Day 1289

Wednesday.


1707.05327
The size evolution of star-firing and quenched galaxies in the IllustrisTNG simulation
Genel, et al

Analyze scaling relations and evolution histories of galaxy sizes in the TNG100, part of the Illustris TNG simulations suite.  Observational qualitative trends of size with stellar mass, SFR and z are reproduced, and a quantitative comparison of projected r-band sizes at 0~<z<~2 shows agreement to better than 0.25 dex.  Follow populations of z=0 galaxies with a range of masses backwards in time along their main progenitor branches, separately for MS and quenched galaxies.  The main findings are as follows.  (i) At M*,z=0>1e9.5 Msun, the main progenitors evolve in different ways, with quenched galaxies hardly growing in median size before quenching, whereas MS  galaxies grow their median size continuously, thus opening a gap from the progenitors of quenched galaxies.  This is partly because the MS high-z progenitors of quenched z=0 galaxies are drawn from the lower end of the size distribution of the overall populations of MS high-z galaxies.  (ii)  Quenched galaxies with M*,z=0>1e9.5 Msun experience a steep size growth on the size-mass plane after their quenching time, but the size growth rate as a function of time is similar to that of MS galaxies.  Hence, the size gap is not closed by z=0.  (iii) At all masses but M*,z=0>1e11 Msun, most of the size (and mass) growth of quenched galaxies occurs while they are still on the MS, and the size variation among quenched galaxies is driven by different degrees of growth on the MS rather than after quenching.