44 research outputs found
Protoclusters at z=5.7: A view from the MultiDark galaxies
Protoclusters, which will yield galaxy clusters at lower redshift, can
provide valuable information on the formation of galaxy clusters. However,
identifying progenitors of galaxy clusters in observations is not an easy task,
especially at high redshift. Different priors have been used to estimate the
overdense regions that are thought to mark the locations of protoclusters. In
this paper, we use mimicked Ly-emitting galaxies at to identify
protoclusters in the MultiDark galaxies, which are populated by applying three
different semi-analytic models to the 1 MultiDark Planck2
simulation. To compare with observational results, we extend the criterion 1 (a
Ly luminosity limited sample), to criterion 2 (a match to the observed
mean galaxy number density). To further statistically study the finding
efficiency of this method, we enlarge the identified protocluster sample
(criterion 3) to about 3500 at and study their final mass distribution.
The number of overdense regions and their selection probability depends on the
semi-analytic models and strongly on the three selection criteria (partly by
design). The protoclusters identified with criterion 1 are associated with a
typical final cluster mass of which is in
agreement with the prediction (within ) of an observed massive
protocluster at . Identifying more protoclusters allows us to
investigate the efficiency of this method, which is more suitable for
identifying the most massive clusters: completeness () drops
rapidly with decreasing halo mass. We further find that it is hard to have a
high purity () and completeness simultaneously.Comment: 10 pages, 4 figures, 2 tables, version matched to the publication in
MNRA
The phase-diagram of cosmological baryons
We investigate the behaviour of cosmological baryons at low redshifts
after reionization through analytic means. In particular, we study the
density-temperature phase-diagram which describes the history of the gas. We
show how the location of the matter in this diagram expresses the
various constraints implied by usual hierarchical scenarios. This yields robust
model-independent results which agree with numerical simulations. The IGM is
seen to be formed via two phases: a ``cool'' photo-ionized component and a
``warm'' component governed by shock-heating. We also briefly describe how the
remainder of the matter is distributed over galaxies, groups and clusters. We
recover the fraction of matter and the spatial clustering computed by numerical
simulations. We also check that the soft X-ray background due to the ``warm''
IGM component is consistent with observations. We find in the present universe
a baryon fraction of 7% in hot gas, 24% in the warm IGM, 38% in the cool IGM,
9% within star-like objects and, as a still un-observed component, 22% of dark
baryons associated with collapsed structures, with a relative uncertainty no
larger than 30% on these numbers.Comment: 17 pages, accepted by A&A. This final version contains a more
detailed discussion of the physics of the IGM and of the properties of the
Warm IG
Mid-IR heterogeneous silicon photonics
In this paper we discuss silicon-based photonic integrated circuit technology for applications beyond the telecommunication wavelength range. Silicon-on-insulator and germanium-on-silicon passive waveguide circuits are described, as well as the integration of III-V semiconductors, IV-VI colloidal nanoparticle films and GeSn alloys on these circuits for increasing the functionality. The strong nonlinearity of silicon combined with the low nonlinear absorption in the mid-infrared is exploited to generate picosecond pulse based supercontinuum sources and optical parametric oscillators that can be used as spectroscopic sensor sources
The three hundred project: The stellar and gas profiles
Using the catalogues of galaxy clusters from The Three Hundred project, modelled with both hydrodynamic simulations (GADGET-X and GADGET-MUSIC), and semi-analytical models (SAMs), we study the scatter and self-similarity of the profiles and distributions of the baryonic components of the clusters: the stellar and gas mass, metallicity, the stellar age, gas temperature, and the (specific) star formation rate. Through comparisons with observational results, we find that the shape and the scatter of the gas density profiles matches well the observed trends including the reduced scatter at large radii which is a signature of self-similarity suggested in previous studies. One of our simulated sets, GADGET-X, reproduces well the shape of the observed temperature profile, while GADGET-MUSIC has a higher and flatter profile in the cluster centre and a lower and steeper profile at large radii. The gas metallicity profiles from both simulation sets, despite following the observed trend, have a relatively lower normalization
Quintessence with a constant equation of state in hyperbolic universes
Quintessence models leading to a constant equation of state are studied in
hyperbolic universes. General properties of the quintessence potentials V(phi)
are discussed, and for some special cases also the exact analytic expressions
for these potentials are derived. It is shown that the observed angular power
spectrum of the cosmic microwave background (CMB) is in excellent agreement
with some of the quintessence models even in cases with negative curvature. It
is emphasized that due to a (w_phi, Omega_phi, Omega_c)-degeneracy a universe
with negative spatial curvature cannot be excluded.Comment: 15 pages, a version with figures in color can be obtained at
http://www.physik.uni-ulm.de/theo/qc/ulm-tp/tp02-13.ps.g
Dynamics and constraints of the dissipative Liouville cosmology
In this article we investigate the properties of the FLRW flat cosmological
models in which the cosmic expansion of the Universe is affected by a dilaton
dark energy (Liouville scenario). In particular, we perform a detailed study of
these models in the light of the latest cosmological data, which serves to
illustrate the phenomenological viability of the new dark energy paradigm as a
serious alternative to the traditional scalar field approaches. By performing a
joint likelihood analysis of the recent supernovae type Ia data (SNIa), the
differential ages of passively evolving galaxies, and the Baryonic Acoustic
Oscillations (BAOs) traced by the Sloan Digital Sky Survey (SDSS), we put tight
constraints on the main cosmological parameters. Furthermore, we study the
linear matter fluctuation field of the above Liouville cosmological models. In
this framework, we compare the observed growth rate of clustering measured with
those predicted by the current Liouville models. Performing a chi^2 statistical
test we show that the Liouville cosmological model provides growth rates that
match sufficiently well with the observed growth rate. To further test the
viability of the models under study, we use the Press-Schechter formalism to
derive their expected redshift distribution of cluster-size halos that will be
provided by future X-ray and Sunyaev-Zeldovich cluster surveys. We find that
the Hubble flow differences between the Liouville and the LambdaCDM models
provide a significantly different halo redshift distribution, suggesting that
the models can be observationally distinguished.Comment: 15 pages, 4 figures, 4 tables, matches version to appear in
Astroparticle Physic