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&

The good, the bad, and the ugly: Statistical quality assessment of SZ detections

We examine three approaches to the problem of source classification in catalogues. Our goal is to determine the confidence with which the elements in these catalogues can be distinguished in populations on the basis of their spectral energy distribution (SED). Our analysis is based on the projection of the measurements onto a comprehensive SED model of the main signals in the considered range of frequencies. We first consider likelihood analysis, which is halfway between supervised and unsupervised methods. Next, we investigate an unsupervised clustering technique. Finally, we consider a supervised classifier based on artificial neural networks. We illustrate the approach and results using catalogues from various surveys, such as X-rays (MCXC), optical (SDSS), and millimetric (Planck Sunyaev-Zeldovich (SZ)). We show that the results from the statistical classifications of the three methods are in very good agreement with each other, although the supervised neural network-based classification shows better performance allowing the best separation into populations of reliable and unreliable sources in catalogues. The latest method was applied to the SZ sources detected by the Planck satellite. It led to a classification assessing and thereby agreeing with the reliability assessment published in the Planck SZ catalogue. Our method could easily be applied to catalogues from future large surveys such as SRG/eROSITA and Euclid.We acknowledge the support of the French Agence Nationale de la Recherche under grant ANR-11-BD56-015. The development of Planck has been supported by: ESA; CNES and CNRS/INSU-IN2P3-INP (France); ASI, CNR, and INAF (Italy); NASA and DoE (USA); STFC and UKSA (UK); CSIC, MICINN and JA (Spain); Tekes, AoF and CSC (Finland); DLR and MPG (Germany); CSA (Canada); DTU Space (Denmark); SER/SSO (Switzerland); RCN (Norway); SFI (Ireland); FCT/MCTES (Portugal); and PRACE (EU).Peer Reviewe

The Good, the Bad, and the Ugly: Statistical quality assessment of SZ detections

International audienceWe examine three approaches to the problem of source classification in catalogues. Our goal is to determine the confidence withwhich the elements in these catalogues can be distinguished in populations on the basis of their spectral energy distribution (SED).Our analysis is based on the projection of the measurements onto a comprehensive SED model of the main signals in the consideredrange of frequencies. We first consider likelihood analysis, which is halfway between supervised and unsupervised methods. Next, weinvestigate an unsupervised clustering technique. Finally, we consider a supervised classifier based on artificial neural networks. Weillustrate the approach and results using catalogues from various surveys, such as X-rays (MCXC), optical (SDSS), and millimetric(Planck Sunyaev-Zeldovich (SZ)). We show that the results from the statistical classifications of the three methods are in very goodagreement with each other, although the supervised neural network-based classification shows better performance allowing the bestseparation into populations of reliable and unreliable sources in catalogues. The latest method was applied to the SZ sources detectedby the Planck satellite. It led to a classification assessing and thereby agreeing with the reliability assessment published in the PlanckSZ catalogue. Our method could easily be applied to catalogues from future large surveys such as SRG/eROSITA and Euclid

High resolution SZ observations at the IRAM 30-m telescope with NIKA

High resolution observations of the thermal Sunyaev-Zel'dovich (tSZ) effect are necessary to allow the use of clusters of galaxies as a probe for large scale structures at high redshifts. With its high resolution and dual-band capability at millimeter wavelengths, the NIKA camera can play a significant role in this context. NIKA is based on newly developed Kinetic Inductance Detectors (KIDs) and operates at the IRAM 30m telescope, Pico Veleta, Spain. In this paper, we give the status of the NIKA camera, focussing on the KID technology. We then present observations of three galaxy clusters: RX J1347.5-1145 as a demonstrator of the NIKA capabilities and the recent observations of CL J1226.9+3332 (z = 0.89) and MACS J0717.5+3745 (z = 0.55). We also discuss prospects for the final NIKA2 camera, which will have a 6.5 arcminute field of view with about 5000 detectors in two bands at 150 and 260 GHz

Detection of the tSZ effect with the NIKA camera

We present the first detection of the thermal Sunyaev-Zel'dovich (tSZ) effect from a cluster of galaxies performed with a KIDs (Kinetic Inductance Detectors) based instrument. The tSZ effect is a distortion of the black body CMB (Cosmic Microwave Background) spectrum produced by the inverse Compton interaction of CMB photons with the hot electrons of the ionized intra-cluster medium. The massive, intermediate redshift cluster RX J1347.5-1145 has been observed using NIKA (New IRAM KIDs arrays), a dual-band (140 and 240 GHz) mm-wave imaging camera, which exploits two arrays of hundreds of KIDs: the resonant frequencies of the superconducting resonators are shifted by mm-wave photons absorption. This tSZ cluster observation demonstrates the potential of the next generation NIKA2 instrument, being developed for the 30m telescope of IRAM, at Pico Veleta (Spain). NIKA2 will have 1000 detectors at 140GHz and 2x2000 detectors at 240GHz, providing in that band also a measurement of the linear polarization. NIKA2 will be commissioned in 2015.Comment: SF2A Proceedings 201

NIKA 2: next-generation continuum/polarized camera at the IRAM 30 m telescope and its prototype

NIKA 2 (New Instrument of Kids Array) is a next generation continuum and polarized instrument successfully installed in October 2015 at the IRAM 30 m telescope on Pico-Veleta (Granada, Spain). NIKA 2 is a high resolution dual-band camera, operating with frequency multiplexed LEKIDs (Lumped Element Kinetic Inductance Detectors) cooled at 100 mK. Dual color images are obtained thanks to the simultaneous readout of a 1020 pixels array at 2 mm and 1140 x 2 pixels arrays at 1.15 mm with a final resolution of 18 and 12 arcsec respectively, and 6.5 arcmin of Field of View (FoV). The two arrays at 1.15 mm allow us to measure the linear polarization of the incoming light. This will place NIKA 2 as an instrument of choice to study the role of magnetic fields in the star formation process. The NIKA experiment, a prototype for NIKA 2 with a reduced number of detectors (about 400 LEKIDs) and FoV (1.8 arcmin), has been successfully operated at the IRAM 30 telescope in several open observational campaigns. The performance of the NIKA 2 polarization setup has been successfully validated with the NIKA prototype.Comment: 5 pages, 4 figures, proceeding for the conference: Extragalactic radio surveys 201