Context.
Characterising the large-scale structure in the Universe from present times to the high redshift epoch of reionisation is essential to constraining the cosmology, the history of star ...formation, and reionisation, to measuring the gas content of the Universe, and to obtaining a better understanding of the physical processes that drive galaxy formation and evolution. Using the integrated emission from unresolved galaxies or gas clouds, line intensity mapping (LIM) provides a new observational window to measure the larger properties of structures. This very promising technique motivates the community to plan for LIM experiments.
Aims.
We describe the development of a large field-of-view instrument, named CONCERTO (for CarbON CII line in post-rEionisation and ReionisaTiOn epoch), operating in the range 130–310 GHz from the APEX 12-m telescope (5100 m above sea level). CONCERTO is a low-resolution spectrometer based on the lumped element kinetic inductance detectors (LEKID) technology. Spectra are obtained using a fast Fourier transform spectrometer (FTS), coupled to a dilution cryostat with a base temperature of 0.1 K. Two two kilo-pixel arrays of LEKID are mounted inside the cryostat that also contains the cold optics and the front-end electronics.
Methods.
We present, in detail, the technological choices leading to the instrumental concept, together with the design and fabrication of the instrument and preliminary laboratory tests on the detectors. We also give our best estimates for CONCERTO sensitivity and give predictions for two of the main scientific goals of CONCERTO, that is, a CII-intensity mapping survey and observations of galaxy clusters.
Results.
We provide a detailed description of the instrument design. Based on realistic comparisons with existing instruments developed by our group (NIKA, NIKA2, and KISS), and on the laboratory characterisation of our detectors, we provide an estimate for CONCERTO sensitivity on the sky. Finally, we describe, in detail, two of the main scientific goals offered by CONCERTO at APEX.
Context.
Large field-of-view imaging and polarimetry instruments operating at millimetre and sub-millimetre wavelengths are fundamental tools to understand the role of magnetic fields in channelling ...filament material into prestellar cores, providing unique insight in the physics of galactic star-forming regions. Among other topics, at extra-galactic scales, polarisation observations of Active Galactic Nuclei (AGNs) will allow us to constrain the possible physical conditions of the emitting plasma from the jets and/or explore the physics of dust inside supernova remnants. The kilo-pixel New IRAM KIDs Array 2 (NIKA2) camera, installed today at the Institut de Radioastronomie Millimétrique (IRAM) 30-m telescope, represents one of the best tools available to astronomers to produce simultaneous intensity and polarimetry maps over large fields at 260 GHz (1.15 mm).
Aims.
The polarisation measurement, in NIKA and NIKA2, is achieved by rapidly modulating the total incoming polarisation. In the end, this allows one to safely isolate the small science signal from the large, un-polarised, and strongly variable, atmospheric background.
Methods.
The polarisation modulation is achieved by inserting a fast rotating half-wave plate (HWP) in the optical beam. In order to allow wide field-of-view observations, the plate has to be large, with a diameter of 250 mm. The modulation of the polarised signal at 12 Hz also requires the waveplate to be sufficiently light. In addition, this key optical element has to exhibit optimal electromagnetic characteristics in terms of transmission and differential phase-shift. For this purpose, three metamaterial HWPs have been developed using the mesh-filter technology. The knowledge acquired in developing the first two single-band HWPs was used to achieve the more challenging performance requirements of the last dual-band HWP. The first and the third waveplates met the requirements for both the NIKA and NIKA2 instruments.
Results.
We first illustrate the design, the technical developments, the fabrication, and laboratory characterisation of the three mesh-HWPs. The deployment of two such elements in the NIKA and NIKA2 instruments at the 30-metre telescope is then described. We conclude with representative examples of astrophysical maps integrating polarimetry.
Context.
Millimetre-wave astronomy is an important tool for both general astrophysics studies and cosmology. A large number of unidentified sources are being detected by the large field-of-view ...continuum instruments operating on large telescopes.
Aims.
New smart focal planes are needed to bridge the gap between the large bandwidth continuum instruments operating on single-dish telescopes and high spectral and angular resolution interferometers (e.g. ALMA in Chile and NOEMA in France). The aim is to perform low to medium spectral resolution observations and select a lower number of potentially interesting sources (i.e. high-redshift galaxies) for further follow-up.
Methods.
We have designed, fabricated, and tested an innovative on-chip spectrometer sensitive in the 85–110 GHz range. It contains 16 channels, each of which covers a frequency band of about 0.2 GHz. A conical horn antenna coupled to a slot in the ground plane collects the radiation and guides it to a millimetre-wave microstrip transmission line placed on the other side of the mono-crystalline substrate. The millimetre-wave line is coupled to a filter-bank spectrometer. Each filter is capacitively coupled to a lumped-element kinetic inductance detector (LEKID). The microstrip configuration provides the benefit of low loss, due to the mono-crystalline substrate, and protects the LEKIDs from illumination by stray un-filtered light.
Results.
