arXiv subjects

Fiona Hoyle

Publications and source records attributed to Fiona Hoyle.

33 records · Page 2Linked to original sources

arXiv2003

The 2dF QSO Redshift Survey - XIII. A Measurement of Lambda from the QSO Power Spectrum

We report on measurements of the cosmological constant, Lambda, and the redshift space distortion parameter beta=Omega_m^0.6/b, based on an analysis of the QSO power spectrum parallel and perpendicular to the observer's line of sight, from the final catalogue of the 2dF QSO Redshift Survey. We derive a joint Lambda - beta constraint from the geometric and redshift-space distortions in the power spectrum. By combining this result with a second constraint based on mass clustering evolution, we break this degeneracy and obtain strong constraints on both parameters. Assuming a flat cosmology and a Lambda cosmology r(z) function to convert from redshift into comoving distance, we find best fit values of Omega_Lambda=0.71^{+0.09}_{-0.17} and beta(z~1.4)=0.45^{+0.09}_{-0.11}. Assuming instead an EdS cosmology r(z) we find that the best fit model obtained, with Omega_Lambda=0.64^{+0.11}_{-0.16} and beta(z~1.4)=0.40^{+0.09}_{-0.09}, is consistent with the Lambda r(z) results, and inconsistent with a Lambda=0 flat cosmology at over 95 per cent confidence.

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arXiv2003

The Luminosity Function of Void Galaxies in the Sloan Digital Sky Survey

(Abridged) The Sloan Digital Sky Survey now extends over a large enough region that galaxies in low density environments can be detected. Rojas et al. have developed a technique to extract more than 1000 void galaxies with delta rho/rho < -0.6 on scales r>7 h^{-1} Mpc from the SDSS. In this paper, we present the luminosity function of these galaxies and compare it to that of galaxies at higher densities. We obtain a measurement of the void galaxy luminosity function over the range -21.5 5A wall galaxies is very similar in shape to that of the void galaxies, with only slightly brighter M_r* values and similar values of alpha. The value of alpha ~ -1.2 found from the void galaxy LF is shallower that that found from CDM models, suggesting that voids are not filled with a large population of dwarf galaxies.

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arXiv2003

The 2dF QSO Redshift Survey - XI. The QSO Power Spectrum

We present a power spectrum analysis of the final 2dF QSO Redshift Survey catalogue containing 22652 QSOs. Utilising the huge volume probed by the QSOs, we can accurately measure power out to scales of ~500Mpc and derive new constraints, at z~1.4, on the matter and baryonic contents of the Universe. Importantly, these new cosmological constraints are derived at an intermediate epoch between the CMB observations at z~1000, and local (z~0) studies of large-scale structure; the average QSO redshift corresponds to a look-back time of approximately two-thirds of the age of the Universe. We find that the amplitude of clustering of the QSOs at z~1.4 is similar to that of present day galaxies. The power spectra of the QSOs at high and low redshift are compared and we find little evidence for any evolution in the amplitude. Assuming a lambda cosmology to derive the comoving distances, r(z), to the QSOs, the power spectrum derived can be well described by a model with shape parameter Gamma=0.13+-0.02. If an Einstein-de Sitter model r(z) is instead assumed, a slightly higher value of Gamma=0.16+-0.03 is obtained. A comparison with the Hubble Volume LCDM simulation shows very good agreement over the whole range of scales considered. A standard (Omega_m=1) CDM model, however, predicts a much higher value of Gamma than is observed, and it is difficult to reconcile such a model with these data. We fit CDM model power spectra (assuming scale-invariant initial fluctuations), convolved with the survey window function, and corrected for redshift space distortions, and find that models with baryon oscillations are slightly preferred, with the baryon fraction Omega_b/Omega_m=0.18+-0.10. The overall shape of the power spectrum provides a strong constraint on Omega_m*h (where h is the Hubble parameter), with Omega_m*h=0.19+-0.05.

