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1. The SAMI Galaxy Survey: reconciling strong emission line metallicity diagnostics using metallicity gradients

   https://doi.org/10.1093/mnras/stab205  

   Poetrodjojo, Henry ; Groves, Brent ; Kewley, Lisa J ; Sweet, Sarah M ; Sanchez, Sebastian F ; Medling, Anne M ; López-Sánchez, Ángel R ; Brough, Sarah ; Cortese, Luca ; van de Sande, Jesse ; et al ( February 2021 , Monthly Notices of the Royal Astronomical Society)

   null (Ed.)

   ABSTRACT We measure the gas-phase metallicity gradients of 248 galaxies selected from Data Release 2 of the SAMI Galaxy Survey. We demonstrate that there are large systematic discrepancies between the metallicity gradients derived using common strong emission line metallicity diagnostics. We determine which pairs of diagnostics have Spearman’s rank coefficients greater than 0.6 and provide linear conversions to allow the accurate comparison of metallicity gradients derived using different strong emission line diagnostics. For galaxies within the mass range 8.5 < log (M/M⊙) < 11.0, we find discrepancies of up to 0.11 dex/Re between seven popular diagnostics in the metallicity gradient–mass relation. We find a suggestion of a break in the metallicity gradient–mass relation, where the slope shifts from negative to positive, occurs between 9.5 < log (M/M⊙) < 10.5 for the seven chosen diagnostics. Applying our conversions to the metallicity gradient–mass relation, we reduce the maximum dispersion from 0.11 dex/Re to 0.02 dex/Re. These conversions provide the most accurate method of converting metallicity gradients when key emission lines are unavailable. We find that diagnostics that share common sets of emission line ratios agree best, and that diagnostics calibrated through the electron temperature provide more consistent results compared to those calibrated through photoionization models. 

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2. Metallicity of Galactic RR Lyrae from Optical and Infrared Light Curves. I. Period–Fourier–Metallicity Relations for Fundamental-mode RR Lyrae

   https://doi.org/10.3847/1538-4357/abefd4  

   Mullen, Joseph P. ; Marengo, Massimo ; Martínez-Vázquez, Clara E. ; Neeley, Jillian R. ; Bono, Giuseppe ; Dall’Ora, Massimo ; Chaboyer, Brian ; Thévenin, Frédéric ; Braga, Vittorio F. ; Crestani, Juliana ; et al ( May 2021 , The Astrophysical Journal)

   null (Ed.)
3. THE MASS-METALLICITY RELATION AT Z~8:DIRECT-METHOD METALLICITY CONSTRAINTS AND NEAR-FUTURE PROSPECTS

   Jones, Tucker ; Sanders, Ryan ; Roberts-Borsani, Guido ; Ellis, Richard S. ; Laporte, Nicolas ; Treu, Tommaso ; Harikane, Yuichi ( July 2020 , The Astrophysical journal)

   Physical properties of galaxies at z>7 are of interest for understanding both the early phases of star formation and the process of cosmic reionization. Chemical abundance measurements offer valuable information on the integrated star formation history, and hence ionizing photon production, as well as the rapid gas accretion expected at such high redshifts. We use reported measurements of [O III] 88μm emission and star formation rate to estimate gas-phase oxygen abundances in five galaxies at z=7.1-9.1 using the direct T_e method. We find typical abundances 12+log(O/H) = 7.9 (∼0.2 times the solar value) and an evolution of 0.9±0.5 dex in oxygen abundance at fixed stellar mass from z≃8 to 0. These results are compatible with theoretical predictions, albeit with large (conservative) uncertainties in both mass and metallicity. We assess both statistical and systematic uncertainties to identify promising means of improvement with the Atacama Large Millimeter Array (ALMA) and the James Webb Space Telescope (JWST). In particular we highlight [O III] 52μm as a valuable feature for robust metallicity measurements. Precision of 0.1-0.2 dex in T_e-based O/H abundance can be reasonably achieved for galaxies at z≈5-8 by combining [O III] 52μm with rest-frame optical strong lines. It will also be possible to probe gas mixing and mergers via resolved T_e-based abundances on kpc scales. With ALMA and JWST, direct metallicity measurements will thus be remarkably accessible in the reionization epoch. 

