Effect Of Peculiar Velocities Research Articles

Non-Gaussian Minkowski functionals and extrema counts in redshift space

In the context of upcoming large-scale structure surveys such as Euclid, it is of prime importance to quantify the effect of peculiar velocities on geometric probes. Hence the formalism to compute in redshift space the geometrical and topological one-point statistics of mildly non-Gaussian 2D and 3D cosmic fields is developed. Leveraging the partial isotropy of the target statistics, the Gram-Charlier expansion of the joint probability distribution of the field and its derivatives is reformulated in terms of the corresponding anisotropic variables. In particular, the cosmic non-linear evolution of the Minkowski functionals, together with the statistics of extrema are investigated in turn for 3D catalogues and 2D slabs. The amplitude of the non-Gaussian redshift distortion correction is estimated for these geometric probes. In 3D, gravitational perturbation theory is implemented in redshift space to predict the cosmic evolution of all relevant Gram-Charlier coefficients. Applications to the estimation of the cosmic parameters sigma(z) and beta=f/b1 from upcoming surveys is discussed. Such statistics are of interest for anisotropic fields beyond cosmology.

The effect of peculiar velocities on the epoch of reionization 21-cm signal

We have used semi-numerical simulations of reionization to study the behaviour of the power spectrum of the EoR 21-cm signal in redshift space. We have considered two models of reionization, one which has homogeneous recombination (HR) and the other incorporating inhomogeneous recombination (IR). We have estimated the observable quantities --- quadrupole and monopole moments of HI power spectrum at redshift space from our simulated data. We find that the magnitude and nature of the ratio between the quadrupole and monopole moments of the power spectrum ($P^s_2 /P^s_0$) can be a possible probe for the epoch of reionization. We observe that this ratio becomes negative at large scales for $x_{HI} \leq 0.7$ irrespective of the reionization model, which is a direct signature of an inside-out reionization at large scales. It is possible to qualitatively interpret the results of the simulations in terms of the fluctuations in the matter distribution and the fluctuations in the neutral fraction which have power spectra and cross-correlation $P_{\Delta \Delta}(k)$, $P_{xx}(k)$ and $P_{\Delta x}(k)$ respectively. We find that at large scales the fluctuations in matter density and neutral fraction is exactly anti-correlated through all stages of reionization. This provides a simple picture where we are able to qualitatively interpret the behaviour of the redshift space power spectra at large scales with varying $x_{HI}$ entirely in terms of a just two quantities, namely $x_{HI}$ and the ratio $P_{xx}/P_{\Delta \Delta}$. The nature of $P_{\Delta x}$ becomes different for HR and IR scenarios at intermediate and small scales. We further find that it is possible to distinguish between an inside-out and an outside-in reionization scenario from the nature of the ratio $P^s_2 /P^s_0$ at intermediate length scales.

The clustering of intermediate-redshift quasars as measured by the Baryon Oscillation Spectroscopic Survey

We measure the quasar two-point correlation function over the redshift range 2.2<z<2.8 using data from the Baryon Oscillation Spectroscopic Survey. We use a homogeneous subset of the data consisting of 27,129 quasars with spectroscopic redshifts---by far the largest such sample used for clustering measurements at these redshifts to date. The sample covers 3,600 square degrees, corresponding to a comoving volume of 9.7(Gpc/h)^3 assuming a fiducial LambdaCDM cosmology, and it has a median absolute i-band magnitude of -26, k-corrected to z=2. After accounting for redshift errors we find that the redshift space correlation function is fit well by a power-law of slope -2 and amplitude s_0=(9.7\pm 0.5)Mpc/h over the range 3<s<25Mpc/h. The projected correlation function, which integrates out the effects of peculiar velocities and redshift errors, is fit well by a power-law of slope -1 and r_0=(8.4\pm 0.6)Mpc/h over the range 4<R<16Mpc/h. There is no evidence for strong luminosity or redshift dependence to the clustering amplitude, in part because of the limited dynamic range in our sample. Our results are consistent with, but more precise than, previous measurements at similar redshifts. Our measurement of the quasar clustering amplitude implies a bias factor of b~3.5 for our quasar sample. We compare the data to models to constrain the manner in which quasars occupy dark matter halos at z~2.4 and infer that such quasars inhabit halos with a characteristic mass of <M>~10^{12}Msun/h with a duty cycle for the quasar activity of 1 per cent.

