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22 papers found.
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Planetary nebulae in M 32 and the bulge of M 31: Line intensities and oxygen abundances

We present spectroscopy of planetary nebulae in M 32 and in the bulge of M 31 that we obtained with the MOS spectrograph at the Canada-France-Hawaii Telescope. Our sample includes 30 planetary nebulae in M 31 and 9 planetary nebulae in M 32. We also observed one HII region in the disk of M 31. We detected [OIII]λ4363 in 18 of the planetary nebulae, 4 in M 32 and 14 in the bulge...

Primordial 4He abundance: a determination based on the largest sample of H II regions with a methodology tested on model H II regions

We verified the validity of the empirical method to derive the 4He abundance used in our previous papers by applying it to CLOUDY (v13.01) models. Using newly published He i emissivities for which we present convenient fits as well as the output CLOUDY case B hydrogen and He i line intensities, we found that the empirical method is able to reproduce the input CLOUDY 4He abundance...

FR II radio galaxies in the Sloan Digital Sky Survey: observational facts

Starting from the Cambridge Catalogues of radio sources, we have created a sample of 401 Fanaroff–Riley type II (FR II) radio sources that have counterparts in the main galaxy sample of the seventh Data release of the Sloan Digital Sky Survey (SDSS) and analyse their radio and optical properties. We find that the luminosity in the Hα line – which we argue gives a better measure...

Planetary nebulae and H ii regions in the spiral galaxy NGC 300 - Clues on the evolution of abundance gradients and on AGB nucleosynthesis

We have obtained deep spectra of 26 planetary nebulae (PNe) and 9 compact H ii regions in the nearby spiral galaxy NGC 300, and analyzed them together with those of the giant H ii regions previously observed. We have determined the physical properties of all these objects and their He, N, O, Ne, S and Ar abundances in a consistent way. We find that, globally, compact H ii regions...

The ionizing radiation from massive stars and its impact on H ii regions: results from modern model atmospheres

We present a detailed comparison of the ionizing spectral energy distributions (SEDs) predicted by four modern stellar atmosphere codes, tlusty, cmfgen, wm-basic and fastwind. We consider three sets of stellar parameters representing a late O-type dwarf (O9.5 V), a mid-O-type (O7 V) dwarf and an early O-type dwarf (O5.5 V). We explore two different possibilities for such a...

Ionization of the diffuse gas in galaxies: hot low-mass evolved stars at work

We revisit the question of the ionization of the diffuse medium in late-type galaxies, by studying NGC 891, the prototype of edge-on spiral galaxies. The most important challenge for the models considered so far was the observed increase of [O iii]/Hβ, [O ii]/Hβ and [N ii]/Hα with increasing distance to the galactic plane. We propose a scenario based on the expected population of...

A comprehensive classification of galaxies in the Sloan Digital Sky Survey: how to tell true from fake AGN?

We use the WHα versus [N ii]/Hα (WHAN) diagram introduced by us in previous work to provide a comprehensive emission-line classification of Sloan Digital Sky Survey galaxies. This classification is able to cope with the large population of weak line galaxies that do not appear in traditional diagrams due to a lack of some of the diagnostic lines. A further advantage of the WHAN...

A detailed study of the H ii region M 43 and its ionizing star - I. Stellar parameters and nebular empirical analysis

Aims. We have selected the Galactic H ii region M 43, a close-by apparently spherical nebula ionized by a single star (HD 37061, B0.5 V) to investigate several topics of recent interest in the field of H ii regions and massive stars. In a series of two papers, we perform a combined, comprehensive study of the nebula and its ionizing star by using as many observational constraints...

The effects of spatially distributed ionization sources on the temperature structure of H ii regions

Spatially resolved studies of star-forming regions show that the assumption of spherical geometry is not realistic in most cases, with a major complication posed by the gas being ionized by multiple non-centrally located stars or star clusters. Geometrical effects including the spatial configuration of ionizing sources affect the temperature and ionization structure of these...

VLT spectroscopy of low-metallicity emission-line galaxies: abundance patterns and abundance discrepancies

Context. We present deep spectroscopy of a large sample of low-metallicity emission-line galaxies. Aims. The main goal of this study is to derive element abundances in these low-metallicity galaxies. Methods. We analyze 121 VLT spectra of H ii regions in 46 low-metallicity emission-line galaxies. Of these spectra 83 are archival VLT/FORS1+UVES spectra of H ii regions in 31 low...

