Transverse Galaxy Velocities from Multiple Topological Images

The study of the kinematics of galaxies within clusters or groups has the limitation that only one of the three velocity components and only two of the three spatial components of a galaxy position in six-dimensional phase space can normally be measured. However, if multiple topological images of a cluster exist, then the radial positions and sky plane mean velocities of galaxies in the cluster may also be measurable from photometry of the two cluster images. The vector arithmetic and principles of the analysis are presented. These are demonstrated by assuming the suggested topological identification of the clusters RX J1347.5-1145 and CL 09104+4109 to be correct and deducing the sky-plane relative velocity component along the axis common to both images of this would-be single cluster. Three out of four of the inferred transverse velocities are consistent with those expected in a rich cluster. A control sample of random `common' sky-plane axes, independent of the topological hypothesis, implies that this is not surprising. This shows that while galaxy kinematics are deducible from knowledge of cosmological topology, it is not easy to use them to refute a specific candidate manifold.Comment: 13 pages, 7 figures, accepted for MNRA

The Cosmological Constant and Quintessence from a Correlation Function Comoving Fine Feature in the 2dF Quasar Redshift Survey

Detections of local maxima in the density perturbation spectrum at characteristic comoving scales L~100-200h^{-1}Mpc have previously been claimed. Here, this cosmic standard ruler is sought in the ``10K'' release of the 2dF QSO Redshift Survey (2QZ-10K), by estimating the comoving, spatial correlation functions \xi(r) of the three-dimensional distribution of the N=2378 quasars in the most completely observed and ``covered'' sky regions, over the three redshift ranges 0.6 < z < 1.1, 1.1 < z < 1.6 and 1.6 < z < 2.2. Because of the selection method of the survey and sparsity of the data, the analysis was done conservatively to avoid non-cosmological artefacts. (i) Avoiding a priori estimates of the length scales of features, local maxima in \xi(r) are found in all three redshift ranges. The requirement that a local maximum be present in all three redshift ranges at a fixed comoving length scale implies strong, purely geometric constraints on the local cosmological parameters. The length scale of the local maximum common to the three redshift ranges is 2L= (244\pm17)h^{-1}Mpc. (ii) For a standard FLRW model, the matter density \Omm and cosmological constant \Omega_\Lambda are constrained to \Omm= 0.25\pm0.10, \Omega_\Lambda=0.65\pm0.25 (68% confidence), \Omm= 0.25\pm0.15, \Omega_\Lambda=0.60\pm0.35 (95%), respectively, from the 2QZ-10K alone. Independently of the SNe Ia data, the zero cosmological constant model (\Omega_\Lambda=0) is rejected at the 99.7% confidence level. (iii) For an effective quintessence (w_Q) model and zero curvature, w_Q<-0.5 (68%), w_Q<-0.35 (95%) are found, again from the 2QZ-10K alone

A weak acceleration effect due to residual gravity in a multiply connected universe

Could cosmic topology imply dark energy? We use a weak field (Newtonian) approximation of gravity and consider the gravitational effect from distant, multiple copies of a large, collapsed (virialised) object today (i.e. a massive galaxy cluster), taking into account the finite propagation speed of gravity, in a flat, multiply connected universe, and assume that due to a prior epoch of fast expansion (e.g. inflation), the gravitational effect of the distant copies is felt locally, from beyond the naively calculated horizon. We find that for a universe with a $T^1xR^2$ spatial section, the residual Newtonian gravitational force (to first order) provides an anisotropic effect that repels test particles from the cluster in the compact direction, in a way algebraically similar to that of dark energy. For a typical test object at comoving distance $\chi$ from the nearest dense nodes of the cosmic web of density perturbations, the pressure-to-density ratio $w$ of the equation of state in an FLRW universe, is w \sim - (\chi/L)^3, where $L$ is the size of the fundamental domain, i.e. of the universe. Clearly, |w|<<1. For a T^3 spatial section of exactly equal fundamental lengths, the effect cancels to zero. For a T^3 spatial section of unequal fundamental lengths, the acceleration effect is anisotropic in the sense that it will *tend to equalise the three fundamental lengths*. Provided that at least a modest amount of inflation occurred in the early Universe, and given some other conditions, multiple connectedness does generate an effect similar to that of dark energy, but the amplitude of the effect at the present epoch is too small to explain the observed dark energy density and its anisotropy makes it an unrealistic candidate for the observed dark energy.Comment: 12 pages, 8 figures, accepted by Astronomy & Astrophysics; v2 includes 3D calculation and result; v3 includes analysis of numerical simulation, matches accepted versio

