268 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
Observing the circumgalactic medium of simulated galaxies through synthetic absorption spectra
We explore the multiphase structure of the circumgalactic medium (CGM) probed
by synthetic spectra through a cosmological zoom-in galaxy formation
simulation. We employ a Bayesian method for modelling a combination of
absorption lines to derive physical properties of absorbers with a formal
treatment of detections, including saturated systems, and non-detections in a
uniform manner. We find that in the lines of sight passing through localized
density structures, absorption lines of low, intermediate and high ions are
present in the spectrum and overlap in velocity space. Low, intermediate and
high ions can be combined to derive the mass-weighted properties of a
density-varying peak, although the ions are not co-spatial within the
structure. By contrast, lines of sight that go through the hot halo only
exhibit detectable HI and high ions. In such lines of sight, the absorption
lines are typically broad due to the complex velocity fields across the entire
halo. We show that the derived gas density, temperature, and metallicity match
closely the corresponding HI mass-weighted averages along the LOS. We also show
that when the data quality allows, our Bayesian technique allows one to recover
the underlying physical properties of LOS by incorporating both detections and
non-detections. It is especially useful to include non-detections, of species
such as NV or NeVIII, when the number of detections of strong absorbers, such
as HI and OVI, is smaller than the number of model parameters (density,
temperature, and metallicity).Comment: Accepted for publication in MNRA
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