737 research outputs found
The Sunyaev-Zeldovich effect in superclusters of galaxies using gasdynamical simulations: the case of Corona Borealis
[Abridged] We study the thermal and kinetic Sunyaev-Zel'dovich (SZ) effect
associated with superclusters of galaxies using the MareNostrum Universe SPH
simulation. We consider superclusters similar to the Corona Borealis
Supercluster (CrB-SC). This paper is motivated by the detection at 33GHz of a
strong temperature decrement in the CMB towards the core of this supercluster.
Multifrequency observations with VSA and MITO suggest the existence of a
thermal SZ effect component in the spectrum of this cold spot, which would
account for roughly 25% of the total observed decrement. We identify nine
regions containing superclusters similar to CrB-SC, obtain the associated SZ
maps and calculate the probability of finding such SZ signals arising from hot
gas within the supercluster. Our results show that WHIM produces a thermal SZ
effect much smaller than the observed value. Neither can summing the
contribution of small clusters and galaxy groups in the region explain the
amplitude of the SZ signal. When we take into account the actual posterior
distribution from the observations, the probability that WHIM can cause a
thermal SZ signal like the one observed is <1%, rising up to a 3.2% when the
contribution of small clusters and galaxy groups is included. If the
simulations provide a suitable description of the gas physics, then we conclude
that the thermal SZ component of the CrB spot most probably arises from an
unknown galaxy cluster along the line of sight. The simulations also show that
the kinetic SZ signal associated with the supercluster cannot provide an
explanation for the remaining 75% of the observed cold spot in CrB.Comment: Accepted for publication in MNRAS. 14 pages, 9 figure
The BaR-SPOrt Experiment
BaR-SPOrt (Balloon-borne Radiometers for Sky Polarisation Observations) is an
experiment to measure the linearly polarized emission of sky patches at 32 and
90 GHz with sub-degree angular resolution. It is equipped with high sensitivity
correlation polarimeters for simultaneous detection of both the U and Q stokes
parameters of the incident radiation. On-axis telescope is used to observe
angular scales where the expected polarization of the Cosmic Microwave
Background (CMBP) peaks. This project shares most of the know-how and
sophisticated technology developed for the SPOrt experiment onboard the
International Space Station. The payload is designed to flight onboard long
duration stratospheric balloons both in the Northern and Southern hemispheres
where low foreground emission sky patches are accessible. Due to the weakness
of the expected CMBP signal (in the range of microK), much care has been spent
to optimize the instrument design with respect to the systematics generation,
observing time efficiency and long term stability. In this contribution we
present the instrument design, and first tests on some components of the 32 GHz
radiometer.Comment: 12 pages, 10 figures, Astronomical Telescopes and Instrumentation
(Polaimetry in Astronomy) Hawaii August 2002 SPIE Meetin
Millimetric observations with a high-altitude 2.6-m ground based telescope
High atmospheric performances are necessary to ensure efficient sub/millimetre cosmological observations from ground. Low atmospheric components fluctuations along the line of sight are a must for best detector applications.
Such site constraints are attained only at in specific places around the world: highaltitude observatories or, equivalently, polar regions. We are currently involved in
cosmological observations with the MITO project from an Alpine ground station which satisfies such requirements: the Testa Grigia mountain at 3500 m a.s.l., AOâItaly. The Chacaltaya laboratory at 5200 m a.s.l. could also be an appropriate mm-site. One of the goals of MITO is the multifrequency observation of nearby rich clusters of galaxies for measuring the Sunyaev-Zelâdovich effect. Combined S-Z and X-ray measurements yield the Hubble constant and other cosmological information. A dedicated instrument has been designed to minimize spurious contaminations on the signals. The telescope is a 2.6 m Cassegrain with a wobbling subreflector and a 4-band single pixel photometer installed at the focal plane. The bolometric detectors are cooled down to 300 mK by a double stage He3-He4 fridge
Millimetric observations with a high-altitude 2.6-m ground based telescope
High atmospheric performances are necessary to ensure efficient sub/millimetre cosmological observations from ground. Low atmospheric components fluctuations along the line of sight are a must for best detector applications.
