1,552 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
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
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
PRELIMINARY CONCERNS ABOUT AGRONOMIC INTERPRETATION OF NDVI TIME SERIES FROM SENTINEL-2 DATA: PHENOLOGY AND THERMAL EFFICIENCY OF WINTER WHEAT IN PIEMONTE (NW ITALY)
Abstract. TELECER project is supported through Rural Development Programme regional action of EU CAP and is aimed at providing Precision Agriculture–devoted services for cereals monitoring in the Piemonte Region (NW-Italy) context. In this work authors explored some general and preliminary issues mainly aimed at demonstrating and formalizing those evident relationships existing between NDVI image time series and the main ordinary agronomic parameters, with special focus on phenology and thermal efficiency of crops as related to Growing Degrees Day (GDD). Winter wheat was investigated and relationships calibrated at field level, making possible to spatially characterise environmental and management effects. Two different analysis were achieved: (i) one aimed at mapping crop phenological metrics, as derivable from NDVI S2 time series; (ii) one aimed at locally modelling relationship linking GDD and NDVI to somehow test the thermal efficiency of crops in the different parts of the study area. The first analysis showed that the end of season appears to be the most constant phenological metric in the study area possibly demonstrating a time concentration of harvest operations in the area. Differently, the peak of season and the start of season metrics showed to be largely varying in the study, thus suggesting to be stronger predictors: (i) of crop development; (ii) of the effects induced by local agronomical practices. Several base temperatures were used to compute correspondent GDD. These were tested against NDVI and modelled by a parabolic model at field level. Model coefficients distribution were analysed and mapped the correspondent agronomic interpretation suggested
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&
Modification of cluster radio halo appearance by the thermal Sunyaev-Zeldovich effect
We discuss the consequences of the spectral and morphological modification of
galaxy cluster radio halos due to the Sunyaev-Zeldovich (SZ) effect for the
interpretation of existing and upcoming high frequency radio observations.
Likely these modifications have affected the interpretation of the existing
Coma cluster radio data. The radio halo emission visible at low (< 5 GHz)
frequencies is at higher (> 10 GHz) frequencies completely over-compensated by
the thermal SZ decrement. Thus, the total radio emission of a galaxy cluster
goes through zero (in comparison to the constant cosmic microwave background
(CMB) emission) at a frequency of several GHz. Since the radio halo brightness
has a narrow radial profile compared to the SZ decrement, a central emission
region is surrounded by a decrement within the intermediate frequency range of
several GHz. The size of this emission regions shrinks with increasing
frequency until the decrement dominates everywhere in the cluster.Comment: accepted by A&A Letters, 4 pages, 3 figurs, typo correcte
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