810 research outputs found
Internal kinematics of isolated modelled disk galaxies
We present a systematic investigation of rotation curves (RCs) of fully
hydrodynamically simulated galaxies, including cooling, star formation with
associated feedback and galactic winds. Applying two commonly used fitting
formulae to characterize the RCs, we investigate systematic effects on the
shape of RCs both by observational constraints and internal properties of the
galaxies. We mainly focus on effects that occur in measurements of intermediate
and high redshift galaxies. We find that RC parameters are affected by the
observational setup, like slit misalignment or the spatial resolution and also
depend on the evolution of a galaxy. Therefore, a direct comparison of
quantities derived from measured RCs with predictions of semi-analytic models
is difficult. The virial velocity V_c, which is usually calculated and used by
semi-analytic models can differ significantly from fit parameters like V_max or
V_opt inferred from RCs. We find that V_c is usually lower than typical
characteristic velocities derived from RCs. V_max alone is in general not a
robust estimator for the virial mass.Comment: 9 pages, 15 figures, accepted for publication in A&
Internal kinematics of modelled interacting disc galaxies
We present an investigation of galaxy-galaxy interactions and their effects
on the velocity fields of disc galaxies in combined N-body/hydrodynamic
simulations, which include cooling, star formation with feedback, and galactic
winds. Rotation curves (RCs) of the gas are extracted from these simulations in
a way that follows the procedure applied to observations of distant, small, and
faint galaxies as closely as possible. We show that galaxy-galaxy mergers and
fly-bys disturb the velocity fields significantly and hence the RCs of the
interacting galaxies, leading to asymmetries and distortions in the RCs.
Typical features of disturbed kinematics are significantly rising or falling
profiles in the direction of the companion galaxy and pronounced bumps in the
RCs. In addition, tidal tails can leave strong imprints on the rotation curve.
All these features are observable for intermediate redshift galaxies, on which
we focus our investigations. We use a quantitative measure for the asymmetry of
rotation curves to show that the appearance of these distortions strongly
depends on the viewing angle. We also find in this way that the velocity fields
settle back into relatively undisturbed equilibrium states after unequal mass
mergers and fly-bys. About 1 Gyr after the first encounter, the RCs show no
severe distortions anymore. These results are consistent with previous
theoretical and observational studies. As an illustration of our results, we
compare our simulated velocity fields and direct images with rotation curves
from VLT/FORS spectroscopy and ACS images of a cluster at z=0.53 and find
remarkable similarities.Comment: 13 pages, 14 figures, accepted for publication in A&A, some
improvements and changes, main conclusions are unaffecte
Optical Spectroscopy of IRAS 02091+6333
We present a detailed spectroscopic investigation, spanning four winters, of
the asymptotic giant branch (AGB) star IRAS 02091+6333. Zijlstra & Weinberger
(2002) found a giant wall of dust around this star and modelled this unique
phenomenon. However their work suffered from the quality of the optical
investigations of the central object. Our spectroscopic investigation allowed
us to define the spectral type and the interstellar foreground extinction more
precisely. Accurate multi band photometry was carried out. This provides us
with the possibility to derive the physical parameters of the system. The
measurements presented here suggest a weak irregular photometric variability of
the target, while there is no evidence of a spectroscopic variability over the
last four years.Comment: 5 pages, Latex, 3 tables, 4 figures, Astron. & Astrophys. - in pres
Internal kinematics of spiral galaxies in distant clusters III. Velocity fields from FORS2/MXU spectroscopy
(Abridged) We study the impact of cluster environment on the evolution of
spiral galaxies by examining their structure and kinematics. Rather than
two-dimensional rotation curves, we observe complete velocity fields by placing
three adjacent and parallel FORS2 MXU slits on each object, yielding several
emission and absorption lines. The gas velocity fields are reconstructed and
decomposed into circular rotation and irregular motions using kinemetry. To
quantify irregularities in the gas kinematics, we define three parameters:
sigma_{PA} (standard deviation of the kinematic position angle), Delta phi (the
average misalignment between kinematic and photometric position angles) and
k_{3,5} (squared sum of the higher order Fourier terms). Using local,
undistorted galaxies from SINGS, these can be used to establish the regularity
of the gas velocity fields. Here we present the analysis of 22 distant galaxies
in the MS0451.6-0305 field with 11 members at z=0.54. In this sample we find
both field (4 out of 8) and cluster (3 out of 4) galaxies with velocity fields
that are both irregular and asymmetric. We show that these fractions are
underestimates of the actual number of galaxies with irregular velocity fields.
