Optical to Near‐Infrared Spectrum of a Massive Evolved Galaxy atz= 1.26

Abstract

We present the optical to near-infrared (IR) spectrum of the galaxy TSPS J1329–0957, a red and bright member of the class of extremely red objects (EROs) at z = 1.26. This galaxy was found in the course of the Tokyo-Stromlo Photometry Survey (TSPS) which we are conducting in the southern sky. The spectroscopic observations were carried out with the Gemini Multi-Object Spectrograph (GMOS) and the Gemini Near Infra-Red Spectrograph (GNIRS) mounted on the Gemini-South telescope. The wide wavelength coverage of 0.6-2.3 μm provides useful clues as to the nature of EROs while most published spectra are limited to a narrower spectral range which is dictated by the need for efficient redshift determination in a large survey. We compare our spectrum with several optical composite spectra obtained in recent large surveys, and with stellar population synthesis models. The effectiveness of using near-IR broadband data, instead of the spectral data, in deriving the galaxy properties are also investigated. We find that TSPS J1329–0957 formed when the universe was 2-3 Gyr old, and subsequently evolved passively to become one of the most massive galaxies found in the z = 1-2 universe. Its early type and estimated stellar mass of M* = 1011.5 M☉ clearly point to this galaxy being a direct ancestor of the brightest elliptical and spheroidal galaxies in the local universe.