225 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
Dark matter substructure and dwarf galactic satellites
A decade ago cosmological simulations of increasingly higher resolution were
used to demonstrate that virialized regions of Cold Dark Matter (CDM) halos are
filled with a multitude of dense, gravitationally-bound clumps. These dark
matter subhalos are central regions of halos that survived strong gravitational
tidal forces and dynamical friction during the hierarchical sequence of merging
and accretion via which the CDM halos form. Comparisons with observations
revealed that there is a glaring discrepancy between abundance of subhalos and
luminous satellites of the Milky Way and Andromeda as a function of their
circular velocity or bound mass within a fixed aperture. This large
discrepancy, which became known as the ``substructure'' or the ``missing
satellites'' problem, begs for an explanation. In this paper I review the
progress made during the last several years both in quantifying the problem and
in exploring possible scenarios in which it could be accommodated and explained
in the context of galaxy formation in the framework of the CDM paradigm of
structure formation. In particular, I show that the observed luminosity
function, radial distribution, and the remarkable similarity of the inner
density profiles of luminous satellites can be understood within hierarchical
CDM framework using a simple model in which efficiency of star formation
monotonically decreases with decreasing virial mass satellites had before their
accretion without any actual sharp galaxy formation threshold.Comment: invited review paper submitted to Advances in Astronomy, 25 pages, 14
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