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 disk central galaxies using a morphologically selected mass-complete sample (M* ≥ 109.5M☉). Considering samples of grouped and ungrouped galaxies, we find the sSFR - M* relations of disk-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 disk galaxies with redshift, even over a ∆z ≈ 0.04 (≈5 . 108yr) 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 disks, with the inflow being determined by the product of the cosmological accretion rate and a fuelling-efficiency - \dot{M}_{b,halo}ζ. In particular, maintaining the paradigm requires \dot{M}_{b,halo}ζ to be independent of the mass Mhalo of the host DMH. Furthermore, it requires the fuelling-efficiency ζ to have a strong redshift dependence (∝(1 + z)2.7 for M* = 1010.3M☉ over z = 0 - 0.13), even though no morphological transformation to spheroids can be invoked to explain this in our disk-dominated sample. The physical mechanisms capable of giving rise to such dependencies of ζ on Mhalo and z for disks are unclear.