Photometric mass estimation and the stellar mass-halo mass relation for low mass galaxies

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 10(5) M-circle dot. 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-* < 10(9) M-circle dot, the halo mass is M-h = 10(10.35 +/- 0.02)(M-*/10(8) M-circle dot)(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-* < 10(9) M-circle dot 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-* similar to 10(3) M-circle dot 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-circle dot, which corresponds to masses of a few percent of M-h, well above values extrapolated from the relationships describing more massive galaxies.

Automated summary

We propose a technique for estimating the mass of dark matter halos in local galaxies based on photometric measurements, allowing us to establish the relationship between stellar mass and halo mass down to stellar masses of 10^(5) M. We find no significant differences among the relationships in four local galaxy clusters or between the clusters and field galaxies, and our results agree with previous studies using abundance matching methods. By fitting a power law to our empirical relationship, we determine that for stellar masses less than 10^(9) M, the halo mass is M_h = 10^(10.35 +/- 0.02)(M_* / 10^(8) M)(0.63 +/- 0.02). However, this relationship is susceptible to systematic modeling errors and the uncertainties quoted refer to the uncertainties in the median relationship. The scatter about the fit in halo mass, including uncertainties from our methodology, is 0.3 dex for galaxies that meet our selection criteria and have stellar masses less than 10^(9) M. Additionally, we apply the same technique to lower luminosity galaxies in the Local Group and find evidence for additional mass beyond the effective radius that is not accounted for by the standard dark matter profile. If this mass is in the form of a central black hole, their masses are in the range of intermediate mass black holes, around 10^((5.7 +/- 0.6)) M, corresponding to a few percent of the halo mass and higher than extrapolated values for more massive galaxies.