Kathryn Kreckel

We investigate how spatial resolution affects emission-line diagnostics in the interstellar medium (ISM) of the Small and Large Magellanic Clouds (SMC and LMC) using SDSS Local Volume Mapper (LVM) data obtained at and degraded to ~19, ~42, ~170 pc (for the SMC) and ~17, ~68, ~272 pc (for the LMC), respectively. We compare the distributions of strong emission-line ratios through 1D and 2D Kolmogorov–Smirnov tests. We deduced that diagnostics involving ionization and density sensitive ratios such as [OIII]λ5007/Hβ, [SII]λλ6717+6731/Hα and [NII]λ6584/Hα are the most strongly impacted by resolution loss in this order. The SMC shows significant deviations even from intermediate scales (~42 pc), whereas for the LMC, the coarsest resolution (~272 pc) remains relatively stable, indicating that the SMC is intrinsically more affected by spatial mixing. Resolution degradation produces a marked homogenization effect: extreme values present at the finest scales are progressively diluted, causing diagnostic diagrams to converge toward their mean loci. Diffuse ionized gas is particularly sensitive to this mixing, while Hα-selected ionized regions exhibit more robust behavior across resolutions. The sensitivity of diagnostic diagrams involving emission-line ratios, equivalent widths, and kinematic properties varies with both spatial resolution and galaxy, with the SMC generally showing stronger changes than the LMC. Our results demonstrate that sub-50 pc resolution is required to resolve the detailed structure of low-metallicity galaxies, and they highlight at least the need for careful interpretation of line-ratio diagnostics in extragalactic studies where coarse spatial resolution is unavoidable.

We present the most comprehensive set of empirical optical strong-line metallicity calibrations to date, based on the DEep Spectra of Ionised REgions Database (DESIRED), the largest compilation of H ii regions and galaxies with direct electron-temperature determinations. We construct a high-quality calibration sample of 2392 spectra: 1029 extragalactic H ii regions, 1296 local star-forming galaxies, and 67 high-redshift (z > 2) galaxies, drawn from 201 independent literature references, spanning 12 + log (O/H) ∈ [6.79, 9.07]. Physical conditions and chemical abundances are derived homogeneously using up-to-date atomic data. We derive 27 strong-line calibrations covering oxygen-, nitrogen-, sulphur-, argon-, and neon-based line ratios, including 4 previously uncalibrated diagnostics, with reported validity ranges and intrinsic dispersions (typically ∼0.15 − 0.35 dex). For the first time in a systematic calibration framework, all relations are presented for both the homogeneous temperature case (t2 = 0) and a scenario including temperature inhomogeneities (t2 > 0), thereby reconciling abundances from recombination lines (RLs) and collisionally excited lines (CELs) and directly tackling the abundance discrepancy problem. A comparison with previous calibrations shows that the DESIRED relations span the broadest validity intervals while remaining anchored to the empirical data. Comparisons with z > 2 galaxies show that several DESIRED calibrations remain consistent with independent high-redshift relations within their intrinsic scatter, whereas others display systematic offsets associated with elevated N/O or harder ionising conditions. Thus, DESIRED calibrations can provide reliable metallicity estimates at high redshift for a subset of diagnostics, while highlighting the need to account for diagnostic-specific redshift evolution.

Context . Multi-wavelength surveys place cloud dispersal at ∼1–5 Myr after massive-star emergence, before the first core-collapse supernovae. Whether a cloud disperses, re-collapses, or leaks Lyman-continuum (LyC) photons depends on how pre-supernova winds, radiation pressure, and photoionised gas pressure ( P _{H II} ) couple to the swept-up shell. Aims . We introduce T RINITY , a 1D thin-shell code that succeeds WARPFIELD and follows stellar feedback across varied initial cloud structures. Methods . T RINITY evolves the bubble-shell structure under winds, supernovae, direct and dust-reprocessed radiation pressure, P _{H II} , and gravity. A phase-aware driving prescription uses higher values of the hot-bubble and photoionised gas pressures in the energy-driven phase and accounts for P _{H II} and direct ram pressure in the momentum-driven phase. The initial cloud may be uniform, a piecewise power law, or a Bonnor-Ebert sphere. Shell structure, hot-bubble cooling, photon absorption, and LyC escape are solved alongside the dynamics. Results . We validated the code against analytic wind and photoionisation limits and explored runs with cloud masses M _cloud = 10 ⁵ –10 ^6.5 M _⊙ , core densities n _core = 10 ³ –10 ⁴ cm ⁻³ , and star-formation efficiencies ε = 0.01–0.30. Including P _{H II} increases the bubble radius by ∼10% at 10 Myr in the fiducial validation run. In a higher-efficiency example, the energy-driven phase lasts on the order of 1 Myr, radiation pressure remains subdominant, and P _{H II} remains dynamically significant after the transition to momentum-dominated evolution. Density structure changes both phase durations and outcomes. At fixed M _cloud , n _core , and ε , homogeneous and shallow profiles re-collapse, while a steep ρ ∝ r ⁻² cloud keeps expanding. In a dispersing grid, Bonnor-Ebert clouds reach their dispersal time ( τ _disp ) much later than homogeneous clouds. Conclusions . The first results show that both P _{H II} and cloud structure are important for a complete dynamical treatment: P _{H II} alters late-time shell expansion, and density structure shifts dispersal thresholds and emergence times for a fixed stellar population. T RINITY provides an efficient framework for mapping feedback dominance across a cloud parameter space and produces the diagnostics needed to compare with resolved H II region observations.

