Engineering topics

Geller, M. J.

Publications and source records attributed to Geller, M. J..

At least 37 records · Page 2

NASA NTRS1984

Seven poor clusters of galaxies

The measurement of 83 new redshifts from galaxies in the region of seven of the poor clusters of galaxies identified by Morgan et al (1975) and Albert et al (1977) has been followed by an estimation of cluster masses through the application of both the virial theorem and the projected mas method. For each system, these two estimates are consistent. For the two clusters with highest X-ray luminosities, the line-of-sight velocity dispersions are about 700 km/sec, while for the five other clusters, the dispersions are of the order of less than about 370 km/sec. The D or cD galaxy in each poor cluster is at the kinematic center of each system.

Beers, T. C.↗

NASA NTRS1984

Observational and theoretical studies of rich clusters with multiple subcondensations

Observational and theoretical studies of the formation and evolution of clusters of galaxies are investigated. The relationship between the properties of individual galaxies and their environment is examined. Perphaps the most remarkable physical result derived from these is the apparent substructure in redishift position space. The distribution of spiral galaxies is quite different from the distribution of the ellipticals. The velocity distribution for the spirals is also substantially broader than the distribution for the ellipticals.

Geller, M. J.↗

NASA NTRS1984

The morphology-density relation - The group connection

The relationship between galaxy morphology and local density is derived from two complete galaxy redshift surveys. This relationship is completely consistent with the one derived by Dressler for a sample of 55 rich clusters. The apparently universal morphology-density relation extends over six orders of magnitude in galaxy space density. There is no dependence of galaxy morphology on density in regions where the dynamical time scale is comparable with or greater than the Hubble time. At densities greater than about 600 galaxies/cu Mpc, S0's dominate the galaxy population. At these densities, stripping mechanisms are likely to affect the galaxy population. At densities greater than about 3000 galaxies/cu Mpc, the fraction of elliptical galaxies rises steeply. In these regions, the collapse time is short compared with typical time scales for the formation of disks.

Postman, M.↗

NASA NTRS1984

Constraints on the anisotropy of the velocity dispersion of the Coma cluster

The dynamics of the Coma cluster are probed through the study of spiral galaxies that have been stripped of gas and ellipticals that have been tidally stripped. Since such stripping is most effective in regions where intergalaxy or cluster gas density is highest, the affected galaxies probably have orbits that take them through the center of the cluster. The Bothun et al. (1982, 1983) data analyzed indicate that the spirals in the cluster center are deficient in H I relative to other spiral members. Observations by Strom and Strom (1978) may indicate the tidal stripping of elliptical galaxies near the cluster center. For both data sets, the most likely models are everywhere isotropic.

Pryor, C.↗

NASA NTRS1984

A redshift survey of the poor cluster A1142

A nearly complete redshift survey of the galaxy cluster A1142 over a 2 sq deg region which includes the central 0.7 Mpc of the cluster is presented which includes 63 new redshifts. Of the 60 galaxies in the region brighter than m(v) = 16.5, about 40 percent are either foreground or background to the cluster. For the 35 cluster members, a mass-to-light ratio of 520 solar masses/solar luminosities is derived, consistent with the results for other well-studied systems.

Geller, M. J.↗

NASA NTRS1984

When clusters are superclusters

Recent research on substructure in clusters and superclusters of galaxies is critically surveyed, with an emphasis on the distinction (based on physical size and dynamic state) between the two classes of structures. The cosmological and large-scale structural implications of substructure in rich clusters are analyzed, using N-body-simulation results, and illustrated for the clusters A98 and A548. Consideration is also given to gravitational lensing of distant quasars by intervening clusters and the interpretation of the matter distribution on scales larger than about 5 Mpc. It is determined that A98 and A548 are superclusters.

Geller, M. J.↗

NASA NTRS1983

The environment of D and cD galaxies

The Dressler (1980) morphological sample of galaxies in clusters is used in an investigation of bright galaxy spatial distribution, which has established that such galaxies with luminous extended halos as the D or cD lie on significant cluster galaxy distribution peaks irrespective of whether they are the brightest cluster member. The mean distance of bright D and cD galaxies from local density peaks is of the order of their halo scales, and the positions of bright galaxies of other morphological types are consistent with their being drawn at random from each morphological population. It is noted that local density peaks with associated d ocD galaxies have a mean density 2-3 times greater than peaks without a D or cD.

