227 research outputs found
Vast planes of satellites in a high resolution simulation of the Local Group: comparison to Andromeda
We search for vast planes of satellites (VPoS) in a high resolution
simulation of the Local Group performed by the CLUES project, which improves
significantly the resolution of former similar studies. We use a simple method
for detecting planar configurations of satellites, and validate it on the known
plane of M31. We implement a range of prescriptions for modelling the satellite
populations, roughly reproducing the variety of recipes used in the literature,
and investigate the occurence and properties of planar structures in these
populations. The structure of the simulated satellite systems is strongly
non-random and contains planes of satellites, predominantly co-rotating, with,
in some cases, sizes comparable to the plane observed in M31 by Ibata et al..
However the latter is slightly richer in satellites, slightly thinner and has
stronger co-rotation, which makes it stand out as overall more exceptional than
the simulated planes, when compared to a random population. Although the
simulated planes we find are generally dominated by one real structure, forming
its backbone, they are also partly fortuitous and are thus not kinematically
coherent structures as a whole. Provided that the simulated and observed planes
of satellites are indeed of the same nature, our results suggest that the VPoS
of M31 is not a coherent disc and that one third to one half of its satellites
must have large proper motions perpendicular to the plane
High resolution simulations of the reionization of an isolated Milky Way - M31 galaxy pair
We present the results of a set of numerical simulations aimed at studying
reionization at galactic scale. We use a high resolution simulation of the
formation of the Milky Way-M31 system to simulate the reionization of the local
group. The reionization calculation was performed with the post-processing
radiative transfer code ATON and the underlying cosmological simulation was
performed as part of the CLUES project. We vary the source models to bracket
the range of source properties used in the literature. We investigate the
structure and propagation of the galatic ionization fronts by a visual
examination of our reionization maps. Within the progenitors we find that
reionization is patchy, and proceeds locally inside out. The process becomes
patchier with decreasing source photon output. It is generally dominated by one
major HII region and 1-4 additional isolated smaller bubbles, which eventually
overlap. Higher emissivity results in faster and earlier local reionization. In
all models, the reionization of the Milky Way and M31 are similar in duration,
i.e. between 203 Myr and 22 Myr depending on the source model, placing their
zreion between 8.4 and 13.7. In all models except the most extreme, the MW and
M31 progenitors reionize internally, ignoring each other, despite being
relatively close to each other even during the epoch of reionization. Only in
the case of strong supernova feedback suppressing star formation in haloes less
massive than 10^9 M_sun, and using our highest emissivity, we find that the MW
is reionized by M31.Comment: Accepted for publication in ApJ. 14 pages, 4 figures, 1 tabl
Pinning down the ram-pressure-induced halt of star formation in the Virgo cluster spiral galaxy NGC 4388. A joint inversion of spectroscopic and photometric data
In a galaxy cluster, the evolution of spiral galaxies depends on their
cluster environment. Ram pressure due to the rapid motion of a spiral galaxy
within the hot intracluster medium removes the galaxy's interstellar medium
from the outer disk. Once the gas has left the disk, star formation stops. The
passive evolution of the stellar populations should be detectable in optical
spectroscopy and multi-wavelength photometry. The goal of our study is to
recover the stripping age of the Virgo spiral galaxy NGC 4388, i.e. the time
elapsed since the halt of star formation in the outer galactic disk using a
combined analysis of optical spectra and photometry. We performed VLT FORS2
long-slit spectroscopy of the inner star-forming and outer gas-free disk of NGC
4388. We developed a non-parametric inversion tool that allows us to
reconstruct the star formation history of a galaxy from spectroscopy and
photometry. The tool was tested on a series of mock data using Monte Carlo
simulations. The results from the non-parametric inversion were refined by
applying a parametric inversion method. The star formation history of the
unperturbed galactic disk is flat. The non-parametric method yields a rapid
decline of star formation < 200 Myr ago in the outer disk. The parametric
method is not able to distinguish between an instantaneous and a long-lasting
star formation truncation. The time since the star formation has dropped by a
factor of two from its pre-stripping value is 190 +- 30 Myr. We are able to
give a precise stripping age that is consistent with revised dynamical models.Comment: 12 pages, 10 figures, accepted for publication in A&
DUSTiER (DUST in the Epoch of Reionization): dusty galaxies in cosmological radiation-hydrodynamical simulations of the Epoch of Reionization with RAMSES-CUDATON
In recent years, interstellar dust has become a crucial topic in the study of
the high and very high redshift Universe. Evidence points to the existence of
high dust masses in massive star forming galaxies already during the Epoch of
Reionization, potentially affecting the escape of ionising photons into the
intergalactic medium. Moreover, correctly estimating dust extinction at UV
wavelengths is essential for precise ultra-violet luminosity function (UVLF)
prediction and interpretation. In this paper, we investigate the impact of dust
on the observed properties of high redshift galaxies, and cosmic reionization.
