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1. CLEAR: Emission-line Ratios at Cosmic High Noon

   https://doi.org/10.3847/1538-4357/ac3919  

   Backhaus, Bren E.; Trump, Jonathan R.; Cleri, Nikko J.; Simons, Raymond; Momcheva, Ivelina; Papovich, Casey; Estrada-Carpenter, Vicente; Finkelstein, Steven L.; Matharu, Jasleen; Ji, Zhiyuan; et al (February 2022, The Astrophysical Journal)

   Abstract We use Hubble Space Telescope Wide Field Camera 3 G102 and G141 grism spectroscopy to measure rest-frame optical emission-line ratios of 533 galaxies atz∼ 1.5 in the CANDELS LyαEmission at Reionization survey. We compare [Oiii]/Hβversus [Sii]/(Hα+ [Nii]) as an “unVO87” diagram for 461 galaxies and [Oiii]/Hβversus [Neiii]/[Oii] as an “OHNO” diagram for 91 galaxies. The unVO87 diagram does not effectively separate active galactic nuclei (AGN) and [Nev] sources from star-forming galaxies, indicating that the unVO87 properties of star-forming galaxies evolve with redshift and overlap with AGN emission-line signatures atz> 1. The OHNO diagram does effectively separate X-ray AGN and [Nev]-emitting galaxies from the rest of the population. We find that the [Oiii]/Hβline ratios are significantly anticorrelated with stellar mass and significantly correlated with $\log \left(L_{\mathrm{H}\beta }\right)$, while [Sii]/(Hα+ [Nii]) is significantly anticorrelated with $\log \left(L_{\mathrm{H}\beta }\right)$. Comparison with MAPPINGS V photoionization models indicates that these trends are consistent with lower metallicity and higher ionization in low-mass and high-star formation rate (SFR) galaxies. We do not find evidence for redshift evolution of the emission-line ratios outside of the correlations with mass and SFR. Our results suggest that the OHNO diagram of [Oiii]/Hβversus [Neiii]/[Oii] will be a useful indicator of AGN content and gas conditions in very high-redshift galaxies to be observed by the James Webb Space Telescope. 

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2. RESOLVE and ECO: Finding Low-metallicity z ∼ 0 Dwarf AGN Candidates Using Optimized Emission-line Diagnostics

   https://doi.org/10.3847/1538-4357/ac6595  

   Polimera, Mugdha S.; Kannappan, Sheila J.; Richardson, Chris T.; Bittner, Ashley S.; Ferguson, Carlynn; Moffett, Amanda J.; Eckert, Kathleen D.; Bellovary, Jillian M.; Norris, Mark A. (May 2022, The Astrophysical Journal)

   Abstract Existing star-forming vs. active galactic nucleus (AGN) classification schemes using optical emission-line diagnostics mostly fail for low-metallicity and/or highly star-forming galaxies, missing AGN in typicalz∼ 0 dwarfs. To recover AGN in dwarfs with strong emission lines (SELs), we present a classification scheme optimizing the use of existing optical diagnostics. We use Sloan Digital Sky Survey emission-line catalogs overlapping the volume- and mass-limited REsolved Spectroscopy Of a Local VolumE (RESOLVE) and Environmental COntex (ECO) surveys to determine the AGN percentage in SEL dwarfs. Our photoionization grids show that the [Oiii]/Hβversus [Sii]/Hαdiagram (Siiplot) and [Oiii]/Hβversus [Oi]/Hαdiagram (Oiplot) are less metallicity sensitive and more successful in identifying dwarf AGN than the popular [Oiii]/Hβversus [Nii]/Hαdiagnostic (Niiplot or “BPT diagram”). We identify a new category of “star-forming AGN” (SF-AGN) classified as star-forming by the Niiplot but as AGN by the Siiand/or Oiplots. Including SF-AGN, we find thez∼ 0 AGN percentage in dwarfs with SELs to be ∼3%–16%, far exceeding most previous optical estimates (∼1%). The large range in our dwarf AGN percentage reflects differences in spectral fitting methodologies between catalogs. The highly complete nature of RESOLVE and ECO allows us to normalize strong emission-line galaxy statistics to the full galaxy population, reducing the dwarf AGN percentage to ∼0.6%–3.0%. The newly identified SF-AGN are mostly gas-rich dwarfs with halo mass <10^11.5M_⊙, where highly efficient cosmic gas accretion is expected. Almost all SF-AGN also have low metallicities (Z≲ 0.4Z_⊙), demonstrating the advantage of our method. 

