Abundance determinations in extragalactic HII regions

The abundance determinations in extragalactic H װ regions are reviewed. The discussion is mainly focused on the different variants of the strong line method (calibrations). However, we do not list and consider in details a numerous relations suggested to convert metallicity-sensitive emission-line combinations into metallicity or temperature estimates. Instead we analyse the foundations of difierent types of calibrations and problems which those calibrations encounter. The empirical (defined by the H װ regions with well-measured abundances) and theoretical or model (defined by the set of photoionization models of H װ regions) metallicity scales are discussed

Interactions and star formation activity in Wolf-Rayet galaxies

We present the main results of the PhD Thesis carried out by L\'opez-S\'anchez (2006), in which a detailed morphological, photometrical and spectroscopical analysis of a sample of 20 Wolf-Rayet (WR) galaxies was realized. The main aims are the study of the star formation and O and WR stellar populations in these galaxies and the role that interactions between low surface companion objects have in the triggering of the bursts. We analyze the morphology, stellar populations, physical conditions, chemical abundances and kinematics of the ionized gas, as well as the star-formation activity of each system.Comment: 16 pages, 15 figure

Metal-THINGS: On the Metallicity and Ionization of ULX Sources in NGC 925

Galaxie

Two types of distribution of the gas velocity dispersion of MaNGA galaxies

The distribution of the gas velocity dispersion σ across the images of 1146 MaNGA galaxies is analyzed. We find that there are two types of distribution of the gas velocity dispersion across the images of galaxies: (i) the distributions of 909 galaxies show a radial symmetry with or without the σ enhancement at the center ("R distribution", radial symmetry in the σ distribution) and (ii) distributions with a band of enhanced σ along the minor axis in the images of 159 galaxies with or without the σ enhancement at the center ("B distribution", band in the σ distribution). The σ distribution across the images of 78 galaxies cannot be reliable classified. We select 806 galaxies with the best defined characteristics (this sample includes 687 galaxies with R distribution and 119 galaxies with B distribution) and compare the properties of galaxies with R and B distributions. We find that the median value of the gas velocity dispersion σm in galaxies with B distribution is higher by around 5 km s-1, on average, than that of galaxies with R distribution. The optical radius R25 of galaxies with B distribution is lower by around 0.1 dex, on average, than that of galaxies with similar masses with R distribution. Thus the properties of a galaxy are related to the type of distribution of the gas velocity dispersion σ across its image. This suggests that the presence of the band of the enhanced gas velocity dispersion can be an indicator of a specific evolution (or a specific stage in the evolution) of a galaxy

On the origin of the luminosity - metallicity relation for late-type galaxies: Spirals to irregulars transition

Accepted for publication in Astronomy and AstrophysicsConsiglio Nazionale delle Ricerche - Biblioteca Centrale - P.le Aldo Moro, 7 Rome / CNR - Consiglio Nazionale delle RichercheSIGLEITItal

The properties and environment of very young galaxies in the local Universe

International audienceIn the local Universe, there are a handful of dwarf compact star-forming galaxies with extremely low oxygen abundances. It has been proposed that they are young, having formed a large fraction of their stellar mass during their last few hundred Myr. However, little is known about the fraction of young stellar populations in more massive galaxies. In a previous article, we analysed  404 000 Sloan Digital Sky Survey spectra to identify a surprisingly large sample of more massive very young galaxies (VYGs), defined to have formed at least |$50{{\ \rm per\ cent}}$| of their stellar mass within the last 1 Gyr. Here, we investigate in detail the properties of a subsample of 207 galaxies that are VYGs according to all three of our spectral models. We compare their properties with those of control sample galaxies (CSGs). We find that VYGs tend to have higher surface brightness and to be more compact, dusty, asymmetric, and clumpy than CSGs. Analysis of a subsample with H i detections reveals that VYGs are more gas rich than CSGs. VYGs tend to reside more in the inner parts of low-mass groups and are twice as likely as CSGs to be interacting with a neighbour galaxy. On the other hand, VYGs and CSGs have similar gas metallicities and large-scale environments (relative to filaments and voids). These results suggest that gas-rich interactions and mergers are the main mechanisms responsible for the recent triggering of star formation in low-redshift VYGs, except for the lowest mass VYGs, where the starbursts would arise from a mixture of mergers and gas infall

