329 research outputs found
Strong Lensing Analysis of the Powerful Lensing Cluster MACS J2135.2-0102 (=0.33)
We present a light-traces-mass (LTM) strong-lensing model of the massive
lensing cluster MACS J2135.2-0102 (=0.33; hereafter MACS2135), known in part
for hosting the Cosmic Eye galaxy lens. MACS2135 is also known to multiply-lens
a 2.3 sub-mm galaxy near the Brightest Cluster Galaxy (BCG), as well as a
prominent, triply-imaged system at a large radius of 37" south of the
BCG. We use the latest available Hubble imaging to construct an accurate
lensing model for this cluster, identifying six new multiply-imaged systems
with the guidance of our LTM method, so that we have roughly quadrupled the
number of lensing constraints. We determine that MACS2135 is amongst the top
lensing clusters known, comparable in size to the Hubble Frontier Fields. For a
source at , we find an effective Einstein radius of
", enclosing . We
make our lens model, including mass and magnification maps, publicly available,
in anticipation of searches for high- galaxies with the James Webb Space
Telescope for which this cluster is a compelling target.Comment: 7 pages, 2 figures (3 subfigures in total), 1 table; Published in
ApJ; V2: accepted versio
Shocks and Tides Quantified in the "Sausage" Cluster, CIZA J2242.8+5301, using N-body/hydro-dynamical Simulations
The colliding cluster, CIZA J2242.8+5301, displays a spectacular, almost 2
Mpc long shock front with a radio based Mach number M ~ 5, that is puzzlingly
large compared with the X-ray estimate of M ~ 2.5. The extent to which the
X-ray temperature jump is diluted by cooler unshocked gas projected through the
cluster currently lacks quantification. Thus, here we apply our self-consistent
N-body/hydro-dynamical code (based on FLASH) to model this binary cluster
encounter. We can account for the location of the shock front and also the
elongated X-ray emission by tidal stretching of the gas and dark matter between
the two cluster centers. The required total mass is Msun
with a 1.3:1 mass ratio favoring the southern cluster component. The relative
velocity we derive is km/s initially between the two main cluster
components, with an impact parameter of 120 kpc. This solution implies that the
shock temperature jump derived from the low angular resolution X-ray satellite
SUZAKU is underestimated by a factor of two, due to cool gas in projection,
bringing the observed X-ray and radio estimates into agreement. We propose that
the complex southern relics in CIZA J2242.8+5301, have been broken up as the
southerly moving "back" shocked gas impacts the gas still falling in along the
collision axis. Finally, we use our model to generate Compton-y maps to
estimate the reduction in radio flux caused by the thermal Sunyaev-Zel'dovich
(SZ) effect. At 30 GHz, this amounts to mJy/arcmin
and mJy/arcmin at the locations of the northern and
southern shock fronts respectively. Our model estimate agrees with previous
empirical estimates that have inferred the measured radio spectra can be
significantly affected by the SZ effect, with implications for charged particle
acceleration models of the radio relics.Comment: 8 pages, 7 figures and 1 table, submitted to the Astrophysical
Journal for publication on March
Multi-Phenomena Modeling of the New Bullet Cluster, ZwCl008.8+52, using N-body/hydrodynamical Simulations
We use hydrodynamical/N-body simulations to interpret the newly discovered
Bullet-cluster-like merging cluster, ZwCl 0008.8+5215 (ZwCl 0008 hereafter),
where a dramatic collision is apparent from multi-wavelength observations. We
have been able to find a self-consistent solution for the radio, X-ray, and
lensing phenomena by projecting an off-axis, binary cluster encounter viewed
just after first core passage. A pair radio relics traces well the leading and
trailing shock fronts that our simulation predict, providing constraints on the
collision parameters. We can also account for the observed distinctive
comet-like X-ray morphology and the positions of the X-ray peaks relative to
the two lensing mass centroids and the two shock front locations. Relative to
the Bullet cluster, the total mass is about 70% lower, ( Msun, with a correspondingly lower infall velocity, km/s,
and an impact parameter of kpc. As a result, the gas component of
the infalling cluster is not trailing significantly behind the associated dark
matter as in the case of the Bullet cluster. The degree of agreement we find
between all the observables provides strong evidence that dark matter is
effectively collisionless on large scales calling into question other claims
and theories that advocate modified gravity.Comment: 9 pages, 3 figures, and 1 table, submitted to the Astrophysical
Journal for publicationon on December 18. Coments are welcom
A Hydrodynamical Solution for the "Twin-Tailed" Colliding Galaxy Cluster "El Gordo"
The distinctive cometary X-ray morphology of the recently discovered massive
galaxy cluster "El Gordo" (ACT-CT J0102-4915; z=0.87) indicates that an
unusually high-speed collision is ongoing between two massive galaxy clusters.
