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Interpreting ALMA Observations of the ISM During the Epoch of Reionisation

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Katz, H 
Kimm, T 


We present cosmological, radiation-hydrodynamics simulations of galaxy formation during the epoch of reionization in an effort towards modelling the interstellar medium (ISM) and interpreting Atacama Large Millimeter Array (ALMA) observations. Simulations with and without stellar radiation are compared at large (Mpc), intermediate (tens of kpc) and small (sub-kpc) scales. At large scales, the dense regions around galaxies reionize first before ultraviolet (UV) photons penetrate the voids; however, considerable amounts of neutral gas remain present within the haloes. The spatial distribution of neutral gas is highly dynamic and is anticorrelated with the presence of stars older than a few Myr. For our specific feedback implementation, most of the metals remain inside the virial radii of haloes, and they are proportionally distributed over the ionized and neutral media by mass. For our most massive galaxy with Mh ∼ 1011 M⊙, the majority of the C ii and O i masses are associated with cold neutral clumps. N ii is more diffuse and arises in warmer gas, while O iii arises in hotter gas with a higher ionization parameter, produced by photoheating and supernovae. If smaller pockets of high-metallicity gas exist in the ISM, the emission from these ions may be observable by ALMA, while the low metallicity of the galaxy may cause these systems to fall below the local [C ii]–star formation rate relation. The presence of dust can cause spatial offsets between UV/Lyman α and [C ii] emissions, as suggested by the recent observations of Maiolino et al. [O iii] may be spatially offset from both of these components since it arises from a different part of density–temperature phase space.



galaxies: evolution, galaxies: formation, galaxies: high-redshift, intergalactic medium, infrared: ISM

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Monthly Notices of the Royal Astronomical Society

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Oxford University Press
Science and Technology Facilities Council (ST/N000927/1)
European Research Council (638707)
This work made considerable use of the open source analysis software PYNBODY (Pontzen et al. 2013). HK thanks Foundation Boustany, the Cambridge Overseas Trust and an Isaac Newton Studentship. Support by ERC Advanced Grant 320596 ‘The Emergence of Structure during the Epoch of reionization’ is gratefully acknowledged. DS acknowledges support by STFC and ERC Starting Grant 638707 ‘Black holes and their host galaxies: coevolution across cosmic time’. This work was performed using the DiRAC/Darwin Supercomputer hosted by the University of Cambridge High Performance Computing Service (, provided by Dell Inc. using the Strategic Research Infrastructure Funding from the Higher Education Funding Council for England and funding from the Science and Technology Facilities Council. This work used the DiRAC Complexity system, operated by the University of Leicester IT Services, which forms part of the STFC DiRAC HPC Facility ( This equipment is funded by BIS National E-Infrastructure capital grant ST/K000373/1 and STFC DiRAC Operations grant ST/K0003259/1. DiRAC is part of the National E-Infrastructure. Furthermore, this work used the DiRAC Data Centric system at Durham University, operated by the Institute for Computational Cosmology on behalf of the STFR DiRAC HPC Facility ( This equipment was funded by the BIS National E-infrastructure capital grant ST/K00042X/1, STFC capital grant ST/K00087X/1, DiRAC operations grant ST/K003267/1 and Durham University. Dirac is part of the National E-Infrastructure.