8 research outputs found
NGC1600 - Cluster or Field Elliptical?
A study of the galaxy distribution in the field of the elliptical galaxy
NGC1600 has been undertaken. Although this galaxy is often classified as a
member of a loose group, all the neighbouring galaxies are much fainter and
could be taken as satellites of NGC1600. The number density profile of galaxies
in the field of this galaxy shows a decline with radius, with evidence of a
background at approximately 1.3 Mpc. The density and number density profile are
consistent with that found for other isolated early-type galaxies. NGC1600
appears as an extended source in X-rays, and the center of the X-ray emission
seems not to coincide with the center of the galaxy. The velocity distribution
of neighbouring galaxies has been measured from optical spectroscopic
observations and shows that the mean radial velocity is approximately 85 km/s
less than that of NGC1600, indicating that the centre of mass could lie outside
the galaxy. The velocity dispersion of the `group' is estimated at 429 km/s.
The inferred mass of the system is therefore of the order of 10^14 solar
masses, a value that corresponds to a large group. NGC1600 therefore shares
some similarities, but is not identical to, the `fossil clusters' detected in
X-ray surveys. Implications of this result for studies of isolated early-type
galaxies are briefly discussed.Comment: 8 pages, 5 figures and 2 table, accepted for publication in the Ap
Extensive spiral structure and corotation resonance
Spiral density wave theories demand that grand design spiral structure be
bounded, at most, between the inner and outer Lindblad resonances of the spiral
pattern. The corotation resonance lies between the outer and inner Lindblad
resonances. The locations of the resonances are at radii whose ratios to each
other are rather independent of the shape of the rotation curve. The measured
ratio of outer to inner extent of spiral structure for a given spiral galaxy
can be compared to the standard ratio of corotation to inner Lindblad resonance
radius. In the case that the measured ratio far exceeds the standard ratio, it
is likely that the corotation resonance is within the bright optical disk.
Studying such galaxies can teach us how the action of resonances sculpts the
appearance of spiral disks. This paper reports observations of 140 disk
galaxies, leading to resonance ratio tests for 109 qualified spirals. It lists
candidates that have a good chance of having the corotation resonance radius
within the bright optical disk.Comment: 29 pages, 7 figure files, AAS late
Observations of a nearby filament of galaxy clusters with the Sardinia Radio Telescope
We report the detection of diffuse radio emission which might be connected to
a large-scale filament of the cosmic web covering a 8deg x 8deg area in the
sky, likely associated with a z~0.1 over-density traced by nine massive galaxy
clusters. In this work, we present radio observations of this region taken with
the Sardinia Radio Telescope. Two of the clusters in the field host a powerful
radio halo sustained by violent ongoing mergers and provide direct proof of
intra-cluster magnetic fields. In order to investigate the presence of
large-scale diffuse radio synchrotron emission in and beyond the galaxy
clusters in this complex system, we combined the data taken at 1.4 GHz obtained
with the Sardinia Radio Telescope with higher resolution data taken with the
NRAO VLA Sky Survey. We found 28 candidate new sources with a size larger and
X-ray emission fainter than known diffuse large-scale synchrotron cluster
sources for a given radio power. This new population is potentially the tip of
the iceberg of a class of diffuse large-scale synchrotron sources associated
with the filaments of the cosmic web. In addition, we found in the field a
candidate new giant radio galaxy.Comment: 35 pages, 30 figures, MNRAS Accepted, A high-resolution version of
the paper can be found at the link
http://erg.oa-cagliari.inaf.it/preprints/paper_filament.pd