The evolution of black holes in cosmological simulations

We investigate the growth of black holes and their effects on the evolution of galaxies through cosmic time in the ΛCDM cosmology by using fully hydrodynamical simulations of structure formation. Gas accretion onto black holes is modelled and improved via a subgrid model that takes into account the circularisation and subsequent viscous transport of infalling material. We incorporate the black hole accretion model in hydrodynamical simulations of relatively small size. The model broadly matches the observed stellar mass fractions in haloes and reproduces the expected correlation between the stellar velocity dispersion and the black hole mass. The distribution of black hole accretion rates is also compatible with observations. Additionally, we use a state-of-the-art hydrodynamic simulation that is designed to produce a virtual Universe that closely matches the observed properties of galaxies such as the galaxy stellar mass function and the relation between the black hole mass and the stellar mass at the present day. The critical part to reproduce the galaxy stellar mass function is the subgrid models of AGN feedback and black hole growth that are based on the model investigated above. We find that the simulation reproduces the black hole mass function at the present day. We investigate the predicted relations between the black hole mass and the stellar mass and the black hole mass and the parent halo mass and their evolution through cosmic time. We find that there is no evolution in approximately the last 10 and a half Giga years (z < 2), while at early times the most massive galaxies were inhabited by more massive black holes. The evolution of these relations are different in large halos and small halos. This can be explained in terms of self-regulation. Black holes living in massive haloes (< 10^12 M ) today self-regulate their growth via AGN feedback that quenches black hole accretion rates and star formation, while the black holes in small haloes rapidly grow without affecting the growth of the galaxy. By looking at the relations between the gas properties and the parent halo mass, we compare the scatter of these relations to the ratio of cumulative accreted mass of black holes to halo mass. We speculate that there is a range of halos that frames the region where black holes start to grow by self-regulation. Finally, we explore the predicted evolution of the AGN luminosity functions in X-ray bands predicted in this simulation. We find remarkable agreement with observations. In addition, we find that the observed downsizing effect of AGNs is well reproduced in the simulation as a natural consequence of reproducing the AGN luminosity functions. We also explore AGN activity in different halos. We find that the massive haloes are inhabited by AGNs with low or non activity while low mass haloes are inhabited by AGNs with high activity that contribute to the hard X ray luminosity function across time

The rise and fall of bars in disc galaxies from z=1z=1 to z=0z=0. The role of the environment

We investigate the influence of the environment on the evolution of barred and unbarred disc galaxies with a mass >10^{10}\Msun from z=1 down to z=0, employing the TNG50 magnetic-hydrodynamical simulation. We find that 49% of z=1 disc galaxies undergoes a morphological transformation, transitioning into either a lenticular or spheroidal, while the other 51% retains the massive disc. The morphological alteration is mostly influenced by the environment. Lenticular and spheroidal galaxies tend to exist in denser environments and have more frequent mergers compared to disc galaxies. We find that over half of the barred galaxies (60.2%) retain the bar structure and have experienced fewer mergers compared to those galaxies that lose their bars (5.6%). These latter ones start with weaker and shorter bars at z=1 influenced by tidal interactions and are frequently observed in more populated areas. Additionally, our study reveals that less than 20% of unbarred galaxies will never develop a bar and exhibit the quietest merger history. Unbarred galaxies that experience bar formation after z=1 exhibit more frequent instances of merging events. Furthermore, tidal interactions with a close companion may account for bar formation in at least one-third of the cases. Our findings highlight that stable bars are prevalent in disc galaxies. Bar evolution may nonetheless be affected by the environment. Interactions with nearby companions or tidal forces caused by mergers have the capacity to disrupt the disc. This perturbance may materialise as the dissolution of the bar, the formation of a bar, or, in its most severe form, the complete destruction of the disc, resulting in morphological transformation. Bars that are weak and short at z=1 and undergo major or minor mergers may eventually dissolve, whereas unbarred galaxies that enter crowded environments or experience a merger may develop a bar.Comment: 20 pages, 18 Figures, accepted for publication in A&A with language corrections and updates in some Figure

Revealing the properties of void galaxies and their assembly using the EAGLE simulation

We explore the properties of central galaxies living in voids using the EAGLE cosmological hydrodynamic simulations. Based on the minimum void-centric distance, we define four galaxy samples: inner void, outer void, wall, and skeleton. We find that inner void galaxies with host halo masses $<10^{12}M_\odot$ have lower stellar mass and stellar mass fractions than those in denser environments, and the fraction of galaxies with star formation (SF) activity and atomic hydrogen (HI) gas decreases with increasing void-centric distance, in agreement with observations. To mitigate the influence of stellar (halo) mass, we compare inner void galaxies to subsamples of fixed stellar (halo) mass. Compared to denser environments, inner void galaxies with $M_{*}= 10^{[9.0-9.5]}M_\odot$ have comparable SF activity and HI gas fractions, but the lowest quenched galaxy fraction. Inner void galaxies with $M_{*}= 10^{[9.5-10.5]}M_\odot$ have the lowest HI gas fraction, the highest quenched fraction and the lowest gas metallicities. On the other hand, inner void galaxies with $M_{*}>10^{10.5}M_\odot$ have comparable SF activity and HI gas fractions to their analogues in denser environments. They retain the highest metallicity gas that might be linked to physical processes that act with lower efficiency in underdense regions, such as AGN feedback. Furthermore, inner void galaxies have the lowest fraction of positive gas-phase metallicity gradients, which are typically associated with external processes or feedback events, suggesting they have more quiet merger histories than galaxies in denser environments. Our findings shed light on how galaxies are influenced by their large-scale environment.Comment: 20 pages,16 figures, revised version with a discussion section and edition in the text. Accepted to MNRA

