Groups of galaxies in the Center for Astrophysics redshift survey

Ramella, M.; Geller, Margaret J.; Huchra, J. P.

doi:10.1086/167777

Cited by 149 publications

(172 citation statements)

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“…Our work suggests that the group has a population of at least 22 galaxies within a velocity range of 1500 km s À1 (see, e.g., Ramella et al 1989) from the median of the central elliptical, NGC 4756. At about 7A5 southwest of NGC 4756, a substructure well separated from NGC 4756 is detected that includes IC 829, MCG À2-33-35, MCG À2-33-36, and MCG À2-33-38, which meets the Hickson criteria for being a compact group.…”

Section: Discussionmentioning

confidence: 72%

Small-Scale Systems of Galaxies. II. Properties of the NGC 4756 Group of Galaxies

et al. 2005

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This paper is part of a series that focuses on investigating galaxy formation and evolution in small-scale systems of galaxies in low-density environments. We present results from a study of the NGC 4756 group, which is dominated by the elliptical galaxy NGC 4756. The characteristics of the group are investigated through (1) the detailed investigation of the morphological, photometric, and spectroscopic properties of nine galaxies among the dominant members of the group; (2) the determination of the photometric parameters of the faint galaxy population in an area of 34 0 ; 34 0 centered on NGC 4756; and (3) an analysis of the X-ray emission in the area based on archival data.The nine member galaxies are located in the core part of the NGC 4756 group (a strip %300 kpc in diameter, H 0 ¼ 70 km s À1 Mpc À1 ), which has a very loose configuration. The central part of the NGC 4756 group contains a significant fraction of early-type galaxies. Three new group members with previously unknown systemic velocities are identified, one of which is type dE. At about 7A5 southwest of NGC 4756 a substructure of the group is detected, including IC 829, MCG À2-33-35, MCG À2-33-36, and MCG À2-33-38, that meets the Hickson criteria for being a compact group. Most of the galaxies in this substructure show interaction signatures. We do not detect apparent fine structure and signatures of recent interaction events in the early-type galaxy population, with the exception of a strong dust lane in the elliptical galaxy MCG À2-33-38. However, this galaxy displays signatures of nuclear activity. Strong [O iii], [ N ii], and [S ii] line emission, combined with comparatively weak but broad H emission, suggests an intermediate Seyfert type classification. Although the area is heavily contaminated by the background cluster A1631, X-ray data suggest the presence of a hot intergalactic medium related to the detected X-ray emission of the group. The present results are discussed in the context of group evolution.

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Section: Discussionmentioning

confidence: 72%

Small-Scale Systems of Galaxies. II. Properties of the NGC 4756 Group of Galaxies

et al. 2005

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“…Ramella et al 1989). The presence of a hot intragroup medium in many groups suggests that X-ray observations can also be used to map out the distribution of mass in the universe.…”

Section: Large-scale Structurementioning

confidence: 99%

X-Ray Properties of Groups of Galaxies

Mulchaey

2000

Annu. Rev. Astron. Astrophys.

250

288

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ROSAT observations indicate that approximately half of all nearby groups of galaxies contain spatially extended X-ray emission. The radial extent of the X-ray emission is typically 50-500 h −1 100 kpc or approximately 10-50% of the virial radius of the group. Diffuse X-ray emission is generally restricted to groups that contain at least one early-type galaxy. X-ray spectroscopy suggests the emission mechanism is most likely a combination of thermal bremsstrahlung and line emission. This interpretation requires that the entire volume of groups be filled with a hot, low-density gas known as the intragroup medium. ROSAT and ASCA observations indicate that the temperature of the diffuse gas in groups ranges from approximately 0.3 keV to 2 keV. Higher temperature groups tend to follow the correlations found for rich clusters between X-ray luminosity, temperature, and velocity dispersion. However, groups with temperatures below approximately 1 keV appear to fall off the cluster LX-T relationship (and possibly the LX-σ and σ-T cluster relationships, although evidence for these latter departures is at the present time not very strong.) Deviations from the cluster LX-T relationship are consistent with preheating of the intragroup medium by an early generation of stars and supernovae. There is now considerable evidence that most X-ray groups are real, physical systems and not chance superpositions or large-scale filaments viewed edge-on. Assuming the intragroup gas is in hydrostatic equilibrium, X-ray observations can be used to estimate the masses of individual systems. ROSAT observations indicate that the typical mass of an X-ray group is ∼ 10 13 h100−1

