1,546 research outputs found
Absolute calibration and beam reconstruction of MITO (a ground-based instrument in the millimetric region)
An efficient sky data reconstruction derives from a precise characterization
of the observing instrument. Here we describe the reconstruction of
performances of a single-pixel 4-band photometer installed at MITO (Millimeter
and Infrared Testagrigia Observatory) focal plane. The strategy of differential
sky observations at millimeter wavelengths, by scanning the field of view at
constant elevation wobbling the subreflector, induces a good knowledge of beam
profile and beam-throw amplitude, allowing efficient data recovery. The
problems that arise estimating the detectors throughput by drift scanning on
planets are shown. Atmospheric transmission, monitored by skydip technique, is
considered for deriving final responsivities for the 4 channels using planets
as primary calibrators.Comment: 14 pages, 6 fiugres, accepted for pubblication by New Astronomy (25
March
Rotation in galaxy clusters from MUSIC simulations with the kinetic Sunyaev-Zel'dovich effect
We propose in this work its application for the detection of possible coherent rotational motions in the hot intra-cluster medium. We select a sample of massive, relaxed and rotating galaxy clusters from Marenostrum-mUltidark SImulations of galaxy Clusters (MUSIC), and we produce mock maps of the temperature distortion produced by the kinetic Sunyaev-Zel'dovich effect by exploring six different lines of sight, in the best observational condition. These maps are compared with the expected signal computed from a suitable theoretical model in two cases: (i) focusing only on the contribution from the rotation, and (ii) accounting also for the cluster bulk motion. We find that the parameters of the model assumed for the radial profile of the rotational velocity, averaged over the considered lines of sight, are in agreement within two standard deviations at most with independent estimates from the simulation data, without being significantly affected by the presence of the cluster bulk term. The amplitude of the rotational signal is, on average, of the order of 23 per cent of the total signal accounting also for the cluster bulk motion, and its values are consistent with the literature. The projected bulk velocity of the cluster is also recovered at the different lines of sight, with values in agreement with the simulation dataASB acknowledges funding from Sapienza Università di Roma - Progetti per Avvio alla Ricerca Anno 2017, prot. AR11715C82402BC
Constraining the evolution of the CMB temperature with SZ measurements from Planck data
The CMB temperature-redshift relation, T_CMB(z)=T_0(1+z), is a key prediction
of the standard cosmology, but is violated in many non standard models.
Constraining possible deviations to this law is an effective way to test the
LambdaCDM paradigm and to search for hints of new physics. We have determined
T_CMB(z), with a precision up to 3%, for a subsample (104 clusters) of the
Planck SZ cluster catalog, at redshift in the range 0.01-- 0.94, using
measurements of the spectrum of the Sunyaev Zel'dovich effect obtained from
Planck temperature maps at frequencies from 70 to 353 GHz. The method adopted
to provide individual determinations of T_CMB(z) at cluster redshift relies on
the use of SZ intensity change, Delta I_SZ(nu), at different frequencies, and
on a Monte-Carlo Markov Chain approach. By applying this method to the sample
of 104 clusters, we limit possible deviations of the form
T_CMB(z)=T_0(1+z)^(1-beta) to be beta= 0.022 +/- 0.018, at 1 sigma uncertainty,
consistent with the prediction of the standard model. Combining these
measurements with previously published results we get beta=0.016+/-0.012.Comment: submitted to JCAP, 21 pages, 8 figure
Millimeter and sub-millimeter atmospheric performance at Dome C combining radiosoundings and ATM synthetic spectra
The reliability of astronomical observations at millimeter and sub-millimeter
wavelengths closely depends on a low vertical content of water vapor as well as
on high atmospheric emission stability. Although Concordia station at Dome C
(Antarctica) enjoys good observing conditions in this atmospheric spectral
windows, as shown by preliminary site-testing campaigns at different bands and
in, not always, time overlapped periods, a dedicated instrument able to
continuously determine atmospheric performance for a wide spectral range is not
yet planned. In the absence of such measurements, in this paper we suggest a
semi-empirical approach to perform an analysis of atmospheric transmission and
emission at Dome C to compare the performance for 7 photometric bands ranging
from 100 GHz to 2 THz. Radiosoundings data provided by the Routine
Meteorological Observations (RMO) Research Project at Concordia station are
corrected by temperature and humidity errors and dry biases and then employed
to feed ATM (Atmospheric Transmission at Microwaves) code to generate synthetic
spectra in the wide spectral range from 100 GHz to 2 THz. To quantify the
atmospheric contribution in millimeter and sub-millimeter observations we are
considering several photometric bands in which atmospheric quantities are
integrated. The observational capabilities of this site at all the selected
spectral bands are analyzed considering monthly averaged transmissions joined
to the corresponding fluctuations. Transmission and pwv statistics at Dome C
derived by our semi-empirical approach are consistent with previous works. It
is evident the decreasing of the performance at high frequencies. We propose to
introduce a new parameter to compare the quality of a site at different
spectral bands, in terms of high transmission and emission stability, the Site
Photometric Quality Factor.Comment: accepted to MNRAS with minor revision
MITO measurements of the Sunyaev-Zeldovich Effect in the Coma cluster of galaxies
We have measured the Sunyaev-Zeldovich effect towards the Coma cluster
(A1656) with the MITO experiment, a 2.6-m telescope equipped with a 4-channel
17 arcminute (FWHM) photometer. Measurements at frequency bands 143+/-15,
214+/-15, 272+/-16 and 353+/-13 GHz, were made during 120 drift scans of Coma.
