The Evolution of Cluster Radio Galaxies at 0.5< z< 1 (original) (raw)
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The Astronomical Journal, 1999
A radio continuum survey of a complete sample of distant (z \ 0.3È0.8) X-rayÈselected clusters has been conducted at 20 cm with the Very Large Array (VLA). The targets for this survey are the complete sample of 19 distant clusters found in the X-rayÈselected Einstein Extended Medium Sensitivity Survey (EMSS) at z º 0.3 and d º [20¡. This survey is complete to a limiting point-source radio power level of log P º 23.5 W Hz~1 km s~1 Mpc~1 and out to Abell cluster radius from the (H 0 \ 75 q 0 \ 0.1) 1 2 brightest cluster galaxy close to the X-ray emission centroid. Of the total of 41 radio sources detected within
The Evolution of the Cluster Environments of Radio Sources at z < 1.8
2002
An analysis of the cluster environments around distant radio galaxies is presented, in particular the results from new NTT deep optical-IR imaging of the fields of radio sources at z ~ 1.6. A net overdensity of K-band galaxies is found, together with a sharp peak in the angular cross-correlation amplitude, centred on the radio galaxies. This excess clustering is associated predominantly with red galaxies, with colours consistent with being old ellipticals at the radio source redshift. A large excess of such red galaxies is seen, particularly within 100 kpc of the radio source. These comprise amongst the most distant red sequences of cluster ellipticals yet discovered, that is, the highest redshift `normal' clusters.
Large scale structures around radio galaxies at z~ 1.5
Arxiv preprint arXiv: …, 2009
We explore the environments of two radio galaxies at z ∼ 1.5, 7C 1751+6809 and 7C 1756+6520, using deep optical and near-infrared imaging. Our data cover 15 × 15arcmin 2 fields around the radio galaxies. We develop and apply BzK color criteria to select cluster member candidates around the radio galaxies and find no evidence of an overdensity of red galaxies within 2 Mpc of 7C 1751+6809.
CLUSTER CANDIDATES AROUND LOW-POWER RADIO GALAXIES AT z ∼ 1-2 IN COSMOS
The Astrophysical Journal, 2014
We search for high redshift (z ∼1-2) galaxy clusters using low luminosity radio galaxies (FR I) as beacons and our newly developed Poisson Probability Method (PPM) based on photometric redshift information and galaxy number counts. We use a sample of 32 FR Is within the Cosmic Evolution Survey (COSMOS) field from Chiaberge et al. (2009) catalog. We derive a reliable subsample of 21 bona fide Low Luminosity Radio Galaxies (LLRGs) and a subsample of 11 High Luminosity Radio Galaxies (HLRGs), on the basis of photometric redshift information and NRAO VLA Sky Survey (NVSS) radio fluxes. The LLRGs are selected to have 1.4 GHz rest frame luminosities lower than the fiducial FR I/FR II divide. This also allows us to estimate the comoving space density of sources with L 1.4 10 32.3 erg s −1 Hz −1 at z 1.1, which strengthens the case for a strong cosmological evolution of these sources. In the fields of the LLRGs and HLRGs we find evidence that 14 and 8 of them reside in rich groups or galaxy clusters, respectively. Thus, overdensities are found around ∼ 70% of the FR Is, independently of the considered subsample. This rate is in agreement with the fraction found for low redshift FR Is and it is significantly higher than that of FR IIs at all redshifts. Although our method is primarily introduced for the COSMOS survey, it may be applied to both present and future wide field surveys such as SDSS Stripe 82, LSST, and Euclid. Furthermore, cluster candidates found with our method are excellent targets for next generation space telescopes such as JWST.
Galaxy Population in a Cluster of Galaxies around the Radio Galaxy 3C 324 at
Publications of the Astronomical Society of Japan, 2001
We discuss the properties of galaxies around the radio galaxy 3C 324 at z = 1.2 based on BV RIK ′ multi-band imaging data. We have applied a photometric-redshift technique to objects in the 3C 324 field, and identified 35 objects as plausible cluster members. We have found that red and luminous members are concentrated in a small region enclosed by a circle of 40 ′′ radius (0.33 Mpc at z = 1.2 for Ω 0 = 0.3, λ 0 = 0.7, H 0 = 70 km s −1 Mpc −1 cosmology) from the 3C 324 galaxy. The 3C 324 cluster is probably much more compact in size compared with the local clusters. We constructed a K ′-band luminosity function of the cluster members and fit a Schechter function, and found the characteristic magnitude to be K ′ * AB = 20.2 ± 0.6. This value is consistent with the extrapolation of the pure passive evolution seen for z < 1 clusters. We have identified eight bright galaxies which form a red color-magnitude sequence. The slope of the sequence is consistent with the passive evolution model down to K ′ AB < 22; we also found that there is no clear age variation in these bright red galaxies. However, seven out of these eight galaxies exhibit a significant excess in the rest UV light with respect to the passive evolution model. This may suggest that the massive early-type galaxies in this high-redshift cluster are still forming stars to some extent. We have confirmed a truncation of the color-magnitude sequence at K ′ AB ∼ 22; faint passively-evolving galaxies may not yet be present in this cluster at z ∼ 1.2. The overall color distribution of the cluster members, selected by the photometric redshift technique, is found to be very broad. We derived the fraction of blue galaxies in this cluster following a definition of Butcher and Oemler (1984), and obtained f B = 0.39 ± 0.28, which is higher than that for z < 1 clusters. This indicates that the star-formation activity of this cluster is, on the average, higher than that of lower redshift counterparts.
