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arXiv · 2610.17200

Interpreting the stacked kinetic SZ signal II: the degeneracy between satellite galaxies and baryonic feedback

Lurdes Ondaro-Mallea·Boryana Hadzhiyska·Raul E. Angulo
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Abstract

The kinetic Sunyaev-Zel'dovich (kSZ) signal stacked around a galaxy sample traces the gas around halos and is a powerful probe of baryonic feedback. Its interpretation, however, depends on the satellite galaxies in the sample. Using the FLAMINGO hydrodynamical simulations and DESI-like samples of luminous red galaxies (LRGs), bright galaxies survey (BGS), and emission-line galaxies (ELGs), we show that satellites and feedback have similar effects: both suppress the small-scale signal. This degeneracy arises because stacking on satellites, which are offset from the centre of their host haloes, mimics the extended gas distribution produced by feedback. Although satellites make up only 20-30% of each sample, they account for 50-80% of the signal because they occupy more massive halos than centrals; thus their imprint on the stacked profiles can be as large as that of feedback. At the precision of current DESI$\times$ACT data, neglecting satellites in the modelling biases the inferred gas fractions low, by up to a factor of two, and overestimates the feedback strength, particularly for the LRG and BGS samples. Remaining agnostic about the satellite population avoids this bias but reduces the constraining power, so robust constraints would require knowing the satellite fraction to better than 10%, for instance from lensing and clustering data of the same galaxy samples. Finally, a further contribution from satellites will become statistically significant with upcoming surveys: satellites trace the anisotropic gas distribution around their host haloes, an effect that contributes 10% of the signal, and will likely require simulation-based models to capture.

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Lurdes Ondaro-Mallea, Boryana Hadzhiyska, Raul E. Angulo. 2026-10-12. Interpreting the stacked kinetic SZ signal II: the degeneracy between satellite galaxies and baryonic feedback. https://arxiv.org/abs/2610.17200

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