Comparison of the SFI peculiar velocities with the IRAS 1.2-Jy gravity field

We present a comparison between the peculiar velocity fields measured from a recently completed l -band Tully–Fisher survey of field spirals (SFI) and that derived from the IRAS 1.2-Jy redshift survey galaxy distribution. The analysis is based on the expansion of these data in redshift space using smooth orthonormal functions, and is performed using low- and high-resolution expansions, with an effective smoothing scale which increases almost linearly with redshift. The effective smoothing scales at 3000 km s⁻¹ are 1500 and 1000 km s⁻¹ for the low- and high-resolution filters. The agreement between the high- and low-resolution SFI velocity maps is excellent. The general features in the filtered SFI and IRAS velocity fields agree remarkably well within 6000 km s⁻¹. This good agreement between the fields allows us to determine the parameter β = Ω^0.6 / b , where Ω is the cosmological density parameter, and b is the linear biasing factor. From a likelihood analysis on the SFI and IRAS modes we find that β = 0.6 ± 0.1, independently of the resolution of the modal expansion. For this value of β, the residual fields for the two filters show no systematic variations within 6000 km s⁻¹. Most remarkable is the lack of any coherent, redshift-dependent dipole flow in the residual field.     

A case devoid of bias: Optical Redshift Survey voids versus IRAS voids

We present a comparison between the voids in two nearly all-sky redshift surveys: the Optical Redshift Survey (ORS) and the IRAS 1.2-Jy survey. While the galaxies in these surveys are selected differently and their populations are known to be biased relative to each other, the two void distributions are similar. We compare the spatial distribution of the two void populations and demonstrate the correlation between them. The voids also agree with regard to the overall void statistics a filling factor of 0.45 of the volume, an average void diameter and an average galaxy underdensity in the voids Our measurements of the underdensities of the voids in the two surveys enable us to estimate the relative bias in the voids between optical and IRAS samples. We find ( b _opt b _IRAS )^void1, showing that on average there is little or no biasing between the two void populations.     

The supergalactic plane revisited with the Optical Redshift Survey

We re-examine the existence and extent of the planar structure in the local galaxy density field, the so-called supergalactic plane (SGP). This structure is studied here in three dimensions using both the new Optical Redshift Survey (ORS) and the IRAS 1.2-Jy redshift survey. The density contrast in a slab of thickness 20  h ⁻¹ Mpc and diameter 80 Mpc aligned with the standard de Vaucouleurs supergalactic coordinates is δ _sgp∼0.5 for both ORS and IRAS . The structure of the SGP is not well described by a homogeneous ellipsoid, although it does appear to be a flattened structure, which we quantify by calculating the moment of inertia tensor of the density field. The directions of the principal axes vary with radius, but the minor axis remains within θ _z ∼30° of the standard SGP Z -axis, out to a radius of 80  h ⁻¹ Mpc, for both ORS and IRAS . However, the structure changes shape with radius, varying between a flattened pancake and a dumbbell, the latter at a radius of ∼50  h ⁻¹ Mpc, where the Great Attractor and Perseus–Pisces superclusters dominate the distribution. This calls to question the connectivity of the 'plane' beyond ∼40  h ⁻¹ Mpc. The configuration found here can be viewed as part of a web of filaments and sheets, rather than as an isolated pancake-like structure. An optimal minimum variance reconstruction of the density field using Wiener filtering, which corrects for both redshift distortion and shot noise, yields a similar misalignment angle and behaviour of axes. The background-independent statistic of axes proposed here can be best used for testing cosmological models by comparison with N -body simulations.     

