Galaxy And Mass Assembly (GAMA): The galaxy stellar mass function to z = 0.1 from the r-band selected equatorial regions

We derive the low-redshift galaxy stellar mass function (GSMF), inclusive of dust corrections, for the equatorial Galaxy And Mass Assembly (GAMA) data set covering 180 deg². We construct the mass function using a density-corrected maximum volume method, using masses corrected for the impact of optically thick and thin dust. We explore the galactic bivariate brightness plane (M_*-μ), demonstrating that surface brightness effects do not systematically bias our mass function measurement above 10^7.5 M_⊙. The galaxy distribution in the M-μ plane appears well bounded, indicating that no substantial population of massive but diffuse or highly compact galaxies are systematically missed due to the GAMA selection criteria. The GSMF is fitted with a double Schechter function, with M* = 10^{10.78±0.01±0.20} M_⊙, φ₁* = (2.93 ± 0.40) × 10^-3 h₇₀³ Mpc^-3, α1 =-0.62 ± 0.03 ± 0.15, φ₂* = (0.63 ± 0.10) × 10^-3 h₇₀³ Mpc^-3 and α2 =-1.50 ± 0.01 ± 0.15. We find the equivalent faint end slope as previously estimated using the GAMA-I sample, although we find a higher value of M*. Using the full GAMA-II sample, we are able to fit the mass function to masses as low as 10^7.5 M_⊙, and assess limits to 10^6.5 M_⊙. Combining GAMA-II with data from G10-COSMOS, we are able to comment qualitatively on the shape of the GSMF down to masses as low as 10⁶ M_⊙. Beyond the well-known upturn seen in the GSMF at 10^9.5, the distribution appears to maintain a single power-law slope from 10⁹ to 10^6.5. We calculate the stellar mass density parameter given our best-estimate GSMF, finding Ω_* = 1.66_-0.23^+0.24 ± 0.97 h ₇₀^-1 × 10^-3, inclusive of random and systematic uncertainties.