Evelyn J. Johnston

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.

Context. The formation pathways of lenticular galaxies (S0s), which morphologically lie between elliptical and spiral galaxies, remain a topic of active research. Environmental effects, merging histories, and pre-processing mechanisms are often proposed as key factors influencing their transformation. However, the relative importance of these processes remains unclear, particularly when compared with other galaxy types. Aims. We investigated and quantified the role of the environment on the formation of S0s. Methods. We used the Hydrangea cosmological zoom-in simulation suite to analyse the environmental histories of S0 galaxies, defined here as quenched disk galaxies, both centrals and satellites. Results. We find that the vast majority (> 85%) of our sample of S0s are satellites in massive haloes (log ₁₀ M ₂₀₀ /M _⊙ > 13), while only ∼10% are centrals in low-mass haloes. Satellite S0s exhibit a highly quiescent merging history, with ∼75% experiencing no significant mergers since z = 2. Centrals show more varied merging histories, although our results may be affected by limited sample size. Contrary to expectations, no clear trends in merger ratios with morphology are observed. However, mergers involving lenticular and spiral galaxies tend to occur in low-density environments and are likely gas-rich, enabling disk reformation. Pre-processing effects in groups are critical, influencing both quenching and morphological transformation. Conclusions. Our results strongly suggest that S0 galaxies predominantly form from faded spirals in clusters, with a minority forming via mergers in smaller haloes. These results are in agreement with previous observations of lenticular galaxies around galaxy clusters.

We present a spatially contiguous spectroscopic analysis of the physical and chemical structure of the Helix Nebula (NGC 7293, PNG 036.1-57.1) using integral-field observations from the SDSS-V Local Volume Mapper (LVM). The nearly complete nebular coverage allows us to map extinction, electron density and temperature, ionisation structure, and chemical abundances within a common dataset. We reconstruct calibrated datacubes from the LVM row-stacked spectra and measure 41 optical emission lines from hydrogen, helium, and collisionally excited ions. The Helix is globally a low-density nebula, with characteristic electron densities of ∼102 cm−3, but shows a strongly structured thermal distribution. Te([O III]) exhibits a U-shaped radial profile, decreasing from the central cavity to intermediate radii and rising toward the outer nebula, while Te([N II]) increases outward and Te([O II]) decreases. These contrasting behaviours show that different diagnostics trace distinct ionisation zones. The spatially resolved abundance analysis yields a near-solar oxygen abundance, 12 + log (O/H) ≃ 8.7, consistent with an approximately chemically homogeneous nebula once ionisation structure is considered. Simulated long-slit extractions show that inferred O/H depends systematically on slit orientation and can remain biased after ionisation correction, demonstrating the importance of spatial coverage in strongly stratified nebulae. We also find sulfur systematically deficient relative to other α-elements, consistent with the planetary-nebula sulfur anomaly. These results highlight the power of wide-field integral-field spectroscopy for linking the thermal, ionisation, and chemical structure of extended planetary nebulae.

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.

Integral-field-unit (IFU) spectroscopy of extended background sources, such as gravitational arcs, delivers many closely spaced absorption sightlines through the circumgalactic medium (CGM) of foreground galaxies. However, the source extent and smearing through the point spread function (PSF) cause each spaxel to integrate light from a region larger than itself. The usually adopted geometric spaxel centre is therefore not representative of where the absorbed flux originates. Informed by high-resolution imaging, we introduce a flux-contribution formalism that reconstructs the spatial origin of the flux in each spaxel by defining flux-weighted coordinates and impact parameters. Using a data-driven simulation built on a real gravitational-arc configuration, we show that spaxel centres are displaced from the flux-weighted positions by |Δ x |∝ θ _PSF (1 − f ), with f the spaxel–source overlap fraction, and that the resulting impact-parameter bias scales with the lensing magnification as μ ^−1/2 . These offsets are largest for off-arc spaxels and flatten the radial column-density profiles. They also inject a coherent geometry-driven scatter that mimics intrinsic CGM structure and that is removed neither by a tighter spaxel selection nor by a finer spatial binning. For identical uncertainties, the spaxel-centre coordinates leave residuals of about twice the noise level ( χ _ν ² ∼ 4), whereas the flux-weighted coordinates recover the input profile to within the uncertainties ( χ _ν ² ∼ 1) and remain robust to a PSF misspecification of ±10%. The method we propose provides a better-motivated and readily adoptable framework for tomographic studies, whether as the primary analysis or as a robustness check on spaxel-centre results.

