The shape of poor groups of galaxies

Plionis, M.; Basilakos, Spyros; Tovmassian, H. M.

doi:10.1111/j.1365-2966.2004.08023.x

Cited by 38 publications

(56 citation statements)

References 35 publications

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“…However, Plionis et al (2004) find a trend of shape with cluster size that is opposite that seen in simulations. From 1168 groups in the UZC-SSRS2 galaxy group catalog, Plionis et al find that poorer groups are more elongated than richer groups, with 85% of poor groups having b P 0:4.…”

Section: Comparisons To Previous Workcontrasting

confidence: 43%

Shapes and Alignments of Galaxy Cluster Halos

Kasun

Evrard

2005

ApJ

188

244

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We present distribution functions and mark correlations of the shapes of massive dark matter halos derived from Hubble volume simulations of a ÃCDM universe. We measure both position and velocity shapes within spheres that encompass a mean density 200 times the critical value and calibrate small-N systematic errors using Poisson realizations of isothermal spheres and higher resolution simulations. For halos more massive than 3 ; 10 14 h À1 M , the shape distribution function peaks at (minor/major, intermediate/major) axial ratios of (0.64, 0.76) in position and is rounder in velocity, peaking at (0.72, 0.82). Halo shapes are rounder at lower mass and/or redshift; the mean minoraxis ratio in position follows hc/ai(M ; z) ¼ c 15;0 ½1 À ln (M/10 15 h À1 M ) (1 þ z) À , with c 15;0 ¼ 0:631 AE 0:001, ¼ 0:023 AE 0:002, and ¼ 0:086 AE 0:004. Position and velocity principal axes are well aligned in direction, with median alignment angle 22 , and the axial ratios in these spaces are correlated in magnitude. We investigate mark correlations of halo pair orientations using two measures: a simple scalar product shows !1% alignment extending to 30 h À1 Mpc, while a filamentary statistic exhibits nonrandom alignment extending to scales $200 h À1 Mpc, 10 times the sample two-point correlation length and well into the regime of negative two-point correlation. Shapes of cluster halos are little affected by the large-scale environment; the distribution of supercluster member minor-axis ratios differs from that of the general population at only the few percent level.

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Section: Comparisons To Previous Workcontrasting

confidence: 43%

Shapes and Alignments of Galaxy Cluster Halos

Kasun

Evrard

2005

ApJ

188

244

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“…Moreover, the formation of large scale structure has a bearing on the intrinsic shape of cluster sized halos (Plionis et al 2004); thus, the 3D cluster morphology could be a device that can be used to constrain cosmological models.…”

Section: Introductionmentioning

confidence: 99%

Cluster geometry and inclinations from deprojection uncertainties

Chakrabarty¹,

Filippis

Russell³

2008

A&A

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Context. The determination of cluster masses is a complex problem that would be aided by information about the cluster shape and orientation (with respect to the line-of-sight). Aims. It is in this context, that we have developed a scheme for identifying the intrinsic morphology and inclination of a cluster, by looking for the signature of the true cluster characteristics in the inter-comparison of the different deprojected emissivity profiles (that all project to the same X-ray brightness distribution) and complimenting this with SZe data when available. Methods. We deproject the cluster X-ray surface brightness profile under assumptions about geometry and inclination that correspond to four extreme scenarios; the deprojection is performed by the non-parametric algorithm DOPING. The formalism is tested with model clusters and is then applied to a sample of 24 clusters. While the shape determination is possible by implementing the X-ray brightness alone, the estimation of the inclination is usually markedly improved upon by the usage of SZe data that is available for the considered sample. Results. We spot 8 prolate systems, 1 oblate and 15 of the clusters in our sample as triaxial. In fact, for systems identified as triaxial, we are able to discern how the three semi-axis lengths compare with each other. This, when compounded by the information about the line-of-sight extent, allows us to constrain the intrinsic axial ratios and the inclination quite tightly.

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“…An important question is whether or not these systems represent real dynamical structures (Hickson 1997). A critical point is that every sample selected based on an apparent density contrast will suffer from projection effects, such as a tendency to select prolate groups radially oriented along the line of sight (Plionis et al 2004), or even transient configurations (Rose 1979).…”

Section: Introductionmentioning

confidence: 99%

A Catalog of Distant Compact Groups Using the Digitized Second Palomar Observatory Sky Survey

et al. 2005

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In this paper we present an objectively defined catalog of 459 small, high-density groups of galaxies out to z $ 0:2 in a region of $6260 deg 2 in the northern sky derived from the Digitized Second Palomar Observatory Sky Survey. Our catalog extends down to r ¼ 19:0 and has a median redshift of z med ¼ 0:12, making it complementary to Hickson's catalog for the nearby universe (z med ¼ 0:03). The depth and angular coverage of this catalog makes it valuable for studies of the general characteristics of small groups of galaxies and how galaxies evolve in and around them. We also examine the relationship between compact groups and large-scale structure.

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The shape of poor groups of galaxies

Cited by 38 publications

References 35 publications

Shapes and Alignments of Galaxy Cluster Halos

Shapes and Alignments of Galaxy Cluster Halos

Cluster geometry and inclinations from deprojection uncertainties

A Catalog of Distant Compact Groups Using the Digitized Second Palomar Observatory Sky Survey

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