Detection of CMB-Cluster Lensing using Polarization Data from SPTpol

We report the first detection of gravitational lensing due to galaxy clusters using only the polarization of the cosmic microwave background (CMB). The lensing signal is obtained using a new estimator that extracts the lensing dipole signature from stacked images formed by rotating the cluster-centered Stokes QU map cutouts along the direction of the locally measured background CMB polarization gradient. Using data from the SPTpol 500  deg^{2} survey at the locations of roughly 18 000 clusters with richness λ≥10 from the Dark Energy Survey (DES) Year-3 full galaxy cluster catalog, we detect lensing at 4.8σ. The mean stacked mass of the selected sample is found to be (1.43±0.40)×10^{14}M_{⊙} which is in good agreement with optical weak lensing based estimates using DES data and CMB-lensing based estimates using SPTpol temperature data. This measurement is a key first step for cluster cosmology with future low-noise CMB surveys, like CMB-S4, for which CMB polarization will be the primary channel for cluster lensing measurements.

Galaxy growth in a massive halo in the first billion years of cosmic history

According to the current understanding of cosmic structure formation, the precursors of the most massive structures in the Universe began to form shortly after the Big Bang, in regions corresponding to the largest fluctuations in the cosmic density field. Observing these structures during their period of active growth and assembly-the first few hundred million years of the Universe-is challenging because it requires surveys that are sensitive enough to detect the distant galaxies that act as signposts for these structures and wide enough to capture the rarest objects. As a result, very few such objects have been detected so far. Here we report observations of a far-infrared-luminous object at redshift 6.900 (less than 800 million years after the Big Bang) that was discovered in a wide-field survey. High-resolution imaging shows it to be a pair of extremely massive star-forming galaxies. The larger is forming stars at a rate of 2,900 solar masses per year, contains 270 billion solar masses of gas and 2.5 billion solar masses of dust, and is more massive than any other known object at a redshift of more than 6. Its rapid star formation is probably triggered by its companion galaxy at a projected separation of 8 kiloparsecs. This merging companion hosts 35 billion solar masses of stars and has a star-formation rate of 540 solar masses per year, but has an order of magnitude less gas and dust than its neighbour and physical conditions akin to those observed in lower-metallicity galaxies in the nearby Universe. These objects suggest the presence of a dark-matter halo with a mass of more than 100 billion solar masses, making it among the rarest dark-matter haloes that should exist in the Universe at this epoch.

Triggered self-assembly of magnetic nanoparticles

Colloidal magnetic nanoparticles are candidates for application in biology, medicine and nanomanufac-turing. Understanding how these particles interact collectively in fluids, especially how they assemble and aggregate under external magnetic fields, is critical for high quality, safe, and reliable deployment of these particles. Here, by applying magnetic forces that vary strongly over the same length scale as the colloidal stabilizing force and then varying this colloidal repulsion, we can trigger self-assembly of these nanoparticles into parallel line patterns on the surface of a disk drive medium. Localized within nanometers of the medium surface, this effect is strongly dependent on the ionic properties of the colloidal fluid but at a level too small to cause bulk colloidal aggregation. We use real-time optical diffraction to monitor the dynamics of self-assembly, detecting local colloidal changes with greatly enhanced sensitivity compared with conventional light scattering. Simulations predict the triggering but not the dynamics, especially at short measurement times. Beyond using spatially-varying magnetic forces to balance interactions and drive assembly in magnetic nanoparticles, future measurements leveraging the sensitivity of this approach could identify novel colloidal effects that impact real-world applications of these nanoparticles.

Detection of B-mode polarization in the cosmic microwave background with data from the South Pole Telescope

Gravitational lensing of the cosmic microwave background generates a curl pattern in the observed polarization. This "B-mode" signal provides a measure of the projected mass distribution over the entire observable Universe and also acts as a contaminant for the measurement of primordial gravity-wave signals. In this Letter we present the first detection of gravitational lensing B modes, using first-season data from the polarization-sensitive receiver on the South Pole Telescope (SPTpol). We construct a template for the lensing B-mode signal by combining E-mode polarization measured by SPTpol with estimates of the lensing potential from a Herschel-SPIRE map of the cosmic infrared background. We compare this template to the B modes measured directly by SPTpol, finding a nonzero correlation at 7.7σ significance. The correlation has an amplitude and scale dependence consistent with theoretical expectations, is robust with respect to analysis choices, and constitutes the first measurement of a powerful cosmological observable.

All-nanoparticle concave diffraction grating fabricated by self-assembly onto magnetically-recorded templates

Using the enormous magnetic field gradients present near the surface of magnetic recording media, we assemble diffraction gratings with lines consisting entirely of self-assembled magnetic nanoparticles that are transferred to flexible polymer thin films. These nanomanufactured gratings have line spacings programmed with commercial magnetic recording and are inherently concave with radii of curvature controlled by varying the polymer film thickness. This manufacturing approach offers a low-cost alternative for realizing concave gratings and more complex optical materials assembled with single-nanometer precision.

