84 research outputs found
MC: Multi-wavelength and dynamical analysis of the merging galaxy cluster ZwCl 0008.8+5215: An older and less massive Bullet Cluster
We analyze a rich dataset including Subaru/SuprimeCam, HST/ACS and WFC3,
Keck/DEIMOS, Chandra/ACIS-I, and JVLA/C and D array for the merging galaxy
cluster ZwCl 0008.8+5215. With a joint Subaru/HST weak gravitational lensing
analysis, we identify two dominant subclusters and estimate the masses to be
M
and 1.2 M. We estimate the
projected separation between the two subclusters to be
924 kpc. We perform a clustering analysis on
confirmed cluster member galaxies and estimate the line of sight velocity
difference between the two subclusters to be 92164 km s. We
further motivate, discuss, and analyze the merger scenario through an analysis
of the 42 ks of Chandra/ACIS-I and JVLA/C and D polarization data. The X-ray
surface brightness profile reveals a remnant core reminiscent of the Bullet
Cluster. The X-ray luminosity in the 0.5-7.0 keV band is
1.70.110 erg s and the X-ray
temperature is 4.900.13 keV. The radio relics are polarized up to 40.
We implement a Monte Carlo dynamical analysis and estimate the merger velocity
at pericenter to be 1800 km s. ZwCl
0008.8+5215 is a low-mass version of the Bullet Cluster and therefore may prove
useful in testing alternative models of dark matter. We do not find significant
offsets between dark matter and galaxies, as the uncertainties are large with
the current lensing data. Furthermore, in the east, the BCG is offset from
other luminous cluster galaxies, which poses a puzzle for defining dark matter
-- galaxy offsets.Comment: 22 pages, 19 figures, accepted for publication in the Astrophysical
Journal on March 13, 201
Neutral hydrogen gas, past and future star-formation in galaxies in and around the 'Sausage' merging galaxy cluster
CIZA J2242.8+5301 (, nicknamed 'Sausage') is an extremely massive
( ), merging cluster with shock waves
towards its outskirts, which was found to host numerous emission-line galaxies.
We performed extremely deep Westerbork Synthesis Radio Telescope HI
observations of the 'Sausage' cluster to investigate the effect of the merger
and the shocks on the gas reservoirs fuelling present and future star formation
(SF) in cluster members. By using spectral stacking, we find that the
emission-line galaxies in the 'Sausage' cluster have, on average, as much HI
gas as field galaxies (when accounting for the fact cluster galaxies are more
massive than the field galaxies), contrary to previous studies. Since the
cluster galaxies are more massive than the field spirals, they may have been
able to retain their gas during the cluster merger. The large HI reservoirs are
expected to be consumed within Gyr by the vigorous SF and AGN
activity and/or driven out by the out-flows we observe. We find that the
star-formation rate in a large fraction of H emission-line cluster
galaxies correlates well with the radio broad band emission, tracing supernova
remnant emission. This suggests that the cluster galaxies, all located in
post-shock regions, may have been undergoing sustained SFR for at least 100
Myr. This fully supports the interpretation proposed by Stroe et al. (2015) and
Sobral et al. (2015) that gas-rich cluster galaxies have been triggered to form
stars by the passage of the shock.Comment: Accepted to MNRAS, 14 pages, 9 figures, 7 table
MC: Dynamical Analysis of the Merging Galaxy Cluster MACS J1149.5+2223
We present an analysis of the merging cluster MACS J1149.5+2223 using
archival imaging from Subaru/Suprime-Cam and multi-object spectroscopy from
Keck/DEIMOS and Gemini/GMOS. We employ two and three dimensional substructure
tests and determine that MACS J1149.5+2223 is composed of two separate mergers
between three subclusters occurring 1 Gyr apart. The primary merger gives
rise to elongated X-ray morphology and a radio relic in the southeast. The
brightest cluster galaxy is a member of the northern subcluster of the primary
merger. This subcluster is very massive
(16.7 M).
The southern subcluster is also very massive
(10.8 M),
yet it lacks an associated X-ray surface brightness peak, and it has been
unidentified previously despite the detailed study of this \emph{Frontier
Field} cluster. A secondary merger is occurring in the north along the line of
sight with a third, less massive, subcluster
(1.20 M).
