Zooming on the internal structure of z≃6 galaxies

Abstract

We present zoom-in, AMR, high-resolution ($\\simeq 30$ pc) simulations of\nhigh-redshift ($z \\simeq 6$) galaxies with the aim of characterizing their\ninternal properties and interstellar medium. Among other features, we adopt a\nstar formation model based on a physically-sound molecular hydrogen\nprescription, and introduce a novel scheme for supernova feedback, stellar\nwinds and dust-mediated radiation pressure. In the zoom-in simulation the\ntarget halo hosts "Dahlia", a galaxy with a stellar mass $M_*=1.6\\times\n10^{10}$M$_\\odot$, representative of a typical $z\\sim 6$ Lyman Break Galaxy.\nDahlia has a total H2 mass of $10^{8.5}$M$_\\odot$, that is mainly concentrated\nin a disk-like structure of effective radius $\\simeq 0.6$ kpc and scale height\n$\\simeq 200$ pc. Frequent mergers drive fresh gas towards the center of the\ndisk, sustaining a star formation rate per unit area of $\\simeq 15 $M$_\\odot$\nyr$^{-1}$ kpc$^{-2}$. The disk is composed by dense ($n \\gtrsim 25$ cm$^{-3}$),\nmetal-rich ($Z \\simeq 0.5 $ Z$_\\odot$) gas, that is pressure-supported by\nradiation. We compute the $158\\mu$m [CII] emission arising from {Dahlia}, and\nfind that $\\simeq 95\\%$ of the total [CII] luminosity\n($L_{[CII]}\\simeq10^{7.5}$ L$_\\odot$) arises from the H2 disk. Although $30\\%$\nof the CII mass is transported out of the disk by outflows, such gas negligibly\ncontributes to [CII] emission, due to its low density ($n \\lesssim 10$\ncm$^{-3}$) and metallicity ($Z\\lesssim 10^{-1}$Z$_\\odot$). Dahlia is\nunder-luminous with respect to the local [CII]-SFR relation; however, its\nluminosity is consistent with upper limits derived for most $z\\sim6$ galaxies.\n