706 research outputs found
Reconstruction of the Cosmic Equation of State for High Redshift
We investigate the possibilities of reconstructing the cosmic equation of
state (EoS) for high redshift. In order to obtain general results, we use two
model-independent approaches. The first reconstructs the EoS using comoving
distance and the second makes use of the Hubble parameter data. To implement
the first method, we use a recent set of Gamma-Ray Bursts (GRBs) measures. To
implement the second method, we generate simulated data using the Sandage-Loeb
() effect; for the fiducial model, we use the model. In both
cases, the statistical analysis is conducted through the Gaussian processes
(non-parametric). In general, we demonstrate that this methodology for
reconstructing the EoS using a non-parametric method plus a model-independent
approach works appropriately due to the feasibility of calculation and the ease
of introducing a priori information ( and ). In the near
future, following this methodology with a higher number of high quality data
will help obtain strong restrictions for the EoS.Comment: 9 pages, 5 figure
The radial abundance gradient of oxygen towards the Galactic anticentre
We present deep optical spectroscopy of eight HII regions located in the
anticentre of the Milky Way. The spectra were obtained at the 10.4m GTC and
8.2m VLT. We determined Te([NII]) for all objects and Te([OIII]) for six of
them. We also included in our analysis an additional sample of 13 inner-disc
Galactic Hii regions from the literature that have excellent T_e
determinations. We adopted the same methodology and atomic dataset to determine
the physical conditions and ionic abundances for both samples. We also detected
the CII and OII optical recombination lines in Sh 2-100, which enables
determination of the abundance discrepancy factor for this object. We found
that the slopes of the radial oxygen gradients defined by the HII regions from
R_25 (= 11.5 kpc) to 17 kpc and those within R_25 are similar within the
uncertainties, indicating the absence of flattening in the radial oxygen
gradient in the outer Milky Way. In general, we found that the scatter of the
O/H ratios of Hii regions is not substantially larger than the observational
uncertainties. The largest possible local inhomogeneities of the oxygen
abundances are of the order of 0.1 dex. We also found positive radial gradients
in Te([O III]) and Te([N II]) across the Galactic disc. The shapes of these
temperature gradients are similar and also consistent with the absence of
flattening of the metallicity distribution in the outer Galactic disc.Comment: 20 pages, 11 figures. Accepted for publication in Monthly Notices of
the Royal Astronomical Societ
Interacting photon-baryon fluid, warm dark matter and the first acoustic peak
The Reduced Relativistic Gas (RRG) model was introduced by A. Sakharov in
1965 for deriving the cosmic microwave background (CMB) spectrum. It was
recently reinvented by some of us to achieve an interpolation between the
radiation and dust epochs in the evolution of the Universe. This model
circumvents the complicated structure of the Boltzmann-Einstein system of
equations and admits a transparent description of warm-dark-matter effects. It
is extended here to include, on a phenomenological basis, an out-of-equilibrium
interaction between radiation and baryons which is supposed to account for
relevant aspects of pre-recombination physics in a simplified manner.
Furthermore, we use the tight-coupling approximation to explore the influence
of both this interaction and of the RRG warmness parameter on the anisotropy
spectrum of the CMB. The predictions of the model are very similar to those of
the {\Lambda}CDM model if both the interaction and the dark-matter warmness
parameters are of the order of or smaller. As far as the warmness
parameter is concerned, this is in good agreement with previous estimations on
the basis of results from structure formation.Comment: 10 pages and 4 figure
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