arXiv subjects

Tatsuya Takekoshi

Publications and source records attributed to Tatsuya Takekoshi.

At least 19 recordsLinked to original sources

arXiv2026

FINER: development of the wideband millimeter-wave receiver system and preparations for first light on the Large Millimeter Telescope

The recent discovery of an excess of luminous galaxies in the early Universe necessitates sensitive and wideband millimeter spectroscopy to understand their rapid growth. To address this, we present the development of the Far-Infrared Nebular Emission Receiver (FINER) for the Large Millimeter Telescope (LMT). The FINER frontend comprises two receivers covering 120-350 GHz (corresponding to ALMA Bands 4+5 and 6+7). The warm optics are designed to enable simultaneous two-band observations. Combined with the 10.24-GHz-wide digital spectrometer array, the system aims to deliver an instantaneous bandwidth approximately five times wider than current ALMA capabilities. We report that the 210-350 GHz receiver has already achieved commissioning-level performance, with sideband rejection further enhanced by the digital sideband separation technique. With installation expected in 2026, we discuss parallel preparations, including integrated testing and commissioning plans for first-look targets.

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arXiv2026

GLTCAM: Concept of Multi-color Millimeter and Submillimeter Camera for the Greenland Telescope

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 Green-land 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 $18'$ 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.

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arXiv2026

Design Method of Quasi-Lumped Element Bandpass Filters Using Superconducting Coplanar Waveguide for Millimeter-Wave Multichroic Imaging

An on-chip band-defining filter coupled with a superconducting photon detector is a promising technology for developing multi-band imaging cameras at millimeter and submillimeter wavelengths. In this paper, we present the design of on-chip bandpass filters based on coplanar waveguide geometry, which can be easily integrated into large-format multi-band detector arrays. A lumped element filter design is suitable not only for achieving a compact footprint but also for suppressing harmonics to reduce band-to-band crosstalk in a multiplexer. However, the coplanar waveguide geometry and the photolithography process rule limit the maximum available inductance and capacitance of lumped elements, which does not sufficiently meet the requirements of filter circuits. To overcome this limitation, we have established a design method for quasi-lumped element filters, in which the maximum element size is relaxed to a quarter wavelength, exceeding the ideal lumped element size. We achieved design solutions for 150, 220, and 270 GHz 8th-order Chebyshev bandpass filters and a triplexer. We also report on the measurement results of a scaled model of the bandpass filter, demonstrating the validity of our proposed filter design.

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arXiv2026

Broadband anti-reflection coating for sub-terahertz optics using dielectric multilayers

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 5-layer ARC achieved reflection losses of 0.2% (average) and 3.2% (maximum) over 130-710 GHz.

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arXiv2026

Development of TIFUUN: Terahertz Integral Field Units with Universal Nanotechnology

TIFUUN (THz Integral Field Units with Universal Nanotechnology) is an ultra-wideband mm-submm wave imaging spectrometer that capitalizes on the highly scalable integrated superconducting spectrometer technology. TIFUUN has two slots for integral field units (IFUs), which can jointly be optimized as open-hardware for each astronomical observation in terms of spatial and spectral coverage. These IFUs can have observation frequencies in the range of 90--360 GHz, with spectral resolution up to $R\equiv F/\Delta F \le 1,000$, with up to $\sim$18,000 kinetic inductance detectors (shared by the two IFUs with a flexible ratio). The ultra-wide 4:1 (2 octave) bandwidth optics fits in a remarkably compact volume, by means of thin silicon lenses and a high chief ray angle design. The first pair of IFUs are being developed for the SUBLIME (Study of the Universe By Line Intensity Mapping Experiments) experiment that aims to map CII emission at redshift $\sim$6 to trace the cosmic large-scale structure and the buildup of galaxies during reionization, using TIFUUN on the ASTE 10-m telescope. The scalability, flexibility and compactness makes TIFUUN a highly compatible and portable system suited also for upcoming telescope facilities in the vicinity, such as FYST and AtLAST/LST.

