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2+We present a methodology for the use of sulphur as global metallicity tracer in galaxies, allowing performing a complete abundance analysis using only the red-to-near-infrared spectral region. We have applied it to a compilation of high-quality data split into two samples: H  ii regions (DHR) in spiral and irregular galaxies, and dwarf galaxies dominated by a strong starburst (H  ii  Gal). Sulphur abundances have been derived by direct methods under the assumption of an ionization structure composed of two zones: an intermediate-ionization one where S++ is originated, and a low-ionization one where S+ is formed. Ionization correction factors (ICF) have been calculated from the Ar/Ar3+ ratio and are shown to correlate with the hardness of the radiation field. Only about 10 per cent of the objects show S3+ contributions to the total abundance larger than 30 per cent. A good correlation exists between sulphur abundance and ionizing temperature with low-metallicity objects being ionized by hotter stars. No correlation is found between ionization parameter and total S/H abundance. Most of the H  ii  Gal objects show S/O ratios below the solar value and a trend for increasing S/O ratios with increasing sulphur abundances, while DHR objects show S/O ratios larger than solar and a tendency for lower S/O ratios for higher metallicities. Finally, we present a calibration of the sulphur abundance through the S 23 parameter that remains single valued up to sulphur abundances well beyond the solar value. S 23 is independent of the ionization parameter and only weakly dependent on ionizing temperature. [ABSTRACT FROM AUTHOR]

This work presents a Bayesian algorithm to fit the recombination and collisionally excited line spectra of gas photoionized by clusters of young stars. The current model consists of 14 dimensions: two electron temperatures, one electron density, the extinction coefficient, the optical depth on the |$\rm He\, \small {I}$| recombination lines, and nine ionic species. The results are in very good agreement with those previously published using the traditional methodology. The probabilistic programming library pymc3 was chosen to explore the parameter space via an NUTs sampler. These machine learning tools provided excellent convergence quality and speed. The primordial helium abundance measured from a multivariable regression using oxygen, nitrogen, and sulfur was |$Y_{\mathrm{ P},\, \mathrm{ O}\!-\!\mathrm{ N}\!-\!\mathrm{ S}}=0.243\pm 0.005$| in agreement with a standard Big Bang scenario. [ABSTRACT FROM AUTHOR]

We present a sample of 22 blue [(B - V)AB < 0.45], luminous (MB,AB < -18.9), metal-poor galaxies in the 0.69☉ and 1/3 Z☉. We find that galaxies in our sample have comparablemetallicities to other intermediate-redshift samples, but are more metal poor than local systems of similar B-band luminosities and star formation activity. The galaxies here show similar properties to the green peas discovered at z ≃ 0.2-0.3, though our galaxies tend to be slightly less luminous. [ABSTRACT FROM AUTHOR]

This work investigates the main mechanism(s) that regulate the specific star formation rate (SSFR) in nearby galaxies, cross-correlating two proxies of this quantity - the equivalent width of the Ha line and the (u - r) colour - with other physical properties (mass, metallicity, environment, morphology, and the presence of close companions) in a sample of ~82 500 galaxies extracted from the Sloan Digital Sky Survey. The existence of a relatively tight 'ageing sequence' in the colour-equivalent width plane favours a scenario where the secular conversion of gas into stars (i.e. nature) is the main physical driver of the instantaneous SSFR and the gradual transition from a 'chemically primitive' (metal-poor and intensely star-forming) state to a 'chemically evolved' (metal-rich and passively evolving) system. Nevertheless, environmental factors (i.e. nurture) are also important. In the field, galaxies may be temporarily affected by discrete 'quenching' and 'rejuvenation' episodes, but such events show little statistical significance in a probabilistic sense, and we find no evidence that galaxy interactions are, on average, a dominant driver of star formation. Although visually classified mergers tend to display systematically higher EW(Ha) and bluer (u - r) colours for a given luminosity, most galaxies with high SSFR have uncertain morphologies, which could be due to either internal or external processes. Field galaxies of early and late morphological types are consistent with the gradual 'ageing' scenario, with no obvious signatures of a sudden decrease in their SSFR. In contrast, star formation is significantly reduced and sometimes completely quenched on a short time-scale in dense environments, where many objects are found on a 'quenched sequence' in the colour-equivalent width plane. [ABSTRACT FROM AUTHOR]

