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Integrated superconducting spectrometer (ISS) technology will enable ultra-wideband, integral-field spectroscopy for (sub)millimeter-wave astronomy, in particular, for uncovering the dust-obscured cosmic star formation and galaxy evolution over cosmic time. Here, we present the development of DESHIMA 2.0, an ISS for ultra-wideband spectroscopy toward high-redshift galaxies. DESHIMA 2.0 is designed to observe the 220–440 GHz band in a single shot, corresponding to a redshift range of z  = 3.3–7.6 for the ionized carbon emission ([C II] 158  μ m). The first-light experiment of DESHIMA 1.0, using the 332–377 GHz band, has shown an excellent agreement among the on-sky measurements, the laboratory measurements, and the design. As a successor to DESHIMA 1.0, we plan the commissioning and the scientific observation campaign of DESHIMA 2.0 on the ASTE 10-m telescope in 2023. Ongoing upgrades for the full octave-bandwidth system include the wideband 347-channel chip design and the wideband quasi-optical system. For efficient measurements, we also develop the observation strategy using the mechanical fast sky-position chopper and the sky-noise removal technique based on a novel data-scientific approach. In the paper, we show the recent status of the upgrades and the plans for the scientific observation campaign.

We report on the cryogenic properties of a low-contraction silicon–aluminum composite, namely Japan Fine Ceramics SA001, to use as a packaging structure for cryogenic silicon devices. SA001 is silicon–aluminum composite material (75% silicon by volume) and has a low thermal expansion coefficient ( ∼ 1/3 that of aluminum). The superconducting transition temperature of SA001 is measured to be 1.18 K, which is in agreement with that of pure aluminum and is thus available as a superconducting magnetic shield material. The residual resistivity of SA001 is 0.065 µΩm, which is considerably lower than equivalent silicon–aluminum composite material. The measured thermal contraction of SA001 immersed in liquid nitrogen is L 293 K - L 77 K L 293 K = 0.12 % , which is consistent with the expected rate obtained from the volume-weighted mean of the contractions of silicon and aluminum. The machinability of SA001 is also confirmed with a demonstrated fabrication of a conical feedhorn array, with a wall thickness of 100 µm. These properties are suitable for packaging applications for large-format superconducting detector devices.

Ultra-wideband, three-dimensional (3D) imaging spectrometry in the millimeter–submillimeter (mm–submm) band is an essential tool for uncovering the dust-enshrouded portion of the cosmic history of star formation and galaxy evolution1–3. However, it is challenging to scale up conventional coherent heterodyne receivers4 or free-space diffraction techniques5 to sufficient bandwidths (≥1 octave) and numbers of spatial pixels2,3 (>102). Here, we present the design and astronomical spectra of an intrinsically scalable, integrated superconducting spectrometer6, which covers 332–377 GHz with a spectral resolution of F/ΔF ~ 380. It combines the multiplexing advantage of microwave kinetic inductance detectors (MKIDs)7 with planar superconducting filters for dispersing the signal in a single, small superconducting integrated circuit. We demonstrate the two key applications for an instrument of this type: as an efficient redshift machine and as a fast multi-line spectral mapper of extended areas. The line detection sensitivity is in excellent agreement with the instrument design and laboratory performance, reaching the atmospheric foreground photon noise limit on-sky. The design can be scaled to bandwidths in excess of an octave, spectral resolution up to a few thousand and frequencies up to ~1.1 THz. The miniature chip footprint of a few cm2 allows for compact multi-pixel spectral imagers, which would enable spectroscopic direct imaging and large-volume spectroscopic surveys that are several orders of magnitude faster than what is currently possible1–3.By using a superconducting integrated circuit to filter incoming millimetre, submillimetre and far-infrared light from distant galaxies, a prototype spectrometer holds promise for wideband spectrometers that are small, sensitive and scalable to wideband spectroscopic imagers.

