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This paper is the second in a series, implementing a classification systemfor Gaia observations of unresolved galaxies. Our goals are to determinespectral classes and estimate intrinsic astrophysical parameters via synthetictemplates. Here we describe (1) a new extended library of synthetic galaxyspectra, (2) its comparison with various observations, and (3) first results ofclassification and parametrization experiments using simulated Gaiaspectrophotometry of this library. Using the PEGASE.2 code, based on galaxyevolution models that take account of metallicity evolution, extinctioncorrection, and emission lines (with stellar spectra based on the BaSeLlibrary), we improved our first library and extended it to cover the domain ofmost of the SDSS catalogue. We produce an extended library of 28885 syntheticgalaxy 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 orless. The library is also produced for 4 random values of redshift in the rangeof 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 thegalaxy type, on two values of the age of the galaxy. The synthetic library wascompared and found to be in good agreement with various observations. The firstresults from the SVM classifiers and parametrizers are promising, indicatingthat Hubble types can be reliably predicted and several parameters estimatedwith low bias and variance.

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