2,777 research outputs found
The Galaxy and its stellar halo: insights on their formation from a hybrid cosmological approach
We use a series of high-resolution simulations of a `Milky-Way' halo coupled
to semi-analytic methods to study the formation of our own Galaxy and of its
stellar halo. The physical properties of our model Milky Way, as well as the
age and metallicity distribution of stars in the different components, are in
relatively good agreement with observational measurements. Assuming that the
stellar halo builds up from the cores of the satellite galaxies that merged
with the Milky Way over its life-time, we are able to study the physical and
structural properties of this component. In agreement with previous work, we
find that the largest contribution to the stellar halo should come from a few
relatively massive (10^8 - 10^10 Msun) satellites, accreted at early times. Our
"stellar halo" does not exhibit any clear metallicity gradient, but higher
metallicity stars are more centrally concentrated than stars of lower
abundance. This indicates that the probability of observing low-metallicity
halo stars increases with distance from the Galactic centre. We find that the
proposed "dual" nature of the Galactic stellar halo can be explained in our
model as a result of a mass-metallicity relation imprinted in the building
blocks of this component.Comment: 20 pages, 14 figures. Minor revisions to match version accepted to
MNRAS. Version with high-resolution figures available at:
http://www.mpa-garching.mpg.de/~lucia/astro-ph/mw_delucia_rev.pd
The evolution of the colour-magnitude relation and of the star formation activity in galaxy clusters since z~0.8
We present recent results on the evolution of the colour-magnitude relation
and of the star formation activity in galaxy clusters since z~0.8. Results are
based on the ESO Distant Cluster Survey (EDisCS) - an ESO large programme aimed
at the study of cluster structure and cluster galaxy evolution over a
significant fraction of cosmic time - and are discussed in the framework of the
current standard paradigm of structure formation.Comment: 8 pages, 5 figure, to appear in ASP Conference Series (Proceedings of
the 1st Subaru International Conference "Panoramic Views of Galaxy Formation
and Evolution", held in Japan, 10-15 December 2007
Nature versus nurture: what regulates star formation in satellite galaxies?
We use our state-of-the-art Galaxy Evolution and Assembly (GAEA)
semi-analytic model to study how and on which time-scales star formation is
suppressed in satellite galaxies. Our fiducial stellar feedback model,
implementing strong stellar driven outflows, reproduces relatively well the
variations of passive fractions as a function of galaxy stellar mass and halo
mass measured in the local Universe, as well as the `quenching' time-scales
inferred from the data. We show that the same level of agreement can be
obtained by using an alternative stellar feedback scheme featuring lower
ejection rates at high redshift, and modifying the treatment for hot gas
stripping. This scheme over-predicts the number densities of low to
intermediate mass galaxies. In addition, a good agreement with the observed
passive fractions can be obtained only by assuming that cooling can continue on
satellites, at the rate predicted considering halo properties at infall, even
after their parent dark matter substructure is stripped below the resolution of
the simulation. For our fiducial model, the better agreement with the observed
passive fractions can be ascribed to: (i) a larger cold gas fraction of
satellites at the time of accretion, and (ii) a lower rate of gas reheating by
supernovae explosions and stellar winds with respect to previous versions of
our model. Our results suggest that the abundance of passive galaxies with
stellar mass larger than ~10^10 Msun is primarily determined by the
self-regulation between star formation and stellar feedback, with environmental
processes playing a more marginal role.Comment: 11 pages, 6 figures, 1 appendix. Accepted for publication in MNRA
What Regulates Galaxy Evolution? Open Questions in Our Understanding of Galaxy Formation and Evolution
In April 2013, a workshop entitled "What Regulates Galaxy Evolution" was held
at the Lorentz Center. The aim of the workshop was to bring together the
observational and theoretical community working on galaxy evolution, and to
discuss in depth of the current problems in the subject, as well as to review
the most recent observational constraints. A total of 42 astrophysicists
attended the workshop. A significant fraction of the time was devoted to
identifying the most interesting "open questions" in the field, and to discuss
how progress can be made. This review discusses the four questions (one for
each day of the workshop) that, in our opinion, were the focus of the most
intense debate. We present each question in its context, and close with a
discussion of what future directions should be pursued in order to make
progress on these problems.Comment: 36 pages, 6 Figures, submitted to New Astronomy Review
Galaxy assembly, stellar feedback and metal enrichment: the view from the GAEA model
One major problem of current theoretical models of galaxy formation is given
by their inability to reproduce the apparently `anti-hierarchical' evolution of
galaxy assembly: massive galaxies appear to be in place since , while
a significant increase of the number densities of low mass galaxies is measured
with decreasing redshift. In this work, we perform a systematic analysis of the
influence of different stellar feedback schemes, carried out in the framework
of GAEA, a new semi-analytic model of galaxy formation. It includes a
self-consistent treatment for the timings of gas, metal and energy recycling,
and for the chemical yields. We show this to be crucial to use observational
measurements of the metallicity as independent and powerful constraints for the
adopted feedback schemes. The observed trends can be reproduced in the
framework of either a strong ejective or preventive feedback model. In the
former case, the gas ejection rate must decrease significantly with cosmic time
(as suggested by parametrizations of the cosmological `FIRE' simulations).
