Showing papers on "Brightest cluster galaxy published in 1979"

Masses and Mass-To-Light Ratios of Galaxies

Abstract: Is there more to a galaxy than meets the eye (or can be seen on a photo­ graph)? Many decades ago, Zwicky (1933) and Smith (1936) showed that if the Virgo cluster of galaxies is bound, the total mass must considerably exceed the sum of the masses of the individual member galaxies; i.e. there appeared to be "missing mass" in the cluster. As more data became avail­ able, the discrepancy persisted between masses of individual galaxies determined from optical rotation curves and the larger average galaxy mass needed to bind groups and clusters (e.g. Neyman, Page & Scott 1961). Recently, however, new information has pointed toward larger total masses for individual galaxies, thus decreasing the traditional discrepancy between various methods of mass measurement. Arguing that thin self­ gravitating stellar disks are unstable against bar-like modes, Ostriker & Peebles (1973) suggested that the disks of normal spiral galaxies must be imbedded in optically undetected, stabilizing massive halos. Ostriker, Peebles & Yahil (1974) and Einasto, Kaasik & Saar (1974) collected observational evidence in support of the existence of such halos (although Burbidge 1975 used similar data to reach the opposite conclusion). At nearly the same time, h igh-resolution 2 1-cm observations of nearby galaxies were showing that H I often extends well beyond the optical

X-ray observations of galaxies in the Virgo cluster.

Abstract: X-ray emission from individual galaxies (other than M87) in the Virgo cluster has been detected using observations from the Einstein X-ray Observatory. One of the galaxies, M86, exhibits extended emission which is interpreted as thermal bremsstrahlung from hot gas being stripped from the galaxy by the ram pressure of the intracluster medium. The observations are discussed in relation to models for the dynamical evolution of clusters of galaxies.

Galaxy correlations and cosmology

Abstract: Correlations in the distribution of galaxies provide some important clues about the structure and evolution of the Universe on scales larger than individual galaxies. In recent years much effort has been devoted to estimating and interpreting galaxy correlations. This is a review of these efforts. It is meant to provide both an introductory overview of the subject and a critical assessment of some recent developments.

Dissipation, merging and the rotation of galaxies

Abstract: The distinction between elliptical and disk galaxies is often explained by invoking different rates of dissipation and star formation in the proto-galactic gas clouds from which they are presumed to have formed1–3. Another possibility is raised by the suggestion that many ellipticals are the remnants of galaxies that merged while suffering the tidal distortion and violent relaxation of a slow encounter4,5. Various N-body simulations indicate that merging can account for many of the observed properties of bright elliptical galaxies6–9, although some reservations have been expressed about the possibility of accounting for their low rotation velocities10. My aim here is to consider a specific model for the formation of disk galaxies by dissipation and the formation of bright ellipticals by merging and to suggest that it can account for their rotation properties in a natural way.

Observations at 610 MHz of radio halos in clusters of galaxies.

Abstract: In a search for diffuse radio sources such as that in the Coma cluster, we made new 610 MHz observations of 32 galaxy clusters with the Green Bank 300 foot (91 m) telescope. For 20 of these clusters the interferometric observations available at the same frequency allowed us to subtract any small high-brightness sources from our data.We detect no Coma-like halos in any other nearby clusters, although some brighter diffuse sources are visible in the interferometric maps of more distant clusters.From the continuity of morphology of the various cluster sources we suggest that the halo sources are fossils of extended radio galaxies such as the head--tail sources.

A binary model for the Coma cluster of galaxies

Abstract: We study the dynamics of galaxies in the Coma cluster and find that the cluster is probably dominated by a central binary of galaxies NGC 4874--NGC4889. We estimate their total mass to be about 3 x 10/sup 14/ M/sub sun/ by two independent methods (assuming in Hubble constant of 100 km s/sup -1/ Mpc/sup -1/). This binary is efficient in dynamically ejecting smaller galaxies, some of of which are seen in projection against the inner 3/sup 0/ radius of the cluster and which, if erroneously considered as bound members, cause a serious overestimate of the mass of the entire cluster. Taking account of the ejected galaxies, we estimate the total cluster mass to be 4--9 x 10/sup 14/ M/sub sun/, with a corresponding mass-to-light ratio for a typical galaxy in the range of 20--120 solar units. The origin of the secondary maximum observed in the radial surface density profile is studied. We consider it to be a remnant of a shell of galaxies which formed around the central binary. This shell expanded, then collapsed into the binary, and is now reexpanding. This is supported by the coincidence of the minimum in the cluster eccentricity and radical velocity dispersion at themore » same radial distance as the secondary maximum. Numerical simulations of a cluster model with a massive central binary and a spherical shell of test particles are performed, and they reproduce the observed shape, galaxy density, and radial velocity distributions in the Coma cluster fairly well. Consequences of extending the model to other clusters are discussed.« less

Surface brightness distributions of elliptical galaxies in the cD clusters A401 and A2670

Abstract: R-band surface photometry is reported for E galaxies located in the cD clusters Abell 401 and Abell 2670. In both aggregates the isophotal radii r/sub 26/ corresponding to ..mu../sub R/=26.0 mag arcsec/sup -2/ are smaller for galaxies located within 1 Mpc of the cluster center. Tidal stripping of galaxies located in the dense central regions of these clusters is suggested as the cause for the apparent differences in galaxy size as a function of cluster position. Study of the frequency distribution of ellipticities among the E galaxies in our sample shows that in A401 the number of flattened (E> or =3) galaxies is abnormally high. In view of the results of our previous surveys which suggest that flattened galaxies are found with higher frequency in flattened clusters, it is noteworthy that for A401 the galaxy distribution on the plane of the sky also exhibits a significant flattening. It is difficult to avoid the conclusion that whatever factors influence the present-epoch shape of a cluster also influence the shape of the member galaxies.

Multiplicity of the first brightest galaxy in a cluster versus Bautz-Morgan type

Abstract: The fraction of multiple first brightest galaxies in Bautz-Morgan type I, I--II clusters is 7 times larger than the fraction in type III clusters. Observational evidence indicates that the 23% (28 out of 112) binary first brightest galaxies in type I clusters are physical systems, which leads to an empirical time scale for merger of >4 x 10/sup 9/ yr. In contrast, the theoretical time scales for merger by dynamical friction and tidal energy exchange are approx.3 x 10/sup 7/ (or 3 x 10/sup 8/) yr.

VV 5-32-63/64 - The 'supermassive double galaxy' in Abell 1775 revisited

Abstract: Spectroscopy is presented for galaxies in A 1775, the cluster containing VV 5-32-63/64, an apparent double galaxy which has long been considered a gravitationally bound system with supermassive components (10 to the 13th solar masses). However, this model has run afoul of recent radio observations, which detected an extremely long straight radio tail emanating from the eastern galaxy in the pair. The present observations indicate that if both galaxies are members of the same cluster, the cluster radial-velocity dispersion (1522 km/sec) is large enough to account for the velocity difference between the two VV galaxies (1650 km/sec). It is therefore suggested that the VV galaxies are not gravitationally bound and need not be supermassive. The large velocity dispersion measured for A 1775 also strains suggested velocity dispersion vs X-ray luminosity relations for clusters of galaxies, as A 1775 has not yet been detected at X-ray wavelengths.