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arXiv2025

The LMT 2 millimeter receiver system (B4R). II. Science demonstration observations toward Orion-KL/OMC-1

We present the results of mapping and single-point spectral scans toward Orion-KL/OMC-1 performed as science demonstrations of a 2 mm SIS receiver, the Band 4 Receiver (B4R), installed on the 50 m Large Millimeter Telescope (LMT). To prove the capabilities of mapping and spectral scans with the B4R on the LMT, commissioning observations were conducted employing the on-the-fly mapping technique toward Orion-KL/OMC-1, which covers a map size of 5$'\times$5$'$. These mapping observations were performed with two frequency settings providing 10 GHz in total (131.4-133.9 GHz and 145.1-147.6 GHz; 136.2-138.7 GHz and 149.9-152.4 GHz) with a frequency resolution of 76.293 kHz. We conducted spectral line identification analysis for the hot core and compact ridge regions in the Orion-KL with a beam size of 11-12$''$. We detected nearly 400 emission lines and identified two recombination lines and 29 molecular species, including isotopologues, deuterated molecules, and vibrational excited states, despite the short integration time. These results are consistent with those of previous studies. The 29 molecular species include nitrogen (N)-bearing complex organic molecules (COMs) and oxygen (O)-bearing COMs. To demonstrate the capability of the B4R in astrochemistry, we conducted detailed analyses of column densities, rotational temperatures, and relative abundances with respect to H$_2$ on two representative COMs, N-bearing C$_2$H$_5$CN and O-bearing CH$_3$OCHO in the central 40$''\times$40$''$ area of the map. The wide bandwidth of 10 GHz enabled the use of 8 and 34 emission lines, respectively. The spatial differences in the physical and chemical properties between these molecules were derived at a spatial resolution of $\sim$12$''$. The B4R on the LMT was successfully demonstrated to be powerful for mapping and spectral scans and to have high potential for the study of interstellar chemistry.

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arXiv2025

The LMT 2 Millimeter Receiver System (B4R). I. Overview and Results of Science Demonstration

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 $\mu$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.

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arXiv2025

Large molecular and dust reservoir of a gravitationally-lensed submillimeter galaxy behind the Lupus-I molecular cloud

We report the Australian Telescope Compact Array and Nobeyama 45 m telescope detection of a remarkably bright $S_\mathrm{1.1mm}$ = 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 $\approx$ 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 $^{12}$CO at redshift $z = 3.753 \pm 0.001$. ALMA 1.3 mm continuum imaging reveals an arc and a spot separated by an angular distance of 1.6 arcsec, indicative of a strongly-lensed dusty star-forming galaxy with respective molecular and dust masses of $\log{M_{\rm mol}/M_\odot} \approx 11.5$ and $\log{M_{\rm dust}/M_\odot} \approx 9.4$ after corrected for $\approx$ 6.6$\times$ gravitational magnification. The inferred dust-to-gas mass ratio is found to be high ($\approx$ 0.0083) among coeval dusty star-forming galaxies, implying the presence of a massive, chemically-enriched reservoir of cool interstellar medium at $z \approx 4$ or 1.6 Gyr after the Big Bang.

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arXiv2024

FINER: Far-Infrared Nebular Emission Receiver for the Large Millimeter Telescope

Unveiling the emergence and prevalence of massive/bright galaxies during the epoch of reionization and beyond, within the first 600 million years of the Universe, stands as a pivotal pursuit in astronomy. Remarkable progress has been made by JWST in identifying an immense population of bright galaxies, which hints at exceptionally efficient galaxy assembly processes. However, the underlying physical mechanisms propelling their rapid growth remain unclear. With this in mind, millimeter and submillimeter-wave spectroscopic observations of redshifted far-infrared spectral lines, particularly the [O III] 88 micron and [C II] 158 micron lines, offers a crucial pathway to address this fundamental query. To this end, we develop a dual-polarization sideband-separating superconductor-insulator-superconductor (SIS) mixer receiver, FINER, for the Large Millimeter Telescope (LMT) situated in Mexico. Harnessing advancements from ALMA's wideband sensitivity upgrade (WSU) technology, FINER covers radio frequencies spanning 120-360 GHz, delivering an instantaneous intermediate frequency (IF) of 3-21 GHz per sideband per polarization, which is followed by a set of 10.24 GHz-wide digital spectrometers. At 40% of ALMA's light-collecting area, the LMT's similar atmospheric transmittance and FINER's 5 times wider bandwidth compared to ALMA culminate in an unparalleled spectral scanning capability in the northern hemisphere, paving the way for finer spectral-resolution detection of distant galaxies.

