Ne/O, Ar/O, and Fe/O ratios) with previous observations and galaxy evolution models. We compile 41 independent star-forming regions -with oxygen abundances between 12 + log(O/H) = 7.58 and 8.75 -, of which 31 have a direct estimate of the electron temperature of the ionized gas.Results. According to their absolute B-magnitude, many of them are not dwarf galaxies, but they should be during their quiescent phase. We found that both c(Hβ) and W abs increase with increasing metallicity. The differences in the N/O ratio is explained assuming differences in the star formation histories. We detected a high N/O ratio in objects showing strong WR features (HCG 31 AC, UM 420, IRAS 0828+2816, III Zw 107, ESO 566-8 and NGC 5253). The ejecta of the WR stars may be the origin of the N enrichment in these galaxies. We compared the abundances provided by the direct method with those obtained through empirical calibrations, finding that (i) the Pilyugin method is the best suited empirical calibration for these star-forming galaxies; (ii) the relations provided by Pettini & Pagel (2004, MNRAS, 348, 59) give acceptable results for objects with 12 + log(O/H) > 8.0; and (iii) the results provided by empirical calibrations based on photoionization models are systematically 0.2-0.3 dex higher than the values derived from the direct method. The O and N abundances and the N/O ratios are clearly related to the optical/NIR luminosity; the dispersion of the data is a consequence of the differences in the star-formation histories. The L-Z relations tend to be tighter when using NIR luminosities, which facilitates distinguishing tidal dwarf galaxies candidates and pre-existing dwarf objects. Galaxies with redder colours tend to have higher oxygen and nitrogen abundances. Conclusions. Our detailed analysis is fundamental to understand the nature of galaxies that show strong starbursts, as well as to know their star formation history and the relationships with the environment. This study is complementary -but usually more powerful-to the less detailed analysis of large galaxy samples that are very common nowadays.

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Section: Nitrogen Enrichment In Wr Galaxiesmentioning

confidence: 99%

Massive star formation in Wolf-Rayet galaxies

López-Sánchez

Esteban

2010

A&A

124

121

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“…In the case of POX 4, we still have to investigate (López-Sánchez et al 2010b) whether its dwarf companion galaxy is a TDG candidate and the interaction was with a nearby diffuse H i cloud, or if this object actually is an independent dwarf galaxy that has crossed the main body of POX 4 (Méndez & Esteban 1997). These six galaxies have a high degree of interaction.…”

Section: Quantification Of the Interaction Featuresmentioning

confidence: 99%

“…-POX 4 is a morphology-disturbed, low-metallicity BCDG showing strong star-forming bursts throughout the galaxy. It seems to be in interaction with a nearby dwarf object that may have passed through the main body of the galaxy, which is the origin of its ring-like morphology (Méndez & Esteban 1997) and kinematics. However, this object may also be a TDG candidate originated by the interaction with a nearby and diffuse H i cloud (López-Sánchez et al 2010b).…”