The prototype spectrometer exhibits a spectral resolution
R = λ
/Δ
λ
≈ 300. The optical noise equivalent power is in the low 10
−16
W Hz
−1/2
range for an incoming power of about 0.2 pW per channel. The device is polarisation-sensitive, with a cross-polarisation lower than 1% for the best channels.
Context. Millimetre-wave continuum astronomy is today an indispensable tool for both general astrophysics studies (e.g. star formation, nearby galaxies) and cosmology (e.g. cosmic microwave ...background and high-redshift galaxies). General purpose, large-field-of-view instruments are needed to map the sky at intermediate angular scales not accessible by the high-resolution interferometers (e.g. ALMA in Chile, NOEMA in the French Alps) and by the coarse angular resolution space-borne or ground-based surveys (e.g. Planck, ACT, SPT). These instruments have to be installed at the focal plane of the largest single-dish telescopes, which are placed at high altitude on selected dry observing sites. In this context, we have constructed and deployed a three-thousand-pixel dual-band (150 GHz and 260 GHz, respectively 2 mm and 1.15 mm wavelengths) camera to image an instantaneous circular field-of-view of 6.5 arcmin in diameter, and configurable to map the linear polarisation at 260 GHz. Aims. First, we are providing a detailed description of this instrument, named NIKA2 (New IRAM KID Arrays 2), in particular focussing on the cryogenics, optics, focal plane arrays based on Kinetic Inductance Detectors, and the readout electronics. The focal planes and part of the optics are cooled down to the nominal 150 mK operating temperature by means of an adhoc dilution refrigerator. Secondly, we are presenting the performance measured on the sky during the commissioning runs that took place between October 2015 and April 2017 at the 30-m IRAM telescope at Pico Veleta, near Granada (Spain). Methods. We have targeted a number of astronomical sources. Starting from beam-maps on primary and secondary calibrators we have then gone to extended sources and faint objects. Both internal (electronic) and on-the-sky calibrations are applied. The general methods are described in the present paper. Results. NIKA2 has been successfully deployed and commissioned, performing in-line with expectations. In particular, NIKA2 exhibits full width at half maximum angular resolutions of around 11 and 17.5 arcsec at respectively 260 and 150 GHz. The noise equivalent flux densities are, at these two respective frequencies, 33±2 and 8±1 mJy s1/2. A first successful science verification run was achieved in April 2017. The instrument is currently offered to the astronomy community and will remain available for at least the following ten years.
We report the design, fabrication, and testing of lumped element kinetic inductance detectors (LEKID) showing performance in line with the requirements of the next generation space telescopes ...operating in the spectral range from 80 GHz to 600 GHz. This range is of particular interest for cosmic microwave background studies. For this purpose we designed and fabricated 100 pixel arrays covering five distinct bands. These wafers were measured via multiplexing, in which a full array is read out using a single pair of lines. We adopted a custom cold black body installed in front of the detectors and regulated at temperatures between 1 K and 20 K. In this paper, we describe in the main design considerations, fabrication processes, testing and data analysis.
In the submillimeter regime, spectral line scans and line intensity mapping (LIM) are new promising probes for the cold gas content and star formation rate of galaxies across cosmic time. However, ...both of these two measurements suffer from field-to-field variance. We study the effect of field-to-field variance on the predicted CO and CII power spectra from future LIM experiments such as CONCERTO, as well as on the line luminosity functions (LFs) and the cosmic molecular gas mass density that are currently derived from spectral line scans. We combined a 117 deg2 dark matter lightcone from the Uchuu cosmological simulation with the simulated infrared dusty extragalactic sky (SIDES) approach. The clustering of the dusty galaxies in the SIDES-Uchuu product is validated by reproducing the cosmic infrared background anisotropies measured by Herschel and Planck. We find that in order to constrain the CO LF with an uncertainty below 20%, we need survey sizes of at least 0.1 deg2. Furthermore, accounting for the field-to-field variance using only the Poisson variance can underestimate the total variance by up to 80%. The lower the luminosity is and the larger the survey size is, the higher the level of underestimate. At z < 3, the impact of field-to-field variance on the cosmic molecular gas density can be as high as 40% for the 4.6 arcmin2 field, but drops below 10% for areas larger than 0.2 deg2. However, at z > 3 the variance decreases more slowly with survey size and for example drops below 10% for 1 deg2 fields. Finally, we find that the CO and CII LIM power spectra can vary by up to 50% in 1 deg2 fields. This limits the accuracy of the constraints provided by the first 1 deg2 surveys. In addition the level of the shot noise power is always dominated by the sources that are just below the detection thresholds, which limits its potential for deriving number densities of faint CII emitters. We provide an analytical formula to estimate the field-to-field variance of current or future LIM experiments given their observed frequency and survey size. The underlying code to derive the field-to-field variance and the full SIDES-Uchuu products (catalogs, cubes, and maps) are publicly available.
Context.
NIKA2 is a dual-band millimetre continuum camera of 2 900 kinetic inductance detectors, operating at 150 and 260 GHz, installed at the IRAM 30-m telescope in Spain. Open to the scientific ...community since October 2017, NIKA2 will provide key observations for the next decade to address a wide range of open questions in astrophysics and cosmology.