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arXiv2002

Three-Dimensional Genus Statistics of Galaxies in the SDSS Early Data Release

We present the first analysis of three-dimensional genus statistics for the SDSS EDR galaxy sample. Due to the complicated survey volume and the selection function, analytic predictions of the genus statistics for this sample are not feasible, therefore we construct extensive mock catalogs from N-body simulations in order to compare the observed data with model predictions. This comparison allows us to evaluate the effects of a variety of observational systematics on the estimated genus for the SDSS sample, including the shape of the survey volume, the redshift distortion effect, and the radial selection function due to the magnitude limit. The observed genus for the SDSS EDR galaxy sample is consistent with that predicted by simulations of a $Λ$-dominated spatially-flat cold dark matter model. Standard ($Ω_0=1$) cold dark matter model predictions do not match the observations. We discuss how future SDSS galaxy samples will yield improved estimates of the genus.

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arXiv2002

Galaxy Voids in Cold Dark Matter Universes

We present predictions for numerous statistics related to the presence of voids in the distribution of galaxies in a cold dark matter model of structure formation using a semi-analytic model of galaxy formation. Our study is able to probe galaxies with masses as low as 10^9Msun/h corresponding to absolute magnitudes of M_bJ-5log(h)=-18.1 and M_r-5log(h)=-18.7. We quantify the void and underdense probability functions, distributions of nearest neighbour distances and void sizes and compute the density profiles of voids. These results are contrasted with the expectations for dark matter (and the difference examined in terms of the galaxy/dark matter biasing relation) and are compared to analytic predictions and observational data where available. The predicted void probability functions are consistent with those measured from the Center for Astrophysics redshift surveys given the rather large uncertainties in this relatively small (for studies of voids) observational sample. The size of the observational sample is too small to probe the bias between galaxies and dark matter that we predict. We also examine the predicted properties of galaxies living within voids and contrast these with the general galaxy population. Our predictions are aimed at forthcoming large galaxy redshift surveys which should for the first time provide statistically accurate measures of the void population.

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arXiv2002

Two-Dimensional Topology of the Sloan Digital Sky Survey

We present the topology of a volume-limited sample of 11,884 galaxies, selected from an apparent-magnitude limited sample of over 100,000 galaxies observed as part of the Sloan Digital Sky Survey (SDSS). The data currently cover three main regions on the sky: one in the Galactic north and one in the south, both at zero degrees declination, and one area in the north at higher declination. Each of these areas covers a wide range of survey longitude but a narrow range of survey latitude, allowing the two dimensional genus to be measured. The genus curves of the SDSS sub-samples are similar, after appropriately normalizing these measurements for the different areas. We sum the genus curves from the three areas to obtain the total genus curve of the SDSS. The total curve has a shape similar to the genus curve derived from mock catalogs drawn from the Hubble Volume Lambda CDM simulation and is similar to that of a Gaussian random field. Likewise, comparison with the genus of the 2dFGRS, after normalization for the difference in area, reveals remarkable similarity in the topology of these samples. We test for the effects of galaxy type segregation by splitting the SDSS data into thirds, based on the u^*- r^* colors of the galaxies, and measure the genus of the reddest and bluest sub-samples. This red/blue split in u^*- r^* is essentially a split by morphology (Strateva et al. 2001). We find that the genus curve for the reddest galaxies exhibits a ``meatball'' shift of the topology -- reflecting the concentration of red galaxies in high density regions -- compared to the bluest galaxies and the full sample, in agreement with predictions from simulations.

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arXiv2002

Testing Stellar Population Models with Star Clusters in the Large Magellanic Cloud

We present high S/N integrated spectra of 24 star clusters in the LMC obtained using the FLAIR spectrograph at the UK Schmidt. The spectra have been placed onto the Lick/IDS system in order to test the calibration of Simple Stellar Population (SSP) models. We have compared the SSP-predicted metallicities of the clusters with literature Ca-Triplet values, and find that there is good agreement in the range --2.10 < [Fe/H] < 0. However, the magnesium indices systematically predict higher metallicities than iron, among the possible explanations for this are that the LMC clusters possess [alpha/Fe] > 0. We present metallicities for 11 clusters with no previous measurements. Comparison of the SSP ages of the clusters (from Balmer lines) with the literature data shows good agreement for the majority. This includes six old globular clusters in our sample, which have ages consistent with their HST CMD turn-offs. However, two clusters, NGC 1754 and NGC 2005, have Hbeta line-strengths which lead to ages which are too young (~8 and ~6 Gyr respectively at 3 sigma) for their HST CMDs. Comparison between the horizontal branch (HB) morphology and Balmer lines of these clusters suggests that blue HBs have increased their Balmer indices by up to ~1.0 angstrom. We conclude that the Lick/IDS indices, used in conjunction with contemporary SSP models, are able to reproduce the ages and metallicities of the LMC clusters reassuringly well. However, SSP model ages derived for metal-poor globular clusters are ambiguous without a priori knowledge of HB morphology (abridged).