The Sloan Digital Sky Survey (SDSS)-V Local Volume Mapper (LVM) is a wide-field integral field spectroscopic survey of the southern Milky Way plane, the Magellanic Clouds, and nearby Local Group galaxies. We used early science observations of the whole body of the nearest nuclear cluster, Omega Centauri, to extend the LVM beyond its primary interstellar-medium science case. The wide LVM field allowed us to precisely map ω Cen’s line-of-sight rotation out to ~3 r _HL or 15′, reaching a maximum value of (8.4 ± 0.8) km s ⁻¹ at r ≈ 4.7′. Within the central region, comparisons with existing VLT MUSE oMEGACat data explicitly show that the unresolved light signal is dominated by a small number of bright stars, with an effective sample size of only ~12 per resolution element. Using Gaia DR3 as an external reference, we verified that the SDSS-V’s LVM reduction pipeline recovers integrated stellar fluxes to 1–4% across six magnitudes of surface brightness. Our resulting total spectrum of ω Cen is one of the highest S/N integrated spectra for any globular or nuclear star cluster. We used it to test four widely used SSP template libraries against the resolved age-metallicity ground truth from oMEGACat. All templates recovered an old, metal-poor population. However, even at signal to noise ratio of ~1300, the inferred mean ages and mean [Fe/H] vary by ~7 Gyr and ~0.4 dex, respectively, across libraries and wavelength ranges, reflecting a systematic floor for integrated-light studies of old multi-population systems.

Mapping the local and distant Universe is key to our understanding of it. For decades, the Sloan Digital Sky Survey (SDSS) has made a concerted effort to map millions of celestial objects to constrain the physical processes that govern our Universe. The most recent and fifth generation of SDSS (SDSS-V) is organized into three scientific “mappers”: the Milky Way Mapper, which aims to chart the various components of the Milky Way and constrain its formation and assembly; the Black Hole Mapper, which focuses on understanding supermassive black holes in distant galaxies across the Universe; and the Local Volume Mapper, which uses integral field spectroscopy to map the ionized interstellar medium in the Local Group. This paper describes the scope and content for the nineteenth data release (DR19) of SDSS, which is the most substantial to date in SDSS-V. DR19 is the first to contain data from all three mappers. Additionally, we also describe nine value-added catalogs that enhance the science that can be conducted with the SDSS-V data. Finally, we discuss how to access SDSS DR19 and provide illustrative examples and tutorials.

The so-called “Galactic center lobe” (GCL) is an extended (~1°) radio continuum feature situated above the Galactic plane, the nature and location of which have been subject to varying claims in the literature. Using new optical integral field spectroscopic observations from the SDSS-V Local Volume Mapper, we confirm the characterization of the GCL as a foreground photoionized H II region, not associated with the Galactic center. We present a new analysis of the ionized gas morphology, line ratio diagnostics, and kinematics. From our [S III ] λ 9532 emission line map, which suffers the least extinction, we identify ionized gas emission throughout a closed outer loop, which does not fill the GCL interior. All optical line ratio diagnostics are consistent with photoionization. By comparing the ionized gas reddening from the Balmer decrement with 3D dust maps, we directly constrain the distance to the GCL to ~2 kpc. [N II ] λ 6583 line kinematics show a uniform velocity structure across the GCL, further confirming that the entire bubble is one structure. The size and emission line morphology is strongly reminiscent of that seen in the nearby Barnard’s Loop, providing a possible analog to explain how this outer shell may be photoionized by a more distant and off-center embedded young cluster. We suggest that the acronym GCL be repurposed to instead abbreviate the name “greatly confused loop”.