Irrespective of the feedback scheme used, our successful models always imply
that up to 60-70 per cent of the baryons reside in an `ejected' reservoir and
are unavailable for cooling at high redshift. The same schemes predict physical
properties of model galaxies (e.g. gas content, colour, age, and metallicity)
that are in much better agreement with observational data than our fiducial
model. The overall fraction of passive galaxies is found to be primarily
determined by internal physical processes, with environment playing a secondary
role.Comment: 30 pages, 19 figures, accepted for publication by MNRAS; note that
corresponding new galaxy catalogues (FIRE model) will soon be made publicly
available at http://gavo.mpa-garching.mpg.de/Millennium
Strong stellar-driven outflows shape the evolution of galaxies at cosmic dawn
We study galaxy mass assembly and cosmic star formation rate (SFR) at
high-redshift (z4), by comparing data from multiwavelength surveys with
predictions from the GAlaxy Evolution and Assembly (GAEA) model. GAEA
implements a stellar feedback scheme partially based on cosmological
hydrodynamical simulations, that features strong stellar driven outflows and
mass-dependent timescale for the re-accretion of ejected gas. In previous work,
we have shown that this scheme is able to correctly reproduce the evolution of
the galaxy stellar mass function (GSMF) up to . We contrast model
predictions with both rest-frame Ultra-Violet (UV) and optical luminosity
functions (LF), which are mostly sensible to the SFR and stellar mass,
respectively. We show that GAEA is able to reproduce the shape and redshift
evolution of both sets of LFs. We study the impact of dust on the predicted LFs
and we find that the required level of dust attenuation is in qualitative
agreement with recent estimates based on the UV continuum slope. The
consistency between data and model predictions holds for the redshift evolution
of the physical quantities well beyond the redshift range considered for the
calibration of the original model. In particular, we show that GAEA is able to
recover the evolution of the GSMF up to z7 and the cosmic SFR density up
to z10.Comment: 6 pages, 2 figures, accepted on ApJ Letter
How `heredity' and `environment' shape galaxy properties
In this review, I give a brief summary of galaxy evolution processes in
hierarchical cosmologies and of their relative importance at different masses,
times, and environments. I remind the reader of the processes that are commonly
included in modern semi-analytic models of galaxy formation, and I comment on
recent results and open issues.Comment: 8 pages, 4 figure, to appear in ASP Conference Series (Proceedings of
the "Cosmic Frontiers" conference held in Durham, 31st July - 4th August
2006
On the scatter in the relation between stellar mass and halo mass: random or halo formation time dependent?
The empirical HOD model of Wang et al. 2006 fits, by construction, both the
stellar mass function and correlation function of galaxies in the local
Universe. In contrast, the semi-analytical models of De Lucia & Blazoit 2007
(DLB07) and Guo et al. 2011 (Guo11), built on the same dark matter halo merger
trees than the empirical model, still have difficulties in reproducing these
observational data simultaneously. We compare the relations between the stellar
mass of galaxies and their host halo mass in the three models, and find that
they are different. When the relations are rescaled to have the same median
values and the same scatter as in Wang et al., the rescaled DLB07 model can fit
both the measured galaxy stellar mass function and the correlation function
measured in different galaxy stellar mass bins. In contrast, the rescaled Guo11
model still over-predicts the clustering of low-mass galaxies. This indicates
that the detail of how galaxies populate the scatter in the stellar mass --
halo mass relation does play an important role in determining the correlation
functions of galaxies. While the stellar mass of galaxies in the Wang et al.
model depends only on halo mass and is randomly distributed within the scatter,
galaxy stellar mass depends also on the halo formation time in semi-analytical
models. At fixed value of infall mass, galaxies that lie above the median
stellar mass -- halo mass relation reside in haloes that formed earlier, while
galaxies that lie below the median relation reside in haloes that formed later.
This effect is much stronger in Guo11 than in DLB07, which explains the
over-clustering of low mass galaxies in Guo11. Our results illustrate that the
assumption of random scatter in the relation between stellar and halo mass as
employed by current HOD and abundance matching models may be problematic in
case a significant assembly bias exists in the real Universe.Comment: 10 pages, 6 figures, published in MNRA
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