F-VIPGI: a new adapted version of VIPGI for FORS2 spectroscopy^⋆

Application to a sample of 16 X-ray selected galaxy clusters at 0.6 ≤ z  ≤ 1.2

¹ Max-Planck-Institut für extraterrestrische Physik (MPE), Giessenbachstrasse 1, 85748 Garching, Germany
e-mail: alessandro.nastasi@mpe.mpg.de
² IASF-INAF - via Bassini 15, 20133 Milano, Italy
³ Institut für Astrophysik Universität Wien, Türkenschanzstr. 17, 1180 Vienna, Austria
⁴ Freelance scientist  

Received: 21 June 2012
Accepted: 3 September 2012

Abstract

Aims. The goal of this paper is twofold. Firstly, we present F-VIPGI, a new version of the VIMOS Interactive Pipeline and Graphical Interface (VIPGI) adapted to handle FORS2 spectroscopic data taken with the standard instrument configuration. Secondly, we investigate the spectro-photometric properties of a sample of galaxies residing in distant X-ray selected galaxy clusters, the optical spectra of which were reduced with this new pipeline.

Methods. We provide basic technical information about the innovations of the new software and refer the reader to the original VIPGI paper for a detailed description of the core functions and performances. As a demonstration of the capabilities of the new pipeline, we then show results obtained for 16 distant (0.65 ≤ z ≤ 1.25) X-ray luminous galaxy clusters selected within the XMM-Newton Distant Cluster Project. We performed a spectral indices analysis of the extracted optical spectra of their members, based on which we created a library of composite high signal-to-noise ratio spectra. We then compared the average spectra of the passive galaxies of our sample with those computed for the same class of objects that reside in the field at similar high redshift and in groups in the local Universe. Finally, We computed the “photometric” properties of our templates and compared them with those of the Coma Cluster galaxies, which we took as representative of the local cluster population.

Results. We demonstrate the capabilities of F-VIPGI, whose strength is an increased efficiency and a simultaneous shortening of FORS2 spectroscopic data reduction time by a factor of ~10 w.r.t. the standard IRAF procedures. We then discuss the quality of the final stacked optical spectra and provide them in electronic form as high-quality spectral templates, representative of passive and star-forming galaxies residing in distant galaxy clusters. By comparing the spectro-photometric properties of our templates with the local and distant galaxy population residing in different environments, we find that passive galaxies in clusters appear to be well evolved already at z ~ 0.8 and even more so than the field galaxies at similar redshift. Even though these findings would point toward a significant acceleration of galaxy evolution in densest environments, we cannot exclude the importance of the mass as the main evolutionary driving element either. The latter effect may indeed be justified by the similarity of our composite passive spectrum with the luminous red galaxies template at intermediate redshift.