Inclusion of sdBs in evolutionary population synthesis for binary stellar populations and the application: the determinations of photo-z and galaxy morphology

TL;DR

This paper enhances evolutionary population synthesis models by including subdwarf B stars, enabling improved estimation of galaxy photometric redshifts and morphologies from spectral energy distributions.

Contribution

It integrates sdB stars into EPS models and applies these to determine galaxy photo-z and morphology using combined spectral and photometric data.

Findings

Enhanced SED models improve galaxy redshift estimates.

Galaxy morphological classifications show systematic differences.

Photometric redshifts fluctuate around spectroscopic values.

Abstract

Subdwarf B stars (sdBs) can significantly change the ultraviolet spectra of populations at age t~1Gyr, and have been even included in the volutionary population synthesis (EPS) models by Han et al. (2007). In this study we present the spectral energy distributions (SEDs) of binary stellar populations (BSPs) by combining the EPS models of Han et al. (2007) and those of the Yunnan group (Zhang et al. 2004, 005), which have included various binary interactions (except sdBs) in EPS models. This set of SEDs is vailable upon request from the authors. Using this set of SEDs of BSPs we build the spectra of Burst, E, S0-Sd and Irr types of galaxies by using the package of Bruzual & Charlot (2003, BC03). Combined with the photometric data (filters and magnitudes), we obtain the photometric redshifts and morphologies of 1502 galaxies by using the Hyperz code of Bolzonella et al. (2000). This sample of galaxies is obtained by removing those objects, mismatched with the SDSS/DR7 and GALEX/DR4, from the catalogue of Fukugita et al. (2007). By comparison the results with the SDSS spectroscopic redshifts and the morphological index of Fukugita et al. (2007), we find that the photo-zs fluctuate with the SDSS spectroscopic redshifts, while the Sa-Sc galaxies in the catalogue of Fukugita et al. (2007) are classified earlier as Burst-E galaxies.