Peculiar velocity reconstruction with the fast action method: tests on mock redshift surveys

We present extensive tests of the fast action method (FAM) for recovering the past orbits of mass tracers in an expanding universe from their redshift-space coordinates at the present epoch. The tests focus on the reconstruction of present-day peculiar velocities using mock catalogues extracted from high-resolution N -body simulations. The method allows for a self-consistent treatment of redshift-space distortions by direct minimization of a modified action for a cosmological gravitating system. When applied to ideal, volume-limited catalogues, FAM recovers unbiased peculiar velocities with a one-dimensional, 1σ error of ∼220 km  s⁻¹  , if velocities are smoothed on a scale of  5 h ⁻¹  Mpc. Alternatively, when no smoothing is applied, FAM predicts nearly unbiased velocities for objects residing outside the highest density regions. In this second case the 1σ error decreases to a level of ∼150 km  s⁻¹  . The correlation properties of the peculiar velocity fields are also correctly recovered on scales larger than  5 h ⁻¹  Mpc. Similar results are obtained when FAM is applied to flux-limited catalogues mimicking the IRAS PSC z survey. In this case FAM reconstructs peculiar velocities with similar intrinsic random errors, while velocity–velocity correlation properties are well reproduced beyond scales of  ∼8 h ⁻¹  Mpc. We also show that FAM provides better velocity predictions than other, competing methods based on linear theory or the Zel'dovich approximation. These results indicate that FAM can be successfully applied to presently available galaxy redshift surveys such as IRAS PSC z .     

Predicting the peculiar velocities of nearby PSCz galaxies using the Least Action Principle

We use the Least Action Principle to predict the peculiar velocities of PSC z galaxies inside cz =2000 km s⁻¹. Linear theory is used to account for tidal effects to cz =15 000 km s⁻¹, and we iterate galaxy positions to account for redshift distortions. As the Least Action Principle is valid beyond linear theory, we can predict reliable peculiar velocities even for very nearby galaxies (i.e., cz ≤500 km s⁻¹). These predicted peculiar velocities are then compared with the observed velocities of 12 galaxies with Cepheid distances. The combination of the PSC z galaxy survey (with its large sky coverage and uniform selection) with the accurate Cepheid distances makes this comparison relatively free from systematic effects. We find that galaxies are good tracers of the mass, even at small (≤10  h ⁻¹ Mpc) scales; under the assumption of no biasing, 0.25≤ β ≤0.75 (at 90 per cent confidence). We use the reliable predicted peculiar velocities to estimate the Hubble constant H ₀ from the local volume without 'stepping up' the distance ladder, finding a confidence range of 65–75 km s⁻¹ Mpc⁻¹ (at 90 per cent confidence).     

The 6dF Galaxy Survey: final redshift release (DR3) and southern large-scale structures

We report the final redshift release of the 6dF Galaxy Survey (6dFGS), a combined redshift and peculiar velocity survey over the southern sky  (| b | > 10°)  . Its 136 304 spectra have yielded 110 256 new extragalactic redshifts and a new catalogue of 125 071 galaxies making near-complete samples with  ( K , H , J , r _F, b _J) ≤ (12.65, 12.95, 13.75, 15.60, 16.75)  . The median redshift of the survey is 0.053. Survey data, including images, spectra, photometry and redshifts, are available through an online data base. We describe changes to the information in the data base since earlier interim data releases. Future releases will include velocity dispersions, distances and peculiar velocities for the brightest early-type galaxies, comprising about 10 per cent of the sample. Here we provide redshift maps of the southern local Universe with   z ≤ 0.1  , showing nearby large-scale structures in hitherto unseen detail. A number of regions known previously to have a paucity of galaxies are confirmed as significantly underdense regions. The URL of the 6dFGS data base is http://www-wfau.roe.ac.uk/6dFGS .     

