We present the results of Chandra observations of 13 optically selected clusters with 0:6 < z < 1:1, discovered via the Red-Sequence Cluster Survey (RCS). All but one are detected at S/N > 3, although three were not observed long enough to support detailed analysis. Surface brightness profiles are fitted to models. Integrated spectra are extracted within R 2500 , and T X and L X information is obtained. We derive gas masses and total masses within R 2500 and R 500 . Cosmologically corrected scaling relations are investigated, and we find the RCS clusters to be consistent with selfsimilar scaling expectations. However, discrepancies exist between the RCS sample and lower z X-ray-selected samples for relationships involving L X , with the higher z RCS clusters having lower L X for a given T X . In addition, we find that gas mass fractions within R 2500 for the high-z RCS sample are lower than expected by a factor of $2. This suggests that the central entropy of these high-z objects has been elevated by processes such as preheating, mergers, and/or AGN outbursts, that their gas is still infalling, or that they contain comparatively more baryonic matter in the form of stars. Finally, relationships between red-sequence optical richness (B gc;red ) and X-ray properties are fitted to the data. For systems with measured T X , we find that optical richness correlates with both T X and mass, having a scatter of $30% with mass for both X-ray-selected and optically selected clusters. However, we also find that X-ray luminosity is not well correlated with richness and that several of our sample members appear to be significantly X-ray faint.
SUN-KASH bridges that connect the nucleoskeleton to the cytoskeleton are only required to maintain nuclear envelope spacing in cells subjected to increased mechanical forces, such as muscle cells.
SURFS UP is a joint Spitzer and HST Exploration Science program using 10 galaxy clusters as cosmic telescopes to study z 7 galaxies at intrinsically lower luminosities, enabled by gravitational lensing, than blank field surveys of the same exposure time. Our main goal is to measure stellar masses and ages of these galaxies, which are the most likely sources of the ionizing photons that drive reionization. Accurate knowledge of the star formation density and star formation history at this epoch is necessary to determine whether these galaxies indeed reionized the universe. Determination of the stellar masses and ages requires measuring rest frame optical light, which only Spitzer can probe for sources at z 7, for a large enough sample of typical galaxies. Our program consists of 550 hours of Spitzer/IRAC imaging covering 10 galaxy clusters with very well-known mass distributions, making them extremely precise cosmic telescopes. We combine our data with archival observations to obtain mosaics with ∼ 30 hours exposure time in both 3.6 µm and 4.5 µm in the central 4 ′ × 4 ′ field and ∼ 15 hours in the flanking fields. This results in 3-σ sensitivity limits of ∼ 26.6 and ∼ 26.2 AB magnitudes for the central field in the IRAC 3.6 and 4.5 µm bands, respectively. To illustrate the survey strategy and characteristics we introduce the sample, present the details of the data reduction and demonstrate that these data are sufficient for in-depth studies of z 7 sources (using a z = 9.5 galaxy behind MACS J1149.5+2223 as an example). For the first cluster of the survey (the Bullet Cluster) we have released all high-level data mosaics and IRAC empirical PSF models. In the future we plan to release these data products for the entire survey.
We study the stellar population properties of the IRAC-detected 6 z 10 galaxy candidates from the Spitzer UltRa Faint SUrvey Program. Using the Lyman Break selection technique, we find a total of 17 galaxy candidates at 6 z 10 from Hubble Space Telescope images (including the full-depth images from the Hubble Frontier Fields program for MACS 1149 and MACS 0717) that have detections at signal-to-noise ratios 3 in at least one of the IRAC 3.6 and 4.5 μm channels. According to the best mass models available for the surveyed galaxy clusters, these IRAC-detected galaxy candidates are magnified by factors of ∼1.2-5.5. Due to the magnification of the foreground galaxy clusters, the rest-frame UV absolute magnitudes M 1600 are between −21.2 and −18.9 mag, while their intrinsic stellar masses are between 2×10 8 M e and 2.9×10 9 M e . We identify two Lyα emitters in our sample from the Keck DEIMOS spectra, one at z Lyα =6.76 (in RXJ 1347) and one at z Lyα =6.32 (in MACS 0454). We find that 4 out of 17 z 6 galaxy candidates are favored by z 1 solutions when IRAC fluxes are included in photometric redshift fitting. We also show that IRAC [3.6]-[4.5] color, when combined with photometric redshift, can be used to identify galaxies which likely have strong nebular emission lines or obscured active galactic nucleus contributions within certain redshift windows.
Measuring dark matter substructure within galaxy cluster haloes is a fundamental probe of the ΛCDM model of structure formation. Gravitational lensing is a technique for measuring the total mass distribution which is independent of the nature of the gravitating matter, making it a vital tool for studying these dark-matter dominated objects. We present a new method for measuring weak gravitational lensing flexion fields, the gradients of the lensing shear field, to measure mass distributions on small angular scales. While previously published methods for measuring flexion focus on measuring derived properties of the lensed images, such as shapelet coefficients or surface brightness moments, our method instead fits a mass-sheet transformation invariant Analytic Image Model (AIM) to each galaxy image. This simple parametric model traces the distortion of lensed image isophotes and constrains the flexion fields. We test the AIM method using simulated data images with realistic noise and a variety of unlensed image properties, and show that it successfully reproduces the input flexion fields. We also apply the AIM method for flexion measurement to Hubble Space Telescope observations of Abell 1689, and detect mass structure in the cluster using flexion measured with the AIM method. We also estimate the scatter in the measured flexion fields due to the unlensed shape of the background galaxies, and find values consistent with previous estimates.
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