The return of the merging galaxy subclusters of El Gordo?

Merging galaxy clusters with radio relics provide rare insights to the merger dynamics as the relics are created by the violent merger process. We demonstrate one of the first uses of the properties of the radio relic to reduce the uncertainties of the dynamical variables and determine the 3D configuration of a cluster merger, ACT-CL J0102-4915, nicknamed El Gordo. From the double radio relic observation and the X-ray observation of a comet-like gas morphology induced by motion of the cool core, it is widely believed that El Gordo is observed shortly after the first core-passage of the subclusters. We employ a Monte Carlo simulation to investigate the three-dimensional (3D) configuration and dynamics of El Gordo. Using the polarization fraction of the radio relic, we constrain the estimate of the angle between the plane of the sky and the merger axis to be $\alpha = 21~{\rm degree} \pm^9_{11}$. We find the relative 3D merger speed of El Gordo to be $2400\pm^{400}_{200}~{\rm km}~{\rm s}^{-1}$ at pericenter. The two possible estimates of the time-since-pericenter are $0.46\pm^{0.09}_{0.16}$ Gyr and $0.91\pm^{0.22}_{0.39}$ Gyr for the outgoing and returning scenario respectively. We put our estimates of the time-since-pericenter into context by showing that if the time-averaged shock velocity is approximately equal to or smaller than the pericenter velocity of the corresponding subcluster in the center of mass frame, the two subclusters are more likely to be moving towards, rather than away, from each other, post apocenter. We compare and contrast the merger scenario of El Gordo with that of the Bullet Cluster, and show that this late-stage merging scenario explains why the southeast dark matter lensing peak of El Gordo is closer to the merger center than the southeast cool core.Comment: Figure 1 explains the configuration of the different components of El Gordo. Figure 9 explains the merger scenario. 20 pages, 23 figures. Accepted by MNRA

Spurious Shear in Weak Lensing with LSST

The complete 10-year survey from the Large Synoptic Survey Telescope (LSST) will image $\sim$ 20,000 square degrees of sky in six filter bands every few nights, bringing the final survey depth to $r\sim27.5$, with over 4 billion well measured galaxies. To take full advantage of this unprecedented statistical power, the systematic errors associated with weak lensing measurements need to be controlled to a level similar to the statistical errors. This work is the first attempt to quantitatively estimate the absolute level and statistical properties of the systematic errors on weak lensing shear measurements due to the most important physical effects in the LSST system via high fidelity ray-tracing simulations. We identify and isolate the different sources of algorithm-independent, \textit{additive} systematic errors on shear measurements for LSST and predict their impact on the final cosmic shear measurements using conventional weak lensing analysis techniques. We find that the main source of the errors comes from an inability to adequately characterise the atmospheric point spread function (PSF) due to its high frequency spatial variation on angular scales smaller than $\sim10'$ in the single short exposures, which propagates into a spurious shear correlation function at the $10^{-4}$--$10^{-3}$ level on these scales. With the large multi-epoch dataset that will be acquired by LSST, the stochastic errors average out, bringing the final spurious shear correlation function to a level very close to the statistical errors. Our results imply that the cosmological constraints from LSST will not be severely limited by these algorithm-independent, additive systematic effects.Comment: 22 pages, 12 figures, accepted by MNRA

MC2:galaxy imaging and redshift analysis of the merging cluster CIZA J2242.8+5301

X-ray and radio observations of CIZA J2242.8+5301 suggest that it is a major cluster merger. Despite being well studied in the X-ray and radio, little has been presented on the cluster structure and dynamics inferred from its galaxy population. We carried out a deep ($i\lt 25$) broadband imaging survey of the system with Subaru SuprimeCam (g and i bands) and the Canada–France–Hawaii Telescope (r band), as well as a comprehensive spectroscopic survey of the cluster area (505 redshifts) using Keck DEep Imaging Multi-Object Spectrograph. We use these data to perform a comprehensive galaxy/redshift analysis of the system, which is the first step to a proper understanding of the geometry and dynamics of the merger, as well as using the merger to constrain self-interacting dark matter. We find that the system is dominated by two subclusters of comparable richness with a projected separation of 6\buildrel{\,\prime}\over{.} 9_{-0.5}^{+0.7} (1.3$_{-0.10}^{+0.13}\;{\rm Mpc}$). We find that the north and south subclusters have similar redshifts of $z\approx 0.188$ with a relative line-of-sight (LOS) velocity difference of 69 ± 190 ${\rm km}\;{{{\rm s}}^{-1}}$. We also find that north and south subclusters have velocity dispersions of $1160_{-90}^{+100}$ and $1080_{-70}^{+100}\;{\rm km}\;{{{\rm s}}^{-1}}$, respectively. These correspond to masses of $16.1_{-3.3}^{+4.6}\times {{10}^{14}}$ and $13.0_{-2.5}^{+4.0}\times {{10}^{14}}$ ${{M}_{\odot }}$, respectively. While velocity dispersion measurements of merging clusters can be biased, we believe the bias in this system to be minor due to the large projected separation and nearly plane-of-sky merger configuration. We also find that the cDs of the north and south subclusters are very near their subcluster centers, in both projection (55 and 85 kpc, respectively) and normalized LOS velocity ($|{\Delta }v|/{{\sigma }_{v}}=0.43\pm 0.13$ and 0.21 ± 0.12 for the north and south, respectively). CIZA J2242.8+5301 is a relatively clean dissociative cluster merger with near 1:1 mass ratio, which makes it an ideal merger for studying merger-associated physical phenomena