A bright X-ray "bullet" leads a "twin-tailed" wake, with the SZ centroid at the
end of the Northern tail. We show how the physical properties of this system
can be determined using our FLASH-based, N-body/hydrodynamic model, constrained
by detailed X-ray, Sunyaev-Zel'dovich (SZ), and Hubble lensing and dynamical
data. The X-ray morphology and the location of the two Dark Matter components
and the SZ peak are accurately described by a simple binary collision viewed
about 480 million years after the first core passage. We derive an impact
parameter of ~300 kpc, and a relative initial infall velocity of ~2250 km/sec
when separated by the sum of the two virial radii assuming an initial total
mass of 2.15x10^(15) Msun and a mass ratio of 1.9. Our model demonstrates that
tidally stretched gas accounts for the Northern X-ray tail along the collision
axis between the mass peaks, and that the Southern tail lies off axis,
comprising compressed and shock heated gas generated as the massive component
plunges through the main cluster. The challenge for LCDM will be to find out if
this physically extreme event can be plausibly accommodated when combined with
the similarly massive, high infall velocity case of the "Bullet cluster" and
other such cases being uncovered in the new SZ based surveys.Comment: 9 pages, 5 Figures and 1 Table, accepted for publication in the
Astrophysical Journa
Mass Distributions of Clusters Using Gravitational Magnification
Lensing in the context of rich clusters is normally quantified from small
image distortions, yielding a relative mass distribution in the limit of weak
lensing. Here we show the magnification effect of lensing can also be mapped
over a cluster, resulting in absolute mass determinations for the weak limit.
Furthermore, given both magnification and distortion measurements, the mass
distribution may be constrained in the strong regime. Methods for obtaining the
magnification using spectroscopic and/or photometric information are discussed,
for object detection within a fixed isophote or to a given flux limit.
A map of the magnification around A1689 is constructed from the observed
depletion of background red galaxy counts.Comment: 10 pages uuencoded, compressed, figures included. Invited Review,
proc of 5th Maryland Dark Matter Oct. 9
Cloning Dropouts: Implications for Galaxy Evolution at High Redshift
The evolution of high redshift galaxies in the two Hubble Deep Fields, HDF-N
and HDF-S, is investigated using a cloning technique that replicates z~ 2-3 U
dropouts to higher redshifts, allowing a comparison with the observed B and V
dropouts at higher redshifts (z ~ 4-5). We treat each galaxy selected for
replication as a set of pixels that are k-corrected to higher redshift,
accounting for resampling, shot-noise, surface-brightness dimming, and the
cosmological model. We find evidence for size evolution (a 1.7x increase) from
z ~ 5 to z ~ 2.7 for flat geometries (Omega_M+Omega_LAMBDA=1.0). Simple scaling
laws for this cosmology predict that size evolution goes as (1+z)^{-1},
consistent with our result. The UV luminosity density shows a similar increase
(1.85x) from z ~ 5 to z ~ 2.7, with minimal evolution in the distribution of
intrinsic colors for the dropout population. In general, these results indicate
less evolution than was previously reported, and therefore a higher luminosity
density at z ~ 4-5 (~ 50% higher) than other estimates. We argue the present
technique is the preferred way to understand evolution across samples with
differing selection functions, the most relevant differences here being the
color cuts and surface brightness thresholds (e.g., due to the (1+z)^4 cosmic
surface brightness dimming effect).Comment: 56 pages, 22 figures, accepted for publication in Ap
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