Empirical calibration of the near-infrared Ca II triplet — IV. The stellar population synthesis models

By A. Vazdekis, A. Cenarro, J. Gorgas, N. Cardiel, R. I. D. A. D. Canarias, Spain, U. Madrid, Calar Alto Observatory, Caha, U. Nottingham and 1 more. 2003

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We present a new evolutionary stellar population synthesis model, which predicts spectral energy distributions for single-age single-metallicity stellar populations (SSPs) at resolution 1.5 Angstrom (FWHM) in the spectral region of the near-infrared Ca II triplet feature. The main ingredient of the model is a new extensive empirical stellar spectral library that has been recently presented by Cenarro et al., which is composed of more than 600 stars with an unprecedented coverage of the stellar atmospheric parameters. Two main products of interest for stellar population analysis are presented. The first is a spectral library for SSPs with metallicities -1.7<[Fe/H]<+0.2, a large range of ages (0.1-18 Gyr) and initial mass function (IMF) types. They are well suited to modelling galaxy data, since the SSP spectra, with flux-calibrated response curves, can be smoothed to the resolution of the observational data, taking into account the internal velocity dispersion of the galaxy, allowing the user to analyse the observed spectrum in its own system. We also produce integrated absorption-line indices (namely CaT*, CaT and PaT) for the same SSPs in the form of equivalent widths. We find the following behaviour for the Ca II triplet feature in old-aged SSPs: (i) the strength of the CaT* index does not change much with time for all metallicities for ages larger than similar to3 Gyr; (ii) this index shows a strong dependence on metallicity for values below [M/H]similar to-0.5; and (iii) for larger metallicities this feature does not show a significant dependence either on age or on the metallicity, being more sensitive to changes in the slope of power-like IMF shapes. The SSP spectra have been calibrated with measurements for globular clusters by Armandroff & Zinn, which are well reproduced, probing the validity of using the integrated Ca II triplet feature for determining the metallicities of these systems. Fitting the models to two early-type galaxies of different luminosities (NGC 4478 and 4365), we find that the Ca II triplet measurements cannot be fitted unless a very dwarf-dominated IMF is imposed, or if the Ca abundance is even lower than the Fe abundance. More details can be found in work by Cenarro et al.

Subfields: Astronomy and Astrophysics, Instrumentation

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Citations in the corpus

Medium-resolution Isaac Newton Telescope library of empirical spectra - II. The stellar atmospheric parameters (2006, background): “…the new generation of stellar population models go beyond the prediction of individual features for a simple stellar population (SSP), and they attempt to synthesize full spectral energy distributions (SEDs) (Vazdekis 1999; Vazdekis & Arimoto 1999; Bruzual & Charlot 2003; Vazdekis et al. 2003).”
Radial variations in the stellar initial mass function of early-type galaxies (2014, result): “Considering that Ca2 decreases with Γb (Vazdekis et al. 2003), the mild Ca2 gradient for the high-mass galaxy is fully consistent with the result that the slope of its IMF tends to decrease outwards.”
An updated MILES stellar library and stellar population models (2011, methodology): “Fake_Sun: best representation of the solar spectrum obtained by combining solar-type stars in our library using the interpolation scheme described in Vazdekis et al. (2003) for the Sun parameters above.”
Evolutionary stellar population synthesis with MILES – I. The base models and a new line index system (2010, background): “Models that employ such libraries are, e.g., Vazdekis (1999), Vazdekis et al. (2003) (hereafter V03), Bruzual & Charlot (2003), Le Borgne et al. (2004).”
SPIDER VIII - constraints on the stellar initial mass function of early-type galaxies from a variety of spectral features (2013, methodology): “We refer the reader to appendix A of Vazdekis et al. (2003) for a detailed description of unimodal and bimodal IMFs.”
Evolutionary population synthesis: models, analysis of the ingredients and application to high‐z galaxies (2004, background): “The dependence of the indices on the IMF is discussed in Saglia et al. (2002) and Vazdekis et al. (2003) and will not bere- peated here, where instead we focus on age and metallicity.”
MIUSCAT: extended MILES spectral coverage – I. Stellar population synthesis models (2012, methodology): “For a full description of the algorithm we refer the reader to Vazdekis et al. (2003) (Appendix B).”
The atmospheric parameters and spectral interpolator for the MILES stars (2011, background): “A good example of local interpolation is Vazdekis et al. (2003).”
COUNTING LOW-MASS STARS IN INTEGRATED LIGHT (2011, background): “82 indices, which are relatively narrow features (see also Vazdekis et al. 2003).”
Systematic variation of the stellar initial mass function with velocity dispersion in early-type galaxies (2012, methodology): “It gives c© 2012 RAS, MNRAS000, 1–5 a closer representation of Kroupa-like IMFs forΓ = 1.3 (see, e.g. Figure 1 of Vazdekis et al. 2003).”
Spectroscopic ages and metallicities of stellar populations : validation of full spectrum fitting (2008, methodology): “Vazdekis/Miles models4 are based on the previous models from (Vazdekis 1999; Vazdekis et al. 2003).”
Spectral models for solar-scaled and α-enhanced stellar populations (2007, result): “These indices were compared to the predictions by BC03, CB07 (with Indo-US library), Vazdekis et al. (2003)7 and Vazdekis et al. (in prepa- 7 These models are based on Cenarro et al. (2002) stellar fitting functions and cover the near-IR wavelength range.”
Coudé-feed stellar spectral library – atmospheric parameters (2010, unknown): “As an alternative to this global interpolation, Vazdekis et al. (2003) developed a Gaussian kernel smoothing, which may be less sensitive to biases, but is more sensitive to the errors on the atmospheric parameters and to the particularities of the stars in the scarcely populated regions of the…”
UV-extended E-MILES stellar population models: young components in massive early-type galaxies (2016, methodology): “For each star, with a given set of atmospheric parameters, we use the spectra of the stars of the library with the closest parameters to apply the interpolation scheme described in Vazdekis et al. (2003) (see Appendix B), as updated in Vazdekis et al. (2015).”
Stellar populations of early-type galaxies in different environments - II. Ages and metallicities (2006, methodology): “The new generation of stellar population models do not only predict individual features as a function of the age and metallicity, but synthesise full spectral energy distributions(SEDs) (Vazdekis 1999; Vazdekis et al. 2003; Bruzual & Charlot 2003; Le Borgne et al. 2004).”
Evolutionary stellar population synthesis with MILES – II. Scaled-solar and α-enhanced models (2015, methodology): “For the MIUSCAT models, we employ the Indo-US stellar library Valdes et al. (2004) to fill-in the gap left in between the MILES range (Paper I) and Ca II triplet range (Vazdekis et al. 2003).”