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

A. Paulino-Afonso, D. Sobral, F. Buitrago, J. Afonso

Abstract
We present new results on the evolution of rest-frame blue/UV sizes and Sérsic indices of Hα-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 Hα-selected galaxies, to quantify the change on the measured structural parameters with redshift. We find typical sizes of 2–3 kpc and Sérsic indices of n∼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 ∼20 per cent bias on the estimate of the median Sérsic 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 re∝(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∼2, as they grow faster towards z∼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≲1.5, across the same period.

Keywords
galaxies: evolution – galaxies: star formation – galaxies: structure.

Monthly Notices of the Royal Astronomical Society
Volume 465, Issue 3, Page 17
2017 March

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Instituto de Astrofísica e Ciências do Espaço Universidade do Porto Faculdade de Ciências da Universidade de Lisboa
Fundação para a Ciência e a Tecnologia COMPETE 2020 PORTUGAL 2020 União Europeia