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1. Measurements of the amplitude-dependent microwave surface resistance of an Au/Nb bilayer

   https://doi.org/10.1088/1361-6668/acf88d  

   Oseroff, Thomas; Sun, Zeming; Liepe, Matthias U (September 2023, Superconductor Science and Technology)

   Abstract Surface properties are critical to the capabilities of superconducting microwave devices. The native oxide of niobium-based devices is thought to consist of a thin normal conducting layer. To improve understanding on the importance of this layer, an attempt was made to replace it with a more easily controlled gold film. A niobium sample host microwave cavity was used to measure the surface resistance in continuous wave operation at $4.0\text{GHz}$and $5.2\text{GHz}$. Sample conditions studied include temperatures ranging from $1.6\text{K}$to $4.2\text{K}$with RF magnetic fields on the sample surface ranging from $\sim 1\text{mT}$to the maximum field before the superconducting properties were lost (quench field). The nominal film thickness of the gold layer was increased from $0.1\text{nm}$to $2.0\text{nm}$in five steps to study the impact of the normal layer thickness on surface resistance on a single niobium substrate. The $0.1\text{nm}$film was found to reduce the surface resistance of the sample and to enhance the quench field. With the exception of the final step from a $1.5\text{nm}$gold film to $2.0\text{nm}$, the magnitude of the surface resistance increased substantially with gold film thickness. The nature of the surface resistance field-dependence appeared to be roughly independent from the gold layer thickness. This initial study provides new perspectives and suggests avenues for optimizing and designing surfaces for resonant cavities in particle accelerators and quantum information applications. 

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2. The EDGE-CALIFA Survey: Spatially Resolved ¹³ CO(1–0) Observations and Variations in ¹² CO(1–0)/ ¹³ CO(1–0) in Nearby Galaxies on Kiloparsec Scales

   https://doi.org/10.3847/1538-4365/acd840  

   Cao, Yixian; Wong, Tony; Bolatto, Alberto D.; Leroy, Adam K.; Rosolowsky, Erik; Utomo, Dyas; Sánchez, Sebastián F.; Barrera-Ballesteros, Jorge K.; Levy, Rebecca C.; Colombo, Dario; et al (August 2023, The Astrophysical Journal Supplement Series)

   Abstract We present¹³CO(J= 1 → 0) observations for the EDGE-CALIFA survey, which is a mapping survey of 126 nearby galaxies at a typical spatial resolution of 1.5 kpc. Using detected¹²CO emission as a prior, we detect¹³CO in 41 galaxies via integrated line flux over the entire galaxy and in 30 galaxies via integrated line intensity in resolved synthesized beams. Incorporating our CO observations and optical IFU spectroscopy, we perform a systematic comparison between the line ratio ${\mathit{}}_{12/13}\equiv I{[}^{12}\mathrm{CO}(J=1\to 0)\left]/I{[}^{13}\mathrm{CO}\right(J=1\to 0\left)\right]$and the properties of the stars and ionized gas. Higher ${\mathit{}}_{12/13}$values are found in interacting galaxies compared to those in noninteracting galaxies. The global ${\mathit{}}_{12/13}$slightly increases with infrared colorF₆₀/F₁₀₀but appears insensitive to other host-galaxy properties such as morphology, stellar mass, or galaxy size. We also present azimuthally averaged ${\mathit{}}_{12/13}$profiles for our sample up to a galactocentric radius of 0.4r₂₅(∼6 kpc), taking into account the¹³CO nondetections by spectral stacking. The radial profiles of ${\mathit{}}_{12/13}$are quite flat across our sample. Within galactocentric distances of 0.2r₂₅, the azimuthally averaged ${\mathit{}}_{12/13}$increases with the star formation rate. However, Spearman rank correlation tests show the azimuthally averaged ${\mathit{}}_{12/13}$does not strongly correlate with any other gas or stellar properties in general, especially beyond 0.2r₂₅from the galaxy centers. Our findings suggest that in the complex environments in galaxy disks, ${\mathit{}}_{12/13}$is not a sensitive tracer for ISM properties. Dynamical disturbances, like galaxy interactions or the presence of a bar, also have an overall impact on ${\mathit{}}_{12/13}$, which further complicates the interpretations of ${\mathit{}}_{12/13}$variations. 

