Tatsuya Takekoshi

Sub-terahertz astronomy requires instruments capable of simultaneous observations across multiple spectral bands, motivating the development of broadband anti-reflection coatings (ARCs). We investigated low-loss dielectrics with refractive indices suitable for multilayer ARCs on polyethylene optical elements and identified candidates that partially meet the requirements. To address the remaining gaps in available refractive indices, we applied dielectric multilayer synthesis by combining newly identified thin materials with controlled bonding to realize the required effective refractive indices. As a result, the fabricated five-layer ARC achieved reflection losses of 0.2% (average) and 3.2% (maximum) over 130–710 GHz.

To investigate the formation history of large-scale structure through the dynamics of galaxy clusters, we are developing a multi-color millimeter and submillimeter-wave continuum camera (GLTCAM) for deployment on the Greenland Telescope (GLT). GLTCAM will observe in six frequency bands—three in the millimeter range (150, 220, and 270 GHz) and three in the submillimeter range (350, 400, and 670 GHz). The optical design provides a compact configuration that fits within the GLT receiver cabin, while delivering diffraction-limited performance over an $18^{\prime }$ field of view with minimal telecentricity error and distortion. A key advantage of this design is its uniform illumination footprint at the cold stop, which helps minimize thermal loading on both the detectors and the cryogenic stages. The focal plane module comprises a quasi-optical bandpass filter, a conical horn array coupled with planar ortho-mode transducers (OMTs), and a superconducting multi-color microwave kinetic inductance detector (MKID) array. Current development efforts are focused on the three-color millimeter-wave module. The detector array employs a single-layer coplanar waveguide (CPW) architecture, which simplifies fabrication and enables scalability to large-format arrays. GLTCAM aims for the early realization of next-generation wide-field, multi-color observations as a pathfinder for future large submillimeter telescopes.

We report on the results of the on-sky test and science demonstration conducted with the 2 mm receiver system, B4R, on the 50 m Large Millimeter Telescope (LMT), located at an altitude of 4600 m in Mexico. The B4R receiver was developed based on the dual-polarization sideband-separating mixer technology of the Atacama Large Millimeter/submillimeter Array and is equipped with a fast Fourier transform digital spectrometer, XFFTS. The primary science objective is the spectroscopic redshift identification of high-redshift dusty star-forming galaxies, complementing the existing 3 mm Redshift Search Receiver by enabling the detection of multiple carbon monoxide lines. Additionally, the B4R receiver broadens the range of science cases possible with the LMT, including astrochemistry, as the 2 mm band encompasses unique molecular lines such as deuterated molecules and shock tracers. During on-site commissioning in 2018 and 2019, we successfully demonstrated on-the-fly mapping and position-switching observations toward the Orion Molecular Cloud 1 and bright high-redshift dusty star-forming galaxies, respectively. We confirmed that the installed B4R system largely met its basic performance specifications. Furthermore, we measured the LMT’s aperture efficiencies across the entire B4R frequency range (130–160 GHz), finding them to be roughly consistent with expectations based on a surface accuracy of 100 μ m and the receiver optics design. These results with the B4R will enable the most sensitive single-dish spectroscopic observations at 2 mm using the LMT.

We developed, characterized, and verified an alignment procedure for the DESHIMA 2.0 instrument, an ultra-wide-band spectrometer operating between 200 and 400 GHz, at the ASTE telescope. To this end, we mounted the warm optics, consisting of a modified Dragonian dual reflector system, on a motor-controlled hexapod. Crucial in the alignment procedure is our sky chopper, which allows fast beam switching. It has a small entrance and exit aperture coupling to the (cold) sky, which creates a measurable signal with respect to the warm cabin environment. By scanning the instrument beam across the entrance aperture of the sky chopper using the hexapod, we found the hexapod configuration that produced the lowest signal on our detectors, implying that the beam is coupled fully to the cold sky and not the warm cabin. We first characterized the alignment procedure in the laboratory, where we used a vat containing liquid nitrogen as the cold source behind the sky chopper. Then, we applied the alignment procedure to DESHIMA 2.0 at ASTE. We found that the alignment procedure significantly improved the aperture efficiency compared with previously reported values of the aperture efficiency of DESHIMA at ASTE, which indicates the veracity of the alignment procedure.

