51 research outputs found
MC2: A Deeper Look at ZwCl 2341.1+0000 with Bayesian Galaxy Clustering and Weak Lensing Analyses
MC2: A Deeper Look at ZwCl 2341.1+0000 with Bayesian Galaxy Clustering and Weak Lensing Analyses
MC2: A Deeper Look at ZwCl 2341.1+0000 with Bayesian Galaxy Clustering and Weak Lensing Analyses
On the absence of radio halos in clusters with double relics
Pairs of radio relics are believed to form during cluster mergers, and are
best observed when the merger occurs in the plane of the sky. Mergers can also
produce radio halos, through complex processes likely linked to turbulent
re-acceleration of cosmic-ray electrons. However, only some clusters with
double relics also show a radio halo. Here, we present a novel method to derive
upper limits on the radio halo emission, and analyse archival X-ray Chandra
data, as well as galaxy velocity dispersions and lensing data, in order to
understand the key parameter that switches on radio halo emission. We place
upper limits on the halo power below the
correlation for some clusters, confirming that clusters with double relics have
different radio properties. Computing X-ray morphological indicators, we find
that clusters with double relics are associated with the most disturbed
clusters. We also investigate the role of different mass-ratios and
time-since-merger. Data do not indicate that the merger mass ratio has an
impact on the presence or absence of radio halos (the null hypothesis that the
clusters belong to the same group cannot be rejected). However, the data
suggests that the absence of radio halos could be associated with early and
late mergers, but the sample is too small to perform a statistical test. Our
study is limited by the small number of clusters with double relics. Future
surveys with LOFAR, ASKAP, MeerKat and SKA will provide larger samples to
better address this issue.Comment: 12 pages, 7 figures, MNRAS accepte
A powerful double radio relic system discovered in PSZ1 G108.18-11.53: Evidence for a shock with non-uniform Mach number?
Diffuse radio emission in the form of radio haloes and relics has been found in a number of merging galaxy clusters. These structures indicate that shock and turbulence associated with the merger accelerate electrons to relativistic energies. We report the discovery of a radio relic + radio halo system in PSZ1 G108.18-11.53 (z = 0.335). This cluster hosts the second most powerful double radio relic system ever discovered. We observed PSZ1 G108.18-11.53 with the Giant Meterwave Radio Telescope and the Westerbork Synthesis Radio Telescope. We obtained radio maps at 147, 323, 607 and 1380 MHz. We also observed the cluster with the Keck telescope, obtaining the spectroscopic redshift for 42 cluster members. From the injection index, we obtained the Mach number of the shocks generating the two radio relics. For the southern shock, we found M = 2.33-0.26+0.19, while the northern shock Mach number goes fromM= 2.20-0.14+0.07 in the north part down toM= 2.00-0.08+0.03 in the southern region. If the relation between the injection index and the Mach number predicted by diffusive shock acceleration theory holds, this is the first observational evidence for a gradient in the Mach number along a galaxy cluster merger shock
Primordial Black Hole Dark Matter Simulations Using PopSyCLE
Primordial black holes (PBHs), theorized to have originated in the early
universe, are speculated to be a viable form of dark matter. If they exist,
they should be detectable through photometric and astrometric signals resulting
from gravitational microlensing of stars in the Milky Way. Population Synthesis
for Compact-object Lensing Events, or PopSyCLE, is a simulation code that
enables users to simulate microlensing surveys, and is the first of its kind to
include both photometric and astrometric microlensing effects, which are
important for potential PBH detection and characterization. To estimate the
number of observable PBH microlensing events we modify PopSyCLE to include a
dark matter halo consisting of PBHs. We detail our PBH population model, and
demonstrate our PopSyCLE + PBH results through simulations of the OGLE-IV and
Roman microlensing surveys. We provide a proof-of-concept analysis for adding
PBHs into PopSyCLE, and thus include many simplifying assumptions, such as
, the fraction of dark matter composed of PBHs, and
, mean PBH mass. Assuming
, we find 3.65 times as many PBH microlensing
events than stellar evolved black hole events, a PBH average peak Einstein
crossing time of 91.4 days, estimate on order of PBH
events within the 8 year OGLE-IV results, and estimate Roman to detect on the
order of PBH microlensing events throughout its planned
microlensing survey
Radio observations of the double-relic galaxy cluster Abell 1240
