Effects of binary stellar populations on direct collapse black hole formation

Abstract: The critical Lyman--Werner flux required for direct collapse blackholes (DCBH) formation, or J${crit}$, depends on the shape of the irradiating spectral energy distribution (SED). The SEDs employed thus far have been representative of {{realistic}} single stellar populations. We study the effect of binary stellar populations on the formation of DCBH, as a result of their contribution to the Lyman--Werner radiation field. Although binary populations with ages $>$ 10 Myr yield a larger LW photon output, we find that the corresponding values of J${crit}$ can be up to 100 times higher than single stellar populations. We attribute this to the shape of the binary SEDs as they produce a sub--critical rate of H$^-$ photodetaching 0.76 eV photons as compared to single stellar populations, reaffirming the role that H$^-$ plays in DCBH formation. This further corroborates the idea that DCBH formation is better understood in terms of a critical region in the H$_2$--H$^-$ photo--destruction rate parameter space, rather than a single value of LW flux.