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arXiv2002

Voids in the PSCz Survey and the Updated Zwicky Catalog

We describe an algorithm to detect voids in galaxy redshift surveys. The method is based on the void finder algorithm of El-Ad & Piran. We apply a series of tests to determine how accurately we are able to recover the volumes of voids using our detection method. We simulate voids of different ellipticity and find that if voids are approximately spherical, our algorithm will recover 100% of the volume of the void. The more elliptical the void, the smaller the fraction of the volume we can recover. We insist that voids lie completely within the survey. Voids close to the edge of the survey will therefore be underestimated in volume. By considering a deeper sample, we estimate the maximal sphere diameters are correct to within 30%. We apply the algorithm to the Point Source Catalogue Survey (PSCz) and the Updated Zwicky Catalog (UZC). The PSCz survey is an almost all-sky survey with objects selected from the IRAS catalog. The UZC covers a smaller area of sky but is optically selected and samples the structures more densely. We detect 35 voids in the PSCz and 19 voids in the UZC with diameter larger than 20h^{-1}Mpc. Using this minimum size threshold, voids have an average effective diameter of 29.8+-3.5 h^{-1}Mpc (PSCz) and 29.2+-2.7 h^{-1}Mpc (UZC) and that they are underdense regions with delta rho /rho values of -0.92+-0.03 (PSCz) and -0.96+-0.01(UZC) respectively. Using this quite stringent threshold for void definition, voids fill up to 40% of the volume of the universe.

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arXiv2001

Two-Dimensional Topology of the 2dF Galaxy Redshift Survey

We study the topology of the publicly available data released by the 2dFGRS. The 2dFGRS data contains over 100,000 galaxy redshifts with a magnitude limit of b_J=19.45 and is the largest such survey to date. The data lie over a wide range of right ascension (75 degree strips) but only within a narrow range of declination (10 degree and 15 degree strips). This allows measurements of the two-dimensional genus to be made. The NGP displays a slight meatball shift topology, whereas the SGP displays a bubble like topology. The current SGP data also have a slightly higher genus amplitude. In both cases, a slight excess of overdense regions are found over underdense regions. We assess the significance of these features using mock catalogs drawn from the Virgo Consortium's Hubble Volume LCDM z=0 simulation. We find that differences between the NGP and SGP genus curves are only significant at the 1 sigma level. The average genus curve of the 2dFGRS agrees well with that extracted from the LCDM mock catalogs. We compare the amplitude of the 2dFGRS genus curve to the amplitude of a Gaussian random field with the same power spectrum as the 2dFGRS and find, contradictory to results for the 3D genus of other samples, that the amplitude of the GRF genus curve is slightly lower than that of the 2dFGRS. This could be due to a a feature in the current data set or the 2D genus may not be as sensitive as the 3D genus to non-linear clustering due to the averaging over the thickness of the slice in 2D. (Abridged)

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arXiv2001

Voids in Galaxy Redshift Surveys

One of the most striking features in galaxy redshift surveys is the ubiquitous presence of voids. However, voids have not been extensively studied due to observational limitations. Until recently, galaxy redshift surveys included only a few voids of diameter > 30 h-1Mpc. The first step in studying voids is the identification process. We outline a method for detecting voids (based on the method of El-Ad and Piran 1997, EP97). We apply it to the PSCz survey, and the Updated Zwicky Catalog. We find that voids have typical diameters of ~30 h-1Mpc and are very underdense regions with (delta rho)/rho ~ -0.95. Up to 40% of volume of the Universe is occupied by voids. We discuss the results from these surveys and our detection algorithm's usefulness for future surveys. The next generation of surveys (such as the Sloan Digital Sky Survey and 2dFGRS) will improve this situation. The surveys will extend to greater depths, allowing a more statistically complete sample of voids to be obtained and the accompanying digital imaging will provide accurate photometry of fainter objects. This will allow us to gain greater insight into the nature of voids, search for possible void galaxies and maybe place constraints on cosmological parameters as voids play a critical role in the evolution of large scale structure.

