Groups of Galaxies.IV. The Multiplicity Function

Richard, Iii Gott J.; Turner, Edwin L.

doi:10.1086/155476

Cited by 39 publications

(12 citation statements)

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“…We find that, for all three group catalogs, the median value of t cross /t H is ∼ 0.15, and 80% of all groups have values less than ∼ 0.29. These numbers can be interpreted in terms of the spherical infall model (Gunn & Gott 1972;Gott & Turner 1977a), or other analytic or numerical models. However, at a first glance, the numbers are encouraging and suggest that most of our groups are likely virialized systems.…”

Section: Summary and Discussionmentioning

confidence: 99%

See 1 more Smart Citation

Percolation Galaxy Groups and Clusters in the SDSS Redshift Survey: Identification, Catalogs, and the Multiplicity Function

Berlind

Frieman

Weinberg

et al. 2006

ASTROPHYS J SUPPL S

374

446

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We identify galaxy groups and clusters in volume-limited samples of the Sloan Digital Sky Survey (SDSS) redshift survey, using a redshift-space friends-of-friends algorithm. We optimize the friends-of-friends linking lengths to recover galaxy systems that occupy the same dark matter halos, using a set of mock catalogs created by populating halos of N-body simulations with galaxies. Extensive tests with these mock catalogs show that no combination of perpendicular and line-of-sight linking lengths is able to yield groups and clusters that simultaneously recover the true halo multiplicity function, projected size distribution, and velocity dispersion. We adopt a linking length combination that yields, for galaxy groups with 10 or more members: a group multiplicity function that is unbiased with respect to the true halo multiplicity function; an unbiased median relation between the multiplicities of groups and their associated halos; a spurious group fraction of less than $1%; a halo completeness of more than $97%; the correct projected size distribution as a function of multiplicity; and a velocity dispersion distribution that is $20% too low at all multiplicities. These results hold over a range of mock catalogs that use different input recipes of populating halos with galaxies. We apply our group-finding algorithm to the SDSS data and obtain three group and cluster catalogs for three volume-limited samples that cover 3495.1 deg 2 on the sky, go out to redshifts of 0.1, 0.068, and 0.045, and contain 57,138, 37,820, and 18,895 galaxies, respectively. We correct for incompleteness caused by fiber collisions and survey edges and obtain measurements of the group multiplicity function, with errors calculated from realistic mock catalogs. These multiplicity function measurements provide a key constraint on the relation between galaxy populations and dark matter halos.

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Section: Summary and Discussionmentioning

confidence: 99%

“…de Vaucouleurs (1971) shifted focus to poorer systems by studying nearby groups of galaxies. Gott & Turner (1977b) made the first measurement of the group multiplicity function using the (Turner & Gott 1976) catalog of groups selected based on the projected surface density of galaxies.…”

Section: Introductionmentioning

confidence: 99%

Percolation Galaxy Groups and Clusters in the SDSS Redshift Survey: Identification, Catalogs, and the Multiplicity Function

Berlind

Frieman

Weinberg

et al. 2006

ASTROPHYS J SUPPL S

374

446

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“…A pure power-law spectrum that failed to turn over or cut off would violate observational constraints on either very large or very small scales, but a power law might be a reasonable approximation to the true power spectrum over some finite range. 'Standard CDM' predicts a post-recombination power spectrum approximately like P (k) ∝ k −1 on comoving scales ∼ 3 − 10 h −1 Mpc, and a variety of observations support this prediction (Gott & Rees 1975;Gott & Turner 1977;Bhavsar, Gott & Aarseth 1981;Gunn 1982;Gott et al 1989Gott et al , 1992. For our power-law spectra, we therefore consider n = −1 and its 'bracketing values' of n = −2 and n = 0.…”

