Constraints on mode couplings and modulation of the CMB with WMAP data

We investigate a possible asymmetry in the statistical properties of the cosmic microwave background temperature field and to do so we construct an estimator aiming at detecting a dipolar modulation. Such a modulation is found to induce correlations between multipoles with $\Delta\ell=1$. Applying this estimator, to the V and W bands of the WMAP data, we found a significant detection in the V band. We argue however that foregrounds and in particular point sources are the origin of this signal.Comment: 14 pages, 14 figure

Cosmic Statistics of Statistics

The errors on statistics measured in finite galaxy catalogs are exhaustively investigated. The theory of errors on factorial moments by Szapudi & Colombi (1996) is applied to cumulants via a series expansion method. All results are subsequently extended to the weakly non-linear regime. Together with previous investigations this yields an analytic theory of the errors for moments and connected moments of counts in cells from highly nonlinear to weakly nonlinear scales. The final analytic formulae representing the full theory are explicit but somewhat complicated. Therefore as a companion to this paper we supply a FORTRAN program capable of calculating the described quantities numerically (abridged).Comment: 18 pages, 9 figures, Latex (MN format), published in MNRAS 310, 428 with slight correction

X-ray Insights Into Interpreting CIV Blueshifts and Optical/UV Continua

We present 0.5-8.0 keV Chandra observations of six bright quasars that represent extrema in quasar emission-line properties -- three quasars each with small and large blueshifts of the CIV emission line with respect to the systemic redshift of the quasars. Supplemented with seven archival Chandra observations of quasars that met our selection criteria, we investigate the origin of this emission-line phenomenon in the general context of the structure of quasars. We find that the quasars with the largest CIV blueshifts show evidence, from joint-spectral fitting, for intrinsic X-ray absorption (N_H ~ 10^22 cm^-2). Given the lack of accompanying CIV absorption, this gas is likely to be highly ionized, and may be identified with the shielding gas in the disk-wind paradigm. Furthermore, we find evidence for a correlation of alpha_uv, the ultraviolet spectral index, with the hardness of the X-ray continuum; an analysis of independent Bright Quasar Survey data from the literature supports this conclusion. This result points to intrinsically red quasars having systematically flatter hard X-ray continua without evidence for X-ray absorption. We speculate on the origins of these correlations of X-ray properties with both CIV blueshift and alpha_uv and discuss the implications for models of quasar structure.Comment: 9 figs, 25 pages, AASTeX; accepted for publication in A

Red Parkes-Quasars: Evidence for Soft X-ray Absorption

The Parkes Half-Jansky Flat Spectrum Sample contains a large number of sources with unusually red optical-to-near-infrared continua. If this is to be interpreted as extinction by dust in the line-of-sight, then associated material might also give rise to absorption in the soft X-ray regime. This hypothesis is tested using broadband (0.1-2.4 keV) data from the {\it ROSAT} All-Sky Survey provided by Siebert et al. (1998). Significant ($>3\sigma$ confidence level) correlations between optical (and near-infrared)--to--soft X-ray continuum slope and optical extinction are found in the data, consistent with absorption by material with metallicity and a range in gas-to-dust ratio as observed in the local ISM. Under this simple model, the soft X-rays are absorbed at a level consistent with the range of extinctions ($0< A_{V}< 6$ magnitudes) implied by the observed optical reddening. Excess X-ray absorption by warm (ionised) gas, (ie. a `warm absorber') is not required.Comment: 23 pages of text, 3 figures, to appear in Jan 10 (1999) issue of The Astrophysical Journa

Weak Lensing Predictions at Intermediate Scales

As pointed out in previous studies, the measurement of the skewness of the convergence field $\kappa$ will be useful in breaking the degeneracy among the cosmological parameters constrained from weak lensing observations. The combination of shot noise and finite survey volume implies that such a measurement is likely to be done in a range of intermediate scales ($0.5'$ to 20') where neither perturbation theory nor the hierarchical ansatz apply. Here we explore the behavior of the skewness of $\kappa$ at these intermediate scales, based on results for the non-linear evolution of the mass bispectrum. We combined different ray-tracing simulations to test our predictions, and we find that our calculations describe accurately the transition from the weakly non-linear to the strongly non-linear regime. We show that the single lens-plane approximation remains accurate even in the non-linear regime, and we explicitly calculate the corrections to this approximation. We also discuss the prospects of measuring the skewness in upcoming weak lensing surveys.Comment: 7 pages, submitted to MNRA

Cosmic Strings Lens Phenomenology: Model of Poisson Energy Distribution

We present a novel approach for investigating lens phenomenology of cosmic strings in order to elaborate detection strategies in galaxy deep field images. To account for the complexity of the projected energy distribution of string networks we assume their lens effects to be similar to those of a straight string carrying a {\em random} lineic energy distribution. In such a model we show that, unlike the case of uniform strings, critical phenomena naturally appear. We explore the properties of the critical lines and caustics. In particular, assuming that the energy coherence length along the string is much smaller than the observation scale, we succeeded in computing the total length of critical lines per unit string length and found it to be $4/\sqrt{3} {\bf E}(3/4)$. The length of the associated caustic lines can also be computed to be $16/(\pi \sqrt{3}) {\bf E}(3/4)$. The picture we obtain here for the phenomenology of cosmic string detection is clearly at variance with common lore.Comment: 10 pages, 5 figures. Minor correction

Rest-frame optical continua of L ~ L*, z>3 quasars: probing the faint end of the high z quasar luminosity function

Near-IR photometry for 20 radio-loud z>3 quasars, 16 of which are radio- selected, are presented. These data sample the rest-frame optical/UV continuum, which is commonly interpreted as emission from an accretion disk. In a previous study, we compared the rest-frame optical/UV continuum shapes of 15 optically bright (V3 quasars with those of 27 low redshift (z~0.1) ones that were matched to the high redshift sample in evolved luminosity (i.e. having luminosities ranging from 1-7 times the characteristic luminosity, L*, where L*~(1+z)^{~3}) to look for signs of evolution in the central engines. We found the continuum shapes at z~0.1 and z>3 similar, consistent with no significant change in the ratio mdot/M, where mdot is the accretion rate with respect to the Eddington rate and M is the black hole mass. This study expands our earlier high redshift sample to lower luminosity, away from extreme objects and towards a luminosity overlap with lower redshift samples. The distribution of rest-frame optical/UV continuum shapes for this fainter sample is broader, extending further to the red than that of the brighter z>3 one. Three quasars from this fainter sample, two radio-selected and one optically-selected, have optical continuum slopes alpha<-1 (F_{nu}~nu^{alpha}). The optically-selected one, LBQS0056+0125, appears to be reddened by dust along the line of sight or in the host galaxy, whereas the radio-selected ones, PKS2215+02 and TXS2358+189, could derive their red continua from the contribution of a relatively strong synchrotron component to the rest-frame optical. These objects may represent a bridge to a population of very red high redshift quasars to which ongoing or future near-IR, optical and deep X-ray surveys will be sensitive.Comment: 16 pages, 6 figures; accepted for publication in MNRA