Ionizing radiation fluctuations and large-scale structure in the Lyman-alpha forest

We investigate the large-scale inhomogeneities of the hydrogen ionizing radiation field in the Universe at redshift z=3. Using a raytracing algorithm, we simulate a model in which quasars are the dominant sources of radiation. We make use of large scale N-body simulations of a LambdaCDM universe, and include such effects as finite quasar lifetimes and output on the lightcone, which affects the shape of quasar light echoes. We create Lya forest spectra that would be generated in the presence of such a fluctuating radiation field, finding that the power spectrum of the Lya forest can be suppressed by as much as 15 % for modes with k=0.05-1 Mpc/h. This relatively small effect may have consequences for high precision measurements of the Lya power spectrum on larger scales than have yet been published. We also investigate another radiation field probe, the cross-correlation of quasar positions and the Lya forest. For both quasar lifetimes which we simulate (10^7 yr and 10^8 yr), we expect to see a strong decrease in the Lya absorption close to other quasars (the ``foreground'' proximity effect). We then use data from the Sloan Digital Sky Survey First Data Release to make an observational determination of this statistic. We find no sign of our predicted lack of absorption, but instead increased absorption close to quasars. If the bursts of radiation from quasars last on average < 10^6 yr, then we would not expect to be able to see the foreground effect. However, the strength of the absorption itself seems to be indicative of rare objects, and hence much longer total times of emission per quasar. Variability of quasars in bursts with timescales > 10^4yr and < 10^6 yr could reconcile these two facts.Comment: Submitted to ApJ, 21 pages, 17 postscript figures, emulateapj.st

A META ANALYSIS OF CONTINGENT VALUES FOR GROUNDWATER QUALITY IN THE UNITED STATES

This paper provides an overview and a meta analysis of existing US contingent valuation studies of groundwater quality. Using 108 observations from 14 studies, core economic variables, risk variables, and elicitation effects are found to systematically influence groundwater values. Other research design features are also investigated.Resource /Energy Economics and Policy,

Compact Nuclei in Galaxies at Moderate Redshift:II. Their Nature and Implications for the AGN Luminosity Function

This study explores the space density and properties of active galaxies to z=0.8. We have investigated the frequency and nature of unresolved nuclei in galaxies at moderate redshift as indicators of nuclear activity such as Active Galactic Nuclei (AGN) or starbursts. Candidates are selected by fitting imaged galaxies with multi-component models using maximum likelihood estimate techniques to determine the best model fit. We select those galaxies requiring an unresolved point-source component in the galaxy nucleus, in addition to a disk and/or bulge component, to adequately model the galaxy light. We have searched 70 WFPC2 images primarily from the Medium Deep Survey for galaxies containing compact nuclei. In our survey of 1033 galaxies, the fraction containing an unresolved nuclear component greater than 5% of the total galaxy light is 9+/-1% corrected for incompleteness. In this second of two papers in this series, we discuss the nature of the compact nuclei and their hosts. We present the upper limit luminosity function (LF) for low-luminosity AGN (LLAGN) in two redshift bins to z=0.8. Mild number density evolution is detected for nuclei at -18 -16 and this flatness, combined with the increase in number density, is inconsistent with pure luminosity evolution. Based on the amount of density evolution observed for these objects, we find that almost all present-day spiral galaxies could have hosted a LLAGN at some point in their lives. We also comment on the likely contribution of these compact nuclei to the soft X-ray background.Comment: 50 pages, 14 figures, to appear in ApJ, April 199

The unquenched Upsilon spectrum

We describe the bottomonium spectrum obtained on the UKQCD dynamical ensembles and its comparison to quenched results. We include a determination of alpha_s and m_b from the dynmaical results.Comment: Lattice 2000 (Heavy Quark Physics

2dF QSO Redshift Survey

With approximately 6000 QSO redshifts,the 2dF QSO redshift survey is already the biggest complete QSO survey. The aim for the survey is to have 25000 QSO redshifts, providing an order of magnitude increase in QSO clustering statistics. We first describe the observational parameters of the 2dF QSO survey. We then describe several highlights of the survey so far, including new estimates of the QSO luminosity function and its evolution. We also review the current status of QSO clustering analyses from the 2dF data. Finally, we discuss how the complete QSO survey will be able to constrain the value of Omega_o by measuring the evolution of QSO clustering, place limits on the cosmological constant via a direct geometrical test and determine the form of the fluctuation power-spectrum out to the approximately 1000 Mpc scales only previously probed by COBE.Comment: 6 pages; to be published in Clustering at High Redshift, Marseille, June 1999, eds. A. Mazure, O. LeFevre, V. Lebru

