Measuring cluster masses with CMB lensing: a statistical approach

We present a method for measuring the masses of galaxy clusters using the imprint of their gravitational lensing signal on the cosmic microwave background (CMB) temperature anisotropies. The method first reconstructs the projected gravitational potential with a quadratic estimator and then applies a matched filter to extract cluster mass. The approach is well-suited for statistical analyses that bin clusters according to other mass proxies. We find that current experiments, such as Planck, the South Pole Telescope and the Atacama Cosmology Telescope, can practically implement such a statistical methodology, and that future experiments will reach sensitivities sufficient for individual measurements of massive systems. As illustration, we use simulations of Planck observations to demonstrate that it is possible to constrain the mass scale of a set of 62 massive clusters with prior information from X-ray observations, similar to the published Planck ESZ-XMM sample. We examine the effect of the thermal (tSZ) and kinetic (kSZ) Sunyaev-Zeldovich (SZ) signals, finding that the impact of the kSZ remains small in this context. The stronger tSZ signal, however, must be actively removed from the CMB maps by component separation techniques prior to reconstruction of the gravitational potential. Our study of two such methods highlights the importance of broad frequency coverage for this purpose. A companion paper presents application to the Planck data on the ESZ-XMM sample.Comment: 9 pages, 5 figures, version accepted for publication in A&

Point Source Confusion in SZ Cluster Surveys

We examine the effect of point source confusion on cluster detection in Sunyaev-Zel'dovich (SZ) surveys. A filter matched to the spatial and spectral characteristics of the SZ signal optimally extracts clusters from the astrophysical backgrounds. We calculate the expected confusion (point source and primary cosmic microwave background [CMB]) noise through this filter and quantify its effect on the detection threshold for both single and multiple frequency surveys. Extrapolating current radio counts, we estimate that confusion from sources below 100 microJy limits single-frequency surveys to 1-sigma detection thresholds of Y 3.10^{-6} arcmin^2 at 30 GHz and Y 10^{-5} arcmin^2 at 15 GHz (for unresolved clusters in a 2 arcmin beam); these numbers are highly uncertain, and an extrapolation with flatter counts leads to much lower confusion limits. Bolometer surveys must contend with an important population of infrared point sources. We find that a three-band matched filter with 1 arcminute resolution (in each band) efficiently reduces confusion, but does not eliminate it: residual point source and CMB fluctuations contribute significantly the total filter noise. In this light, we find that a 3-band filter with a low-frequency channel (e.g, 90+150+220 GHz) extracts clusters more effectively than one with a high frequency channel (e.g, 150+220+300 GHz).Comment: Accepted for publication in Astronomy & Astrophysics; Updated grant information in acknowledgement

Anchoring the Experience of Highly Diverse Students on the EMship+ Master: All Aboard!

The prestigious Erasmus Mundus Joint Master Degrees capitalize on diversity to achieve academic excellence; this is the case of the EMship+ Master in Ship Design. The highly varied cultural and academic background of the students however raises a learning and teaching challenge. Firstly, I assessed the diversity of the student cohort with an evidence-based approach to identify the dominant learning styles, and align the teaching to promote student engagement. Secondly, I created a more technology-enhanced learning environment thanks to an innovative use of lecture capture. The research ascertained the success and evidence of the positive impact of the refined teaching style and integration of technology using the quantitative data collected. Here, I outline the strength and limitations of the innovative solutions adopted to alleviate the difficulty of teaching highly disparate groups of students, demonstrating the need to gain knowledge of the students to construct an engaging learning environment

Refined masses and distance of the young binary Haro 1-14 C

We aim to refine the dynamical masses of the individual component of the low-mass pre-main sequence binary Haro 1-14 C. We combine the data of the preliminary orbit presented previously with new interferometric observations obtained with the four 8m telescopes of the Very Large Telescope Interferometer. The derived masses are M_a=0.905\pm0.043\,\Msun and M_b=0.308\pm0.011\,\Msun for the primary and secondary components, respectively. This is about five times better than the uncertainties of the preliminary orbit. Moreover, the possibility of larger masses is now securely discarded. The new dynamical distance, $d=96\pm\,9\,$pc, is smaller than the distance to the Ophiuchus core with a significance of $2.6\,\sigma$. Fitting the spectral energy distribution yields apparent diameters of \phi_a=0.13\pm0.01\mas and \phi_b=0.10\pm0.01\mas (corresponding to \Ra=1.50\,\Rsun and \Rb=1.13\,\Rsun) and a visual extinction of $A_v\approx1.75$. Although the revised orbit has a nearly edge-on geometry, the system is unlikely to be a long-period eclipsing binary. The secondary in Haro~1-14C is one of the few low-mass, pre-main sequence stars with an accurately determined dynamical mass and distance

Observation of Droplet Size Oscillations in a Two-Phase Fluid under Shear Flow

Experimental observations of droplet size sustained oscillations are reported in a two-phase flow between a lamellar and a sponge phase. Under shear flow, this system presents two different steady states made of monodisperse multilamellar droplets, separated by a shear-thinning transition. At low and high shear rates, the droplet size results from a balance between surface tension and viscous stress whereas for intermediate shear rates, it becomes a periodic function of time. A possible mechanism for such kind of oscillations is discussed

Quasar Host Environments: The view from Planck

We measure the far-infrared emission of the general quasar (QSO) population using Planck observations of the Baryon Oscillation Spectroscopic Survey QSO sample. By applying multi-component matched multi-filters to the seven highest Planck frequencies, we extract the amplitudes of dust, synchrotron and thermal Sunyaev-Zeldovich (SZ) signals for nearly 300,000 QSOs over the redshift range $0.1<z<5$. We bin these individually low signal-to-noise measurements to obtain the mean emission properties of the QSO population as a function of redshift. The emission is dominated by dust at all redshifts, with a peak at $z \sim 2$, the same location as the peak in the general cosmic star formation rate. Restricting analysis to radio-loud QSOs, we find synchrotron emission with a monochromatic luminosity at $100\,\rm{GHz}$ (rest-frame) rising from $\overline{L_{\rm synch}}=0$ to $0.2 \, {\rm L_\odot} {\rm Hz}^{-1}$ between $z=0$ and 3. The radio-quiet subsample does not show any synchrotron emission, but we detect thermal SZ between $z=2.5$ and 4; no significant SZ emission is seen at lower redshifts. Depending on the supposed mass for the halos hosting the QSOs, this may or may not leave room for heating of the halo gas by feedback from the QSO.Comment: 14 pages, 11 figures, accepted by A&

Experimental Investigation into Modern Hydofoils-Assisted Monohulls: How Hydrodynamically Efficient are they?

Despite the omnipresence of hydrofoil-assisted racing monohulls and the inherent development phases to refine their designs, very little scientific data has reached the public domain. Moreover, following the trend set by racing yachts, the cruising industry is now looking at the implementation of foils onto leisure vessels, with several already built. This paper therefore presents a hydrodynamic comparison of three contemporary options, namely a Dynamic Stability System, a Dali-Moustache and a Chistera foil, that have been towing tank tested on a 1:10 scale model of a 50 ft racer-cruiser hull. The analysis presented focuses on the resistance, side force, heave and trim, as well as the induced drag factor and effective draft of each design, eventually resulting in a conclusion on the most suitable configuration for leisure craft applications, and providing experimental data relative to hydrofoils. At this stage, the interest is purely hydrodynamic, and does not yet account for the additional righting moment provided by the foils and the impact on sailing performance