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4. Zwicky Transient Facility and Globular Clusters: The RR Lyrae gri-band Period–Luminosity–Metallicity and Period–Wesenheit–Metallicity Relations

   https://doi.org/10.3847/1538-3881/ac617e  

   Ngeow, Chow-Choong ; Bhardwaj, Anupam ; Dekany, Richard ; Duev, Dmitry A. ; Graham, Matthew J. ; Groom, Steven L. ; Mahabal, Ashish A. ; Masci, Frank J. ; Medford, Michael S. ; Riddle, Reed ( April 2022 , The Astronomical Journal)

   Based on time-series observations collected from the Zwicky Transient Facility (ZTF), we derived period–luminosity–metallicity (PLZ) and period–Wesenheit–metallicity (PWZ) relations for RR Lyrae located in globular clusters. We have applied various selection criteria to exclude RR Lyrae with problematic or spurious light curves. These selection criteria utilized information on the number of data points per light curve, amplitudes, colors, and residuals on the period–luminosity and/or period–Wesenheit relations. Due to blending, a number of RR Lyrae in globular clusters were found to be anomalously bright and have small amplitudes of their ZTF light curves. We used our final sample of ∼750 RR Lyrae in 46 globular clusters covering a wide metallicity range (−2.36 dex < [Fe/H] < −0.54 dex) to derive PLZ and PWZ relations in thegribands. In addition, we have also derived the period–color–metallicity and, for the first time, the period-Q-index-metallicity relations, where theQ-index is extinction-free by construction. We have compared our various relations to empirical and theoretical relations available in the literature and found a good agreement with most studies. Finally, we applied our derived PLZ relation to a dwarf galaxy, Crater II, and found that its true distance modulus should be larger than the most recent determination.

    

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5. Spatially resolved gas-phase metallicity in FIRE-2 dwarfs: late-time evolution of metallicity relations in simulations with feedback and mergers

   https://doi.org/10.1093/mnras/stac1958  

   Porter, Lori E. ; Orr, Matthew E. ; Burkhart, Blakesley ; Wetzel, Andrew ; Ma, Xiangcheng ; Hopkins, Philip F. ; Emerick, Andrew ( July 2022 , Monthly Notices of the Royal Astronomical Society)

   We present an analysis of spatially resolved gas-phase metallicity relations in five dwarf galaxies ($\rm \mathit{M}_{halo} \approx 10^{11}\, {\rm M}_\odot$, $\rm \mathit{M}_\star \approx 10^{8.8}{-}10^{9.6}\, {\rm M}_\odot$) from the FIRE-2 (Feedback in Realistic Environments) cosmological zoom-in simulation suite, which include an explicit model for sub-grid turbulent mixing of metals in gas, near z ≈ 0, over a period of 1.4 Gyr, and compare our findings with observations. While these dwarf galaxies represent a diverse sample, we find that all simulated galaxies match the observed mass–metallicity (MZR) and mass–metallicity gradient (MZGR) relations. We note that in all five galaxies, the metallicities are effectively identical between phases of the interstellar medium (ISM), with 95 ${{\ \rm per\ cent}}$ of the gas being within ±0.1 dex between the cold and dense gas (T < 500 K and nH > 1 cm−3), ionized gas (near the H αT ≈ 104 K ridge-line), and nebular regions (ionized gas where the 10 Myr-averaged star formation rate is non-zero). We find that most of the scatter in relative metallicity between cold dense gas and ionized gas/nebular regions can be attributed to either local starburst events or metal-poor inflows. We also note the presence of a major merger in one of our galaxies, m11e, with a substantial impact on the metallicity distribution in the spatially resolved map, showing two strong metallicity peaks and triggering a starburst in the main galaxy.

    

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