Galaxy Alignments in Very X-ray Luminous Clusters at z>0.5

We present the results of a search for galaxy alignments in 12 galaxy clusters at z>0.5, a statistically complete subset of the very X-ray luminous clusters from the MAssive Cluster Survey (MACS). Using high-quality images taken with the Hubble Space Telescope (HST) that render measurement errors negligible, we find no radial galaxy alignments within 500 kpc of the cluster centres for a sample of 545 spectroscopically confirmed cluster members. A mild, but statistically insignificant trend favouring radial alignments is observed within a radius of 200 kpc and traced to galaxies on the cluster red sequence. Our results for massive clusters at z>0.5 are in stark contrast to the findings of previous studies which find highly significant radial alignments of galaxies in nearby clusters at z~0.1 out to at least half the virial radius using imaging data from the SDSS. The discrepancy becomes even more startling if radial alignment becomes more prevalent at decreasing clustercentric distance, as suggested by both our and previous work. We investigate and discuss potential causes for the disparity between our findings based on HST images of clusters at z>0.5 and those obtained using groundbased images of systems at z~0.1. We conclude that the most likely explanation is either dramatic evolution with redshift (in the sense that radial alignments are less pronounced in dynamically younger systems) or the presence of systematic biases in the analysis of SDSS imaging data that cause at least partly spurious alignment signals.Comment: 10 pages, 11 figures, and 1 table. Accepted for publication in MNRA

Redshift and Shear Calibration: Impact on Cosmic Shear Studies and Survey Design

The cosmological interpretation of weak lensing by large-scale structures requires knowledge of the redshift distribution of the source galaxies. Current lensing surveys are often calibrated using external redshift samples which span a significantly smaller sky area in comparison to the lensing survey, and are thus subject to sample variance. Some future lensing surveys are expected to be calibrated in the same way, in particular the fainter galaxy populations where the entire color coverage, and hence photometric redshift estimate, could be challenging to obtain. Using N-body simulations, we study the impact of this sample variance on cosmic shear analysis and show that, to first approximation, it behaves like a shear calibration error 1+/-epsilon. Using the Hubble Deep Field as a redshift calibration survey could therefore be a problem for current lensing surveys. We discuss the impact of the redshift distribution sampling error and a shear calibration error on the design of future lensing surveys, and find that a lensing survey of area Theta square degrees and limiting magnitude m_lim}, has a minimum shear and redshift calibration accuracy requirements given by epsilon = epsilon_0 10^{beta(m_lim-24.5)} / sqrt(Theta/ 200). Above that limit, lensing surveys would not reach their full potential. Using the galaxy number counts from the Hubble Ultra-Deep Field, we find (epsilon_0,beta)=(0.015,-0.18) and (epsilon_0,beta)=(0.011,-0.23) for ground and space based surveys respectively. Lensing surveys with no or limited redshift information and/or poor shear calibration accuracy will loose their potential to analyse the cosmic shear signal in the sub-degree angular scales, and therefore complete photometric redshift coverage should be a top priority for future lensing surveys.Comment: Accepted version to Astroparticle Physic

Illuminating Choices for Library Prep: A Comparison of Library Preparation Methods for Whole Genome Sequencing of Cryptococcus neoformans Using Illumina HiSeq.

The industry of next-generation sequencing is constantly evolving, with novel library preparation methods and new sequencing machines being released by the major sequencing technology companies annually. The Illumina TruSeq v2 library preparation method was the most widely used kit and the market leader; however, it has now been discontinued, and in 2013 was replaced by the TruSeq Nano and TruSeq PCR-free methods, leaving a gap in knowledge regarding which is the most appropriate library preparation method to use. Here, we used isolates from the pathogenic fungi Cryptococcus neoformans var. grubii and sequenced them using the existing TruSeq DNA v2 kit (Illumina), along with two new kits: the TruSeq Nano DNA kit (Illumina) and the NEBNext Ultra DNA kit (New England Biolabs) to provide a comparison. Compared to the original TruSeq DNA v2 kit, both newer kits gave equivalent or better sequencing data, with increased coverage. When comparing the two newer kits, we found little difference in cost and workflow, with the NEBNext Ultra both slightly cheaper and faster than the TruSeq Nano. However, the quality of data generated using the TruSeq Nano DNA kit was superior due to higher coverage at regions of low GC content, and more SNPs identified. Researchers should therefore evaluate their resources and the type of application (and hence data quality) being considered when ultimately deciding on which library prep method to use

Hemodynamic optimization in severe trauma: a systematic review and meta-analysis.

