Groups of Galaxies in the Northern CfA Redshift Survey

Ramella, M.; Pisani, A.; Geller, Margaret J.

doi:10.1086/118270

Cited by 104 publications

(183 citation statements)

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“…However, it seems equally possible that this gas is in the form of stars. This would also be consistent with a higher mass-to-light ratio for large clusters than for groups (Girardi et al 2000;Adami et al 1998;Hradecky et al 2000;Ramella, Pisani, & Geller 1997), although see David, Jones, & Forman (1995). Weak lensing of groups should provide useful constraints; preliminary results indicate the mass-to-light ratios of groups are somewhat lower than those of clusters (Hoekstra, Franx, & Kuijken 2000).…”

Section: The Modelmentioning

confidence: 53%

Explaining the Entropy Excess in Clusters and Groups of Galaxies without Additional Heating

Bryan¹

2000

The Astrophysical Journal

138

172

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The X-ray luminosity and temperature of clusters and groups of galaxies do not scale in a self-similar manner. This has often been interpreted as a sign that the intracluster medium has been substantially heated by nongravitational sources. In this Letter, we propose a simple model that instead uses the properties of galaxy formation to explain the available observations. Drawing on available observations, we show that there is evidence that the efficiency of galaxy formation was higher in groups than in clusters. If confirmed, this would deplete the low-entropy gas in groups, increase their central entropy, and decrease their X-ray luminosity. A simple, empirical, hydrostatic model appears to match both the luminosity-temperature relation of clusters and the properties of their internal structure.

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Section: The Modelmentioning

confidence: 53%

Explaining the Entropy Excess in Clusters and Groups of Galaxies without Additional Heating

Bryan¹

2000

The Astrophysical Journal

138

172

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“…In fact, owing to the small number of galaxies for each group, one must rely on members as assigned by the group-selection algorithm, rather than using refined methods to reject interlopers as performed in clusters or very well sampled groups (e.g., 12 groups of Zabludoff & Mulchaey 1998a; 20 groups of Mahdavi et al 1999). In particular, the resulting group properties may depend on the choice of the groupselection algorithm and its free parameters (e.g., Pisani et al 1992;Frederic 1995;Ramella et al 1997). In fact, in the case of the NOG catalog, although the HG and PG groups have a large overlap in their members, the surviving difference in membership leads to differences in their main properties (cf.…”

Section: Data Sample and Group Propertiesmentioning

confidence: 99%

Morphology and luminosity segregation of galaxies in nearby loose groups

Girardi

Rigoni

Mardirossian

et al. 2003

A&A

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Abstract.We study morphology and luminosity segregation of galaxies in loose groups. We analyze the two catalogs of groups identified in the Nearby Optical Galaxy (NOG) sample, by means of hierarchical and percolation "friends-of-friends" methods (HG and PG catalogs, respectively). In the first part of our analysis we consider 387 and 436 groups of HG and PG and compare morphology-(luminosity-) weighted to unweighted group properties: velocity dispersion, mean pairwise distance, and mean groupcentric distance of member galaxies. The second part of our analysis is based on two ensemble systems, one for each catalog, built by suitably combining together galaxies of all groups (1584 and 1882 galaxies for HG and PG groups). We find that earlier-type (brighter) galaxies are more clustered and lie closer to the group centers, both in position and in velocity, than later-type (fainter) galaxies. Spatial segregations are stronger than kinematical segregations. These effects are generally detected at the ∼ >3-sigma level. Luminosity segregation is shown to be independent of morphology segregation. Our main conclusions are strengthened by the detection of segregation in both hierarchical and percolation catalogs. Our results agree with a continuum of segregation properties of galaxies in systems, from low-mass groups to massive clusters.

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“…We kept only the structures with more than 4 galaxies and less than 40 galaxies (to be consistent with Merchan et al 2000). Structures with less than or with 3 galaxies are possibly close superposition effects and not real dynamical structures (Ramella et al 1997). Structures with more than 40 galaxies are likely to be rich clusters or diffuse elongated filaments of galaxies.…”

Section: Application To the Ssrs2 Catalog: Group Detection And Analysismentioning

confidence: 99%

“…Ramella et al 1997). About 85% of the sample has a mass in the range [5 × 10 12 ; 4 × 10 14 ] solar masses and 97.5% has a mass in the range [10 12 ; 4×10 14 ] solar masses.…”

Section: Velocity Dispersions and Massesmentioning

confidence: 99%

Group analysis in the SSRS2 catalog

Adami¹,

Mazure²

2002

A&A

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Abstract. We present an automated method to detect populations of groups in galaxy redshift catalogs. This method uses both analysis of the redshift distribution along lines of sight in fixed cells to detect elementary structures and a friend-of-friend algorithm to merge these elementary structures into physical structures. We apply this method to the SSRS2 galaxy redshift catalog. The groups detected with our method are similar to group catalogs detected with pure friend-of-friend algorithms. They have similar mass distribution, similar abundance versus redshift, a similar 2-point correlation function (modeled by a power law: (r/r0) γ with r0 = 7 h −1 Mpc and γ = −1.79) and the same redshift completeness limit, close to 5000 km s −1 . If instead of SSRS2, we use catalogs of the new generation (deep redshift surveys obtained with 10 m class telescopes), it would lead to a completeness limit of z ∼ 0.7. We model the luminosity function for nearby galaxy groups by a Schechter function with parameters M * SSRS2 = (−19.99 ± 0.36) + 5 logh and α = −1.46 ± 0.17 to compute the mass to light ratio. The median value of the mass to light ratio is 360 hM /L (in the SSRS2 band, close to a B band magnitude) and we deduce a relation between mass to light ratio and velocity dispersion σ (M/L = (3.79 ± 0.64)σ − (294 ± 570)). The more massive the group, the higher the mass to light ratio, and therefore, the larger the amount of dark matter inside the group. Another explanation is a significant stripping of the gas of the galaxies in massive groups as opposed to low mass groups. This extends to groups of galaxies the mild tendency already detected for rich clusters of galaxies. Finally, we detect a barely significant fundamental plane for these groups (L ∝ R 2.26±1.39 Vir × σ 2.93±1.64 for groups with more than 8 galaxies) but it is much less narrow than for clusters of galaxies.

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Groups of Galaxies in the Northern CfA Redshift Survey

Cited by 104 publications

References 0 publications

Explaining the Entropy Excess in Clusters and Groups of Galaxies without Additional Heating

Explaining the Entropy Excess in Clusters and Groups of Galaxies without Additional Heating

Morphology and luminosity segregation of galaxies in nearby loose groups

Group analysis in the SSRS2 catalog

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