Interpreting the Transmission Windows of Distant Quasars

We propose the Apparent Shrinking Criterion (ASC) to interpret the spatial extent, R_w, of transmitted flux windows in the absorption spectra of high-z quasars. The ASC can discriminate between the two regimes in which R_w corresponds either to the physical size, R_HII, of the quasar HII region, or to the distance, R^{max}_w, at which the transmitted flux drops to =0.1 and a Gunn-Peterson (GP) trough appears. In the first case (HR regime), one can determine the IGM mean HI fraction, x_HI; in the second (PR regime), the value of R_w allows to measure the local photoionization rate and the local enhancement of the photoionization rate, Gamma_G, due to nearby/intervening galaxies. The ASC has been tested against radiative transfer+SPH numerical simulations, and applied to 15 high-z (z>5.8) quasars sample from Fan et al. (2006). All sample quasars are found to be in the PR regime; hence, their observed spectral properties (inner flux profile, extent of transmission window) cannot reliably constrain the value of x_HI. Four sample quasars show evidence for a local enhancement (up to 50%) in the local photoionization rate possibly produced by a galaxy overdensity. We discuss the possible interpretations and uncertainties of this result.Comment: 10 pages, 2 figures, accepted for publication in MNRA

Intergalactic UV Background Radiation Field

We have performed proximity effect analysis of low and high resolution data, considering detailed frequency and redshift dependence of the AGN spectra processed through galactic and intergalactic material. We show that such a background flux, calculated using the observed distribution of AGNs, falls short of the value required by the proximity effect analysis by a factor of $\ge$ 2.7. We have studied the uncertainty in the value of the required flux due to its dependence on the resolution, description of column density distribution, systemic redshifts of QSOs etc. We conclude that in view of these uncertainties the proximity effect is consistent with the background contributed by the observed AGNs and that the hypothesized presence of an additional, dust extinct, population of AGNs may not be necessary.Comment: To be published in the Journal of Astronomy and Astrophysics aasms, 2 figures, 2 tables. Paper replaced to include the figure

Cosmic crystallography using short-lived objects - active galactic nuclei

Cosmic crystallography is based on the principle that peaks in the pair separation histogram (PSH) of objects in a catalogue should be induced by the high number of topologically lensed pairs that are separated by Clifford translations, in excess to ``random'' pairs of objects. Here we present modifications of this method that successively improve the signal-to-noise ratio by removing a large part of the noise and then false signals induced by selection effects. Given the transient nature of the most readily available tracer objects, active galactic nuclei (AGNs), the former is possible because a natural filter for removing many of the noise pairs is available: when counting pairs of objects in order to create PSHs, only those with nearly identical redshifts need to be counted. This redshift filter (a maximum value of $\Delta z/z = 0.005$) was applied to a compilation of AGN catalogues. Further noise was removed by applying a second filter, a maximum angle $\Delta \theta =0.075$ rad, and a minimum number of pairs \protect\npairs=3 to find each ``bunch of pairs'' (BoP) where the {\em vectors} (in Euclidean comoving space) defined by pairs are required to be nearly equal, whereas in the PSH only the {\em lengths} must be nearly equal. These filters reveal significant signals, which, however, are due to selection effects. A third filter, a minimum length \Lselec=150 {\hMpc} between the (parallel) vectors in a BoP, is found to effectively remove these selection effect pairs. After application of these successive filters, no significant topological signal was found.Comment: 9 pages, 8 figures, matches the version accepted by Astronomy & Astrophysic