This work studies the relation between gas-phase oxygen abundance and stellar-to-gas fraction in nearby galaxies. We first derive the theoretical prediction, and argue that this relation is fundamental, in the sense that it must be verified regardless of the details of the gas accretion and star formation histories. Moreover, it should hold on 'local' scales, i.e. in regions of the order of 1 kpc. These predictions are then compared with a set of spectroscopic observations, including both integrated and resolved data. Although the results depend somewhat on the adopted metallicity calibration, observed galaxies are consistent with the predicted relation, imposing tight constraints on the mass-loading factor of (enriched) galactic winds. The proposed parametrization of the star fraction-metallicity relation is able to describe the observed dependence of the oxygen abundance on gas mass at fixed stellar mass. However, the 'local' mass-metallicity relation also depends on the relation between stellar and gas surface densities. [ABSTRACT FROM AUTHOR]

We present the PPAK Integral Field Spectroscopy (IFS) Nearby Galaxies Survey (PINGS), a two-dimensional spectroscopic mosaicking of 17 nearby disc galaxies in the optical wavelength range. This project represents the first attempt to obtain continuous coverage spectra of the whole surface of a galaxy in the nearby Universe. The final data set comprises more than 50 000 individual spectra, covering in total an observed area of nearly 80 arcmin . The observations will be supplemented with broad-band and narrow-band imaging for those objects without publicly available images in order to maximize the scientific and archival values of the data set. In this paper we describe the main astrophysical issues to be addressed by the PINGS project, present the galaxy sample and explain the observing strategy, the data reduction process and all uncertainties involved. Additionally, we give some scientific highlights extracted from the first analysis of the PINGS sample. A companion paper will report on the first results obtained for NGC 628: the largest IFS survey on a single galaxy. [ABSTRACT FROM AUTHOR]

We summarize the results obtained from our suite of chemical evolution models for spiral disks, computed for different total masses and star formation efficiencies. Once the gas, stars and star formation radial distributions are reproduced, we analyze the Oxygen abundances radial profiles for gas and stars, in addition to stellar averaged ages and global metallicity. We examine scenarios for the potential origin of the apparent flattening of abundance gradients in the outskirts of disk galaxies, in particular the role of molecular gas formation prescriptions. [ABSTRACT FROM PUBLISHER]

We have computed a series of realistic and self-consistent models of the emitted spectra of H ii galaxies. Our models combine different codes of chemical evolution, evolutionary population synthesis and photoionization. The emitted spectrum of H ii galaxies is reproduced by means of the photoionization codecloudy, using as ionizing spectrum the spectral energy distribution of the modelled H ii galaxy, which in turn is calculated according to a star formation history and a metallicity evolution given by a chemical evolution model that follows the abundances of 15 different elements. The contribution of emission lines to the broad-band colours is explicitly taken into account. The results of our code are compared with photometric and spectroscopic data of H ii galaxies. Our technique reproduces observed diagnostic diagrams, abundances, equivalent width–colour and equivalent width–metallicity relations for local H ii galaxies. [ABSTRACT FROM AUTHOR]

