Day 1018

Monday.


1512.01235
Breathing FIRE: How stellar feedback drives radial migration, rapid size fluctuations, and population gradients in low-mass galaxies
El-Badry, Wentzel, Geht, HOkins, Keres, Chan, Faucher-Giguère

Examine the effects of stellar feedback and bursty SF on low-mass galaxies (M*=2e6-5e10 Msun) using Feedback in Realistic Environments (FIRE) simulations.  Investigate the impact on the stalls component: kinematics, radial migration, size evolution, and population gradients.  Feedback-driven outflows-inflows drive significant radial stellar migration over both short and long timescales via two processes: (1) outflowing/infalling gas can remain star fomring, producing young stars that migrate ~1 kpc and within their first 100 Myr, and (2) gas outflows/inflows drive strong fluctuations in a the global potential, transferring energy to all stars.  These processes produce several dramatic effects.  First, galaxies' effective radii can fluctuate by factors of >2 over ~200 Myr, and these rapid size fluctuations can account for much of the observed scatter in radius at fixes M*. Second, the cumulative effects of many outflow/infall episodes steadily heat stellar orbits, causing old stars to migrate outward most strongly.  This age dependent radial migration mixes -- and even inverts---intrinsic age and metallicity gradients.  Thus, the galactic-archaeology approach of calculating radial  star-formation histories from stellar populations at z=0 can be severely biased.  These effects are strongest at M*~1e7-9.6 Msun, the same regime where feedback most efficiently cores galaxies.  Thus, detailed measurements of stellar kinematics in low-mass galaxies can strongly constrain feedback models and test baryonic solutions to small-scale problems in LCDM.