The abundance discrepancy problem refers to the systematic differences observed between chemical abundances derived from collisionally excited lines (CELs) and recombination lines (RLs) of heavy ions. It remains a major unsolved problem in the study of ionized nebulae and is quantified by the abundance discrepancy factor (ADF). In this work, we present a deep integral field spectroscopic data set of the entire Lagoon Nebula (M8), obtained by the Sloan Digital Sky Survey V Local Volume Mapper project, at a spatial resolution of 0.21 pc spaxel ⁻¹ . This unique data set allows us, for the first time, to investigate spatially resolved maps of oxygen RL intensities (O ii V1), together with maps of H i RLs, heavy-ion CELs, and dust attenuation across a whole H ii region. We map the electron temperature using CELs and RLs of O ²⁺ and CELs of N ⁺ , and we map the electron density using CELs of S ⁺ . We derive CEL-based ionic and elemental oxygen abundances and, for the first time, a spatially resolved map of the RL-based O ²⁺ abundance in an H ii region. These measurements enable construction of the first spatially resolved ADF(O ²⁺ ) map of an H ii region and yield a global mean ADF of ∼0.47 ± 0.02 dex. Focusing on the central region of M8, where ionization is dominated by the O-type star Her 36, we find radial variations in the ADF, ranging between ∼0.35 and 0.50 dex. Our findings provide novel constraints on the spatial behavior and origin of the abundance discrepancy in the H ii regions.

Newly formed stars profoundly affect their environment by depositing energy and momentum into the surrounding gas. However, only a fraction of the stellar feedback is retained in the cloud, and observational constraints are needed to improve our understanding of this process. In a sample of 19 nearby galaxies, we matched H II regions from PHANGS–MUSE to their ionizing stellar source from PHANGS–HST and measured the percentage of ionizing radiation that leaks into the surrounding diffuse ionised gas (DIG). Based on a catalogue in which each H II region is powered by a single young and massive stellar association, we measure a photon escape fraction of f _esc = 82 ₋₂₄ ⁺¹² %. We obtain comparable results when using different procedures to match the ionised gas to its source. All samples in our study contain a substantial fraction of objects (up to 20%), in which the stellar source is insufficient to produce the H α flux observed from the nebula. Many of these cases are probably related to uncertain age estimates, but we also find numerous regions for which a significant fraction of the ionising photon budget is contributed by stars that reside outside the boundaries of the H II region. This finding motivates the use of an alternative galaxy-wide approach in which we include all H II regions and stellar sources, not just those that show a clear overlap. When we sum the ionisation budget over entire galaxies, we measure slightly lower, but consistent values.

Polycyclic aromatic hydrocarbon (PAH) emission is widely used to trace the distribution of molecular gas in the interstellar medium, exhibiting a tight correlation with CO(2–1) emission across nearby galaxies. Using PHANGS-JWST and PHANGS-Atacama Large Millimeter/submillimeter Array (ALMA) data, we identify localized regions where this correlation fails, with CO flux exceeding that predicted from 7.7 μ m PAH emission by more than an order of magnitude. These outlier regions are found in 20 out of 70 galaxies and are located in galaxy centers and bars, without signs of massive star formation. We explore two scenarios to explain the elevated CO-to-PAH ratios, which can either be due to suppressed PAH emission or enhanced CO emissivity. We examine PAH emission in other bands (3.3 and 11.3 μ m) and the dust-continuum-dominated bands (10 and 21 μ m), finding consistently high CO-to-PAH (or CO-to-dust continuum) emission ratios, suggesting that 7.7 μ m PAH emission is not particularly suppressed. In some outlier regions, PAH sizes and spectral energy distribution of the radiation differ slightly from nearby control regions with normal CO-to-PAH ratios, though without a consistent trend. We find that the outlier regions show higher CO velocity dispersions (Δ v _CO ). This increase in Δ v _CO lowers CO optical depth and raises its emissivity for a given gas mass. Our results favor a scenario where shear along the bar lanes and shocks at the bar ends elevate CO emissivity, leading to the breakdown of the CO–PAH correlation. Future JWST spectroscopy and deep ALMA observations of CO isotopologues will provide critical tests of this scenario.