Section: Initial Conditionsmentioning

confidence: 99%

Cosmic voids and biased galaxy formation

Little¹,

Weinberg

1994

Monthly Notices of the Royal Astronomical Society

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Using cosmological N -body simulations and the void probability function (VPF), we investigate the statistical properties of voids within a wide range of initially Gaussian models for the origin of large-scale structure. We study the dependence of the VPF on cosmological parameters, on the power spectrum of primordial fluctuations, and on assumptions about galaxy formation. We pay particular attention to the ability of the VPF to diagnose 'biased galaxy formation': the preferential formation of galaxies in regions of high background density and corresponding suppression of galaxy formation in regions of low background density. We find that the VPF is insensitive to the cosmic density parameter Ω 0 and the cosmological constant λ 0 , provided that fluctuations are normalized to a fixed rms amplitude on scales ∼ 8 h −1 Mpc. In the absence of biasing, the VPF is also insensitive to the shape of the initial power spectrum. The VPF does depend on the prescription adopted for biased galaxy formation, in the obvious sense that a scheme that more efficiently suppresses galaxy formation in low density regions leads to larger voids. Biased models have systematically higher VPFs than unbiased models, but for a given biasing scheme the VPF is relatively insensitive to the value of the bias factor b, the ratio of rms galaxy fluctuations to rms mass fluctuations. Thus, while the VPF can distinguish unbiased models from some biased models, it is probably not a useful way to constrain the bias factor; uncertainties in the appropriate choice of biasing prescription overwhelm the mild dependence on b.We compare the predictions of our models to the most extensive VPF observations published to date. These data do not require strong biasing; Gaussian models in which galaxies trace mass can reproduce the VPF data to within the errors expected from the current finite volume fluctuations. Models with the moderate biasing predicted by cosmological simulations that incorporate gas dynamics yield a slightly better match to the data. Models in which galaxy formation is strongly suppressed in low density regions produce an excess of large, empty voids.

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“…In the BFS88 analysis the UVX criterion was tightened to u 2 b , 20X5Y reducing contamination to 25 per cent while keeping 85 per cent of the QSOs. The UVX catalogue was then split into two magnitude-limited samples, 17X9 , b , 19X9 and 17X9 , b , 20X65X The galaxy catalogue consists of all galaxies to a limit of b J 20X0 and the cluster sample was created using à friends-of-friends' algorithm (Gott & Turner 1977;Stevenson, Fong & Shanks 1988). Groups of seven or more galaxies with density greater than 8 times the average for the field were classed as clusters, which amounted to 10 per cent of the total number of galaxies.…”

Section: S Tat I S T I C a L G R Av I Tat I O N A L L E N S I N Gmentioning

confidence: 99%

Statistical lensing of faint QSOs by galaxy clusters

Croom

Shanks

1999

Monthly Notices of the Royal Astronomical Society

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We investigate the anti-correlation between faint high redshift QSOs and low redshift galaxy groups found by Boyle, Fong & Shanks (1988), on the assumption that it is caused by gravitational lensing of a flat QSO number count, rather than any other systematic effect (e.g dust). An isothermal sphere lens model, requires a velocity dispersion of 1286+72-91 km/s. Addition of a constant density plane reduces this to 1143+109-153 km/s, while the plane density is 0.081+-0.032h g/cm**2. Both these values are considerably larger than the 400-600km/s expected for poor clusters and groups and imply that the mass associated with such groups is ~4 times larger than inferred from virial analyses. If due to lensing, this measurement clearly tends to favour high values of Omega_0. We demonstrate how an estimate of Omega_0 may be obtained, finding Omega_0=1.3(n/3x10^-4h^3Mpc^-3)(r/1Mpc)(sigma/1286km/s)^2. Systematic uncertainties in r, the extent of the anti-correlation, and n, the group space density, currently dominate this determination, but this will be a route to estimating Omega_0 in improved galaxy-QSO datasets where systematics can be better controlled. We compared our result to that of Williams & Irwin (1998) who find a positive correlation between bright LBQS QSOs and APM galaxies. Adapting the analysis of Williams & Irwin to our use of galaxy groups, we find agreement between the amplitude of the positive cross-correlation found for bright QSOs and the negative cross-correlation found for faint QSOs. This analysis leads to a common estimate of Omega_0*sigma_8~3-4. This, however, is significantly higher than indicated from several other analyses. Further tests of the accuracy of galaxy-QSO cross-correlations and their implications for Omega_0 and sigma_8 will soon be available from the new 2dF QSO catalogue.Comment: Alteration to astro-ph abstrac

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Groups of Galaxies.IV. The Multiplicity Function

Cited by 39 publications

References 0 publications

Percolation Galaxy Groups and Clusters in the SDSS Redshift Survey: Identification, Catalogs, and the Multiplicity Function

Percolation Galaxy Groups and Clusters in the SDSS Redshift Survey: Identification, Catalogs, and the Multiplicity Function

Cosmic voids and biased galaxy formation

Statistical lensing of faint QSOs by galaxy clusters

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