1,368 research outputs found
A flat faint end of the Fornax cluster galaxy luminosity function
We analyse the photometric properties of the early-type Fornax cluster dwarf
galaxy population (M_V>-17 mag), based on a wide field imaging study of the
central cluster area in V and I band-passes with IMACS/Magellan at Las Campanas
Observatory. We create a fiducial sample of ~100 Fornax cluster dwarf
ellipticals (dEs) with -16.6<M_V<-8.8 mag in the following three steps: (1) To
verify cluster membership, we measured I-band surface brightness fluctuations
(SBF) distances to candidate dEs known from previous surveys; (2) We
re-assessed morphological classifications for those candidate dEs that are too
faint for SBF detection; and (3) We searched for new candidate dEs in the
size-luminosity regime close to the resolution limit of previous surveys. The
resulting fiducial dE sample follows a well-defined surface brightness -
magnitude relation, showing that Fornax dEs are about 40% larger than Local
Group dEs. The sample also defines a colour-magnitude relation similar to that
of Local Group dEs. The early-type dwarf galaxy luminosity function in Fornax
has a very flat faint end slope alpha = -1.1 +/- 0.1. We compare the number of
dwarfs per unit mass with those in other environments and find that the Fornax
cluster fits well into a general trend of a lack of high-mass dwarfs in more
massive environments.Comment: 5 pages, 4 figures, to appear in the proceedings of IAU Symposium 244
'Dark galaxies and lost baryons', Cambridge University Press, editors J. I.
Davies & M. D. Disne
Preventing extinction and outbreaks in chaotic populations
Interactions in ecological communities are inherently nonlinear and can lead
to complex population dynamics including irregular fluctuations induced by
chaos. Chaotic population dynamics can exhibit violent oscillations with
extremely small or large population abundances that might cause extinction and
recurrent outbreaks, respectively. We present a simple method that can guide
management efforts to prevent crashes, peaks, or any other undesirable state.
At the same time, the irregularity of the dynamics can be preserved when chaos
is desirable for the population. The control scheme is easy to implement
because it relies on time series information only. The method is illustrated by
two examples: control of crashes in the Ricker map and control of outbreaks in
a stage-structured model of the flour beetle Tribolium. It turns out to be
effective even with few available data and in the presence of noise, as is
typical for ecological settings.Comment: 10 pages, 6 figure
Intra Cluster Globular Clusters around NGC 1399 in Fornax?
We investigate whether the globular clusters (GCs) in the recently published
sample of GCs in the Fornax cluster by Bergond and coworkers are indeed
intra-cluster objects. We combine the catalogue of radial velocity measurements
by Bergond et al. with our CTIO MOSAIC photometry in the Washington system and
analyse the relation of metal-poor and metal-rich GCs with their host galaxies.
The metal-rich GCs appear to be kinematically associated with their respective
host galaxies. The vast majority of the metal-poor GCs found in between the
galaxies of the Fornax cluster have velocities which are consistent with them
being members of the very extended NGC 1399 GC system. We find that when the
sample is restricted to the most accurate velocity measurements, the GC
velocity dispersion profile can be described with a mass model derived for the
NGC 1399 GC system within 80 kpc. We identify one ``vagrant'' GC whose radial
velocity suggests that it is not bound to any galaxy unless its orbit has a
very large apogalactic distance.Comment: 4 pages, 4 figures, accepted for publication as a Letter in A&
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