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1. VERTICO. IV. Environmental Effects on the Gas Distribution and Star Formation Efficiency of Virgo Cluster Spirals

   https://doi.org/10.3847/1538-4357/ac9d3c  

   Villanueva, Vicente ; Bolatto, Alberto D. ; Vogel, Stuart ; Brown, Tobias ; Wilson, Christine D. ; Zabel, Nikki ; Ellison, Sara ; Stevens, Adam R. H. ; Jiménez Donaire, María Jesús ; Spekkens, Kristine ; et al ( December 2022 , The Astrophysical Journal)

   We measure the molecular-to-atomic gas ratio,R_mol, and the star formation rate (SFR) per unit molecular gas mass, SFE_mol, in 38 nearby galaxies selected from the Virgo Environment Traced in CO (VERTICO) survey. We stack ALMA¹²CO (J= 2−1) spectra coherently using Hivelocities from the VIVA survey to detect faint CO emission out to galactocentric radiir_gal∼ 1.2r₂₅. We determine the scale lengths for the molecular and stellar components, finding a ∼3:5 relation compared to ∼1:1 in field galaxies, indicating that the CO emission is more centrally concentrated than the stars. We computeR_molas a function of different physical quantities. While the spatially resolvedR_molon average decreases with increasing radius, we find that the mean molecular-to-atomic gas ratio within the stellar effective radiusR_e,R_mol(r<R_e), shows a systematic increase with the level of Hi, truncation and/or asymmetry (H_Iperturbation). Analysis of the molecular- and the atomic-to-stellar mass ratios withinR_e,$R_{\star }^{\mathrm{mol}}(r<R_e)$and$R_{\star }^{\mathrm{atom}}(r<R_e)$, shows that VERTICO galaxies have increasingly lower$R_{\star }^{\mathrm{atom}}(r<R_e)$for larger levels of H_Iperturbation (compared to field galaxies matched in stellar mass), but no significant change in$R_{\star }^{\mathrm{m}\mathrm{o}\mathrm{l}}(r<R_e)$. We also measure a clear systematic decrease of the SFE_molwithinR_e, SFE_mol(r<R_e), with increasingly perturbed Hi. Therefore, compared to field galaxies from the field, VERTICO galaxies are more compact in CO emission in relation to their stellar distribution, but increasingly perturbed atomic gas increases theirR_moland decreases the efficiency with which their molecular gas forms stars.

    

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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)

   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${\mathit{}}_{12/13}\equiv I{[}^{12}\mathrm{CO}(J=1\to 0)]/I{[}^{13}\mathrm{CO}(J=1\to 0)]$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. Tuning metal/superconductor to insulator/superconductor coupling via control of proximity enhancement between NbSe 2 monolayers

   https://doi.org/10.1088/1361-648X/acbf92  

   Chiatti, Olivio ; Mihov, Klara ; Griffin, Theodor U. ; Grosse, Corinna ; Alemayehu, Matti B. ; Hite, Kyle ; Hamann, Danielle ; Mogilatenko, Anna ; Johnson, David C. ; Fischer, Saskia F. ( March 2023 , Journal of Physics: Condensed Matter)

   The interplay between charge transfer and electronic disorder in transition-metal dichalcogenide multilayers gives rise to superconductive coupling driven by proximity enhancement, tunneling and superconducting fluctuations, of a yet unwieldy variety. Artificial spacer layers introduced with atomic precision change the density of states by charge transfer. Here, we tune the superconductive coupling between$\text{NbS}{\text{e}}_{\text{2}}$monolayers from proximity-enhanced to tunneling-dominated. We correlate normal and superconducting properties in${\left[{\left(\text{SnSe}\right)}_{1+\delta }\right]}_m{\left[\text{NbS}{\text{e}}_{\text{2}}\right]}_1$tailored multilayers with varying SnSe layer thickness ($m=1-15$). From high-field magnetotransport the critical fields yield Ginzburg–Landau coherence lengths with an increase of$140\mathrm{\%}$cross-plane ($m=1-9$), trending towards two-dimensional superconductivity for$m>9$. We show cross-overs between three regimes: metallic with proximity-enhanced coupling ($m=1-4$), disordered-metallic with intermediate coupling ($m=5-9$) and insulating with Josephson tunneling ($m>9$). Our results demonstrate that stacking metal mono- and dichalcogenides allows to convert a metal/superconductor into an insulator/superconductor system, prospecting the control of two-dimensional superconductivity in embedded layers.

    

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4. Optical spectral weight, phase stiffness, and T c bounds for trivial and topological flat band superconductors

   https://doi.org/10.1073/pnas.2106744118  

   Verma, Nishchhal ; Hazra, Tamaghna ; Randeria, Mohit ( August 2021 , Proceedings of the National Academy of Sciences)

   We present exact results that give insight into how interactions lead to transport and superconductivity in a flat band where the electrons have no kinetic energy. We obtain bounds for the optical spectral weight for flat-band superconductors that lead to upper bounds for the superfluid stiffness and the two-dimensional (2D)$T_c$. We focus on on-site attraction$\left|U\right|$on the Lieb lattice with trivial flat bands and on the π-flux model with topological flat bands. For trivial flat bands, the low-energy optical spectral weight${\tilde{D}}_{\text{low}}\le \tilde{n}\left|U\right|\mathrm{\Omega }/2$with$\tilde{n}=min\left(n,2-n\right)$, where n is the flat-band density and Ω is the Marzari–Vanderbilt spread of the Wannier functions (WFs). We also obtain a lower bound involving the quantum metric. For topological flat bands, with an obstruction to localized WFs respecting all symmetries, we again obtain an upper bound for${\tilde{D}}_{low}$linear in$\left|U\right|$. We discuss the insights obtained from our bounds by comparing them with mean-field and quantum Monte Carlo results.

    

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5. Coherent gravitational waveforms and memory from cosmic string loops

   https://doi.org/10.1088/1361-6382/aba28b  

   Aurrekoetxea, Josu C. ; Helfer, Thomas ; Lim, Eugene A. ( September 2020 , Classical and Quantum Gravity)

   We construct, for the first time, the time-domain gravitational wave strain waveform from the collapse of a strongly gravitating Abelian Higgs cosmic string loop in full general relativity. We show that the strain exhibits a large memory effect during merger, ending with a burst and the characteristic ringdown as a black hole is formed. Furthermore, we investigate the waveform and energy emitted as a function of string width, loop radius and string tensionGμ. We find that the mass normalized gravitational wave energy displays a strong dependence on the inverse of the string tensionE_GW/M₀∝ 1/Gμ, with$E_{\text{GW}}/M_0\sim \mathcal{O}(1)\%$at the percent level, for the regime whereGμ≳ 10⁻³. Conversely, we show that the efficiency is only weakly dependent on the initial string width and initial loop radii. Using these results, we argue that gravitational wave production is dominated by kinematical instead of geometrical considerations.

    

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