1,233 research outputs found
Multiscale Analysis of the Gradient of Linear Polarisation
We propose a new multiscale method to calculate the amplitude of the gradient
of the linear polarisation vector using a wavelet-based formalism. We
demonstrate this method using a field of the Canadian Galactic Plane Survey
(CGPS) and show that the filamentary structure typically seen in gradients of
linear polarisation maps depends strongly on the instrumental resolution. Our
analysis reveals that different networks of filaments are present on different
angular scales. The wavelet formalism allows us to calculate the power spectrum
of the fluctuations seen in gradients of linear polarisation maps and to
determine the scaling behaviour of this quantity. The power spectrum is found
to follow a power law with gamma ~ 2.1. We identify a small drop in power
between scales of 80 < l < 300 arcmin, which corresponds well to the overlap in
the u-v plane between the Effelsberg 100-m telescope and the DRAO 26-m
telescope data. We suggest that this drop is due to undersampling present in
the 26-m telescope data. In addition, the wavelet coefficient distributions
show higher skewness on smaller scales than at larger scales. The spatial
distribution of the outliers in the tails of these distributions creates a
coherent subset of filaments correlated across multiple scales, which trace the
sharpest changes in the polarisation vector P within the field. We suggest that
these structures may be associated with highly compressive shocks in the
medium. The power spectrum of the field excluding these outliers shows a
steeper power law with gamma ~ 2.5.Comment: 12 pages, 12 figure
Diffuse radio emission in MACS J0025.41222: the effect of a major merger on bulk separation of ICM components
Mergers of galaxy clusters are among the most energetic events in the
Universe. These events have significant impact on the intra-cluster medium,
depositing vast amounts of energy - often in the form of shocks - as well as
heavily influencing the properties of the constituent galaxy population. Many
clusters have been shown to host large-scale diffuse radio emission, known
variously as radio haloes and relics. These sources arise as a result of
electron (re-)acceleration in cluster-scale magnetic fields, although the
processes by which this occurs are still poorly understood. We present new,
deep radio observations of the high-redshift galaxy cluster MACS
J0025.41222, taken with the GMRT at 325 MHz, as well as new analysis of all
archival X-ray observations. We aim to investigate the potential of
diffuse radio emission and categorise the radio population of this cluster,
which has only been covered previously by shallow radio surveys. We produce
low-resolution maps of MACS J0025.41222 through a combination of uv-tapering
and subtracting the compact source population. Radial surface brightness and
mass profiles are derived from the data. We also derive a 2D map of
the ICM temperature. For the first time, two sources of diffuse radio emission
are detected in MACS J0025.41222, on linear scales of several hundred kpc.
Given the redshift of the cluster and the assumed cosmology, these sources
appear to be consistent with established trends in power scaling relations for
radio relics. The X-ray temperature map presents evidence of an asymmetric
temperature profile and tentative identification of a temperature jump
associated with one relic. We classify the pair of diffuse radio sources in
this cluster as a pair of radio relics, given their consistency with scaling
relations, location toward the cluster outskirts, and the available X-ray data.Comment: 20 pages, 15 figures, accepted for publication in A&
Pre service teachers’ development of pedagogic content knowledge: a multifaceted case study
One important aspect of research with regards to teacher’s knowledge is explaining in detail how student teachers develop their pedagogic content knowledge. Pedagogic content knowledge is multidimensional, such research needs to be able to represent a rich picture of how pre-service teachers develop this knowledge during a teacher education programme. Therefore, research into teachers’ pedagogic content knowledge requires not only multiple instruments for its exploration but also multi-method triangulation of data analysis. In this way not only are perspectives of pedagogic content knowledge explored but the practicality of focusing on and studying pedagogic content knowledge can also be estimated by corroborating the data to represent a rich picture of pedagogic content knowledge. Thus, this paper illustrates the so-called multifaceted case study that was conducted at a university Department of Educational Studies in England. Quantitative and qualitative data that resulted from the study were analysed and interpreted to measure whether the instruments and research design are adequate for constructing the judgment of the nature of pedagogic content knowledge among student teachers