A strategy for tissue self-organization that is robust to cellular heterogeneity and plasticity

Developing tissues contain motile populations of cells that can self-organize into spatially ordered tissues based on differences in their interfacial surface energies. However, it is unclear how self-organization by this mechanism remains robust when interfacial energies become heterogeneous in either time or space. The ducts and acini of the human mammary gland are prototypical heterogeneous and dynamic tissues comprising two concentrically arranged cell types. To investigate the consequences of cellular heterogeneity and plasticity on cell positioning in the mammary gland, we reconstituted its self-organization from aggregates of primary cells in vitro. We find that self-organization is dominated by the interfacial energy of the tissue–ECM boundary, rather than by differential homo- and heterotypic energies of cell–cell interaction. Surprisingly, interactions with the tissue–ECM boundary are binary, in that only one cell type interacts appreciably with the boundary. Using mathematical modeling and cell-type-specific knockdown of key regulators of cell–cell cohesion, we show that this strategy of self-organization is robust to severe perturbations affecting cell–cell contact formation. We also find that this mechanism of self-organization is conserved in the human prostate. Therefore, a binary interfacial interaction with the tissue boundary provides a flexible and generalizable strategy for forming and maintaining the structure of two-component tissues that exhibit abundant heterogeneity and plasticity. Our model also predicts that mutations affecting binary cell–ECM interactions are catastrophic and could contribute to loss of tissue architecture in diseases such as breast cancer

GALEX UV Color-Magnitude Relations and Evidence for Recent Star Formation in Early-type Galaxies

We have used the GALEX UV photometric data to construct a first near-ultraviolet (NUV) color-magnitude relation (CMR) for the galaxies pre-classified as early-type by SDSS studies. The NUV CMR is a powerful tool for tracking the recent star formation history in early-type galaxies, owing to its high sensitivity to the presence of young stellar populations. Our NUV CMR for UV-weak galaxies shows a well-defined slope and thus will be useful for interpreting the restframe NUV data of distant galaxies and studying their star formation history. Compared to optical CMRs, the NUV CMR shows a substantially larger scatter, which we interpret as evidence of recent star formation activities. Roughly 15% of the recent epoch (z < 0.13) bright (M[r] < -22) early-type galaxies show a sign of recent (< 1Gyr) star formation at the 1-2% level (lower limit) in mass compared to the total stellar mass. This implies that low level residual star formation was common during the last few billion years even in bright early-type galaxies.Comment: This paper will be published as part of the Galaxy Evolution Explorer (GALEX) Astrophysical Journal Letters Special Issue. Links to the full set of papers will be available at http://www.galex.caltech.edu/PUBLICATIONS/ after November 22, 200

The Hubble Space Telescope Cluster Supernova Survey: V. Improving the Dark Energy Constraints Above z>1 and Building an Early-Type-Hosted Supernova Sample

