Detalles de publicación
PP 026057
CONCERTO: forward modeling of interferograms for calibration
(1) LAM, (2) IPAG, (3) IAC, (4) IAC, (5) LPSC, (6) Institut Néel, (7) Cardiff Uni., (8) Univ. Diego Portales, (9) ESO, (10) Univ. Valparaiso
Context. The CarbON [CII] line in post-rEionisation and ReionisaTiOn epoch (CONCERTO) instrument is a low-resolution mapping Fourier-transform spectrometer, based on lumped-element kinetic inductance detector (LEKID) technology, operating at 130-310 GHz. It was installed on the 12-meter APEX telescope in Chile in April 2021 and operated until December 2022. CONCERTO’s main science goal is to constrain the [CII] line fluctuations at high redshift. To reach that goal CONCERTO observed 1.4 deg2 in the COSMOS field.
Aims. To ensure accurate calibration of the data, we have developed a forward model capable of simulating both the spectral response and the corresponding interferograms for each scan of observation in the COSMOS field. We present the modelling approach that enables us to reproduce the expected instrument outputs under controlled input conditions and provides a framework for the different calibration steps, including the absolute brightness calibration of the spectra.
Methods. We constructed a dedicated analysis pipeline to characterise the raw interferometric data (interferograms) obtained under a broad range of atmospheric conditions at APEX. Using the forward model, we measured the interferogram alignment with the optical path difference (zero path difference, ZPD) and the relative response of each KID (flatfield). Together, these elements enable a robust characterisation of the instrument’s spectral brightness calibration.
Results. We demonstrate that the zero path difference systematically varies with elevation and across detectors, with variations that are consistent with small optical misalignments and elevation-dependent mechanical effects in the optical structure. The full measurement of these variations allow us to construct a data base that is used to accurately determine the zero path difference for each measured individual interferogram. The flatfield shows systematic variations with detector position but is extremely stable with time and atmospheric contribution. The accurate determination of the zero path differences and flatfields allows us to construct spectral cubes that combine all detectors and all blocks of data. Finally we present a novel method to calibrate the absolute brightness of those spectral cubes, which is immune to the exact knowledge of the bandpasses and directly applicable to extended emission.
Conclusions. Our analysis establishes a framework for precise calibration directly from on-sky data. This approach ensures reliable performance for cosmological and astrophysical applications and can be readily adapted to future Martin–Puplett interferometer–based Fourier-transform spectrometers.
Aims. To ensure accurate calibration of the data, we have developed a forward model capable of simulating both the spectral response and the corresponding interferograms for each scan of observation in the COSMOS field. We present the modelling approach that enables us to reproduce the expected instrument outputs under controlled input conditions and provides a framework for the different calibration steps, including the absolute brightness calibration of the spectra.
Methods. We constructed a dedicated analysis pipeline to characterise the raw interferometric data (interferograms) obtained under a broad range of atmospheric conditions at APEX. Using the forward model, we measured the interferogram alignment with the optical path difference (zero path difference, ZPD) and the relative response of each KID (flatfield). Together, these elements enable a robust characterisation of the instrument’s spectral brightness calibration.
Results. We demonstrate that the zero path difference systematically varies with elevation and across detectors, with variations that are consistent with small optical misalignments and elevation-dependent mechanical effects in the optical structure. The full measurement of these variations allow us to construct a data base that is used to accurately determine the zero path difference for each measured individual interferogram. The flatfield shows systematic variations with detector position but is extremely stable with time and atmospheric contribution. The accurate determination of the zero path differences and flatfields allows us to construct spectral cubes that combine all detectors and all blocks of data. Finally we present a novel method to calibrate the absolute brightness of those spectral cubes, which is immune to the exact knowledge of the bandpasses and directly applicable to extended emission.
Conclusions. Our analysis establishes a framework for precise calibration directly from on-sky data. This approach ensures reliable performance for cosmological and astrophysical applications and can be readily adapted to future Martin–Puplett interferometer–based Fourier-transform spectrometers.