Breaks in surface brightness profiles and radial abundance gradients in the discs of spiral galaxies

We examine the relation between breaks in the surface brightness profiles and radial abundance gradients within the optical radius in the discs of 134 spiral galaxies from the CALIFA survey. The distribution of the radial abundance (in logarithmic scale) in each galaxy was fitted by simple and broken linear relations. The surface brightness profile was fitted assuming pure and broken exponents for the disc. We find that the maximum absolute difference between the abundances in a disc given by broken and pure linear relations is less than 0.05 dex in the majority of our galaxies and exceeds the scatter in abundances for 26 out of 134 galaxies considered. The scatter in abundances around the broken linear relation is close (within a few percent) to that around the pure linear relation. The breaks in the surface brightness profiles are more prominent. The scatter around the broken exponent in a number of galaxies is lower by a factor of two or more than that around the pure exponent. The shapes of the abundance gradients and surface brightness profiles within the optical radius in a galaxy may be different. A pure exponential surface brightness profile may be accompanied by a broken abundance gradient and vise versa. There is no correlation between the break radii of the abundance gradients and surface brightness profiles. Thus, a break in the surface brightness profile does not need to be accompanied by a break in the abundance gradient.© ESO, 2017.Peer Reviewe

Circumnuclear regions of different BPT types in star-forming MaNGA galaxies: AGN detectability

© ESO 2020. We consider the circumnuclear regions of star-forming MaNGA galaxies. The spaxels spectra are classified as active-galactic-nucleus-like (AGN-like), H» II-region-like (or SF-like), and intermediate (INT) spectra according to their positions on the Baldwin-Phillips-Terlevich (BPT) diagram. There are the following four configurations of the radiation distributions in the circumnuclear regions in (massive) galaxies: (1) AGN+INT, the innermost region of the AGN-like radiation is surrounded by a ring of radiation of the intermediate type; (2) INT, the central area of radiation of the intermediate type; (3) SF+INT, the inner region of the H» II-region-like radiation is surrounded by a ring of radiation of the intermediate type; and (4) SF, the central area of the H» II-region-like radiation only. The low ionization nuclear emission line regions (LINERs) of configurations 1 and 2 are examined. The spaxel spectra of the LINERs form a sequences on the BPT diagram, that is, they lie along the known AGN-SF mixing line trajectories. The diagnostic line ratios of the spaxels spectra change smoothly with radius, from AGN-like (or INT) line ratios at the galactic center to H» II-region-like at larger galactocentric distances. This is in agreement with the paradigm that the LINERs are excited by AGN activity. We found that the AGN and INT radiation in the circumnuclear region is accompanied by an enhanced gas velocity dispersion σgas. The radius of the area of the AGN and INT radiation is similar to the radius of the area with enhanced σgas, and the central σgas, c correlates with the luminosity of the AGN+INT area. We assume that the gas velocity dispersion can serve as an indicator of the AGN activity. An appreciable enhancement of σgas, c was also measured in the SF-type centers of massive galaxies. The values of σgas, c for the SF-type centers partly overlap with those of the AGN-type centers. This suggests that the manifestation of the circumnuclear region as AGN or as SF on the BPT diagram depends not only on the value of σgas, c (the level of the AGN activity) but it is also governed by an additional parameter(s). We find that there is a demarcation line between the positions of the AGN-type and SF-type objects on the central gas velocity dispersion - central Hα surface brightness diagram, in the sense that an object with a given value of σgas, c is an AGN-type only if the central Hα surface brightness is lower than some value