We present ACS, NICMOS, and Keck AO-assisted photometry of 20 Type Ia supernovae SNe Ia from the HST Cluster Supernova Survey. The SNe Ia were discovered over the redshift interval 0.623 < z < 1.415. Fourteen of these SNe Ia pass our strict selection cuts and are used in combination with the world's sample of SNe Ia to derive the best current constraints on dark energy. Ten of our new SNe Ia are beyond redshift $z=1$, thereby nearly doubling the statistical weight of HST-discovered SNe Ia beyond this redshift. Our detailed analysis corrects for the recently identified correlation between SN Ia luminosity and host galaxy mass and corrects the NICMOS zeropoint at the count rates appropriate for very distant SNe Ia. Adding these supernovae improves the best combined constraint on the dark energy density \rho_{DE}(z) at redshifts 1.0 < z < 1.6 by 18% (including systematic errors). For a LambdaCDM universe, we find \Omega_\Lambda = 0.724 +0.015/-0.016 (68% CL including systematic errors). For a flat wCDM model, we measure a constant dark energy equation-of-state parameter w = -0.985 +0.071/-0.077 (68% CL). Curvature is constrained to ~0.7% in the owCDM model and to ~2% in a model in which dark energy is allowed to vary with parameters w_0 and w_a. Tightening further the constraints on the time evolution of dark energy will require several improvements, including high-quality multi-passband photometry of a sample of several dozen z>1 SNe Ia. We describe how such a sample could be efficiently obtained by targeting cluster fields with WFC3 on HST.Comment: 27 pages, 11 figures. Submitted to ApJ. This first posting includes updates in response to comments from the referee. See http://www.supernova.lbl.gov for other papers in the series pertaining to the HST Cluster SN Survey. The updated supernova Union2.1 compilation of 580 SNe is available at http://supernova.lbl.gov/Unio

The Cluster Lensing and Supernova Survey with Hubble (CLASH): Strong Lensing Analysis of Abell 383 from 16-Band HST WFC3/ACS Imaging

We examine the inner mass distribution of the relaxed galaxy cluster Abell 383 in deep 16-band HST/ACS+WFC3 imaging taken as part of the CLASH multi-cycle treasury program. Our program is designed to study the dark matter distribution in 25 massive clusters, and balances depth with a wide wavelength coverage to better identify lensed systems and generate precise photometric redshifts. This information together with the predictive strength of our strong-lensing analysis method identifies 13 new multiply-lensed images and candidates, so that a total of 27 multiple-images of 9 systems are used to tightly constrain the inner mass profile, $d\log \Sigma/d\log r\simeq -0.6\pm 0.1$ (r<160 kpc). We find consistency with the standard distance-redshift relation for the full range spanned by the lensed images, 1.01<z<6.03, with the higher redshift sources deflected through larger angles as expected. The inner mass profile derived here is consistent with the results of our independent weak-lensing analysis of wide-field Subaru images, with good agreement in the region of overlap. The overall mass profile is well fitted by an NFW profile with M_{vir}=(5.37^{+0.70}_{-0.63}\pm 0.26) x 10^{14}M_{\odot}/h and a relatively high concentration, c_{vir}=8.77^{+0.44}_{-0.42}\pm 0.23, which lies above the standard c-M relation similar to other well-studied clusters. The critical radius of Abell 383 is modest by the standards of other lensing clusters, r_{E}\simeq16\pm2\arcsec (for z_s=2.55), so the relatively large number of lensed images uncovered here with precise photometric redshifts validates our imaging strategy for the CLASH survey. In total we aim to provide similarly high-quality lensing data for 25 clusters, 20 of which are X-ray selected relaxed clusters, enabling a precise determination of the representative mass profile free from lensing bias. (ABRIDGED)Comment: 15 pages, 14 figures, 2 tabels; V3 matches the submitted version later published in Ap

GALEX Ultraviolet Photometry of Globular Clusters in M31

We present ultraviolet photometry for globular clusters (GCs) in M31 from 15 square deg of imaging using the Galaxy Evolution Explorer (GALEX). We detect 200 and 94 GCs with certainty in the near-ultraviolet (NUV; 1750 - 2750 Angstroms) and far-ultraviolet (FUV; 1350 - 1750 Angstroms) bandpasses, respectively. Our rate of detection is about 50% in the NUV and 23% in the FUV, to an approximate limiting V magnitude of 19. Out of six clusters with [Fe/H]>-1 seen in the NUV, none is detected in the FUV bandpass. Furthermore, we find no candidate metal-rich clusters with significant FUV flux, because of the contribution of blue horizontal-branch (HB) stars, such as NGC 6388 and NGC 6441, which are metal-rich Galactic GCs with hot HB stars. We show that our GALEX photometry follows the general color trends established in previous UV studies of GCs in M31 and the Galaxy. Comparing our data with Galactic GCs in the UV and with population synthesis models, we suggest that the age range of M31 and Galactic halo GCs are similar.Comment: This paper will be published as part of the Galaxy Evolution Explorer (GALEX) Astrophysical Journal Letters Special Issue. Links to the full set of papers will be available at http://www.galex.caltech.edu/PUBLICATIONS/ after November 22, 200