196 research outputs found
The impact of binary-star yields on the spectra of galaxies
One of the complexities in modelling integrated spectra of stellar populations is the effect of interacting binary stars besides Type Ia supernovae (SNeIa). These include common envelope systems, cataclysmic variables, novae, and are usually ignored in models predicting the chemistry and spectral absorption line strengths in galaxies. In this paper, predictions of chemical yields from populations of single and binary stars are incorporated into a galactic chemical evolution model to explore the significance of the effects of these other binary yields. Effects on spectral line strengths from different progenitor channels of SNeIa are also explored. Small systematic effects are found when the yields from binaries, other than SNeIa, are included, for a given star formation history. These effects are, at present, within the observational uncertainties on the line strengths. More serious differences can arise in considering different types of SNIa models, their rates and contributions
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
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
Cosmic Variance and the Inhomogeneous UV Luminosity Function of Galaxies During Reionization
When the first galaxies formed and starlight escaped into the intergalactic
medium to reionize it, galaxy formation and reionization were both highly
inhomogeneous in time and space, and fully-coupled by mutual feedback. To show
how this imprinted the UV luminosity function (UVLF) of reionization-era
galaxies, we use our large-scale, radiation-hydrodynamics simulation CoDa II to
derive the time- and space-varying halo mass function and UVLF, from
-15. That UVLF correlates strongly with local reionization redshift:
earlier-reionizing regions have UVLFs that are higher, more extended to
brighter magnitudes, and flatter at the faint end than later-reionizing regions
observed at the same . In general, as a region reionizes, the faint-end
slope of its local UVLF flattens, and, by (when reionization ended), the
global UVLF, too, exhibits a flattened faint-end slope, `rolling-over' at
. CoDa II's UVLF is broadly consistent with
cluster-lensed galaxy observations of the Hubble Frontier Fields at -8,
including the faint end, except for the faintest data point at , based on
one galaxy at . According to CoDa II, the probability of
observing the latter is . However, the effective volume searched at
this magnitude is very small, and is thus subject to significant cosmic
variance. We find that previous methods adopted to calculate the uncertainty
due to cosmic variance underestimated it on such small scales by a factor of
2-4, primarily by underestimating the variance in halo abundance when the
sample volume is small.Comment: 16 pages, 16 figures, accepted by MNRAS 07/20/23, comments welcom
The Evolution of Central Group Galaxies in Hydrodynamical Simulations
We trace the evolution of central galaxies in three ~10^13 M_sun galaxy
groups simulated at high resolution in cosmological hydrodynamical simulations.
The evolution in the group potential leads, at z=0, to central galaxies that
are massive, gas-poor early-type systems supported by stellar velocity
dispersion resembling either elliptical or S0 galaxies. Their z~2-2.5 main
progenitors are massive M* ~ 3-10 x 10^10 M_sun, star forming (20-60 M_sun/yr)
galaxies which host substantial reservoirs of cold gas (~5 x 10^9 M_sun) in
extended gas disks. Our simulations thus show that star forming galaxies
observed at z~2 are likely the main progenitors of central galaxies in galaxy
groups at z=0. Their central stellar densities stay approximately constant from
z~1.5 down to z=0. Instead, the galaxies grow inside-out, by acquiring a
stellar envelope outside the innermost ~2 kpc. Consequently the density within
the effective radius decreases by up to two orders of magnitude. Both major and
minor mergers contribute to most of the mass accreted outside the effective
radius and thus drive the evolution of the half-mass radii. In one of the three
simulated groups the short central cooling time leads to a dramatic
rejuvenation of the central group galaxy at z<1, affecting its morphology,
kinematics and colors. This episode is eventually terminated by a group-group
merger. Our simulations demonstrate that, in galaxy groups, the interplay
between halo mass assembly, galaxy merging and gas accretion has a substantial
influence on the star formation histories and z=0 morphologies of central
galaxies.[Abridged]Comment: 28 pages, 23 figures, 9 tables, accepted to APJ (revised to match
accepted version
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