To this end, we couple a physical model for dust production to the fully
coupled radiation-hydrodynamics cosmological simulation code RAMSES-CUDATON,
and perform a , , simulation, that we call DUSTiER for DUST in
the Epoch of Reionization. It yields galaxies with dust masses and UV slopes
compatible with constraints at z . We find that extinction has a
dramatic impact on the bright end of the UVLF, even as early as , and
our dusty UVLFs are in better agreement with observations than dust-less UVLFs.
The fraction of obscured star formation rises up to 55% at , in
agreement with some of the latest results from ALMA. Finally, we find that dust
reduces the escape of ionising photons from galaxies more massive than (brighter than MAB1600) by >10%, and possibly up to
80-90% for our most massive galaxies. Nevertheless, we find that the ionising
escape fraction is first and foremost set by neutral Hydrogen in galaxies, as
the latter produces transmissions up to 100 times smaller than through dust
alone.Comment: submitted to MNRAS, 1st report received: under revision Have
partially addressed referee's concerns, namely that the model predicts high
dust masses and redder bright galaxies than expected, by discussing this
aspect around the relevant results. Work is being carried out to present a
clearer parameter exploration of the dust mode
II.5 Where to find the CoRoT data?
This book is dedicated to all the people interested in the CoRoT mission and the beautiful data that were delivered during its six year duration. Either amateurs, professional, young or senior researchers, they will find treasures not only at the time of this publication but also in the future twenty or thirty years. It presents the data in their final version, explains how they have been obtained, how to handle them, describes the tools necessary to understand them, and where to find them. It also highlights the most striking first results obtained up to now. CoRoT has opened several unexpected directions of research and certainly new ones still to be discovered
Mergers and Mass Accretion Rates in Galaxy Assembly: The Millennium Simulation Compared to Observations of z~2 Galaxies
Recent observations of UV-/optically selected, massive star forming galaxies
at z~2 indicate that the baryonic mass assembly and star formation history is
dominated by continuous rapid accretion of gas and internal secular evolution,
rather than by major mergers. We use the Millennium Simulation to build new
halo merger trees, and extract halo merger fractions and mass accretion rates.
We find that even for halos not undergoing major mergers the mass accretion
rates are plausibly sufficient to account for the high star formation rates
observed in z~2 disks. On the other hand, the fraction of major mergers in the
Millennium Simulation is sufficient to account for the number counts of
submillimeter galaxies (SMGs), in support of observational evidence that these
are major mergers. When following the fate of these two populations in the
Millennium Simulation to z=0, we find that subsequent mergers are not frequent
enough to convert all z~2 turbulent disks into elliptical galaxies at z=0.
