  Constraints on the number and luminosity of the sources of the cosmic
neutrinos detected by IceCube have been set by targeted searches for point
sources. We set complementary constraints by using the 2MASS Redshift Survey
(2MRS) catalogue, which maps the matter distribution of the local Universe.
Assuming that the distribution of the neutrino sources follows that of matter
we look for correlations between `warm' spots on the IceCube skymap and the
2MRS matter distribution. Through Monte Carlo simulations of the expected
number of neutrino multiplets and careful modelling of the detector performance
(including that of IceCube-Gen2) we demonstrate that sources with local density
exceeding $10^{-6} \, \text{Mpc}^{-3}$ and neutrino luminosity $L_{\nu}
\lesssim 10^{42} \, \text{erg} \, \text{s}^{-1}$ ($10^{41} \, \text{erg} \,
\text{s}^{-1}$) will be efficiently revealed by our method using IceCube
(IceCube-Gen2). At low luminosities such as will be probed by IceCube-Gen2, the
sensitivity of this analysis is superior to requiring statistically significant
direct observation of a point source.
