arXiv subjects

F. Pajot

Publications and source records attributed to F. Pajot.

At least 37 records · Page 2Linked to original sources

arXiv2018

Thermal architecture for the QUBIC cryogenic receiver

QUBIC, the QU Bolometric Interferometer for Cosmology, is a novel forthcoming instrument to measure the B-mode polarization anisotropy of the Cosmic Microwave Background. The detection of the B-mode signal will be extremely challenging; QUBIC has been designed to address this with a novel approach, namely bolometric interferometry. The receiver cryostat is exceptionally large and cools complex optical and detector stages to 40 K, 4 K, 1 K and 350 mK using two pulse tube coolers, a novel 4He sorption cooler and a double-stage 3He/4He sorption cooler. We discuss the thermal and mechanical design of the cryostat, modelling and thermal analysis, and laboratory cryogenic testing.

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arXiv2018

Athena X-IFU synthetic observations of galaxy clusters to probe the chemical enrichment of the Universe

Answers to the metal production of the Universe can be found in galaxy clusters, notably within their Intra-Cluster Medium (ICM). The X-ray Integral Field Unit (X-IFU) on board the next-generation European X-ray observatory Athena (2030s) will provide the necessary leap forward in spatially-resolved spectroscopy required to disentangle the intricate mechanisms responsible for this chemical enrichment. In this paper, we investigate the future capabilities of the X-IFU in probing the hot gas within galaxy clusters. From a test sample of four clusters extracted from cosmological hydrodynamical simulations, we present comprehensive synthetic observations of these clusters at different redshifts (up to z = 2) and within the scaled radius R500 performed using the instrument simulator SIXTE. Through 100 ks exposures, we demonstrate that the X-IFU will provide spatially-resolved mapping of the ICM physical properties with little to no biases (<5%) and well within statistical uncertainties. The detailed study of abundance profiles and abundance ratios within R500 also highlights the power of the X-IFU in providing constraints on the various enrichment models. From synthetic observations out to z = 2, we also quantify its ability to track the chemical elements across cosmic time with excellent accuracy, and thereby to investigate the evolution of metal production mechanisms as well as the link to the stellar initial mass-function. Our study demonstrates the unprecedented capabilities of the X-IFU in unveiling the properties of the ICM but also stresses the data analysis challenges faced by future high-resolution X-ray missions such as Athena.

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arXiv2018

NIKA 150 GHz polarization observations of the Crab nebula and its spectral energy distribution

The Crab nebula is a supernova remnant exhibiting a highly polarized synchrotron radiation at radio and millimeter wavelengths. It is the brightest source in the microwave sky with an extension of 7 by 5 arcminutes and commonly used as a standard candle for any experiment which aims at measuring the polarization of the sky. Though its spectral energy distribution has been well characterized in total intensity, polarization data are still lacking at millimetre wavelengths. We report in this paper high resolution (18 arcsec FWHM) observations of the Crab nebula in total intensity and linear polarization at 150 GHz with the NIKA camera. NIKA, operated at the IRAM 30 m telescope from 2012 to 2015, is a camera made of Lumped Element Kinetic Inductance Detectors (LEKIDs) observing the sky at 150 and 260 GHz. From these observations we are able to reconstruct the spatial distribution of the polarization degree and angle of the Crab nebula, which is found to be compatible with previous observations at lower and higher frequencies. Averaging across the source and using other existing data sets we find that the Crab nebula polarization angle is consistent with being constant over a wide range of frequencies with a value of -87.7$^\circ$ +- 0.3 in Galactic coordinates. We also present the first estimation of the Crab nebula spectral energy distribution polarized flux in a wide frequency range: 30-353 GHz. Assuming a single power law emission model we find that the polarization spectral index $β_{pol}$ = - 0.347 +- 0.026 is compatible with the intensity spectral index $β$ = - 0.323 +- 0.001.

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arXiv2018

In-flight measurement of Planck telescope emissivity

The Planck satellite in orbit mission ended in October 2013. Between the end of Low Frequency Instrument (LFI) routine mission operations and the satellite decommissioning, a dedicated test was also performed to measure the Planck telescope emissivity. The scope of the test was twofold: (i) to provide, for the first time in flight, a direct measure of the telescope emissivity; and (ii) to evaluate the possible degradation of the emissivity by comparing data taken in flight at the end of mission with those taken during the ground telescope characterization. The emissivity was determined by heating the Planck telescope and disentangling the system temperature excess measured by the LFI radiometers. Results show End of Life (EOL) performance in good agreement with the results from the ground optical tests and from in-flight indirect estimations measured during the Commissioning and Performance Verification (CPV) phase. Methods and results are presented and discussed.