Aims.
Our aim is to present the calibration method and the performance assessment of NIKA2 after one year of observation.
Methods.
We used a large data set acquired between January 2017 and February 2018 including observations of primary and secondary calibrators and faint sources that span the whole range of observing elevations and atmospheric conditions encountered by the IRAM 30-m telescope. This allowed us to test the stability of the performance parameters against time evolution and observing conditions. We describe a standard calibration method, referred to as the “Baseline” method, to translate raw data into flux density measurements. This includes the determination of the detector positions in the sky, the selection of the detectors, the measurement of the beam pattern, the estimation of the atmospheric opacity, the calibration of absolute flux density scale, the flat fielding, and the photometry. We assessed the robustness of the performance results using the Baseline method against systematic effects by comparing results using alternative methods.
Results.
We report an instantaneous field of view of 6.5′ in diameter, filled with an average fraction of 84%, and 90% of valid detectors at 150 and 260 GHz, respectively. The beam pattern is characterised by a FWHM of 17.6″ ± 0.1″ and 11.1″ ± 0.2″, and a main-beam efficiency of 47%±3%, and 64%±3% at 150 and 260 GHz, respectively. The point-source rms calibration uncertainties are about 3% at 150 GHz and 6% at 260 GHz. This demonstrates the accuracy of the methods that we deployed to correct for atmospheric attenuation. The absolute calibration uncertainties are of 5%, and the systematic calibration uncertainties evaluated at the IRAM 30-m reference Winter observing conditions are below 1% in both channels. The noise equivalent flux density at 150 and 260 GHz are of 9 ± 1 mJy s
1/2
and 30 ± 3 mJy s
1/2
. This state-of-the-art performance confers NIKA2 with mapping speeds of 1388 ± 174 and 111 ± 11 arcmin
2
mJy
−2
h
−1
at 150 and 260 GHz.
Conclusions.
With these unique capabilities of fast dual-band mapping at high (better that 18″) angular resolution, NIKA2 is providing an unprecedented view of the millimetre Universe.
The characterization of the Intracluster Medium (ICM) properties of high-redshift galaxy clusters is fundamental to our understanding of large-scale structure formation processes. We present the ...results of a multiwavelength analysis of the very massive cluster MOO J1142+1527 at a redshift z = 1.2 discovered as part of the Massive and Distant Clusters of WISE Survey. This analysis is based on high angular resolution Chandra X-ray and NIKA2 Sunyaev-Zel'dovich (SZ) data. The cluster thermodynamic radial profiles have been obtained with unprecedented precision at this redshift and up to 0.7R500, thanks to the combination of high-resolution X-ray and SZ data. The comparison between the galaxy distribution mapped in infrared by Spitzer and the morphological properties of the ICM derived from the combined analysis of the Chandra and NIKA2 data leads us to the conclusion that the cluster is an ongoing merger. We have estimated a systematic uncertainty on the cluster total mass that characterizes both the impact of the observed deviations from spherical symmetry and of the core dynamics on the mass profile. We further combine the X-ray and SZ data at the pixel level to obtain maps of the temperature and entropy distributions. We find a relatively low-entropy core at the position of the X-ray peak and high-temperature regions located on its south and west sides. This work demonstrates that the addition of spatially resolved SZ observations to low signal-to-noise X-ray data brings a high information gain on the characterization of the evolution of ICM thermodynamic properties at z > 1.
The Crab nebula is a supernova remnant exhibiting a highly polarized synchrotron radiation at radio and millimetre wavelengths. It is the brightest source in the microwave sky with an extension of 7 ...by 5 arcmin, and is commonly used as a standard candle for any experiment which aims to measure 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 observations (18′′ FWHM) 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° ± 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 βpol = – 0.347 ± 0.026 is compatible with the intensity spectral index β = – 0.323 ± 0.001.
Substructures in the hot gas atmosphere 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 substructures. In this paper, we apply structure-enhancement filtering algorithms to high-resolution tSZ observations (e.g., NIKA) of distant clusters in order to search for pressure discontinuities, compressions, and secondary peaks in the ICM. The same filters are applied to toy-model images and to synthetic tSZ images extracted from RHAPSODY-G cosmological hydrodynamic simulations, in order to better interpret the extracted features. We also study the noise propagation through the filters and quantify the impact of systematic effects, such as data-processing-induced artifacts and point-source residuals, the latter being identified as the dominant potential contaminant. In three of our six NIKA-observed clusters we identify features at high signal-to-noise ratio that show clear evidence for merger events. In MACS J0717.5+3745 (z = 0.55), three strong pressure gradients are observed on the east, southeast, and west sectors, and two main peaks in the pressure distribution are identified. We observe a lack of tSZ compact structure in the cool-core cluster PSZ1 G045.85+57.71 (z = 0.61), and a tSZ gradient ridge dominates in the southeast. In the highest redshift cluster, CL J1226.9+3332 (z = 0.89), we detect a ridge pressure gradient of ~45 arcsec (360 kpc) in length associated with a secondary pressure peak in the west 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 substructures in clusters, even at high redshift. 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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