We are developing an ultra-wideband spectroscopic instrument, DESHIMA (DEep Spectroscopic HIgh-redshift MApper), based on the technologies of an on-chip filter bank and microwave kinetic inductance detector (MKID) to investigate dusty starburst galaxies in the distant universe at millimeter and submillimeter wavelengths. An on-site experiment of DESHIMA was performed using the ASTE 10-m telescope. We established a responsivity model that converts frequency responses of the MKIDs to line-of-sight brightness temperature. We estimated two parameters of the responsivity model using a set of skydip data taken under various precipitable water vapor (PWV 0.4–3.0 mm) conditions for each MKID. The line-of-sight brightness temperature of sky is estimated using an atmospheric transmission model and the PWVs. As a result, we obtain an average temperature calibration uncertainty of 1 σ = 4 %, which is smaller than other photometric biases. In addition, the average forward efficiency of 0.88 in our responsivity model is consistent with the value expected from the geometrical support structure of the telescope. We also estimate line-of-sight PWVs of each skydip observation using the frequency response of MKIDs and confirm the consistency with PWVs reported by the Atacama Large Millimeter/submillimeter Array.

We developed a simple add-on, cryogen-free, and low-power consumption calibrator for a new transition-edge sensor (TES) bolometer camera mounted on the ASTE 10-m telescope. To measure the responsivity of the TES bolometers and accurately correct for the nonlinearity and atmospheric extinction, we designed a motor-driven rotating filter wheel system installed in front of the cryostat window. This calibrator is required to cover the loading power under various atmospheric conditions, which corresponds to precipitable water vapor (PWV) of 0.5–4 mm. For this range of PWV, 25–100 K blackbodies are necessary for the observing bands of 1.1 and 0.85 mm. To simulate the temperature range, bolometers in the cryostat are also optically coupled to the low-temperature stage ( < 4  K) inside the cryostat by spherical mirrors. In addition, we used moderately absorptive polystyrene plates that are placed between a spherical mirror and the cryostat window. Various combinations of filters result in eight different temperatures by the filter wheel system and simulate the atmospheric emission under various weather conditions at the ASTE site.

We developed and deployed a simple add-on multi-temperature calibrator for our multicolor transition edge sensor (TES) bolometer camera aimed at simultaneous observation with observing wavelengths of 1.1 and 0.85 mm. To cover the power loading level from the atmospheric emission corresponding to precipitable water vapor (PWV) of 0.5–4 mm, the calibrator consists of spherical mirrors to show the low-temperature stages of the cryostat and filters with moderate opacity to mimic the eight-temperature cold blackbodies. The loading powers introduced by each filter were self-calibrated by measuring the load curves of the TES bolometers when a filter was placed in front of the cryostat window. Each science observation was preceded by the calibration process, which measures the response of the TES bolometers to the atmosphere and filters of various opacities. Then, the responsivities of TES bolometers were derived to convert their output signal to the loading power and correct for the nonlinearity inherent in its response. Furthermore, the loading power falling on the TES bolometers from atmospheric emission measured at various PWV was in good correlation with the PWV measured with the radiometer, which enables the atmospheric extinction correction by fast and sensitive bolometers compared to the available radiometers with the modest sampling speeds.

We established a design method for a Magic-T with a single-layer dielectric/metal structure suitable for both wideband and multi-element applications for millimeter and submillimeter wave imaging observations. The design method was applied to a Magic-T with a coupled-line, stubs, and single-stage impedance transformers in a frequency-scaled model (6–14 GHz) that is relatively easy to demonstrate through manufacturing and evaluation. The major problem is that using the conventional perfect matching condition for a coupled-line alone produces an impractically large width coplanar coupled-line (CPCL) to satisfy the desired bandwidth ratio. In our study, by removing this constraint and optimizing impedances utilizing a circuit simulator with high computation speed, we found a solution with a ∼ 180 μm wide CPCL, which is approximately an order of magnitude smaller than the conventional analytical solution. Furthermore, considering the effect of transition discontinuities in the transmission lines, we optimized the line length and obtained a design solution with return loss < − 20 dB, amplitude imbalance < 0.1 dB, and phase imbalance < 0.5 ∘ from 6.1 to 14.1 GHz.

