30 research outputs found
Brightest Cluster Galaxy Alignments in Merging Clusters
The orientations of brightest cluster galaxies (BCGs) and their host clusters
tend to be aligned, but the mechanism driving this is not clear. To probe the
role of cluster mergers in this process, we quantify alignments of 38 BCGs in
22 clusters undergoing major mergers (up to Gyr after first
pericenter). We find alignments entirely consistent with those of clusters in
general. This suggests that alignments are robust against major cluster
mergers. If, conversely, major cluster mergers actually help orient the BCG,
such a process is acting quickly because the orientation is in place within
Gyr after first pericenter.Comment: accepted to Ap
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
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
Distribution of H-alpha Emitters in Merging Galaxy Clusters
Studies of star formation in various galaxy cluster mergers have reached
apparently contradictory conclusions regarding whether mergers stimulate star
formation, quench it, or have no effect. Because the mergers studied span a
range of time since pericenter (TSP), it is possible that the apparent effect
on star formation is a function of TSP. We use a sample of 12 bimodal mergers
to assess the star formation as a function of TSP. We measure the equivalent
width of the H-alpha emission line in member galaxies in each
merger, classify galaxies as emitters or non-emitters, and then classify
emitters as star-forming galaxies (SFG) or active galactic nucleus (AGN) based
on the [NII] line. We quantify the distribution of SFG and AGN
relative to non-emitters along the spatial axis defined by the subcluster
separation. The SFG and AGN fractions vary from merger to merger, but show no
trend with TSP. The spatial distribution of SFG is consistent with that of
non-emitters in eight mergers, but show significant avoidance of the system
center in the remaining four mergers, including the three with the lowest TSP.
If there is a connection between star formation activity and TSP, probing it
further will require more precise TSP estimates and more mergers with TSP in
the range of 0-400 Myr.Comment: accepted to A
MC: Subaru and Hubble Space Telescope Weak-Lensing Analysis of the Double Radio Relic Galaxy Cluster PLCK G287.0+32.9
The second most significant detection of the Planck Sunyaev Zel'dovich
survey, PLCK~G287.0+32.9 () boasts two similarly bright radio relics
and a radio halo. One radio relic is located kpc northwest of the
X-ray peak and the other Mpc to the southeast. This large difference
suggests that a complex merging scenario is required. A key missing puzzle for
the merging scenario reconstruction is the underlying dark matter distribution
in high resolution. We present a joint Subaru Telescope and {\it Hubble Space
Telescope} weak-lensing analysis of the cluster. Our analysis shows that the
mass distribution features four significant substructures. Of the
substructures, a primary cluster of mass
$M_{200\text{c}}=1.59^{+0.25}_{-0.22}\times 10^{15} \ h^{-1}_{70} \
\text{M}_{\odot}M_{200\text{c}}=1.16^{+0.15}_{-0.13}\times 10^{14} \ h^{-1}_{70} \
\text{M}_{\odot}\sim 400\sim 2M_{200\text{c}}=1.68^{+0.22}_{-0.20}\times
10^{14} \ h^{-1}_{70} \ \text{M}_{\odot}M_{200\text{c}}=1.87^{+0.24}_{-0.22}\times 10^{14} \ h^{-1}_{70} \
\text{M}_{\odot}$, is northwest of the X-ray peak and beyond the NW radio
relic.Comment: 19 pages, 14 figures; Accepted to Ap
Multi-wavelength Analysis of the Merging Galaxy Cluster A115
A115 is a merging galaxy cluster at with a number of remarkable
features including a giant ( Mpc) radio relic, two asymmetric X-ray
peaks with trailing tails, and a peculiar line-of-sight velocity structure. We
present a multi-wavelength study of A115 using optical imaging data from
Subaru, X-ray data from , and spectroscopic data from the Keck/DEIMOS
and MMT/Hectospec instruments. Our weak-lensing analysis shows that the cluster
is comprised of two subclusters whose mass centroids are in excellent agreement
with the two BCG positions ("). By modeling A115 with a
superposition of two Navarro-Frenk-White halos, we determine the masses of the
northern and southern subclusters to be and , respectively. Combining the two halos, we estimate the total
cluster mass to be
at Mpc. These weak-lensing masses are
significantly (a factor of 3-10) lower than what is implied by the X-ray and
optical spectroscopic data. We attribute the difference to the gravitational
and hydrodynamic disruption caused by the collision between the two
subclusters.Comment: 20 pages, 17 figures, Accepted for publication in Ap
Gravitational Microlensing Event Statistics for the Zwicky Transient Facility
Microlensing surveys have discovered thousands of events with almost all
events discovered within the Galactic bulge or toward the Magellanic clouds.
The Zwicky Transient Facility (ZTF), while not designed to be a microlensing
campaign, is an optical time-domain survey that observes the entire northern
sky every few nights including the Galactic plane. ZTF observes
stars in g-band and r-band and can significantly contribute to the observed
microlensing population. We predict that ZTF will observe 1100
microlensing events in three years of observing within degrees
latitude of the Galactic plane, with 500 events in the outer Galaxy
(). This yield increases to 1400 (800) events
by combining every three ZTF exposures, 1800 (900) events if ZTF
observes for a total of five years, and 2400 (1300) events for a
five year survey with post-processing image stacking. Using the microlensing
modeling software PopSyCLE, we compare the microlensing populations in the
Galactic bulge and the outer Galaxy. We also present an analysis of the
microlensing event ZTF18abhxjmj to demonstrate how to leverage these population
statistics in event modeling. ZTF will constrain Galactic structure, stellar
populations, and primordial black holes through photometric microlensing.Comment: 19 pages, 13 figures, 5 tables, accepted to ApJ (6/4/2020),
microlensing simulation catalogs available at
https://portal.nersc.gov/project/uLens/Galactic_Microlensing_Distribution