The evolution of the oxygen abundance gradients in star-forming galaxies in the EAGLE simulations

We analyse the evolution of the oxygen abundance gradient of star-forming galaxies with stellar mass M*≥10 9 M ⊙in the EAGLE simulation o v er the redshift range z = [0, 2.5]. We find that the median metallicity gradient of the simulated galaxies is close to zero at all z, whereas the scatter around the median increases with z. The metallicity gradients of individual galaxies can evolve from strong to weak and vice versa, since mostly low-metallicity gas accretes on to the galaxy, resulting in enhanced star formation and ejection of metal-enriched gas by energy feedback. Such episodes of enhanced accretion, mainly dominated by major mergers, are more common at higher z and hence contribute to increasing the diversity of gradients. For galaxies with ne gativ e metallicity gradients, we find a redshift evolution of ∼-0 . 03 de x kpc -1 /δz. A positiv e mass dependence is found at z ≤0.5, which becomes slightly stronger for higher redshifts and, mainly, for M*< 10 9 . 5 M ⊙. Only galaxies with ne gativ e metallicity gradients define a correlation with galaxy size, consistent with an inside-out formation scenario. Our findings suggest that major mergers and/or significant gas accretion can drive strong ne gativ e or positiv e metallicity gradients. The first ones are preferentially associated with disc-dominated galaxies, and the second ones with dispersion-dominated systems. The comparison with forthcoming observations at high redshift will allow a better understanding of the potential role of metallicity gradients as a chemical probe of galaxy formation.Fil: Tissera, Patricia Beatriz. Pontificia Universidad Católica de Chile; Chile. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Rosas Guevara, Yetli. Donostia International Physic Center (dipc);Fil: Sillero Ros, Guillermo Emanuel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; ArgentinaFil: Pedrosa, Susana Elizabeth. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Theuns, Tom. University Of Durham. Dep.of Physics; Reino UnidoFil: Bignone, Lucas Axel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentin

Supermassive black holes in cosmological simulations - II : the AGN population and predictions for upcoming X-ray missions

In large-scale hydrodynamical cosmological simulations, the fate of massive galaxies is mainly dictated by the modelling of feedback from active galactic nuclei (AGNs). The amount of energy released by AGN feedback is proportional to the mass that has been accreted on to the black holes (BHs), but the exact subgrid modelling of AGN feedback differs in all simulations. While modern simulations reliably produce populations of quiescent massive galaxies at z = 10(45) erg s(-1) (although this is sensitive to AGN variability), and leads to smaller fractions of AGN in massive galaxies than in the observations at zPeer reviewe

Dependence of the Star Formation Efficiency on the Parameters of Molecular Cloud Formation Simulations

We investigate the response of the star formation efficiency (SFE) to the main parameters of simulations of molecular cloud formation by the collision of warm diffuse medium (WNM) cylindrical streams, neglecting stellar feedback and magnetic fields. The parameters we vary are the Mach number of the inflow velocity of the streams, Msinf, the rms Mach number of the initial background turbulence in the WNM, and the total mass contained in the colliding gas streams, Minf. Because the SFE is a function of time, we define two estimators for it, the "absolute" SFE, measured at t = 25 Myr into the simulation's evolution (sfeabs), and the "relative" SFE, measured 5 Myr after the onset of star formation in each simulation (sferel). The latter is close to the "star formation rate per free-fall time" for gas at n = 100 cm^-3. We find that both estimators decrease with increasing Minf, although by no more than a factor of 2 as Msinf increases from 1.25 to 3.5. Increasing levels of background turbulence similarly reduce the SFE, because the turbulence disrupts the coherence of the colliding streams, fragmenting the cloud, and producing small-scale clumps scattered through the numerical box, which have low SFEs. Finally, the SFE is very sensitive to the mass of the inflows, with sferel decreasing from ~0.4 to ~0.04 as the the virial parameter in the colliding streams increases from ~0.15 to ~1.5. This trend is in partial agreement with the prediction by Krumholz & McKee (2005), since the latter lies within the same range as the observed efficiencies, but with a significantly shallower slope. We conclude that the observed variability of the SFE is a highly sensitive function of the parameters of the cloud formation process, and may be the cause of significant scatter in observational determinations.Comment: 19 pages, submitted to MNRA