Atmospheric monitoring in the mm and sub-mm bands for cosmological observations: CASPER2

Cosmological observations from ground at millimetre and sub-millimetre wavelengths are affected by atmospheric absorption and consequent emission. The low and high frequency (sky noise) fluctuations of atmospheric performance imply careful observational strategies and/or instrument technical solutions. Measurements of atmospheric emission spectra are necessary for accurate calibration procedures as well as for site testing statistics. CASPER2, an instrument to explore the 90-450 GHz (3-15 1/cm) spectral region, was developed and verified its operation in the Alps. A Martin-Puplett Interferometer (MPI) operates comparing sky radiation, coming from a field of view (fov) of 28 arcminutes (FWHM) collected by a 62-cm in diameter Pressman-Camichel telescope, with a reference source. The two output ports of the interferometer are detected by two bolometers cooled down to 300 mK inside a wet cryostat. Three different and complementary interferometric techniques can be performed with CASPER2: Amplitude Modulation (AM), Fast-Scan (FS) and Phase Modulation (PM). An altazimuthal mount allows the sky pointing, possibly co-alligned to the optical axis of the 2.6-m in diameter telescope of MITO (Millimetre and Infrared Testagrigia Observatory, Italy). Optimal timescale to average acquired spectra is inferred by Allan variance analysis at 5 fiducial frequencies. We present the motivation for and design of the atmospheric spectrometer CASPER2. The adopted procedure to calibrate the instrument and preliminary performance of the instrument are described. Instrument capabilities were checked during the summer observational campaign at MITO in July 2010 by measuring atmospheric emission spectra with the three different procedures.Comment: 11 pages, 9 figures, 2 tables, Accepted for publication in MNRA

On the coherent rotation of diffuse matter in numerical simulations of galaxy clusters

We present a study on the coherent rotation of the intracluster medium and dark matter components of simulated galaxy clusters extracted from a volume-limited sample of the MUSIC project. The set is re-simulated with three different recipes for the gas physics: $(i)$ non-radiative, $(ii)$ radiative without AGN feedback, and $(iii)$ radiative with AGN feedback. Our analysis is based on the 146 most massive clusters identified as relaxed, 57 per cent of the total sample. We classify these objects as rotating and non-rotating according to the gas spin parameter, a quantity that can be related to cluster observations. We find that 4 per cent of the relaxed sample is rotating according to our criterion. By looking at the radial profiles of their specific angular momentum vector, we find that the solid body model is not a suitable description of rotational motions. The radial profiles of the velocity of the dark matter show a prevalence of the random velocity dispersion. Instead, the intracluster medium profiles are characterized by a comparable contribution from the tangential velocity and the dispersion. In general, the dark matter component dominates the dynamics of the clusters, as suggested by the correlation between its angular momentum and the gas one, and by the lack of relevant differences among the three sets of simulations.Comment: 12 pages, updated to match the MNRAS versio

The Sunyaev-Zeldovich MITO Project

Compton scattering of the cosmic microwave background radiation by electrons in the hot gas in clusters of galaxies - the Sunyaev-Zeldovich effect - has long been recognized as a uniquely important feature, rich in cosmological and astrophysical information. We briefly describe the effect, and emphasize the need for detailed S-Z and X-ray measurements of nearby clusters in order to use the effect as a precise cosmological probe. This is the goal of the MITO project, whose first stage consisted of observations of the S-Z effect in the Coma cluster. We report the results of these observations.Comment: To appear in Proceedings of `Understanding our Universe at the close of XXth century', School held Apr 25 - May 6 2000, Cargese, 16 pages LaTeX, 2 figures ps (using elsart.sty & elsart.cls), text minor revisio

The Three Hundred Project: Dynamical state of galaxy clusters and morphology from multi-wavelength synthetic maps

We study the connection between morphology and dynamical state of the simulated galaxy clusters in $z\in[0,1.031]$ from THE THREE HUNDRED Project. We quantify cluster dynamical state using a combination of dynamical indicators from theoretical measures and compare this combined parameter, $\chi$, with the results from morphological classifications. The dynamical state of the cluster sample shows a continuous distribution from dynamically relaxed, more abundant at lower redshift, to hybrid and disturbed. The dynamical state presents a clear dependence on the radius, with internal regions more relaxed than outskirts. The morphology from multi-wavelength mock observation of clusters in X-ray, optical, and Sunyaev-Zel'dovich (SZ) effect images, is quantified by $M$ -- a combination of six parameters for X-ray and SZ maps and the offsets between the optical position of the Brightest Central Galaxy (BCG) and the X-ray/SZ centroids. All the morphological parameters are highly correlated with each other, while they show a moderately strong correlation with the dynamical $\chi$ parameter. The X-ray or SZ peaks are less affected by the dynamical state than centroids, which results in reliable tracers of the cluster density peak. The principal source of contamination in the relaxed cluster fraction, inferred from morphological parameters, is due to dynamically hybrid clusters. Compared to individual parameters, which consider only one aspect of cluster property (e.g. only clumping or asymmetry), the combined morphological and dynamical parameters ($M$ and $\chi$) collect more information and provide a single and more accurate estimation of the cluster dynamical state.Comment: 18 pages, 12 figures. Accepted for publication in MNRA

