Gas infall into atomic cooling haloes: on the formation of protogalactic discs and supermassive black holes at z > 10

Abstract

We have performed cosmo-hydro simulations using the RAMSES code to study atomic cooling (ACHs) haloes at z=10 with masses 5E7Msun<~M<~2E9Msun. We assume primordial gas and H2-cooling and prior star-formation have been suppressed. We analysed 19 haloes (gas and DM) at a resolution of ~10 (proper) pc, selected from a total volume of ~2E3 (comoving) Mpc3. This is the largest statistical hydro-sim. study of ACHs at z>10 to date. We examine the morphology, angular momentum (AM), thermodynamic, and turbulence of these haloes, in order to assess the prevalence of disks and supermassive black holes (SMBHs). We find no correlation between either the magnitude or the direction of the AM of the gas and its parent DM halo. Only 3 haloes form rotationally supported cores. Two of the most massive haloes form massive, compact overdense blobs. These blobs have an accretion rate ~0.5 Msun/yr (at a distance of 100 pc), and are possible sites of SMBH formation. Our results suggest that the degree of rotational support and the fate of the gas in a halo is determined by its large-scale environment and merger history. In particular, the two haloes forming blobs are located at knots of the cosmic web, cooled early on, and experienced many mergers. The gas in these haloes is lumpy and highly turbulent, with Mach N. >~ 5. In contrast, the haloes forming rotationally supported cores are relatively more isolated, located midway along filaments, cooled more recently, and underwent fewer mergers. Thus, the gas in these haloes is less lumpy and less turbulent (Mach <~ 4), and could retain most of its AM. The remaining 14 haloes have intermediate properties. If verified in a larger sample of haloes and with additional physics, our results will have implications for observations of the highest-redshift galaxies and quasars with JWST.