1,371 research outputs found
The "toothbrush-relic": evidence for a coherent linear 2-Mpc scale shock wave in a massive merging galaxy cluster?
Some merging galaxy clusters host diffuse extended radio emission, so-called
radio halos and relics. Here we present observations between 147 MHz and 4.9
GHz of a new radio-selected galaxy cluster 1RXS J0603.3+4214 (z=0.225). The
cluster is also detected as an extended X-ray source in the RASS. It hosts a
large bright 1.9 Mpc radio relic, an elongated ~2 Mpc radio halo, and two
smaller radio relics. The large radio relic has a peculiar linear morphology.
For this relic we observe a clear spectral index gradient, in the direction
towards the cluster center. We performed Rotation Measure (RM) Synthesis
between 1.2 and 1.7 GHz. The results suggest that for the west part of the
large relic some of the Faraday rotation is caused by ICM and is not only due
to galactic foregrounds. We also carried out a detailed spectral analysis of
this radio relic and created radio color-color diagrams. We find (i) an
injection spectral index of -0.6 to -0.7, (ii) steepening spectral index and
increasing spectral curvature in the post-shock region, and (iii) an overall
power-law spectrum between 74 MHz and 4.9 GHz with \alpha=-1.10 \pm 0.02.
Mixing of emission in the beam from regions with different spectral ages is
probably the dominant factor that determines the shape of the radio spectra.
Changes in the magnetic field, total electron content, or adiabatic
gains/losses do not play a major role. A model in which particles are
(re)accelerated in a first order Fermi process at the front of the relic
provides the best match to the observed spectra. We speculate that in the
post-shock region particles are re-accelerated by merger induced turbulence to
form the radio halo as the relic and halo are connected. The 1RXS J0603.3+4214
merger is probably more complex than the "simple'" binary merger events that
are thought to give rise to symmetric double radio relics.Comment: 22 pages, 22 figures, accepted for publication in A\&A on September
3, 201
Validation of vertical ground reaction forces on individual limbs calculated from kinematics of horse locomotion
The purpose of this study was to determine whether individual limb forces could be calculated accurately from kinematics of trotting and walking horses. We collected kinematic data and measured vertical ground reaction forces on the individual limbs of seven Warmblood dressage horses, trotting at 3.4 m
A low frequency sub-arcsecond view of powerful radio galaxies in rich-cluster environments: 3C 34 and 3C 320
Models of radio galaxy physics have been primarily based on high frequency
(1 GHz) observations of their jets, hotspots, and lobes. Without
highly resolved low frequency observations, which provide information on older
plasma, our understanding of the dynamics of radio galaxies and their
interaction with their environment is limited. Here, we present the first
sub-arcsecond (0.3") resolution images at 144 MHz of two powerful radio
galaxies situated in rich cluster environments, namely 3C 34 and 3C 320, using
the International Low Frequency Array Telescope. We detect for the first time
at low frequencies a plethora of structures in these objects, including
strikingly large filaments across the base of the lobes in both sources, which
are spatially associated with dense regions in the ambient medium. For 3C 34 we
report a spectral flattening in the region of the central filament, suggesting
that the origin of the filaments is related to the presence of large-scale
ordered magnetic fields. We also report periodic total intensity and spectral
index banding of diffuse emission in the eastern lobe, seen for the first time
in radio galaxy lobes. The hotspot complexes are resolved into multiple
fragments of varying structure and spectral index; we discuss the implications
for particle acceleration and jet termination models. We find at most smooth
gradients in the spectral behaviour of the hotspot structure suggesting that
particle acceleration, if present, may be occurring throughout the complex, in
contrast to simple models, but different jet termination models may apply to
both sources.Comment: 16 pages, 7 figures, 2 tables. Accepted for publication in Monthly
Notices of the Royal Astronomical Society, 2023 February 0
A LOFAR mini-survey for low-frequency radio emission from the nearest brown dwarfs
We have conducted a mini-survey for low-frequency radio emission from some of the closest brown dwarfs to the Sun with rapid rotation rates: SIMP J013656.5 +093347, WISEPC 150649.97+702736.0, and WISEPA J174124.26+255319.5.We have placed robust 3s upper limits on the flux density in the 111 – 169 MHz frequency range for these targets: WISE 1506: < 0:72 mJy; WISE 1741: < 0:87 mJy; SIMP 0136: < 0:66 mJy. At 8 hours of integration per target to achieve these limits, we find that systematic and detailed study of this class of object at LOFAR frequencies will require a substantial dedication of resources
LoTSS jellyfish galaxies: II. Ram pressure stripping in groups versus clusters
Numerous examples of ram pressure stripping in galaxy clusters are present in
