2023MNRAS.519..871Z

We present a photometric halo mass estimation technique for local galaxies that enables us to establish the stellar mass-halo mass (SMHM) relation down to stellar masses of 10⁵ M_⊙. We find no detectable differences among the SMHM relations of four local galaxy clusters or between the cluster and field relations and we find agreement with extrapolations of previous SMHM relations derived using abundance matching approaches. We fit a power law to our empirical SMHM relation and find that for adopted NFW dark matter profiles and for M_* < 10⁹ M_⊙, the halo mass is M_h = 10^10.35 ± 0.02^(M_*/10⁸ M_⊙)^0.63 ± 0.02^. The normalization of this relation is susceptible to systematic modelling errors that depend on the adopted dark matter potential and the quoted uncertainties refer to the uncertainties in the median relation. For galaxies with M_* < 10⁹ M_⊙ that satisfy our selection criteria, the scatter about the fit in M_h, including uncertainties arising from our methodology, is 0.3 dex. Finally, we place lower luminosity Local Group galaxies on the SMHM relationship using the same technique, extending it to M_* ∼ 10³ M_⊙ and suggest that some of these galaxies show evidence for additional mass interior to the effective radius beyond that provided by the standard dark matter profile. If this mass is in the form of a central black hole, the black hole masses are in the range of intermediate mass black holes, 10^(5.7 ± 0.6)^ M_⊙, which corresponds to masses of a few percent of M_h, well above values extrapolated from the relationships describing more massive galaxies.