The values of the (ir)regularity parameters for cluster galaxies are not very
different from those of the field galaxies, implying that there are isolated
field galaxies that are as distorted as the cluster members. None of the
deviations in our small sample correlate with photometric/structural properties
like luminosity or disk scale length in a significant way.
Our 3D-spectroscopic method successfully maps the velocity field of distant
galaxies, enabling the importance and efficiency of cluster specific
interactions to be assessed quantitatively.Comment: accepted for publication in A&A, high resolution version available at
http://www.astro.rug.nl/~kutdemir/papers
Ram pressure stripping of the multiphase ISM in the Virgo cluster spiral galaxy NGC 4438
Ram pressure stripping of the multiphase ISM is studied in the perturbed
Virgo cluster spiral galaxy NGC 4438. This galaxy underwent a tidal interaction
~100 Myr ago and is now strongly affected by ram pressure stripping. Deep VLA
radio continuum observations at 6 and 20 cm are presented. We detect prominent
extraplanar emission to the west of the galactic center, which extends twice as
far as the other tracers of extraplanar material. The spectral index of the
extraplanar emission does not steepen with increasing distance from the galaxy.
This implies in situ re-acceleration of relativistic electrons. The comparison
with multiwavelength observations shows that the magnetic field and the warm
ionized interstellar medium traced by Halpha emission are closely linked. The
kinematics of the northern extraplanar Halpha emission, which is ascribed to
star formation, follow those of the extraplanar CO emission. In the western and
southern extraplanar regions, the Halpha measured velocities are greater than
those of the CO lines. We suggest that the ionized gas of this region is
excited by ram pressure. The spatial and velocity offsets are consistent with a
scenario where the diffuse ionized gas is more efficiently pushed by ram
pressure stripping than the neutral gas. We suggest that the recently found
radio-deficient regions compared to 24 mum emission are due to this difference
in stripping efficiency.Comment: 8 pages, 6 figures, A&A, accepted for publicatio
Making space for experiences
Leisure and retail providers need to understand the elements of the visitor experience and the way in which they evaluate their satisfaction. This article suggests a holistic prism model of the interaction between the management and the visitor in a leisure space. This is applied to a netnographic study of visitors to a folk festival to illustrate the interconnectiveness of the different attributes causing dissatisfaction. It found that the physical and operational attributes were evaluated not through a checklist of individual features but as hindrances to the visitor's desire to make best use of the time. Visitors also evaluated the experience in the light of their own values and concerns, passing judgement on the values communicated by the management. At the heart of the experience was the enjoyment of choosing from an abundant offer and discovering something new. The main attraction is often only the pretext for enjoying the company of friends so places to meet before and chill-out afterwards are vital to the experience. The distinctiveness of the setting, the food and drink can become the sensory cues which give the event or location its uniqueness. The challenge to retail and leisure organisations is to design these elements of a memorable experience into their offerings
Political branding: sense of identity or identity crisis? An investigation of the transfer potential of the brand identity prism to the UK Conservative Party
Brands are strategic assets and key to achieving a competitive advantage. Brands can be seen as a heuristic device, encapsulating a series of values that enable the consumer to make quick and efficient choices. More recently, the notion of a political brand and the rhetoric of branding have been widely adopted by many political parties as they seek to differentiate themselves, and this has led to an emerging interest in the idea of the political brand. Therefore, this paper examines the UK Conservative Party brand under David Cameron’s leadership and examines the applicability of Kapferer’s brand identity prism to political branding. This paper extends and operationalises the brand identity prism into a ‘political brand identity network’ which identifies the inter-relatedness of the components of the corporate political brand and the candidate political brand. Crucial for practitioners, this model can demonstrate how the brand is presented and communicated to the electorate and serves as a useful mechanism to identify consistency within the corporate and candidate political brands
