120 research outputs found
The Atacama Cosmology Telescope: The Two-season ACTPol Sunyaev–Zel\u27dovich Effect Selected Cluster Catalog
Galaxy alignments: An overview
The alignments between galaxies, their underlying matter structures, and the
cosmic web constitute vital ingredients for a comprehensive understanding of
gravity, the nature of matter, and structure formation in the Universe. We
provide an overview on the state of the art in the study of these alignment
processes and their observational signatures, aimed at a non-specialist
audience. The development of the field over the past one hundred years is
briefly reviewed. We also discuss the impact of galaxy alignments on
measurements of weak gravitational lensing, and discuss avenues for making
theoretical and observational progress over the coming decade.Comment: 43 pages excl. references, 16 figures; minor changes to match version
published in Space Science Reviews; part of a topical volume on galaxy
alignments, with companion papers at arXiv:1504.05546 and arXiv:1504.0546
Planck Sunyaev-Zel'dovich Cluster Mass Calibration using Hyper Suprime-Cam Weak Lensing
Using 140 deg Subaru Hyper Suprime-Cam (HSC) survey data, we stack
the weak lensing (WL) signal around five Planck clusters found within the
footprint. This yields a 15 detection of the mean Planck cluster mass
density profile. The five Planck clusters span a relatively wide mass range,
with a mean mass of . The ratio of the stacked
Planck Sunyaev-Zel'dovich (SZ) mass to the stacked WL mass is . This mass bias is
consistent with previous WL mass calibrations of Planck clusters within the
errors. We discuss the implications of our findings for the calibration of SZ
cluster counts and the much discussed tension between Planck SZ cluster counts
and Planck CDM cosmology.Comment: 12 pages, 2 tables, 7 figures, accepted to PASJ special issu
Galaxy alignments: Observations and impact on cosmology
Galaxy shapes are not randomly oriented, rather they are statistically
aligned in a way that can depend on formation environment, history and galaxy
type. Studying the alignment of galaxies can therefore deliver important
information about the physics of galaxy formation and evolution as well as the
growth of structure in the Universe. In this review paper we summarise key
measurements of galaxy alignments, divided by galaxy type, scale and
environment. We also cover the statistics and formalism necessary to understand
the observations in the literature. With the emergence of weak gravitational
lensing as a precision probe of cosmology, galaxy alignments have taken on an
added importance because they can mimic cosmic shear, the effect of
gravitational lensing by large-scale structure on observed galaxy shapes. This
makes galaxy alignments, commonly referred to as intrinsic alignments, an
important systematic effect in weak lensing studies. We quantify the impact of
intrinsic alignments on cosmic shear surveys and finish by reviewing practical
mitigation techniques which attempt to remove contamination by intrinsic
alignments.Comment: 52 pages excl. references, 16 figures; minor changes to match version
published in Space Science Reviews; part of a topical volume on galaxy
alignments, with companion papers arXiv:1504.05456 and arXiv:1504.0554
Evidence for the inside-out growth of the stellar mass distribution in galaxy clusters since z ~ 1
International audienceWe study the radial number density and stellar mass density distributions of satellite galaxies in a sample of 60 massive clusters at 0.04 <z< 0.26 selected from the Multi-Epoch Nearby Cluster Survey (MENeaCS) and the Canadian Cluster Comparison Project (CCCP). In addition to ~10 000 spectroscopically confirmed member galaxies, we use deep ugri-band imaging to estimate photometric redshifts and stellar masses, and then statistically subtract fore- and background sources using data from the COSMOS survey. We measure the galaxy number density and stellar mass density distributions in logarithmically spaced bins over 2 orders of magnitude in radial distance from the BCGs. For projected distances in the range 0.1 <R/R200< 2.0, we find that the stellar mass distribution is well-described by an NFW profile with a concentration of c = 2.03 ± 0.20. However, at smaller radii we measure a significant excess in the stellar mass in satellite galaxies of about 1011M⊙ per cluster, compared to these NFW profiles. We do obtain good fits to generalised NFW profiles with free inner slopes and to Einasto profiles. To examine how clusters assemble their stellar mass component over cosmic time, we compare this local sample to the GCLASS cluster sample at z ~ 1, which represents the approximate progenitor sample of the low-z clusters. This allows for a direct comparison, which suggests that the central parts (R< 0.4 Mpc) of the stellar mass distributions of satellites in local galaxy clusters are already in place at z ~ 1, and contain sufficient excess material for further BCG growth. Evolving towards z = 0, clusters appear to assemble their stellar mass primarily onto the outskirts, making them grow in an inside-out fashion
The return of the merging galaxy subclusters of El Gordo?
