The luminosity function of galaxies in cluster A2670

Tago

et al. 2005

A&A

Abstract. We find groups and clusters of galaxies using the Data Releases DR1 and DR3 of the Sloan Digital Sky Survey. We calculate a low-resolution density field with a smoothing length of 10 h −1 Mpc to characterise the density of the cluster environment, and a medium-resolution density field with a smoothing length of 2 h −1 Mpc to characterise the galaxy environment. We determine the luminosity function of clusters, and investigate properties of galaxies and clusters in various environments. We show that clusters in a high-density environment are about 5 times more luminous than in a low-density environment, and luminosities of galaxies in different environments differ by a factor of ∼25. We see similar effects in numerical simulations -simulated clusters in a high-density environment are ∼100 times more massive than those in a low-density environment.Comparison of the density distribution in simulations at various epochs shows that in large low-density regions (voids) dynamical evolution is very slow and stops early. In contrast, in large regions of higher density (superclusters) dynamical evolution starts early and continues until the present; here particles cluster early, and by merging of smaller groups very rich systems of galaxies form.

Section: Luminosity/mass Functions In Real and Simulated Clusterssupporting

confidence: 78%

Toward understanding environmental effects in SDSS clusters

Tago

et al. 2005

A&A

“…Just (1959) has found a slight richness-distance correlation in Abell's catalog; however, the effect is small and is probably explained by a slight incompleteness (10%) of the catalog for distant clusters (Paal, 1964). When more accurate determinations have been made, it has been found that the Abell richness generally correlated well with the number of galaxies, but that the Abell richness may be significantly in error in some individual cases (Mottmann and Abell, 1977;Dressier, 1980a). Thus the Abell richnesses are very useful for statistical studies, but must be used with caution in studies of individual clusters.…”

Section: B Redshiftsmentioning

confidence: 99%

X-ray emission from clusters of galaxies

1986

Clusters of galaxies are gravitationally bound configurations containing typically hundreds of galaxies in a region about 10 cm in size. They range from irregular clusters, with strong subclustering, no strong central concentration, and mainly spiral galaxies, to regular clusters, with smooth and centrally condensed galaxy distributions containing few spiral galaxies. Observations of these clusters of galaxies show that they are bright x-ray sources, with luminosities of 1043 45 ergs/sec. It is now established that the emission mechanism is thermal bremsstrahlung from hot (-10 K}, low-density (-10 atoms/cm ) gas. This intracluster gas has a distribution similar to that of the galaxies in the cluster and fills the space between the galaxies. Remarkably, the total mass of hot gas in a typical cluster is similar to the total mass in all the stars in all the galaxies in the cluster. The x-ray spectra of clusters show strong x-ray line emission from iron and other heavy elements; this indicates that a significant portion of the intracluster gas must have been ejected from galaxies in the cluster. Recent x-ray observations from the Einstein x-ray satellite show that intracluster gas is cooling in some clusters and being accreted ontc large, central galaxies. X-ray images from Einstein also suggest that the morphology of the gas mirrors the dynamical state of the cluster. In this paper the x-ray observations of clusters of galaxies are reviewed. Related optical and radio measurements of clusters are also summarized. Theories for the physical state, distribution, origin, and evolution of the intracluster medium are extensively discussed. Finally, the author comments. on the prospects for future x-ray observations.

“…In the calculation of weights we assumed that galaxy luminosities are distributed according to a double powerlaw function that was popular in the past (see, e.g. , Christensen 1975;Kiang 1976;Abell 1977;Mottmann & Abell 1977):…”

Section: Luminosities Of Groupsmentioning

confidence: 99%

Groups of galaxies in the SDSS Data Release 5

Tago¹,

Einasto²,

Saar³

et al. 2008

A&A

117

Aims. We extract groups of galaxies from the SDSS Data Release 5 to study the supercluster-void network and environmental properties of groups therein. Groups of galaxies as density enhancements can be used to determine the luminosity density field of the supercluster-void network. Methods. We use a modified friends-of-friends (FoF) method with slightly variable linking lengths in transverse and radial directions to eliminate selection effects and to reliably find as many groups as possible. To determine the scaling of the linking length we calibrated group sizes and mean galaxy number densities within groups by shifting nearby groups to larger distances. Results. Our final sample contains 17 143 groups in the equatorial, and 33 219 groups in the northern part of the DR5 survey. The group catalogue is available at the CDS. Conclusions. The mean sizes and velocity dispersions of our groups practically do not change with their distance. This means that the selection effects have been properly taken into account when generating the group catalogue.