Massive black hole remnants of the first stars - I. Abundance in present-day galactic haloes

Abstract

We investigate the possibility that present-day galaxies and their dark matter haloes contain a population of massive black holes (MBHs) that form by hierarchical merging of the black hole remnants of the first stars in the Universe. Some of the MBHs may be large enough or close enough to the centre of the galactic host that they merge within a Hubble time. We estimate to what extent this process could contribute to the mass of the supermassive black holes (SMBHs) observed in galactic centres today. The relation between SMBH and galactic bulge mass in our model displays the same slope as that found in observations. Many MBHs will not reach the centre of the host halo, however, but continue to orbit within it. In doing so MBHs may remain associated with remnants of the satellite halo systems of which they were previously a part. Using a semi-analytical approach that explicitly accounts for dynamical friction, tidal disruption and encounters with galactic discs, we follow the hierarchical merging of MBH systems and their subsequent dynamical evolution inside the respective host haloes. We predict the mass and abundance of MBHs in present-day galactic haloes, and also estimate the MBH mass accretion rates as well as bolometric luminosities for two accretion scenarios. MBHs that have not undergone recent merging will retain associated dark matter cusps that were enhanced by black hole accretion growth, and may be possible sources of gamma-rays via neutralino annihilations.

GRAVITATIONAL WAVES AND STALLED SATELLITES FROM MASSIVE GALAXY MERGERS ATz⩽ 1

“…However, the possibility of "stalled" mergers, where a smaller satellite black hole resides in the outer regions of a massive host galaxy, is an interesting candidate as a model for ULXs. Indeed, several authors have studied the dynamics of stalled mergers and their viability as ULX sources (Islam et al 2003(Islam et al , 2004a(Islam et al , 2004b(Islam et al , 2004cVolonteri & Perna 2005). Given the rarity of very massive galaxies, the probability of a merger with a comparable-mass galaxy is small.…”

Intermediate-mass Black Holes and Dark Matter at the Galactic Center

“…If indeed all merging substructures, to be envisaged for example as protoglobular clusters in typical bulge formation models or more generally, protodwarf galaxies, contain IMBHs, then not only does this provide a natural pathway for forming the central nuclear star cluster (NSC) and SMBH along with the bulge and stellar halo in the Milky Way Galaxy (MWG; Antonini et al 2015), but also a robust prediction: there should be a large population of massive BHs that failed to merge (Islam et al 2004;Rashkov & Madau 2014).…”

“…Hence the IMBH occupation number, allowing for a duty cycle, must be significantly higher, by at least an order of magnitude. Simulations of formation of SMBH by mergers of IMBHs suggest that Ω IMBH ∼ 10 −3 Ω baryon (Islam et al 2004;Rashkov & Madau 2014 The idea that PBHs could be 1% or more of DM has been revived by the aLIGO detection of four confirmed binary merging BHs of mass 10-30 M , although the predicted mass fraction of PBHs required is modeldependent, ranging from ∼100% (Bird et al 2016) to ∼1% (Sasaki et al 2016;. Observations, most notably from gravitational microlensing (Alcock et al 2001), dwarf galaxy heating (Brandt 2016) and CMB distortions (Ali-Haïmoud & Kamionkowski 2017), favor the lower range.…”

GLAST Sensitivity to Point Sources of Dark Matter Annihilation

“…In the first one, IMBHs form in rare, overdense regions at high redshift, z ∼ 20, as remnants of Population III stars, and have a characteristic mass-scale of a few 10 2 M ⊙ [46] (the formation of mild mini-spikes around these objects was also discussed in Ref. [47,48,49]). In this scenario, these black holes serve as the seeds for the growth of super-massive black holes found in galactic spheroids [50].…”