Jason Tumlinson

Situated on opposite sides of the Large Magellanic Cloud (LMC), the star-forming regions N11 and 30 Doradus trace different evolutionary stages. Approximately 2 Myr more evolved, N11 serves as a proxy for later evolutionary stages of 30 Doradus. We study the (1) kinematics, (2) column density distribution, (3) ionization conditions, and (4) mass, mass outflow rate, and mass loading factor of the outflows from N11 and compare them with the wind from 30 Doradus. We probe N11 along 24 “down-the-barrel” sight lines using UV absorption-line observations from the Hubble Space Telescope Ultraviolet Legacy Library of Young Stars as Essential Standards survey and H i 21 cm emission-line observations from the Galactic All Sky Survey and Galactic Australian Square Kilometre Array Pathfinder. N11 predominantly generates a slow-moving wind that reaches speeds of ∼90 km s ⁻¹ beyond the LMC’s disk. At v _LSR ≤ +175 km s ⁻¹ , the origin of the gas clouds becomes ambiguous; they could be associated with the LMC and/or the Milky Way. The fast- and slow-moving absorbers have medium (4 km s ^–1 ≲ b ≲ 10 km s ⁻¹ ) to broad ( b ≳ 15.0 km s ⁻¹ ) widths, indicating the influence of nonthermal processes. We estimate that the outflows are ∼25%–69% ionized. Assuming that these winds are symmetric about both sides of the LMC, N11 has ejected M _baryon,sym = (3.7 ± 1.5) × 10 ⁵ M _⊙ of gas at a rate of 0.02–0.07 M _⊙ yr ⁻¹ . The N11 stellar activity drives this material out at an efficiency—described by the mass-loading factor—of η sym = 2 . 2 − 1.3 + 0.9 . These winds correspond to 2%–4% of the global LMC outflow for the low-ionization species.

Atomic hydrogen (H i ) is a useful tracer of gas in and around galaxies, and can be found in extended disklike structures well beyond a system’s optical extent. Here, we investigate the properties of extended H i disks that emerge in six Milky Way-mass galaxies using cosmological zoom-in simulations from the Figuring Out Gas and Galaxies in Enzo (FOGGIE) suite. This paper focuses on the observability of the extended H i in these systems. We find overall agreement with observational constraints on the H i size–mass relation. To facilitate direct comparisons with observations, we present synthetic H i 21 cm emission cubes. By spatially filtering our synthetic cubes to characterize the absence of short baselines in interferometric maps, we find that such observations at 20 Mpc retain ∼96%−99% of total H i emission on average, but can miss up to ∼15% of H i signal outside the central disk due to missing short spacings. This effect is small for more isolated systems, but more significant for more strongly interacting systems, as there is a more diffuse signal. This preferentially removes low column density, low velocity dispersion gas in the circumgalactic medium (CGM). The amount of observable material depends strongly on its distribution, distance, and the system’s observed orientation, preventing the formulation of a simple correction factor. Therefore, to fully characterize extended disks, their CGMs, and the interfaces between them, including data from large single-dish radio telescopes, is likely necessary.

Understanding the thermodynamic properties of the circumgalactic medium (CGM) is key to uncovering the baryon cycle in galaxies. Here, we present spatial and kinematic relationships between Mg ii and O vi , as representatives for low- and high-ion-bearing gas, in the cosmological zoom-in galaxy simulation suite FOGGIE, a set of Milky Way–like galaxy simulations with high CGM resolution. We find the O vi -bearing gas exists as a diffuse halo around the Galactic disk, while the Mg ii -bearing gas is more centrally located. We investigate the covering fraction, probability of co-observation, and cokinematic correspondence of these ions using two different analysis methods. We make both mock sightlines using two-dimensional projections of our simulations, treating these cells as integrated lines of sight, and we create one-dimensional ray objects and use the Synthetic Absorption Line Surveyor Application code to investigate individual gas structures that contribute most to the line-of-sight column densities, which we call mock absorbers. We explore the relative kinematics of these mock absorbers and find Mg ii and O vi appear to have a cokinematic relationship when looking at absorber pairs with the closest relative velocity, like in J. K. Werk et al. However, this does not necessarily correspond to a close spatial separation, meaning many O vi and Mg ii absorber pairs only appear to be cokinematic but are physically unrelated. Taking a more holistic look at Mg ii and O vi absorber pairs reveals a much weaker correlation between these two ions.

