A full chemical network treatment of supermassive black hole seed formation from dark matter annihilation or decay

Abstract

The recent discoveries of high-redshift quasars at $z\sim6-10.1$ present a challenge to conventional supermassive black hole (SMBH) formation scenarios: their central SMBHs are too large to have grown from early stellar remnants, even under efficient super-Eddington accretion. An alternative approach is the direct collapse of primordial, dust- and metal-free gas clouds into black hole seeds as early as $z\sim20$. To prevent fragmentation from highly efficient molecular hydrogen cooling and allow such a collapse, a strong flux of UV photons is required to photodissociate molecular hydrogen, suppressing star formation. We investigate whether the decay or annihilation of dark matter with masses below $\sim200$ eV can produce sufficient UV radiation, both from the cosmological background and within early dark matter halos. Using thermal simulations of a one-zone primordial gas cloud model with the Grackle chemistry and cooling library, we map the resulting gas behavior across a range of dark matter lifetimes, cross sections, and masses. From this, we determine regions of parameter space where direct collapse into an SMBH is possible and the corresponding maximum halo mass required.