The moderating effect of brand orientation on inter-firm market orientation and performance
While prior research has shown that market and brand orientation
are key contributors to successful business performance, research to
date has not fully explored how inter firm collaboration for these two
key orientations can enhance business performance. The purpose of
the paper is to investigate the relationship between inter-firm market
and performance; to test for the moderating role of brand orientation
in that relationship. A total of 169 completed pairs of surveys were
collected of small and medium enterprises operating internationally
in a variety of industries in Switzerland. The results show that inter-firm
market and brand orientation are two antecedents of marketing and
financial performance. The impact of inter-firm market on marketing
and financial performance is significant when the brand orientation
is favorable. This study extends previous research by examining the
moderating role of brand orientation on inter firm market orientation,
which is important, especially for firms wanting to increase their brand
reputation by entering into partnerships with other firms. Further
research is indicated, to identify the key moderators of the driving
force of inter-firm market in relation to business performance and
the reason why maintaining a strong brand presence is important in
the international marketplace
4098 galaxy clusters to z~0.6 in the Sloan Digital Sky Survey equatorial Stripe 82
We present a catalogue of 4098 photometrically selected galaxy clusters with
a median redshift = 0.32 in the 270 square degree 'Stripe 82' region of the
Sloan Digital Sky Survey (SDSS), covering the celestial equator in the Southern
Galactic Cap (-50 < RA < 59 deg, |Dec| < 1.25 deg). Owing to the multi-epoch
SDSS coverage of this region, the ugriz photometry is ~2 magnitudes deeper than
single scans within the main SDSS footprint. We exploit this to detect clusters
of galaxies using an algorithm that searches for statistically significant
overdensities of galaxies in a Voronoi tessellation of the projected sky. 32%
of the clusters have at least one member with a spectroscopic redshift from
existing public data (SDSS Data Release 7, 2SLAQ & WiggleZ), and the remainder
have a robust photometric redshift (accurate to ~5-9% at the median redshift of
the sample). The weighted average of the member galaxies' redshifts provides a
reasonably accurate estimate of the cluster redshift. The cluster catalogue is
publicly available for exploitation by the community to pursue a range of
science objectives. In addition to the cluster catalogue, we provide a linked
catalogue of 18,295 V<21 mag quasar sight-lines with impact parameters within
<3 Mpc of the cluster cores selected from the catalogue of Veron et al. (2010).
The background quasars cover 0.25 < z < 2, where MgII absorption-line systems
associated with the clusters are detectable in optical spectra.Comment: 10 pages, 2 figures, accepted for publication in MNRAS. Catalogues
available at http://www.physics.mcgill.ca/~jimgeach/stripe8
Bayesian Exponential Random Graph Models with Nodal Random Effects
We extend the well-known and widely used Exponential Random Graph Model
(ERGM) by including nodal random effects to compensate for heterogeneity in the
nodes of a network. The Bayesian framework for ERGMs proposed by Caimo and
Friel (2011) yields the basis of our modelling algorithm. A central question in
network models is the question of model selection and following the Bayesian
paradigm we focus on estimating Bayes factors. To do so we develop an
approximate but feasible calculation of the Bayes factor which allows one to
pursue model selection. Two data examples and a small simulation study
illustrate our mixed model approach and the corresponding model selection.Comment: 23 pages, 9 figures, 3 table
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