Massive early-type galaxies follow a tight relation between the mass of their central supermassive black hole (MBH) and their stellar mass (M⋆). The origin of observed positive outliers from this... Show moreMassive early-type galaxies follow a tight relation between the mass of their central supermassive black hole (MBH) and their stellar mass (M⋆). The origin of observed positive outliers from this relation with extremely high MBH (> 109M⊙) remains un- clear. We present a study of such outliers in the Hydrangea/C-EAGLE cosmological hydrodynamical simulations, designed to enable the study of high-mass galaxy forma- tion and evolution in cluster environments. We find 69 MBH(M⋆) outliers at z = 0, defined as those with MBH > 107M⊙ and MBH/M⋆ > 0.01. This paper focusses on a sample of 5 extreme outliers, that have been selected based on their MBH and M⋆ values, which are comparable to the most recent estimates of observed positive out- liers. This sample of 5 outliers, classified as “Black hole monster galaxies” (BMGs), was traced back in time to study their origin and evolution. In agreement with the results of previous simulations for lower-mass MBH(M⋆) outliers, we find that these galaxies became outliers due to a combination of their early formation times and tidal stripping. For BMGs with MBH > 109M⊙, major mergers (with a stellar mass ratio of μ > 0.25) at early times (z > 2) precede the rapid growth of their supermassive BHs. Furthermore, the scatter in the relation between MBH and stellar velocity dispersion, σ, correlates positively with the scatter in [Mg/Fe](σ). This indicates that the alpha enhancement of these galaxies, which is closely related to their star formation history, is related to the growth of their central BHs. Show less
Lagos, C. del P.; Schaye, J.; Bahé, Y.; Sande, J. van de; Kay, S.T.; Barnes, D.; ... ; Vecchia, C. Dalla 2018
