Disparate effects of circumgalactic medium angular momentum in IllustrisTNG and SIMBA

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Abstract
In this study, we examine the role of the circumgalactic medium (CGM) angular momentum (jCGM) on star formation in galaxies, whose influence is currently not well understood. The analysis utilises central galaxies from two hydrodynamical simulations, SIMBA and IllustrisTNG. We observe a substantial divergence in how star formation rates correlate with CGM angular momentum between the two simulations. Specifically, quenched galaxies in IllustrisTNG show higher jCGM than their star-forming counterparts with similar stellar masses, while the reverse is true in SIMBA. This difference is attributed to the distinct active galactic nucleus (AGN) feedback mechanisms active in each simulation. Moreover, both simulations demonstrate similar correlations between jCGM and environmental angular momentum (jEnv) in star-forming galaxies, but these correlations change notably when kinetic AGN feedback is present. In IllustrisTNG, quenched galaxies consistently show higher jCGM compared to their star-forming counterparts with the same jEnv, a trend not seen in SIMBA. Examining different AGN feedback models in SIMBA, we further confirm that AGN feedback significantly influences the CGM gas distribution, although the relationship between the cold gas fraction and the star formation rate (SFR) remains largely stable across different feedback scenarios.

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