Compton Heating of the Intergalactic Medium by the Hard X-ray Background

High-resolution hydrodynamics simulations of the Ly-alpha forest in cold dark matter dominated cosmologies appear to predict line widths that are substantially narrower than those observed. Here we point out that Compton heating of the intergalactic gas by the hard X-ray background (XRB), an effect neglected in all previous investigations, may help to resolve this discrepancy. The rate of gain in thermal energy by Compton scattering will dominate over the energy input from hydrogen photoionization if the XRB energy density is 0.2x/ times higher than the energy density of the UV background at a given epoch, where x is the hydrogen neutral fraction in units of 1e-6 and is the mean X-ray photon energy in units of m_ec^2. The numerical integration of the time-dependent rate equations shows that the intergalactic medium approaches a temperature of about 1.5e4 K at z>3 in popular models for the redshift evolution of the extragalactic background radiation. The importance of Compton heating can be tested experimentally by measuring the Ly-alpha line-width distribution as a function of redshift, thus the Lyman-alpha forest may provide a useful probe of the evolution of the XRB at high redshifts.Comment: LaTeX, 10 pages, 2 figures, final version to be published in the Ap

The 2dF QSO Redshift Survey

We present preliminary results from the 2-degree Field (2dF) QSO Redshift Survey currently under way at the Anglo-Australian Telescope. This survey aims to determine the redshifts of >25000 QSOs over a redshift range of 0.3<z<3.0 with the primary goal of investigating large-scale structure in the Universe to high redshift and at very large scales (~1000h-1Mpc). We describe the photometric procedure used to select QSO candidates for spectroscopic observation. We then describe results from our first 2dF observations, which have so far measured the redshifts for over 1000 QSOs. We already find a significant detection of clustering and have also found one close pair of QSOs (separation 17'') which are gravitational lens candidates. To keep up to date with the current progress of the survey see: http://msowww.anu.edu.au/~rsmith/QSO_Survey/qso_surv.htmlComment: 5 pages Latex including 6 figures, To appear in the proceedings of "Evolution of Large Scale Structure: From Recombination to Garching", held August 199

A comparison of the optical properties of radio-loud and radio-quiet quasars

We have made radio observations of 87 optically selected quasars at 5 GHz with the VLA in order to measure the radio power for these objects and hence determine how the fraction of radio-loud quasars varies with redshift and optical luminosity. The sample has been selected from the recently completed Edinburgh Quasar Survey and covers a redshift range of 0.3 < z < 1.5 and an optical absolute magnitude range of -26.5 < M_{B} < -23.5 (h, q_{0} = 1/2). We have also matched up other existing surveys with the FIRST and NVSS radio catalogues and combined these data so that the optical luminosity-redshift plane is now far better sampled than previously. We have fitted a model to the probability of a quasar being radio-loud as a function of absolute magnitude and redshift and from this model infer the radio-loud and radio-quiet optical luminosity functions. The radio-loud optical luminosity function is featureless and flatter than the radio-quiet one. It evolves at a marginally slower rate if quasars evolve by density evolution, but the difference in the rate of evolutions of the two different classes is much less than was previously thought. We show, using Monte-Carlo simulations, that the observed difference in the shape of the optical luminosity functions can be partly accounted for by Doppler boosting of the optical continuum of the radio-loud quasars and explain how this can be tested in the future.Comment: 33 pages, 9 postscript figures, uses the AAS aaspp4 LaTeX style file, to appear in the 1 February 1999 issue of The Astrophysical Journa

The Evolution of Radio Galaxies at Intermediate Redshift

We describe a new estimate of the radio galaxy 1.4 GHz luminosity function and its evolution at intermediate redshifts (z~0.4). Photometric redshifts and color selection have been used to select Bj<23.5 early-type galaxies from the Panoramic Deep Fields, a multicolor survey of two 25 sq deg fields. Approximately 230 radio galaxies have then been selected by matching early-type galaxies with NVSS radio sources brighter than 5 mJy. Estimates of the 1.4 GHz luminosity function of radio galaxies measure significant evolution over the observed redshift range. For an Omega_M=1 cosmology the evolution of the radio power is consistent with luminosity evolution where P(z)=P(0)(1+z)^{k_L} and 3<k_L<5. The observed evolution is similar to that observed for UVX and X-ray selected AGN and is consistent with the same physical process being responsible for the optical and radio luminosity evolution of AGN.Comment: 26 pages, 9 Figures, Accepted for Publication in A

QSO clustering and the AAT 2dF redshift survey

We review previous results on the clustering and environments of QSOs. We show that the correlation length for QSOs derived from existing surveys is r~5/h Mpc, similar to the observed correlation length for field galaxies at the present epoch. The galaxy environment for z<1 radio-quiet QSOs is also consistent with field galaxies. The evolution of the QSO correlation length with redshift is currently uncertain, largely due to the small numbers of QSOs (~2000) in surveys suitable for clustering analysis. We report on intial progress with the AAT 2dF QSO redshift survey, which, once completed will comprise almost 30000 QSOs. With over 1000 QSOs already observed, it is already the largest single homogeneous QSO survey. We discuss prospects for deriving limits on cosmological parameters from this survey, and on the evolution of large-scale structure in the Universe.Comment: Invited talk at RS meeting on 'Large Scale Structure in the Universe' held at the Royal Society on 25-26 March 1998 14 pages, 11 figre