36 research outputs found
Quantum correlations between two distant cavity QED systems coupled by a mechanical resonator
Achieving quantum correlations between two distant systems is a desirable
feature for quantum networking. In this work, we study a system composed of two
quantum emitter-cavity subsystems spatially separated. A mechanical resonator
couples to either both quantum emitters or both cavities leading to quantum
correlations between both subsystems such as non-local light-matter dressed
states and cavity-cavity normal mode splitting. These indirect couplings can be
explained by an effective Hamiltonian for large energy detuning between the
mechanical resonator and the atoms/cavities. Moreover, it is found optimal
conditions for the physical parameters of the system in order to maximize the
entanglement of such phonon-mediated couplings
Halo based reconstruction of the cosmic mass density field
We present the implementation of a halo based method for the reconstruction
of the cosmic mass density field. The method employs the mass density
distribution of dark matter haloes and its environments computed from
cosmological N-body simulations and convolves it with a halo catalog to
reconstruct the dark matter density field determined by the distribution of
haloes. We applied the method to the group catalog of Yang etal (2007) built
from the SDSS Data Release 4. As result we obtain reconstructions of the cosmic
mass density field that are independent on any explicit assumption of bias. We
describe in detail the implementation of the method, present a detailed
characterization of the reconstructed density field (mean mass density
distribution, correlation function and counts in cells) and the results of the
classification of large scale environments (filaments, voids, peaks and sheets)
in our reconstruction. Applications of the method include morphological studies
of the galaxy population on large scales and the realization of constrained
simulations.Comment: Accepted for publication in MNRA
Halo concentrations in the standard LCDM cosmology
We study the concentration of dark matter halos and its evolution in N-body
simulations of the standard LCDM cosmology. The results presented in this paper
are based on 4 large N-body simulations with about 10 billion particles each:
the Millennium-I and II, Bolshoi, and MultiDark simulations. The MultiDark (or
BigBolshoi) simulation is introduced in this paper. This suite of simulations
with high mass resolution over a large volume allows us to compute with
unprecedented accuracy the concentration over a large range of scales (about
six orders of magnitude in mass), which constitutes the state-of-the-art of our
current knowledge on this basic property of dark matter halos in the LCDM
cosmology. We find that there is consistency among the different simulation
data sets. We confirm a novel feature for halo concentrations at high
redshifts: a flattening and upturn with increasing mass. The concentration
c(M,z) as a function of mass and the redshift and for different cosmological
parameters shows a remarkably complex pattern. However, when expressed in terms
of the linear rms fluctuation of the density field sigma(M,z), the halo
concentration c(sigma) shows a nearly-universal simple U-shaped behaviour with
a minimum at a well defined scale at sigma=0.71. Yet, some small dependences
with redshift and cosmology still remain. At the high-mass end (sigma < 1) the
median halo kinematic profiles show large signatures of infall and highly
radial orbits. This c-sigma(M,z) relation can be accurately parametrized and
provides an analytical model for the dependence of concentration on halo mass.
When applied to galaxy clusters, our estimates of concentrations are
substantially larger -- by a factor up to 1.5 -- than previous results from
smaller simulations, and are in much better agreement with results of
observations. (abridged)Comment: Submitted to MNRA
The Redshift Evolution of LCDM Halo Parameters: Concentration, Spin, and Shape
We present a detailed study of the redshift evolution of dark matter halo
structural parameters in a LambdaCDM cosmology. We study the mass and redshift
dependence of the concentration, shape and spin parameter in Nbody simulations
spanning masses from 10^{10} Msun/h to 10^{15} Msun/h and redshifts from 0 to
2. We present a series of fitting formulas that accurately describe the time
evolution of the concentration-mass relation since z=2. Using arguments based
on the spherical collapse model we study the behaviour of the scale length of
the density profile during the assembly history of haloes, obtaining physical
insights on the origin of the observed time evolution of the concentration mass
relation. We also investigate the evolution with redshift of dark matter halo
shape and its dependence on mass. Within the studied redshift range the
relation between halo shape and mass can be well fitted by a power law. Finally
we show that although for z=0 the spin parameter is practically mass
independent, at increasing redshift it shows a increasing correlation with
mass.Comment: 12 pages, 11 figures, accepted to MNRAS, minor changes to previous
versio
Mass and pressure constraints on galaxy clusters from interferometric SZ observations
Following on our previous study of an analytic parametric model to describe
the baryonic and dark matter distributions in clusters of galaxies with
spherical symmetry, we perform an SZ analysis of a set of simulated clusters
and present their mass and pressure profiles. The simulated clusters span a
wide range in mass, 2.0 x 10^14 Msun < M200 < 1.0 x 10^15Msun, and observations
with the Arcminute Microkelvin Imager (AMI) are simulated through their
Sunyaev- Zel'dovich (SZ) effect. We assume that the dark matter density follows