We report the Australian Telescope Compact Array and Nobeyama 45 m telescope detection of a remarkably bright (S _1.1mm = 44 mJy) submillimeter galaxy MM J154506.4−344318 in emission lines at 48.5 and 97.0 GHz, respectively. We also identify part of an emission line at ≈218.3 GHz using the Atacama Large Millimeter/submillimeter Array (ALMA). Together with photometric redshift estimates and the ratio between the line and infrared luminosities, we conclude that the emission lines are most likely to be the J = 2–1, 4–3, and 9–8 transitions of ¹²CO at redshift z = 3.753 ± 0.001. ALMA 1.3 mm continuum imaging reveals an arc and a spot separated by an angular distance of 1 . ″ 6 , indicative of a strongly lensed dusty star-forming galaxy with respective molecular and dust masses of log M mol / M ⊙ ≈ 11.5 and log M dust / M ⊙ ≈ 9.4 after being corrected for ≈6.6× gravitational magnification. The inferred dust-to-gas mass ratio is found to be high (≈0.0083) among coeval dusty star-forming galaxies, implying the presence of a massive, chemically enriched reservoir of cool interstellar medium at z ≈ 4, or 1.6 Gyr after the Big Bang.

Context. Integrated superconducting spectrometers (ISSs) for wide-band submillimeter (submm) astronomy use quasi-optical systems for coupling radiation from the telescope to the instrument. Misalignment in these systems is detrimental to the system performance. The common method of using an optical laser to align the quasi-optical components requires an accurate alignment of the laser to the submm beam from the instrument, which is not always guaranteed to a sufficient accuracy. Aims. We develop an alignment strategy for wide-band ISSs that directly uses the submm beam of the wide-band ISS. The strategy should be applicable in both telescope and laboratory environments. Moreover, the strategy should deliver similar quality of the alignment across the spectral range of the wide-band ISS. Methods. We measured the misalignment in a quasi-optical system operating at submm wavelengths using a novel phase and amplitude measurement scheme that is capable of simultaneously measuring the complex beam patterns of a direct-detecting ISS across a harmonic range of frequencies. The direct detection nature of the microwave kinetic inductance detectors in our device-under-test, DESHIMA 2.0, necessitates the use of this measurement scheme. Using geometrical optics, the measured misalignment, a mechanical hexapod, and an optimisation algorithm, we followed a numerical approach to optimise the positioning of corrective optics with respect to a given cost function. Laboratory measurements of the complex beam patterns were taken across a harmonic range between 205 and 391 GHz and were simulated through a model of the ASTE telescope in order to assess the performance of the optimisation at the ASTE telescope. Results. Laboratory measurements show that the optimised optical setup corrects for tilts and offsets of the submm beam. Moreover, we find that the simulated telescope aperture efficiency is increased across the frequency range of the ISS after the optimisation.

We present emission maps ( 1 .′ 5 × 1 .′ 5 scale, corresponding to 0.18 pc) of the DCN (J = 2 − 1) and DCO⁺ (J = 2 − 1) lines in the 2 mm band toward the Orion KL region obtained with the 2 mm receiver system named B4R installed on the Large Millimeter Telescope. The DCN emission shows a peak at the Orion KL hot core position, whereas no DCO⁺ emission has been detected there. The DCO⁺ emission shows enhancement at the west side of the hot core, which is well shielded from the UV radiation from OB massive stars in the Trapezium cluster. We have derived the abundance ratio of DCN/DCO⁺ at three representative positions where both species have been detected. The gas components with V _LSR ≈ 7.5–8.7 km s⁻¹ are associated with low abundance ratios of ∼4–6, whereas much higher abundance ratios (∼22–30) are derived for the gas components with V _LSR ≈ 9.2–11.6 km s⁻¹. We have compared the observed abundance ratio to our chemical models and found that the observed differences in the DCN/DCO⁺ abundance ratios are explained by different densities.