For efficient spectroscopic redshift identification of early galaxies in the northern hemisphere, we aim to combine the Large Millimeter Telescope (LMT) with a wide-band heterodyne receiver, FINER, which will cover radio frequencies of 120–360 GHz and offer a 3–21 GHz intermediate frequency (IF) per sideband and polarization. To take full advantage of such wide IFs, we present a novel 10.24-GHz-wide digital spectrometer, DRS4 (Elecs Industry Co., Ltd.). It incorporates 20.48 Gsps samplers with an FPGA-based digital signal processing module. To mitigate the noise contamination from the image sideband, it is equipped with a digital sideband separation function to improve the sideband rejection up to 25 dB. Laboratory performance evaluations show that it exhibits an Allan time of at least ~ 100 s and a total power dynamic range of at least 7 dB. These results demonstrate its capability of instantaneously wide-band spectroscopy toward high-redshift galaxies with position-switching observations.
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 [Oiii] 88 μm and [Cii] 158 μm 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.
We report the development of the new 4-beam, 2-polarization, 2-sideband, 100 GHz band SIS receiver "FOREST" (FOur beam REceiver System on the 45-m Telescope) and the results from commissioning and observations on the Nobeyama 45-m Telescope operated by Nobeyama Radio Observatory, a branch of National Astronomical Observatory of Japan. FOREST aims to add new capabilities of large-area mapping and simultaneous multi-line observation at 80 { 116 GHz band to the Nobeyama 45-m Telescope, which is one of the largest millimeter radio telescopes in the world. The configuration of the four beams is a quadrate of 2 x 2 with the separation between adjacent beams of 50". Beam size of each beam is ~ 15" at 115 GHz. Receiver noise temperature is as low as that of ALMA Band 3 receivers, so that mapping speed is more than four times as high as that of the other 100 GHz band receivers on the 45-m Telescope. The IF bandwidth is 8 GHz (4 { 12 GHz) realizing simultaneous 12CO(J = 1-0), 13CO(J = 1-0), and C18O(J = 1-0) observations. Cooled components inside of cryostat are modularized per beam. IF signals from the cryostat are processed by the room temperature IF system, and then passed to spectrometers. We have installed the FOREST receiver into the Nobeyama 45-m Telescope, evaluated its performance, and made large area mapping observations. These demonstrate the excellent performance of the FOREST receiver and the Nobeyama 45-m Telescope.
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