Towards a library of synthetic galaxy spectra and preliminary results of classification and parametrization of unresolved galaxies for Gaia. II

¹ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany e-mail: vivitsal@mpia-hd.mpg.de
² Department of Astrophysics Astronomy & Mechanics, Faculty of Physics, University of Athens, 15783 Athens, Greece
³ Institut d'Astrophysique de Paris, 98bis Bd Arago, 75014 Paris, France
⁴ Université de Paris-Sud XI, IAS, 91405 Orsay Cedex, France
⁵ IAA, National Observatory of Athens, PO Box 20048, 118 10 Athens, Greece
⁶ Dionysos Satellite Observatory, National Technical University of Athens, 15780 Athens, Greece
⁷ INAF, Padova Observatory, Vicolo dell'Osservatorio 5, 35122 Padova, Italy
⁸ Université Pierre et Marie Curie, 4 place Jussieu, 75005 Paris, France

Received: 9 March 2009
Accepted: 8 June 2009

Abstract

Aims. This paper is the second in a series, implementing a classification system for Gaia observations of unresolved galaxies. Our goals are to determine spectral classes and estimate intrinsic astrophysical parameters via synthetic templates. Here we describe (1) a new extended library of synthetic galaxy spectra; (2) its comparison with various observations; and (3) first results of classification and parametrization experiments using simulated Gaia spectrophotometry of this library.

Methods. Using the PÉGASE.2 code, based on galaxy evolution models that take account of metallicity evolution, extinction correction, and emission lines (with stellar spectra based on the BaSeL library), we improved our first library and extended it to cover the domain of most of the SDSS catalogue. Our classification and regression models were support vector machines (SVMs).

Results. We produce an extended library of 28 885 synthetic galaxy spectra at zero redshift covering four general Hubble types of galaxies, over the wavelength range between 250 and 1050 nm at a sampling of 1 nm or less. The library is also produced for 4 random values of redshift in the range of 0–0.2. It is computed on a random grid of four key astrophysical parameters (infall timescale and 3 parameters defining the SFR) and, depending on the galaxy type, on two values of the age of the galaxy. The synthetic library was compared and found to be in good agreement with various observations. The first results from the SVM classifiers and parametrizers are promising, indicating that Hubble types can be reliably predicted and several parameters estimated with low bias and variance.