Pages | FINER

Publications

Sat, 03 Jun 2023 18:21:00 +0000

Instrument papers

Kang, H., Kojima, T., Sakai, T., Tamura, Y., Ishii, S., et al. 2026, “A Wideband Millimeter-wave Receiver at 210–350 GHz for LMT-FINER”, Proc. SPIE, arXiv:2606.25637
Taniguchi, A., Tamura, Y., Sakai, T., Hagimoto, M., Hashimoto, T., et al. 2026, “FINER: development of the wideband millimeter-wave receiver system and preparations for first light on the Large Millimeter Telescope”, Proc. SPIE, arXiv:2607.03265
Tamura, Y., Sakai, T., Kawabe, R., Kojima, T., Taniguchi, A., et al. 2024, “FINER: Far-Infrared Nebular Emission Receiver for the Large Millimeter Telescope”, Proc. SPIE, 13102, 131020G, doi:10.1117/12.3017788, arXiv:2406.07975
Kang, H., et al. 2024, “Development status of wideband millimeter-wave receivers for LMT-FINER”, Proc. SPIE, 13102, 131020J, doi:10.1117/12.3018190, arXiv:2406.07974
Hagimoto, M., Taniguchi, A., et al. 2024, “A 10.24-GHz-wide digital spectrometer array system for LMT-FINER: system design and laboratory performance verification”, Proc. SPIE, 13102, 131020V, doi:10.1117/12.3018296, arXiv:2406.07978

B4R, the precursor of FINER

Yonetsu, T., Kawabe, R., Yoshimura, Y., Taniguchi, K., Shimajiri, Y., et al. 2025, “The LMT 2 millimeter receiver system (B4R). II. Science demonstration observations toward Orion-KL/OMC-1”, arXiv:2511.21845
Kawabe, R., Sakai, T., Tanaka, K., Taniguchi, A., Hatsukade, B., Tamura, Y., et al. 2025, “The LMT 2 Millimeter Receiver System (B4R). I. Overview and Results of Science Demonstration”, AJ, 170, 350, doi:10.3847/1538-3881/ae12eb

SIS mixer technology

Kojima, T., et al. 2020, A&A, 640, L9 (ADS)
Kojima, T., et al. 2017, IEEE Trans. Terahertz Sci. Technol., 7, 694 (ADS)

FAQ

Thu, 06 Apr 2023 16:26:33 +0000

How can I use FINER?

FINER will be offered on the LMT through the regular LMT Call for Proposals after commissioning. Observing time on the LMT is allocated to the LMT partner communities, and eligibility to propose follows the rules of each Call; there is currently no formal route for proposers outside the LMT partnership.

When does FINER come online?

FINER is expected to come online in 2027, after installation and commissioning on the LMT.

Can I join FINER development?

Yes. We welcome new collaborators in the development of FINER. Please contact the PI, Yoichi Tamura (Nagoya University; ytamura (at) nagoya-u.jp).

Receiver

Thu, 06 Apr 2023 16:26:29 +0000

Specifications

FINER is a dual-polarization, sideband-separating (2SB) SIS receiver system. The table below summarizes the configuration installed for first light and the design goals of the full system.

General
Number of bands	2 (one band observed at a time at first light)
Number of beams per band	1
Number of polarizations per band	2
Number of sidebands per band	2 (2SB)

	Band 4 (first light)	Band 6+7	Band 4+5 (planned upgrade)
Radio frequency	≈138–178 GHz	≈210–351 GHz	120–210 GHz
Intermediate frequency (per sideband, per polarization)	4–8 GHz	4–20 GHz	4–20 GHz
Receiver noise temperature (SSB, design goal)	—	75 K	45 K

Measured performance will be reported here after commissioning on the LMT.

System overview

At first light FINER has two front-end receivers in a single cryostat: a Band 4 MMIC receiver and a wideband Band 6+7 receiver, both developed at NAOJ. A wideband Band 4+5 receiver covering 120–210 GHz is planned as a later upgrade. IF switches select which band feeds the four IF chains, so one band is observed at a time; simultaneous dual-band observation is an option for a future optics upgrade.

Figure. Block diagram of the full FINER system (design).

Optics

The FINER warm optics picks off the beam after the LMT’s M4 mirror with a pair of motorized mirrors (the “periscope”), which can be set and stowed remotely. A chopper with a blackbody load is used for intensity calibration. A fast sky chopper for quick position switching is planned in a later phase. The spatial resolution (PSF size) is about 7 arcsec × (frequency / 200 GHz)⁻¹.

Front-end receivers

The front-end receivers exploit the high critical current density SIS mixer technology developed for the ALMA Wideband Sensitivity Upgrade (WSU) (Kojima et al. 2017, 2020; Kang et al. 2026), which provides a wide instantaneous frequency coverage.

