213 research outputs found
Formation of Dark Matter Haloes in a Homogeneous Dark Energy Universe
Several independent cosmological tests have shown evidences that the energy
density of the Universe is dominated by a dark energy component, which cause
the present accelerated expansion. The large scale structure formation can be
used to probe dark energy models, and the mass function of dark matter haloes
is one of the best statistical tools to perform this study. We present here a
statistical analysis of mass functions of galaxies under a homogeneous dark
energy model, proposed in the work of Percival (2005), using an observational
flux-limited X-ray cluster survey, and CMB data from WMAP. We compare, in our
analysis, the standard Press-Schechter (PS) approach (where a Gaussian
distribution is used to describe the primordial density fluctuation field of
the mass function), and the PL (Power Law) mass function (where we apply a
nonextensive q-statistical distribution to the primordial density field). We
conclude that the PS mass function cannot explain at the same time the X-ray
and the CMB data (even at 99% confidence level), and the PS best fit dark
energy equation of state parameter is , which is distant from the
cosmological constant case. The PL mass function provides better fits to the
HIFLUGCS X-ray galaxy data and the CMB data; we also note that the
parameter is very sensible to modifications in the PL free parameter, ,
suggesting that the PL mass function could be a powerful tool to constrain dark
energy models.Comment: 4 pages, 2 figures, Latex. Accepted for publication in the
International Journal of Modern Physics D (IJMPD)
A new approach to the study of quasi-normal modes of rotating stars
We propose a new method to study the quasi-normal modes of rotating
relativistic stars. Oscillations are treated as perturbations in the frequency
domain of the stationary, axisymmetric background describing a rotating star.
The perturbed quantities are expanded in circular harmonics, and the resulting
2D-equations they satisfy are integrated using spectral methods in the
(r,theta)-plane. The asymptotic conditions at infinity, needed to find the mode
frequencies, are implemented by generalizing the standing wave boundary
condition commonly used in the non rotating case. As a test, the method is
applied to find the quasi-normal mode frequencies of a slowly rotating star.Comment: 24 pages, 7 figures, submitted to Phys. Rev.
Where does galactic dust come from?
Here we investigate the origin of the dust mass (Mdust) observed in the Milky Way (MW) and of dust scaling relations found in a sample of local galaxies from the DGS and KINGFISH surveys. To this aim, we model dust production from Asymptotic Giant Branch (AGB) stars and supernovae (SNe) in simulated galaxies forming along the assembly of aMW-like halo in a well-resolved cosmic volume of 4 cMpc using the GAMESH pipeline. We explore the impact of different sets of metallicity and mass-dependent AGB and SN dust yields on the predicted Mdust. Our results show that models accounting for grain destruction by the SN reverse shock predict a total dust mass in the MW, that is a factor of ~4 less than observed, and cannot reproduce the observed galaxy-scale relations between dust and stellar masses, and dust-togas ratios and metallicity, with a smaller discrepancy in galaxies with low metallicity (12 + log(O/H) < 7.5) and low stellar masses (Mstar < 107 M⊙). In agreement with previous studies, we suggest that competing processes in the interstellar medium must be at play to explain the observed trends. Our result reinforces this conclusion by showing that it holds independently of the adopted AGB and SN dust yields
New Constraints on the Variable Equation of State Parameter from X-Ray Gas Mass Fractions and SNe Ia
Recent measurements are suggesting that we live in a flat Universe and that
its present accelerating stage is driven by a dark energy component whose
equation of state may evolve in time. Assuming two different parameterizations
for the function , we constrain their free parameters from a joint
analysis involving measurements from X-Ray luminosity of galaxy clusters and
SNe type Ia data.Comment: paper, 6 pages, 1 figure Accepted by Int. Journal of Modern Physics D
(IJPMD
Supernova dust yields: the role of metallicity, rotation, and fallback
Supernovae (SNe) are considered to have a major role in dust enrichment of
high redshift galaxies and, due to the short lifetimes of interstellar grains,
in dust replenishment of local galaxies. Here we explore how SN dust yields
depend on the mass, metallicity, and rotation rate of the progenitor stars, and
on the properties of the explosion. To this aim, assuming uniform mixing inside
the ejecta, we quantify the dust mass produced by a sample of SN models with
progenitor masses , metallicity , rotation rate and ~km/s, that
explode with a fixed energy of ~erg (FE models) or with
explosion properties calibrated to reproduce the - relation
inferred from SN observations (CE models). We find that rotation favours more
efficient dust production, particularly for more massive, low metallicity
stars, but that metallicity and explosion properties have the largest effects
on the dust mass and its composition. In FE models, SNe with are more efficient at forming dust: between 0.1 and 1 is
formed in a single explosion, with a composition dominated by silicates, carbon
and magnetite grains when , and by carbon and magnetite grains
when . In CE models, the ejecta are massive and metal-rich and
dust production is more efficient. The dust mass increases with and it is