Early Science with the Karoo Array Telescope: a Mini-Halo Candidate in Galaxy Cluster Abell 3667
Abell 3667 is among the most well-studied galaxy clusters in the Southern
Hemisphere. It is known to host two giant radio relics and a head-tail radio
galaxy as the brightest cluster galaxy. Recent work has suggested the
additional presence of a bridge of diffuse synchrotron emission connecting the
North-Western radio relic with the cluster centre. In this work, we present
full-polarization observations of Abell 3667 conducted with the Karoo Array
Telescope at 1.33 and 1.82 GHz. Our results show both radio relics as well as
the brightest cluster galaxy. We use ancillary higher-resolution data to
subtract the emission from this galaxy, revealing a localised excess, which we
tentatively identify as a radio mini-halo. This mini-halo candidate has an
integrated flux density of mJy beam at 1.37 GHz,
corresponding to a radio power of P
W Hz, consistent with established trends in mini-halo power scaling.Comment: 17 pages, 10 figures, accepted MNRA
An upper limit on the strength of the extragalactic magnetic field from ultra-high-energy cosmic-ray anisotropy
If ultra-high-energy cosmic rays originate from extragalactic sources, the
offsets of their arrival directions from these sources imply an upper limit on
the strength of the extragalactic magnetic field. The Pierre Auger
Collaboration has recently reported that anisotropy in the arrival directions
of cosmic rays is correlated with several types of extragalactic objects. If
these cosmic rays originate from these objects, they imply a limit on the
extragalactic magnetic field strength of B < 0.7-2.2 x 10^-9 (lambda_B / 1
Mpc)^-1/2 G for coherence lengths lambda_B < 100 Mpc and B < 0.7-2.2 x 10^-10 G
at larger scales. This is comparable to existing upper limits at lambda_B = 1
Mpc, and improves on them by a factor 4-12 at larger scales. The principal
source of uncertainty in our results is the unknown cosmic-ray composition.Comment: 9 pages, 3 figures, accepted by Ap
Investigating the source of Planck-detected AME: high resolution observations at 15 GHz
The Planck 28.5 GHz maps were searched for potential Anomalous Microwave
Emission (AME) regions on the scale of or smaller, and several
new regions of interest were selected. Ancillary data at both lower and higher
frequencies were used to construct spectral energy distributions (SEDs), which
seem to confirm an excess consistent with spinning dust models. Here we present
higher resolution observations of two of these new regions with the Arcminute
Microkelvin Imager Small Array (AMI SA) between 14 and 18 GHz to test for the
presence of a compact (10 arcmin or smaller) component. For
AME-G107.1+5.2, dominated by the {\sc Hii} region S140, we find evidence for
the characteristic rising spectrum associated with the either the spinning dust
mechanism for AME or an ultra/hyper-compact \textsc{Hii} region across the AMI
frequency band, however for AME-G173.6+2.8 we find no evidence for AME on
scales of arcmin.Comment: 13 pages, 8 figures, 4 tables. Submitted to Advances in Astronomy AME
Special Issu
To blame? The effects of moralized feedback on implicit racial bias
Implicit bias training (IBT) is now frequently provided by employers, in order to raise awareness of the problems related to implicit biases, and of how to safeguard against discrimination that may result. However, as Atewologun et al (2018) have noted, there is very little systematicity in IBT, and there are many unknowns about what constitutes good IBT. One important issue concerns the tone of information provided regarding implicit bias. This paper engages this question, focusing in particular on the observation that much bias training is delivered in exculpatory tone, emphasising that individuals are not to blame for possessing implicit biases. Normative guidance around IBT exhorts
practitioners to adopt this strategy (Moss-Racusin et al 2014). However, existing evidence about the effects of moralized feedback about implicit bias is equivocal (Legault et al 2011; Czopp et al 2006). Through a series of studies, culminating in an experiment with a pre-registered analysis plan, we develop a paradigm for evaluating the impact of moralized feedback on participants’ implicit racial bias scores. We also conducted exploratory analyses of the impact on their moods, and behavioural intentions. Our results indicated that an exculpatory tone, rather than a blaming or neutral tone, did not make participants less resistant to changing their attitudes and behaviours. In fact, participants in the blame condition had significantly stronger explicit intentions to change future behaviour than those in the ‘no feedback’ condition (see experiment 3). These results indicate that considerations of
efficacy do not support the need for implicit bias feedback to be exculpatory. We tease out the implications of these findings, and directions for future research
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