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arXiv2018

QUBIC - The Q&U Bolometric Interferometer for Cosmology - A novel way to look at the polarized Cosmic Microwave Background

In this paper we describe QUBIC, an experiment that takes up the challenge posed by the detection of primordial gravitational waves with a novel approach, that combines the sensitivity of state-of-the art bolometric detectors with the systematic effects control typical of interferometers. The so-called "self-calibration" is a technique deeply rooted in the interferometric nature of the instrument and allows us to clean the measured data from instrumental effects. The first module of QUBIC is a dual band instrument (150 GHz and 220 GHz) that will be deployed in Argentina during the Fall 2018.

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arXiv2017

Sub-structure and merger detection in resolved NIKA Sunyaev-Zel'dovich images of distant clusters

Sub-structures in the hot gas of galaxy clusters are related to their formation history and to the astrophysical processes at play in the intracluster medium (ICM). The thermal Sunyaev-Zel'dovich (tSZ) effect is directly sensitive to the line-of-sight integrated ICM pressure, and is thus particularly adapted to study ICM sub-structures. We apply structure-enhancement filtering algorithms to high resolution tSZ observations of distant clusters, in order to search for pressure discontinuities, compressions, as well as secondary peaks in the ICM. The same filters are applied to synthetic tSZ images extracted from RHAPSODY-G hydrodynamic simulations, in order to better interpret the extracted features. We also study the noise propagation trough the filters and quantify the impact of systematic effects, point source residuals being identified as the dominant potential contaminant. In 3 of our 6 NIKA clusters we identify features at high S/N that show clear evidence for merger events. In MACSJ0717 (z=0.55), three strong pressure gradients are observed on the E, SE and W sectors, and two main peaks in the pressure distribution are identified. We observe a lack of tSZ compact structure in the cool-core cluster PSZ1G045.85 (z=0.61), and a tSZ gradient ridge dominates in the SE. In the highest z cluster, CLJ1227 (z=0.89), we detect a ~45" (360 kpc) long ridge pressure gradient associated with a secondary pressure peak in the W region. Our results show that current tSZ facilities have now reached the angular resolution and sensitivity to allow an exploration of the details of pressure sub-structures in clusters, even at high z. This opens the possibility to quantify the impact of the dynamical state on the relation between the tSZ signal and the mass of clusters, which is important when using tSZ clusters to test cosmological models. This work also marks the first NIKA cluster sample data release.

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arXiv2017

Mapping the hot gas temperature in galaxy clusters using X-ray and Sunyaev-Zel'dovich imaging

We propose a method to map the temperature distribution of the hot gas in galaxy clusters that uses resolved images of the thermal Sunyaev-Zel'dovich (tSZ) effect in combination with X-ray data. Application to images from the New IRAM KIDs Array (NIKA) and XMM-Newton allows us to measure and determine the spatial distribution of the gas temperature in the merging cluster MACS J0717.5+3745, at $z=0.55$. Despite the complexity of the target object, we find a good morphological agreement between the temperature maps derived from X-ray spectroscopy only -- using XMM-Newton ($T_{\rm XMM}$) and Chandra ($T_{\rm CXO}$) -- and the new gas-mass-weighted tSZ+X-ray imaging method ($T_{\rm SZ}$). We correlate the temperatures from tSZ+X-ray imaging and those from X-ray spectroscopy alone and find that $T_{\rm SZ}$ is higher than $T_{\rm XMM}$ and lower than $T_{\rm CXO}$ by $\sim 10\%$ in both cases. Our results are limited by uncertainties in the geometry of the cluster gas, contamination from kinetic SZ ($\sim 10\%$), and the absolute calibration of the tSZ map ($7\%$). Investigation using a larger sample of clusters would help minimise these effects.

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arXiv2017

Probing changes of dust properties along a chain of solar-type prestellar and protostellar cores in Taurus with NIKA

The characterization of dust properties in the interstellar medium (ISM) is key for star formation. Mass estimates are crucial to determine gravitational collapse conditions for the birth of new stellar objects in molecular clouds. However, most of these estimates rely on dust models that need further observational constraints from clouds to prestellar and protostellar cores. We present results of a study of dust emissivity changes based on mm-continuum data obtained with the NIKA camera at the IRAM-30m telescope. Observing dust emission at 1.15 mm and 2 mm allows us to constrain the dust emissivity index ($β$) in the Rayleigh-Jeans tail of the dust spectral energy distribution (SED) far from its peak emission, where the contribution of other parameters (i.e. dust temperature) is important. Focusing on the Taurus molecular cloud, a low-mass star-forming regions in the Gould Belt, we analyze the emission properties of several distinct objects in the B213 filament: three prestellar cores, two Class-0/I protostellar cores and one Class-II object. By means of the ratio of the two NIKA channel-maps, we show that in the Rayleigh-Jeans approximation the dust emissivity index varies among the objects. For one prestellar and two protostellar cores, we produce a robust study using Herschel data to constrain the dust temperature of the sources. By using the Abel transform inversion technique we get accurate radial $β$ profiles. We find systematic spatial variations of $β$ in the protostellar cores that is not observed in the prestellar core. While in the former case $β$ decreases toward the center, in the latter it remains constant. Moreover, $β$ appears anticorrelated with the dust temperature. We discuss the implication of these results in terms of dust grain evolution between pre- and protostellar cores.

