XID+PRIMA, II: Stepping Through Hyperspectral Imaging to Deblend PRIMAger Beyond the Extragalactic Confusion Limit

TL;DR

This paper introduces a Bayesian hyperspectral imaging method, XID+stepwise, that effectively deblends and measures fluxes of faint extragalactic sources beyond the confusion limit in FIR surveys, enhancing the scientific potential of PRIMAger.

Contribution

The paper presents a novel sequential Bayesian deblending approach utilizing hyperspectral data to recover faint source fluxes beyond traditional confusion limits.

Findings

Achieves flux recovery 1.3-3.4 times fainter than the confusion limit.

Demonstrates detection of IR-luminous galaxies at z~2 in most channels.

Confusion noise does not limit key science when using XID+ with PRIMAger data.

Abstract

The PRobe far-Infrared Mission for Astrophysics concept aims to map large areas with spectral coverage and sensitivities inaccessible to previous FIR space telescopes, covering 25-235um. We synthesise images representing a deep imaging survey, with realistic instrumental and confusion noise, reflecting the latest PRIMAger instrument specifications. We present a new Bayesian modelling approach XID+stepwise that exploits PRIMAger's hyperspectral imaging to derive self-consistent, informative flux priors by sequentially propagating constraints from short to long wavelengths. With Euclid-like prior source positions, this method recovers fluxes to within 20% to 0.2-0.7 mJy across 45-84 um, which correspond to factors of 1.3-3.4 fainter than the confusion limit. For the most confusion-dominated channels, accurate fluxes are measured to 0.9, 2.5, 7.6 and 14.8 mJy at 92, 126, 183 and 235 um, respectively, which are factors of 3-5 better than the confusion limit. Using a deeper Euclid-based prior catalogue and weak ancillary flux priors at 25 um yields further improvements, reaching up to a factor ~7 fainter than the confusion limit at 96 um. Additionally, we demonstrate that positional priors from blind source detection followed by deblending via XID+ enables PRIMAger to achieve sensitivity beyond the confusion limits using PRIMAger data alone. We show that IR-luminous galaxies at z~2 are robustly detected in a large fraction of the PRIMAger channels (>98% in 12 out of the 16 considered channels), providing dense sampling of the FIR SED even for sources several factors below the confusion limit. We explore the impact on our results for a range of systematic effects, including cirrus contamination, optical degradation, and calibration uncertainties. These findings indicate that confusion noise will not limit the key science from PRIMA extragalactic imaging surveys when employing XID+.