OBJECTIVE: Severe trauma can be associated with significant hemorrhagic shock and impaired organ perfusion. We hypothesized that goal-directed therapy would confer morbidity and mortality benefits in major trauma. METHODS: The MedLine, Embase and Cochrane Controlled Clinical Trials Register databases were systematically searched for randomized, controlled trials of goal-directed therapy in severe trauma patients. Mortality was the primary outcome of this review. Secondary outcomes included complication rates, length of hospital and intensive care unit stay, and the volume of fluid and blood administered. Meta-analysis was performed using RevMan software, and the data presented are as odds ratios for dichotomous outcomes and as mean differences (MDs) and standard MDs for continuous outcomes. RESULTS: Four randomized, controlled trials including 419 patients were analyzed. Mortality risk was significantly reduced in goal-directed therapy-treated patients, compared to the control group(OR=0.56, 95%CI: 0.34-0.92). Intensive care (MD: 3.7 days 95%CI: 1.06-6.5)and hospital length of stay (MD: 3.5 days,95%CI: 2.75-4.25) were significantly shorter in the protocol group patients.There were no differences in reported total fluid volume or blood transfusions administered. Heterogeneity in reporting among the studies prevented quantitative analysis of complications. CONCLUSION: Following severe trauma, early goal-directed therapy was associated with lower mortality and shorter durations of intensive care unit and hospital stays. The findings of this analysis should be interpreted with caution due to the presence of significant heterogeneity and the small number of th

Optimal Surveys for Weak Lensing Tomography

Weak lensing surveys provide a powerful probe of dark energy through the measurement of the mass distribution of the local Universe. A number of ground-based and space-based surveys are being planned for this purpose. Here, we study the optimal strategy for these future surveys using the joint constraints on the equation of state parameter wn and its evolution wa as a figure of merit by considering power spectrum tomography. For this purpose, we first consider an `ideal' survey which is both wide and deep and exempt from systematics. We find that such a survey has great potential for dark energy studies, reaching one sigma precisions of 1% and 10% on the two parameters respectively. We then study the relative impact of various limitations by degrading this ideal survey. In particular, we consider the effect of sky coverage, survey depth, shape measurements systematics, photometric redshifts systematics and uncertainties in the non-linear power spectrum predictions. We find that, for a given observing time, it is always advantageous to choose a wide rather than a deep survey geometry. We also find that the dark energy constraints from power spectrum tomography are robust to photometric redshift errors and catastrophic failures, if a spectroscopic calibration sample of 10^4-10^5 galaxies is available. The impact of these systematics is small compared to the limitations that come from potential uncertainties in the power spectrum, due to shear measurement and theoretical errors. To help the planning of future surveys, we summarize our results with comprehensive scaling relations which avoid the need for full Fisher matrix calculations.Comment: Submitted to MNRAS. 10 pages, including 13 figures and 2 table

The three-dimensional geometry and merger history of the massive galaxy cluster MACS J0358.8-2955

We present results of a combined X-ray/optical analysis of the dynamics of the massive cluster MACS J0358.8-2955 (z=0.428) based on observations with the Chandra X-ray Observatory, the Hubble Space Telescope, and the Keck-I telescope on Mauna Kea. MACS J0358.8-2955 is found to be one of the most X-ray luminous clusters known at z>0.3, featuring L_X(<r_500) = 4.24*10^45 erg/s, kT = (9.55 +0.58/-0.37) keV, M^{3D}_{gas}(<r_500) = (9.18+/-1.45)*10^13 M_sun, and M^{3D}_{tot}(<r_500) = (1.12+/-0.18)*10^15 M_sun. The system's high velocity dispersion of (1440 +130/-110) km/s (890 km/s when the correct relativistic equation is used), however, is inflated by infall along the line of sight, as the result of a complex merger of at least three sub-clusters. One collision proceeds close to head-on, while the second features a significant impact parameter. The temperature variations in the intra-cluster gas, two tentative cold fronts, the radial velocities measured for cluster galaxies, and the small offsets between collisional and non-collisional cluster components all suggest that both merger events are observed close to core passage and along axes that are greatly inclined with respect to the plane of the sky. A strong-lensing analysis of the system anchored upon three triple-image systems (two of which have spectroscopic redshifts) yields independent constraints on the mass distribution. For a gas fraction of 8.2%, the resulting strong-lensing mass profile is in good agreement with our X-ray estimates, and the details of the mass distribution are fully consistent with our interpretation of the three-dimensional merger history of this complex system.Comment: 17 pages, 17 figures, and 4 tables. Accepted for publication in MNRA