45 research outputs found
HeCS-SZ: The Hectospec Survey of Sunyaev-Zeldovich Selected Clusters
We estimate cluster masses and velocity dispersions for 123 clusters from
optical spectroscopy to compare the Sunyaev-Zeldovich (SZ) mass proxy and
dynamical masses. Our new survey, HeCS-SZ (Hectospec Cluster Survey of
SZ-selected clusters), includes 7,721 new or remeasured redshifts from
MMT/Hectospec observations of 24 SZ-selected clusters at redshifts
=0.05-0.20 and not in previous surveys. We supplement the Hectospec data
with spectra from the Sloan Digital Sky Survey (SDSS) and cluster data from the
Cluster Infall Regions in SDSS (CIRS) project and the Hectospec Cluster Survey
(HeCS), our Hectospec survey of clusters selected by X-ray flux. We measure the
scaling relation between velocity dispersion and SZ mass estimates from the
integrated Compton parameter for an SZ complete sample of 83 clusters. The
observed relation agrees very well with a simple virial scaling from mass
(based on SZ) to velocity dispersion. The SZ mass estimates (calibrated with
hydrostatic X-ray mass estimates) are not significantly biased. Further, the
velocity dispersion of cluster galaxies is consistent with the expected
velocity dispersion of dark matter particles, indicating that galaxies are good
dynamical tracers (i.e., velocity bias is small). Significant mass bias in SZ
mass estimates could relieve tension between cosmological results from Planck
SZ cluster counts and Planck CMB data. However, the excellent agreement between
our measured velocity dispersions and those predicted from a virial scaling
relation suggests that any SZ mass bias is too small to reconcile SZ and CMB
results. In principle, SZ mass bias and velocity bias of galaxies could
conspire to yield good agreement, but the required velocity bias is
, outside the range of plausible models
of velocity bias in the literature.Comment: submitted to ApJ, 13 pages, 14 figures, 123 cluster
A WISE View of a Nearby Supercluster A2199
We use Wide-field Infrared Survey Explorer (WISE) data covering the entire
region (~130 deg^2) of the A2199 supercluster at z=0.03 to study the
mid-infrared (MIR) properties of supercluster galaxies. We identify a `MIR
star-forming sequence' in the WISE [3.4]-[12] color-12 \mu m luminosity
diagram, consisting of late-type, star-forming galaxies. At a fixed star
formation rate (SFR), the MIR-detected galaxies at 22 \mu m or 12 \mu m tend to
be more metal rich and to have higher surface brightness than those without MIR
detection. Using these MIR-detected galaxies, we construct the IR luminosity
function (LF) and investigate its environmental dependence. Both total IR (TIR)
and 12 \mu m LFs are dominated by late-type, star-forming galaxies. The
contribution of active galactic nuclei (AGN)-host galaxies increases with both
TIR and 12 \mu m luminosities. The contribution of early-type galaxies to the
12 \mu m LFs increases with decreasing luminosity. The faint-end slope of the
TIR LFs does not change with environment, but the change of faint-end slope in
the 12 \mu m LFs with the environment is significant: there is a steeper
faint-end slope in the cluster core than in the cluster outskirts. This
steepening results primarily from the increasing contribution of early-type
galaxies toward the cluster. These galaxies are passively evolving, and contain
old stellar populations with weak MIR emission from the circumstellar dust
around asymptotic giant branch stars.Comment: 14 pages, 14 figures. To appear in Ap
Measuring the Ultimate Halo Mass of Galaxy Clusters: Redshifts and Mass Profiles from the Hectospec Cluster Survey (HeCS)
The infall regions of galaxy clusters represent the largest gravitationally bound structures in a LambdaCDM universe. Measuring cluster mass profiles into the infall regions provides an estimate of the ultimate mass of these halos. We use the caustic technique to measure cluster mass profiles from galaxy redshifts obtained with the Hectospec Cluster Survey (HeCS), an extensive spectroscopic survey of galaxy clusters with MMT/Hectospec. We survey 58 clusters selected by X-ray flux at 0.1 \u3c z \u3c 0.3. The survey includes 22,680 unique MMT/Hectospec redshifts for individual galaxies; 10,145 of these galaxies are cluster members. For each cluster, we acquired high signal-to-noise spectra for ~200 cluster members and a comparable number of foreground/background galaxies. The cluster members trace out infall patterns around the clusters. The members define a very narrow red sequence. We demonstrate that the determination of velocity dispersion is insensitive to the inclusion of bluer members (a small fraction of the cluster population). We apply the caustic technique to define membership and estimate the mass profiles to large radii. The ultimate halo mass of clusters (the mass that remains bound in the far future of a LambdaCDM universe) is on average (1.99 ± 0.11)M 200, a new observational cosmological test in essential agreement with simulations. Summed profiles binned in M 200 and in LX demonstrate that the predicted Navarro-Frenk-White form of the density profile is a remarkably good representation of the data in agreement with weak lensing results extending to large radius. The concentration of these summed profiles is also consistent with theoretical predictions
