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The South Pole Telescope (SPT) is a 10 m diameter, wide-field, offset Gregorian telescope with a 966 pixel, multicolor, millimeter-wave, bolometer camera. It is located at the Amundsen-Scott South Pole station in Antarctica. The design of the SPT emphasizes careful control of spillover and scattering, to minimize noise and false signals due to ground pickup. The key initial project is a large-area survey at wavelengths of 3, 2, and 1.3 mm, to detect clusters of galaxies via the Sunyaev-Zel’dovich effect and to measure the small-scale angular power spectrum of the cosmic microwave background (CMB). The data will be used to characterize the primordial matter power spectrum and to place constraints on the equation of state of dark energy. A second-generation camera will measure the polarization of the CMB, potentially leading to constraints on the neutrino mass and the energy scale of inflation.

In the past decade, our understanding of how stars and galaxies formed during the first 5 billion years after the Big Bang has been revolutionized by observations that leverage gravitational lensing by intervening masses, which act as natural cosmic telescopes to magnify background sources. Previous studies have harnessed this effect to probe the distant Universe at ultraviolet, optical, infrared and millimetre wavelengths1,2,3,4,5,6. However, strong-lensing studies of young, star-forming galaxies have never extended into X-ray wavelengths, which uniquely trace high-energy phenomena. Here, we report an X-ray detection of star formation in a highly magnified, strongly lensed galaxy. This lensed galaxy, seen during the first third of the history of the Universe, is a low-mass, low-metallicity starburst with elevated X-ray emission, and is a likely analogue to the first generation of galaxies. Our measurements yield insight into the role that X-ray emission from stellar populations in the first generation of galaxies may play in reionizing the Universe. This observation paves the way for future strong-lensing-assisted X-ray studies of distant galaxies reaching orders of magnitude below the detection limits of current deep fields, and previews the depths that will be attainable with future X-ray observatories.

X-ray, optical and infrared observations reveal a very high rate of star formation in the core of an extremely luminous galaxy cluster; this starburst seems to be triggered by a cooling flow of the dense intracluster plasma. A cool-running galaxy cluster Theory predicts that the hot intracluster plasma in the cores of some galaxy clusters is dense enough to cool radiatively during the cluster's lifetime. This should lead to continuous 'cooling flows' of gas sinking towards the cluster centre, yet until now no substantial cooling flow had been observed. New optical and X-ray observations of the galaxy cluster SPT-CLJ2344-424316 at z = 0.596 reveal it to be exceptionally luminous, with a remarkably strong cooling flow equivalent to more than 3,000 solar masses per year. The central galaxy of the cluster appears to be experiencing a massive starburst, which suggests that the feedback source thought to be responsible for preventing runaway cooling in nearby cool-core clusters is not yet established in this cluster. In the cores of some clusters of galaxies the hot intracluster plasma is dense enough that it should cool radiatively in the cluster’s lifetime 1 , 2 , 3 , leading to continuous ‘cooling flows’ of gas sinking towards the cluster centre, yet no such cooling flow has been observed. The low observed star-formation rates 4 , 5 and cool gas masses 6 for these ‘cool-core’ clusters suggest that much of the cooling must be offset by feedback to prevent the formation of a runaway cooling flow 7 , 8 , 9 , 10 . Here we report X-ray, optical and infrared observations of the galaxy cluster SPT-CLJ2344-4243 (ref. 11 ) at redshift z = 0.596. These observations reveal an exceptionally luminous (8.2 × 10 45  erg s −1 ) galaxy cluster that hosts an extremely strong cooling flow (around 3,820 solar masses a year). Further, the central galaxy in this cluster appears to be experiencing a massive starburst (formation of around 740 solar masses a year), which suggests that the feedback source responsible for preventing runaway cooling in nearby cool-core clusters may not yet be fully established in SPT-CLJ2344-4243. This large star-formation rate implies that a significant fraction of the stars in the central galaxy of this cluster may form through accretion of the intracluster medium, rather than (as is currently thought) assembling entirely via mergers.

The stability of Al–Mn transition edge sensor (TES) bolometers is studied as we vary the engineered TES transition, heat capacity, and/or coupling between the heat capacity and TES. We present thermal structure measurements of each of the 39 designs tested. The data is accurately fit by a two-body bolometer model, which allows us to extract the basic TES parameters that affect device stability. We conclude that parameters affecting device stability can be engineered for optimal device operation, and present the model parameters extracted for the different TES designs.

Upcoming experiments aim to produce high fidelity polarization maps of the cosmic microwave background. To achieve the required sensitivity, we are developing monolithic, feedhorn-coupled transition edge sensor polarimeter arrays operating at 150 GHz. We describe this focal plane architecture and the current status of this technology, focusing on single-pixel polarimeters being deployed on the Atacama B-mode Search (ABS) and an 84-pixel demonstration feedhorn array backed by four 10-pixel polarimeter arrays. The feedhorn array exhibits symmetric beams, cross-polar response <−23 dB and excellent uniformity across the array. Monolithic polarimeter arrays, including arrays of silicon feedhorns, will be used in the Atacama Cosmology Telescope Polarimeter (ACTPol) and the South Pole Telescope Polarimeter (SPTpol) and have been proposed for upcoming balloon-borne instruments.

