Abstract
We present galactic spectroscopic data from a pencil beam of 10.75′ × 7.5′ 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 R ≤ 23, for which the statistical properties of the sample are well understood. We divide emission-line galaxies into star-forming galaxies, Low Ionization Nuclear Emission line Regions (LINERs), and Seyferts by using emission-line ratios of [OII], 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 ∼ 0.6 – 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 2.5 Gyr Faint absorption-line galaxies in the cluster at z = 0.29 also had significant star formation during the previous 2 – 3 Gyr, but their brighter counterparts seem to be only composed of old stars. At z ∼ 0.8, 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 ≤ z ≤ 0.65, we find that 23% of the early-type galaxies have LINER-like spectra with Hβ in absorption and have 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 AGNs, but to the population of ‘retired galaxies’ recently identified by Cid Fernandes et al. in the Sloan Digital Sky Survey (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.
Highlights
In the course of an investigation of the diffuse intergalactic light in X-ray emitting clusters at intermediate redshifts (Melnick et al 1999), we detected a puzzling S-shaped arc-like structure in the ROSAT cluster RX J0054.0-2823 (Faure et al 2007), which we tentatively identified as the gravitationally lensed image of a background galaxy at a redshift between z=0.5 and z=1.0
There is a moderate decrease in the 4000Abreak at z ≥ 0.65 ranging from 5% at z ∼ 0.65 to 7% at z ∼ 0.82 and up to 15% at z ∼ 1, while the Hδ absorption line becomes stronger at z ≥ 0.65 (Table 8), suggesting the presence of increasing numbers of A stars at higher redshifts
We have presented a catalogue of galaxy spectra in a pencil beam survey of ∼ 10.75′ × 7.5′, and used these data to make an analysis of the spectral energy distribution of a magnitude limited sample up to z ∼ 1, concentrating on absorption and low ionization emission-line systems
Summary
In the course of an investigation of the diffuse intergalactic light in X-ray emitting clusters at intermediate redshifts (Melnick et al 1999), we detected a puzzling S-shaped arc-like structure in the ROSAT cluster RX J0054.0-2823 (Faure et al 2007), which we tentatively identified as the gravitationally lensed image of a background galaxy at a redshift between z=0.5 and z=1.0. The vast majority of our individual spectra reduced to zero redshift have S/N ratios per 2.6Apixel larger than 3 at 4200A This resolution is very well adapted to the detection of small equivalent width [OII] emission, which is expected to be found in bulge dominated galaxies with small disks, in some LINERs, in “mixed” mergers between E/S0 and star-forming objects, and perhaps in some post-starbursts galaxies. Several studies suggest that the bulk of stars in early-type cluster galaxies had a formation redshift of z ≥ 3, while those in lower density environments may have formed later, but still at z ≥ 1.5 − 2 (for reviews see Renzini 2006; Renzini 2007).
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