Prof Gavin Dalton

Abstract:

We present a detailed analysis of the two-point correlation function, ξ (σ, π) from the 2dF Galaxy Redshift purvey (2dFGRS). The large size of the catalogue, which contains ∼220 000 redshifts, allows us to make high-precision measurements of various properties of the galaxy clustering pattern. The effective redshift at which our estimates are made is z s ≈ 0.15, and similarly the effective luminosity, Ls ≈ 1.4L*. We estimate the redshift-space correlation function, ξ(s), from which we measure the redshift-space clustering length, S0 = 6. 82 ± 0.28 h^-1 Mpc. We also estimate the projected correlation function, Ξ (σ), and the real-space correlation function, ξ(r), which can be fit by a power law (r/r0)^-γr, with r0 = 5.05 ± 0.26 h^-1 Mpc, γr = 1.67 ± 0.03. For r ≳ 20 h^-1 Mpc, ξ drops below a power law as, for instance, is expected in the popular A cold dark matter model. The ratio of amplitudes of the real- and redshift-space correlation functions on scales of 8-30 h^-1 Mpc gives an estimate of the redshift-space distortion parameter β. The quadrupole moment of ξ(σ, π) on scales 30-40 h^-1 Mpc provides another estimate of β. We also estimate the distribution function of pairwise peculiar velocities, f(v), including rigorously the significant effect due to the infall velocities, and we find that the distribution is well fit by an exponential form. The accuracy of our ξ(σ, π) measurement is sufficient to constrain a model, which simultaneously fits the shape and amplitude of ξ(r) and the two redshift-space distortion effects parametrized by β and velocity dispersion, a. We find β= 0.49 ± 0.09 and a = 506 ± 52 km s^-1, although the best-fitting values are strongly correlated. We measure the variation of the peculiar velocity dispersion with projected separation, a(σ), and find that the shape is consistent with models and simulations. This is the first time that β and f(v) have been estimated from a self-consistent model of galaxy velocities. Using the constraints on bias from recent estimates, and taking account of redshift evolution, we conclude that β (L = L*,z = 0) = 0.47 ± 0.08, and that the present-day matter density of the Universe, Ωm ≈ 0.3, consistent with other 2dFGRS estimates and independent analyses.

Abstract:

Results of optical identification of the ASCA Lynx Deep Survey are presented. Six X-ray sources are detected in the 2-7 keV band using the Solid-State Imaging Spectrometer in a ∼20′ × 20′ field of view with fluxes larger than ∼4 × 10-14 ergs s -1 cm-2 in the band. Follow-up optical spectroscopic observations were made, and five out of six sources are identified with active galactic nuclei/quasi-stellar objects (AGNs/QSOs) at redshifts of 0.5-1.3. We also identify two more additional X-ray sources detected in a soft X-ray band with AGNs/QSOs. We find that three QSOs identified are located at z ∼ 1.3. Two rich clusters and several groups of galaxies are also placed at the same redshift in the surveyed field, and projected separations between the QSOs and the clusters are 3-8 Mpc at the redshift.

Abstract:

We have calculated the two-point correlation functions in redshift space, Ζ (σ, π), for galaxies of different spectral types in the 2dF Galaxy Redshift Survey. Using these correlation functions, we are able to estimate values of the linear redshift-space distortion parameter, β ≡ Ωm^0.6/b, the pairwise velocity dispersion, a, and the real-space correlation function, Ζ(r), for galaxies with both relatively low star formation rates (for which the present rate of star formation is less than 10 per cent of its past averaged value) and galaxies with higher current star formation activity. At small separations, the real-space clustering of passive galaxies is very much stronger than that of the more actively star-forming galaxies; the correlation-function slopes are, respectively, 1.93 and 1.50, and the relative bias between the two classes is a declining function of scale. On scales larger than 10 h^-1 Mpc, there is evidence that the relative bias tends to a constant, b passive/bactive ≃ 1. This consistent with the similar degrees of redshift-space distortions seen in the correlation functions of the two classes - the contours of Ζ(σ, π) require β active = 0.49 ± 0.13 and βpassive = 0-48 ± 0.14. The pairwise velocity dispersion is highly correlated with β. Despite this, a significant difference is seen between the two classes. Over the range 820 h^-1 Mpc, the pairwise velocity dispersion has mean values of 416 ± 76 and 612 ± 92 km s^-1 for the active and passive galaxy samples, respectively. This is consistent with the expectation from morphological segregation, in which passively evolving galaxies preferentially inhabit the cores of high-mass virialized regions.