Redshift-space distortion of the 21-cm background from the epoch of reionization - I. Methodology re-examined

The peculiar velocity of the intergalactic gas responsible for the cosmic 21cm background from the epoch of reionization and beyond introduces an anisotropy in the three-dimensional power spectrum of brightness temperature fluctuations. Measurement of this anisotropy by future 21cm surveys is a promising tool for separating cosmology from 21cm astrophysics. However, previous attempts to model the signal have often neglected peculiar velocity or only approximated it crudely. This paper re-examines the effects of peculiar velocity on the 21cm signal in detail, improving upon past treatment and addressing several issues for the first time. (1) We show that properly accounting for finite optical depth eliminates the unphysical divergence of 21cm brightness temperature in overdense regions of the IGM found by previous work that employed the usual optically-thin approximation. (2) The approximation made previously to circumvent the diverging brightness temperature problem by capping velocity gradient can misestimate the power spectrum on all scales. (3) The observed power spectrum in redshift-space remains finite even in the optically-thin approximation if one properly accounts for the redshift-space distortion. However, results that take full account of finite optical depth show that this approximation is only accurate in the limit of high spin temperature. (4) The linear theory for redshift-space distortion results in ~30% error in the observationally relevant wavenumber range, at the 50% ionized epoch. (5) We describe and test two numerical schemes to calculate the 21cm signal from reionization simulations to incorporate peculiar velocity effects in the optically-thin approximation accurately. One is particle-based, the other grid-based, and while the former is most accurate, we demonstrate that the latter is computationally more efficient and can achieve sufficient accuracy. [Abridged]

GRAVITATIONAL POTENTIAL ENVIRONMENT OF GALAXIES. I. SIMULATION

We extend the concept of galaxy environment from the local galaxy number density to the gravitational potential and its functions like the shear tensor. For this purpose we examine whether or not one can make an accurate estimation of the gravitational potential from an observational sample which is finite in volume, biased due to galaxy biasing, and subject to redshift space distortion. Dark halos in a $\Lambda$CDM simulation are used in this test. We find that one needs to stay away from the sample boundaries by more than 30$h^{-1}$Mpc to reduce the error within 20% of the root mean square values of the potential or the shear tensor. The error due to the galaxy biasing can be significantly reduced by using the galaxy mass density field instead of the galaxy number density field. The error caused by the redshift space distortion can be effectively removed by correcting galaxy positions for the peculiar velocity effects. We inspect the dependence of dark matter halo properties on four environmental parameters; local density, gravitational potential, and the ellipticity and prolateness of the shear tensor. We find the local density has the strongest correlation with halo properties. This is evidence that the internal physical properties of dark halos are mainly controlled by small-scale physics. In high density regions dark halos are on average more massive and spherical, and have higher spin parameter and velocity dispersion. In high density regions dark halos are on average more massive and spherical, and have higher spin parameter and velocity dispersion. We also study the relation between the environmental parameters and the subtypes of dark halos. The spin parameter of satellite halos depends only weakly on the local density for all mass ranges studied while that of isloated or central halos depends more sensitively on the local density. (abridged)

Tracing large-scale structure at high redshift with Lyman-α emitters: the effect of peculiar velocities

We investigate the effect of peculiar velocities on the redshift space distribution of z>~2 galaxies, and we focus in particular on Ly-alpha emitters. We generate catalogues of dark matter (DM) halos and identify emitters with halos of the same co-moving space density (M(Ly-alpha emitters) ~ 3x10^11 M_sun). We decompose the peculiar velocity field of halos into streaming, gradient and random components, and compute and analyse these as a function of scale. Streaming velocities are determined by fluctuations on very large scales, strongly affected by sample variance, but have a modest impact on the interpretation of observations. Gradient velocities are the most important as they distort structures in redshift space, changing the thickness and orientation of sheets and filaments. Random velocities are typically below or of the same order as the typical observational uncertainty on the redshift. We discuss the importance of these effects for the interpretation of data on the large-scale structure as traced by Ly-alpha emitters (or similar kinds of astrophysical high-redshift objects), focusing on the induced errors in the viewing angles of filaments. We compare our predictions of velocity patterns for Ly-alpha emitters to observations and find that redshift clumping of Ly-alpha emitters, as reported for instance in the fields of high-redshift radio galaxies, does not allow to infer whether an observed field is sampling an early galaxy overdensity.

