47 research outputs found
Dynamical Masses of RCS Galaxy Clusters
A multi-object spectroscopy follow-up survey of galaxy clusters selected from
the Red-sequence Cluster Survey (RCS) is being completed. About forty clusters
were chosen with redshifts from 0.15 to 0.6, and in a wide range of richnesses.
One of the main science drivers of this survey is a study of internal dynamics
of clusters. We present some preliminary results for a subset of the clusters,
including the correlation of optical richness with mass, and the mass-to-light
ratio as a function of cluster mass.Comment: 5 pages, 5 figures, to appear in the Proceedings of IAU Colloquium
195: "Outskirts of Galaxy Clusters: intense life in the suburbs", Torino
Italy, March 200
Spectroscopy of moderately high-redshift RCS-1 clusters
We present spectroscopic observations of 11 moderately high-redshift (z~0.7-
1.0) clusters from the first Red-Sequence Cluster Survey (RCS-1). We find
excellent agreement between the red-sequence estimated redshift and the
spectroscopic redshift, with a scatter of 10% at z>0.7. At the high-redshift
end (z>~0.9) of the sample, we find two of the systems selected are projections
of pairs of comparably rich systems, with red-sequences too close to
discriminate in (R-z') colour. In one of these systems, the two components are
close enough to be physically associated. For a subsample of clusters with
sufficient spectroscopic members, we examine the correlation between B_gcR
(optical richness) and the dynamical mass inferred from the velocity
dispersion. We find these measurements to be compatible, within the relatively
large uncertainties, with the correlation established at lower redshift for the
X-ray selected CNOC1 clusters and also for a lower redshift sample of RCS-1
clusters. Confirmation of this and calibration of the scatter in the relation
will require larger samples of clusters at these and higher redshifts.
[abridged]Comment: AJ accepted. 30 pages, 7 figures (figure 5 reduced quality
The DDO IVC Distance Project: Survey Description and the Distance to G139.6+47.6
We present a detailed analysis of the distance determination for one
intermediate Velocity Cloud (IVC G139.6+47.6) from the ongoing DDO IVC Distance
Project. Stars along the line of sight to G139.6+47.6 are examined for the
presence of sodium absorption attributable to the cloud, and the distance
bracket is established by astrometric and spectroscopic parallax measurements
of demonstrated foreground and background stars. We detail our strategy
regarding target selection, observational setup, and analysis of the data,
including a discussion of wavelength calibration and sky subtraction
uncertainties. We find a distance estimate of 129 (+/- 10) pc for the lower
limit and 257 (+211-33) pc for the upper limit. Given the high number of stars
showing absorption due to this IVC, we also discuss the small-scale covering
factor of the cloud and the likely significance of non-detections for
subsequent observations of this and other similar IVC's. Distance measurements
of the remaining targets in the DDO IVC project will be detailed in a companion
paper.Comment: 10 pages, 6 figures, LaTe
Spectroscopic Confirmation of Two Massive Red-Sequence-Selected Galaxy Clusters at z ~ 1.2 in the SpARCS-North Cluster Survey
The Spitzer Adaptation of the Red-sequence Cluster Survey (SpARCS) is a deep z'-band imaging survey covering the Spitzer Wide-Area Infrared Extragalactic Survey (SWIRE) Legacy fields designed to create the first large homogeneously selected sample of massive clusters at z > 1 using an infrared adaptation of the cluster red-sequence method. We present an overview of the northern component of the survey which has been observed with Canada-France-Hawaii Telescope (CFHT)/MegaCam and covers 28.3 deg^2. The southern component of the survey was observed with Cerro Tololo Inter-American Observatory (CTIO)/MOSAICII, covers 13.6 deg^2, and is summarized in a companion paper by Wilson et al. We also present spectroscopic confirmation of two rich cluster candidates at z ~ 1.2. Based on Nod-and-Shuffle spectroscopy from GMOS-N on Gemini, there are 17 and 28 confirmed cluster members in SpARCS J163435+402151 and SpARCS J163852+403843 which have spectroscopic redshifts of 1.1798 and 1.1963, respectively. The clusters have velocity dispersions of 490 ± 140 km s^(–1) and 650 ± 160 km s^(–1), respectively, which imply masses (M_(200)) of (1.0 ± 0.9) × 10^(14) M_⊙ and (2.4 ± 1.8) × 10^(14) M_⊙. Confirmation of these candidates as bonafide massive clusters demonstrates that two-filter imaging is an effective, yet observationally efficient, method for selecting clusters at z > 1
Spectroscopic Confirmation of a Massive Red-Sequence-Selected Galaxy Cluster at z = 1.34 in the SpARCS-South Cluster Survey
The Spitzer Adaptation of the Red-sequence Cluster Survey (SpARCS) is a
z'-passband imaging survey, consisting of deep (z' ~ 24 AB) observations made
from both hemispheres using the CFHT 3.6m and CTIO 4m telescopes. The survey
was designed with the primary aim of detecting galaxy clusters at z >~ 1. In
tandem with pre-existing 3.6um observations from the Spitzer Space Telescope
SWIRE Legacy Survey, SpARCS detects clusters using an infrared adaptation of
the two-filter red-sequence cluster technique. The total effective area of the
SpARCS cluster survey is 41.9 deg^2. In this paper, we provide an overview of
the 13.6 deg^2 Southern CTIO/MOSAICII observations. The 28.3 deg^2 Northern
CFHT/MegaCam observations are summarized in a companion paper by Muzzin et al.