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“…Small galaxy groups have been investigated extensively at low redshift (Burbidge & Burbidge 1960 ;Huchra & Geller 1982 ;Ramella, Geller, & Huchra 1989 ;, Mahdavi & Geller 2001 and at intermediate redshift (Carlberg et al 2001) to show that the total mass of a virialized group is dominated by dark matter. One action of the dark matter is to cause dynamical friction, whose in-spiral timescale varies in proportion to p3/o.…”

Section: Introductionmentioning

confidence: 99%

Environment and Galaxy Evolution at Intermediate Redshift in the CNOC2 Survey

Carlberg

Yee

Morris

et al. 2001

ApJ

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The systematic variation of galaxy colors and types with clustering environment could either be the result of local conditions at formation or subsequent environmental e †ects as larger scale structures draw together galaxies whose stellar mass is largely in place. Below redshift 0.7 galaxy luminosities (k-corrected and evolution compensated) are relatively invariant, whereas galaxy star formation rates, as reÑected in their colors, are a "" transient ÏÏ property that have a wide range for a given luminosity. The relations between these galaxy properties and the clustering properties are key statistics for understanding the forces driving late-time galaxy evolution. At z D 0.4 the comoving galaxy correlation length, mear 0 , sured in the CNOC2 sample is strongly color dependent, rising from 2 h~1 Mpc to nearly 10 h~1 Mpc as the volume-limited subsamples range from blue to red. The luminosity dependence of at z D 0.4 is r 0 weak below in the R band, although there is an upturn at high luminosity, where its interpretation L * depends on separating it from the relation. In the B band there is a slow, smooth increase of r 0 -color r 0 with luminosity, at least partially related to the color dependence. Study of the evolution of galaxies within groups, which create much of the strongly nonlinear correlation signal, allows a physical investigation of the source of these relations. The dominant e †ect of the group environment on star formation is seen in the radial gradient of the mean galaxy colors, which on the average become redder than the Ðeld toward the group centers. The color di †erentiation begins around the dynamical radius of virialization of the groups. The redder-than-Ðeld trend applies to groups with a line-of-sight velocity dispersion, km s~1. There is an indication, somewhat statistically insecure, that the high-luminosity galp 1 [ 150 axies in groups with km s~1 become bluer toward the group center. Monte Carlo orbit intep 1 \ 125 grations initiated at the measured positions and velocities show that the rate of galaxy merging in the km s~1 groups is very low, whereas for km s~1 about 25% of the galaxies will merge p 1 [ 150 p 1 \ 150 in 0.5 Gyr. We conclude that the higher velocity dispersion groups largely act to suppress star formation relative to the less clustered Ðeld, leading to "" embalmed ÏÏ galaxies. On the other hand, the low velocity dispersion groups are prime sites of both strong merging and enhanced star formation that leads to the formation of some new massive galaxies at intermediate redshifts. The tidal Ðelds within the groups appear to be a strong candidate for the physical source of the reduction of star formation in group galaxies relative to Ðeld. Tides operate e †ectively at all velocity dispersions to remove gas-rich companions and low-density gas in galactic halos. We Ðnd a close resemblance of the color-dependent galaxy luminosity function evolution in the Ðeld and groups, suggesting that the clustering-dependent star formation reduction mechanism is important for the e...

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Groups of galaxies in the Center for Astrophysics redshift survey

Cited by 149 publications

References 0 publications

Small-Scale Systems of Galaxies. II. Properties of the NGC 4756 Group of Galaxies

Small-Scale Systems of Galaxies. II. Properties of the NGC 4756 Group of Galaxies

X-Ray Properties of Groups of Galaxies

Environment and Galaxy Evolution at Intermediate Redshift in the CNOC2 Survey

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