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arXiv · 1011.1947

Low-ionization galaxies and evolution in a pilot survey up to z = 1

E. Giraud·Q. -S. Gu·J. Melnick·H. Quintana·F. Selman·I. Toledo·P. Zelaya
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Abstract

We present galaxy spectroscopic data on a pencil beam of $10.75' \times7.5'$ centered on the X-ray cluster RXJ0054.0-2823 at $z = 0.29$. We study the spectral evolution of galaxies from $z=1$ down to the cluster redshift in a magnitude-limited sample at $\rm R\leq23$, for which the statistical properties of the sample are well understood. We divide emission-line galaxies in star-forming galaxies, LINERs, and Seyferts by using emission-line ratios of [OII], $\rm Hβ$, and [OIII], and derive stellar fractions from population synthesis models. We focus our analysis on absorption and low-ionization galaxies. For absorption-line galaxies we recover the well known result that these galaxies have had no detectable evolution since $z\sim0.6-0.7$, but we also find that in the range $z=0.65-1$ at least 50% of the stars in bright absorption systems are younger than 2.5Gyr. Faint absorption-line galaxies in the cluster at $z = 0.29$ also had significant star formation during the previous 2-3Gyr, while their brighter counterparts seem to be composed only of old stars. At $z\sim0.8$, our dynamically young cluster had a truncated red-sequence. This result seems to be consistent with a scenario where the final assembly of E/S0 took place at $z<1$. In the volume-limited range $0.35\leq z\leq0.65$ we find that 23% of the early-type galaxies have LINER-like spectra with $\rm Hβ$ in absorption and a significant component of A stars. The vast majority of LINERs in our sample have significant populations of young and intermediate-aged stars and are thus not related to AGN, but to the population of `retired galaxies' recently identified by Cid-Fernandes et al. (2010) in the SDSS. Early-type LINERs with various fractions of A stars, and E+A galaxies appear to play an important role in the formation of the red sequence.

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E. Giraud, Q. -S. Gu, J. Melnick, H. Quintana, F. Selman, I. Toledo, P. Zelaya. 2010-11-09. Low-ionization galaxies and evolution in a pilot survey up to z = 1. https://doi.org/10.1088/1674-4527%2F11%2F3%2F001

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