Young and turbulent: the early life of massive galaxy progenitors

Abstract

We present results from the "Ponos" simulation suite on the early evolution of a massive, M vir (z = 0) = 1.2×1013 M galaxy. At z 6, before feedback from a central supermassive black hole becomes dominant, the main galaxy has a stellar mass ∼ 2 × 10 9 M and a star formation rate ∼ 20 M yr −1 . The galaxy sits near the expected main sequence of starforming galaxies at those redshifts, and resembles moderately star-forming systems observed at z > 5. The high specific star formation rate results in vigorous heating and stirring of the gas by supernovae feedback, and the galaxy develops a thick and turbulent disc, with gas velocity dispersion ∼ 40 km s −1 , rotation to dispersion ratio ∼ 2, and with a significant amount of gas at ∼ 10 5 K. The Toomre parameter always exceeds the critical value for gravito-turbulence, Q ∼ 1.5−2, mainly due to the contribution of warm/hot gas inside the disc. Without feedback, a nearly gravito-turbulent regime establishes with similar gas velocity dispersion and lower Q. We propose that the "hot and turbulent" disc regime seen in our simulations, unlike the "cold and turbulent" gravito-turbulent regime of massive clumpy disc galaxies at z ∼ 1 − 2, is a fundamental characterisation of main sequence galaxies at z 6, as they can sustain star formation rates comparable to those of low-mass starbursts at z = 0. This results in no sustained coherent gas inflows through the disc, and in fluctuating and anisotropic mass transport, possibly postponing the assembly of the bulge and causing the initial feeding of the central black hole to be highly intermittent.

Global torques and stochasticity as the drivers of massive black hole pairing in the young Universe

“…We study the evolution of the pairing of MBHs embedded in a starforming main-sequence galaxy at z 7. Our initial conditions are taken from the z = 7.32 snapshot of the high-resolution cosmological zoom-in simulation PonosHydro (PH; presented in Fiacconi et al 2017) -the precursor run -to which we add the MBHs, as described in detail in Section 2.2.1. We run our simulation using the smoothed particle hydrodynamics, N-body code GASOLINE2 2 (Stadel 2001;Wadsley, Stadel & Quinn 2004;Wadsley, Keller & Quinn 2017), using a set-up that is virtually identical to the parameters set for the PH run in Fiacconi et al (2017).…”

High-redshift quasars and their host galaxies – I. Kinematical and dynamical properties and their tracers

“…To refine the zoom-in region up to the desired resolution, we follow the approach reported in Fiacconi et al (2017):…”

The Mass, Color, and Structural Evolution of Today’s Massive Galaxies Since z ∼ 5

“…Fiacconi et al (2016b) simulated the assembly of the main progenitor of a z=0 ultra-massive elliptical, and found the progenitor to be disk-dominated, with an exponential brightness profile at z 6 > that had experienced several major mergers at z 9 > . The "survival", or more accurately, the reassembly of the disk after a major merger is feasible, provided the major mergers are sufficiently gas rich (e.g., Hopkins et al 2009).…”

“…The "survival", or more accurately, the reassembly of the disk after a major merger is feasible, provided the major mergers are sufficiently gas rich (e.g., Hopkins et al 2009). Fiacconi et al (2016b) also calculated the Toomre parameter for their simulated disk and found it to be stable against fragmentation for all resolved spatial scales, with the disk supported by a turbulent interstellar medium thought to be due to feedback from star formation. They also predict that gas-rich starforming disks at z 5 > should not host a significant bulge, but rather be built up by mergers occurring at z 2 4 < < (Fiacconi et al 2016a).…”