Large‐Scale Structure atz= 1.2 Outlined by MgiiAbsorbers

The largest known structure in the high-redshift universe is mapped by at least 18 quasars and spans ~5° × 25 on the sky, with a quasar spatial overdensity of 6-10 times above the mean. This large quasar group provides an extraordinary laboratory ~100 × 200 × 200 h-3 comoving Mpc3 in size (q0 = 0.5, Λ = 0, H0 = 100 h km s-1 Mpc-1) covering 1.20 < z < 1.39 in redshift. One approach to establishing how large quasar groups relate to mass (galaxy) enhancements is to probe their gas content and distribution via background quasars. We performed a survey for Mg II absorption systems in a ~25 × 25 subfield in the large quasar group and found 38 absorbers to a rest equivalent width limit of W0 = 0.3 A over 0.69 < z < 2.02. Only 24 absorbers were expected; thus, we find a 2 σ overdensity over all redshifts in our survey. We have found the large quasar group to be associated with 11 Mg II absorption systems at 1.2 < z < 1.4; 0.02%-2.05% of simulations with random Mg II redshifts match or exceed this number in that redshift interval, depending on the normalization method used. The minimal spanning tree test also supports the existence of a structure of Mg II absorbers coincident with the large quasar group and additionally indicates a foreground structure populated by Mg II absorbers and quasars at z ~ 0.8. Finally, we find a tendency for Mg II absorbers over all redshifts in our survey to correlate with field quasars (i.e., quasars both inside and outside of the large quasar group) at a projected scale length on the sky of 9 h-1 Mpc and a velocity difference |Δv| = 3000-4500 km s-1. While the correlation is on a scale consistent with observed galaxy-active galactic nucleus distributions, the nonzero velocity offset could be due to the periphery effect, in which quasars tend to populate the outskirts of clusters of galaxies and metal absorption systems, or to peculiar velocity effects.

Peculiar velocity effects in high-resolution microwave background experiments

We investigate the impact of peculiar velocity effects due to the motion of the solar system relative to the cosmic microwave background (CMB) on high resolution CMB experiments. It is well known that on the largest angular scales the combined effects of Doppler shifts and aberration are important; the lowest Legendre multipoles of total intensity receive power from the large CMB monopole in transforming from the CMB frame. On small angular scales aberration dominates and is shown here to lead to significant distortions of the total intensity and polarization multipoles in transforming from the rest frame of the CMB to the frame of the solar system. We provide convenient analytic results for the distortions as series expansions in the relative velocity of the two frames, but at the highest resolutions a numerical quadrature is required. Although many of the high resolution multipoles themselves are severely distorted by the frame transformations, we show that their statistical properties distort by only an insignificant amount. Therefore, the cosmological parameter estimation is insensitive to the transformation from the CMB frame (where theoretical predictions are calculated) to the rest frame of the experiment.

Probing the dark energy with quasar clustering.

We show through Monte Carlo simulations that the Alcock-Paczyński test, as applied to quasar clustering, is a powerful tool to probe the cosmological density and equation of state parameters Omega(m0), Omega(x0), and w. By taking into account the effect of peculiar velocities upon the correlation function we obtain for the Two-Degree Field QSO Redshift Survey the predicted confidence contours for the cosmological constant (w = -1) and spatially flat (Omega(m0)+Omega(x0) = 1) cases. For w = -1, the test is especially sensitive to the difference Omega(m0)-Omega(Lambda0), thus being ideal to combine with cosmic microwave background results. For the flat case, it is competitive with future supernova and galaxy number count tests, besides being complementary to them.

