8 research outputs found
Revisiting the statistical isotropy of GRB sky distribution
The assumption of homogeneity and isotropy on large scales is one of the main
hypotheses of the standard cosmology. In this paper, we test the hypothesis of
isotropy from the two-point angular correlation function of 2626 gamma-ray
bursts (GRB) of the FERMI GRB catalogue. We show that the uncertainties in the
GRB positions induce spurious anisotropic signals in their sky distribution.
However, when such uncertainties are taken into account no significant evidence
against the large-scale statistical isotropy is found. This result remains
valid even for the sky distribution of short-lived GRB, contrarily to previous
reports.Comment: 9 pages, 10 figures, 2 tables, match accepted versio
Can the angular scale of cosmic homogeneity be used as a cosmological test?
In standard cosmology, the cosmic homogeneity scale is the transition scale
above which the patterns arising from non-uniformities -- such as groups and
clusters of galaxies, voids, and filaments -- become indistinguishable from a
random distribution of sources. Recently, different groups have investigated
the feasibility of using such a scale as a cosmological test and arrived at
different conclusions. In this paper, we complement and extend these studies by
exploring the evolution of the spatial () and angular ()
homogeneity scales with redshift, assuming a spatially flat, -Cold
Dark Matter %(CDM) universe and linear cosmological perturbation
theory. We confirm previous results concerning the non-monotonicity of
with the matter density parameter but also show
that it exhibits a monotonical behavior with the Hubble constant within a
large redshift interval. More importantly, we find that, for ,
the angular homogeneity scale not only presents a monotonical behavior with
and but is quite sensitive to , especially at higher
redshifts. These results, therefore, raise the possibility of using
as a new, model-independent way to constrain cosmological parameters.Comment: 10 pages, 24 figure
The angular scale of homogeneity with SDSS-IV DR16 Luminous Red Galaxies
We report measurements of the angular scale of cosmic homogeneity
() using the recently released luminous red galaxy sample of the
sixteenth data release of the Sloan Digital Sky Survey (SDSS-IV LRG DR16). It
consists of a model-independent method, as we only use the celestial
coordinates of these objects to carry out such an analysis. The observational
data is divided into thin redshift bins, namely , ,
and , in order to avoid projection biases, and we estimate our
uncertainties through a bootstrap method and a suite of mock catalogues. We
find that the LRGs exhibit an angular scale of homogeneity consistent with the
predictions of the standard cosmology within the redshift interval studied.
Considering the bootstrap method, in which the measurements are obtained in a
model-independent way, we found at 1 level that deg, deg and
deg. Such results are in good
agreement with the ones obtained using mock catalogues built under the
assumption of the standard cosmological model.Comment: 13 pages, 4 figures, 3 tables. References updated; matches version
published in JCA
How does an incomplete sky coverage affect the Hubble Constant variance?
We address the tension between local and the CMB measurements of the Hubble Constant using simulated Type Ia Supernova (SN) data-sets. We probe its directional dependence by means of a hemispherical comparison through the entire celestial sphere as an estimator of the cosmic variance. We perform Monte Carlo simulations assuming isotropic and non-uniform distributions of data points, the latter coinciding with the real data. This allows us to incorporate observational features, such as the sample incompleteness, in our estimation. We obtain that this tension can be alleviated to for isotropic realizations, and for non-uniform ones. We also find that the variance is largely reduced if the data-sets are augmented to 4 and 10 times the current size. Future surveys will be able to tell whether the Hubble Constant tension happens due to unaccounted cosmic variance, or whether it is an actual indication of physics beyond the standard cosmological model