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3. Meta-diagrams for 2-parameter Persistence

   Clause, N.; Dey, T. K.; Memoli, F.; Wang, B. (June 2023, LIPIcs, Volume 258, SoCG 2023, Complete Volume)

   We first introduce the notion of meta-rank for a 2-parameter persistence module, an invariant that captures the information behind images of morphisms between 1D slices of the module. We then define the meta-diagram of a 2-parameter persistence module to be the Möbius inversion of the meta-rank, resulting in a function that takes values from signed 1-parameter persistence modules. We show that the meta-rank and meta-diagram contain information equivalent to the rank invariant and the signed barcode. This equivalence leads to computational benefits, as we introduce an algorithm for computing the meta-rank and meta-diagram of a 2-parameter module M indexed by a bifiltration of n simplices in O(n^3) time. This implies an improvement upon the existing algorithm for computing the signed barcode, which has O(n^4) time complexity. This also allows us to improve the existing upper bound on the number of rectangles in the rank decomposition of M from O(n^4) to O(n^3). In addition, we define notions of erosion distance between meta-ranks and between meta-diagrams, and show that under these distances, meta-ranks and meta-diagrams are stable with respect to the interleaving distance. Lastly, the meta-diagram can be visualized in an intuitive fashion as a persistence diagram of diagrams, which generalizes the well-understood persistent diagram in the 1-parameter setting. 

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4. In‐situ determination of the HfO ₂ –Ta ₂ O ₅ ‐temperature phase diagram up to 3000°C

   https://doi.org/10.1111/jace.16271  

   McCormack, Scott_J; Tseng, Kuo‐Pin; Weber, Richard_J_K; Kapush, Denys; Ushakov, Sergey_V; Navrotsky, Alexandra; Kriven, Waltraud_M (January 2019, Journal of the American Ceramic Society)

   Abstract The previously unknown experimental HfO₂–Ta₂O₅‐temperature phase diagram has been elucidated up to 3000°C using a quadrupole lamp furnace and conical nozzle levitator system equipped with a CO₂laser, in conjunction with synchrotron X‐ray diffraction. These in‐situ techniques allowed the determination of the following: (a) liquidus, solidus, and invariant transformation temperatures as a function of composition from thermal arrest experiments, (b) determination of equilibrium phases through testing of reversibility via in‐situ X‐ray diffraction, and (c) molar volume measurements as a function of temperature for equilibrium phases. From these, an experimental HfO₂–Ta₂O₅‐temperature phase diagram has been constructed which is consistent with the Gibbs Phase Rule. 

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5. Stabilizing far-from-equilibrium (Mo,Ti)S ₂ thin films by metal sulfurization at reduced temperature

   https://doi.org/10.1116/6.0002227  

   Li, Yifei; Reidy, Kate; Penn, Aubrey; Lee, Seng Huat; Wang, Baoming; Ye, Kevin; Mao, Zhiqiang; Ross, Frances M.; Jaramillo, R. (March 2023, Journal of Vacuum Science & Technology A)

   We report the synthesis of large-area, high-Ti-content, Mo 1−x Ti x S 2 alloy thin films in the 2H phase at temperature as low as 500 °C using a scalable two-step method of metal film deposition, followed by sulfurization in H 2 S. Film processing at higher temperature accelerates Ti segregation, film coarsening, and the formation of TiS 2 in the 1T phase. Crystal growth at higher temperature results in the formation of multiple binary sulfide phases, in agreement with the equilibrium phase diagram. Making highly metastable, smooth, and uniform single-phase alloy films, therefore, hinges on developing low-temperature processing. Our results are relevant to the development of technologies based on designer transition metal dichalcogenide alloys, including in photonic integrated circuits and gas sensing. 

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