Merging galaxy clusters with radio relics provide rare insights to the merger
dynamics as the relics are created by the violent merger process. We
demonstrate one of the first uses of the properties of the radio relic to
reduce the uncertainties of the dynamical variables and determine the 3D
configuration of a cluster merger, ACT-CL J0102-4915, nicknamed El Gordo. From
the double radio relic observation and the X-ray observation of a comet-like
gas morphology induced by motion of the cool core, it is widely believed that
El Gordo is observed shortly after the first core-passage of the subclusters.
We employ a Monte Carlo simulation to investigate the three-dimensional (3D)
configuration and dynamics of El Gordo. Using the polarization fraction of the
radio relic, we constrain the estimate of the angle between the plane of the
sky and the merger axis to be . We find
the relative 3D merger speed of El Gordo to be at pericenter. The two possible estimates of the
time-since-pericenter are Gyr and
Gyr for the outgoing and returning scenario
respectively. We put our estimates of the time-since-pericenter into context by
showing that if the time-averaged shock velocity is approximately equal to or
smaller than the pericenter velocity of the corresponding subcluster in the
center of mass frame, the two subclusters are more likely to be moving towards,
rather than away, from each other, post apocenter. We compare and contrast the
merger scenario of El Gordo with that of the Bullet Cluster, and show that this
late-stage merging scenario explains why the southeast dark matter lensing peak
of El Gordo is closer to the merger center than the southeast cool core.Comment: Figure 1 explains the configuration of the different components of El
Gordo. Figure 9 explains the merger scenario. 20 pages, 23 figures. Accepted
by MNRA
Source Selection for Cluster Weak Lensing Measurements in the Hyper Suprime-Cam Survey
We present optimized source galaxy selection schemes for measuring cluster
weak lensing (WL) mass profiles unaffected by cluster member dilution from the
Subaru Hyper Suprime-Cam Strategic Survey Program (HSC-SSP). The ongoing
HSC-SSP survey will uncover thousands of galaxy clusters to . In
deriving cluster masses via WL, a critical source of systematics is
contamination and dilution of the lensing signal by cluster {members, and by
foreground galaxies whose photometric redshifts are biased}. Using the
first-year CAMIRA catalog of 900 clusters with richness larger than 20
found in 140 deg of HSC-SSP data, we devise and compare several
source selection methods, including selection in color-color space (CC-cut),
and selection of robust photometric redshifts by applying constraints on their
cumulative probability distribution function (PDF; P-cut). We examine the
dependence of the contamination on the chosen limits adopted for each method.
Using the proper limits, these methods give mass profiles with minimal dilution
in agreement with one another. We find that not adopting either the CC-cut or
P-cut methods results in an underestimation of the total cluster mass
() and the concentration of the profile (). The level of
cluster contamination can reach as high as at
Mpc/ for low-z clusters without cuts, while employing either the P-cut or
CC-cut results in cluster contamination consistent with zero to within the 0.5%
uncertainties. Our robust methods yield a detection of the
stacked CAMIRA surface mass density profile, with a mean mass of
.Comment: 19 pages, 4 tables, 12 figures, accepted to PASJ special issu
Herschel and ALMA observations of the ISM in massive high-redshift galaxy clusters
The Sunyaev-Zel'dovich effect (SZE) can be used to select samples of galaxy clusters that are essentially mass-limited out to arbitrarily high redshifts. I will present results from an investigation of the star formation properties of galaxies in four massive clusters, extending to z~1, which were selected on the basis of their SZE decrements in the Atacama Cosmology Telescope (ACT) survey. All four clusters have been imaged with Herschel/PACS (tracing star formation rate) and two with ALMA (tracing dust and cold gas mass); newly discovered ALMA CO(4-3) and [CI] line detections expand an already large sample of spectroscopically confirmed cluster members. Star formation rate appears to anti-correlate with environmental density, but this trend vanishes after controlling for stellar mass. Elevated star formation and higher CO excitation are seen in "El Gordo," a violent cluster merger, relative to a virialized cluster at a similar high (z~1) redshift. Also exploiting ATCA 2.1 GHz observations to identify radio-loud active galactic nuclei (AGN) in our sample, I will use these data to develop a coherent picture of how environment influences galaxies' ISM properties and evolution in the most massive clusters at early cosmic times
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