We present LOFAR 120 − 168 MHz images of the merging galaxy cluster Abell 1240 that hosts double radio relics. In combination with the GMRT 595 − 629 MHz and VLA 2 − 4 GHz data, we characterised the spectral and polarimetric properties of the radio emission. The spectral indices for the relics steepen from their outer edges towards the cluster centre and the electric field vectors are approximately perpendicular to the major axes of the relics. The results are consistent with the picture that these relics trace large-scale shocks propagating outwards during the merger. Assuming diffusive shock acceleration (DSA), we obtain shock Mach numbers of M = 2.4 and 2.3 for the northern and southern shocks, respectively. For M ≲ 3 shocks, a pre-existing population of mildly relativistic electrons is required to explain the brightness of the relics due to the high (> 10 per cent) particle acceleration efficiency required. However, for M ≳ 4 shocks the required efficiency is ≳ 1% and ≳ 0.5%, respectively, which is low enough for shock acceleration directly from the thermal pool. We used the fractional polarization to constrain the viewing angle to ≥ 53 ± 3° and ≥ 39 ± 5° for the northern and southern shocks, respectively. We found no evidence for diffuse emission in the cluster central region. If the halo spans the entire region between the relics (∼1.8 Mpc) our upper limit on the power is P1.4 GHz = (1.4 ± 0.6) × 1023 W Hz−1 which is approximately equal to the anticipated flux from a cluster of this mass. However, if the halo is smaller than this, our constraints on the power imply that the halo is underluminous
Particle re-acceleration and Faraday-complex structures in the RXC\ua0J1314.4-2515 galaxy cluster
Radio relics are sites of electron (re)acceleration inmerging galaxy clusters but the mechanism of acceleration and the topology of the magnetic field in and near relics are yet to be understood. We are carrying out an observational campaign on double relic galaxy clusters starting with RXC J1314.4-2515. With Jansky Very Large Array multiconfiguration observations in the frequency range 1-4 GHz, we perform both spectral and polarization analyses, using the rotation measure (RM) synthesis technique. We use archival XMM-Newton observations to constrain the properties of the shocked region. We discover a possible connection between the activity of a radio galaxy and the emission of the eastern radio relic. In the northern elongated arc of the western radio relic, we detect polarized emission with an average polarization fraction of 31 % at 3 GHz and we derive the Mach number of the underlying X-ray shock. Our observations reveal low levels of fractional polarization and Faraday-complex structures in the southern region of the relic, which point to the presence of thermal gas and filamentary magnetic field morphology inside the radio emitting volume. We measured largely different RM dispersion from the two relics. Finally, we use cosmological magnetohydrodynamical simulations to constrain the magnetic field, viewing angle, and to derive the acceleration efficiency of the shock. We find that the polarization properties of RXC J1314.4-2515 are consistent with a radio relic observed at 70 degrees with respect to the line of sight and that the efficient re-acceleration of fossil electrons has taken place
Evidence for a merger induced shock wave in ZwCl\,0008.8+5215 with {\it Chandra} and {\it Suzaku}
We present the results from new deep {\it Chandra} (~ks) and {\it
Suzaku} ( ks) observations of the merging galaxy cluster
ZwCl\,0008.8+5215 (). Previous radio observations revealed the
presence of a double radio relic located diametrically west and east of the
cluster center. Using our new {\it Chandra} data, we find evidence for the
presence of a shock at the location of the western relic, RW, with a Mach
number from the density jump. We also
measure and
from the temperature jump, with {\it
Chandra} and {\it Suzaku} respectively. These values are consistent with the
Mach number estimate from a previous study of the radio spectral index, under
the assumption of diffusive shock acceleration (). Interestingly, the western radio relic does not
entirely trace the X-ray shock. A possible explanation is that the relic traces
fossil plasma from nearby radio galaxies which is re-accelerated at the shock.
For the eastern relic we do not detect an X-ray surface brightness
discontinuity, despite the fact that radio observations suggest a shock with
. The low surface brightness and
reduced integration time for this region might have prevented the detection.
{\it Chandra} surface brightness profile suggests ,
while {\it Suzaku} temperature measurements found
. Finally, we also detect a merger
induced cold front on the western side of the cluster, behind the shock that
traces the western relic.Comment: 21 pages, 15 figures, 4 tables; accepted for publication in Ap
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