31 research outputs found
High Redshift CDM Cosmology: To Bin or not to Bin?
We construct observational Hubble and angular diameter distance
mock data with baseline Planck CDM input values, before
fitting the CDM model to study evolution of probability density
functions (PDFs) of best fit cosmological parameters across redshift bins. We find that PDF peaks only agree with the
input parameters in low redshift () bins for and
constraints, and in all redshift bins when and
constraints are combined. When input parameters are not recovered, we observe
that PDFs exhibit non-Gaussian tails towards larger values and
shifts to (less pronounced) peaks at smaller values. This flattening
of the PDF is expected as and observations only constrain
combinations of cosmological parameters at higher redshifts, so uniform PDFs
are expected. Our analysis leaves us with a choice to bin high redshift data in
the knowledge that we may be unlikely to recover Planck values, or conduct full
sample analysis that biases CDM inferences to the lower redshift
Universe.Comment: 6 pages, 9 figure
Putting Flat CDM In The (Redshift) Bin
Flat CDM cosmology is specified by two constant fitting parameters
in the late Universe, the Hubble constant and matter density (today)
. In the cosmology literature, one typically \textit{assumes} that
there is no redshift evolution of cosmological parameters when one fits data
sets. Here, in mock observational Hubble data we demonstrate evolution in
distributions of best fit parameters with effective redshift. As a result,
considerably different best fits from Planck-CDM
cannot be precluded in high redshift bins. We explore if observational Hubble
data, Type Ia supernovae and standardisable quasar samples exhibit redshift
evolution of best fit CDM parameters. In all samples, we confirm an
increasing (decreasing ) trend with increasing bin redshift.
Through comparison with mocks, we confirm that similar behaviour can arise
randomly within the flat CDM model with probabilities as low as ().Comment: 5 pages, 10 figures; v2 added explanations and appendi
Quasar standardization : overcoming selection biases and redshift evolution
Quasars (QSOs) are extremely luminous active galactic nuclei currently observed up to redshift z = 7.642. As such, they have the potential to be the next rung of the cosmic distance ladder beyond Type Ia supernovae, if they can reliably be used as cosmological probes. The main issue in adopting QSOs as standard candles (similarly to gamma-ray bursts) is the large intrinsic scatter in the relations between their observed properties. This could be overcome by finding correlations among their observables that are intrinsic to the physics of QSOs and not artifacts of selection biases and/or redshift evolution. The reliability of these correlations should be verified through well-established statistical tests. The correlation between the ultraviolet and X-ray fluxes developed by Risaliti & Lusso is one of the most promising relations. We apply a statistical method to correct this relation for redshift evolution and selection biases. Remarkably, we recover the the same parameters of the slope and the normalization as Risaliti & Lusso. Our results establish the reliability of this relation, which is intrinsic to the QSO properties and not merely an effect of selection biases or redshift evolution. Hence, the possibility to standardize QSOs as cosmological candles, thereby extending the Hubble diagram up to z = 7.54
How to obtain accurate CAMELSPIN or ROESY spectra with identical low-power pulses for both the preparation and the mixing intervals
Frequency offset effects and their elimination in NMR rotating-frame cross-relaxation spectroscopy
HYALURONATE TETRASACCHARIDE-CUII INTERACTION: A NMR STUDY
The coordination of Cu(II) to a hyaluronate tetrasaccharide (HA(t)) was investigated in aqueous solution by C-13 and H-1 relaxation measurements at two magnetic fields, 9 and 14 T The HA(t) interaction with the metal ion was monitored following the nuclear paramagnetic relaxation enhancements R-1p and R-2p produced by the copper addition. The data analysis shows that the paramagnetic effect is differently experienced by the nuclei in different monosaccharide residues. A molecular model for the complex HA(t)-Cu(II) was built taking into account the experimental data. The model shows the presence of two binding sites, both involving the carboxylate groups of the two glucuronic acid units. The first site, that best simulates the HA binding site, is located on the ligand core, while the second one is located on the terminal glucuronic acid residue. Both binding sites involve, in addition to the carboxylate groups, the O4 oxygens of the glucuronic acid residues