264 research outputs found
NIHAO XIX: How supernova feedback shapes the galaxy baryon cycle
We have used the NIHAO simulations to explore how supernovae (SNe) affect
star formation in galaxies. We find that SN feedback operates on all scales
from the interstellar medium (ISM) to several virial radii. SNe regulate star
formation by preventing condensation of HI into H and by moving cold
neutral gas to the hot HII phase. The first effect explains why the cold
neutral gas in dwarf galaxies forms stars inefficiently. The second maintains
the hot ISM of massive galaxies (HII vents out at lower masses). At , the outflow rate follows the relation:
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to of the gas expelled from galaxies escapes from the halo
(ejective feedback) but outflows are dominated by cold swept-up gas, most of
which falls back onto the galaxy on a Gyr timescale. This `fountain
feedback' reduces the masses of galaxies by a factor of two to four, since gas
spends half to three quarter of its time in the fountain. Less than of
the ejected gas mixes with the hot circumgalactic medium and this gas is
usually not reaccreted. On scales as large as , galactic winds
divert the incoming gas from cosmic filaments and prevent if from accreting
onto galaxies (pre-emptive feedback). This process is the main reason for the
low baryon content of ultradwarves.Comment: Submitted for publication in MNRA
Concentration, Spin and Shape of Dark Matter Haloes as a Function of the Cosmological Model: WMAP1, WMAP3 and WMAP5 results
We investigate the effects of changes in the cosmological parameters between
the WMAP 1st, 3rd, and 5th year results on the structure of dark matter haloes.
We use a set of simulations that cover 5 decades in halo mass ranging from the
scales of dwarf galaxies (V_c ~30 km/s) to clusters of galaxies (V_c ~ 1000
km/s). We find that the concentration mass relation is a power law in all three
cosmologies. However the slope is shallower and the zero point is lower moving
from WMAP1 to WMAP5 to WMAP3. For haloes of mass log(M_200/Msun) = 10, 12, and
14 the differences in the concentration parameter between WMAP1 and WMAP3 are a
factor of 1.55, 1.41, and 1.29, respectively. As we show, this brings the
central densities of dark matter haloes in good agreement with the central
densities of dwarf and low surface brightness galaxies inferred from their
rotation curves, for both the WMAP3 and WMAP5 cosmologies. We also show that
none of the existing toy models for the concentration-mass relation can
reproduce our simulation results over the entire range of masses probed. In
particular, the model of Bullock et al (B01) fails at the higher mass end (M >
1e13 Msun), while the NFW model of Navarro, Frenk & White (1997) fails
dramatically at the low mass end (M < 1e12 Msun). We present a new model, based
on a simple modification of that of B01, which reproduces the
concentration-mass relations in our simulations over the entire range of masses
probed (1e10 Msun < M < 1e15 Msun). Haloes in the WMAP3 cosmology (at a fixed
mass) are more flatted compared to the WMAP1 cosmology, with a medium to long
axis ration reduced by ~10 %. Finally, we show that the distribution of halo
spin parameters is the same for all three cosmologies.Comment: 16 pages, 16 figures, references updated, minor changes. Accepted for
publication on MNRAS. WMAP5 simulations available upon reques
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