We perform a Monte Carlo dynamical analysis on the main merger and estimate a
collision speed at pericenter of 2770 km
s. We show the merger to be returning from apocenter with core
passage occurring 1.16 Gyr before the observed
state. We identify the line of sight merging subcluster in a strong lensing
analysis in the literature and show that it is likely bound to MACS J1149
despite having reached an extreme collision velocity of 4000 km
s.Comment: 17 pages, 12 figure
The role of cluster mergers and travelling shocks in shaping the H luminosity function at : `sausage' and `toothbrush' clusters
The most extreme cluster mergers can lead to massive cluster-wide travelling
shock waves. The CIZA J2242.8+5301 ('sausage') and 1RXS J0603.3+4213
(`toothbrush') clusters () host enormous radio-emitting shocks with
simple geometry. We investigate the role of mergers and shocks in shaping the
H luminosity function, using custom-made narrow-band filters matching
the cluster redshifts mounted on the INT. We surveyed deg for
each cluster and found line emitters in the `sausage' (volume of
Mpc for H at ) and in the
`toothbrush' ( Mpc for H at ), out of
which (`sausage') and (`toothbrush') are expected to be H. We
build luminosity functions for the field-of-view down to an average limiting
star formation rate of M yr, find good agreement with
field luminosity functions at , but significant differences between the
shapes of the luminosity functions for the two clusters. We discover extended,
tens-of-kpc-wide H haloes in galaxies neighbouring relics, which were
possibly disrupted by the passage of the shock wave. By comparing the `sausage'
cluster with blank fields and other clusters, we also uncover an order of
magnitude boost (at level) in the normalisation of the
luminosity function in the relic areas. Our results suggest that cluster
mergers may play an important role in the evolution of cluster galaxies through
shock-induced star formation.Comment: Accepted for publication in MNRAS, 14 pages, 9 figure
Surface brightness discontinuities in radio halos. Insights from the MeerKAT Galaxy Cluster Legacy Survey
Dynamical motions in the ICM can imprint distinctive features on the X-ray
images that map the thermal emission from clusters, such as sharp surface
brightness discontinuities due to shocks and cold fronts. The gas dynamics
during cluster mergers may also drive large-scale turbulence in the ICM which
in turn generates extended synchrontron sources known as radio halos. The
presence of surface brightness edges in the thermal gas of clusters has been
established by a number of X-ray observations. In contrast, edges in radio
halos have been observed only in a handful of cases. Our goal is to search for
new radio surface brightness discontinuities in the ICM. We inspected the
images of the Bullet Cluster and the other 25 radio halos reported in the
MeerKAT Galaxy Cluster Legacy Survey. To aid the identification of surface
brightness discontinuities, we applied a gradient filtering edge detection
method to the radio images. We found that the adopted filtering technique is
helpful to identify surface brightness edges in radio images, allowing us to
identify at least one gradient in half of the radio halos studied. For the
Bullet Cluster, we found excellent agreement between the locations of the 4
radio discontinuities detected and X-ray edges. This similarity informs us that
there is substantial interplay between thermal and non-thermal components in
galaxy clusters. This interplay is likely due to the forzen-in ICM magnetic
field which mediates the advection of cosmic rays while being dragged by
thermal gas flows. We conclude that radio halos are shaped by dynamical motions
in the ICM and that they often display surface brightness discontinuities
apparently co-located with edges in the thermal gas emission. Our results
demonstrate that new and future generations of radio telescopes will provide a
complementary approach to X-rays to efficiently detect shocks and cold fronts
in the ICM.Comment: 10 pages, 5 figures, 1 table (excluding Appendixes). Abstract
abridged to meet arXiv requirements. Submitted to A&
Merger-driven multi-scale ICM density perturbations: testing cosmological simulations and constraining plasma physics
The hot intracluster medium (ICM) provides a unique laboratory to test
multi-scale physics in numerical simulations and probe plasma physics.
Utilizing archival Chandra observations, we measure density fluctuations in the
ICM in a sample of 80 nearby (z<1) galaxy clusters and infer scale-dependent
velocities within regions affected by mergers (r<R2500c), excluding cool-cores.
Systematic uncertainties (e.g., substructures, cluster asymmetries) are
carefully explored to ensure robust measurements within the bulk ICM. We find
typical velocities ~220 (300) km/s in relaxed (unrelaxed) clusters, which
translate to non-thermal pressure fractions ~4 (8) per cent, and clumping
factors ~1.03 (1.06). We show that density fluctuation amplitudes could
distinguish relaxed from unrelaxed clusters in these regions. Comparison with
density fluctuations in cosmological simulations shows good agreement in
merging clusters. Simulations underpredict the amplitude of fluctuations in
relaxed clusters on length scales <0.75 R2500c, suggesting these systems are
most sensitive to missing physics in the simulations. In clusters hosting radio
halos, we examine correlations between gas velocities, turbulent dissipation
rate, and radio emission strength/efficiency to test turbulent re-acceleration
of cosmic ray electrons. We measure a weak correlation, driven by a few outlier
clusters, in contrast to some previous studies. Finally, we present upper
limits on effective viscosity in the bulk ICM of 16 clusters, showing it is
systematically suppressed by at least a factor of 8, and the suppression is a
general property of the ICM. Confirmation of our results with direct velocity
measurements will be possible soon with XRISM
The rise and fall of star-formation in merging galaxy clusters
CIZA J2242.8+5301 (`Sausage') and 1RXS J0603.3+4213 (`Toothbrush') are two
low-redshift (), massive (), post-core
passage merging clusters, which host shock waves traced by diffuse radio
emission. To study their star-formation properties, we uniformly survey the
`Sausage' and `Toothbrush' clusters in broad and narrow band filters and select
a sample of and line emitters, down to a rest-frame equivalent
width ({\AA}). We robustly separate between H and higher redshift
emitters using a combination of optical multi-band (B, g, V, r, i, z) and
spectroscopic data. We build H luminosity functions for the entire
cluster region, near the shock fronts, and away from the shock fronts and find
striking differences between the two clusters. In the dynamically younger,
Gyr old `Sausage' cluster we find numerous () H emitters above a
star-formation rate (SFR) of M_{\sun} yr surprisingly located
in close proximity to the shock fronts, embedded in very hot intra-cluster
medium plasma. The SFR density for the cluster population is at least at the
level of typical galaxies at . Down to the same star-formation rate,
the possibly dynamically more evolved `Toothbrush' cluster has only
H galaxies. The cluster H galaxies fall on the SFR-stellar mass
relation for the field. However, the `Sausage' cluster has an
H emitter density times that of blank fields. If the shock passes
through gas-rich cluster galaxies, the compressed gas could collapse into dense
clouds and excite star-formation for a few Myr. This process ultimately
leads to a rapid consumption of the molecular gas, accelerating the
transformation of gas-rich field spirals into cluster S0s or ellipticals.Comment: Accepted for publication in MNRAS after minor referee report. 21
pages, 15 figures, 5 table
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