Stellar mass functions of galaxies, discs and spheroids at z ~ 0.1

We present the stellar mass functions (SMFs) and mass densities of galaxies, and their spheroid and disc components in the local (z ~ 0.1) Universe over the range 8.9 ≤ log(M/M_⊙) ≤ 12 from spheroid+disc decompositions and corresponding stellar masses of a sample of over 600 000 galaxies in the Sloan Digital Sky Survey Data Release Seven spectroscopic sample. The galaxy SMF is well represented by a single Schechter function (M^* = 11.116 ± 0.011, α = -1.145 ± 0.008), though with a hint of a steeper faint end slope. The corresponding stellar mass densities are (2.670 ± 0.110), (1.687 ± 0.063) and (0.910 ± 0.029)× 10⁸M_⊙Mpc^-3 for galaxies, spheroids and discs, respectively. We identify a crossover stellar mass of log(M/M_⊙) = 10.3 ± 0.030 at which the spheroid and disc SMFs are equal. Relative contributions of four distinct spheroid/disc dominated sub-populations to the overall galaxy SMF are also presented. The mean disc-to-spheroid stellar mass ratio shows a five-fold disc dominance at the low-mass end, decreasing monotonically with a corresponding increase in the spheroidal fraction till the two are equal at a galaxy stellar mass, log(M/M_⊙) = 10.479 ± 0.013; the dominance of spheroids then grows with increasing stellar mass. The relative numbers of composite disc and spheroid-dominated galaxies show peaks in their distributions, perhaps indicative of a preferred galaxy mass. Our characterization of the low-redshift galaxy population provides stringent constraints for numerical simulations to reproduce.