MC2^2: 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 $\sim$1 Gyr apart. The primary merger gives rise to elongated X-ray morphology and a radio relic in the southeast. The brightest cluster galaxy is a member of the northern subcluster of the primary merger. This subcluster is very massive (16.7$^{+\text{1.25}}_{-\text{1.60}}\times\text{10}^{\text{14}}$ M$_{\odot}$). The southern subcluster is also very massive (10.8$^{+\text{3.37}}_{-\text{3.54}}\times\text{10}^{\text{14}}$ M$_{\odot}$), 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$^{+\text{0.19}}_{-\text{0.34}}\times\text{10}^{\text{14}}$ M$_{\odot}$). We perform a Monte Carlo dynamical analysis on the main merger and estimate a collision speed at pericenter of 2770$^{+\text{610}}_{-\text{310}}$ km s$^{-\text{1}}$. We show the merger to be returning from apocenter with core passage occurring 1.16$^{+\text{0.50}}_{-\text{0.25}}$ 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 $\sim$4000 km s$^{-\text{1}}$.Comment: 17 pages, 12 figure

MC2^2: 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$_{200}=\text{5.7}^{+\text{2.8}}_{-\text{1.8}}\times\text{10}^{\text{14}}\,\text{M}_{\odot}$ and 1.2$^{+\text{1.4}}_{-\text{0.6}}\times10^{14}$ M$_{\odot}$. We estimate the projected separation between the two subclusters to be 924$^{+\text{243}}_{-\text{206}}$ 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 92$\pm$164 km s$^{-\text{1}}$. We further motivate, discuss, and analyze the merger scenario through an analysis of the 42 ks of Chandra/ACIS-I and JVLA/C and D polarization data. The X-ray surface brightness profile reveals a remnant core reminiscent of the Bullet Cluster. The X-ray luminosity in the 0.5-7.0 keV band is 1.7$\pm$0.1$\times$10$^{\text{44}}$ erg s$^{-\text{1}}$ and the X-ray temperature is 4.90$\pm$0.13 keV. The radio relics are polarized up to 40$\%$. We implement a Monte Carlo dynamical analysis and estimate the merger velocity at pericenter to be 1800$^{+\text{400}}_{-\text{300}}$ km s$^{-\text{1}}$. 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

A rectangular waveguide cell for measurement of the shielding effectiveness of anisotropic materials

A method for measuring the shielding effectiveness of planar anisotropic materials using a rectangular waveguide cell is proposed. Computational models are used to verify the behaviour of the cell and validate its ability to measure shielding effectiveness. Results of measurements on a control sample and three carbon-fibre composite laminates in a GTEM cell are presented. A dynamic range of 70 dB with a capability to discriminate 20 dB of anisotropy is achieved in the frequency range 400-1600 MHz using cubic cells of side length 200 mm and 300 mm

Neutral hydrogen gas, past and future star-formation in galaxies in and around the 'Sausage' merging galaxy cluster

CIZA J2242.8+5301 ($z = 0.188$, nicknamed 'Sausage') is an extremely massive ($M_{200}\sim 2.0 \times 10^{15}M_\odot$ ), 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 $\sim0.75-1.0$ 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$\alpha$ 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

Genetic and phenotypic divergence in an island bird: isolation by distance, by colonization or by adaptation?

Discerning the relative roles of adaptive and nonadaptive processes in generating differences among populations and species, as well as how these processes interact, is a fundamental aim in biology. Both genetic and phenotypic divergence across populations can be the product of limited dispersal and gradual genetic drift across populations (isolation by distance), of colonization history and founder effects (isolation by colonization) or of adaptation to different environments preventing migration between populations (isolation by adaptation). Here, we attempt to differentiate between these processes using island populations of Berthelot's pipit (Anthus berthelotii), a passerine bird endemic to three Atlantic archipelagos. Using microsatellite markers and approximate Bayesian computation, we reveal that the northward colonization of this species ca. 8500years ago resulted in genetic bottlenecks in the colonized archipelagos. We then show that high levels of genetic structure exist across archipelagos and that these are consistent with a pattern of isolation by colonization, but not with isolation by distance or adaptation. Finally, we show that substantial morphological divergence also exists and that this is strongly concordant with patterns of genetic structure and bottleneck history, but not with environmental differences or geographic distance. Overall, our data suggest that founder effects are responsible for both genetic and phenotypic changes across archipelagos. Our findings provide a rare example of how founder effects can persist over evolutionary timescales and suggest that they may play an important role in the early stages of speciation