We have obtained long-slit observations in the optical and near-infrared of 12 circumnuclear H ii regions [circumnuclear star-forming regions (CNSFR)] in the early-type spiral galaxies NGC 2903, 3351 and 3504 with the aim of deriving their chemical abundances. Only for one of the regions, the [S iii]λ6312 Å was detected providing, together with the nebular [S iii] lines at λλ9069, 9532 Å, a value of the electron temperature of . A semi-empirical method for the derivation of abundances in the high metallicity regime is presented. We obtain abundances which are comparable to those found in high metallicity disc H ii regions from direct measurements of electron temperatures and consistent with solar values within the errors. The region with the highest oxygen abundance is R3+R4 in NGC 3504, , about 1.5 solar if the solar oxygen abundance is set at the value derived by Asplund, Grevesse & Sauval, . Region R7 in NGC 3351 has the lowest oxygen abundance of the sample, about 0.6 times solar. In all the observed CNSFR the O/H abundance is dominated by the O+/H+ contribution, as is also the case for high metallicity disc H ii regions. For our observed regions, however, also the S+/S2+ ratio is larger than one, contrary to what is found in high metallicity disc H ii regions for which, in general, the sulphur abundances are dominated by S2+/H+. The derived N/O ratios are in average larger than those found in high metallicity disc H ii regions and they do not seem to follow the trend of N/O versus O/H which marks the secondary behaviour of nitrogen. On the other hand, the S/O ratios span a very narrow range between 0.6 and 0.8 of the solar value. As compared to high metallicity disc H ii regions, CNSFR show values of the O23 and the N2 parameters whose distributions are shifted to lower and higher values, respectively, hence, even though their derived oxygen and sulphur abundances are similar, higher values would in principle be obtained for the CNSFR if pure empirical methods were used to estimate abundances. CNSFR also show lower ionization parameters than their disc counterparts, as derived from the [S ii]/[S iii]. Their ionization structure also seems to be different with CNSFR showing radiation field properties more similar to H ii galaxies than to disc high metallicity H ii regions. [ABSTRACT FROM AUTHOR]

The main objective of this work is to check if the star formation efficiency plays a relevant role in the evolution of the relative abundance N/O. In order to explore this idea, we analyse the evolution of the nitrogen-to-oxygen ratio as predicted by a set of computed theoretical models. These models consist of simulated galaxies with different total masses which are evolved assuming different collapse time-scales and different star formation efficiencies. The combinations of these two parameters produce different star formation histories, which in turn have, as we show, an important impact on the resulting N/O ratio. Since we want to check the effect of variations in these efficiencies on our model results, the same stellar yield sets are used for all of them. The selected yields have an important primary nitrogen contribution coming from low- and intermediate-mass stars, which implies that N is ejected with a certain delay with respect to O. It allows us to obtain, as we demonstrate, a dispersion of results in the N/O–O/H plane when star formation efficiencies vary which is in general agreement with observations. The model results for the N/O abundance ratio are in good agreement with most observational data trends. In particular, the behaviour shown by the extragalactic H ii regions is well reproduced with present-time resulting abundances. Furthermore, the low N/O values estimated for high-redshift objects, such as those obtained for damped Lyman α galaxies, as well as the higher (and constant) values of N/O observed for irregular and dwarf galaxies or halo stars, can be simultaneously obtained with our models at the same low oxygen abundances 12 + log(O/H) ∼ 7. We therefore conclude that, even though there seems to be a general belief that abundance ratios depend mostly on stellar yields, these are not the only parameter at work when both elements are ejected by stars of different mass ranges, and that differences in the star formation history of galaxies and regions within them are a key factor to explain the data in the N/O–O/H plane. [ABSTRACT FROM AUTHOR]

We propose a methodology to perform a self-consistent analysis of the physical properties of the emitting gas of H ii galaxies adequate to the data that can be obtained with the 21st century technology. This methodology requires the production and calibration of empirical relations between the different line temperatures that should supersede currently used ones based on very simple, and poorly tested, photoionization model sequences. As a first step to reach these goals, we have obtained simultaneous blue to far red long-slit spectra with the William Herschel Telescope (WHT) of three compact H ii galaxies selected from the Sloan Digital Sky Survey (SDSS) Data Release 2 (DR2) spectral catalogue using the INAOE Virtual Observatory superserver. Our spectra cover the range from 3200 to 10 500 Å, including the Balmer jump, the [O ii] lines, the [S iii] λλ 9069, 9532 Å doublet as well as various weak auroral lines such as [O iii] λ 4363 Å and [S iii] λ 6312 Å. For the three objects, we have measured at least four line temperatures, T([O iii]), T([S iii]), T([O ii]) and T([S ii]), and the Balmer continuum temperature T(Bac). These measurements and a careful and realistic treatment of the observational errors yield total oxygen abundances with accuracies between 5 and 9 per cent. These accuracies are expected to improve as better calibrations based on more precise measurements, both on electron temperatures and densities, are produced. We have compared our obtained spectra with those downloaded from the SDSS DR3 finding a satisfactory agreement. The analysis of these spectra yields values of line temperatures and elemental ionic and total abundances which are in general agreement with those derived from the WHT spectra, although for most quantities they can only be taken as estimates since, due to the lack of direct measurements of the required lines, theoretical models had to be used whose uncertainties are impossible to quantify. The ionization structure found for the observed objects from the O+/O2+ and S+/S2+ ratios points to high values of the ionizing radiation, as traced by the values of the ‘softness parameter’η which is less than 1 for the three objects. The use of line temperatures derived from T([O iii]) based on current photoionization models yields for the two highest excitation objects, much higher values of η which would imply lower ionizing temperatures. This is, however, inconsistent with the ionization structure as probed by the measured emission-line intensities. Finally, we have measured the T(Bac) for the three observed objects and derived temperature fluctuations. Only for one of the objects, the temperature fluctuation is significant and could lead to higher oxygen abundances by about 0.20 dex. [ABSTRACT FROM AUTHOR]

