arXiv subjects

W. J. Sutherland

Publications and source records attributed to W. J. Sutherland.

27 records · Page 2Linked to original sources

arXiv2002

Studying large-scale structure with the 2dF Galaxy Redshift Survey

The 2dF Galaxy Redshift Survey is the first to observe more than 100,000 redshifts. This allows precise measurements of many of the key statistics of galaxy clustering, in particular redshift-space distortions and the large-scale power spectrum. This paper presents the current 2dFGRS results in these areas. Redshift-space distortions are detected with a high degree of significance, confirming the detailed Kaiser distortion from large-scale infall velocities, and measuring the distortion parameter beta equiv Omega_m^{0.6}/b = 0.43 +- 0.07. The power spectrum is measured to < 10% accuracy for k > 0.02 h Mpc^{-1}, and is well fitted by a CDM model with Omega_m h = 0.20 +- 0.03 and a baryon fraction of 0.15 +- 0.07. A joint analysis with CMB data requires Omega_m = 0.29 +- 0.05, assuming scalar fluctuations, but no priors on other parameters. Two methods are used to determine the large-scale bias parameter: an internal bispectrum analysis yields b = 1.04 +- 0.11, in very good agreement with the b = 1.10 +- 0.08 obtained from a joint 2dFGRS+CMB analysis, again assuming scalar fluctuations. These figures refer to galaxies of approximate luminosity 2L^*; luminosity dependence of clustering is detected at high significance, and is well described by b/b^* = 0.85 + 0.15(L/L^*).

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arXiv2001

The 2dF Galaxy Redshift Survey: Spectra and redshifts

The 2dF Galaxy Redshift Survey (2dFGRS) is designed to measure redshifts for approximately 250000 galaxies. This paper describes the survey design, the spectroscopic observations, the redshift measurements and the survey database. The 2dFGRS uses the 2dF multi-fibre spectrograph on the Anglo-Australian Telescope, which is capable of observing 400 objects simultaneously over a 2-degree diameter field. The source catalogue for the survey is a revised and extended version of the APM galaxy catalogue, and the targets are galaxies with extinction-corrected magnitudes brighter than b_J=19.45. The main survey regions are two declination strips, one in the southern Galactic hemisphere spanning 80deg x 15deg around the SGP, and the other in the northern Galactic hemisphere spanning 75deg x 10deg along the celestial equator; in addition, there are 99 fields spread over the southern Galactic cap. The survey covers 2000 sq.deg and has a median depth of z=0.11. Adaptive tiling is used to give a highly uniform sampling rate of 93% over the whole survey region. Redshifts are measured from spectra covering 3600A-8000A at a two-pixel resolution of 9.0A and a median S/N of 13 per pixel. All redshift identifications are visually checked and assigned a quality parameter Q in the range 1-5; Q>=3 redshifts are 98.4% reliable and have an rms uncertainty of 85 km/s. The overall redshift completeness for Q>=3 redshifts is 91.8%, but this varies with magnitude from 99% for the brightest galaxies to 90% for objects at the survey limit. The 2dFGRS database is available on the WWW at http://www.mso.anu.edu.au/2dFGRS

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arXiv2000

The 1-point PDF of the Initial Conditions of our Local Universe from the IRAS PSC redshift catalogue

The algorithm ZTRACE of Monaco & Efstathiou (1999) is applied to the IRAS PSCz catalogue to reconstruct the initial conditions of our local Universe with a resolution down to ~5 Mpc/h. The 1-point PDF of the reconstructed initial conditions is consistent with the assumptions that (i) IRAS galaxies trace mass on scales of ~5 Mpc/h, and (ii) the statistics of primordial density fluctuations is Gaussian. We use simulated PSCz catalogues, constructed from N-body simulations with Gaussian initial conditions, to show that local non-linear bias can cause the recovered initial PDF (assuming no bias) to be non-Gaussian. However, for plausible bias models, the distortions of the recovered PDF would be difficult to detect using the volume finely sampled by the PSCz catalogue. So, for Gaussian initial conditions, a range of bias models remain compatible with our PSCz reconstruction results.

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arXiv2000

The PSCz Catalogue

We present the catalogue, mask, redshift data and selection function for the PSCz survey of 15411 IRAS galaxies across 84% of the sky. Most of the IRAS data is taken from the Point Source Catalog, but this has been supplemented and corrected in various ways to improve the completeness and uniformity. We quantify the known imperfections in the catalogue, and we assess the overall uniformity, completeness and data quality. We find that overall the catalogue is complete and uniform to within a few percent at high latitudes and 10% at low latitudes. Ancillary information, access details, guidelines and caveats for using the catalogue are given.