Comparison of the ENEAR peculiar velocities with the PSCz gravity field

We present a comparison between the peculiar velocity field measured from the ENEAR all-sky D _n– σ catalogue and that derived from the galaxy distribution of the IRAS Point Source Catalog Redshift Survey (PSC z ). The analysis is based on a modal expansion of these data in redshift space by means of spherical harmonics and Bessel functions. The effective smoothing scale of the expansion is almost linear with redshift reaching 1500 km s⁻¹ at 3000 km s⁻¹. The general flow patterns in the filtered ENEAR and PSC z velocity fields agree well within 6000 km s⁻¹, assuming a linear biasing relation between the mass and the PSC z galaxies. The comparison allows us to determine the parameter     where Ω is the cosmological density parameter and b is the linear biasing factor. A likelihood analysis of the ENEAR and PSC z modes yields     in good agreement with values obtained from Tully–Fisher surveys.     

Redshift-space distortions in the PSCz galaxy catalogue

We apply a spherical harmonic analysis to the Point Source Redshift Survey (PSC z ), to compute the real-space galaxy power spectrum and the degree of redshift distortion caused by peculiar velocities. We employ new parameter eigenvector and hierarchical data compression techniques, allowing a much larger number of harmonic modes to be included, and correspondingly smaller error bars. Using 4644 harmonic modes, compressed to 2278, we find that the IRAS redshift-space distortion parameter is     and the amplitude of galaxy clustering on a scale of     is     . Combining these we find the amplitude of mass perturbations is     . While this is compatible with results from the cosmic microwave background (CMB), with a small degree of tilt, it disagrees with the amplitude of matter perturbations estimated from the abundance of clusters by a factor of 2, independent of cosmology. A preliminary model fitting analysis combining the CMB with either the PSC z or cluster abundances shows that the cosmological matter density parameter     , and the IRAS bias parameter     . However, the cluster abundances suggest that     and     , while the PSC z requires     and     . Given the physics of galaxy formation is poorly constrained, we conclude that IRAS galaxies and mass are only partially correlated.     

Non-linear redshift distortions: the two-point correlation function

We consider a situation where the density and peculiar velocities in real space are linear, and we calculate ξ _s , the two-point correlation function in redshift space, incorporating all non-linear effects which arise as a consequence of the map from real to redshift space. Our result is non-perturbative and it includes the effects of possible multi-streaming in redshift space. We find that the deviations from the predictions of the linear redshift distortion analysis increase for the higher spherical harmonics of ξ _s . While the deviations are insignificant for the monopole ξ ₀, the hexadecapole ξ ₄ exhibits large deviations from the linear predictions. For a COBE normalized     ,     cold dark matter (CDM) power spectrum, our results for ξ ₄ deviate from the linear predictions by a factor of two on the scale of ∼10  h ⁻¹ Mpc. The deviations from the linear predictions depend separately on f (Ω) and b . This holds the possibility of removing the degeneracy that exists between these two parameters in the linear analysis of redshift surveys which yields only     .
We also show that the commonly used phenomenological model, where the non-linear redshift two-point correlation function is calculated by convolving the linear redshift correlation function with an isotropic pair velocity distribution function, is a limiting case of our result.     

Large-scale bias in the Universe — II. Redshift-space bispectrum

The determination of the density parameter Ω₀ from the large-scale distribution of galaxies is one of the major goals of modern cosmology. However, if galaxies are biased tracers of the underlying mass distribution, linear perturbation theory leads to a degeneracy between Ω₀ and the linear bias parameter b , and the density parameter cannot be estimated. In Matarrese, Verde &38; Heavens we developed a method based on second-order perturbation theory to use the bispectrum to lift this degeneracy by measuring the bias parameter in an Ω₀-independent way. The formalism was developed assuming that one has perfect information on the positions of galaxies in three dimensions. In galaxy redshift surveys, the three-dimensional information is imperfect, because of the contaminating effects of peculiar velocities, and the resulting clustering pattern in redshift space is distorted. In this paper we combine second-order perturbation theory with a model for collapsed, virialized structures, to extend the method to redshift space, and demonstrate that the method should be successful in determining with reasonable accuracy the bias parameter from state-of-the-art surveys such as the Anglo-Australian 2 degree Field Survey and the Sloan Digital Sky Survey.     