We investigated the structural evolution and formation pathways of lenticular (S0) galaxies using the Hydrangea suite of cosmological hydrodynamical simulations. Simulated galaxies reproduce the observed mass–size relation from the SAMI and MaNGA surveys, enabling a direct comparison between morphology, angular momentum, and size growth. We show that the S0 population occupies a characteristic V-shaped locus in the mass–size plane, which arises from the superposition of two physically distinct formation channels. Low-mass S0s are predominantly faded-formed S0s that quenched after infall into their present-day host halo but retain the disk sizes of their star-forming progenitors. In contrast, high-mass S0s are merger-formed S0s that quenched before infall and exhibit structural properties and size evolution similar to those of ellipticals, consistent with pre-processing in group environments. By tracing their histories back to z = 1, we find that faded-formed S0s experience minimal structural evolution after quenching, whereas merger-formed S0s grow significantly in size through dissipationless interactions. These divergent evolutionary pathways explain both the slope break and the overall scatter of the S0 mass–size relation, demonstrating that lenticular galaxies arise from multiple formation mechanisms that leave distinct structural imprints.

Context. Giant Low Surface Brightness galaxies (gLSBGs), such as Malin 1, host extended stellar and gaseous discs exceeding 100 kpc in radius. Their formation and evolution remain debated, with interactions with satellite galaxies and accretion streams proposed as key contributors. Malin 1 presents multiple nearby and distant satellites. Additionally, it exhibits two giant stellar streams, the largest extending 200 kpc in projection, likely related to past interactions. Aims. We investigate the orbital dynamics of Malin 1’s satellites and their possible connections with the observed stellar streams, testing their nature with different formation scenarios. Methods. We constructed gravitational potentials for Malin 1 using optical and rotation curve data, incorporating stellar, gaseous, and dark matter (DM) components. We explored a wide orbital parameter space to determine whether the candidate progenitors of the stellar streams could have originated from past interactions, testing both Navarro-Frenk-White (NFW) and the pseudo-isothermal (ISO) halo profiles. Results. Among several explored scenarios, some produced bound orbital solutions. The ISO halo model, with mass of M_ ̊m Virial ≈ 2.6 ≈ 1.4 10^ 12 favours bound satellite orbits more than the NFW model, that has a lower mass of M_ ̊m Virial 10^ 12 These orbital models show that the giant stellar streams could be substructures of some satellites galaxies located along their leading and trailing orbital trajectories. Furthermore, our analysis indicates that the most distant Malin 1 satellite (eM1) could have reached its orbital pericentre sim1.6 Gyr ago, while the nearest companions could have interacted as early as sim100 Myr ago. At the same time, one of the closest companions would still be under a strong interaction. Another close companion displays both leading and trailing arms in a radial orbit, although it also shows a polar orbit. Furthermore, we identify some unbound orbital solutions that could link some satellites with streams. Conclusions. The observed alignment of satellites and streams indicates that past interactions likely shaped aspects of Malin 1’s morphology. Our orbital modelling constrains possible progenitors of the observed stellar streams and their orbital histories, providing new insights into the dynamical evolution of gLSBGs. Our findings are consistent with results reported very recently by other studies using Malin 1 kinematic data.

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”.

In this era of large surveys and statistical studies of galaxies, the beauty in the details of individual galaxies is often lost. In this paper we present a deep study of the spiral galaxy with MUSE, exploring the spatially resolved stellar and ionised gas properties to understand how it formed and evolved over time. The unusually deep observations of this galaxy with MUSE give us a rare opportunity to study this phenomenon with a better spatial resolution than can normally be achieved with the current IFU surveys of galaxies at a similar redshift (z We analyse the stellar and gas kinematics, as well as the spatially resolved stellar populations and gas properties, including gas metallicity and the dominant ionisation sources. The derived properties include the stellar mass, radial profiles of luminosity- and mass-weighted mean ages and metallicities, and ionised gas characteristics such as E(B-V), Hα extinction, dust-corrected Hα flux, oxygen abundance using the O3N2 calibrator, Hα luminosity, and the Hα-based star formation rate. Analysis of the stellar populations revealed a negative metallicity gradient, and the mass-weighted ages showed uniformly flat ages across the disc while the luminosity-weighted ages show a negative gradient. We find that the gas metallicity and star formation rate density also drop in the central region of the galaxy where the older luminosity-weighted stellar populations are found. Analysis of the WHAN and WHaD diagrams reveal that in fact the central region is retired, while the rest of the disc is star-forming. We conclude that is a nice example of a central low-ionisation emission-line region (cLIER) galaxy, where the central kpc is dominated by old, metal-poor stars with little star formation. The cLIER emission is primarily powered by hot evolved stars, while the rest of the disc displays ongoing star formation. These findings are consistent with a scenario of inside-out quenching.