Intrinsic galaxy alignments in CAMELS simulations and the significant impact of baryon model

ABSTRACT We present a detection of the intrinsic galaxy alignments in the hydrodynamic suite of the Cosmology and Astrophysics with MachinE Learning Simulations (CAMELS). We find that the alignment amplitude depends significantly on cosmological and supernova feedback parameters – specifically $\Omega _m$, $\sigma _8$, $A_{\text{SN1}}$, $A_{\text{SN2}}$ – while no dependence on active galactic nucleus (AGN) feedback is observed (due to the limited simulation volume $(25\, h^{-1}\, \text{Mpc})^3$). The dependence on $\sigma _8$ vanishes when projected correlation functions $w_{m+}$ are normalized by matter density correlations $w_{mm}$, consistent with predictions from linear alignment models. We find alignment amplitudes in quiescent galaxies to exceed those in star-forming galaxies by an order of magnitude. Moreover, examining orientation-only correlation functions from ellipticity-normalized galaxies $\tilde{w}_{m+}$, we confirm that alignment signals retain sensitivity to supernova feedback across full, star forming, quiescent, and ellipticity-normalized samples. Finally, we find evidence that supernova feedback impacts alignment signals differently in star-forming versus quiescent populations, suggesting that distinct alignment mechanisms operate across galaxy types. Our results offer key insights for understanding galaxy formation and alignment models for future weak gravitational lensing analyses.