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The impact of chemistry on the structure of high-z galaxies

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Ferrara, A 
Bovino, S 
Vallini, L 
Gallerani, S 


To improve our understanding of high-z galaxies we study the impact of H2 chemistry on their evolution, morphology and observed properties. We compare two zoom-in high-resolution (30 pc) simulations of prototypical M∼1010M galaxies at z=6. The first, "Dahlia", adopts an equilibrium model for H2 formation, while the second, "Alth{\ae}a", features an improved non-equilibrium chemistry network. The star formation rate (SFR) of the two galaxies is similar (within 50%), and increases with time reaching values close to 100 M/yr at z=6. They both have SFR-stellar mass relation consistent with observations, and a specific SFR of ≃5Gyr−1. The main differences arise in the gas properties. The non-equilibrium chemistry determines the H H2~transition to occur at densities >300cm−3, i.e. about 10 times larger than predicted by the equilibrium model used for Dahlia. As a result, Alth{\ae}a features a more clumpy and fragmented morphology, in turn making SN feedback more effective. Also, because of the lower density and weaker feedback, Dahlia sits 3σ away from the Schmidt-Kennicutt relation; Alth{\ae}a, instead nicely agrees with observations. The different gas properties result in widely different observables. Alth{\ae}a outshines Dahlia by a factor of 7 (15) in [CII]~157.74μm (H2~17.03μm) line emission. Yet, Alth{\ae}a is under-luminous with respect to the locally observed [CII]-SFR relation. Whether this relation does not apply at high-z or the line luminosity is reduced by CMB and metallicity effects remains as an open question.



methods: numerical, galaxies: evolution, galaxies: formation, galaxies: high-redshift, galaxies: ISM, infrared: general

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Monthly Notices of the Royal Astronomical Society

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Oxford University Press (OUP)
Science and Technology Facilities Council (ST/M001172/1)
European Research Council (695671)