Galaxy And Mass Assembly (GAMA): Gas fuelling of spiral galaxies in the local Universe II. - Direct measurement of the dependencies on redshift and host halo mass of stellar mass growth in central disc galaxies

We present a detailed analysis of the specific star formation rate-stellar mass (sSFR-M_*) of z ≤ 0.13 disc central galaxies using a morphologically selected mass-complete sample (M_* ≥ 10^9.5M_⊙). Considering samples of grouped and ungrouped galaxies, we find the sSFR-M_* relations of disc-dominated central galaxies to have no detectable dependence on host dark-matter halo (DMH) mass, even where weak-lensing measurements indicate a difference in halo mass of a factor ≳ 5.We further detect a gradual evolution of the sSFR-M_* relation of non-grouped (field) central disc galaxies with redshift, even over a Δ_z ≈ 0.04 (≈5 × 10⁸ yr) interval, while the scatter remains constant. This evolution is consistent with extrapolation of the 'main sequence of star-forming-galaxies' from previous literature that uses larger redshift baselines and coarser sampling. Taken together, our results present new constraints on the paradigm under which the SFR of galaxies is determined by a self-regulated balance between gas inflows and outflows, and consumption of gas by star formation in discs, with the inflow being determined by the product of the cosmological accretion rate and a fuelling efficiency - -M_b,haloζ. In particular, maintaining the paradigm requires -M_b,haloζ to be independent of themass M_halo of the host DMH. Furthermore, it requires the fuelling efficiency ζ to have a strong redshift dependence (∝(1 + z)^2.7 forM_* = 10^10.3M_⊙ over z = 0-0.13), even though no morphological transformation to spheroids can be invoked to explain this in our disc-dominated sample. The physical mechanisms capable of giving rise to such dependencies of ζ on M_halo and z for discs are unclear.