Bibcode
Sánchez-Almeida, J.; Terlevich, R.; Terlevich, E.; Cid Fernandes, R.; Morales-Luis, A. B.
Referencia bibliográfica
The Astrophysical Journal, Volume 756, Issue 2, article id. 163 (2012).
Fecha de publicación:
9
2012
Revista
Número de citas
28
Número de citas referidas
24
Descripción
We describe a simple step-by-step guide to qualitative interpretation of
galaxy spectra. Rather than an alternative to existing automated tools,
it is put forward as an instrument for quick-look analysis and for
gaining physical insight when interpreting the outputs provided by
automated tools. Though the recipe is for general application, it was
developed for understanding the nature of the Automatic Spectroscopic
K-means-based (ASK) template spectra. They resulted from the
classification of all the galaxy spectra in the Sloan Digital Sky Survey
data release 7, thus being a comprehensive representation of the galaxy
spectra in the local universe. Using the recipe, we give a description
of the properties of the gas and the stars that characterize the ASK
classes, from those corresponding to passively evolving galaxies, to H
II galaxies undergoing a galaxy-wide starburst. The qualitative analysis
is found to be in excellent agreement with quantitative analyses of the
same spectra. We compare the mean ages of the stellar populations with
those inferred using the code STARLIGHT. We also examine the estimated
gas-phase metallicity with the metallicities obtained using
electron-temperature-based methods. A number of byproducts follow from
the analysis. There is a tight correlation between the age of the
stellar population and the metallicity of the gas, which is stronger
than the correlations between galaxy mass and stellar age, and galaxy
mass and gas metallicity. The galaxy spectra are known to follow a
one-dimensional sequence, and we identify the luminosity-weighted mean
stellar age as the affine parameter that describes the sequence. All ASK
classes happen to have a significant fraction of old stars, although
spectrum-wise they are outshined by the youngest populations. Old stars
are metal-rich or metal-poor depending on whether they reside in passive
galaxies or in star-forming galaxies.
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