43 research outputs found
Probing the Cosmological Principle in the counts of radio galaxies at different frequencies
According to the Cosmological Principle, the matter distribution on very
large scales should have a kinematic dipole that is aligned with that of the
CMB. We determine the dipole anisotropy in the number counts of two all-sky
surveys of radio galaxies. For the first time, this analysis is presented for
the TGSS survey, allowing us to check consistency of the radio dipole at low
and high frequencies by comparing the results with the well-known NVSS survey.
We match the flux thresholds of the catalogues, with flux limits chosen to
minimise systematics, and adopt a strict masking scheme. We find dipole
directions that are in good agreement with each other and with the CMB dipole.
In order to compare the amplitude of the dipoles with theoretical predictions,
we produce sets of lognormal realisations. Our realisations include the
theoretical kinematic dipole, galaxy clustering, Poisson noise, simulated
redshift distributions which fit the NVSS and TGSS source counts, and errors in
flux calibration. The measured dipole for NVSS is times larger than
predicted by the mock data. For TGSS, the dipole is almost times
larger than predicted, even after checking for completeness and taking account
of errors in source fluxes and in flux calibration. Further work is required to
understand the nature of the systematics that are the likely cause of the
anomalously large TGSS dipole amplitude.Comment: 13 pages, 8 figures, 2 tables; Significant improvements. Version
accepted by JCA
Forecasting cosmological constraints from age of high-z galaxies
We perform Monte Carlo simulations based on current age estimates of high-z
objects to forecast constraints on the equation of state (EoS) of the dark
energy. In our analysis, we use two different EoS parameterizations, namely,
the so-called CPL and its uncorrelated form and calculate the improvements on
the figure of merit for both cases. Although there is a clear dependence of the
FoM with the size and accuracy of the synthetic age samples, we find that the
most substantial gain in FoM comes from a joint analysis involving age and
baryon acoustic oscillation data.Comment: 4 pages, 13 figures, late
The dipole anisotropy of WISE x SuperCOSMOS number counts
We probe the isotropy of the Universe with the largest all-sky photometric
redshift dataset currently available, namely WISE~~SuperCOSMOS. We
search for dipole anisotropy of galaxy number counts in multiple redshift
shells within the range, for two subsamples drawn from the
same parent catalogue. Our results show that the dipole directions are in good
agreement with most of the previous analyses in the literature, and in most
redshift bins the dipole amplitudes are well consistent with CDM-based
mocks in the cleanest sample of this catalogue. In the range, however,
we obtain a persistently large anisotropy in both subsamples of our dataset.
Overall, we report no significant evidence against the isotropy assumption in
this catalogue except for the lowest redshift ranges. The origin of the latter
discrepancy is unclear, and improved data may be needed to explain it.Comment: 5 pages, 4 figures, 2 tables. Published in MNRA