Confidence levels of evolutionary synthesis models

Cerviño, M.; Valls–Gabaud, D.; Luridiana, V.; Mas-Hesse, J. M.

doi:10.1051/0004-6361:20011266

Cited by 109 publications

(159 citation statements)

References 19 publications

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“…The transition between the two regimes happens in the age range 4-5.5 Ma and it is due to a softening of the ionizing continua in such age range. Comparing with the evolution of the cluster T eff , defined as in Mas-Hesse & Kunth (1991), the change in the slope is associated with a cluster T eff ∼ 3.5×10 4 K following the results from Cerviño & Mas-Hesse (1994) and Cerviño et al (2002b) 3 . Such cluster T eff is not due to the predominance of a specific type of star but to a mix of different types of stars.…”

Section: Collisional Linesmentioning

confidence: 71%

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On emission-line spectra obtained from evolutionary synthesis models

Villaverde

Cerviño

Luridiana

2010

A&A

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Aims. In this paper we study the influence of the ionizing cluster mass on the emission line spectrum of H ii regions in order to determine the influence of low mass clusters on the integrated emission line spectra of galaxies. Methods. For this purpose, we present a grid of photoionization models that covers metallicities from Z = 0.001 to Z = 0.040, ages from 0.1 to 10 Ma (with a time step of 0.1 Ma), and cluster initial masses from 1 to 10 7 M . The stellar masses follow a Salpeter initial mass function (IMF) in an instantaneous burst mode of star formation. We obtain power-law scale-relations between emission-line luminosities and ionizing cluster masses from the grids and we evaluate the dependences on the ionizing cluster mass for some line luminosities, equivalent widths and line ratios. Results. Power-law scale-relations are shown to be useful tools to obtain robust diagnostics, as examples: (a) Hα/Hβ ratio varies from the usually assumed value of 2.86, these variations imply the existence of a lower limit to the attainable precision in extinction star formation rate indicator for ages older than ∼4.5 Ma. We also show that the ionizing cluster mass dependence explains why empirical calibrations produce more reliable diagnostics of some emission lines than photoionization models grids. Finally, we show preliminary results about the contribution of low mass clusters (M < 10 4 M ) to the integrated emission line spectra of galaxies, which can be as high as 80% for some relevant lines.

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Section: Collisional Linesmentioning

confidence: 71%

“…EW(Hβ) depends mainly on the metallicity (Cerviño & Mas-Hesse 1994) and age of the cluster with almost no variations due to the size of the cluster, if sampling effects are not considered (but see Cerviño et al 2000Cerviño et al , 2002b.…”

Section: Hβ Equivalent Widthmentioning

confidence: 99%

On emission-line spectra obtained from evolutionary synthesis models

Villaverde

Cerviño

Luridiana

2010

A&A

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“…Evolutionary synthesis models assume average numbers of stars with different effective temperatures and luminosities determined by the stellar evolution and the stellar birth rate: the number of stars with a given mass that were born at a given time (parametrized by the initial mass function, IMF, and the star formation history, SFH). The averages correctly describe the asymptotic properties of clusters with infinite (or a very large) number of stars (see Cerviño & Valls-Gabaud 2009;Cerviño & Luridiana 2005, for more detailed explanations). In more realistic cases, this proportionality is only valid as the average of several clusters, but it is not always a reliable representation of individual clusters.…”

Section: Introductionmentioning

confidence: 81%

Modeling the ionizing spectra of H II regions: individual stars versus stellar ensembles

