315 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
A scale-dependent cosmology for the inhomogeneous Universe
A scale-dependent cosmology is proposed in which the Robertson-Walker metric
and the Einstein equation are modified in such a way that , and
the age of the Universe all become scale-dependent. Its implications on the
observational cosmology are discussed.Comment: 7 pages, in RevTex. To be appeared in TAUP '9
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&
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
The ATESP 5 GHz radio survey. II. Physical properties of the faint radio population
One of the most debated issues about sub-mJy radio sources, which are
responsible for the steepening of the 1.4 GHz source counts, is the origin of
their radio emission. Particularly interesting is the possibility of combining
radio spectral index information with other observational properties to assess
whether the sources are triggered by star formation or nuclear activity. The
aim of this work is to study the optical and near infrared properties of a
complete sample of 131 radio sources with S>0.4 mJy, observed at both 1.4 and 5
GHz as part of the ATESP radio survey. We use deep multi-colour (UBVRIJK)
images, mostly taken in the framework of the ESO Deep Public Survey, to
optically identify and derive photometric redshifts for the ATESP radio
sources. Deep optical coverage and extensive colour information are available
for 3/4 of the region covered by the radio sample. Typical depths of the images
are U~25, B~26, V~25.4, R~25.5, I~24.3, 19.5<K_s<20.2, J<22.2. Optical/near
infrared counterparts are found for ~78% (66/85) of the radio sources in the
region covered by the deep multi-colour imaging, and for 56 of these reliable
estimates of the redshift and type are derived. We find that many of the
sources with flat radio spectra are characterised by high radio-to-optical
ratios (R>1000), typical of classical powerful radio galaxies and quasars.
Flat-spectrum sources with low R values are preferentially identified with
early type galaxies, where the radio emission is most probably triggered by
low-luminosity active galactic nuclei. Considering both early type galaxies and
quasars as sources with an active nucleus, such sources largely dominate our
sample (78%). Flat-spectrum sources associated with early type galaxies are
quite compact (d<10-30 kpc), suggesting core-dominated radio emission.Comment: 15 pages, 13 figures, accepted for pubblication 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
The ATESP Radio Survey II. The Source Catalogue
This paper is part of a series reporting the results of the Australia
Telescope ESO Slice Project (ATESP) radio survey obtained at 1400 MHz with the
Australia Telescope Compact Array (ATCA) over the region covered by the ESO
Slice Project (ESP) galaxy redshift survey. The survey consists of 16 radio
mosaics with ~8"x14" resolution and uniform sensitivity (1sigma noise level ~79
microJy) over the whole area of the ESP redshift survey (~26 sq. degrees at
decl. -40 degr). Here we present the catalogue derived from the ATESP survey.
We detected 2960 distinct radio sources down to a flux density limit of ~0.5
mJy (6sigma), 1402 being sub-mJy sources. We describe in detail the procedure
followed for the source extraction and parameterization. The internal accuracy
of the source parameters was tested with Monte Carlo simulations and possible
systematic effects (e.g. bandwidth smearing) have been quantified.Comment: 14 pages, 14 Postscript figures, Accepted for publication in A&A
Suppl. Corrected typos and added Journal Referenc
- …