Feedback-regulated star formation on galactic and cosmological scales

A central problem in
galaxy formation is to understand why star formation is so inefficient. Within
individual galaxies, gas is converted into stars at a rate two orders of
magnitude slower than unimpeded gravitational collapse predicts, a fact
embodied in the low normalization of the observed Kennicutt-Schmidt (K-S)
relationship between star formation rate surface density and gas surface
density. Star formation in galaxies is also globally inefficient in the sense
that the stellar mass in dark matter halos is a small fraction of the universal
baryon fraction. I will show that these two facts can be explained by the
self-regulation of star formation by feedback from massive stars. Within
galaxies, stellar feedback drives turbulence that supports the interstellar
medium against collapse and the K-S law is set by the low strength of gravity
relative to stellar feedback. The energy input from the same stellar feedback
processes drive powerful galactic outflows that remove most of the gas accreted
from the intergalactic medium before it has time to turn into stars. Using
cosmological hydrodynamical simulations from our FIRE project ("Feedback
In Realistic Environments"), I will show that gas removal by star
formation-driven galactic winds successfully explains the observed galaxy
stellar mass function, at least for galaxies less massive than the Milky Way.
Feedback from massive black holes may be required to explain the quenching of
more massive galaxies. Motivated by recent observations, I will discuss the
physics of galactic winds driven by active galactic nuclei.

Event Type: 
Seminar
Collection/Series: 
Scientific Area(s): 
Event Date: 
Mardi, Novembre 5, 2013 - 11:00 to 12:30
Location: 
Space Room