Back-end spectrometers

Wideband spectrometers (DRS4, ELECS Inc.). Two DRS4 chassis digitize eight 10.24 GHz-wide basebands with 3-bit, 20.48 GSa/s analog-to-digital converters and provide spectra with 20 MHz resolution (Hagimoto et al. 2024). Sideband separation is also performed digitally.
High-resolution spectrometers (XFFTS, RPG). The XFFTS spectrometers of the LMT 2-mm receiver B4R (2.5 GHz bandwidth, 88 kHz resolution) remain available for high-resolution spectroscopy.

Data and software

FINER is controlled from the LMT Telescope Control System. The data format and the reduction pipeline are being developed together with the LMT team.

Technical documents

Document	Version	Download
FINER proposal to the LMT	Version A, 15 June 2023	PDF (5 MB)

The proposal describes the original design and plan; the configuration and schedule have since been updated as described on this page.

References

See Publications for the instrument papers.

Science

Thu, 06 Apr 2023 16:26:23 +0000

Galaxy formation in the first half of the epoch of reionization

Background

The James Webb Space Telescope (JWST) has found more than a hundred candidate galaxies at redshifts z > 8, when the Universe was less than about 600 million years old, and has confirmed some of them spectroscopically out to z ≈ 14. The bright end of their ultraviolet luminosity function evolves surprisingly little with redshift (Harikane et al. 2022), which means that massive galaxies had to grow very efficiently within a short time. This places a stringent constraint on models of cosmic structure formation.

To understand what drives this rapid growth, we need spectroscopy that answers two questions:

How common are bright, massive galaxies in the early epoch of reionization (their number density)?
What physical conditions control their growth (metallicity, ionization state and gas density)?

Far-infrared nebular emission lines

The far-infrared fine-structure line of doubly ionized oxygen, [O III] 88 µm, was proposed as a powerful tracer for identifying the redshifts of the most distant galaxies (Inoue et al. 2014). ALMA observations of this line revealed extremely high [O III]/[C II] ratios, indicating highly ionized gas filling these young galaxies (Inoue et al. 2016), and held the record for the most distant spectroscopic redshift obtained with ALMA until 2022 (Hashimoto et al. 2018). Even in the JWST era, [O III] 88 µm at z > 9 is as detectable as the rest-frame ultraviolet lines observed with JWST/NIRSpec.

However, ALMA in the southern hemisphere cannot easily observe high-declination fields. Many bright galaxies at z > 8 found in northern deep fields, such as GOODS-North and CEERS, remain unexplored in the far-infrared lines (Figure 1).

Figure 1. UV absolute magnitude versus spectroscopic redshift of galaxies at z > 6. Green and blue circles are galaxies with and without ALMA detections; red crosses are galaxies in northern fields. Adapted from Harikane et al. 2025, ApJ, 980, 138 (colour coding by M. Hagimoto).

Key science goals

With FINER on the 50-m LMT in Mexico (latitude 19°N), we aim to:

identify the spectroscopic redshifts of bright galaxies at z ≈ 8–15 in the northern sky using [O III] 88 µm and [C II] 158 µm, including galaxies confirmed by JWST and photometric candidates from wide-field surveys such as Euclid and Roman;
detect [O III] 88 µm from a bright Lyman break galaxy in a single night of observation;
measure the number density of bright galaxies in the first half of the epoch of reionization and diagnose their interstellar medium.

How FINER helps

A typical photometric redshift uncertainty of Δz ≈ 1 at z ≈ 10 requires a spectral coverage of more than 30 GHz to find the line. FINER covers about 38 GHz in a single tuning, whereas the current ALMA needs four or more tunings for the same range (Figure 2). Combined with 40% of ALMA’s collecting area and a high-altitude site (4,600 m), this offers the most sensitive spectral-scanning capability among millimeter and submillimeter telescopes in the northern hemisphere (Figure 3).

Figure 2. The [O III] 88 µm line of the z = 8.31 galaxy MACS0416_Y1 was found after four ALMA tunings (Tamura et al. 2019). The orange bars show the frequency range FINER covers in a single tuning (19 GHz × 2 sidebands).

Figure 3. Expected [O III] 88 µm and [C II] 158 µm flux densities of a bright Lyman break galaxy (M_UV = −21.5) at z = 8–15, compared with the minimum 5σ-detectable flux density of LMT-FINER in 10 hours (gray). The bars in the inset compare the instantaneous IF bandwidths of FINER and the current ALMA (Tamura et al. 2024).

Further science cases

FINER also offers unique capabilities for a broad range of science, including:

the Solar System (planetary atmospheres and comets),
the interstellar medium and astrochemistry,
star formation,
nearby galaxies,
distant dusty star-forming galaxies, including spectroscopic follow-up of galaxies detected with TolTEC.

See the FINER proposal (PDF) for details.