Galaxy and Mass Assembly (GAMA): the stellar mass budget of galaxy spheroids and discs

We build on a recent photometric decomposition analysis of 7506 Galaxy and Mass Assembly (GAMA) survey galaxies to derive stellar mass function fits to individual spheroid and disc component populations down to a lower mass limit of log(M_*/M_⊙) = 8. We find that the spheroid/disc mass distributions for individual galaxy morphological types are well described by single Schechter function forms. We derive estimates of the total stellar mass densities in spheroids (ρ_spheroid = 1.24 ± 0.49 × 10⁸ M_⊙ Mpc ^-3h_0.7) and discs (ρ_disc = 1.20 ± 0.45 × 10⁸ M_⊙ Mpc ^-3h_0.7), which translates to approximately 50 per cent of the local stellar mass density in spheroids and 48 per cent in discs. The remaining stellar mass is found in the dwarf `little blue spheroid' class, which is not obviously similar in structure to either classical spheroid or disc populations. We also examine the variation of component mass ratios across galaxy mass and group halo mass regimes, finding the transition from spheroid to disc mass dominance occurs near galaxy stellar mass ∼10¹¹ M_⊙ and group halo mass ∼10^12.5 M_⊙h^-1. We further quantify the variation in spheroid-to-total mass ratio with group halo mass for central and satellite populations as well as the radial variation of this ratio within groups.