Multi-flavour SMBH seeding and evolution in cosmological environments

Abstract

We study the genesis, environment and growth of super-massive black hole (SMBH) seeds from different formation channels, from PopIII remnants to massive seeds, modeled within the L-Galaxies semi-analytic code. We run the model on the merger trees of the Millennium-II simulation (MR-II), as its high halo-mass resolution (M vir,res ∼ 10 7 M h −1 ) allows to study in a relatively large cosmological volume (L box = 100 Mpc h −1 ) the evolution of atomiccooling halos (T vir 10 4 K) where intermediate-mass and heavy seeds are expected to form. We track the formation of these seeds according to the background and the local variations of the chemical enrichment and the UV-flux produced by star formation. Not being able to resolve the first mini-halos (T vir ∼10 3 K), we account for the formation of PopIII remnants in a sub-grid fashion, using the results of the GQd model. We find that the descendants of light seeds numerically dominate among the population of SMBHs at all masses and z. The much rarer intermediate-mass and heavy seeds form in dense environments where close neighbors provide the required UV illumination. We also include the formation of heavy seeds in the mergers of gas-rich massive galaxies, who are also very rare in the MR-II volume. We then track the evolution through gas accretion and mergers of this multi-flavour population of black hole seeds down to the local Universe. Our model produces a z=0 population of SMBHs whose statistical properties meet current constraints. In the dwarf-mass regime, where observations are still scarce, we predict that the scaling relation between BH and stellar mass is flatter than in the high-mass range. We also find that the BH occupation fraction highly depends on the seeding efficiency. Finally, a fraction of BHs hosted in dwarf galaxies at z = 0 never grow since their formation at z > 6. This supports the idea that some local low-mass systems might harbour central compact objects which are remnant of the high-z BH-formation processes.

The Black Hole Mass Function across Cosmic Time. II. Heavy Seeds and (Super)Massive Black Holes

“…In Figure 11, we illustrate the overall BH mass function from the stellar to the (super)massive regime over more than 10 For reference, in Figure 11, we have also illustrated as colored boxes the mass and density ranges expected from other classic seed formation channels (taken from Volonteri et al 2021; see their Figure 1): remnants of the first massive Population III stars (red box), direct collapse of primordial gas clouds (green box), and runaway stellar or BH mergers in compact primeval star clusters (yellow box). These distributions mainly originate in (proto)galaxies at z  10 and are then progressively eroded (but not substantially refurnished) at lower redshifts, when the seeds merge together or accrete gas and become more massive BHs (e.g., Mayer & Bonoli 2019;Volonteri et al 2021;Spinoso et al 2022;Trinca et al 2022). This is at variance with our framework, where heavy seeds are continuously produced across cosmic time by the migration and merging of stellar mass BHs associated with star formation in galaxies.…”

“…1): remnants of the first massive pop-III stars (red box), direct collapse of primordial gas clouds (green box), and runaway stellar or BH mergers in compact primeval star clusters (yellow box). These distributions mainly originates in (proto)galaxies at z 10, and are then progressively eroded (but not substantially refurnished) at lower redshifts, when the seeds merge together or accrete gas and become more massive BHs (e.g., Mayer & Bonoli 2019;Volonteri et al 2021;Trinca et al 2022;Spinoso et al 2022). This is at variance with our framework, where heavy seeds are continuously produced across cosmic times by the migration and merging of stellar-mass BHs associated to star formation in galaxies.…”

“…On the other hand, moving toward lower redshifts the mass function in the (super)massive range increases because relic BHs grown by disk accretion accumulate, while the number of intermediate mass BHs diminishes since the dynamical friction process becomes less efficient and the overall production of stellar mass BHs also lowers (following the progressive decline in the amount of star-formation within galaxies). This is at the origin of the discontinuity (or gap; see Trinca et al 2022 andSpinoso et al 2022 for a similar behavior) between the intermediate and (super)massive mass function around M • 10 6 M ; it is pleasing that this transition occurs at around the typical value usually considered to separate intermediate from supermassive BHs.…”

Massive black hole binaries in LISA: multimessenger prospects and electromagnetic counterparts

“…Finally, the actual distribution of observed MBHBs might arise from a combination of the three astrophysical models we adopted in this study (see for example [121,122]). For simplicity, here we did not considered mixed astrophysical formation models.…”

Galaxy fields of LISA massive black hole mergers in a simulated Universe

“…On the other hand, some theoretical works have made attempts to suppress the large excess of faint AGNs seen in most of the SAMs and hydrodynamical simulations (see e.g Hirschmann et al 2014;Griffin et al 2019;Habouzit et al 2022). For instance, invoking empirical relations for obscuring accreting black holes or varying the efficiency of the seeding process could be plausible mechanisms (see e.g Degraf et al 2010;Fanidakis et al 2012;DeGraf & Sijacki 2020;Spinoso et al 2022). Nevertheless, no clear answer has been proposed yet and further investigations are needed.…”