literature; however, substantially less work has been focused on ram pressure
stripping in lower mass groups. In this work we use the LOFAR Two-metre Sky
Survey (LoTSS) to search for jellyfish galaxies in ~500 SDSS groups (z<0.05),
making this the most comprehensive search for ram pressure stripping in groups
to date. We identify 60 jellyfish galaxies in groups with extended, asymmetric
radio continuum tails, which are found across the entire range of group mass
from . We
compare the group jellyfish galaxies identified in this work with the LoTSS
jellyfish galaxies in clusters presented in Roberts et al. (2021), allowing us
to compare the effects of ram pressure stripping across three decades in
group/cluster mass. We find that jellyfish galaxies are most commonly found in
clusters, with the frequency decreasing towards the lowest mass groups. Both
the orientation of observed radio continuum tails, and the positions of group
jellyfish galaxies in phase space, suggest that galaxies are stripped more
slowly in groups relative to clusters. Finally, we find that the star formation
rates of jellyfish galaxies in groups are consistent with `normal' star-forming
group galaxies, which is in contrast to cluster jellyfish galaxies that have
clearly enhanced star formation rates. On the whole, there is clear evidence
for ongoing ram pressure stripping in galaxy groups (down to very low group
masses), though the frequency of jellyfish galaxies and the strength of ram
pressure stripping appears smaller in groups than clusters. Differences in the
efficiency of ram pressure stripping in groups versus clusters likely
contributes to the positive trend between quenched fraction and host halo mass
observed in the local Universe.Comment: 10 pages, 7 figures, 1 appendix, accepted for publication in A&
Deep VLA Observations of the Cluster 1RXS J0603.3+4214 in the Frequency Range of 1–2 GHz
We report L-band VLA observations of 1RXS J0603.3+4214, a cluster that hosts
a bright radio relic, known as the Toothbrush, and an elongated giant radio
halo. These new observations allow us to study the surface brightness
distribution down to one arcsec resolution with very high sensitivity. Our
images provide an unprecedented detailed view of the Toothbrush, revealing
enigmatic filamentary structures. To study the spectral index distribution, we
complement our analysis with published LOFAR and GMRT observations. The bright
`brush' of the Toothbrush shows a prominent narrow ridge to its north with a
sharp outer edge. The spectral index at the ridge is in the range
. We suggest that the ridge is caused by projection
along the line of sight. With a simple toy model for the smallest region of the
ridge, we conclude that the magnetic field is below and varies
significantly across the shock front. Our model indicates that the actual Mach
number is higher than that obtained from the injection index and agrees well
with the one derived from the overall spectrum, namely . The radio halo shows an average spectral index of
and a slight gradient from north to south. The
southernmost part of the halo is steeper and possibly related to a shock front.
Excluding the southernmost part, the halo morphology agrees very well with the
X-ray morphology. A power-law correlation is found between the radio and X-ray
surface brightnessComment: 23 pages, 21 figures, accepted for publication in Ap
Measuring cavity powers of active galactic nuclei in clusters using a hybrid X-ray–radio method. A new window on feedback opened by subarcsecond LOFAR-VLBI observations
Measurements of the quantity of radio-mode feedback injected by an active galactic nucleus into the cluster environment have mostly
relied on X-ray observations, which reveal cavities in the intracluster medium excavated by the radio lobes. However, the sensitivity
required to accurately constrain the dimensions of these cavities has proven to be a major limiting factor and is the main bottleneck
on high-redshift measurements. We describe a hybrid method based on a combination of X-ray and radio observations, which aims to
enhance our ability to study radio-mode feedback. In this paper, we present one of the first samples of galaxy clusters observed with
the International LOFAR Telescope (ILT) at 144 MHz and use this sample to test the hybrid method at lower frequencies than before.
By comparing our measurements with results found in literature based on the traditional method using only X-ray observations, we
find that the hybrid method provides consistent results to the traditional method. In addition, we find that the correlation between the
traditional method and the hybrid method improves as the X-ray cavities are more clearly defined. This suggests that using radio lobes
as proxies for cavities may help to circumvent systematic uncertainties in the cavity volume measurements. Encouraged by the high
volume of unique ILT observations successfully processed, this hybrid method enables radio-mode feedback to be studied at high
redshifts for the first time even for large samples of clusters
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