We present a statistical study of a very large sample of H ii galaxies taken from the literature. We focus on the differences in several properties between galaxies that show the auroral line [O iii]λ4363 and those that do not present this feature in their spectra. It turns out that objects without this auroral line are more luminous, are more metal-rich and present a lower ionization degree. The underlying population is found to be much more important for objects without the [O iii]λ4363 line, and the effective temperature of the ionizing star clusters of galaxies not showing the auroral line is probably lower. We also study the subsample of H ii galaxies whose properties most closely resemble the properties of the intermediate-redshift population of luminous compact blue galaxies (LCBGs). The objects from this subsample are more similar to the objects not showing the [O iii]λ4363 line. It might therefore be expected that the intermediate- redshift population of LCBGs is powered by very massive, yet somewhat aged, star clusters. The oxygen abundance of LCBGs would be greater than the average oxygen abundance of local H ii galaxies. [ABSTRACT FROM AUTHOR]

We present a generalization of the multiphase chemical evolution model (CEM) applied to a wide set of theoretical galaxies with different masses and evolutionary rates. This generalized set of models has been computed using the so-called universal rotation curve from Persic, Salucci&Steel to calculate the radial mass distribution of 44 theoretical protogalaxies. This distribution is a fundamental input which, besides its own effect on the galaxy evolution, defines the characteristic collapse time-scale or gas infall rate on to the disc. We have adopted 10 sets of values, between 0 and 1, for the molecular cloud and star formation efficiencies, as corresponding to their probability nature, for each one of the radial distributions of total mass. Thus, we have constructed a biparametric grid of models, depending on those efficiency sets and on the rotation velocity, whose results are valid in principle for any spiral or irregular galaxy. The model results provide the time-evolution of different regions of the disc and the halo along galactocentric distance, measured by the gas (atomic and molecular) and stellar masses, the star formation rate (SFR) and chemical abundances of 14 elements, for a total of 440 models. This grid may be used to estimate the evolution of a given galaxy for which only present time information, such as radial distributions of elemental abundances, gas densities and/or star formation, which are the usual observational constraints of chemical evolution models (CEMs), is available. [ABSTRACT FROM AUTHOR]

ABSTRACT The ionizing stellar populations of 11 H ii regions in the spiral galaxies: NGC 628, 925, 1232 and 1637, all of them reported to have solar or oversolar abundances according to empirical calibrations, have been analysed using stellar population synthesis models. Four of the observed regions in the sample show features which indicate the presence of a population of Wolf–Rayet (WR) stars with ages between 2.3 and 4.1 Myr. This population is sufficient to explain the emission line spectrum of the low-metallicity region H13 in NGC 628, taking into account the uncertainties involved in both observations and model computations. This is not the case for the rest of the regions for which a second ionizing population is required to simultaneously reproduce both the WR features and the emission line spectrum. Composite populations are also found for half of the regions without WR features, although in this case, the result is based only on the emission line spectrum analysis. For two of the regions showing WR features, no consistent solution is found, as the population containing WR stars produces a spectral energy distribution which is too hard to explain the emission of the gas. Several solutions are proposed to solve this problem. [ABSTRACT FROM AUTHOR]