Limitations to the Accuracy of Cosmic Background Radiation Anisotropy Measurements: Atmospheric Fluctuations

We discuss the ultimate limits posed by atmospheric fluctuations to observations of cosmic background anisotropies (CBAs) in ground-based and balloon-borne experiments both in the radio and millimetric regions. We present correlation techniques useful in separating CBAs from atmospheric fluctuations. An experimental procedure is discussed for testing a site in view of possible CBA observations. Four sites with altitudes ranging from 0 up to 3.5 km have been tested

Testing generalized scalar-tensor theories of gravity with clusters of galaxies

We test the generalized scalar-tensor theory in static systems, namely galaxy clusters. The Degenerate higher-order scalar-tensor (DHOST) theory modifies the Newtonian potential through effective Newtonian constant and $\Xi_1$ parameter in the small scale, which modifies the hydrostatic equilibrium. We utilize the well-compiled X-COP catalog consisting of 12 clusters with Intra Cluster Medium (ICM) pressure profile by Sunyaev-Zeldovich effect data and temperature profile by X-ray data for each cluster. We perform a fully Bayesian analysis modeling Navarro-Frenk-White (NFW) for the mass profile, and the simplified Vikhlinin model for the electron density. Carefully selecting suitable clusters to present our results, we find a mild to moderate, i.e, $\sim 2\sigma$ significance for a deviation from the standard scenario in 4 of the clusters. However, in terms of Bayesian evidence, we find either equivalent or mild preference for GR. We estimate a joint constraint of $\Xi_1 = -0.030 \pm 0.043$ using 8 clusters, for a modification from a $\Lambda$CDM scenario. This limit is in very good agreement with theoretical ones and an order of magnitude more stringent than the previous constraint obtained using clusters. We also quote a more conservative limit of $\Xi_1 = -0.061 \pm 0.074$. Finally, we comment on the tentative redshift dependence ($\Xi_1(z)$), finding a mild preference ($\lesssim 2\sigma$) for the same.Comment: Comments are Welcom

Morphological estimators on Sunyaev-Zel'dovich maps of MUSIC clusters of galaxies

The determination of the morphology of galaxy clusters has important repercussions for cosmological and astrophysical studies of them. In this paper, we address the morphological characterization of synthetic maps of the Sunyaev-Zel'dovich (SZ) effect for a sample of 258 massive clusters (Mvir> 5×1014h-1M⊙at z=0), extracted from theMUSIC hydrodynamical simulations. Specifically, we use five known morphological parameters (which are already used in X-ray) and two newly introduced ones, and we combine them in a single parameter. We analyse two sets of simulations obtained with different prescriptions of the gas physics (non-radiative and with cooling, star formation and stellar feedback) at four red shifts between 0.43 and 0.82. For each parameter, we test its stability and efficiency in discriminating the true cluster dynamical state, measured by theoretical indicators. The combined parameter is more efficient at discriminating between relaxed and disturbed clusters. This parameter had a mild correlation with the hydrostatic mass (~0.3) and a strong correlation (~0.8) with the offset between the SZ centroid and the cluster centre of mass. The latter quantity is, thus, the most accessible and efficient indicator of the dynamical state for SZ studiesThis work has been partially supported by funding from Sapienza University of Rome - Progetti di Ricerca Anno 2015 prot. C26A15LXNR. GY and FS acknowledge financial support from MINECO/FEDER under research grant AYA2015-63810-P. ER acknowledge financial contribution from the agreement ASI-INAF n 2017-14-H.

The Three Hundred Project: quest of clusters of galaxies morphology and dynamical state through Zernike Polynomials

The knowledge of the dynamical state of galaxy clusters allows to alleviate systematics when observational data from these objects are applied in cosmological studies. Evidence of correlation between the state and the morphology of the clusters is well studied. The morphology can be inferred by images of the surface brightness in the X-ray band and of the thermal component of the Sunyaev-Zel'dovich (tSZ) effect in the millimetre range. For this purpose, we apply, for the first time, the Zernike polynomial decomposition, a common analytic approach mostly used in adaptive optics to recover aberrated radiation wavefronts at the telescopes pupil plane. With this novel way we expect to correctly infer the morphology of clusters and so possibly, their dynamical state. To verify the reliability of this new approach we use more than 300 synthetic clusters selected in THE THREE HUNDRED project at different redshifts ranging from 0 up to 1.03. Mock maps of the tSZ, quantified with the Compton parameter, $y$-maps, are modelled with Zernike polynomials inside $R_{500}$, the cluster reference radius. We verify that it is possible to discriminate the morphology of each cluster by estimating the contribution of the different polynomials to the fit of the map. The results of this new method are correlated with those of a previous analysis made on the same catalogue, using two parameters that combine either morphological or dynamical-state probes. We underline that instrumental angular resolution of the maps has an impact mainly when we extend this approach to high-redshift clusters.Comment: 16 pages, 10 figures, 6 tables (including appendix A and B). Accepted for publication in MNRA