A spectroscopic redshift survey of extraordinarily bright millimetre-wave-selected sources of carbon monoxide line emission — originating from star-forming molecular gas — shows that at least ten of these sources lie at redshifts greater than four, indicating that the fraction of dusty starburst galaxies at high redshifts is greater than previously thought. ALMA focused on star-forming galaxies Luminous, dusty, starburst galaxies were abundant in the early Universe, but it has been difficult to measure the complete redshift distribution of these objects, especially at the highest redshifts. The ALMA interferometer in Chile, now coming on-stream, provides high-resolution imaging at the millimetre/submillimetre wavelengths at which star-forming gases are best observed. Using ALMA, Joaquin Vieira and co-workers targeted carbon monoxide line emissions from gravitationally lensed galaxies discovered in a wide-field survey using the South Pole Telescope. The ten z > 4 objects revealed in this work more than double the number of spectroscopically confirmed, ultra-luminous galaxies discovered at extreme redshifts. Two sources at z = 5.7 are among the most distant ultra-luminous starburst galaxies known, seen as they were about a billion years after the Big Bang. In the past decade, our understanding of galaxy evolution has been revolutionized by the discovery that luminous, dusty starburst galaxies were 1,000 times more abundant in the early Universe than at present 1 , 2 . It has, however, been difficult to measure the complete redshift distribution of these objects, especially at the highest redshifts ( z  > 4). Here we report a redshift survey at a wavelength of three millimetres, targeting carbon monoxide line emission from the star-forming molecular gas in the direction of extraordinarily bright millimetre-wave-selected sources. High-resolution imaging demonstrates that these sources are strongly gravitationally lensed by foreground galaxies. We detect spectral lines in 23 out of 26 sources and multiple lines in 12 of those 23 sources, from which we obtain robust, unambiguous redshifts. At least 10 of the sources are found to lie at z  > 4, indicating that the fraction of dusty starburst galaxies at high redshifts is greater than previously thought. Models of lens geometries in the sample indicate that the background objects are ultra-luminous infrared galaxies, powered by extreme bursts of star formation.

We introduce picasso, a model designed to predict thermodynamic properties of the intracluster medium based on the properties of halos in gravity-only simulations. The predictions result from the combination of an analytical gas model, mapping gas properties to the gravitational potential, and of a machine learning model to predict the model parameters for individual halos based on their scalar properties, such as mass and concentration. Once trained, the model can be applied to make predictions for arbitrary potential distributions, allowing its use with flexible inputs such as N-body particle distributions or radial profiles. We present the model, and train it using pairs of gravity-only and hydrodynamic simulations. We show that when trained to learn the mapping from gravity-only to non-radiative hydrodynamic simulations, picasso can make remarkably accurate and precise predictions of intracluster gas thermodynamics, with percent-level bias and \\(\\sim 20 \\%\\) scatter for \\(r / R_{500c} \\in [0.1,1]\\). Training the model on hydrodynamic simulations including sub-resolution physics modeling yields robust predictions as well, albeit with the introduction of a radius-dependent bias and an increase in scatter. We further show that the model can be trained to make accurate predictions from very minimal halo information, down to mass and concentration, at the cost of modestly reduced precision. picasso is made publicly available as a Python package at https://github.com/fkeruzore/picasso, which includes trained models that can be used to make predictions easily and efficiently, in a fully auto-differentiable and hardware-accelerated framework

Synthetic datasets generated from large-volume gravity-only simulations are an important tool in the calibration of cosmological analyses. Their creation often requires accurate inference of baryonic observables from the dark matter field. We explore the effectiveness of a baryon pasting algorithm in providing precise estimations of three-dimensional gas thermodynamic properties based on gravity-only simulations. We use the Borg Cube, a pair of simulations originating from identical initial conditions, with one run evolved as a gravity-only simulation, and the other incorporating non-radiative hydrodynamics. Matching halos in both simulations enables comparisons of gas properties on an individual halo basis. This comparative analysis allows us to fit for the model parameters that yield the closest agreement between the gas properties in both runs. To capture the redshift evolution of these parameters, we perform the analysis at five distinct redshift steps, spanning from \\(z=0\\) to \\(2\\). We find that the investigated algorithm, utilizing information solely from the gravity-only simulation, achieves few-percent accuracy in reproducing the median intracluster gas pressure and density, albeit with a scatter of approximately 20%, for cluster-scale objects up to \\(z=2\\). We measure the scaling relation between integrated Compton parameter and cluster mass (\\(Y_{500c} | M_{500c}\\)), and find that the imprecision of baryon pasting adds less than 5% to the intrinsic scatter measured in the hydrodynamic simulation. We provide best-fitting values and their redshift evolution, and discuss future investigations that will be undertaken to extend this work.

A new receiver for the South Pole Telescope, SPT-3G, was deployed in early 2017 to map the cosmic microwave background at 95, 150, and 220 GHz with ∼ 16,000 detectors, 10 times more than its predecessor SPTpol. The increase in detector count is made possible by lenslet-coupled trichroic polarization-sensitive pixels fabricated at Argonne National Laboratory, new 68 × frequency-domain multiplexing readout electronics, and a higher-throughput optical design. The enhanced sensitivity of SPT-3G will enable a wide range of results including constraints on primordial B-mode polarization, measurements of gravitational lensing of the CMB, and a galaxy cluster survey. Here we present an overview of the instrument and its science objectives, highlighting its measured performance and plans for the upcoming 2018 observing season.

We present a measurement of gravitational lensing over 1500 deg\\(^2\\) of the Southern sky using SPT-3G temperature data at 95 and 150 GHz taken in 2018. The lensing amplitude relative to a fiducial Planck 2018 \\(\\Lambda\\)CDM cosmology is found to be \\(1.020\\pm0.060\\), excluding instrumental and astrophysical systematic uncertainties. We conduct extensive systematic and null tests to check the robustness of the lensing measurements, and report a minimum-variance combined lensing power spectrum over angular multipoles of \\(50

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