Title
QUALITATIVE INTERPRETATION OF GALAXY SPECTRA
Author
ROBERTO GIOVANNI TERLEVICH AFONSO
Elena Kirilovsky Terlevich
Access level
Open Access
Subjects
Summary or description
We describe a simple step-by-step guide to qualitative interpretation of galaxy spectra (Fig. 11). Rather than an alternative to existing automated tools, it is put forward as an instrument for quicklook analysis, and for gaining physical insight when interpreting the outputs provided by automated tools. Though the recipe is of 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 (SDSS-DR7), 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 HII 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 1-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.
Publisher
The Astrophysical Journal
Publish date
July 17, 2012
Publication type
Article
Publication version
Accepted Version
Information Resource
Format
application/pdf
Language
English
Audience
Students
Researchers
General public
Citation suggestion
Sánchez Almeida, J., et al., (2012), QUALITATIVE INTERPRETATION OF GALAXY SPECTRA, The Astrophysical Journal, Vol. 756(2):1-17
Source repository
Repositorio Institucional del INAOE
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