The 2dF QSO Redshift Survey - VI. Measuring Λ andβfrom 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 from these distortions. We apply this model to a detailed simulation of the final 25k 2QZ, produced using the Virgo Consortium's huge Hubble Volume N-body ΛCDM (cold dark matter) light-cone simulation. We confirm the conclusions of Ballinger et al.: the shapes of the redshift-space and geometric distortions are very similar, and discriminating between the two to produce a purely geometric constraint on Λ is difficult. When all the uncertainties in measuring for the 2QZ are taken into account, we find that only a joint 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 ±0.1, and Ωm to ±0.25, using the final catalogue. We apply the method to the 2QZ catalogue of 10 000 quasars (QSOs) and find that this incomplete catalogue marginally favours a Λ cosmology, obtaining best-fitting values of and . However, Einstein–de Sitter models are only rejected at the 1.4σ level in the current survey. The rejection of lambda-dominated models is stronger at ∼2σ.

Geometric Distortion of the Correlation Function of Lyman‐Break Galaxies

The number of galaxies with measured redshifts > 1 is at present rapidly increasing, allowing for measurements of their correlation function. The correlations function is measured in redshift space, as a function of angular separation and velocity difference. The relation between angle and velocity difference depends on the cosmological model through the factor H(z)D(z), where H(z) is the Hubble parameter and D(z) is the angular diameter distance. Therefore, the cosmological model can be constrained by measuring this factor from the shape of the contours of the redshift space correlation function, if the effect of peculiar velocities can be taken into account. Here, we investigate this method applied to the high redshift Lyman-break galaxies. The high bias factor of this galaxy population should suppress peculiar velocity effects, leaving the cosmological distortion as the main contribution to the anisotropy of the correlation function. We estimate the shot noise and cosmic variance errors using linear theory. A field size of at least 0.2 square degrees is required to distinguish the Einstein-de Sitter model from the flat Lambda=0.7 model, if 1.25 Lyman-break galaxies are measured per square arc minute. With a field of 1 square degrees, the cosmological constant can be measured to 20 % accuracy if it is large (> 0.5). Other equations of state for a scalar field can also be constrained.

Measuring the Cosmological Geometry from the Lyα Forest along Parallel Lines of Sight

The possibility of measuring the cosmological geometry using the redshift space correlation function of the Lyα forest in multiple lines of sight as a function of angular and velocity separation is discussed. The geometric parameter to be measured is f(z)≡c-1H(z)DA(z), where H(z) is the Hubble constant and DA(z) the angular diameter distance at redshift z. The correlation function is computed in linear theory, assuming that the Lyα forest is a result of gravitational instability in a photoionized intergalactic medium. We describe a method to measure the correlation from observations with the Gaussianization procedure of Croft et al. to map the observed Lyα forest transmitted flux to an approximation of the linear density field. The effect of peculiar velocities on the shape of the recovered power spectrum is pointed out. We estimate the error in recovering the f(z) factor from observations due to the variance in the Lyα absorbers. We show that at least ~25 pairs of quasars (separations <3') are needed to distinguish a flat Ω0=1 universe from a universe with Ω0=0.2, ΩΛ=0.8. A second parameter that is obtained from the correlation function of the Lyα forest is βΩ(z)0.6/b (affecting the magnitude of the peculiar velocities), where b is a linear theory bias of the Lyα forest. In the theory of the Lyα forest assumed here, the parameter β can be predicted from numerical simulations; once β is known, the number of quasar pairs needed to constrain f is reduced to about six. On small scales, where the correlation function is higher, f(z) should be measurable with fewer quasars, but nonlinear effects must then be taken into account. The anisotropy of the nonlinear redshift space correlation function as a function of scale should also provide a precise quantitative test of the gravitational instability theory of the Lyα forest.

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

The determination of the density parameter $\Omega_0$ 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 $\Omega_0$ and the linear bias parameter $b$, and the density parameter cannot be estimated. In Matarrese, Verde & Heavens (1997) 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 $\Omega_0$-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, virialised 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.

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 & 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.