We present long-slit observations in the optical and near-infrared of 14 H ii regions in the spiral galaxies NGC 628, 925, 1232 and 1637, all of them reported to have solar or oversolar abundances according to empirical calibrations. For seven of the observed regions, ion-weighted temperatures from optical forbidden auroral to nebular line ratios are obtained and, for six of them, the oxygen abundances derived by standard methods turn out to be significantly lower than solar. The other one, named CDT1 in NGC 1232, shows an oxygen abundance of , and constitutes, to the best of our knowledge, the first high-metallicity H ii region for which accurate line temperatures, and hence elemental abundances, have been derived. For the rest of the regions no line temperature measurements could be made, and the metallicity has been determined by means of both detailed photoionization modelling and the sulphur abundance parameter S[sub 23]. Only one of these regions shows values of O[sub 23] and S[sub 23] implying a solar or oversolar metallicity. According to our analysis, only two of the observed regions can therefore be considered as of high metallicity. These two fit the trends previously found in other high-metallicity H ii regions, i.e., N/O and S/O abundance ratios seem to be higher and lower than solar respectively. [ABSTRACT FROM AUTHOR]

We analyse the evolution with redshift of the radial gradient of oxygen abundances in spiral disks resulting from our MULCHEM chemical evolution models, computed for galaxies of different sizes or masses, studying the relationships between the gradients and galaxy characteristics as the stellar mass, the size, the gas fraction or the star formation rate for z < 4. [ABSTRACT FROM AUTHOR]

We propose a methodology to perform a self-consistent analysis of the physical properties of the emitting gas of HII galaxies adequate to the data that can be obtained with the XXI century technology. This methodology requires the production and calibration of empirical relations between the different line temperatures that should superseed currently used ones based on very simple, and poorly tested, photo-ionization model sequences.To reach these goals we have obtained simultaneous blue to far red longslit spectra with the William Herschel Telescope (WHT) in La Palma and the 3.5m telescope at the Centro Astronómico Hispano Alemán (CAHA) of three (Hägele et al. 2006.MNRAS.372.293) and seven (Hägele et al. in preparation) compact HII galaxies respectively. The objects were selected from the Sloan Digital Sky Survey (SDSS) Data Release 3 (DR3) spectral catalog using the INAOE Virtual Observatory superserver.For the observed objects we have measured at least four line temperatures: T([OIII]), T([SIII]), T([OII]) and T([SII]), and in three cases also T([NII]). The relation between T([SIII]) and T([OIII]) can be fitted with a unique empirical calibration. The actual fit to the data is: T([SIII]) = (1.19±0.08) T([OIII]) – (0.32±0.10). In contrast, for the relation between T([OII]) and T([OIII]) there is no single empirical calibration and it is not possible to give an estimate of the error introduced by the application of this procedure.We have also measured the Balmer continuum temperature T(Bac) for the three WHT objects and derived the temperature fluctuations as defined by Peimbert (1967). Only for one of these objects, the temperature fluctuation is significant and could lead to higher oxygen abundances by about 0.20 dex (Hägele et al. 2006.MNRAS.372.293).The measurements of several different line temperatures and a careful and realistic treatment of the observational errors yield total oxygen abundances with accuracies between 5 and 10%. The fractional error is as low as 2% for the ionic O2+/H+ ratio and increases to 15% for the O+/H+ ratio. These accuracies are expected to improve as better calibrations based on more precise measurements, both on electron temperatures and densities, are produced. The accuracies are lower in the case of the abundances of sulphur (of the order of 20% for S+ and 12% for S2+), the error increases further (up to 30%) for the total abundance of sulphur due to the uncertainties in the ionization correction fractions (ICF). This is in contrast with the small errors quoted for line temperatures other than T([OIII]) in the literature, in part due to the commonly adopted methodology of deriving them from the measured T([OIII]) through theoretical relations. These relations are obtained from photoionization models and no uncertainty is attached to them. If this methodology were to be adopted, the theoretical relations should be adequately tested and empirical relations between the relevant line temperatures should be obtained in order to quantify the corresponding model uncertainties. [ABSTRACT FROM PUBLISHER]