Groups of galaxies. I - Nearby groups

Huchra, J.; Geller, Margaret J.

doi:10.1086/160000

Cited by 815 publications

(827 citation statements)

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“…Huchra & Geller 1982;Press & Davis 1982). For a full description of the algorithm see Yang et al (2005Yang et al ( , 2007, however in short, the groups are initially populated by connecting galaxies through a standard FoF approach (with very small linking lengths) and group memberships are iteritively updated under the assumption that the distribution of galaxies in phase space follows that of a spherical NFW profile (Navarro et al 1997).…”

Section: Optically Identified Galaxy Clustersmentioning

confidence: 99%

Connecting optical and X-ray tracers of galaxy cluster relaxation

Roberts

Parker

Hlavacek-Larrondo

2018

Monthly Notices of the Royal Astronomical Society

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Substantial effort has been devoted in determining the ideal proxy for quantifying the morphology of the hot intracluster medium in clusters of galaxies. These proxies, based on X-ray emission, typically require expensive, high-quality X-ray observations making them difficult to apply to large surveys of groups and clusters. Here, we compare optical relaxation proxies with X-ray asymmetries and centroid shifts for a sample of SDSS clusters with high-quality, archival X-ray data from Chandra and XMM-Newton. The three optical relaxation measures considered are: the shape of the member-galaxy projected velocity distribution -measured by the Anderson-Darling (AD) statistic, the stellar mass gap between the most-massive and second-most-massive cluster galaxy, and the offset between the most-massive galaxy (MMG) position and the luminosityweighted cluster centre. The AD statistic and stellar mass gap correlate significantly with X-ray relaxation proxies, with the AD statistic being the stronger correlator. Conversely, we find no evidence for a correlation between X-ray asymmetry or centroid shift and the MMG offset. High-mass clusters (M halo > 10 14.5 M ) in this sample have X-ray asymmetries, centroid shifts, and Anderson-Darling statistics which are systematically larger than for low-mass systems. Finally, considering the dichotomy of Gaussian and non-Gaussian clusters (measured by the AD test), we show that the probability of being a non-Gaussian cluster correlates significantly with X-ray asymmetry but only shows a marginal correlation with centroid shift. These results confirm the shape of the radial velocity distribution as a useful proxy for cluster relaxation, which can then be applied to large redshift surveys lacking extensive X-ray coverage.

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Section: Optically Identified Galaxy Clustersmentioning

confidence: 99%

Connecting optical and X-ray tracers of galaxy cluster relaxation

Roberts

Parker

Hlavacek-Larrondo

2018

Monthly Notices of the Royal Astronomical Society

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“…Galaxies are initially assigned to groups using a traditional "friends-of-friends" (FOF) algorithm (e.g. Huchra & Geller 1982) with very small linking lengths. The luminosityweighted centres of FOF groups with at least two members are then taken as the centres of potential groups and all galaxies not yet associated with a FOF group are treated as tentative centres for potential groups.…”

Section: Group Samplementioning

confidence: 99%

Evidence of pre-processing and a dependence on dynamical state for low-mass satellite galaxies

Roberts¹,

Parker²

2017

Monthly Notices of the Royal Astronomical Society

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We study the dependence of satellite star formation rate and morphology on group dynamics for a sample of SDSS groups. We classify the group dynamical state and study satellite properties for populations of galaxies at small and large group-centric radii. For galaxies at large radii we find no differences in the star-forming or disc fraction for those in Gaussian groups compared to those in non-Gaussian groups. By comparing the star-forming and disc fractions of infalling galaxies to field galaxies we find evidence for the pre-processing of both star formation rate and morphology. The strength of pre-processing increases with halo mass and is highest for low-mass galaxies infalling onto high-mass haloes. We show that the star formation rate of galaxies at small radii correlates with group dynamical state, with galaxies in nonGaussian groups showing enhanced star-forming fractions compared to galaxies in Gaussian groups. Similar correlations are not seen for the disc fractions of galaxies at small radii. This seems to suggest that either the mechanisms driving star formation quenching at small halo-centric radii are more efficient in dynamically relaxed groups, or that non-Gaussian groups have assembled more recently and therefore satellites of the groups will have been exposed to these transforming mechanisms for less time.

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“…The redshiftspace distortions (fingers of God) for groups were supressed as described in detail in Tempel et al (2014). Galaxy groups were determined using the friends-of-friends cluster analysis method introduced in cosmology by Zeldovich et al (1982) and Huchra & Geller (1982). A galaxy belongs to a group of galaxies if this galaxy has at least one group member galaxy closer than a linking length.…”

Section: Datamentioning

confidence: 99%

Sloan Great Wall as a complex of superclusters with collapsing cores

Einasto

Lietzen

Gramann

et al. 2016

A&A

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Context. The formation and evolution of the cosmic web is governed by the gravitational attraction of dark matter and antigravity of dark energy (cosmological constant). In the cosmic web, galaxy superclusters or their high-density cores are the largest objects that may collapse at present or during the future evolution. Aims. We study the dynamical state and possible future evolution of galaxy superclusters from the Sloan Great Wall (SGW), the richest galaxy system in the nearby Universe. Methods. We calculated supercluster masses using dynamical masses of galaxy groups and stellar masses of galaxies. We employed normal mixture modelling to study the structure of rich SGW superclusters and search for components (cores) in superclusters. We analysed the radial mass distribution in the high-density cores of superclusters centred approximately at rich clusters and used the spherical collapse model to study their dynamical state. Results. The lower limit of the total mass of the SGW is approximately M = 2.5 × 10 16 h −1 M . Different mass estimators of superclusters agree well, the main uncertainties in masses of superclusters come from missing groups and clusters. We detected three high-density cores in the richest SGW supercluster (SCl 027) and two in the second richest supercluster (SCl 019). They have masses of 1.2−5.9 × 10 15 h −1 M and sizes of up to ≈60 h −1 Mpc. The high-density cores of superclusters are very elongated, flattened perpendicularly to the line of sight. The comparison of the radial mass distribution in the high-density cores with the predictions of spherical collapse model suggests that their central regions with radii smaller than 8 h −1 Mpc and masses of up to M = 2 × 10 15 h −1 M may be collapsing. Conclusions. The rich SGW superclusters with their high-density cores represent dynamically evolving environments for studies of the properties of galaxies and galaxy systems.

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Groups of galaxies. I - Nearby groups

Cited by 815 publications

References 0 publications

Connecting optical and X-ray tracers of galaxy cluster relaxation

Connecting optical and X-ray tracers of galaxy cluster relaxation

Evidence of pre-processing and a dependence on dynamical state for low-mass satellite galaxies

Sloan Great Wall as a complex of superclusters with collapsing cores

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