Velocity Dispersion and the Redshift-Space Power Spectrum

A large (N ~ 17 × 106) high-resolution N-body simulation of a standard cold dark matter (CDM) universe is used to investigate the effects of peculiar velocities on the power spectrum of galaxies in redshift space. The unprecedented dynamical range of the simulation code allows galaxy halos to be resolved in the numerical data while maintaining good statistical sampling on large scales. We present evidence that the redshift-space power spectrum Ps(k) can be related to its real-space counterpart by means of a simple filter function which reflects both small-scale velocity dispersion and large-scale linear flows. After transformation to redshift space, we find that the power spectrum is insensitive to the normalization of the CDM model at scales below 20 h-1 Mpc. Hence Ps(k) does not provide an unambiguous cosmological constraint at small scales. Nonetheless, it is significant that the redshift-space power spectra from CDM models with two different normalizations both compare remarkably well with results from the galaxies in the IRAS 1.2 Jy survey (Fisher et al.) on scales between 1 and 50 h-1 Mpc. By excluding a fraction of the most tightly bound halos, we create a galaxy catalog with 80% of the original objects in the lower normalization model that matches both the IRAS power spectrum and the inferred pairwise velocity dispersion on megaparsec scales. Thus, in contrast to previous reports, we find that the CDM scenario does not produce excess power at small scales.

The luminosity function of the CfA Redshift Survey

We use the CfA Redshift Survey of galaxies with m_z_ &lt; 15.5 to calculate the galaxy luminosity function over the range -13&lt;= M_Z_ &lt;= - 22. The sample includes 9063 galaxies distributed over 2.1 Sr. For galaxies with velocities cz &gt;= 2500 km s^-1^, where the effects of peculiar velocities are small, the luminosity function is well represented by a Schechter function with parameters phi}_*_ = 0.04 +/- 0.01 Mpc^-3^, M_*_ = - 18.8 +/- 0.3 and α = - 1.0 +/- 0.2. When we include all galaxies with cz &gt;= 500 km s^-1^, the number of galaxies in the range -16 &lt;= M_Z_ &lt;= -13 exceeds the extrapolation of the Schechter function by a factor of 3.1 +/- 0.5. This faint-end excess is not caused by the local peculiar velocity field but may be partially explained by small scale errors in the Zwicky magnitudes. Even with a scale error as large as 0.2 mag mag^-1^, which is unlikely, the excess is still a factor of 1.8 +/- 0.3. If real, this excess affects the interpretation of deep counts of field galaxies.

The distribution of IRAS galaxies on linear and nonlinear scales

view Abstract Citations (28) References (38) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Distribution of IRAS Galaxies on Linear and Nonlinear Scales Sheth, Ravi K. ; Mo, H. J. ; Saslaw, William C. Abstract We analyze the galaxy distribution functions for voids and counts-in- cells using the IRAS catalog. Angular diameter scales, the largest probed to date, range from 0.5^deg^ to 30^deg^, corresponding to linear diameters <~40 h^-1^ Mpc. The analysis develops a new technique which has no free parameters. On all scales, the results agree closely with predictions of simple gravitational galaxy clustering. The value of b_pattern_ for the IRAS galaxies at a cell diameter of 30^deg^ is 0.62 +/- 0.03. It is nearly independent of scale for angular diameters >~ 20^deg^. We also develop a new method for using the projected distribution functions to estimate the average amplitude, -ɛ, and scale, r_neg_ where the spatial two-point galaxy correlation function, ξ_2_ becomes negative. This technique is sensitive to the negative range of ξ_2_ and is independent of the peculiar velocity effects which make measurements of the spatial correlation function uncertain on some scales. It shows that a large class of CDM-related models, with linear biasing, appears to be inconsistent with the IRAS distribution. We discuss some implications for the selection of the IRAS galaxies, the scale invariance of higher order moments of the IRAS distribution function, and the evidence that initial conditions for galaxy clustering were Gaussian. Publication: The Astrophysical Journal Pub Date: June 1994 DOI: 10.1086/174167 Bibcode: 1994ApJ...427..562S Keywords: Distribution Functions; Galactic Clusters; Infrared Astronomy; Linearity; Nonlinearity; Numerical Analysis; Spatial Distribution; Voids; Astronomical Catalogs; Correlation; Gravitational Effects; Infrared Astronomy Satellite; Sky Surveys (Astronomy); Astrophysics; COSMOLOGY: LARGE-SCALE STRUCTURE OF UNIVERSE; COSMOLOGY: THEORY; GALAXIES: CLUSTERING; INFRARED: GALAXIES; METHODS: NUMERICAL full text sources ADS |

