Qualitative interpretation of galaxy spectra

Abstract

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 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. 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.

Simple step-by-step guide to interpreting galaxy spectra. Accepted for publication in ApJ. 17 pages with 21 figures

References in corpus (9)

• The Host Galaxies and Classification of Active Galactic Nuclei
• The MAPPINGS III Library of Fast Radiative Shock Models
• The Sloan Digital Sky Survey Quasar Catalog IV. Fifth Data Release
• Natural Downsizing in Hierarchical Galaxy Formation
• Recovering galaxy star formation and metallicity histories from spectra using VESPA
• The star formation history and metal content of the "Green Peas". New detailed GTC-OSIRIS spectrophotometry of three galaxies
• Precision abundance analysis of bright HII galaxies
• The temperature and ionization structure of the emitting gas in HII galaxies: Implications for the accuracy of abundance determinations
• The colours of BL Lac objects: a new approach to their classification

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