235 research outputs found
Hubble Space Telescope survey of the Perseus Cluster -IV: Compact stellar systems in the Perseus Cluster core and Ultra Compact Dwarf formation in star forming filaments
We present the results of the first search for Ultra Compact Dwarfs (UCDs) in
the Perseus Cluster core, including the region of the cluster around the
unusual Brightest Cluster Galaxy (BCG) NGC 1275. Utilising Hubble Space
Telescope Advanced Camera for Surveys imaging, we identify a sample of 84 UCD
candidates with half-light radii 10 pc < r_e < 57 pc out to a distance of 250
kpc from the cluster centre, covering a total survey area of ~70 armin^2. All
UCDs in Perseus lie in the same size-luminosity locus seen for confirmed UCDs
in other regions of the local Universe. The majority of UCDs are brighter than
M_R = -10.5, and lie on an extrapolation of the red sequence followed by the
Perseus Cluster dwarf elliptical population to fainter magnitudes. However,
three UCD candidates in the vicinity of NGC 1275 are very blue, with colours
(B-R)_0 < 0.6 implying a cessation of star formation within the past 100 Myr.
Furthermore, large blue star clusters embedded in the star forming filaments
are highly indicative that both proto-globular clusters (GCs) and proto-UCDs
are actively forming at the present day in Perseus. We therefore suggest star
forming filaments as a formation site for some UCDs, with searches necessary in
other low redshift analogues of NGC 1275 necessary to test this hypothesis. We
also suggest that tidal disruption of dwarf galaxies is another formation
channel for UCD formation in the core of Perseus as tidal disruption is ongoing
in this region as evidenced by shells around NGC 1275. Finally, UCDs may simply
be massive GCs based on strong similarities in the colour trends of the two
populations.Comment: 18 pages, 20 figures, 3 tables. Accepted for publication in MNRA
The Baryonic Halos of Elliptical Galaxies: Radial Distribution of Globular Clusters and Diffuse Hot Gas
For a sample of 9 well-studied giant ellipticals we compare the projected
radial distribution of their red and blue globular cluster (GC) subpopulations
with their host galaxy stellar and X-ray surface brightness profiles. We
support previous findings that the surface density distribution of red
(metal-rich) GCs follows that of the host galaxy starlight. We find good
agreement between the outer slope of the blue GC surface density and that of
the galaxy X-ray emission. This coincidence of projected radial profiles is
likely due to the fact that both blue GCs and X-ray emitting hot gas share the
same gravitational potential in equilibrium. When deprojected the X-ray
emitting hot gas has a radial density dependence that is the square root of
that for the GC density. We further show that the energy per unit mass for blue
GCs is roughly half that of the hot gas.Comment: 11 pages, 5 figures, accepted for publication in MNRA
Analysis of sloppiness in model simulations: unveiling parameter uncertainty when mathematical models are fitted to data
This work introduces a Bayesian approach to assess the sensitivity of model
outputs to changes in parameter values, constrained by the combination of prior
beliefs and data. This novel approach identifies stiff parameter combinations
that strongly affect the quality of the model-data fit while simultaneously
revealing which of these key parameter combinations are informed primarily from
the data or are also substantively influenced by the priors. We focus on the
very common context in complex systems where the amount and quality of data are
low compared to the number of model parameters to be collectively estimated,
and showcase the benefits of our technique for applications in biochemistry,
ecology, and cardiac electrophysiology. We also show how stiff parameter
combinations, once identified, uncover controlling mechanisms underlying the
system being modeled and inform which of the model parameters need to be
prioritized in future experiments for improved parameter inference from
collective model-data fitting
Reheating and leptogenesis in a SUGRA inspired brane inflation
We have studied extensively phenomenological implications in a specific model
of brane inflation driven by background supergravity, via thermal history of
the universe and leptogenesis pertaining to the particle physics phenomenology
of the early universe. Using the one loop corrected inflationary potential we
have investigated for the analytical expression as well as the numerical
estimation for brane reheating temperature for standard model particles. This
results in some novel features of reheating from this type of inflation which
have serious implications in the production of heavy Majorana neutrinos needed
for leptogenesis through the reheating temperature. We have also derived the
expressions for the gravitino abundance during reheating and radiation
dominated era. We have further estimated different parameters at the epoch of
phase transition and revealed their salient features. At the end we have
explicitly given an estimate of the amount of CP violation through the
effective CP phase which is related to baryon asymmetry as well as gravitino
dark matter abundance.Comment: 9 pages, 4 figures, Accepted for publication in Nuclear Physics
The SLUGGS Survey: stellar kinematics, kinemetry and trends at large radii in 25 early-type galaxies
Due to longer dynamical time-scales, the outskirts of early-type galaxies retain the footprint of their formation and assembly. Under the popular two-phase galaxy formation scenario, an initial in situ phase of star formation is followed by minor merging and accretion of ex situ stars leading to the expectation of observable transitions in the kinematics and stellar populations on large scales. However, observing the faint galactic outskirts is challenging, often leaving the transition unexplored. The large-scale, spatially resolved stellar kinematic data from the SAGES Legacy Unifying Galaxies and GlobularS (SLUGGS) survey are ideal for detecting kinematic transitions. We present kinematic maps out to 2.6 effective radii on average, kinemetry profiles, measurement of kinematic twists and misalignments, and the average outer intrinsic shape of 25 SLUGGS galaxies. We find good overall agreement in the kinematic maps and kinemetry radial profiles with literature. We are able to confirm significant radial modulations in rotational versus pressure support of galaxies with radius so that the central and outer rotational properties may be quite different. We also test the suggestion that galaxies may be more triaxial in their outskirts and find that while fast rotating galaxies were already shown to be axisymmetric in their inner regions, we are unable to rule out triaxiality in their outskirts.We compare our derived outer kinematic information to model predictions from a two-phase galaxy formation scenario. We find that the theoretical range of local outer angular momentum agrees well with our observations, but that radial modulations are much smaller than predicted
Effects of antiplatelet therapy on stroke risk by brain imaging features of intracerebral haemorrhage and cerebral small vessel diseases: subgroup analyses of the RESTART randomised, open-label trial
Background
Findings from the RESTART trial suggest that starting antiplatelet therapy might reduce the risk of recurrent symptomatic intracerebral haemorrhage compared with avoiding antiplatelet therapy. Brain imaging features of intracerebral haemorrhage and cerebral small vessel diseases (such as cerebral microbleeds) are associated with greater risks of recurrent intracerebral haemorrhage. We did subgroup analyses of the RESTART trial to explore whether these brain imaging features modify the effects of antiplatelet therapy
Exploring PERMA in spectator sport: Applying positive psychology to examine the individual-level benefits of sport consumption
Sport spectating provides numerous benefits for sport organisations and individuals. In this paper we use a positive psychology approach to examine the individual-level benefits of sport consumption in order to investigate the activation of five domains of well-being: positive emotions, engagement, relationships, meaning, and accomplishment (PERMA). Using a two-study panel research design, we collected qualitative data from a sample of Australian Rules Football consumers. In the first study, we explored how the PERMA domains were activated during the season. Study two included a follow-up interview with eight initial respondents in the off-season. We found evidence of four PERMA domains that were activated in the sport spectator context by a variety of consumer experiences. The emergence of these domains in both studies suggests sport marketers would benefit from actions including: creating more social spaces within their stadiums, hosting regular off-season events, and creating social-media based competitions which promote fan engagement and interactions throughout the calendar year
- …