Beers, T. C.↗

NASA NTRS1983

First-ranked galaxies in groups

A statistical analysis of five group catalogs shows that the B(0) magnitudes of first-ranked group members are consistent with a statistical model in which the luminosities of all group members are drawn from the same distribution. As in the Hickson compact groups, indications are that first-ranked group members are only rarely the products of distinctive evolutionary processes. Distance-dependent selection effects can introduce spurious correlations among group parameters which may appear to support environment-dependent evolution of the first-ranked group members.

Geller, M. J.↗

NASA NTRS1983

Star formation in blue galaxies. I - Ultraviolet, optical, and infrared observations of NGC 4214 and NGC 4670

NGC 4214 and NGC 4760 have been observed between 1150 A and 1950 A with the IUE satellite, and new infrared and optical broad-band photometry have been obtained. The spectra of both galaxies are dominated by O stars, and, in the spectrum of NGC 4214, the C IV 1550 A line exhibits a P Cygni profile indicative of hot stars with large mass-loss rates. Although the optical spectra of both galaxies are dominated by strong narrow emission lines, no strong emission lines are seen in the UV (the observed Ly-alpha flux is dominated by geocoronal emission). Both galaxies contain giant H II region complexes in which the energy (in particular, the H-beta luminosity and the ultraviolet continuum) is provided by several hundred O stars. The comparison of the observed UVOIR energy distributions with evolutionary population models indicates that the regions observed consist of young 'bursts' of star formation superposed on an underlying old population. The initial mass function for this epoch of star formation is constrained to be similar in slope to or flatter than the Salpeter function.

Geller, M. J.↗

NASA NTRS1983

The Cancer Cluster - An unbound collection of groups

A surface density contour map of the Cancer Cluster derived from galaxy counts in the Zwicky catalog is presented. The contour map shows that the galaxy distribution is clumpy. When this spatial distribution is combined with nearly complete velocity information, the clumps stand out more clearly; there are significant differences in the mean velocities of the clumps which exceed their internal velocity dispersions. The Cancer Cluster is not a proper 'cluster' but is a collection of discrete groups, each with a velocity dispersion of approximately 300 km/s, separating from one another with the cosmological flow. The mass-to-light ratio for galaxies in the main concentration is approximately 320 solar masses/solar luminosities (H sub 0 = 100 km/s Mpc).

Geller, M. J.↗

NASA NTRS1983

Galaxy clusters with multiple components. II - Abell 115

Abell 115 is a galaxy cluster with two large enhancements in X-ray surface brightness. A map of the galaxy distribution over an extended region reveals the presence of three primary clumps of galaxies. Two of these correspond to the peaks in the X-ray surface brightness. A third clump, 7 arcmin to the east of the pair, has no X-ray emission detected by the Einstein Observatory. Redshifts are measured for 29 galaxies in the region; 10 are certainly members of foreground groups. A115, at z approximately 0.2, is the highest redshift cluster for which any extensive attempt has been made to study the system dynamics.

Beers, T. C.↗

NASA NTRS1982

Substructure within clusters of galaxies

Surface number density contour maps based on Dressler's (1976, 1980) studies of 65 rich clusters are presented to demonstrate the frequent occurrence of substructure in these dense systems. A prescription is given for examining the significance of such structure and it is shown that structure on scales equal to or larger than 0.24 Mpc (H0 = 100 km/s Mpc) is present in approximately 40% of the clusters in this sample. Many of the remaining clusters are elongated. The contour plots are useful for comparison with X-ray surface brightness maps. Together with available velocity data, they also serve warning that many rich clusters may not be simply characterized by a single core radius and velocity dispersion.

