Stellar mass dependence of galaxy size–dark matter halo radius relation probed by Subaru-HSC survey weak lensing measurements

Abstract

ABSTRACT We investigate the stellar mass dependence of the galaxy size–dark matter halo radius relation for low-redshift galaxies using weak gravitational lensing measurements. Our sample consists of ∼38 000 galaxies more massive than $10^{8}\, {\rm M}_{\odot }\, h^{-2}$ and within z < 0.3 drawn from the overlap of Galaxy And Mass Assembly survey data release 4 and HSC-SSP PDR2. We divide our sample into a number of stellar mass bins and measure stacked weak lensing signals. We model the signals using a conditional stellar mass function to infer the stellar mass–halo mass relation. We fit a single Sérsic model to HSC i-band images of our galaxies and obtain their three-dimensional half-light radii. We use these measurements to construct a median galaxy size–mass relation. We then combine these relations to infer the galaxy size–halo radius relation. We confirm that this relation appears linear, given the statistical errors, i.e. the ratio of galaxy size to halo radius remains constant over two orders of magnitudes in stellar mass above $\sim 10^{9} \, {\rm M}_{\odot }\, h^{-2}$. Extrapolating the stellar mass–halo mass relation below this limit, we see an indication of a decreasing galaxy size–halo radius ratio with the decline in stellar mass. At stellar mass $\sim 10^{8} \, {\rm M}_{\odot }\, h^{-2}$, the ratio becomes 30 per cent smaller than its value in linear regime. The possible existence of a such trend in dwarf galaxy sectors calls for either modification in models employing a constant fraction of halo angular momentum transferred to explain sizes of dwarfs or else points towards our lack of knowledge about dark matter haloes of low-mass galaxies.