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arXiv1999

On density and velocity fields and beta from the IRAS PSCz survey

We present a version of the Fourier Bessel method first introduced by Fisher et al (1994) and Zaroubi et al (1994) with two extensions: (a) we amend the formalism to allow a generic galaxy weight which can be constant rather than the more conventional overweighting of galaxies at high distances, and (b) we correct for the masked zones by extrapolation of Fourier Bessel modes rather than by cloning from the galaxy distribution in neighbouring regions. We test the procedure extensively on N-body simulations and find that it gives generally unbiased results but that the reconstructed velocities tend to be overpredicted in high-density regions. Applying the formalism to the PSZz redshift catalog, we find that beta = 0.7 +/- 0.5 from a comparison of the reconstructed Local Group velocity to the CMB dipole. From an anisotropy test of the velocity field, we find that beta = 1 CDM models models normalized to the current cluster abundance can be excluded with 90% confidence. The density and velocity fields reconstructed agree with the fields found by Branchini et al (1998) in most points. We find a back-infall into the Great Attractor region (Hydra-Centaurus region) but tests suggest that this may be an artifact. We identify all the major clusters in our density field and confirm the existence of some previously identified possible ones.

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arXiv1996

The nature of the supersoft X-ray source RX~J0513--69

We present spectroscopy and photometry of the LMC supersoft binary system RX~J0513.9-6951. We derive a refined spectroscopic period of P$=0.761\pm0.004$~d, which is consistent with the value obtained from long term photometric monitoring (P$=0.76278\pm0.00005$~d). We see bipolar outflow components of He{\sc ii} and H$β$, with velocities of $\sim 3800$\,km\,s$^{-1}$, strongly suggesting that the compact object is a white dwarf. Using all the available optical and X-ray data, we construct a theoretical model to explain the principal features of the unusual variability of this source. In particular, we note that X-ray outbursts have only been seen at times of optical minima. From this, we conclude that the most likely cause of the X-ray outbursts is a photospheric contraction during a nuclear shell burning phase, rather than a thermonuclear flash or shocked emission. The system probably comprises a relatively massive white dwarf accreting at a high rate ($\sim 10^{-6} M_{\odot}~{\rm yr}^{-1}$) from an evolved donor star, and is observed close to pole-on.

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arXiv1996

The APM Galaxy Survey III: An Analysis of Systematic Errors in the Angular Correlation Function and Cosmological Implications

We present measurements of the angular two-point galaxy correlation function, $w(theta)$, from the APM Galaxy Survey. The performance of various estimators of $w$ is assessed using simulated galaxy catalogues and analytic arguments. Several error analyses show that residual plate-to-plate errors do not bias our estimates of $w$ by more than $10^{-3}$. Direct comparison between our photometry and external CCD photometry of over 13,000 galaxies from the Las Campanas Deep Redshift Survey shows that the rms error in the APM plate zero points lies in the range 0.04-0.05 magnitudes, in agreement with our previous estimates. We estimate the effects on $w$ of atmospheric extinction and obscuration by dust in our Galaxy and conclude that these are negligible. We use our best estimates of the systematic errors in the survey to calculate corrected estimates of $w$. Deep redshift surveys are used to determine the selection function of the APM Galaxy Survey, and this is applied in Limber's equation to compute how $w$ scales as a function of limiting magnitude. Our estimates of $w$ are in excellent agreement with the scaling relation, providing further evidence that systematic errors in the APM survey are small. We explicitly remove large-scale structure by applying filters to the APM galaxy maps and conclude that there is still strong evidence for more clustering at large scales than predicted by the standard scale-invariant cold dark matter (CDM) model. We compare the APM $w$ and the three dimensional power spectrum derived by inverting $w$, with the predictions of scale-invariant CDM models. We show that the observations require $Gamma=Omega_0 h$ in the range 0.2-0.3 and are incompatible with the value $Gamma=0.5$ of the standard CDM model.

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arXiv1994

The Two-Point Correlation Function of Rich Clusters of Galaxies: Results from an Extended APM Cluster Redshift Survey

We present new estimates of the spatial two-point correlation function of rich clusters of galaxies selected from the APM Galaxy Survey. We have measured redshifts for a sample of $364$ clusters out to a depth of $\sim 450\hmpc$. The clusters have a mean space density of $\bar{n} = 3.4\times 10^{-5}\hmpccc$. The two-point correlation function, $ξ_{cc}$, for this sample is equal to unity at a pair-separation of $r_0 = 14.3\pm1.75\hmpc$ (2$σ$ errors), consistent with our earlier results from a smaller sample. The new observations provide an accurate determination of the shape of $ξ_{cc}$ to pair-separations of about $50\hmpc$. Our results show that $ξ_{cc}$ has a higher amplitude than expected according to the standard $Ω=1$ cold dark matter (CDM) model on spatial scales $2\simlt s \simlt 50\hmpc$, but are in good agreement with scale-invariant fluctuations in either a low density CDM model or a critical density universe made up of a mixture of hot and cold dark matter. Our results provide strong constraints on so called `co-operative' models of galaxy formation in which the galaxy formation process introduces large-scale structure in the galaxy distribution.

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arXiv1993

The Apm Galaxy Survey IV: Redshifts of Rich Clusters of Galaxies

We present redshifts for a sample of 229 clusters selected from the APM Galaxy Survey, 189 of which are new redshift determinations. Non-cluster galaxy redshifts have been rejected from this sample using a likelihood ratio test based on the projected and apparent magnitude distributions of the cluster fields. We test this technique using cluster fields in which redshifts have been measured for more than 10 galaxies. Our redshift sample is nearly complete and has been used in previous papers to study the three dimensional distribution of rich clusters of galaxies. 157 of the clusters in our sample are listed in the Abell catalogue or supplement, and the remainder are new cluster identifications.

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