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arXiv2024

Development Status of Wideband Millimeter-Wave Receivers for LMT-FINER

Spectroscopic observations of the far-infrared [O III] and [C II] lines present a pathway to explore the mechanisms of the emergence of massive galaxies in the epoch of reionization and beyond, which is one of the most fundamental questions in astronomy. To address this question, the Far-Infrared Nebular Emission Receiver (FINER) project is developing two wideband dual-polarization sideband-separating heterodyne receivers at 120--210 GHz and 210--360 GHz for the Large Millimeter Telescope (LMT) in Mexico. Compared with Atacama Large Millimeter/submillimeter Array (ALMA), LMT provides 40% of ALMA's light-collecting area and a similar atmospheric transmittance, but FINER plans to have an instantaneous intermediate frequency (IF) of 3--21 GHz per sideband per polarization which is five times wider than current ALMA's bandwidth. Therefore, FINER is going to offer cutting-edge spectral scanning capability in the next several years. The project is currently in an active development phase. In this proceeding, the latest development status for FINER, including the optics, wideband waveguide components as well as low-noise superconductor-insulator-superconductor (SIS) mixers is reported.

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arXiv2024

A Design Method of an Ultra-Wideband and Easy-to-Array Magic-T: A 6-14 GHz Scaled Model for a mm/submm Camera

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 $\sim$ 180 $\rm μ$m 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$^\circ$ from 6.1 GHz to 14.1 GHz.

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arXiv2024

Large-Scale Mapping Observations of DCN and DCO$^+$ toward Orion KL

We present emission maps (1.5'$\times$1.5' scale, corresponding to 0.18 pc) of the DCN ($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 (LMT). 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 $V_{\rm {LSR}} \approx 7.5-8.7$ km/s are associated with low abundance ratios of $\sim4-6$, whereas much higher abundance ratios ($\sim22-30$) are derived for the gas components with $V_{\rm {LSR}} \approx 9.2-11.6$ km/s. 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.

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arXiv2023

An Unbiased CO Survey Toward the Northern Region of the Small Magellanic Cloud with the Atacama Compact Array. II. CO Cloud Catalog

The nature of molecular clouds and their statistical behavior in subsolar metallicity environments are not fully explored yet. We analyzed data from an unbiased CO($J$ = 2-1) survey at the spatial resolution of ~2 pc in the northern region of the Small Magellanic Cloud with the Atacama Compact Array to characterize the CO cloud properties. A cloud-decomposition analysis identified 426 spatially/velocity-independent CO clouds and their substructures. Based on the cross-matching with known infrared catalogs by Spitzer and Herschel, more than 90% CO clouds show spatial correlations with point sources. We investigated the basic properties of the CO clouds and found that the radius--velocity linewidth ($R$-$σ_{v}$) relation follows the Milky Way-like power-low exponent, but the intercept is ~1.5 times lower than that in the Milky Way. The mass functions ($dN/dM$) of the CO luminosity and virial mass are characterized by an exponent of ~1.7, which is consistent with previously reported values in the Large Magellanic Cloud and in the Milky Way.

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arXiv2023

Cosmic-ray-driven enhancement of the C$^0$/CO abundance ratio in W51C

We examine spatial variations of the C$^0$/CO abundance ratio ($X_{\mathrm{C/CO}}$) in the vicinity of the $γ$-ray supernova remnant W51C, based on [CI] ($^3P_1$-$^3P_0$), $^{12}$CO(1-0), and $^{13}$CO(1-0) observations with the ASTE and Nobeyama 45-m telescopes. We find that $X_{\mathrm{C/CO}}$ varies in a range of 0.02-0.16 (0.05 in median) inside the molecular clouds of $A_V>$100 mag, where photodissociation of CO by the interstellar UV is negligible. Furthermore, $X_{\mathrm{C/CO}}$ is locally enhanced up to by a factor of four near the W51C center, depending on the projected distance from the W51C center. In high-$A_V$ molecular clouds, $X_{\mathrm{C/CO}}$ is determined by the ratio of the cosmic-ray (CR) ionization rate to the H$_2$ density, and we find no clear spatial variation of the H$_2$ density against the projected distance. Hence, the high CR ionization rate may locally enhance $X_{\mathrm{C/CO}}$ near the W51C center. We also find that the observed spatial extent of the enhanced $X_{\mathrm{C/CO}}$ ($\sim$17 pc) is consistent with the diffusion distance of CRs with the energy of 100 MeV. The fact suggests that the low-energy CRs accelerated in W51C enhance $X_{\mathrm{C/CO}}$. The CR ionization rate at the $X_{\mathrm{C/CO}}$-enhanced cloud is estimated to be 3$\times$10$^{-16}$ s$^{-1}$ on the basis of time-dependent PDR simulations of $X_{\mathrm{C/CO}}$, the value of which is 30 times higher than that in the standard Galactic environment. These results demonstrate that [CI] is a powerful probe to investigate the interaction between CRs and the interstellar medium for a wide area in the vicinity of supernova remnants.

