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Baryonic matter only accounts for 5% of the mass-energy density of our universe, where the other 95% is shared between dark energy and dark matter. Measurements of the early universe predict a certain baryon fraction, that is not detected in the later stages of the cosmic evolution, and this discrepancy between predicted and observed baryons is known as the “missing baryon” problem. Cosmological simulations predict that a significant fraction of the missing baryons could be found in the form of the warm–hot intergalactic medium (WHIM) trapped inside large scale structures that constitute the cosmic web. WHIM can be detected using the thermal Sunyaev-Zel’dovich effect, as the amplitude of its spectral distortion scales linearly with the electron pressure integrated along the line of sight. This effect has been extensively used by space and ground based CMB experiments to study clusters and filament candidates. In this work, we present results on the detection of hot gas between pairs of candidate interacting galaxy clusters obtained with the latest high resolution (1.65′), high sensitivity Compton-y maps from ACT. We consider a set of candidate double cluster systems extracted from a preliminary ACT-DR6 catalog of clusters blindly detected with a matched filter approach. We then aligned and stacked these cluster pairs in order to increase the SNR and detect the faint SZ signal due to warm-hot filaments of gas connecting them. This sample focuses on short filaments with a projected length ℓ fil < 10 Mpc and typical halo mass M 500 ~ 2 × 10 14 M ⊙ . Additionally, we study individual pairs of clusters to identify promising candidates for follow-up observations using higher (10 − 20′′) resolution millimeter cameras or X-ray satellites.

The MIllimeter Sardinia radio Telescope Receiver based on Array of Lumped elements KIDs, MISTRAL, is a cryogenic LEKID camera, operating in the W band ( 77 - 103 GHz ) from the Gregorian focus of the 64-m aperture Sardinia Radio Telescope (SRT), in Italy. This instrument features a high angular resolution ( ∼ 12 arcsec ) and a wide instantaneous field of view ( ∼ 4 arcmin ), allowing continuum surveys of the mm-wave sky with many scientific targets, including observations of galaxy clusters via the Sunyaev–Zel’dovich effect. In May 2023, MISTRAL has been installed at SRT for the technical commissioning. In this contribution, we will describe the MISTRAL instrument focusing on the laboratory characterization of its focal plane: a ∼ 400 -pixel LEKID array. We will show the optical performance of the detectors highlighting the procedure for the identification of the pixels on the focal plane, the measurements of the optical responsivity and NEP, and the estimation of the optical efficiency.

We describe the design and performance of the cryostat and the multi-stage sub-K single-shot sorption cooler for the MIllimeter Sardinia Radio Telescope Receiver based on Array of Lumped elements kids (MISTRAL) experiment. MISTRAL is a W-band (77 - 103 GHz) Ti/Al bi-layer Lumped Elements Kinetic Inductance Detectors (LEKIDs) camera working at the Gregorian focus of the 64 m aperture Sardinia Radio Telescope (SRT), located in Sardinia (Italy). The cryogenic system, based on a 1.5 W at 4.2 K Pulse Tube (PT) cryocooler, provides the 4 K base temperature for the sub-K refrigerator, and cools down the cold optics and the filters chain of the instrument. The sub-K sorption cooler consists of two intermediate stages, 4 He and 3 He sorption refrigerators that allow to reduce the heat load on the ultra-cold head, and a twin stage of 3 He sorption refrigerator providing the 0.2 K operation temperature for the 415-pixel array of LEKIDs. MISTRAL experiment was installed at SRT in May 2023, the technical commissioning started in June 2023. We will show the performance of the system in the laboratory.

Galaxy clusters and surrounding medium, can be studied using X-ray bremsstrahlung emission and Sunyaev Zel’dovich (SZ) effect. Both astrophysical probes, sample the same environment with different parameters dependance. The SZ effect is relatively more sensitive in low density environments and thus is useful to study the filamentary structures of the cosmic web. In addition, observations of the matter distribution require high angular resolution in order to be able to map the matter distribution within and around galaxy clusters. MISTRAL is a camera working at 90GHz which, once coupled to the Sardinia Radio Telescope (SRT), can reach 12″ angular resolution over 4′ field of view (f.o.v.). The forecasted sensitivity drives to a Noise Equivalent Flux Density of ≃ 10–15 mJy √ s and the mapping speed is MS = 380′ 2 mJy −2 h −1 . MISTRAL was recently installed at the focus of the SRT and soon will take its first photons.

