Metallicity gradients in small and nearby spiral galaxies
  Spectra of HII regions obtained with Gemini/GMOS are used to derive the
radial metallicity gradients of four small, low-mass spiral galaxies. The
analysis of the outer disk of one of them, NGC 1058, uncovers the
characteristic flattening found in similar extended disk galaxies. After
combining these data with published long-slit observations of nearby spiral
galaxies, no evidence for a dependence of the disk scale length-normalized
metallicity gradients with stellar mass is found, down to log(M*/Msun) ~ 8.5.
The abundance gradients derived from these observations are compared to
predictions from recent cosmological simulations of galaxy evolution, finding
that in several cases the simulations fail to reproduce the mean steepening of
the gradients, expressed in dex/kpc, with decreasing stellar mass for
present-day galaxies, or do not extend to sufficiently small stellar masses for
a meaningful comparison. The mean steepening of the abundance gradients (in
dex/kpc) with decreasing disk scale length is in qualitative agreement with
predictions from the inside-out model of Boissier & Prantzos, although the
predicted slopes are systematically steeper than observed. This indicates the
necessity of including processes such as outflows and radial mixing in similar
models of galactic chemical evolution. Published spatially resolved metallicity
and photometric data of dwarf irregular galaxies suggest that significant, but
transitory, metallicity gradients can develop for systems that have experienced
recent (t < 100 Myr) enhanced star formation in their inner disks.