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arXiv2022

DESHIMA 2.0: development of an integrated superconducting spectrometer for science-grade astronomical observations

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 lab 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.

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arXiv2022

Material properties of a low contraction and resistivity silicon-aluminum composite for cryogenic detectors

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 a silicon--aluminum composite material (75% silicon by volume) and has a low thermal expansion coefficient ($\sim$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 $\mathrm{μΩm}$, which is considerably lower than an equivalent silicon--aluminum composite material. The measured thermal contraction of SA001 immersed in liquid nitrogen is $\frac{L_{293\mathrm{K}}-L_{77\mathrm{K}}}{L_{293\mathrm{K}}}=0.12$%, 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 $\mathrm{μm}$. These properties are suitable for packaging applications for large-format superconducting detector devices.

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arXiv2021

An Unbiased CO Survey Toward the Northern Region of the Small Magellanic Cloud with the Atacama Compact Array. I. Overview: CO Cloud Distributions

We have analyzed the data from a large-scale CO survey toward the northern region of the Small Magellanic Cloud (SMC) obtained with the Atacama Compact Array (ACA) stand-alone mode of ALMA. The primary aim of this study is to comprehensively understand the behavior of CO as an H$_2$ tracer in a low-metallicity environment ($Z\sim0.2~Z_{\odot}$). The total number of mosaic fields is $\sim$8000, which results in a field coverage of 0.26$~$degree$^{2}$ ($\sim$2.9 $\times$10$^{5}$$~$pc$^2$), corresponding to $\sim$10$\%$ area of the galaxy. The sensitive $\sim$2$~$pc resolution observations reveal the detailed structure of the molecular clouds previously detected in the single-dish NANTEN survey. We have detected a number of compact CO clouds within lower H$_2$ column density ($\sim$10$^{20}$$~$cm$^{-2}$) regions whose angular scale is similar to the ACA beam size. Most of the clouds in this survey also show peak brightness temperature as low as $<$1$~$K, which for optically thick CO emission implies an emission size much smaller than the beam size, leading to beam dilution. The comparison between an available estimation of the total molecular material traced by thermal dust emission and the present CO survey demonstrates that more than $\sim$90$\%$ H$_2$ gas cannot be traced by the low-$J$ CO emission. Our processed data cubes and 2-D images are publicly available.

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arXiv2021

A data-scientific noise-removal method for efficient submillimeter spectroscopy with single-dish telescopes

For submillimeter spectroscopy with ground-based single-dish telescopes, removing noise contribution from the Earth's atmosphere and the instrument is essential. For this purpose, here we propose a new method based on a data-scientific approach. The key technique is statistical matrix decomposition that automatically separates the signals of astronomical emission lines from the drift noise components in the fast-sampled (1--10 Hz) time-series spectra obtained by a position-switching (PSW) observation. Because the proposed method does not apply subtraction between two sets of noisy data (i.e., on-source and off-source spectra), it improves the observation sensitivity by a factor of $\sqrt{2}$. It also reduces artificial signals such as baseline ripples on a spectrum, which may also help to improve the effective sensitivity. We demonstrate this improvement by using the spectroscopic data of emission lines toward a high-redshift galaxy observed with a 2-mm receiver on the 50-m Large Millimeter Telescope (LMT). Since the proposed method is carried out offline and no additional measurements are required, it offers an instant improvement on the spectra reduced so far with the conventional method. It also enables efficient deep spectroscopy driven by the future 50-m class large submillimeter single-dish telescopes, where fast PSW observations by mechanical antenna or mirror drive are difficult to achieve.

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