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arXiv2001

The 2dF QSO Redshift Survey - IV. The QSO Power Spectrum from the 10k Catalogue

(ABRIDGED) We present a power spectrum analysis of the 10K catalogue from the 2dF QSO Redshift Survey. We compare the redshift-space power spectra of QSOs to those measured for galaxies and Abell clusters at low redshift and find that they show similar shapes in their overlap range, 50-150h^{-1}Mpc, with P_QSO(k)\propto k^{-1.4}. The amplitude of the QSO power spectrum at z~1.4 is almost comparable to that of galaxies at the present day if Omega_m=0.3 and Omega_Lambda=0.7 (the Lambda cosmology), and a factor of ~3 lower if Omega_m=1 (the EdS cosmology) is assumed. The amplitude of the QSO power spectrum is a factor of ~10 lower than that measured for Abell clusters at the present day. At larger scales, the QSO power spectra continue to rise robustly to ~400 h^{-1}Mpc, implying more power at large scales than in the APM galaxy power spectrum measured by Baugh & Efstathiou. We split the QSO sample into two redshift bins and find little evolution in the amplitude of the power spectrum. The QSO power spectrum may show a spike feature at ~90h^{-1}Mpc assuming the Lambda cosmology or ~65 h^{-1}Mpc assuming an EdS cosmology. Although the spike appears to reproduce in both the North and South strips and in two independent redshift ranges, its statistical significance is still marginal and more data is needed to test further its reality. We compare the QSO power spectra to CDM models to obtain a constraint on the shape parameter, Gamma. For two choices of cosmology (Omega_m=1, Omega_Lambda=0 and Omega_m=0.3, Omega_Lambda=0.7), we find the best fit model has Gamma~0.1 +-0.1.

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arXiv2001

The 2dF QSO Redshift Survey - VI. Measuring Lambda and Beta from Redshift-space Distortions in the Power Spectrum

When the 2dF QSO Redshift Survey (2QZ) is complete, a powerful geometric test for the cosmological constant will be available. By comparing the clustering along and across the line of sight and modelling the effects of peculiar velocities and bulk motions in redshift space, geometric distortions, which occur if the wrong cosmology is assumed, can be detected. In this paper we investigate the effect of geometric and redshift-space distortions in the power spectrum parallel and perpendicular to the observer's line of sight. Ballinger et al. developed a model to estimate the cosmological constant, $Λ$, and the important parameter $β\approx Ω_m^{0.6}/b$ from these distortions. We apply this model to a detailed simulation of the final 25k 2QZ, produced using the Virgo Consortium's huge {\it Hubble Volume} N-body $Λ$-CDM light cone simulation. We confirm the conclusions of Ballinger et al.; the shape of the redshift-space and geometric distortions are very similar. When all the uncertainties are taken into account we find that only a joint $Λ- β$ constraint is possible. By combining this result with a second constraint based on mass clustering evolution, however, we can make significant progress. We predict that this method should allow us to constrain $β$ to approximately $\pm0.1$, and $Ω_{m}$ to $\pm0.25$ using the final catalogue. We apply the method to the 2QZ catalogue of 10000 QSOs and find that this incomplete catalogue marginally favours a $Λ$ cosmology.

