5,491 research outputs found
On the interplay between star formation and feedback in galaxy formation simulations
We investigate the star formation-feedback cycle in cosmological galaxy
formation simulations, focusing on progenitors of Milky Way (MW)-sized
galaxies. We find that in order to reproduce key properties of the MW
progenitors, such as semi-empirically derived star formation histories and the
shape of rotation curves, our implementation of star formation and stellar
feedback requires 1) a combination of local early momentum feedback via
radiation pressure and stellar winds and subsequent efficient supernovae
feedback, and 2) efficacy of feedback that results in self-regulation of the
global star formation rate on kiloparsec scales. We show that such
feedback-driven self-regulation is achieved globally for a local star formation
efficiency per free fall time of . Although this
value is larger that the value usually inferred
from the Kennicutt-Schmidt (KS) relation, we show that it is consistent with
direct observational estimates of in molecular clouds.
Moreover, we show that simulations with local efficiency of reproduce the global observed KS relation. Such simulations
also reproduce the cosmic star formation history of the Milky Way sized
galaxies and satisfy a number of other observational constraints. Conversely,
we find that simulations that a priori assume an inefficient mode of star
formation, instead of achieving it via stellar feedback regulation, fail to
produce sufficiently vigorous outflows and do not reproduce observations. This
illustrates the importance of understanding the complex interplay between star
formation and feedback and the detailed processes that contribute to the
feedback-regulated formation of galaxies.Comment: 20 pages, 13 figures, accepted for publication in Ap
Simulations of disk galaxies with cosmic ray driven galactic winds
We present results from high-resolution hydrodynamic simulations of isolated
SMC- and Milky Way-sized galaxies that include a model for feedback from
galactic cosmic rays (CRs). We find that CRs are naturally able to drive winds
with mass loading factors of up to ~10 in dwarf systems. The scaling of the
mass loading factor with circular velocity between the two simulated systems is
consistent with \propto v_c^{1-2} required to reproduce the faint end of the
galaxy luminosity function. In addition, simulations with CR feedback reproduce
both the normalization and the slope of the observed trend of wind velocity
with galaxy circular velocity. We find that winds in simulations with CR
feedback exhibit qualitatively different properties compared to SN driven
winds, where most of the acceleration happens violently in situ near star
forming sites. In contrast, the CR-driven winds are accelerated gently by the
large-scale pressure gradient established by CRs diffusing from the
star-forming galaxy disk out into the halo. The CR-driven winds also exhibit
much cooler temperatures and, in the SMC-sized system, warm (T~10^4 K) gas
dominates the outflow. The prevalence of warm gas in such outflows may provide
a clue as to the origin of ubiquitous warm gas in the gaseous halos of galaxies
detected via absorption lines in quasar spectra.Comment: ApJL accepted. Replaced with accepted version. Minor revision in
response to referee comment
Towards a complete accounting of energy and momentum from stellar feedback in galaxy formation simulations
Stellar feedback plays a key role in galaxy formation by regulating star
formation, driving interstellar turbulence and generating galactic scale
outflows. Although modern simulations of galaxy formation can resolve scales of
10-100 pc, star formation and feedback operate on smaller, "subgrid" scales.
Great care should therefore be taken in order to properly account for the
effect of feedback on global galaxy evolution. We investigate the momentum and
energy budget of feedback during different stages of stellar evolution, and
study its impact on the interstellar medium using simulations of local star
forming regions and galactic disks at the resolution affordable in modern
cosmological zoom-in simulations. In particular, we present a novel subgrid
model for the momentum injection due to radiation pressure and stellar winds
from massive stars during early, pre-supernova evolutionary stages of young
star clusters. Early injection of momentum acts to clear out dense gas in star
forming regions, hence limiting star formation. The reduced gas density
mitigates radiative losses of thermal feedback energy from subsequent supernova
explosions, leading to an increased overall efficiency of stellar feedback. The
detailed impact of stellar feedback depends sensitively on the implementation
and choice of parameters. Somewhat encouragingly, we find that implementations
in which feedback is efficient lead to approximate self-regulation of global
star formation efficiency. We compare simulation results using our feedback
implementation to other phenomenological feedback methods, where thermal
feedback energy is allowed to dissipate over time scales longer than the formal
gas cooling time. We find that simulations with maximal momentum injection
suppress star formation to a similar degree as is found in simulations adopting
adiabatic thermal feedback.Comment: ApJ submitted. For a high-resolution version of the paper, see
http://kicp.uchicago.edu/~agertz
El proceso kafkiano a la ciencia y la razón de p. K. Feyerabend
Cinquenes Jornades de Foment de la Investigació de la FCHS (Any 1999-2000
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