大天巨星系红移巡天

星系的红移巡天是观测宇宙学中最基本的工作,有关宇宙大尺度结构研究中的许多关键问题,例如宇宙中最大结构的尺度,宇宙中大尺度结构的拓扑特征,以及有关宇宙物质分布的密度场和速度场的许多基本性质的研究,都依赖于覆盖面积足够大、极限星等足够暗的完备的星系红移大样本．通过对巡天的覆盖天区、巡天深度、选样方法、巡样率等方面的分析,比较了最近已完成的一些红移巡天（IRAS、CfA、SSRS、ORS和LCRS等）并对计划中的2dF和SDSS巡天计划作了简要介绍．     

The redshift-space two-point correlation function of ELAIS-S1 galaxies

We investigate the clustering properties of galaxies in the recently completed ELAIS-S1 redshift survey through their spatial two-point autocorrelation function. We used a subsample of the ELAIS-S1 catalogue covering approximately 4 deg² and consisting of 148 objects selected at 15 μm with a flux >0.5 mJy and a redshift   z < 0.5  . We detected a positive signal in the correlation function that in the range of separations  1–10  h ⁻¹ Mpc  is well approximated by a power law with a slope  γ= 1.4 ± 0.25  and a correlation length   s ₀= 5.4 ± 1.2  h ⁻¹ Mpc  , at the 90 per cent significance level. This result is in good agreement with the redshift-space correlation function measured in more local samples of mid-infrared-selected galaxies such as the IRAS Point Source Catalog (PSC z ) redshift survey. This suggests a lack of significant clustering evolution of infrared-selected objects out to   z = 0.5  that is further confirmed by the consistency found between the correlation functions measured in a local  ( z < 0.2)  and a distant  (0.2 < z < 0.5)  subsample of ELAIS-S1 galaxies. We also confirm that optically selected galaxies in the local redshift surveys, especially those of the SDSS sample, are significantly more clustered than infrared objects.     

Large-scale structure of galaxies in the Ophiuchus region

The large-scale structure around the Ophiuchus cluster of galaxies in the vicinity of the Galactic Centre ( l =05, b =95, cz =8500 km s⁻¹) is investigated on the basis of a galaxy survey and spectroscopic observations made for a 12°×17° area. The galaxy survey was performed using six ESO/SERC Sky Survey Atlas films, and 4021 galaxies were detected in total. Recession velocities were newly obtained for 179 galaxies to make the total number of galaxies in the survey area with known velocities 219.
In the distribution of bright galaxies, we identified seven new clumps of galaxies. Comparing the surface number density of bright galaxies with the Galactic extinction, which is estimated from the 100‐μm flux density in the IRAS Sky Survey Atlas, we demonstrate that the seven clumps are not spurious as a result of the inhomogeneity of the Galactic extinction. Among the seven clumps, two are found to be clusters and four to be groups on the basis of the histogram of recession velocities and the number of member galaxies. The Ophiuchus cluster, two newly identified clusters, and four groups are all concentrated at 9000 km s⁻¹. Field galaxies are also distributed centred at 8500 km s⁻¹. Hence field galaxies occupy a common three-dimensional region with galaxies in the clusters and groups, and altogether they form a large-scale structure of supercluster size. As opposed to the overdensity in the supercluster region, the mean number density of galaxies in the velocity range 0–5000 km s⁻¹ is only 25 per cent of the mean number density of the Universe, comparable with the density of the well-known Böotes void. Hence this nearby three-dimensional region in Ophiuchus is a void of galaxies also.     

