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

TL;DR

This study detects intrinsic galaxy alignments in CAMELS simulations, revealing their dependence on cosmological and supernova feedback parameters, with implications for galaxy formation and weak lensing models.

Contribution

It demonstrates the significant impact of baryon feedback models on galaxy alignment signals, highlighting the role of supernova feedback and galaxy type in alignment mechanisms.

Findings

Alignment amplitude depends on cosmological and supernova feedback parameters.

No observed dependence on AGN feedback within the simulation volume.

Alignment signals differ between star-forming and quiescent galaxies.

Abstract

We present a detection of the intrinsic galaxy alignments in the CAMELS suite of hydrodynamic simulations. 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 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.