Villaverde

Cerviño

Luridiana

2010

A&A

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Aims. We study how IMF sampling affects the ionizing flux and emission line spectra of low mass stellar clusters. Methods. We performed 2 × 10 6 Monte Carlo simulations of zero-age solar-metallicity stellar clusters covering the 20−10 6 M mass range. We study the distribution of cluster stellar masses, M clus , ionizing fluxes, Q(H 0 ), and effective temperatures, T clus eff . We compute photoionization models that broadly describe the results of the simulations and compare them with photoionization grids.Results. Our main results are: (a) a large number of low mass clusters (80% for M clus = 100 M ) are unable to form an H ii region. (b) There are a few overluminous stellar clusters that form H ii regions. These overluminous clusters preserve statistically the mean value of Q(H 0 ) obtained by synthesis models, but the mean value cannot be used as a description of particular clusters. (c) The ionizing continuum of clusters with M clus < ∼ 10 4 M is more accurately described by an individual star with self-consistent effective temperature (T * eff ) and Q(H 0 ) than by the ensemble of stars (or a cluster T clus eff ) produced by synthesis models. (d) Photoionization grids of stellar clusters cannot be used to derive the global properties of low mass clusters. Conclusions. Although variations in the upper mass limit, m up , of the IMF would reproduce the effects of IMF sampling, we find that an ad hoc law that relates m up to M clus in the modeling of stellar clusters is useless, since: (a) it does not cover the whole range of possible cases; and (b) the modeling of stellar clusters with an IMF is motivated by the need to derive the global properties of the cluster: however, in clusters affected by sampling effects we have no access to global information of the cluster but only particular information about a few individual stars.

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“…Some of these can be quantified using selected information provided by continuous population synthesis models (e.g. Lançon & Mouhcine 2000;Cerviño et al 2002;Cerviño & Luridiana 2004, 2006, but others require using discrete population synthesis models (Barbaro & Bertelli 1977;Girardi & Bica 1993;Bruzual 2002;Deveikis et al 2008;Piskunov et al 2009;Popescu & Hanson 2010). The predicted luminosity and colour distributions depend strongly on the total mass (or star number) in the cluster, and can be far from Gaussian even when the total mass exceeds 10 5 M .…”

Section: Introductionmentioning

confidence: 99%

Accounting for stochastic fluctuations when analysing the integrated light of star clusters

Fouesneau¹,

Lançon²

2010

A&A

110

132

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Context. Star clusters are studied widely both as benchmarks for stellar evolution models and in their own right. Cluster age distributions and mass distributions within galaxies are probes of star formation histories and of cluster formation and disruption processes. The vast majority of clusters in the Universe are small, and it is well known that the integrated fluxes and colours of all but the most massive ones have broad probability distributions, owing to small numbers of bright stars. Aims. This paper goes beyond describing predicted probability distributions to present results of the analysis of cluster energy distributions in an explicitly stochastic context. Methods. The method developed is Bayesian. It provides posterior probability distributions in the age-mass-extinction space, using multi-wavelength photometric observations and a large collection of Monte-Carlo simulations of clusters of finite stellar masses. The main priors are the assumed intrinsic distributions of current mass and current age for clusters in a galaxy. Both UBVI and UBVIK data sets are considered, and the study conducted in this paper is restricted to the solar metallicity. Results. We first use the collection of simulations to reassess and explain errors arising from the use of standard analysis methods, which are based on continuous population synthesis models: systematic errors on ages and random errors on masses are large, while systematic errors on masses tend to be smaller. The age-mass distributions obtained after analysis of a synthetic sample are very similar to those found for real galaxies in the literature. The Bayesian approach, on the other hand, is very successful in recovering the input ages and masses over ages ranging between 20 Myr and 1.5 Gyr, with only limited systematics that we explain. Conclusions. Considering stochasticity is important, more important for instance than the choice of adding or removing near-IR data in many cases. We found no immediately obvious reason to reject priors inspired by previous (standard) analyses of cluster populations in galaxies, i.e., cluster distributions that scale with mass as M −2 and are uniform on a logarithmic age scale.

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Confidence levels of evolutionary synthesis models

Cited by 109 publications

References 19 publications

On emission-line spectra obtained from evolutionary synthesis models

On emission-line spectra obtained from evolutionary synthesis models

Modeling the ionizing spectra of H II regions: individual stars versus stellar ensembles

Accounting for stochastic fluctuations when analysing the integrated light of star clusters

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