Large radio and mm–wave telescopes use very sensitive detectors requiring cryogenic cooling to reduce detector noise. Pulse Tubes (PT) cryocoolers are widely used to reach temperatures of a few K, defining the base temperature of further sub–K stages. This technology represents an effective solution for continuous operation, featuring high stability and reduced vibration levels on the detectors. However, the compressor used to operate the PT is a significant source of microphonics and electrical noise, making its use at the focus of large steerable telescopes not advisable. This calls for long flexible helium lines between the compressor, operated at the base of the radio telescope, and the cold–head, mounted in the receivers cabin with the receiver detectors. The distance between the receiver cabin and the base can be >100 m long for large radio telescopes. In the framework of our development of the MIllimetric Sardinia radio Telescope Receiver based on Array of Lumped elements kids (MISTRAL), a W–band camera working at the Gregorian focus of the 64 m aperture Sardinia Radio Telescope (SRT) with an array of Lumped Elements Kinetic Inductance Detectors (LEKID), we have developed a cryogenic system based on a PT refrigerator as the first cooling stage. Here we describe the MISTRAL cryogenic system and focus on the validation of the use of a commercial PT Cryocooler with 100 m helium lines running from the cold head to the compressor unit. The configuration allows us to operate the 0.9 W PT reaching below 4.2 K with 0.5 W dissipation.

The MIllimetric Sardinia radio Telescope Receiver based on Array of Lumped elements KIDs, MISTRAL, is a cryogenic W-band (77–103 GH) LEKID camera which will be integrated at the Gregorian focus of the 64 m aperture Sardinia Radio Telescope, in Italy, in Autumn 2022. This instrument, thanks to its high angular resolution ( ∼ 13 arcsec ) and the wide instantaneous field of view ( ∼ 4 arcmin ), will allow continuum surveys of the mm-wave sky with a variety of scientific targets, spanning from extragalactic astrophysics to solar system science. In this contribution, we will describe the design of the MISTRAL camera, with a particular focus on the optimisation and test of a prototype of the focal plane.

MISTRAL is a new facility instrument open to the scientific community that will help investigate the ’missing baryon’ problem, as well as many other scientific cases from extragalactic astrophysics to solar system science. The MIllimeter Sardinia radio Telescope Receiver based on Array of Lumped elements KIDs (MISTRAL) is a cryogenic W-band camera, operating at 90 GHz (frequency band 78-103 GHz), equipped with 415 LEKIDs which has been mounted at the Gregorian focus of the 64 m fully steerable radio telescope Sardinia Radio Telescope (SRT), in Italy, in May 2023. MISTRAL will take advantage of its 12 ′′ of angular resolution, a 4 ′ wide instantaneous field of view and its high sensitivity, which will make this camera one of the most competitive instrument to observe the mm-wave sky. MISTRAL is currently under technical commissioning and in this contribution we will report the current status and performances of the instrument as well as the operations done during the first year of technical commissioning.

MISTRAL is a millimetric camera working in the W-band (78–103 GHz) which will take data from the Sardinia Radio Telescope, the Italian 64-m radio telescope located 50 km form Cagliari, at 600m above the sea level, in Sardinia. It is being built as a facility instrument by the Sapienza University for INAF, that manages the radio telescope, under a PON contract. It will consist of a compact cryostat hosting the re–imaging optics, cooled at 4K, and a 408–pixel array of photon–noise limited lumped element kinetic inductance detectors fabricated at CNR-IFN and cooled at a base temperature lower than 300mK. MISTRAL will be able to investigate a long list of scientific targets spanning from extragalactic astrophysics to solar system science, with high angular resolution (~ 12 arcsec), including Sunyaev Zel’dovich effect measurements and the study of the Cosmic Web.

The Q&U Bolometric Interferometer for Cosmology (QL’BIC) is the first bolometric interferometer designed to measure the primordial B -mode polarization of the Cosmic Microwave Background (CMB). Bolometric interferometry is a novel technique that combines the sensitivity of bolometric detectors with the control of systematic effects that is typical of interferometry, both key features in the quest for the faint signal of the primordial B -modes. A unique feature is the so-called “spectral imaging”, i.e., the ability to recover the sky signal in several sub-bands within the physical band during data analysis. This feature provides an in-band spectral resolution of ∆ v / v ~ 0.04 that is unattainable by a traditional imager. This is a key tool for controlling the Galactic foregrounds contamination. In this paper, we describe the principles of bolometric interferometry, the current status of the QU BIC experiment and future prospects.