We describe the observations and data analysis that involved extraction of the
S-Z signal by employing a spatial and spectral de-correlation scheme to remove
a dominant atmospheric component. The deduced values of the thermal S-Z effect
in the first three bands are DT_{0} = -179+/-38,-33+/-81,170+/-35 microKelvin
in the cluster center. The corresponding optical depth, tau=(4.1+/-0.9)
10^{-3}, is consistent (within errors) with both the value from a previous low
frequency S-Z measurement, and the value predicted from the X-ray deduced gas
parameters.Comment: Ap.J.Letters accepted, 4 pages, 2 figure
Jointly fitting weak lensing, x-ray, and Sunyaev-Zel'dovich data to constrain scalar-tensor theories with clusters of galaxies
Degenerate higher-order scalar-tensor (DHOST) theories are considered the most general class of scalar-tensor theories with an additional scalar field. DHOST theories modify the laws of gravity even at galaxy clusters scale hence affecting the weak lensing, x-ray, and Sunyaev-Zel'dovich observables. We derive the theoretical expression for the lensing convergence κ and the pressure profile P of clusters in the framework of DHOST theories and quantify how much they deviate from their general relativity counterparts. We argue that combined measurements of κ, P, and of the electron number density ne can constrain both the cluster parameters and some effective parameters of the DHOST theory. We carry on a Fisher matrix forecasts analysis to investigate whether this is indeed the case considering different scenarios for the spatial resolution and errors on the measured quantities
Cosmic Microwave Background Temperature at Galaxy Clusters
We have deduced the cosmic microwave background (CMB) temperature in the Coma
cluster (A1656, ), and in A2163 () from spectral
measurements of the Sunyaev-Zel'dovich (SZ) effect over four passbands at radio
and microwave frequencies. The resulting temperatures at these redshifts are
K and K, respectively. These values confirm the expected
relation , where K is the value
measured by the COBE/FIRAS experiment. Alternative scaling relations that are
conjectured in non-standard cosmologies can be constrained by the data; for
example, if or , then
and (at 95% confidence). We
briefly discuss future prospects for more precise SZ measurements of at
higher redshifts.Comment: 13 pages, 1 figure, ApJL accepted for publicatio
Triple Experiment Spectrum of the Sunyaev-Zeldovich Effect in the Coma Cluster: H_0
The Sunyaev-Zeldovich (SZ) effect was previously measured in the Coma cluster
by the Owens Valley Radio Observatory and Millimeter and IR Testa Grigia
Observatory experiments and recently also with the Wilkinson Microwave
Anisotropy Probe satellite. We assess the consistency of these results and
their implications on the feasibility of high-frequency SZ work with
ground-based telescopes. The unique data set from the combined measurements at
six frequency bands is jointly analyzed, resulting in a best-fit value for the
Thomson optical depth at the cluster center, tau_{0}=(5.35 \pm 0.67) 10^{-3}.
The combined X-ray and SZ determined properties of the gas are used to
determine the Hubble constant. For isothermal gas with a \beta density profile
we derive H_0 = 84 \pm 26 km/(s\cdot Mpc); the (1\sigma) error includes only
observational SZ and X-ray uncertainties.Comment: 11 pages, 1 figur
Biased total mass of cool core galaxy clusters by Sunyaev-Zel'dovich effect measurements
The Sunyaev Zel'dovich (SZ) effect from galaxy clusters is one of the most
powerful cosmological tools for investigating the large-scale Universe. The big
advantage of the SZ effect is its redshift independence, which is not the case
for visible and X-ray observations. It allows us to directly estimate the
cluster's total mass from the integrated comptonization parameter Y, even for
distant clusters. However, not having a full knowing intra-cluster medium (ICM)
physics can affect the results. By taking self-similar temperature and density
profiles of the ICM into account, we studied how different ICM morphologies can
affect the cluster total mass estimation. With the help of the high percentage
of cool core (CC) clusters, as observed so far, the present analysis focuses on
studying this class of objects. A sample of eight nearby (0.1 < z < 0.5) and
high-mass (M > 10^(14) M_sun) clusters observed by Chandra was considered. We
simulated SZ observations of these clusters through X-ray derived information
and analyzed the mock SZ data again with the simplistic assumption of an
isothermal beta-model profile for the ICM. The bias on the recovered cluster
total mass using different sets of assumptions is estimated to be 50% higher in
the case of hydrostatic equilibrium. Possible contributions to the total bias
due to the line-of-sight integration and the considered ICM template are taken
into account. The large biases on total mass recovery firmly support, if still
necessary, cluster modeling based on more sophisticated universal profiles as
derived by X-ray observations of local objects and hydrodynamical simulations.Comment: 11 pages, 4 figures; minor revisions. Accepted for publication in A&
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