The impact of chemistry on the structure of high-z galaxies [GA]

http://arxiv.org/abs/1707.04259


To improve our understanding of high-z galaxies we study the impact of H${2}$ chemistry on their evolution, morphology and observed properties. We compare two zoom-in high-resolution (30 pc) simulations of prototypical $M{\star}\sim 10^{10} {\rm M}{\odot}$ galaxies at $z=6$. The first, “Dahlia”, adopts an equilibrium model for H${2}$ 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 ${\rm M}{\odot}/\rm yr$ at $z=6$. They both have SFR-stellar mass relation consistent with observations, and a specific SFR of $\simeq 5\, {\rm Gyr}^{-1}$. The main differences arise in the gas properties. The non-equilibrium chemistry determines the H$\rightarrow$ H${2}$~transition to occur at densities $> 300\,{cm}^{-3}$, 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 $3\sigma$ 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]~$157.74\,\mu{\rm m}$ (H$_{2}$~$17.03\,\mu{\rm m}$) 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.

Read this paper on arXiv…

A. Pallottini, A. Ferrara, S. Bovino, et. al.
Mon, 17 Jul 17
22/45

Comments: 18 pages, 13 Figures 1 Table, accepted for publication in MNRAS