1,215 research outputs found
The significance of the integrated Sachs-Wolfe effect revisited
We revisit the state of the integrated Sachs-Wolfe (ISW) effect measurements
in light of newly available data and address criticisms about the measurements
which have recently been raised. We update the data set previously assembled by
Giannantonio et al. to include new data releases for both the cosmic microwave
background (CMB) and the large-scale structure (LSS) of the Universe. We find
that our updated results are consistent with previous measurements. By fitting
a single template amplitude, we now obtain a combined significance of the ISW
detection at the 4.4 sigma level, which fluctuates by 0.4 sigma when
alternative data cuts and analysis assumptions are considered. We also make new
tests for systematic contaminations of the data, focusing in particular on the
issues raised by Sawangwit et al. Amongst them, we address the rotation test,
which aims at checking for possible systematics by correlating pairs of
randomly rotated maps. We find results consistent with the expected data
covariance, no evidence for enhanced correlation on any preferred axis of
rotation, and therefore no indication of any additional systematic
contamination. We publicly release the results, the covariance matrix, and the
sky maps used to obtain them.Comment: 19 pages, 10 figures. MNRAS in pres
The Interplay of Cluster and Galaxy Evolution
We review here the interplay of cluster and galaxy evolution. As a case
study, we consider the Butcher-Oemler effect and propose that it is the result
of the changing rate of cluster merger events in a hierarchical universe. This
case study highlights the need for new catalogs of clusters and groups that
possess quantified morphologies. We present such a sample here, namely the
Sloan Digital Sky Survey (SDSS) C4 Catalog, which has been objectively-selected
from the SDSS spectroscopic galaxy sample. We outline here the C4 algorithm and
present first results based on the SDSS Early Data Release, including an X-ray
luminosity-velocity dispersion (L_x-sigma) scaling relationship (as a function
of cluster morphology), and the density-SFR relation of galaxies within C4
clusters (Gomez et al. 2003). We also discuss the merger of Coma and the
NGC4839 group, and its effect on the galaxy populations in these systems. We
finish with a brief discussion of a new sample of Hdelta-selected galaxies
(i.e., k+a, post--starburst galaxies) obtained from the SDSS spectroscopic
survey.Comment: Invited review at the JENAM 2002 Workshop on "Galaxy Evolution in
Groups and Clusters", Porto, Sep 5-7 2002, eds. Lobo, Serote-Roos and
Biviano, Kluwer in pres
Tracking Dark Energy with the ISW effect: short and long-term predictions
We present an analysis of the constraining power of future measurements of
the Integrated Sachs-Wolfe (ISW) effect on models of the equation of state of
dark energy as a function of redshift, w(z). To achieve this, we employ a new
parameterization of w, which utilizes the mean value of w(z) () as an
explicit parameter. This helps to separate the information contained in the
estimation of the distance to the last scattering surface (from the CMB) from
the information contained in the ISW effect. We then use Fisher analysis to
forecast the expected uncertainties in the measured parameters from future ISW
observations for two models of dark energy with very different time evolution
properties. For example, we demonstrate that the cross-correlation of Planck
CMB data and LSST galaxy catalogs will provide competitive constraints on w(z),
compared to a SNAP-like SNe project, for models of dark energy with a rapidly
changing equation of state (e.g. 'Kink' models). Our work confirms that, while
SNe measurements are more suitable for constraining variations in w(z) at low
redshift, the ISW effect can provide important independent constraints on w(z)
at high z.Comment: 15 pages, 17 figures. Added discussion, references, 2 new figures.
Minor errors fixed in the calculation. The predicted ISW constraints on w(z)
are slightly tighter. Matches the version accepted to PR
Testing Emergent Gravity on Galaxy Cluster Scales
Verlinde's theory of Emergent Gravity (EG) describes gravity as an emergent
phenomenon rather than a fundamental force. Applying this reasoning in de
Sitter space leads to gravity behaving differently on galaxy and galaxy cluster
scales; this excess gravity might offer an alternative to dark matter. Here we
test these ideas using the data from the Coma cluster and from 58 stacked
galaxy clusters. The X-ray surface brightness measurements of the clusters at
along with the weak lensing data are used to test the theory.
We find that the simultaneous EG fits of the X-ray and weak lensing datasets
are significantly worse than those provided by General Relativity (with cold
dark matter). For the Coma cluster, the predictions from Emergent Gravity and
General Relativity agree in the range of 250 - 700 kpc, while at around 1 Mpc
scales, EG total mass predictions are larger by a factor of 2. For the cluster
stack the predictions are only in good agreement at around the 1 - 2 Mpc
scales, while for Mpc EG is in strong tension with the data.
According to the Bayesian information criterion analysis, GR is preferred in
all tested datasets; however, we also discuss possible modifications of EG that
greatly relax the tension with the data.Comment: 19 pages, 5 figures, 5 tables, accepted for publication on JCA
Ascent, descent, nullity and defect of linear operators
This thesis is intended to be a survey of nullity and defect of linear operators on the one hand, and ascent and descent on the other, and the relationships between these concepts. These quantities are of considerable use in the discussion of linear operators, e.g. compact operators
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