  How well can we infer host dark matter halo masses of individual galaxies?
Based on the halo occupation distribution (HOD) framework, we analytically
compute the number of neighboring galaxies within a cylinder of some redshift
interval and radius in transverse comoving distance. The result is used to
derive the conditional probability distribution function (PDF) of the host halo
mass of a galaxy, given the neighboring galaxy counts. We compare our analytic
results with those obtained using a realistic mock galaxy catalog, finding
reasonable agreements. We find the optimal cylinder radius to be $\sim
0.5-1h^{-1}{\rm Mpc}$ for the inference of halo masses. The PDF is generally
broad, and sometimes has two peaks at low- and high-mass regimes, because of
the effect of chance projection along the line-of-sight. Potential applications
and extensions of the new theoretical framework developed herein are also
discussed.
