The structural and size evolution of star-forming galaxies over the last 11 Gyr

We present new results on the evolution of rest- frame blue/ UV sizes and Sersic indices of H alpha- selected star- forming galaxies over the last 11 Gyr. We investigate how the perceived evolution can be affected by a range of biases and systematics such as cosmological dimming and resolution effects. We use GALFIT and an artificial redshifting technique, which includes the luminosity evolution of Ha- selected galaxies, to quantify the change on the measured structural parameters with redshift. We find typical sizes of 2- 3 kpc and Sersic indices of II alpha 1.2, close to pure exponential discs all the way from z = 2.23 to z = 0.4. At z = 0, we find typical sizes of 4- 5 kpc. Our results show that, when using GALFIT, cosmological dimming has a negligible impact on the derived effective radius for galaxies with < 10 kpc, but we find an similar to 20 per cent bias on the estimate of the median Sersic indices, rendering galaxies more disc- like. Star- forming galaxies have grown on average by a factor of 2- 3 in the last 11 Gyr with r(e) alpha ( 1 + z)(-0.75). By exploring the evolution of the stellar mass- size relation, we find evidence for a stronger size evolution of the most massive star-forming galaxies since z similar to 2, as they grow faster towards z similar to 0 when compared to the lower stellar mass counterparts. As we are tracing the rest- frame blue/ UV, we are likely witnessing the growth of discs where star formation is ongoing in galaxies while their profiles remain close to exponential discs, n less than or similar to 1.5, across the same period.