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

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.

Fitting the integrated spectral energy distributions of galaxies

“…In order to create a smooth grid, the input parameters (i.e. p1, p2, gas infall and galactic winds) were allowed to vary over a range of values(see Tsalmantza et al 2007Tsalmantza et al , 2009. At this point, while of course guided by prior knowledge of the properties of galaxies, the parameter distribution is chosen nearly ad-hoc.…”

Detecting stars, galaxies, and asteroids withGaia

“…Gaia's objective is to unravel the kinematical, dynamical, and chemical structure and evolution of our Galaxy, the Milky Way (e.g., Gómez et al 2010). In addition, Gaia's data will revolutionise many other areas of astronomy, e.g., stellar structure and evolution, stellar variability, double and multiple stars, solar-system bodies, extra-galactic objects, fundamental physics, and exoplanets (e.g., Pourbaix 2008;Tanga et al 2012;Mignard & Klioner 2010;Eyer et al 2011;Sozzetti 2011;Mouret 2011;Tsalmantza et al 2009;Krone-Martins et al 2013). During its five-year lifetime, Gaia will survey the full sky and repeatedly observe the brightest 1000 million objects, down to 20th magnitude (e.g., de Bruijne et al 2010).…”

GaiaUniverse model snapshot

“…The adopted library of synthetic spectra at low resolution was created Tsalmantza et al (2009) based on the Pegase-2 (Tsalmantza et al 2009), with five different inclinations (0.00, 22.5, 45.0, 67.5, 90.0) for non-elliptical galaxies, and at 11 redshifts (from 0. to 2. by step of 0.2). For all inclinations, the Pegase-2 spectra were computed with internal extinction by transfer model with two geometries either slab or spheroid, depending on type.…”