Star formation: Lyman-α emitters in the SSA 22 protocluster Many different populations of young star-forming galaxies in the early Universe are known, but the relationships between them and the cosmic large-scale structure are still not well understood. One group, the Lyman-α emitters, are thought to be young, low-mass galaxies with ages of around 10 8 years. An overdensity of them in one region of the sky is believed to mark a forming protocluster. Galaxies that are bright at submillimetre wavelengths are undergoing violent episodes of star formation, so the question of whether they are also associated with the protocluster naturally arises. Tamura et al . report an enhancement of submillimetre galaxies near the core of the SSA 22 protocluster, and a large-scale correlation between the submillimetre galaxies and the low-mass Lyman-α emitters, suggesting synchronous formation of the two very different types of star-forming galaxies within the same structure at high redshift. Young, star-forming galaxies can be characterized by their strong Lyman-α emission. An overdensity of such a population in one region of the sky is believed to mark a forming proto-cluster. An enhancement of submillimetre galaxies near the core of this proto-cluster, and a large-scale correlation between the submillimetre galaxies and the low-mass Lyman-a emitters suggests synchronous formation of the two different types of star-forming galaxies. Lyman-α emitters are thought to be young, low-mass galaxies with ages of ∼10 8  yr (refs 1 , 2 ). An overdensity of them in one region of the sky (the SSA 22 field) traces out a filamentary structure in the early Universe at a redshift of z  ≈ 3.1 (equivalent to 15 per cent of the age of the Universe) and is believed to mark a forming protocluster 3 , 4 . Galaxies that are bright at (sub)millimetre wavelengths are undergoing violent episodes of star formation 5 , 6 , 7 , 8 , and there is evidence that they are preferentially associated with high-redshift radio galaxies 9 , so the question of whether they are also associated with the most significant large-scale structure growing at high redshift (as outlined by Lyman-α emitters) naturally arises. Here we report an imaging survey of 1,100-μm emission in the SSA 22 region. We find an enhancement of submillimetre galaxies near the core of the protocluster, and a large-scale correlation between the submillimetre galaxies and the low-mass Lyman-α emitters, suggesting synchronous formation of the two very different types of star-forming galaxy within the same structure at high redshift. These results are in general agreement with our understanding of the formation of cosmic structure.

We report on the performance of two types of SQUID gradiometers developed for the readout of magnetic calorimeters. Our previously developed low dissipation SQUID gradiometer optimized for low temperature operation has demonstrated the flux noise level of under a magnetic field of 2.5 mT and 150 mK. With a cylindrical Au:Er paramagnetic sensor mounted inside the octagonal pickup washer of the SQUID gradiometer, we succeeded in detecting X-ray signals. However, our achieved energy resolution was 47.2±2.1 eV at 5.9 keV limited by the high operating temperature of 150 mK and by a magnetic field, small for that temperature, due to the limited critical current of the field coils. Based on these results, we fabricated new arrays of SQUID gradiometer by tuning the line width and the number of turns of the field coils and shunt resistance to realize a lower noise level and a larger magnetic field. Furthermore, arrays of SQUID gradiometer with meander patterned pickup washer was fabricated which provides a stronger coupling between the paramagnetic sensor and the pickup washer, and a larger magnetic field at the sensor.

Lyman-α emitters are thought to be young, low-mass galaxies with ages of ~10^sup 8^ yr (refs 1, 2). An overdensity of them in one region of the sky (the SSA 22 field) traces out a filamentary structure in the early Universe at a redshift of z [asymptotically =] 3.1 (equivalent to 15 per cent of the age of the Universe) and is believed to mark a forming protocluster. Galaxies that are bright at (sub)millimetre wavelengths are undergoing violent episodes of star formation, and there is evidence that they are preferentially associated with high-redshift radio galaxies, so the question of whether they are also associated with the most significant large-scale structure growing at high redshift (as outlined by Lyman-α emitters) naturally arises. Here we report an imaging survey of 1,100-µm emission in the SSA 22 region. We find an enhancement of submillimetre galaxies near the core of the protocluster, and a large-scale correlation between the submillimetre galaxies and the low-mass Lyman-α emitters, suggesting synchronous formation of the two very different types of star-forming galaxy within the same structure at high redshift. These results are in general agreement with our understanding of the formation of cosmic structure. [PUBLICATION ABSTRACT]