Section: Appendix A: Final Summary Of Individual Galaxiesmentioning

confidence: 99%

Massive star formation in Wolf-Rayet galaxies

López-Sánchez

2010

A&A

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Aims. We performed a comprehensive analysis of a sample of 20 starburst galaxies that show a substantial population of very young massive stars, most of them classified as Wolf-Rayet galaxies. Methods. In this paper, the last in the series, we analyze the global properties of our galaxy sample using multiwavelength data extracted from our own observations (Hα fluxes, B and H-band magnitudes) and from the literature, which include X-ray, FUV, FIR, and radio (both H i spectral line and 1.4 GHz radio-continuum) measurements.Results. The agreement between our Hα-based star-formation rates (Sfr) and those provided by indicators at other wavelengths is remarkable, but we consider that the new Hα-based calibration provided by Calzetti et al. (2007, ApJ, 666, 870) should be preferred to older calibrations. The FUV-based Sfr provides a powerful tool for analyzing the star-formation activity on both global and local scales independently to the Hα emission. We provide empirical relationships between the ionized gas mass, neutral gas mass, dust mass, stellar mass, and dynamical mass with the B-luminosity. Although all mass estimations increase with increasing luminosity, we find important deviations to the general trend in some objects, which seem to be the consequence of their particular evolutionary histories. The analysis of the mass-to-light ratios give similar results. We investigate the mass-metallicity relations and conclude that both the nature and the star-formation history are needed to understand the relationships between both properties. The majority of the galaxies follow a Schmidt-Kennicutt scaling law of star-formation that agrees with that reported in individual star-forming regions within M 51 but not with that found in normal spiral galaxies. Dwarf galaxies seem to be forming stars more efficiently than the outskirts of spiral galaxies. We find a relation between the reddening coefficient and the warm dust mass indicating that the extinction is mainly internal to the galaxies. The comparison with the closed-box model also indicates that the environment has strongly affected their evolution. Conclusions. Considering all multiwavelength data, we found that 17 up to 20 galaxies are clearly interacting or merging with lowluminosity dwarf objects or H i clouds. The remaining three galaxies (Mkn 5, SBS 1054+364, and SBS 1415+437) show considerable divergences of some properties when comparing with similar objects. Many of the interacting/merging features are only detected when deep optical spectroscopy and a detailed multiwavelength analysis, including H i observations, are obtained. We conclude that interactions do play a fundamental role in the triggering mechanism of the strong star-formation activity observed in dwarf starburst galaxies.

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“…Supersonic line widths have been observed in many intense star formation sites both in nearby galaxies (30 Dor, Chu & Kennicutt 1994;Melnick et al 1999;NGC 604, Yang et al 1996;NGC 2363, Roy et al 1992González-Delgado et al 1994) and in more distant dwarf galaxies (Izotov et al 1996;Homeier & Gallagher 1999;Marlowe et al 1995;Mendez & Esteban 1997;Sidoli et al 2006;Rozas et al 2006). In these studies, gravitational broadening through virial motions of ionized gas clouds (Melnick 1977;Terlevich & Melnick 1981) and multiple unresolved kinematical components along the line of sight (Chu & Kennicutt 1994) have been proposed as explanations for the broadening of the brightest component (what we refer to as c1).…”

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confidence: 94%

Hubble Space TelescopeSpace Telescope Imaging Spectrograph Spectroscopy of the Environment in the Starburst Core of M82

Westmoquette

Smith

Gallagher

et al. 2007

ApJ

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We present optical HST STIS observations made with two slits crossing four of the optically brightest starburst clumps near the nucleus of M82. These provide H kinematics, extinction, electron density, and emission measures. From the radial velocity curves derived from both slits we confirm the presence of a stellar bar. We derive a new model for the orientation of the bar and disk with respect to the main starburst clumps and the cluster M82-A1. We propose that clump A has formed within the bar region as a result of gas interactions between the bar orbits, whereas region C lies at the edge of the bar and regions D and E are located farther out from the nucleus but heavily obscured. We derive extremely high interstellar densities of 500Y900 cm À3 , corresponding to ISM pressures of P/k % (0:5Y1:0) ; 10 7 cm À3 K, and discuss the implications of the measured gas properties on the production and evolution of the galactic wind. Despite varying pressures, the ionization parameter is uniform down to parsec scales, and we discuss why this might be so. Where the signal-to-noise ratios of our spectra are high enough, we identify multiple emission-line components. Through detailed Gaussian line fitting, we identify a ubiquitous broad (200Y300 km s À1 ) underlying component to the bright H line and discuss the physical mechanism(s) that could be responsible for such widths. We conclude that evaporation and/or ablation of material from interstellar gas clouds caused by the impact of highenergy photons and fast flowing cluster winds produce a highly turbulent layer on the surface of the clouds from which the emission arises.

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Broad Low‐Intensity Wings in the Emission‐Line Profiles of Four Wolf‐Rayet Galaxies

Cited by 36 publications

References 44 publications

Massive star formation in Wolf-Rayet galaxies

Massive star formation in Wolf-Rayet galaxies

Massive star formation in Wolf-Rayet galaxies

Hubble Space TelescopeSpace Telescope Imaging Spectrograph Spectroscopy of the Environment in the Starburst Core of M82

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