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3. A Chandra X-Ray Survey of Optically Selected Close Galaxy Pairs: Unexpectedly Low Occupation of Active Galactic Nuclei

   https://doi.org/10.3847/1538-4357/acc5e1  

   He, Lin; Hou, Meicun; Li, Zhiyuan; Feng, Shuai; Liu, Xin (May 2023, The Astrophysical Journal)

   Abstract High-resolution X-ray observations offer a unique tool for probing the still-elusive connection between galaxy mergers and active galactic nuclei (AGNs). We present an analysis of nuclear X-ray emission in an optically selected sample of 92 close galaxy pairs (with projected separations ≲20 kpc and line-of-sight velocity offsets <500 km s⁻¹) at low redshift ( $\overline{z}\sim 0.07$), based on archival Chandra observations. The parent sample of galaxy pairs is constructed without imposing an optical classification of nuclear activity, thus it is largely free of selection effect for or against the presence of an AGN. Nor is this sample biased for or against gas-rich mergers. An X-ray source is detected in 70 of the 184 nuclei, giving a detection rate of $38{\%}_{-5\%}^{+5\%}$, down to a 0.5–8 keV limiting luminosity of ≲10⁴⁰erg s⁻¹. The detected and undetected nuclei show no systematic difference in their host galaxy properties such as galaxy morphology, stellar mass, and stellar velocity dispersion. When potential contamination from star formation is avoided (i.e.,L_{2−10 keV}> 10⁴¹erg s⁻¹), the detection rate becomes $18{\%}_{-3\%}^{+3\%}$(32/184), which shows no excess compared to the X-ray detection rate of a comparison sample of optically classified single AGNs. The fraction of pairs containing dual AGN is only $2{\%}_{-2\%}^{+2\%}$. Moreover, most nuclei at the smallest projected separations probed by our sample (a few kiloparsecs) have an unexpectedly low apparent X-ray luminosity and Eddington ratio, which cannot be solely explained by circumnuclear obscuration. These findings suggest that close galaxy interaction is not a sufficient condition for triggering a high level of AGN activity. 

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4. Noise in the LIGO livingston gravitational wave observatory due to trains

   https://doi.org/10.1088/1361-6382/acf01f  

   Glanzer, J.; Soni, S.; Spoon, J.; Effler, A.; González, G. (September 2023, Classical and Quantum Gravity)

   Abstract Environmental seismic disturbances limit the sensitivity of LIGO gravitational wave detectors. Trains near the LIGO Livingston detector produce low frequency (0.5– $10\mathrm{H}\mathrm{z}$) ground noise that couples into the gravitational wave sensitive frequency band (10– $100\mathrm{H}\mathrm{z}$) through light reflected in mirrors and other surfaces. We investigate the effect of trains during the Advanced LIGO third observing run, and propose a method to search for narrow band seismic frequencies responsible for contributing to increases in scattered light. Through the use of the linear regression tool Lasso (least absolute shrinkage and selection operator) and glitch correlations, we identify the most common seismic frequencies that correlate with increases in detector noise as 0.6– $0.8\mathrm{H}\mathrm{z}$, 1.7– $1.9\mathrm{H}\mathrm{z}$, 1.8– $2.0\mathrm{H}\mathrm{z}$, and 2.3– $2.5\mathrm{H}\mathrm{z}$in the LIGO Livingston corner station. 

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5. Study the structure of the low-lying states of ²⁰⁶ Po

   https://doi.org/10.1088/1402-4896/ad4521  

   Kocheva, D; Rainovski, G; Jolie, J; Beckers, M; Blazhev, A; Esmaylzadeh, A; Fransen, C; Gladnishki, K A; Pietralla, N; Scheck, M; et al (May 2024, Physica Scripta)

   Abstract The nucleus²⁰⁶Po was studied in the two proton transfer reaction²⁰⁴Pb(¹⁶O,¹⁴C)²⁰⁶Po and the lifetime of the first excited 2⁺state was determined by utilizing the Recoil Distance Doppler Shift method. The experimental results are compared with shell-model calculations based on different effective interactions. The calculations qualitatively reproduced the experimentally observed $B(E2;2_1^{+}\to 0_1^{+})$value, suggesting that the $2_1^{+}$state of²⁰⁶Po exhibits a collective nature. However, the employed effective interactions revealed some limitations, particularly in their description of the $4_{1,2}^{+}$states. These results emphasize the importance of understanding the properties of low-lying states, especially their evolution from single-particle dynamics to collective modes, in evaluating various effective nuclear interactions. 

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