A search for satellite galaxies of nearby star-forming galaxies with resolved stars in LBT-SONG

ABSTRACT We present results from a resolved stellar population search for dwarf satellite galaxies of six nearby (D < 5 Mpc), sub-Milky Way mass hosts using deep (m ∼ 27 mag) optical imaging from the Large Binocular Telescope. We perform image simulations to quantify our detection efficiency for dwarfs over a large range in luminosity and size, and develop a fast catalogue-based emulator that includes a treatment of unresolved photometric blending. We discover no new dwarf satellites, but we recover two previously known dwarfs (DDO 113 and LV J1228+4358) with MV < −12 that lie in our survey volume. We preview a new theoretical framework to predict satellite luminosity functions using analytical probability distribution functions and apply it to our sample, finding that we predict one fewer classical dwarf and one more faint dwarf (MV ∼ −7.5) than we find in our observational sample (i.e. the observational sample is slightly top-heavy). However, the overall number of dwarfs in the observational sample (2) is in good agreement with the theoretical expectations. Interestingly, DDO 113 shows signs of environmental quenching and LV J1228+4358 is tidally disrupting, suggesting that low-mass hosts may affect their satellites more severely than previously believed.

Improving ultrasonic imaging of aluminum plates using phase modulation

Ultrasonic imaging using arrays is a widespread technique used in medical imaging, with increasing use in industry. Conventional techniques use amplitude information from the ultrasonic signals to produce the images. These amplitude images can be produced with high quality, but can also present limitations regarding dead zone, artifacts and detection of far reflectors. Coherence images based on the signal phase have been explored in some works, and produce an image that indicates the presence of a defect. In this work we explore he effect of phase modulation of the ultrasonic signal and its effect on the corresponding coherence image. Simulations and experimental tests in an aluminum plate using Lamb waves and a linear piezoelectric array show that the phase modulation hasadvantages over coherence images without phase modulation for defect indication.

A synthetic Roman Space Telescope High-Latitude Imaging Survey: simulation suite and the impact of wavefront errors on weak gravitational lensing

ABSTRACT The Nancy Grace Roman Space Telescope (Roman) mission is expected to launch in the mid-2020s. Its weak lensing program is designed to enable unprecedented systematics control in photometric measurements, including shear recovery, point spread function (PSF) correction, and photometric calibration. This will enable exquisite weak lensing science and allow us to adjust to and reliably contribute to the cosmological landscape after the initial years of observations from other concurrent Stage IV dark energy experiments. This potential requires equally careful planning and requirements validation as the mission prepares to enter its construction phase. We present a suite of image simulations based on galsim that are used to construct a complex, synthetic Roman weak lensing survey that incorporates realistic input galaxies and stars, relevant detector non-idealities, and the current reference 5-yr Roman survey strategy. We present a first study to empirically validate the existing Roman weak lensing requirements flowdown using a suite of 12 matched image simulations, each representing a different perturbation to the wavefront or image motion model. These are chosen to induce a range of potential static and low- and high-frequency time-dependent PSF model errors. We analyse the measured shapes of galaxies from each of these simulations and compare them to a reference, fiducial simulation to infer the response of the shape measurement to each of these modes in the wavefront model. We then compare this to existing analytic flowdown requirements, and find general agreement between the empirically derived response and that predicted by the analytic model.

Influence of plasmon excitations on atomic-resolution quantitative 4D scanning transmission electron microscopy

Scanning transmission electron microscopy (STEM) allows to gain quantitative information on the atomic-scale structure and composition of materials, satisfying one of todays major needs in the development of novel nanoscale devices. The aim of this study is to quantify the impact of inelastic, i.e. plasmon excitations (PE), on the angular dependence of STEM intensities and answer the question whether these excitations are responsible for a drastic mismatch between experiments and contemporary image simulations observed at scattering angles below $$\sim $$ ∼ 40 mrad. For the two materials silicon and platinum, the angular dependencies of elastic and inelastic scattering are investigated. We utilize energy filtering in two complementary microscopes, which are representative for the systems used for quantitative STEM, to form position-averaged diffraction patterns as well as atomically resolved 4D STEM data sets for different energy ranges. The resulting five-dimensional data are used to elucidate the distinct features in real and momentum space for different energy losses. We find different angular distributions for the elastic and inelastic scattering, resulting in an increased low-angle intensity ($$\sim $$ ∼ 10–40 mrad). The ratio of inelastic/elastic scattering increases with rising sample thickness, while the general shape of the angular dependency is maintained. Moreover, the ratio increases with the distance to an atomic column in the low-angle regime. Since PE are usually neglected in image simulations, consequently the experimental intensity is underestimated at these angles, which especially affects bright field or low-angle annular dark field imaging. The high-angle regime, however, is unaffected. In addition, we find negligible impact of inelastic scattering on first-moment imaging in momentum-resolved STEM, which is important for STEM techniques to measure internal electric fields in functional nanostructures. To resolve the discrepancies between experiment and simulation, we present an adopted simulation scheme including PE. This study highlights the necessity to take into account PE to achieve quantitative agreement between simulation and experiment. Besides solving the fundamental question of missing physics in established simulations, this finally allows for the quantitative evaluation of low-angle scattering, which contains valuable information about the material investigated.

Where Is the Unmatched Transition Metal in Substoichiometric Diboride Line Compounds?

<div>The atomic structure and local composition of high quality epitaxial substoichiometric titanium</div><div>diboride (TiB_1.9) thin film, deposited by unbalanced magnetron sputtering, were studied using</div><div>analytical high-resolution scanning transmission electron microscopy, density functional theory</div><div>and image simulations. The unmatched Ti is pinpointed to planar defects on {1-100} prismatic</div><div>planes and attributed to the absence of B between Ti planes that locally relaxes the structure.</div><div>This mechanism allows the line compound to accommodate the off-stoichiometry and remain</div><div>a line compound between defects. The planar defects are embedded in otherwise stoichiometric</div><div>TiB₂ and are delineated by insertion of dislocations. An accompanied decrease in Ti-Ti bond</div><div>lengths along and across the faults is observed.</div><div>Introduction</div>

Where Is the Unmatched Transition Metal in Substoichiometric Diboride Line Compounds?

<div>The atomic structure and local composition of high quality epitaxial substoichiometric titanium</div><div>diboride (TiB_1.9) thin film, deposited by unbalanced magnetron sputtering, were studied using</div><div>analytical high-resolution scanning transmission electron microscopy, density functional theory</div><div>and image simulations. The unmatched Ti is pinpointed to planar defects on {1-100} prismatic</div><div>planes and attributed to the absence of B between Ti planes that locally relaxes the structure.</div><div>This mechanism allows the line compound to accommodate the off-stoichiometry and remain</div><div>a line compound between defects. The planar defects are embedded in otherwise stoichiometric</div><div>TiB₂ and are delineated by insertion of dislocations. An accompanied decrease in Ti-Ti bond</div><div>lengths along and across the faults is observed.</div><div>Introduction</div>