Estimating LuSEE-Night's Sensitivity to Cα Radio Recombination Lines
Abstract
Carbon radio recombination lines (CRRLs) arising from the cold neutral medium (CNM) of the interstellar medium are potential foregrounds in the 1-50 MHz band that LuSEE-Night will observe from the lunar far side. CRRLs are sensitive probes of the temperature, density, and radiation field of the CNM, and LuSEE-Night will provide sky-averaged measurements in a poorly explored frequency range. We model CRRLs across this band, accounting for doppler, collisional, and radiation broadening, and we estimate line strengths using two independent methods - fixing either the peak or the frequency-integrated optical depth - applied both uniformly across the sky and with region-dependent values informed by prior low-frequency observations. We simulate LuSEE-Night's expected response to these CRRLs and further convolve the beam-diluted spectra with LuSEE-Night's polyphase-filter-bank spectrometer response, including its zoomed-mode frequency resolution of ∼390 Hz, to obtain the expected observed brightness temperature. Using these simulated spectra, we estimate the integration time required to detect individual CRRLs at SNR=5 across the six sky models considered. Required integration times range from as short as 30 hours (in the most optimistic model where the optical depth across the sky is ∼10−3) to 27.6 years (in the most conservative models where the optical depth across the sky is ∼10−4). Stacking the 361 simulated Cα lines between 10 and 50 MHz reduces the integration time needed for an SNR=5 detection to ∼11 minutes and ∼151 hours respectively, indicating that LuSEE-Night has realistic chances of making a stacked detection of Cα RRLs within a realistic mission lifetime, even under the most conservative optical-depth assumptions.
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BibTeX
@misc{yousuf2026estimating,
title = {{Estimating LuSEE-Night's Sensitivity to Cα Radio Recombination Lines}},
author = {Fatima Yousuf and Aurelia Gerber and Zack Li and Akshatha Vydula and Stuart D. Bale and David W. Barker and Jack Burns and Christian H. Bye and Hugo Camacho and Cristina-Maria Cordun and Adam Fahs and Sonia Ghosh and Keith Goetz and Robert Grimm and Sven Herrmann and Joshua J. Hibbard and Oliver Jeong and Marc Klein-Wolt and Léon V. E. Koopmans and Joel Krajewski and Corentin K. Louis and Milan Maksimović and Ryan McLean and Raul A. Monsalve and Arnur Nigmetov and Paul O'Connor and Aaron Parsons and Michel Piat and Marc Pulupa and Rugved Pund and David Rapetti and Kaja M. Rotermund and Benjamin R. B. Saliwanchik and Jack Singal and Anže Slosar and Nikolai Stefanov and David Sundkvist and Aritoki Suzuki and Harish K. Vedantham and Philippe Zarka},
howpublished = {arXiv},
year = {2026},
month = nov,
doi = {10.48550/arxiv.2611.03828},
eprint = {2611.03828},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2611.03828},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Estimating LuSEE-Night's Sensitivity to Cα Radio Recombination Lines
AU - Fatima Yousuf
AU - Aurelia Gerber
AU - Zack Li
AU - Akshatha Vydula
AU - Stuart D. Bale
AU - David W. Barker
AU - Jack Burns
AU - Christian H. Bye
AU - Hugo Camacho
AU - Cristina-Maria Cordun
AU - Adam Fahs
AU - Sonia Ghosh
AU - Keith Goetz
AU - Robert Grimm
AU - Sven Herrmann
AU - Joshua J. Hibbard
AU - Oliver Jeong
AU - Marc Klein-Wolt
AU - Léon V. E. Koopmans
AU - Joel Krajewski
AU - Corentin K. Louis
AU - Milan Maksimović
AU - Ryan McLean
AU - Raul A. Monsalve
AU - Arnur Nigmetov
AU - Paul O'Connor
AU - Aaron Parsons
AU - Michel Piat
AU - Marc Pulupa
AU - Rugved Pund
AU - David Rapetti
AU - Kaja M. Rotermund
AU - Benjamin R. B. Saliwanchik
AU - Jack Singal
AU - Anže Slosar
AU - Nikolai Stefanov
AU - David Sundkvist
AU - Aritoki Suzuki
AU - Harish K. Vedantham
AU - Philippe Zarka
PY - 2026
DA - 2026/11/02
PB - arXiv
DO - 10.48550/arxiv.2611.03828
UR - https://arxiv.org/abs/2611.03828
AB - Carbon radio recombination lines (CRRLs) arising from the cold neutral medium (CNM) of the interstellar medium are potential foregrounds in the 1-50 MHz band that LuSEE-Night will observe from the lunar far side. CRRLs are sensitive probes of the temperature, density, and radiation field of the CNM, and LuSEE-Night will provide sky-averaged measurements in a poorly explored frequency range. We model CRRLs across this band, accounting for doppler, collisional, and radiation broadening, and we estimate line strengths using two independent methods - fixing either the peak or the frequency-integrated optical depth - applied both uniformly across the sky and with region-dependent values informed by prior low-frequency observations. We simulate LuSEE-Night's expected response to these CRRLs and further convolve the beam-diluted spectra with LuSEE-Night's polyphase-filter-bank spectrometer response, including its zoomed-mode frequency resolution of ∼390 Hz, to obtain the expected observed brightness temperature. Using these simulated spectra, we estimate the integration time required to detect individual CRRLs at SNR=5 across the six sky models considered. Required integration times range from as short as 30 hours (in the most optimistic model where the optical depth across the sky is ∼10^−3) to 27.6 years (in the most conservative models where the optical depth across the sky is ∼10^−4). Stacking the 361 simulated Cα lines between 10 and 50 MHz reduces the integration time needed for an SNR=5 detection to ∼11 minutes and ∼151 hours respectively, indicating that LuSEE-Night has realistic chances of making a stacked detection of Cα RRLs within a realistic mission lifetime, even under the most conservative optical-depth assumptions.
ER -