a Navarro, Frenk and White (NFW) profile and that the gas pressure is described
by a generalised NFW (GNFW) profile. By numerically exploring the probability
distributions of the cluster parameters given simulated interferometric SZ data
in the context of Bayesian methods, we investigate the capability of this model
and analysis technique to return the simulated clusters input quantities. We
show that considering the mass and redshift dependency of the cluster halo
concentration parameter is crucial in obtaining an unbiased cluster mass
estimate and hence deriving the radial profiles of the enclosed total mass and
the gas pressure out to r200.Comment: 5 pages, 2 tables, 3 figure
Reconstructing the Cosmic Velocity and Tidal Fields with Galaxy Groups Selected from the Sloan Digital Sky Survey
[abridge]Cosmic velocity and tidal fields are important for the understanding
of the cosmic web and the environments of galaxies, and can also be used to
constrain cosmology. In this paper, we reconstruct these two fields in SDSS
volume from dark matter halos represented by galaxy groups. Detailed mock
catalogues are used to test the reliability of our method against uncertainties
arising from redshift distortions, survey boundaries, and false identifications
of groups by our group finder. We find that both the velocity and tidal fields,
smoothed on a scale of ~2Mpc/h, can be reliably reconstructed in the inner
region (~66%) of the survey volume. The reconstructed tidal field is used to
split the cosmic web into clusters, filaments, sheets, and voids, depending on
the sign of the eigenvalues of tidal tensor. The reconstructed velocity field
nicely shows how the flows are diverging from the centers of voids, and
converging onto clusters, while sheets and filaments have flows that are
convergent along one and two directions, respectively. We use the reconstructed
velocity field and the Zel'dovich approximation to predict the mass density
field in the SDSS volume as function of redshift, and find that the mass
distribution closely follows the galaxy distribution even on small scales. We
find a large-scale bulk flow of about 117km/s in a very large volume,
equivalent to a sphere with a radius of ~170Mpc/h, which seems to be produced
by the massive structures associated with the SDSS Great Wall. Finally, we
discuss potential applications of our reconstruction to study the environmental
effects of galaxy formation, to generate initial conditions for simulations of
the local Universe, and to constrain cosmological models. The velocity, tidal
and density fields in the SDSS volume, specified on a Cartesian grid with a
spatial resolution of ~700kpc/h, are available from the authors upon request.Comment: 35 pages, 13 figures, accepted for publication in MNRA
Extreme and long-term drought in the La Plata Basin: event evolution and impact assessment until September 2022
The current drought conditions across the Parana-La Plata Basin (LPB) in Brazil-Argentina have been the worst since 1944. While this area is characterized by a rainy season with a peak from October to April, the hydrological year 2020-2021 was very deficient in rainfall, and the situation extended into the 2021-2022 hydrological year. Below-normal rainfall was dominant in south-eastern Brazil, northern Argentina, Paraguay, and Uruguay, suggesting a late onset and weaker South American Monsoon and the continuation of drier conditions since 2021. In fact, in 2021 Brazilian south and south-east regions faced their worst droughts in nine decades, raising the spectre of possible power rationing given the grid dependence on hydroelectric plants. The ParanĂĄ-La Plata Basin drought induced damages to agriculture and reduced crop production, including soybeans and maize, with effects on global crop markets. The drought situation continued in 2022 in the Pantanal region. Dry meteorological conditions are still present in the region at the end of September 2022 with below-average precipitation anomalies. Soil moisture anomaly and vegetation conditions are worst in the lower part of the La Plata Basin, in the southern regions. Conversely, upper and central part of the basin show partial and temporary recovery
Galaxy cluster mass reconstruction project - I. Methods and first results on galaxy-based techniques
This paper is the first in a series in which we perform an extensive comparison of various galaxy-based cluster mass estimation techniques that utilize the positions, velocities and colours of galaxies. Our primary aim is to test the performance of these cluster mass estimation techniques on a diverse set of models that will increase in complexity. We begin by providing participating methods with data from a simple model that delivers idealized clusters, enabling us to quantify the underlying scatter intrinsic to these mass estimation techniques. The mock catalogue is based on a Halo Occupation Distribution (HOD) model that assumes spherical Navarro, Frenk and White (NFW) haloes truncated at Râââ, with no substructure nor colour segregation, and with isotropic, isothermal Maxwellian velocities. We find that, above 1014MÊ, recovered cluster masses are correlated with the true underlying cluster mass with an intrinsic scatter of typically a factor of 2. Below 1014MÊ, the scatter rises as the number of member galaxies drops and rapidly approaches an order of magnitude. We find that richness-based methods deliver the lowest scatter, but it is not clear whether such accuracy may simply be the result of using an over-simplistic model to populate the galaxies in their haloes. Even when given the true cluster membership, large scatter is observed for the majority non-richness-based approaches, suggesting that mass reconstruction with a low number of dynamical tracers is inherently problematic