The mass profiles of dwarf galaxies from Dark Energy Survey lensing

Abstract

We present a novel approach to extracting dwarf galaxies from photometric data to measure their average halo mass profile with weak lensing. We characterize their stellar mass and redshift distributions with a spectroscopic calibration sample. By combining the similar to 5000deg(2) multiband photometry from the Dark Energy Survey and redshifts from the Satellites Around Galactic Analogs Survey with an unsupervised machine learning method, we select a low-mass galaxy sample spanning redshifts z<0.3 and divide it into three mass bins. From low to high median mass, the bins contain [146 420, 330 146, 275 028] galaxies and have median stellar masses of log(10)(M-*/M-circle dot)=[8.52(+0.57-0.76),9.02(+0.50-0.64),9.49(+0.50-0.58)] . We measure the stacked excess surface mass density profiles, Delta Sigma(R), of these galaxies using galaxy-galaxy lensing with a signal-to-noise ratio of [14, 23, 28]. Through a simulation-based forward-modelling approach, we fit the measurements to constrain the stellar-to-halo mass relation and find the median halo mass of these samples to be log(10)(M-halo/M-circle dot) = [10.67(+0.2-0.4), 11.01(+0.14-0.27), 11.40(+0.08-0.15)]. The cold dark matter profiles are consistent with NFW (Navarro, Frenk, and White) profiles over scales less than or similar to 0.15h(-1) Mpc. We find that similar to 20 per cent of the dwarf galaxy sample are satellites. This is the first measurement of the halo profiles and masses of such a comprehensive, low-mass galaxy sample. The techniques presented here pave the way for extracting and analysing even lower mass dwarf galaxies and for more finely splitting galaxies by their properties with future photometric and spectroscopic survey data.