279 research outputs found
Dumb-bell galaxies in southern clusters: Catalog and preliminary statistical results
The dominant galaxy of a rich cluster is often an object whose formation and evolution is closely connected to the dynamics of the cluster itself. Hoessel (1980) and Schneider et al. (1983) estimate that 50 percent of the dominant galaxies are either of the dumb-bell type or have companions at projected distances less than 20 kpc, which is far in excess of the number expected from chance projection (see also Rood and Leir 1979). Presently there is no complete sample of these objects, with the exception of the listing of dumb-bell galaxies in BM type I and I-II clusters in the Abell statistical sample of Rood and Leir (1979). Recent dynamical studies of dumb-bell galaxies in clusters (Valentijn and Casertano, 1988) still suffer from inhomogeneity of the sample. The fact that it is a mixture of optically and radio selected objects may have introduced an unknown biases, for instance if the probability of radio emission is enhanced by the presence of close companions (Stocke, 1978, Heckman et al. 1985, Vettolani and Gregorini 1988) a bias could be present in their velocity distribution. However, this situation is bound to improve: a new sample of Abell clusters in the Southern Hemisphere has been constructed (Abell et al., 1988 hereafter ACO), which has several advantages over the original northern catalog. The plate material (IIIaJ plates) is of better quality and reaches fainter magnitudes. This makes it possible to classify the cluster types with a higher degree of accuracy, as well as to fainter magnitudes. The authors therefore decided to reconsider the whole problem constructing a new sample of dumb-bell galaxies homogeneously selected from the ACO survey. Details of the classification criteria are given
An Atlas of H-alpha and R Images and Radial Profiles of 29 Bright Isolated Spiral Galaxies
Narrow-band H-alpha+[NII] and broadband R images and surface photometry are
presented for a sample of 29 bright (M_B < -18) isolated S0-Scd galaxies within
a distance of 48 Mpc. These galaxies are among the most isolated nearby spiral
galaxies of their Hubble classifications as determined from the Nearby Galaxies
Catalog (Tully 1987a).Comment: To appear in Astrophysical Journal Supplement Series. 17 pages,
including 8 atlas pages in JPEG format. Version with high resolution figures
available at http://www1.union.edu/~koopmanr/preprints.htm
Radio-optically selected clusters of galaxies. II. The cluster sample
We present a sample of 171 candidate groups and clusters of galaxies at
intermediate redshift over an area of ~550 square degrees at the South Galactic
Pole selected by using optically identified radio sources from the NRAO VLA Sky
Survey as tracers of dense environment. Out of these 171 candidates, 76 have a
counterpart in the literature while 95 of them are previously unknown clusters.
This paper presents the cluster selection technique, based on the search of
excesses in the optical surface density of galaxies near identified
radiogalaxies, and the first spectroscopic results aimed to confirm the
presence of a cluster. Spectroscopy for 11 candidates led to the detection of 9
clusters at redshift in the range 0.13 - 0.3, with estimated velocity
dispersions ranging from values typical of clusters to those of galaxy groups.
These results show that this technique represents a powerful tool for the
selection of homogeneous samples of intermediate redshift clusters over a wide
range of richness.Comment: 13 pages, 3 Postscript and 2 GIF figures. Accepted for publication in
A&
Caltech Faint Galaxy Redshift Survey VII: Data Analysis Techniques and Redshifts in the Field J0053+1234
We present the techniques used to determine redshifts and to characterize the
spectra of objects in the Caltech Faint Galaxy Redshift Survey in terms of
spectral classes and redshift quality classes. These are then applied to
spectra from an investigation of a complete sample of objects with mag
in a 2 by 7.3 arcmin^2 field at J005325+1234. Redshifts were successfully
obtained for 163 of the 195 objects in the sample; these redshifts lie in the
range [0.173, 1.44] and have a median of 0.58 (excluding 24 Galactic stars).
The sample includes two broad lined AGNs and one QSO.Comment: 20 pages, Latex, 3 figures, accepted for publication in the ApJ
Supplement
Observations of the nucleus of M100
The galaxy M100 = NGC 4321 is a spiral galaxy in which a bright Type II Supernova was discovered on April 19, 1979. Its spectral evolution was followed with IUE for more than two months (refs. 1,2). At all epochs, the spectrum was dominated by continuous radiation on which emission and absorption features were superimposed. The equivalent width of most of the absorption features appeared not to vary with time suggesting that they originated in the interstellar media of M100 and our own galaxy
- …