dominated by silicates, at all [Fe/H].Comment: MNRAS, in pres
Evolution of dwarf galaxies hosting GW150914-like events
Here we present a detailed analysis of the properties and evolution of different dwarf galaxies, candidates to host the coalescence of black hole binary systems generating GW150914-like events. By adopting a novel theoretical framework coupling the binary population synthesis code SEBA with the Galaxy formationmodel GAMESH, we can investigate the detailed evolution of these objects in awell-resolved cosmological volume of 4 cMpc, having aMilkyWay (MW)- like galaxy forming at its centre. We identify three classes of interesting candidate galaxies: MW progenitors, dwarf satellites, and dwarf galaxies evolving in isolation. We find that (i) despite differences in individual histories and specific environments the candidates reduce to only nine representative galaxies; (ii) among them, 3c44 per cent merge into the MW halo progenitors by the redshift of the expected signal, while the remaining dwarfs are found as isolated or as satellites of the MW and their evolution is strongly shaped by both peculiar dynamical history and environmental feedback; (iii) a stringent condition for the environments where GW150914-like binaries can form comes from a combination of the accretion history of their dark matter haloes and the radiative feedback in the high-redshift universe; and (iv) by comparing with the observed catalogues from the DGS and ALLSMOG surveys we find two observed dwarfs respecting the properties predicted by our model. We finally note how the present analysis opens the possibility to build future strategies for host galaxy identification
Structural analysis of Fe/Ni(001) films by photoelectron diffraction
The structure of Fe films, epitaxially grown on Ni(001), has been studied in the 0-14 ML coverage range by means of photoelectron diffraction (PD) in the forward scattering regime. Quantitative analysis by a multiple scattering approach has been performed on Fe films at a coverage of 3 and 7 ML. Analysis of the 3-ML data showed that growth was not layer-by-layer but rather occurred through islands nucleation and that transition from the pseudomorphic fee to the bcc phase was located in this early stage of growth. In fact, best fit was obtained by calculations on a 2 ML bcc(110)/3 ML fcc(001) Fe film with the bcc[111]parallel to fcc[110] in-plane orientation. Interlayer spacings of 2.05 +/- 0.068 Angstrom, 2.01 +/- 0.03 Angstrom, and 1.85 +/- 0.03 Angstrom were found in the bcc region, between bcc and fee layers and in the fee region, respectively. Best-fit in-plane nearest-neighbors (n-n) distance was 2.49 +/- 0.02 Angstrom, in registry with that of the Ni substrate. To analyze the 7-ML data a 4 ML bcc(110)/3 ML fcc(001) film was employed, varying the fitting parameters in the bcc region only. Best fit was obtained for an interlayer spacing of 2.04 +/- 0.04 Angstrom and in plane n-n distance of 2.47 +/- 0.01 Angstrom. At 14 ML the PD pattern collected over a 94 degrees azimuthal range displayed symmetry around the [110] substrate direction, which was explained by the equipopulation of the 4 bcc(110) domains satisfying the bcc[111]parallel to fcc[110] alignment
FFF-based high-throughput sequence shortlisting to support the development of aptamer-based analytical strategies
Aptamers are biomimetic receptors that are increasingly exploited for the development of optical and electrochemical aptasensors. They are selected in vitro by the SELEX (Systematic Evolution of Ligands by Exponential Enrichment) procedure, but although they are promising recognition elements, for their reliable applicability for analytical purposes, one cannot ignore sample components that cause matrix effects. This particularly applies when different SELEX-selected aptamers and related truncated sequences are available for a certain target, and the choice of the aptamer should be driven by the specific downstream application. In this context, the present work aimed at investigating the potentialities of asymmetrical flow field-flow fractionation (AF4) with UV detection for the development of a screening method of a large number of anti-lysozyme aptamers towards lysozyme, including randomized sequences and an interfering agent (serum albumin). The possibility to work in native conditions and selectively monitor the evolution of untagged aptamer signal as a result of aptamer-protein binding makes the devised method effective as a strategy for shortlisting the most promising aptamers both in terms of affinity and in terms of selectivity, to support subsequent development of aptamer-based analytical devices. Graphical abstract: [Figure not available: see fulltext.
Stochastic backgrounds of gravitational waves from extragalactic sources
Astrophysical sources emit gravitational waves in a large variety of
processes occurred since the beginning of star and galaxy formation. These
waves permeate our high redshift Universe, and form a background which is the
result of the superposition of different components, each associated to a
specific astrophysical process. Each component has different spectral
properties and features that it is important to investigate in view of a
possible, future detection. In this contribution, we will review recent
theoretical predictions for backgrounds produced by extragalactic sources and
discuss their detectability with current and future gravitational wave
observatories.Comment: 10 pages, 9 figures, proceedings of the GWDAW 10 Conference,
submitted to Class. & Quantum Gra
- …