Extended structures around yso in Mid-IR broad emission features

We present CO(1-0) observations toward the soft gamma-ray repeater SGR 1806-20. We discuss the implications on the distance to the X-ray counterpart: AX 1805.7-2025. We also present an upper limit at = 1.3 mm for the thermal emission from dust and high resolution IRAS maps of the region. SGR 1806-20 is very likely associated with the H II complex W31. The G10.0-0.3 supernova remnant (SNR) could be expanding in the very low density region produced by the wind of the bright O9-B2 star recently detected.National Academy of Sciences / National Research Council Resident Research Associate     

Intervening O vi Quasar Absorption Systems at Low Redshift: A Significant Baryon Reservoir

Far-UV echelle spectroscopy of the radio-quiet QSO H1821+643 (zem=0.297), obtained with the Space Telescope Imaging Spectrograph (STIS) at approximately 7 km s-1 resolution, reveals four definite O vi absorption-line systems and one probable O vi absorber at 0.15相似文献   

Estimates for the luminosity function of galaxies and its evolution

A new method is presented to obtain a non-parametric maximum likelihood estimate of the luminosity function and the selection function of a flux-limited redshift survey. The method parametrizes the selection function as a series of stepwise power laws and allows possible evolution of the luminosity function. We also propose a new technique to estimate the rate of evolution of the luminosity function. This is based on a minimization of the observed large-scale power with respect to the evolutionary model. We use an ensemble of mock surveys extracted from an N -body simulation to verify the power of this method. We apply our estimators to the 1.2-Jy survey of IRAS galaxies. We find a far-infrared luminosity function in good agreement with previously published results and evidence for rather strong evolution. If the comoving number density of IRAS galaxies is assumed to scale ∝ (1 +  z ) ^P , we estimate P  = 4.3 ± 1.4.     

A primordial feature at the scale of superclusters of galaxies

We investigate a spatially flat cold dark matter model (with the matter density parameter     with a primordial feature in the initial power spectrum. We assume that there is a bump in the power spectrum of density fluctuations at wavelengths     , which corresponds to the scale of superclusters of galaxies . There are indications for such a feature in the power spectra derived from redshift surveys and also in the power spectra derived from peculiar velocities of galaxies. We study the mass function of clusters of galaxies, the power spectrum of the cosmic microwave background (CMB) temperature fluctuations, the rms bulk velocity and the rms peculiar velocity of clusters of galaxies. The baryon density is assumed to be consistent with the big bang nucleosynthesis value. We show that with an appropriately chosen feature in the power spectrum of density fluctuations at the scale of superclusters, the mass function of clusters, the CMB power spectrum, the rms bulk velocity and the rms peculiar velocity of clusters are in good agreement with the observed data.     

The Gaussian cell two-point 'energy-like' equation: application to large-scale galaxy redshift and peculiar motion surveys

We introduce a simple linear equation relating the line-of-sight peculiar-velocity and density contrast correlation functions. The relation, which we call the Gaussian cell two-point 'energy-like' equation , is valid at the distant-observer limit and requires Gaussian smoothed fields. In the variance case, i.e. at zero lag, the equation is similar in its mathematical form to the Irvine–Layzer cosmic energy equation. β estimation with this equation from the Point Source Catalogue Redshift (PSC) survey and the SEcat catalogue of peculiar velocities is carried out, returning a value of  β= 0.44 ± 0.08  . The applicability of the method for the 6dF galaxy redshift and peculiar motions survey is demonstrated with mock data where it is shown that β could be determined with ≈10 per cent accuracy. The prospects for constraining the dark energy equation of state with this method from the kinematic and thermal Sunyaev–Zel'dovich cluster surveys are discussed. The equation is also used to construct a non-parametric mass-density power-spectrum estimator from peculiar-velocity data.     

Density distribution of matter on 75-Mpc scales derived by the POTENT method from the bulk motions of RFGC galaxies

The data on the peculiar velocities of 1493 RFGC flat spiral galaxies processed using the POTENT method allowed the density distribution of matter, including dark matter, on 75-Mpc scales to be reconstructed. Well-known attractors (the Great Attractor, the Perseus—Pisces and Coma superclusters) and voids are separated from the distribution. In general, the density distribution is close to that of IRAS galaxies, suggesting that the luminous-to-dark matter density ratio is constant. The masses of the main attractors were estimated.