Similarly, mergers cannot transform the compact SMGs/red sequence galaxies at
z~2 into observed massive cluster ellipticals at z=0. We argue therefore, that
secular and internal evolution must play an important role in the evolution of
a significant fraction of z~2 UV-/optically and submillimeter selected galaxy
populations.Comment: 5 pages, 4 figures, Accepted for publication in Ap
Impact of the Specific Mutation in KRAS Codon 12 Mutated Tumors on Treatment Efficacy in Patients with Metastatic Colorectal Cancer Receiving Cetuximab-Based First-Line Therapy: A Pooled Analysis of Three Trials
Purpose: This study investigated the impact of specific mutations in codon 12 of the Kirsten-ras (KRAS) gene on treatment efficacy in patients with metastatic colorectal cancer (mCRC). Patients: Overall, 119 patients bearing a KRAS mutation in codon 12 were evaluated. All patients received cetuximab-based first-line chemotherapy within the Central European Cooperative Oncology Group (CECOG), AIO KRK-0104 or AIO KRK-0306 trials. Results: Patients with KRAS codon 12 mutant mCRC showed a broad range of outcome when treated with cetuximab-based first-line regimens. Patients with tumors bearing a KRAS p.G12D mutation showed a strong trend to a more favorable outcome compared to other mutations (overall survival 23.3 vs. 14-18 months; hazard ratio 0.66, range 0.43-1.03). An interaction model illustrated that KRAS p.G12C was associated with unfavorable outcome when treated with oxaliplatin plus cetuximab. Conclusion: The present analysis suggests that KRAS codon 12 mutation may not represent a homogeneous entity in mCRC when treated with cetuximab-based first-line therapy. Copyright (C) 2012 S. Karger AG, Base
Differential stellar population models: how to reliably measure [Fe/H] and [alpha/Fe] in galaxies
We present differential stellar population models, which allow improved
determinations of the ages, iron and alpha-element abundances of old stellar
populations from spectral fitting. These new models are calibrated at solar
abundances using the predictions from classical, semi-empirical stellar
population models. We then use the predictive power of fully synthetic models
to compute predictions for different [Fe/H] and [alpha/Fe]. We show that these
new differential models provide remarkably accurate fits to the integrated
optical spectra of the bulge globular clusters NGC6528 and NGC6553, and that
the inferred [Fe/H] and [alpha/Fe] agree with values derived elsewhere from
stellar photometry and spectroscopy. The analysis of a small sample of SDSS
early-type galaxies further confirms that our alpha-enhanced models provide a
better fit to the spectra of massive ellipticals than the solar-scaled ones.
Our approach opens new opportunities for precision measurements of abundance
ratios in galaxies.Comment: 5 pages, 5 figures, MNRAS in pres
The inhomogeneous reionization times of present-day galaxies
Today's galaxies experienced cosmic reionization at different times in different locations. For the first time, reionization (50% ionized) redshifts, z R , at the location of their progenitors are derived from new, fully coupled radiation-hydrodynamics simulation of galaxy formation and reionization at z > 6, matched to N-body simulation to z = 0. Constrained initial conditions were chosen to form the well-known structures of the local universe, including the Local Group and Virgo, in a (91 Mpc)3 volume large enough to model both global and local reionization. Reionization simulation CoDa I-AMR, by CPU-GPU code EMMA, used (2048)3 particles and (2048)3 initial cells, adaptively refined, while N-body simulation CoDa I-DM2048, by Gadget2, used (2048)3 particles, to find reionization times for all galaxies at z = 0 with masses M(z = 0) ≥ 108 M ⊙. Galaxies with reionized earlier than the universe as a whole, by up to ~500 Myr, with significant scatter. For Milky Way–like galaxies, z R ranged from 8 to 15. Galaxies with typically reionized as late or later than globally averaged 50% reionization at , in neighborhoods where reionization was completed by external radiation. The spread of reionization times within galaxies was sometimes as large as the galaxy-to-galaxy scatter. The Milky Way and M31 reionized earlier than global reionization but later than typical for their mass, neither dominated by external radiation. Their most-massive progenitors at z > 6 had z R =9.8 (MW) and 11 (M31), while their total masses had z R = 8.2 (both)
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