Optical to Near-IR Spectrum of a Massive Evolved Galaxy at z = 1.26

TL;DR

This study presents a detailed optical to near-IR spectrum of a massive, evolved galaxy at z=1.26, revealing its passive evolution and massive stellar content, and compares spectral and broad-band data for galaxy property estimation.

Contribution

It provides the first wide-wavelength spectrum of an ERO at z=1.26, comparing spectral and broad-band methods to derive galaxy properties, and discusses galaxy evolution implications.

Findings

Galaxy formed 2-3 Gyr after the Big Bang.

Stellar mass estimated at 10^{11.5} solar masses.

Galaxy evolved passively into a massive elliptical.

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 um 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 broad-band 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* = 10^{11.5} Msun clearly point to this galaxy being a direct ancestor of the brightest elliptical and spheroidal galaxies in the local universe.