83 research outputs found
Low-metallicity stellar halo populations as tracers of dark matter haloes
We analyse the density profiles of the stellar halo populations in eight
Milky-Way mass galaxies, simulated within the -Cold Dark Matter
scenario. We find that accreted stars can be well-fitted by an Einasto profile,
as well as any subsample defined according to metallicity. We detect a clear
correlation between the Einasto fitting parameters of the low-metallicity
stellar populations and those of the dark matter haloes. The correlations for
stars with [Fe/H] allow us to predict the shape of the dark matter
profiles within residuals of per cent, in case the contribution from
in situ stars remains small. Using Einasto parameters estimated for the stellar
halo of the Milky Way and assuming the later formed with significant
contributions from accreted low-mass satellite, our simulations predict and kpc for its dark matter profile. These values,
combined with observed estimations of the local dark matter density, yield an
enclosed dark matter mass at kpc in the range M, in agreement with recent observational results. These
findings suggest that low-metallicity stellar haloes could store relevant
information on the DM haloes. Forthcoming observations would help us to further
constrain our models and predictions.Comment: 5 pages,3 figures, MNRAS Letters accepte
Towards a more realistic population of bright spiral galaxies in cosmological simulations
We present an update to the multiphase SPH galaxy formation code by
Scannapieco et al. We include a more elaborate treatment of the production of
metals, cooling rates based on individual element abundances, and a scheme for
the turbulent diffusion of metals. Our SN feedback model now transfers energy
to the ISM in kinetic and thermal form, and we include a prescription for the
effects of radiation pressure from massive young stars on the ISM. We calibrate
our new code on the well studied Aquarius haloes and then use it to simulate a
sample of 16 galaxies with halo masses between 1x10^11 and 3x10^12 M_sun. In
general, the stellar masses of the sample agree well with the stellar mass to
halo mass relation inferred from abundance matching techniques for redshifts
z=0-4. There is however a tendency to overproduce stars at z>4 and to
underproduce them at z<0.5 in the least massive haloes. Overly high SFRs at z<1
for the most massive haloes are likely connected to the lack of AGN feedback in
our model. The simulated sample also shows reasonable agreement with observed
star formation rates, sizes, gas fractions and gas-phase metallicities at
z=0-3. Remaining discrepancies can be connected to deviations from predictions
for star formation histories from abundance matching. At z=0, the model
galaxies show realistic morphologies, stellar surface density profiles,
circular velocity curves and stellar metallicities, but overly flat metallicity
gradients. 15 out of 16 of our galaxies contain disk components with kinematic
disk fraction ranging between 15 and 65 %. The disk fraction depends on the
time of the last destructive merger or misaligned infall event. Considering the
remaining shortcomings of our simulations we conclude that even higher
kinematic disk fractions may be possible for LambdaCDM haloes with quiet merger
histories, such as the Aquarius haloes.Comment: 26 pages, 20 figures, accepted for publication in MNRA
Clues for the origin of the fundamental metallicity relations. I: The hierarchical building up of the structure
We analyse the evolutionary history of galaxies formed in a hierarchical
scenario consistent with the concordance -CDM model focusing on the
study of the relation between their chemical and dynamical properties. Our
simulations consistently describe the formation of the structure and its
chemical enrichment within a cosmological context. Our results indicate that
the luminosity-metallicity (LZR) and the stellar mass-metallicity (MZR)
relations are naturally generated in a hierarchical scenario. Both relations
are found to evolve with redshift. In the case of the MZR, the estimated
evolution is weaker than that deduced from observational works by approximately
0.10 dex. We also determine a characteristic stellar mass, , which segregates the simulated galaxy population
into two distinctive groups and which remains unchanged since , with a
very weak evolution of its metallicity content. The value and role played by
is consistent with the characteristic mass estimated from the SDSS galaxy
survey by Kauffmann et al. (2004). Our findings suggest that systems with
stellar masses smaller than are responsible for the evolution of this
relation at least from . Larger systems are stellar dominated and
have formed more than 50 per cent of their stars at , showing very
weak evolution since this epoch. We also found bimodal metallicity and age
distributions from , which reflects the existence of two different
galaxy populations. Although SN feedback may affect the properties of galaxies
and help to shape the MZR, it is unlikely that it will significantly modify
since, from this stellar mass is found in systems with circular
velocities larger than 100 \kms.Comment: 17 pages, 13 figures. Minor changes to match accepted version.
Accepted October 3 MNRA
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