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Interpreting ALMA Observations of the ISM During the Epoch of Reionisation

, , , and . (2016)cite arxiv:1612.01786Comment: 32 Pages, 25 figures, Submitted to MNRAS, Abstract abridged for arXiv.

Abstract

We present cosmological, radiation-hydrodynamics simulations of galaxy formation during the epoch of reionisation in an effort towards modelling the interstellar medium (ISM) and interpreting ALMA observations. Simulations with and without stellar radiation are compared at large (Mpc), intermediate (tens of kpc), and small (sub kpc) scales to highlight the differences local stellar radiation can make for the distribution of neutral hydrogen internally to galaxy and externally on the surrounding filaments and intergalactic medium (IGM). At large scales, we find that the dense regions around galaxies reionise first before UV photons penetrate the voids; however, there remains a considerable amount of neutral gas present within the galaxies. The spatial distribution of neutral gas is highly dynamic and is anti-correlated with the presence of stars older than a few Myrs. Likewise, H$_2$ masses in the galaxies are extremely time variable and sensitive to the presence of these same stars. For our specific feedback implementation, most of the metals remain inside the virial radii of galaxies and they are proportionally distributed over the ionised and neutral medium by mass. For our most massive galaxy with $\rm M_h\sim10^11$M$_ødot$, we find that the majority of the CII mass in the galaxy is associated with cold neutral clumps, similar to OI. NII is more diffuse and arises in warmer gas while OIII is associated with the hotter gas produced by photo-heating and supernovae that has a higher ionisation parameter. If small pockets of high metallicity gas exist in the ISM, the emission from these ions may be observable by ALMA while the naturally low metallicity of the galaxy will cause these systems to fall below the local CII-SFR relation. abridged

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[1612.01786] Interpreting ALMA Observations of the ISM During the Epoch of Reionisation

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