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arXiv2001

The 2dF QSO Redshift Survey - VII. Constraining Cosmology from Redshift Space Distortions via xi(sigma,pi)

We describe a method from which cosmology may be constrained from the 2QZ Survey. By comparing clustering properties parallel and perpendicular to the line of sight and by modeling the effects of redshift space distortions, we are able to study geometric distortions in the clustering pattern which occur if a wrong cosmology is assumed when translating redshifts into comoving distances. Using mock 2QZ catalogues, drawn from the Hubble Volume simulation, we find, that there is a degeneracy between the geometric and the redshift-space distortions that makes it difficult to obtain an unambiguous estimate of Omega_{m}(0) from the geometric tests alone. However, we demonstrate a new method to determine the cosmology which works by combining the above geometric test with a test based on the evolution of the QSO clustering amplitude. We find that we are able to break the degeneracy and that independent constraints to +-20% (1 sigma) accuracy on Omega_{m}(0) and +-10% (1 sigma) accuracy on beta_{QSO}(z) should be possible in the full 2QZ survey. Finally we apply the method to the 10k catalogue of 2QZ QSOs. The smaller number of QSOs and the current status of the Survey mean that a strong result on cosmology is not possible but we do constrain beta_{QSO}(z) to 0.35+-0.2. By combining this constraint with the further constraint available from the amplitude of QSO clustering, we find tentative evidence favouring a model with non-zero Omega_{Lambda}(0), although an Omega_{m}(0)=1 model provides only a marginally less good fit. A model with Omega_{Lambda}(0)=1 is ruled out. The results are in agreement with those found by Outram et al. using a similar analysis in Fourier space. (Abridged)

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arXiv2000

Higher Order Clustering in the Durham/UKST and Stromlo-APM Galaxy Redshift Surveys

We present a counts-in-cells analysis of clustering in the optically selected Durham/UKST and Stromlo-APM Galaxy Redshift Surveys. Minimum variance estimates of the second moment, skewness (S_3) and kurtosis (S_4) of the count probability distribution are extracted from a series of volume limited samples of varying radial depth. The corresponding theoretical error calculation takes into account all sources of statistical error on the measurement of the moments, and is in good agreement with the dispersion over mock redshift catalogues. The errors that we find on S_3 and S_4 are larger than those quoted in previous studies, in spite of the fact that the surveys we consider cover larger volumes. S_3 varies little with cell size, with values in the range 1.8-2.2 and errors ~20%, for cubical cells of side 3-20 h^{-1}Mpc. Direct measurements of S_3 are possible out to ~35 h^{-1}Mpc, though with larger errors. A significant determination of S_4 is only possible for one scale, l=6 h^{-1}Mpc, with S_4~5. We compare our results with theoretical predictions from N-body simulations of cold dark matter universes. Qualitatively, the skewness of the dark matter has the same form as that of the galaxies. However, the amplitude of the galaxy S_3 is lower than that predicted for the dark matter. Our measurements of S_3 are consistent with the predictions of a simple model in which initially Gaussian fluctuations in the dark matter evolve gravitationally, if a second order bias term is specified, in addition to the traditional linear bias, in order to describe the relation between the distribution of galaxies and dark matter.

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arXiv2000

The Durham/UKST Galaxy Redshift Survey - VII. Redshift-space distortions in the power spectrum

We investigate the effect of redshift-space distortions in the power spectrum parallel and perpendicular to the observer's line of sight, P(k_par,k_perp), using the optically selected Durham/UKST Galaxy Redshift Survey. On small, non-linear scales anisotropy in the power-spectrum is dominated by the galaxy velocity dispersion; the `Finger of God' effect. On larger, linear scales coherent peculiar velocities due to the infall of galaxies into overdense regions are the main cause of anisotropy. According to gravitational instability theory these distortions depend only on the density and bias parameters via beta. Geometrical distortions also occur if the wrong cosmology is assumed, although these would be relatively small given the low redshift of the survey. To quantify these effects, we assume the real-space power spectrum of the APM Galaxy Survey, and fit a simple model for the redshift-space and geometrical distortions. Assuming a flat Omega = 1 universe, we find values for the one-dimensional pairwise velocity dispersion of sigma_p = 410 +- 170 km/s, and beta = 0.38 +- 0.17. An open Omega = 0.3, and a flat Omega = 0.3, Lambda = 0.7 universe yield sigma_p = 420 km/s, beta = 0.40, and sigma_p = 440 km/s, beta = 0.45 respectively, with comparable errors. These results are consistent with estimates using the two-point galaxy correlation function, xi(sigma,pi), and favour either a low-density universe with Omega ~ 0.3 if galaxies trace the underlying mass distribution, or a bias factor of b ~ 2.5 if Omega = 1.

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