Quantification of Bronchial Circulation Perfusion in Rats

The bronchial circulation is thought to be the primary blood supply for pulmonary carcinomas. Thus, we have developed a method for imaging and quantifying changes in perfusion in the rat lung due to development of the bronchial circulation. A dual-modality micro-CT/SPECT system was used to detect change in perfusion in two groups of rats: controls and those with a surgically occluded left pulmonary artery. Both groups were imaged following injections on separate days i) 2mCi of Tc99m labeled macroaggregated albumin (MAA) into the left carotid artery (IA) and ii) a similar injection into the femoral vein (IV). The IA injection resulted in Tc99m accumulation in capillaries of the systemic circulation including the bronchial circulation, whereas the IV resulted in Tc99m accumulation in the pulmonary capillaries. Ordered subset expectation maximization (OSEM) was used to reconstruct the SPECT image volumes and a Feldkamp algorithm was used to reconstruct the micro-CT image volumes. The micro-CT and SPECT volumes were registered, the SPECT image volume was segmented using the right and left lung boundaries defined from the micro-CT volume, and the ratio of IA radioactivity accumulation in the left lung to IV radioactivity accumulation in both lungs was used as a measure of left lung flow via the bronchial circulation. This ratio was ~0.02 for the untreated rats compared to the treated animals that had an increased flow ratio of ~0.21 40 days after left pulmonary artery occlusion. This increase in flow to the occluded left lung via the bronchial circulation suggests this will be a useful model for further investigating antiangiogenic treatments

Quantification of Bronchial Circulation Perfusion in Rats

The bronchial circulation is thought to be the primary blood supply for pulmonary carcinomas. Thus, we have developed a method for imaging and quantifying changes in perfusion in the rat lung due to development of the bronchial circulation. A dual-modality micro-CT/SPECT system was used to detect change in perfusion in two groups of rats: controls and those with a surgically occluded left pulmonary artery. Both groups were imaged following injections on separate days i) 2mCi of Tc99m labeled macroaggregated albumin (MAA) into the left carotid artery (IA) and ii) a similar injection into the femoral vein (IV). The IA injection resulted in Tc99m accumulation in capillaries of the systemic circulation including the bronchial circulation, whereas the IV resulted in Tc99m accumulation in the pulmonary capillaries. Ordered subset expectation maximization (OSEM) was used to reconstruct the SPECT image volumes and a Feldkamp algorithm was used to reconstruct the micro-CT image volumes. The micro-CT and SPECT volumes were registered, the SPECT image volume was segmented using the right and left lung boundaries defined from the micro-CT volume, and the ratio of IA radioactivity accumulation in the left lung to IV radioactivity accumulation in both lungs was used as a measure of left lung flow via the bronchial circulation. This ratio was ~0.02 for the untreated rats compared to the treated animals that had an increased flow ratio of ~0.21 40 days after left pulmonary artery occlusion. This increase in flow to the occluded left lung via the bronchial circulation suggests this will be a useful model for further investigating antiangiogenic treatments

The rise and fall of star-formation in z∼0.2\bf z\sim0.2 merging galaxy clusters

CIZA J2242.8+5301 (`Sausage') and 1RXS J0603.3+4213 (`Toothbrush') are two low-redshift ($z\sim0.2$), massive ($\sim2\times10^{15}M_\odot$), 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 $201$ and $463$ line emitters, down to a rest-frame equivalent width ($13${\AA}). We robustly separate between H$\alpha$ and higher redshift emitters using a combination of optical multi-band (B, g, V, r, i, z) and spectroscopic data. We build H$\alpha$ 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, $1$ Gyr old `Sausage' cluster we find numerous ($59$) H$\alpha$ emitters above a star-formation rate (SFR) of $0.17$ M_{\sun} yr$^{-1}$ 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 $z\sim2$. Down to the same star-formation rate, the possibly dynamically more evolved `Toothbrush' cluster has only $9$ H$\alpha$ galaxies. The cluster H$\alpha$ galaxies fall on the SFR-stellar mass relation $z\sim0.2$ for the field. However, the `Sausage' cluster has an H$\alpha$ emitter density $>20$ 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 $100$ 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