(2008). In this paper, we also report spectroscopic confirmation of SpARCS
J003550-431224, a very rich galaxy cluster at z = 1.335, discovered in the
ELAIS-S1 field. To date, this is the highest spectroscopically confirmed
redshift for a galaxy cluster discovered using the red-sequence technique.
Based on nine confirmed members, SpARCS J003550-431224 has a preliminary
velocity dispersion of 1050 +/- 230 km/s. With its proven capability for
efficient cluster detection, SpARCS is a demonstration that we have entered an
era of large, homogeneously-selected z > 1 cluster surveys.Comment: 10 pages, 6 Figures, Submitted to the Ap
A z=0.9 supercluster of X-ray luminous, optically-selected, massive galaxy clusters
We report the discovery of a compact supercluster structure at z=0.9. The
structure comprises three optically-selected clusters, all of which are
detected in X-rays and spectroscopically confirmed to lie at the same redshift.
The Chandra X-ray temperatures imply individual masses of ~5x10^14 Msun. The
X-ray masses are consistent with those inferred from optical--X-ray scaling
relations established at lower redshift. A strongly-lensed z~4 Lyman break
galaxy behind one of the clusters allows a strong-lensing mass to be estimated
for this cluster, which is in good agreement with the X-ray measurement.
Optical spectroscopy of this cluster gives a dynamical mass in good agreement
with the other independent mass estimates. The three components of the
RCS2319+00 supercluster are separated from their nearest neighbor by a mere <3
Mpc in the plane of the sky and likely <10 Mpc along the line-of-sight, and we
interpret this structure as the high-redshift antecedent of massive (~10^15
Msun) z~0.5 clusters such as MS0451.5-0305.Comment: ApJ Letters accepted. 5 pages in emulateapj, 3 figure
Spectroscopic Confirmation of Three Red-sequence Selected Galaxy Clusters at z = 0.87, 1.16, and 1.21 from the SpARCS Survey
The Spitzer Adaptation of the Red-sequence Cluster Survey (SpARCS) is a z'-passband imaging survey of the 50 deg^2 Spitzer SWIRE Legacy fields, designed with the primary aim of creating the first large, homogeneously selected sample of massive clusters at z > 1. SpARCS uses an infrared adaptation of the two-filter cluster red-sequence technique. In this paper, we report Keck/LRIS spectroscopic confirmation of two new exceptionally rich galaxy clusters, SpARCS J161315+564930 at z = 0.871 ± 0.002, with 14 high-confidence members and a rest-frame velocity dispersion of σ_v = 1230 ± 320 km s^(–1), and SpARCS J161641+554513 at z = 1.161 ± 0.003, with seven high-confidence members (including one active galactic nucleus) and a rest-frame velocity dispersion of σ_v = 950 ± 330 km s^(–1). We also report confirmation of a third new system, SpARCS J161037+552417 at z = 1.210 ± 0.002, with seven high-confidence members and a rest-frame velocity dispersion of σ v = 410 ± 300 km s^(–1). These three new spectroscopically confirmed clusters further demonstrate the efficiency and effectiveness of two-filter imaging for detecting bona fide galaxy clusters at high redshift. We conclude by demonstrating that prospects are good for the current generation of surveys aiming to estimate cluster redshifts and masses at z ≳ 1 directly from optical-infrared imaging
Spectroscopic Confirmation of Two Massive Red-sequence-selected Galaxy Clusters at Z ~ Approximately Equal to 1.2 in the Sparcs-North Cluster Survey
The Spitzer Adaptation of the Red-sequence Cluster Survey (SpARCS) is a deep z -band imaging survey covering the Spitzer SWIRE Legacy fields designed to create the first large homogeneously-selected sample of massive clusters at z > 1 using an infrared adaptation of the cluster red-sequence method. We present an overview of the northern component of the survey which has been observed with CFHT/MegaCam and covers 28.3 deg(sup 2). The southern component of the survey was observed with CTIO/MOSAICII, covers 13.6 deg(sup 2), and is summarized in a companion paper by Wilson et al. (2008). We also present spectroscopic confirmation of two rich cluster candidates at z approx. 1.2. Based on Nod-and- Shuffle spectroscopy from GMOS-N on Gemini there are 17 and 28 confirmed cluster members in SpARCS J163435+402151 and SpARCS J163852+403843 which have spectroscopic redshifts of 1.1798 and 1.1963, respectively. The clusters have velocity dispersions of 490 +/- 140 km/s and 650 +/- 160 km/s, respectively which imply masses (M(sub 200)) of (1.0 +/- 0.9) x 10(exp 14) Stellar Mass and (2.4 +/- 1.8) x 10(exp 14) Stellar Mass. Confirmation of these candidates as bonafide massive clusters demonstrates that two-filter imaging is an effective, yet observationally efficient, method for selecting clusters at z > 1