9,966 research outputs found
Signatures of Galaxy-Cluster Interactions: Tully-Fisher Observations at z~0.1
We have obtained new optical imaging and spectroscopic observations of 78
galaxies in the fields of the rich clusters Abell 1413 (z = 0.14), Abell 2218
(z = 0.18) and Abell 2670 (z = 0.08). We have detected line emission from 25
cluster galaxies plus an additional six galaxies in the foreground and
background, a much lower success rate than what was found (65%) for a sample of
52 lower-richness Abell clusters in the range 0.02 < z < 0.08. We have combined
these data with our previous observations of Abell 2029 and Abell 2295 (both at
z = 0.08), which yields a sample of 156 galaxies. We evaluate several
parameters as a function of cluster environment: Tully-Fisher residuals,
H-alpha equivalent width, and rotation curve asymmetry, shape and extent.
Although H-alpha is more easily detectable in galaxies that are located further
from the cluster cores, we fail to detect a correlation between H-alpha extent
and galaxy location in those where it is detected, again in contrast with what
is found in the clusters of lesser richness. We fail to detect any
statistically significant trends for the other parameters in this study. The
zero-point in the z~0.1 Tully-Fisher relation is marginally fainter (by 1.5
sigma) than that found in nearby clusters, but the scatter is essentially
unchanged.Comment: 27 pages including 5 figures; accepted for publication in the
Astronomical Journa
The frequency and properties of young tidal dwarf galaxies in nearby gas-rich groups
We present high-resolution Giant Metrewave Radio Telescope (GMRT) HI
observations and deep Canada-France-Hawaii Telescope (CFHT) optical imaging of
two galaxy groups: NGC 4725/47 and NGC 3166/9. These data are part of a
multi-wavelength unbiased survey of the gas-rich dwarf galaxy populations in
three nearby interacting galaxy groups. The NGC 4725/47 group hosts two tidal
knots and one dIrr. Both tidal knots are located within a prominent HI tidal
tail, appear to have sufficient mass (M_gas~10^8 M_sol) to evolve into
long-lived tidal dwarf galaxies (TDGs) and are fairly young in age. The NGC
3166/9 group contains a TDG candidate, AGC 208457, at least three dIrrs and
four HI knots. Deep CFHT imaging confirms that the optical component of AGC
208457 is bluer -- with a 0.28 mag g-r colour -- and a few Gyr younger than its
purported parent galaxies. Combining the results for these groups with those
from the NGC 871/6/7 group reported earlier, we find that the HI properties,
estimated stellar ages and baryonic content of the gas-rich dwarfs clearly
distinguish tidal features from their classical counterparts. We optimistically
identify four potentially long-lived tidal objects associated to three separate
pairs of interacting galaxies, implying that TDGs are not readily produced
during interaction events as suggested by some recent simulations. The tidal
objects examined in this survey also appear to have a wider variety of
properties than TDGs of similar mass formed in current simulations of
interacting galaxies, which could be the result of pre- or post-formation
environmental influences.Comment: 18 pages, 14 figures, accepted for publication in MNRA
Recommended from our members
Ulcerative C2 neurocutaneous dysesthesia (trigeminal trophic syndrome in an alternative distribution)
Trigeminal trophic syndrome is an uncommon condition characterized by paresthesia, itch, and self-inflicted wounds following the trigeminal dermatome(s). Similar processes adhering to cervical nerve distributions have been reported, calling into question the specificity of trigeminal trophic syndrome for the trigeminal network. Herein, we report patient with trigeminal trophic syndrome adhering to the C2 dermatome, a previously unreported distribution
Approximation Algorithms for the Capacitated Domination Problem
We consider the {\em Capacitated Domination} problem, which models a
service-requirement assignment scenario and is also a generalization of the
well-known {\em Dominating Set} problem. In this problem, given a graph with
three parameters defined on each vertex, namely cost, capacity, and demand, we
want to find an assignment of demands to vertices of least cost such that the
demand of each vertex is satisfied subject to the capacity constraint of each
vertex providing the service. In terms of polynomial time approximations, we
present logarithmic approximation algorithms with respect to different demand
assignment models for this problem on general graphs, which also establishes
the corresponding approximation results to the well-known approximations of the
traditional {\em Dominating Set} problem. Together with our previous work, this
closes the problem of generally approximating the optimal solution. On the
other hand, from the perspective of parameterization, we prove that this
problem is {\it W[1]}-hard when parameterized by a structure of the graph
called treewidth. Based on this hardness result, we present exact
fixed-parameter tractable algorithms when parameterized by treewidth and
maximum capacity of the vertices. This algorithm is further extended to obtain
pseudo-polynomial time approximation schemes for planar graphs
- …