Such site constraints are attained only at in specific places around the world: highaltitude observatories or, equivalently, polar regions. We are currently involved in
cosmological observations with the MITO project from an Alpine ground station which satisfies such requirements: the Testa Grigia mountain at 3500 m a.s.l., AOâItaly. The Chacaltaya laboratory at 5200 m a.s.l. could also be an appropriate mm-site. One of the goals of MITO is the multifrequency observation of nearby rich clusters of galaxies for measuring the Sunyaev-Zelâdovich effect. Combined S-Z and X-ray measurements yield the Hubble constant and other cosmological information. A dedicated instrument has been designed to minimize spurious contaminations on the signals. The telescope is a 2.6 m Cassegrain with a wobbling subreflector and a 4-band single pixel photometer installed at the focal plane. The bolometric detectors are cooled down to 300 mK by a double stage He3-He4 fridge
Non-parametric deprojection of NIKA SZ observations: Pressure distribution in the Planck-discovered cluster PSZ1 G045.85+57.71
The determination of the thermodynamic properties of clusters of galaxies at
intermediate and high redshift can bring new insights into the formation of
large-scale structures. It is essential for a robust calibration of the
mass-observable scaling relations and their scatter, which are key ingredients
for precise cosmology using cluster statistics. Here we illustrate an
application of high resolution arcsec) thermal Sunyaev-Zel'dovich (tSZ)
observations by probing the intracluster medium (ICM) of the \planck-discovered
galaxy cluster \psz\ at redshift , using tSZ data obtained with the
NIKA camera, which is a dual-band (150 and 260~GHz) instrument operated at the
IRAM 30-meter telescope. We deproject jointly NIKA and \planck\ data to extract
the electronic pressure distribution from the cluster core () to its outskirts () non-parametrically for the
first time at intermediate redshift. The constraints on the resulting pressure
profile allow us to reduce the relative uncertainty on the integrated Compton
parameter by a factor of two compared to the \planck\ value. Combining the tSZ
data and the deprojected electronic density profile from \xmm\ allows us to
undertake a hydrostatic mass analysis, for which we study the impact of a
spherical model assumption on the total mass estimate. We also investigate the
radial temperature and entropy distributions. These data indicate that \psz\ is
a massive ( M) cool-core cluster.
This work is part of a pilot study aiming at optimizing the treatment of the
NIKA2 tSZ large program dedicated to the follow-up of SZ-discovered clusters at
intermediate and high redshifts. (abridged)Comment: 16 pages, 10 figure
NIKA2: a mm camera for cluster cosmology
Galaxy clusters constitute a major cosmological probe. However, Planck 2015
results have shown a weak tension between CMB-derived and cluster-derived
cosmological parameters. This tension might be due to poor knowledge of the
cluster mass and observable relationship.
As for now, arcmin resolution Sunyaev-Zeldovich (SZ) observations ({\it e.g.}
SPT, ACT and Planck) only allowed detailed studies of the intra cluster medium
for low redshift clusters () high
resolution and high sensitivity SZ observations are needed. With both a wide
field of view (6.5 arcmin) and a high angular resolution (17.7 and 11.2 arcsec
at 150 and 260 GHz), the NIKA2 camera installed at the IRAM 30-m telescope
(Pico Veleta, Spain) is particularly well adapted for these observations. The
NIKA2 SZ observation program will map a large sample of clusters (50) at
redshifts between 0.5 and 0.9. As a pilot study for NIKA2, several clusters of
galaxies have been observed with the pathfinder, NIKA, at the IRAM 30-m
telescope to cover the various configurations and observation conditions
expected for NIKA2.