Recovering the real density field of galaxies from redshift space

This paper proposes a number of methods for recovering the true, real-space large-scale density distributions from redshift data sets. On the largest scales, the effects of peculiar velocities is to compress the galaxy clustering along the line of sight and consequently the density gradient in the radial direction is enhanced in comparison with the density gradient perpendicular to the line of sight. We calculate the relation between the density gradients in real and redshift space in the linear regime and show that it is a simple function of the density parameter, Omega. By considering the anisotropy of density gradients in redshift space it is possible, in principle, to obtain information about the value of Omega. Using N-body simulations we examine different methods for correcting the effects of large-scale velocities to obtain the true density distributions. We derive the peculiar velocity field from the redshift data and iterate to place each galaxy at a distance consistent with its measured redshift and its derived velocity. Linear theory, as well as second-order solutions for the peculiar velocity field are tested. The density distributions in low-density regions predicted by both linear theory and second-order theory are similar, and in good agreement with the true density field in the simulation. The use of the second-order corrections improves the prediction of the density field in high-density regions.

Clustering of Galaxies in Redshift Space: Velocity Distortion of the Power Spectrum and Correlation Function

view Abstract Citations (31) References (24) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Clustering of Galaxies in Redshift Space: Velocity Distortion of the Power Spectrum and Correlation Function Gramann, Mirt ; Cen, Renyue ; Bahcall, Neta A. Abstract Large-scale N-body simulations are used to investigate the distorting effects of peculiar velocities on the shape of the power spectrum and correlation function of galaxies as measured in redshift space. The distortion effect is studied over a large range of scales, from the nonlinear small scales of ∼1 h-1 Mpc to the linear regime of 400 h-1 Mpc. The distortions cause the redshift space power spectrum to be steeper than the real spectrum; the redshift space spectrum is enhanced over the real spectrum on large scales, in agreement with linear theory (Kaiser 1987), and is suppressed on small scales. The transition scale to the linear regime depends on the density parameter, Ω. For Ω = 0.2, the redshift space power spectrum is linearly enhanced on scales ≥ 60 h-1 Mpc; for Ω = 1, the linear enhancement is reached only for ∼200 h-1 Mpc. An analytic expression relating the redshift space power spectrum to the real space spectrum is derived; it is a function of Ω and of scale. The ratio of the redshift to real space correlation functions for separations 1-20 h-1 Mpc is also investigated. A comparison of observations with simulations in redshift space reveals that the power spectrum of IRAS and optical galaxies are consistent with the spectrum of the standard Ω = 1 CDM model, as well as with the power spectra of the Ω ≍ 0.2 CDM model and the Ω = 1 HDM model. Consistency is also found for the correlation functions. Publication: The Astrophysical Journal Pub Date: December 1993 DOI: 10.1086/173497 Bibcode: 1993ApJ...419..440G Keywords: COSMOLOGY: THEORY; GALAXIES: CLUSTERING full text sources ADS |

Redshift space clustering of galaxies and cold dark matter model

The distorting effect of peculiar velocities on the power speturm and correlation function of IRAS and optical galaxies is studied. The observed redshift space power spectra and correlation functions of IRAS and optical the galaxies over the entire range of scales are directly compared with the corresponding redshift space distributions using large-scale computer simulations of cold dark matter (CDM) models in order to study the distortion effect of peculiar velocities on the power spectrum and correlation function of the galaxies. It is found that the observed power spectrum of IRAS and optical galaxies is consistent with the spectrum of an Omega = 1 CDM model. The problems that such a model currently faces may be related more to the high value of Omega in the model than to the shape of the spectrum. A low-density CDM model is also investigated and found to be consistent with the data.