Galaxy evolution in clusters up to z = 1.0
Monthly Notices of the Royal Astronomical Society, 2004
We present a combined study of the colour-magnitude relation, colour distribution and luminosity function (LF) of a sample of 24 clusters at redshifts 0.3 < z < 1. The sample is largely composed of X-ray selected/detected clusters. Most of the clusters at redshifts z < 0.6 display X-ray luminosity or richness typical of poor clusters or groups, rather than the more typical, massive clusters studied in literature at redshifts z 0.3. All our clusters, including groups, display a colour-magnitude relation consistent with a passively evolving stellar population formed at a redshift z f 2, in accordance with observed galaxy populations in more massive clusters studied at comparable redshifts. Colours and luminosity functions (LFs) show that the cluster galaxy population is consistent with the presence of at least two components: old systems formed at high redshift that have evolved passively from that epoch, together with a galaxy population displaying more recent star formation. The former population forms at 2 z f 5, the latter at redshifts z < 1. A model in which stars do not evolve is clearly rejected both by the colour of reddest galaxies and by the characteristic luminosity m * measures. All clusters (with one possible exception) are detected independently by an almost three-dimensional optical search employing sky position and colour -this despite the primary X-ray selection and low X-ray flux/optical richness displayed by most of the sample.
The Clustering of Radio Galaxies: Biasing and Evolution Versus Stellar Mass
The Astrophysical Journal, 2015
We study the angular clustering of ∼ 6 × 10 5 NVSS sources on scales > ∼ 50h −1 Mpc in the context of the ΛCDM scenario. The analysis partially relies on the redshift distribution of 131 radio galaxies, inferred from the Hercules and CENSORS survey, and an empirical fit to the stellar to halo mass (SHM) relation. For redshifts z < ∼ 0.7, the fraction of radio activity versus stellar mass evolves as f RL ∼ M α0+α1z * where α 0 = 2.529±0.184 and α 1 = 1.854 +0.708 −0.761. The estimate on α 0 is largely driven by the results of Best et al. (2005), while the constraint on α 1 is new. We derive a biasing factor b(z = 0.5) = 2.093 +0.164 −0.109 between radio galaxies and the underlying mass. The function b(z) = 0.33z 2 + 0.85z + 1.6 fits well the redshift dependence. We also provide convenient parametric forms for the redshift dependent radio luminosity function, which are consistent with the redshift distribution and the NVSS source count versus flux.
Galaxy evolution in clusters from z=1 to z=0
Proceedings of the International Astronomical Union, 2004
The XMM-LSS project is detecting distant clusters of low mass, quite comparable in mass to the ones in the local universe. This allows a direct comparison of galaxy properties at different redshifts in "similar" clusters. We present here first results on the evolution of the reddest galaxies in 25 clusters/groups at 0.3 < ∼ z < ∼ 1.0 and for the whole galaxy population in the same clusters. The emerging picture from the current study is that the counterparts of present day clusters tend to show two or more distinct populations : a relatively old (z f > 2 − 5) population evolving passively together with a younger population, ostensibly responsible for the apparent brightening of the characteristic magnitudes, m * .
Radio-optically selected clusters of galaxies
Astronomy and Astrophysics, 2001
In order to study the status and the possible evolution of clusters of galaxies at intermediate redshifts (z ∼ 0.1 − 0.3), as well as their spatial correlation and relationship with the local environment, we built a sample of candidate groups and clusters of galaxies using radiogalaxies as tracers of dense environments. This technique-complementary to purely optical or X-ray cluster selection methods-represents an interesting tool for the selection of clusters in a wide range of richness, so to make it possible to study the global properties of groups and clusters of galaxies, such as their morphological content, dynamical status and number density, as well as the effect of the environment on the radio emission phenomena. In this paper we describe the compilation of a catalogue of ∼ 16 000 radio sources in the region of the South Galactic Pole extracted from the publicly available NRAO VLA Sky Survey maps, and the optical identification procedure with galaxies brighter than bJ = 20.0 in the EDSGC Catalogue. The radiogalaxy sample, valuable for the study of radio source populations down to low flux levels, consists of 1288 identifications and has been used to detect candidate groups and clusters associated to NVSS radio sources. In a companion paper we will discuss the cluster detection method, the cluster sample as well as first spectroscopic results.