tokens: Figure 8. The dependence of dimensionless critical accretion rate on IBHs dimensionless mass m M /(10M ). Solid, dashed, and dotted curves correspond to JWST detection limit, that of MM without the confusion effect being taken into account, and that of MM with this effect being accounted, respectively. Figure 9. The dependence of the parameter on m M /(10M ). Curves of different styles describe the same cases as in Fig. 8 . Figure 10. Same as Fig. 9 , but now the dependence of parameter eff is shown. Figure 11. The minimal number of black holes within CMZ needed for observations with JWST and MM, for fixed values of the efficiency parameter , as a function of mass. Solid, dashed, and dotted curves corresponding to observations with JWST and MM without and with the confusion limit being taken into account. Curves with progressively larger values of N bh for a given value of m correspond to progressively smaller values of . The accretion rate given by expression ( 1 ) should be smaller than its critical value for 1. This requirement sets a limit of the possibility of observations of IBHs by a given instrument and for a given value of the density of the interstellar medium, IBH mass, and velocity. In order to compare ( 1 ) with , we express the accretion rate given by equation ( 1 ) in terms of our characteristic unit: , set c s 0 in equation ( 1 ), substitute there our chosen value of density of interstellar medium 3.34 10 22 gcm 3 and assume that a typical IBH velocity 225kms 1 . We obtain where . To begin with, let us consider a black hole travelling at the typical velocity and set in equation( 17 ). In this case from the requirement that for 1, we get lower limits on black hole masses, M crit , available for observations. For larger black hole masses, the condition gives a lower limit on the efficiency parameter , which is shown in Fig. 9 . One can see from this figure that JWST and MM without taking into account the confusion effect could be able to observe IBHs with masses larger than M crit 30M , while allowing for the confusion effect MM is able to detect IBHs only when M 90M , respectively. The range of available values of is rather limited to 0.1 even for the largest considered black hole mass 100M when the confusion effect is neglected and 0.8 in the opposite case. That should be relatively large may be a problem for observations since some works suggest significantly smaller values, see e.g. Igumenshchev Narayan ( 2002 ). On the other hand, assuming that high accretion efficiency is sustained and taking into account that the available volume of CMZ 10 6 pc 3 , it could be possible to observe IBHs with number density as small as 10 6 pc 3 . Available values of and M crit can be smaller in a situation when there are many IBHs within CMZ, with their number N bh 1 and, accordingly, their number density 10 6 pc 3 . In this case, assuming the Maxwellian statistics of distribution of IBHs over velocities we can estimate the number of IBHs
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