Comparing Dense Galaxy Cluster Redshift Surveys with Weak Lensing Maps
We use dense redshift surveys of nine galaxy clusters at to
compare the galaxy distribution in each system with the projected matter
distribution from weak lensing. By combining 2087 new MMT/Hectospec redshifts
and the data in the literature, we construct spectroscopic samples within the
region of weak-lensing maps of high (70--89%) and uniform completeness. With
these dense redshift surveys, we construct galaxy number density maps using
several galaxy subsamples. The shape of the main cluster concentration in the
weak-lensing maps is similar to the global morphology of the number density
maps based on cluster members alone, mainly dominated by red members. We cross
correlate the galaxy number density maps with the weak-lensing maps. The cross
correlation signal when we include foreground and background galaxies at
0.5 is % larger than for cluster members alone
at the cluster virial radius. The excess can be as high as 30% depending on the
cluster. Cross correlating the galaxy number density and weak-lensing maps
suggests that superimposed structures close to the cluster in redshift space
contribute more significantly to the excess cross correlation signal than
unrelated large-scale structure along the line of sight. Interestingly, the
weak-lensing mass profiles are not well constrained for the clusters with the
largest cross correlation signal excesses (20% for A383, A689 and A750). The
fractional excess in the cross correlation signal including foreground and
background structures could be a useful proxy for assessing the reliability of
weak-lensing cluster mass estimates.Comment: 22 pages, 19 figures, 2 tables. To appear in ApJ. Paper with high
resolution figures is available at
http://astro.kias.re.kr/~hshwang/ms_hwang20141014.pd
The HectoMAP Cluster Survey - I. redMaPPer Clusters
We use the dense HectoMAP redshift survey to explore the properties of 104
redMaPPer cluster candidates. The redMaPPer systems in HectoMAP cover the full
range of richness and redshift (0.08 0.60). Fifteen systems included in
the Subaru/Hyper Suprime-Cam public data release are bona fide clusters. The
median number of spectroscopic members per cluster is . We include
redshifts of 3547 member candidates listed in the redMaPPer catalog whether
they are cluster members or not. We evaluate the redMaPPer membership
probability spectroscopically. The scaled richness ({\lambda}rich/S) provided
by redMaPPer correlates tightly with the spectroscopic richness regardless of
the cluster redshift and appears to be a better mass proxy than the original
richness, {\lambda}rich. The purity (number of real systems) in redMaPPer
exceeds 90% even at the lowest richness; however, there is some incompleteness.
Five massive galaxy clusters (M M)
associated with X-ray emission in the HectoMAP region are missing from the
catalog.Comment: submitted to ApJ, a revised version in response to the referee's
comments, 15 pages, 14 figures, 3 tables; data will be available when the
paper is accepte
A Redshift Survey of the Strong Lensing Cluster Abell 383
Abell 383 is a famous rich cluster (z = 0.1887) imaged extensively as a basis
for intensive strong and weak lensing studies. Nonetheless there are few
spectroscopic observations. We enable dynamical analyses by measuring 2360 new
redshifts for galaxies with r and within 50 of the
BCG (Brightest Cluster Galaxy: R.A., Decl). We apply the caustic technique to identify 275 cluster
members within 7 Mpc of the hierarchical cluster center. The BCG lies
within km s and 21 kpc of the hierarchical
cluster center; the velocity dispersion profile of the BCG appears to be an
extension of the velocity dispersion profile based on cluster members. The
distribution of cluster members on the sky corresponds impressively with the
weak lensing contours of Okabe et al. (2010) especially when the impact of
foreground and background structure is included. The values of R =
Mpc and M = M obtained by application of the caustic technique agree well
with recent completely independent lensing measures. The caustic estimate
extends direct measurement of the cluster mass profile to a radius of Mpc.Comment: 29 pages, 9 figures, ApJ accepte