Spectral stacking of radio-interferometric data
Abstract
Context. Mapping molecular line emission beyond the bright low-J CO transitions is still challenging in extragalactic studies, even with the latest generation of (sub-)millimetre interferometers, such as ALMA and NOEMA. Aims. We summarise and test a spectral stacking method that has been used in the literature to recover low-intensity molecular line emission, such as HCN(1-0), HCO + (1-0), and even fainter lines in external galaxies. The goal is to study the capabilities and limitations of the stacking technique when applied to imaged interferometric observations. Methods. The core idea of spectral stacking is to align spectra of the low S/N spectral lines to a known velocity field calculated from a higher S/N line expected to share the kinematics of the fainter line (e.g. CO(1-0) or 21 cm emission). Then these aligned spectra can be coherently averaged to produce potentially high S/N spectral stacks. Here we used imaged simulated interferometric and total power observations at different S/N levels, based on real CO observations. Results. For the combined interferometric and total power data, we find that the spectral stacking technique is capable of recovering the integrated intensities even at low S/N levels across most of the region where the high S/N prior is detected. However, when stacking interferometer-only data for low S/N emission, the stacks can miss up to 50% of the emission from the fainter line.
Conclusions.A key result of this analysis is that the spectral stacking method is able to recover the true mean line intensities in low S/N cubes and to accurately measure the statistical significance of the recovered lines. To facilitate the application of this technique we provide a public Python package, called PYSTACKER.
Related
- The ViSta method for optimized stacking of broadband interferometric data in the Fourier domain
- Radio Interferometric Calibration with the Exponential Map
- SIFARI: Self-Supervised Interferometric Fitting for Astronomical Radio Imaging
- Estimating the spectral resolution of a radio data cube from its noise properties
- Spectral and Polarization Properties of Coherent Radio Emission from Relativistic Magnetized Pair Plasma Shocks
BibTeX
@article{neumann2026spectral,
title = {{Spectral stacking of radio-interferometric data}},
author = {Lukas Neumann and Jakob S den Brok and Frank Bigiel and Adam Leroy and Antonio Usero and Ashley T Barnes and Ivana Bešlić and Cosima Eibensteiner and Malena Held and María J Jiménez-Donaire and Jérôme Pety and Erik W Rosolowsky and Eva Schinnerer and Thomas G Williams},
journal = {Astronomy \& Astrophysics - A\&A},
year = {2026},
month = sep,
doi = {10.1051/0004-6361/202346129},
url = {https://hal.science/hal-05761294v1},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Spectral stacking of radio-interferometric data
AU - Lukas Neumann
AU - Jakob S den Brok
AU - Frank Bigiel
AU - Adam Leroy
AU - Antonio Usero
AU - Ashley T Barnes
AU - Ivana Bešlić
AU - Cosima Eibensteiner
AU - Malena Held
AU - María J Jiménez-Donaire
AU - Jérôme Pety
AU - Erik W Rosolowsky
AU - Eva Schinnerer
AU - Thomas G Williams
PY - 2026
DA - 2026/09/23
JO - Astronomy & Astrophysics - A&A
DO - 10.1051/0004-6361/202346129
UR - https://hal.science/hal-05761294v1
AB - Context. Mapping molecular line emission beyond the bright low-J CO transitions is still challenging in extragalactic studies, even with the latest generation of (sub-)millimetre interferometers, such as ALMA and NOEMA. Aims. We summarise and test a spectral stacking method that has been used in the literature to recover low-intensity molecular line emission, such as HCN(1-0), HCO + (1-0), and even fainter lines in external galaxies. The goal is to study the capabilities and limitations of the stacking technique when applied to imaged interferometric observations. Methods. The core idea of spectral stacking is to align spectra of the low S/N spectral lines to a known velocity field calculated from a higher S/N line expected to share the kinematics of the fainter line (e.g. CO(1-0) or 21 cm emission). Then these aligned spectra can be coherently averaged to produce potentially high S/N spectral stacks. Here we used imaged simulated interferometric and total power observations at different S/N levels, based on real CO observations. Results. For the combined interferometric and total power data, we find that the spectral stacking technique is capable of recovering the integrated intensities even at low S/N levels across most of the region where the high S/N prior is detected. However, when stacking interferometer-only data for low S/N emission, the stacks can miss up to 50% of the emission from the fainter line. Conclusions.A key result of this analysis is that the spectral stacking method is able to recover the true mean line intensities in low S/N cubes and to accurately measure the statistical significance of the recovered lines. To facilitate the application of this technique we provide a public Python package, called PYSTACKER.
SN - 0004-6361
SN - 1432-0746
ER -