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arXiv2017

QUBIC Technical Design Report

QUBIC is an instrument aiming at measuring the B mode polarisation anisotropies at medium scales angular scales (30-200 multipoles). The search for the primordial CMB B-mode polarization signal is challenging, because of many difficulties: smallness of the expected signal, instrumental systematics that could possibly induce polarization leakage from the large E signal into B, brighter than anticipated polarized foregrounds (dust) reducing to zero the initial hope of finding sky regions clean enough to have a direct primordial B-modes observation. The QUBIC instrument is designed to address all aspects of this challenge with a novel kind of instrument, a Bolometric Interferometer, combining the background-limited sensitivity of Transition-Edge-Sensors and the control of systematics allowed by the observation of interference fringe patterns, while operating at two frequencies to disentangle polarized foregrounds from primordial B mode polarization. Its characteristics are described in details in this Technological Design Report.

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arXiv2017

Polarimetry at millimeter wavelengths with the NIKA camera: calibration and performance

Magnetic fields, which play a major role in a large number of astrophysical processes from galactic to cosmological scales, can be traced via observations of dust polarization as demonstrated by the Planck satellite results. In particular, low-resolution observations of dust polarization have demonstrated that Galactic filamentary structures, where star formation takes place, are associated to well organized magnetic fields. A better understanding of this process requires detailed observations of galactic dust polarization on scales of 0.01 to 0.1 pc. Such high-resolution polarization observations can be carried out at the IRAM 30 m telescope using the recently installed NIKA2 camera, which features two frequency bands at 260 and 150 GHz (respectively 1.15 and 2.05 mm), the 260 GHz band being polarization sensitive. NIKA2 so far in commissioning phase, has its focal plane filled with ~3300 detectors to cover a Field of View (FoV) of 6.5 arcminutes diameter. The NIKA camera, which consisted of two arrays of 132 and 224 Lumped Element Kinetic Inductance Detectors (LEKIDs) and a FWHM (Full-Width-Half-Maximum) of 12 and 18.2 arcsecond at 1.15 and 2.05 mm respectively, has been operated at the IRAM 30 m telescope from 2012 to 2015 as a test-bench for NIKA2. NIKA was equipped of a room temperature polarization system (a half wave plate (HWP) and a grid polarizer facing the NIKA cryostat window). The fast and continuous rotation of the HWP permits the quasi simultaneous reconstruction of the three Stokes parameters, I, Q and U at 150 and 260 GHz. This paper presents the first polarization measurements with KIDs and reports the polarization performance of the NIKA camera and the pertinence of the choice of the polarization setup in the perspective of NIKA2. (abridged)

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arXiv2016

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.

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arXiv2016

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 $(< 20$ arcsec) thermal Sunyaev-Zel'dovich (tSZ) observations by probing the intracluster medium (ICM) of the \planck-discovered galaxy cluster \psz\ at redshift $z = 0.61$, 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 ($R \sim 0.02\, R_{500}$) to its outskirts ($R \sim 3\, R_{500}$) 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 ($M_{500} \sim 5.5 \times 10^{14}$ M$_{\odot}$) 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)

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arXiv2016

The NIKA2 commissioning campaign: performance and first results

The New IRAM KID Array 2 (NIKA 2) is a dual-band camera operating with three frequency-multiplexed kilopixels arrays of Lumped Element Kinetic Inductance Detectors (LEKID) cooled at 150 mK. NIKA 2 is designed to observe the intensity and polarisation of the sky at 1.15 and 2.0 mm wavelength from the IRAM 30 m telescope. The NIKA 2 instrument represents a huge step in performance as compared to the NIKA pathfinder instrument, which has already shown state-of-the-art detector and photometric performance. After the commissioning planned to be accomplished at the end of 2016, NIKA 2 will be an IRAM resident instrument for the next ten years or more. NIKA 2 should allow the astrophysical community to tackle a large number of open questions reaching from the role of the Galactic magnetic field in star formation to the discrepancy between cluster-based and CMB-based cosmology possibly induced by the unknown cluster physics. We present an overview of the commissioning phase together with some first results.

