Spectroscopic ages and metallicities of stellar populations : validation of full spectrum fitting

By M. Koleva, Ph. Prugniel, P. Ocvirk, D. L. Borgne, C. Soubiran. 2008

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Fitting whole spectra at intermediate spectral resolution (R= 1000–3000), to derive physical properties of stellar populations, appears as an optimized alternative to methods based on spectrophotometric indices: it uses all the redundant information contained in the signal. This paper addresses the validation of the method and it investigates the quality of the population models together with the reliability of the fitting procedures. Our method compares observed optical spectra with models to derive the age, metallicity and line broadening due to the internal kinematics. It is insensitive to the shape of the continuum and the results are consistent with Lick indices but three times more precise. We are using two algorithms: steckmap, a non-parametric regularized program and nbursts a parametric non-linear minimization. We compare three spectral synthesis models for single stellar populations (SSPs): Pegase-HR, Galaxev and Vazdekis/Miles, and we analyse spectra of Galactic clusters whose populations are known from studies of colour–magnitude diagrams (CMD) and spectroscopy of individual stars. We find the following. (1) The quality of the models critically depends on the stellar library they use, and in particular on its coverage in age, metallicity and surface gravity of the stars. Pegase-HR and Vazdekis/Miles are consistent, while the comparison between Pegase-HR and Bruzual & Charlot shows some systematics reflecting the limitations of the stellar library (STELIB) used to generate the latter models. (2) The two fitting programs are consistent. (3) For globular clusters and M67 spectra, the method restitutes metallicities in agreement with spectroscopy of stars with a precision of 0.14 dex. (4) The spectroscopic ages are very sensitive to the presence of a blue horizontal branch (BHB) or of blue stragglers. A BHB morphology results in a young SSP-equivalent age. Fitting a free amount of blue stars in addition to the SSP model to mimic the BHB improves and stabilizes the fit and restores ages in agreement with CMDs studies. This method is potentially able to disentangle age or BHB effects in extragalactic clusters. Full spectrum fitting is reliable method to derive the parameters of a stellar population.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/cf4774595320dffca95ea37641b08f32c30d4c71

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Citations in the corpus

Fitting the integrated spectral energy distributions of galaxies (2010, methodology): “Care needs to be taken that the wavelength calibration of both models and data are better than a tenth of a pixel over the full wavelength range (this is not always the case, see e.g. Koleva et al. 2008).”
Evidence of Environmental Dependencies of Type Ia Supernovae from the Nearby Supernova Factory indicated by Local H$\alpha$ (2013, methodology): “The University of Lyon Spectroscopic analysis Software1 (ULySS, Koleva et al. 2008, 2009) is used to disentangle the stellar and gas components.”
ULySS: a full spectrum fitting package (2009, methodology): “When determining the stellar kinematics by fitting one or several constant CMPs (i. e., fixed spectra, like stars or models without free parameter) the additive term may be required toabsorb the template mismatch (Koleva et al. 2008b).”
Post-starburst galaxies: more than just an interesting curiosity (2008, background): “At low redshift, the quality of spectra and models now allow the analysis of large spectral regions (Cid Fernandes et al. 2005; Tojeiro et al. 2007; Wild et al. 2007; Koleva et al. 2008).”
THE NGC 404 NUCLEUS: STAR CLUSTER AND POSSIBLE INTERMEDIATE-MASS BLACK HOLE (2010, methodology): “All of these involved fitting a small subsample (∼10) of the SSPs with ages ranging from 1 Myr to 20 Gyr (see Walcher et al. 2006; Koleva et al. 2008, for a more complete discussion of stellar population synthesis).”
Stellar Population Inference with Prospector (2020, methodology): “Previous work has shown the integrated-light spectral fitting of globular cluster data returns generally unreliable ages (Koleva et al. 2008; Conroy et al. 2018).”
A comprehensive classification of galaxies in the SDSS: How to tell true from fake AGN? (2010, background): “This feature is almost certainly an artifact of incomplete modelling of the horizontal branch phase (Koleva et al. 2008; Ocvirk 2010; Cid Fernandes & González Delgado 2010).”
Four new observational H(z) data from luminous red galaxies in the Sloan Digital Sky Survey data release seven (2012, methodology): “There are many methods to learn the age and metallicity of stellar systems from a spectrum, such as SED fitting, spectrophotometric indices (e.g., Lick, Rose indices) and full spectrum fitting(Koleva et al., 2008).”
Stellar population gradients in galaxy discs from the CALIFA survey - The influence of bars (2014, background): “Basically, the existing degeneracy between the metallicity and the velocity dispersion (Koleva et al. 2008) biases the mean-weighted metallicites if both parameters are fitted at the same time.”
Evolutionary stellar population synthesis with MILES – I. The base models and a new line index system (2010, methodology): “For an extensive comparison of our newly synthesized SSP SEDs with the models of other authors we refer the reader to the recently published paper of Koleva et al. (2008) and Cid-Fernandes & González (2010)1.”
Modeling the Panchromatic Spectral Energy Distributions of Galaxies (2013, background): “Koleva et al. (2008) investigated the accuracy of full spectrum fitting codes at recovering metallicities.”