Modeling the emission line sequence of galaxies

Using a sample of unprecedented size (about 400 objects) of H ii galaxies in which the oxygen abundances have been obtained using the temperature derived from the [O iii] λ4363/5007 line ratio, we confirm that the H ii galaxies form a very narrow sequence in many diagrams relating line ratios and Hβ equivalent width. We divide our sample in three metallicity bins, each of which...

The temperature structure of dusty planetary nebulae

We have analyzed the effects of photoelectric heating by dust grains in photoionization models of planetary nebulae. We have shown that this process is particularly important if planetary nebulae contain a population of small grains. The presence of such grains would solve a number of problems that have found no satisfactory solution so far: i) the thermal energy deficit in some...

Planetary nebulae in M33: probes of asymptotic giant branch nucleosynthesis and interstellar medium abundances*

We have obtained deep optical spectrophotometry of 16 planetary nebulae (PNe) in M33, mostly located in the central 2 kpc of the galaxy, with the Subaru and Keck telescopes. We have derived electron temperatures and chemical abundances from the detection of the [O iii] λ4363 line for the whole sample. We have found one object with an extreme nitrogen abundance, 12 + log(N/H) = 9...

Global emission line trends in spiral galaxies: The reddening and metallicity sequences

We have explored the emission line trends in the integrated spectra of normal spiral galaxies of the Nearby Field Galaxy Survey (Jansen et al. [CITE], b), in order to investigate the relationships between dust extinction, metallicity and some macroscopic properties of spiral galaxies. We found a very strong correlation between the Hβ and Hα equivalent widths, implying that the...

Modelling of aspherical nebulae – I. A quick pseudo-3D photoionization code

We describe a pseudo-3D photoionization code, nebu_3d, and its associated visualization tool, visneb_3d, which are able to treat a wide variety of nebular geometries easily and rapidly, by combining models obtained with a 1D photoionization code. The only requirement for the code to work is that the ionization source is unique and not extended. It is applicable as long as the...

Enrichment of the interstellar medium by metal-rich droplets and the abundance bias in H ii regions

We critically examine a scenario for the enrichment of the interstellar medium (ISM) in which supernova ejecta follow a long (108 yr) journey before falling back onto the galactic disk in the form of metal-rich “droplets”, These droplets do not become fully mixed with the interstellar medium until they become photoionized in H ii regions. We investigate the hypothesis that the...

An evolutionary catalogue of galactic post-AGB and related objects

Aims.With the ongoing AKARI infrared sky survey, of much greater sensitivity than IRAS, a wealth of post-AGB objects may be discovered. It is thus time to organize our present knowledge of known post-AGB stars in the galaxy with a view to using it to search for new post-AGB objects among AKARI sources.Methods.We searched the literature available on the NASA Astrophysics Data...

Alternative diagnostic diagrams and the ‘forgotten’ population of weak line galaxies in the SDSS

A numerous population of weak line galaxies (WLGs) is often left out of statistical studies on emission-line galaxies (ELGs) due to the absence of an adequate classification scheme, since classical diagnostic diagrams, such as [O iii]/Hβ versus [N ii]/Hα (the BPT diagram), require the measurement of at least four emission lines. This paper aims to remedy this situation by...

Galactic planetary nebulae with Wolf-Rayet nuclei - II. A consistent observational data set

We present high resolution spectrophotometric data for a sample of 34 planetary nebulae with [WC] spectral type central stars (WRPNe) in our Galaxy. The observed objects cover a wide range in stellar characteristics: early and late [WC] type stars, as well as weak-emission line stars (WELS). Physical conditions in the nebulae (electron density and temperatures) have been obtained...

The history of star-forming galaxies in the Sloan Digital Sky Survey

This paper, the sixth in the Semi-Empirical Analysis of Galaxies series, studies the evolution of 82 302 star-forming (SF) galaxies from the Sloan Digital Sky Survey. Star formation histories (SFHs) are derived from detailed spectral fits obtained with our publicly available spectral synthesis code starlight. Our main goals are to explore new ways to derive SFHs from the...