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arXiv2016

High angular resolution SZ observations with NIKA and NIKA2

NIKA2 (New IRAM KID Arrays) is a dual band (150 and 260 GHz) imaging camera based on Kinetic Inductance Detectors (KIDs) and designed to work at the IRAM 30 m telescope (Pico Veleta, Spain). Built on the experience of the NIKA prototype, NIKA2 has been installed at the 30 m focal plane in October 2015 and the commissioning phase is now ongoing. Through the thermal Sunyaev-Zeldovich (tSZ) effect, NIKA2 will image the ionized gas residing in clusters of galaxies with a resolution of 12 and 18 arcsec FWHM (at 150 and 260 GHz, respectively). We report on the recent tSZ measurements with the NIKA camera and discuss the future objectives for the NIKA2 SZ large Program, 300h of observation dedicated to SZ science. With this program we intend to perform a high angular resolution follow-up of a cosmologically-representative sample of clusters belonging to SZ catalogues, with redshift greater than 0.5. The main output of the program will be the study of the redshift evolution of the cluster pressure profile as well as that of the scaling laws relating the cluster global properties.

astro-ph.CO↗

arXiv2016

High-resolution tSZ cartography of clusters of galaxies with NIKA at the IRAM 30-m telescope

The thermal Sunyaev-Zeldovich effect (tSZ) is a powerful probe to study clusters of galaxies and is complementary with respect to X-ray, lensing or optical observations. Previous arcmin resolution tSZ observations ({\it e.g.} SPT, ACT and Planck) only enabled detailed studies of the intra-cluster medium morphology for low redshift clusters ($z < 0.2$). Thus, the development of precision cosmology with clusters requires high angular resolution observations to extend the understanding of galaxy cluster towards high redshift. NIKA2 is a wide-field (6.5 arcmin field of view) dual-band camera, operated at $100 \ {\rm mK}$ and containing $\sim 3300$ KID (Kinetic Inductance Detectors), designed to observe the millimeter sky at 150 and 260 GHz, with an angular resolution of 18 and 12 arcsec respectively. The NIKA2 camera has been installed on the IRAM 30-m telescope (Pico Veleta, Spain) in September 2015. The NIKA2 tSZ observation program will allow us to observe a large sample of clusters (50) at redshift ranging between 0.5 and 1. As a pathfinder for NIKA2, several clusters of galaxies have been observed at the IRAM 30-m telescope with the NIKA prototype to cover the various configurations and observation conditions expected for NIKA2.

astro-ph.CO↗

arXiv2016

High angular resolution Sunyaev-Zel'dovich observations of MACS J1423.8+2404 with NIKA: Multiwavelength analysis

The prototype of the NIKA2 camera, NIKA, is an instrument operating at the IRAM 30-m telescope, which can observe simultaneously at 150 and 260GHz. One of the main goals of NIKA2 is to measure the pressure distribution in galaxy clusters at high resolution using the thermal SZ (tSZ) effect. Such observations have already proved to be an excellent probe of cluster pressure distributions even at high redshifts. However, an important fraction of clusters host submm and/or radio point sources, which can significantly affect the reconstructed signal. Here we report on <20" resolution observations at 150 and 260GHz of the cluster MACSJ1424, which hosts both radio and submm point sources. We examine the morphology of the tSZ signal and compare it to other datasets. The NIKA data are combined with Herschel satellite data to study the SED of the submm point source contaminants. We then perform a joint reconstruction of the intracluster medium (ICM) electronic pressure and density by combining NIKA, Planck, XMM-Newton, and Chandra data, focusing on the impact of the radio and submm sources on the reconstructed pressure profile. We find that large-scale pressure distribution is unaffected by the point sources because of the resolved nature of the NIKA observations. The reconstructed pressure in the inner region is slightly higher when the contribution of point sources are removed. We show that it is not possible to set strong constraints on the central pressure distribution without accurately removing these contaminants. The comparison with X-ray only data shows good agreement for the pressure, temperature, and entropy profiles, which all indicate that MACSJ1424 is a dynamically relaxed cool core system. The present observations illustrate the possibility of measuring these quantities with a relatively small integration time, even at high redshift and without X-ray spectroscopy.

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arXiv2016

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.

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arXiv2016

The NIKA2 instrument, a dual-band kilopixel KID array for millimetric astronomy

NIKA2 (New IRAM KID Array 2) is a camera dedicated to millimeter wave astronomy based upon kilopixel arrays of Kinetic Inductance Detectors (KID). The pathfinder instrument, NIKA, has already shown state-of-the-art detector performance. NIKA2 builds upon this experience but goes one step further, increasing the total pixel count by a factor $\sim$10 while maintaining the same per pixel performance. For the next decade, this camera will be the resident photometric instrument of the Institut de Radio Astronomie Millimetrique (IRAM) 30m telescope in Sierra Nevada (Spain). In this paper we give an overview of the main components of NIKA2, and describe the achieved detector performance. The camera has been permanently installed at the IRAM 30m telescope in October 2015. It will be made accessible to the scientific community at the end of 2016, after a one-year commissioning period. When this happens, NIKA2 will become a fundamental tool for astronomers worldwide.

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