Search for isolated Galactic Centre stellar mass black holes in the IR and sub-mm range

We investigate a possibility to find an accreting isolated black hole (IBH) with mass $1-100~\mathrm{M}_{\odot}$ within Central Galactic Molecular Zone (CMZ) in the submillimetre and IR spectral range with help of planned space observatories James Webb Space Telescope (JWST) and Millimetron (MM). We assume the spherical mode of accretion. We develop the simplest possible quantitative model of the formation of radiation spectrum in this range due to synchrotron emission and show that it fully agrees with the more complicated model of Ipser and Price 1982 for expected values of accretion rate. If a substantial fraction of LIGO events was caused by merger of primordial black holes, the JWST would be able to find them provided that there is a cusp in distribution of dark matter in the Galaxy and that the accretion efficiency parameter $\lambda $ defined as the ratio of accretion rate onto IBH to its Bondi-Hoyle-Lyttleton value is larger than $\sim 10^{-2}$. A comparable amount of IBHs is also predicted by recent models of their formation due to stellar evolution. MM capabilities are hampered by the effect of confusion due to distant submillimetre galaxies, but it can also be used for such purposes if the confusion effect is properly dealt with. In case of efficient accretion with $\lambda \sim 1$, both instruments could detect IBHs even when their number densities are as low as $10^{-6}~\mathrm{pc}^{-3}$.
Comment: 29 pages, 12 figures, accepted to MNRAS