Abstract
We explore the ability of four different inverse population synthesis codes
to recover the physical properties of galaxies from their spectra by SED
fitting. Three codes, DynBaS, TGASPEX, and GASPEX, have been implemented by the
authors and are described in detail in the paper. STARLIGHT, the fourth code,
is publicly available. DynBaS selects dynamically a different spectral basis to
expand the spectrum of each target galaxy; TGASPEX uses an unconstrained age
basis, whereas GASPEX and STARLIGHT use for all fits a fixed spectral basis
selected a priori by the code developers. Variable and unconstrained basis
reflect the peculiarities of the fitted spectrum and allow for simple and
robust solutions to the problem of extracting galaxy parameters from spectral
fits. We assemble a Synthetic Spectral Atlas of Galaxies (SSAG), comprising
100,000 galaxy spectra corresponding to an equal number of star formation
histories based on the recipe of Chen et al. (2012). We select a subset of 120
galaxies from SSAG with a colour distribution similar to that of local galaxies
in the seventh data release (DR7) of the Sloan Digital Sky Survey (SDSS) and
produce 30 random noise realisations for each of these spectra. For each
spectrum we recover the mass, mean age, metallicity, internal dust extinction,
and velocity dispersion characterizing the dominant stellar population in the
problem galaxy. All methods produce almost perfect fits to the target spectrum,
but the recovered physical parameters can differ significantly. Our tests
provide a quantitative measure of the accuracy and precision with which these
parameters are recovered by each method. From a statistical point of view all
methods yield similar precisions, whereas DynBaS produces solutions with
minimal systematic biases in the distributions of residuals for all of these
parameters.
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