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The role of gas fraction and feedback in the stability and evolution of galactic discs: implications for cosmological galaxy formation models

Abstract : High-redshift star-forming galaxies often have irregular morphologies with giant clumps containing up to 108-109 solar masses of gas and stars. The origin and evolution of giant clumps are debated both theoretically and observationally. In most cosmological simulations, high-redshift galaxies have regular spiral structures or short-lived clumps, in contradiction with many idealized high-redshift disc models. Here, we test whether this discrepancy can be explained by the low gas fractions of galaxies in cosmological simulations. We present a series of simulations with varying gas fractions, from 25 per cent, typical of galaxies in most cosmological simulations, to 50 per cent, typical of observed galaxies at 1.5 < z < 3. We find that gas-poor models have short-lived clumps, that are unbound and mostly destroyed by galactic shear, even with weak stellar feedback. In contrast, gas-rich models form long-lived clumps even with boosted stellar feedback. This shows that the gas mass fraction is the primary physical parameter driving violent disc instabilities and the evolution of giant clumps on ~108 yr time-scales, with lower impact from the calibration of the stellar feedback. Many cosmological simulations of galaxy formation have relatively gas-poor galactic discs, which could explain why giant clumps are absent or short-lived in such models. Similar baryonic and dark matter mass distribution could produce clumpy galaxies with long-lived clumps at z ~ 2 if the gas fraction was in better agreement with observations.
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Submitted on : Thursday, August 4, 2022 - 2:37:56 PM
Last modification on : Saturday, August 6, 2022 - 3:43:21 AM

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Jérémy Fensch, Frédéric Bournaud. The role of gas fraction and feedback in the stability and evolution of galactic discs: implications for cosmological galaxy formation models. Monthly Notices of the Royal Astronomical Society, 2021, 505, pp.3579-3589. ⟨10.1093/mnras/stab1489⟩. ⟨insu-03745700⟩

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