Frequency multiplexed superconducting quantum interference device readout of large bolometer arrays for cosmic microwave background measurements

A technological milestone for experiments employing transition edge sensor bolometers operating at sub-Kelvin temperature is the deployment of detector arrays with 100s-1000s of bolometers. One key technology for such arrays is readout multiplexing: the ability to read out many sensors simultaneously on the same set of wires. This paper describes a frequency-domain multiplexed readout system which has been developed for and deployed on the APEX-SZ and South Pole Telescope millimeter wavelength receivers. In this system, the detector array is divided into modules of seven detectors, and each bolometer within the module is biased with a unique ∼MHz sinusoidal carrier such that the individual bolometer signals are well separated in frequency space. The currents from all bolometers in a module are summed together and pre-amplified with superconducting quantum interference devices operating at 4 K. Room temperature electronics demodulate the carriers to recover the bolometer signals, which are digitized separately and stored to disk. This readout system contributes little noise relative to the detectors themselves, is remarkably insensitive to unwanted microphonic excitations, and provides a technology pathway to multiplexing larger numbers of sensors.

Pattern transfer nanomanufacturing using magnetic recording for programmed nanoparticle assembly

We report a novel nanomanufacturing technique that incorporates patterned arrays built entirely from Fe₃O₄ nanoparticles into a flexible and transparent polymer film. First, the nanoparticles are patterned using the enormous magnetic field gradients at the surface of commercial disk drive media, and then the resulting architecture is transferred to the surface of a polymer film by spin-coating and peeling. Since the particles are immobilized by the field gradients during the spin-coating process, the patterned array is preserved after peeling. To demonstrate the potential of this technology, we fabricate a 5 mm diameter all-nanoparticle diffraction grating capable of producing a white-light optical spectrum. We also demonstrate several extensions to this technology, where, by adding an external magnetic field during assembly, we create both periodic variations in topography, as well as a nanocomposite with two vertically and horizontally separated nanoparticle layers. As this technique leverages the nanometer resolution inherent in current magnetic recording technology, strong potential exists for low-cost nanomanufacturing of optical and electronic devices from a variety of nanomaterials with ∼10 nm resolution.

South Pole Telescope optics

The South Pole Telescope is a 10 m diameter, wide-field, offset Gregorian telescope with a 966-pixel, millimeter-wave, bolometer array receiver. The telescope has an unusual optical system with a cold stop around the secondary. The design emphasizes low scattering and low background loading. All the optical components except the primary are cold, and the entire beam from prime focus to the detectors is surrounded by cold absorber.

Optical performance of frequency-selective bolometers

Frequency-selective bolometers (FSBs) are a new type of detector for millimeter and submillimeter wavelengths that are transparent to all but a narrow range of frequencies as set by characteristics of the absorber itself. Therefore stacks of FSBs tuned to different frequencies provide a low-loss compact method for utilizing a large fraction of the light collected by a telescope. Tests of prototype FSBs indicate that the absorption spectra are well predicted by models, that peak absolute absorption efficiencies of the order of 50% are attainable, and that their out-of-band transmission is high.

Time-resolved measurement of propagating spin waves in ferromagnetic thin films

We measure the propagation of spatially localized spin waves in NiFe thin films through local inductive detection of the dynamic magnetization. A pulsed magnetic field excites a linear superposition of spin wave modes with a distribution that is predominantly driven by the spatial dependence of the in-plane excitation field. The results of numerical micromagnetic calculations exhibit excellent agreement with experiment and show that a comprehensive account of spatial nonuniformity and propagation is necessary to accurately measure the intrinsic damping rate.

Transesophageal atrial pacing: importance of the atrial-esophageal relationship

To determine the thresholds for transesophageal atrial capture, as well as factors that might influence the thresholds, the authors measured the minimal current and pulse duration required to pace the atrium through transesophageal bipolar lead systems in 32 patients during 42 trials. Mathematical modeling suggested that the current density at the posterior atrial wall was dependent upon the current delivered, the electrode distance, and, most importantly, the esophageal-atrial geometry, expressed as the distance from the esophagus to the excitable tissue. To examine this esophageal-atrial distance, 17 different patients, aged 11 months to 44 years, were studied concurrently with either computerized tomography or magnetic resonance imaging of the chest. The thresholds needed to capture the atrium from the esophagus were 13.2 +/- 3.7 mA at a pulse duration of 5.8 +/- 3.1 msec. Further, the data demonstrated that the threshold for transesophageal atrial pacing was poorly related to the patient's age or size. The fit between these data and the mathematical model suggested that the distance between the left atrial posterior wall and the esophagus was approximately 5-6 mm. Likewise, the minimal esophageal-atrial distance as measured by the two imaging techniques was equal to or less than 3.3 mm. These observations suggest that the distance (anterior-posterior dimension) between left atrial posterior wall and the esophagus is small and remains constant despite obvious changes in somatic and linear growth.