Nika2: A mm camera for cluster cosmology
Galaxy clusters constitute a major cosmological probe. However, Planck 2015 results have shown a weak tension between CMB-derived and cluster-derived cosmological parameters. This tension might be due to poor knowledge of the cluster mass and observable relationship. As for now, arcmin resolution Sunyaev-Zeldovich (SZ) observations (e.g. SPT, ACT and Planck) only allowed detailed studies of the intra cluster medium for low redshift clusters (z 0:5) high resolution and high sensitivity SZ observations are needed. With both a wide field of view (6.5 arcmin) and a high angular resolution (17.7 and 11.2 arcsec at 150 and 260 GHz), the NIKA2 camera installed at the IRAM 30-m telescope (Pico Veleta, Spain) is particularly well adapted for these observations. The NIKA2 SZ observation program will map a large sample of clusters (50) at redshifts between 0.5 and 0.9. As a pilot study for NIKA2, several clusters of galaxies have been observed with the pathfinder, NIKA, at the IRAM 30-m telescope to cover the various configurations and observation conditions expected for NIKA2
The MUSIC of CLASH: predictions on the concentration-mass relation
We present the results of a numerical study based on the analysis of the
MUSIC-2 simulations, aimed at estimating the expected concentration-mass
relation for the CLASH cluster sample. We study nearly 1400 halos simulated at
high spatial and mass resolution, which were projected along many
lines-of-sight each. We study the shape of both their density and
surface-density profiles and fit them with a variety of radial functions,
including the Navarro-Frenk-White, the generalised Navarro-Frenk-White, and the
Einasto density profiles. We derive concentrations and masses from these fits
and investigate their distributions as a function of redshift and halo
relaxation. We use the X-ray image simulator X-MAS to produce simulated Chandra
observations of the halos and we use them to identify objects resembling the
X-ray morphologies and masses of the clusters in the CLASH X-ray selected
sample. We also derive a concentration-mass relation for strong-lensing
clusters. We find that the sample of simulated halos which resemble the X-ray
morphology of the CLASH clusters is composed mainly by relaxed halos, but it
also contains a significant fraction of un-relaxed systems. For such a sample
we measure an average 2D concentration which is ~11% higher than found for the
full sample of simulated halos. After accounting for projection and selection
effects, the average NFW concentrations of CLASH clusters are expected to be
intermediate between those predicted in 3D for relaxed and super-relaxed halos.
Matching the simulations to the individual CLASH clusters on the basis of the
X-ray morphology, we expect that the NFW concentrations recovered from the
lensing analysis of the CLASH clusters are in the range [3-6], with an average
value of 3.87 and a standard deviation of 0.61. Simulated halos with X-ray
morphologies similar to those of the CLASH clusters are affected by a modest
orientation bias.Comment: 21 pages, 16 figures, 3 tables, submitted to Ap
Multistrip multigap symmetric RPC
Abstract The characteristics of a symmetric multigap resistive plate chamber with multistrip readout electrode, recently developed by us, continued to be investigated. Studies of the time resolution, efficiency, average charge and dark rate as a function of applied voltage and the influence of the angle of incidence of the detected particle on these observables have been performed. Different type of discriminators have been tested
Mapping the kinetic Sunyaev-Zel'dovich effect toward MACS J0717.5+3745 with NIKA
Measurement of the gas velocity distribution in galaxy clusters provides
insight into the physics of mergers, through which large scale structures form
in the Universe. Velocity estimates within the intracluster medium (ICM) can be
obtained via the Sunyaev-Zel'dovich (SZ) effect, but its observation is
challenging both in term of sensitivity requirement and control of systematic
effects, including the removal of contaminants. In this paper we report
resolved observations, at 150 and 260 GHz, of the SZ effect toward the triple
merger MACS J0717.5+3745 (z=0.55), using data obtained with the NIKA camera at
the IRAM 30m telescope. Assuming that the SZ signal is the sum of a thermal
(tSZ) and a kinetic (kSZ) component and by combining the two NIKA bands, we
extract for the first time a resolved map of the kSZ signal in a cluster. The
kSZ signal is dominated by a dipolar structure that peaks at -5.1 and +3.4
sigma, corresponding to two subclusters moving respectively away and toward us
and coincident with the cold dense X-ray core and a hot region undergoing a
major merging event. We model the gas electron density and line-of-sight
velocity of MACS J0717.5+3745 as four subclusters. Combining NIKA data with
X-ray observations from XMM-Newton and Chandra, we fit this model to constrain
the gas line-of-sight velocity of each component, and we also derive, for the
first time, a velocity map from kSZ data (i.e. that is model-dependent). Our
results are consistent with previous constraints on the merger velocities, and
thanks to the high angular resolution of our data, we are able to resolve the
structure of the gas velocity. Finally, we investigate possible contamination
and systematic effects with a special care given to radio and submillimeter
galaxies. Among the sources that we detect with NIKA, we find one which is
likely to be a high redshift lensed submillimeter galaxy.Comment: 19 pages, 9 figures, accepted in A&
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