We study the role of feedback from supernovae and black holes in the evolution of the star formation rate function (SFRF) of z ∼ 4 − 7 galaxies. We use a new set of cosmological hydrodynamic simulations, ANGUS (AustraliaN GADGET-3 early Universe Simulations), run with a modified and improved version of the parallel TreePM-smoothed particle hydrodynamics code GADGET-3 called P-GADGET3(XXL), that includes a self-consistent implementation of stellar evolution and metal enrichment. In our simulations both Supernova (SN) driven galactic winds and Active Galactic Nuclei (AGN) act simultaneously in a complex interplay. The SFRF is insensitive to feedback prescription at z > 5, meaning that it cannot be used to discriminate between feedback models during reionisation. However, the SFRF is sensitive to the details of feedback prescription at lower redshift. By exploring different SN driven wind velocities and regimes for the AGN feedback, we find that the key factor for reproducing the observed SFRFs is a combination of "strong" SN winds and early AGN feedback in low mass galaxies. Conversely, we show that the choice of initial mass function and inclusion of metal cooling have less impact on the evolution of the SFRF. When variable winds are considered, we find that a non-aggressive wind scaling is needed to reproduce the SFRFs at z 4. Otherwise, the amount of objects with low SFRs is greatly suppressed and at the same time winds are not effective enough in the most massive systems.

We investigate quasar outflows at z 6 by performing zoom-in cosmological hydrodynamical simulations. By employing the SPH code GADGET-3, we zoom in the 2R 200 region around a 2×1012 M ⊙ halo at z = 6, inside a (500 Mpc) 3 comoving volume. We compare the results of our AGN runs with a control simulation in which only stellar/SN feedback is considered. Seeding 10 5 M ⊙ BHs at the centers of 10 9 M ⊙ halos, we find the following results. BHs accrete gas at the Eddington rate over z = 9 − 6. At z = 6, our most-massive BH has grown to M BH = 4 × 10 9 M ⊙ . Fast (v r > 1000 km/s), powerful (Ṁ out ∼ 2000M ⊙ /yr) outflows of shock-heated low-density gas form at z ∼ 7, and propagate up to hundreds kpc. Star-formation is quenched over z = 8 − 6, and the total SFR (SFR surface density near the galaxy center) is reduced by a factor of 5 (1000). We analyse the relative contribution of multiple physical process: (i) disrupting cosmic filamentary cold gas inflows, (ii) reducing central gas density, (iii) ejecting gas outside the galaxy; and find that AGN feedback has the following effects at z = 6. The inflowing gas mass fraction is reduced by ∼ 12%, the high-density gas fraction is lowered by ∼ 13%, and ∼ 20% of the gas outflows at a speed larger than the escape velocity (500 km/s). We conclude that quasar-host galaxies at z 6 are accreting non-negligible amount of cosmic gas, nevertheless AGN feedback quenches their star formation dominantly by powerful outflows ejecting gas out of the host galaxy halo.

We present ALMA observations of the CO(6-5) and [CII] emission lines and the sub-millimeter continuum of the z ∼ 6 quasi-stellar object (QSO) SDSS J231038.88+185519.7. Compared to previous studies, we have analyzed a synthetic beam that is ten times smaller in angular size, we have achieved ten times better sensitivity in the CO(6-5) line, and two and half times better sensitivity in the [CII] line, enabling us to resolve the molecular gas emission. We obtain a size of the dense molecular gas of 2.9 ± 0.5 kpc, and of 1.4 ± 0.2 kpc for the 91.5 GHz dust continuum. By assuming that CO(6-5) is thermalized, and by adopting a CO to H2 conversion factor αCO = 0.8 M⊙K−1 (km s)−1 pc2, we infer a molecular gas mass of M(H2) = (3.2±0.2)×1010 M⊙. Assuming that the observed CO velocity gradient is due to an inclined rotating disk, we derive a dynamical mass of Mdynsin2(i)=(2.4 ± 0.5)×1010 M⊙, which is a factor of approximately two smaller than the previously reported estimate based on [CII]. Regarding the central black hole, we provide a new estimate of the black hole mass based on the C IV emission line detected in the VLT/X-shooter spectrum: MBH = (1.8 ± 0.5)×109 M⊙. We find a molecular gas fraction of μ = M(H2)/M* ∼ 4.4, where M∗ ≈ Mdyn − M(H2) − M(BH). We derive a ratio νrot/σ ≈ 1 − 2 suggesting high gas turbulence, outflows/inflows and/or complex kinematics due to a merger event. We estimate a global Toomre parameter Q ∼ 0.2 − 0.5, indicating likely cloud fragmentation. We compare, at the same angular resolution, the CO(6-5) and [CII] distributions, finding that dense molecular gas is more centrally concentrated with respect to [CII]. We find that the current BH growth rate is similar to that of its host galaxy.

We investigate two modes of coupling the feedback energy from a central AGN to the neighbouring gas in galaxy simulations: kinetic -velocity boost, and thermal -heating. We formulate kinetic feedback models for energy-driven wind (EDW) and momentum-driven wind (MDW), using two free parameters: feedback efficiency ǫ f , and AGN wind velocity v w . A novel numerical algorithm is implemented in the SPH code GADGET-3, to prevent the expansion of a hole in the gas distribution around the BH. We perform simulations of isolated evolution and merger of disk galaxies, of Milky-Way mass as well as lower and higher masses. We find that in the isolated galaxy BH kinetic feedback generates intermittent bipolar jet-like gas outflows. We infer that current prescriptions for BH subgrid physics in galaxy simulations can grow the BH to observed values even in an isolated disk galaxy. The BH growth is enhanced in a galaxy merger, which consequently requires different model parameters to fit the observations than an isolated case. Comparing the [M BH − σ ⋆ ] relation obtained in our simulations with observational data, we conclude that it is possible to find parameter sets for a fit in all the models (e.g. v w = 10000 km/s and ǫ f = 0.25 for BH kinetic EDW), except for the case with MDW feedback in a galaxy merger, in which the BH is always too massive. The BH thermal feedback implementation of within the multiphase star-formation model is found to have negligible impact on gas properties; and the effect claimed in all previous studies is attributed to gas depletion around the BH by the creation of an artificial hole. The BH mass accretion rate in our simulations exhibit heavy fluctuations. The star formation rate is quenched with feedback by removal of gas. The circumgalactic medium (CGM) gas at galactocentric distances (20 − 100)h −1 kpc are found to give the best metallicity observational diagnostic to distinguish between BH models.