Geller, M. J.↗

NASA NTRS1982

Galaxy clusters with multiple components. I - The dynamics of Abell 98

The nature and evolution of rich galaxy clusters containing multiple condensations is studied. Velocities for 13 members of A98 are presented and the determination of dynamical properties of the individual subclusters is substantially improved. The application of techniques for quantifying gravitational scale lengths are stressed without invocation of the symmetry arguments demanded by the usual parameter fitting procedures. The entire A98 cluster is modeled as a two-body system. The probability that A98 is bound is found to be 98 percent. From this model and the results of previous N-body simulations, it is shown that the most likely description of the system is that it reached maximum expansion about 3.5 billion years ago and is presently in a state of collapse. The subclusters will merge in another three billion years.

Beers, T. C.↗

NASA NTRS1982

Abell 2069 - An X-ray cluster of galaxies with multiple subcondensations

X-ray and optical observations of the cluster Abell 2069 are presented. The cluster is at a mean redshift of 0.116. The cluster shows multiple condensations in both the X-ray emission and in the galaxy surface density and, thus, does not appear to be relaxed. There is a close correspondence between the gas and galaxy distributions which indicates that the galaxies in this system do map the mass distribution, contrary to what might be expected if low-mass neutrinos dominate the cluster mass.

Gioia, I. M.↗

NASA NTRS1981

Study of the fluctuations in the cosmic X-ray background

The emerging picture indicates that neither the total cosmic X-ray background (CXB) flux nor the fluctuations are completely dominated by any single class of sources. Quasars clearly contribute a substantial fraction of the total flux while galaxy cluster X-ray sources and galactic nuclear activity also make nonnegligible contributions. It appears that from the large angular scale CXB galaxy correlations that no class of relatively low liminosity X-ray sources associated with galaxies can play a major role in supplying the total flux. The origin of the fluctuations looks more complex. It is hard to avoid the conclusion that the NGP-SGP difference and some other features of the CXB map are associated with the local anisotropy in the galactic distribution (the local supercluster). It also appears reasonable to some suppose that at least some large angular structures in the CXB are due to emission from hot galactic halo gs.

Turner, E. L.↗

NASA NTRS1980

The correlation of the cosmic X-ray background with the light of galaxies

Models for the origin of the cosmic X-ray background (CXB) radiation attribute it to numerous weak, unresolved discrete sources (e.g., active galactic nuclei), to some diffuse emission mechanism (e.g., thermal bremmstrahlung from a hot intergalactic plasma), or to an unresolved population of discrete sources which evolve substantially with redshift (e.g., quasars). It is shown that the comparison of the CXB flux variations with flux variations in the light from galaxies can measure the relative contribution of these possible sources of the CXB. Applying the technique to available Uhuru data, it is found that the absence of correlation between the optical flux variations and the X-ray flux variations sets an upper limit of approximately 50% on the fraction of the CXB originating with any classes of X-ray sources substantially represented among bright (apparent photographic magnitude less than or equal to 15.5) galaxies. The data are consistent with nearly all of the CXB being due to diffuse emission or to a class of sources whose density increases rapidly with redshift.

Turner, E. L.↗

NASA NTRS1978

X-ray observation of IC 4329 A

X-rays from the extreme type 1 Seyfert galaxy IC 4329 A have been observed with the rotating modulation collimator on board SAS 3. In addition to establishing IC 4329 A as an X-ray source, the SAS 3 data require that the source be extended, that there be at least one other nearby source, or both.

Delvaille, J. P.↗

NASA NTRS1978

Contribution of intermediate luminosity X-ray galaxies to the background - Anon 0945-30

Evidence that the galaxy A0945-30 is a new extragalactic X-ray source was found from an analysis of rotating modulation collimator quick-look data collected from the SAS 3 X-ray observatory. A strong piece of evidence was the hydrogen column density of 3 plus or minus 1 times 10 to the 22nd power per sq cm for a power law spectrum extending to about 35 keV inferred from HEAO 1 data. Observations indicate that the galaxy is an early type spiral with a bright nucleus. A faint star alongside the galaxy within the 90% confidence X-ray source error circle is an F dwarf with no indication of emission features. Spectra of the galaxy in the red and blue show sharp, intermediate strength emission lines of forbidden O III, forbidden N II, and H-alpha together with strong Mg, Fe, Ca absorption features characteristic of a normal stellar continuum in the galactic nucleus.

Schnopper, H. W.↗