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 $0.1 < z < 1.2$ 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 $r \gtrsim 10$ 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

Acoustic Oscillations in the Early Universe and Today

During its first ~100,000 years, the universe was a fully ionized plasma with a tight coupling by Thompson scattering between the photons and matter. The trade--off between gravitational collapse and photon pressure causes acoustic oscillations in this primordial fluid. These oscillations will leave predictable imprints in the spectra of the cosmic microwave background and the present day matter-density distribution. Recently, the BOOMERANG and MAXIMA teams announced the detection of these acoustic oscillations in the cosmic microwave background (observed at redshift ~1000). Here, we compare these CMB detections with the corresponding acoustic oscillations in the matter-density power spectrum (observed at redshift ~0.1). These consistent results, from two different cosmological epochs, provide further support for our standard Hot Big Bang model of the universe.Comment: To appear in the journal Science. 6 pages, 1 color figur

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