Observing the circumgalactic medium (CGM) in emission lines from ionized gas enables direct mapping of its spatial and kinematic structure, offering new insight into the gas flows that regulate galaxy evolution. Using the high-resolution Figuring Out Gas & Galaxies In Enzo (FOGGIE) simulations, we generate mock emission-line maps for six Milky Way–mass halos. Different lines (e.g., H α , O vi ) trace distinct CGM phases and structures, highlighting the need for multispecies observations. We quantify the observable CGM mass fraction as a function of instrument spatial resolution and surface brightness sensitivity, finding that sensitivity is the dominant factor limiting detectability across all ions. At fixed sensitivity, higher spatial resolution reveals more structures; at fixed spatial resolution, higher sensitivity recovers a higher percentage of the total mass. We construct emissivity-weighted projected velocity maps and compare line-of-sight velocities between emission lines. O vi shows the largest kinematic deviation from H α , while Mg ii and Si ii most closely follow H α velocities. Distinguishing these phases out to 50 kpc from the galaxy center requires spectral resolution better than 30 km s ⁻¹ for most ion pairs. Separating inflowing from outflowing gas based on projected kinematics requires high spectral resolution: at 30 km s ⁻¹ , more than 80% of gas above the emission detection threshold can be distinguished kinematically, but this fraction drops to < 40% with a resolution of 200 km s ⁻¹ . Our results provide predictions for future instruments, showing that recovering the multiphase structure and kinematics of the CGM in emission will require both high sensitivity and fine kinematic resolution.

Atomic hydrogen (H i ) is an important component of gas in and around galaxies and forms extended disklike structures well beyond the extent of starlight. Here we investigate the properties and evolution of extended H i disks that emerge in six Milky Way–mass galaxies using cosmological zoom-in simulations from the Figuring Out Gas and Galaxies in Enzo (FOGGIE) suite. We focus on the formation, evolution, and morphology of extended gaseous disks that emerge in all six systems. We find that the median H i column densities drop sharply at the disk edge, with the mean column densities outside the disk dominated by dense ( N _HI ∼ 10 ¹⁹ cm ⁻² ), clumpy structures. All systems have significant misaligned features (warps or polar rings) at some point in their evolution; however, their frequencies, lifetimes, and origins vary significantly. We find that the morphologies of the FOGGIE disks are correlated with properties of their circumgalactic medium (CGM). We place these systems along a continuum based on how populated their CGMs are with H i relative to their central disk. All systems kinematically settle similarly by z = 0. The less populated systems tend to form coherently rotating, thin, extended disks while the more populated systems do not. Location on this continuum is independent of disk and halo mass, implying a relation to local environmental factors. Our results indicate a connection between CGM content and disk formation that is not yet fully understood. A second paper investigates observational aspects of these structures.

The circumgalactic medium (CGM) is host to gas flows into and out of galaxies and regulates galaxy growth, but the multiphase, diffuse gas in this region is challenging to observe. We investigate the properties of gas giving rise to O vi emission from the CGM that upcoming missions, such as the Aspera smallsat, will be able to map in local galaxies. We use the FOGGIE simulations to predict the O vi emission from edge-on galaxies across the redshift range z = 1 → 0. O vi emission is brightest surrounding small, clumpy structures near the galaxy where the gas density is high. Most of the O vi surface brightness originates from collisionally ionized, T ∼ 10 ^5.5 K, inflowing gas and is not preferentially aligned with the major or minor axis of the galaxy disk. Simulated galaxies with higher halo masses, higher median CGM gas density, and higher star formation rates produce brighter and more widespread O vi emission in their CGM. We show that while O vi emission primarily originates in inflowing gas, turning off outflows in a simulation without star formation feedback eliminates most of the O vi emission. Enrichment from feedback is necessary to mix with the inflowing gas and allow it to glow in O vi . Collectively, our findings point toward a picture where O vi emission traces warm, ionized envelopes of cooler clouds that are accreting onto the galaxy in a metal-enriched galactic fountain. Finally, we show that the detection limit of Aspera is sufficient to detect O vi emission tens of kiloparsecs from the galaxy center for ∼ L ^⋆ galaxies.

We present a UV absorption-line analysis of the circumgalactic medium (CGM) of Sextans B, a dwarf irregular galaxy at 1.3 Mpc distance on the outer frontier of the Local Group (LG). Using Hubble Space Telescope Cosmic Origins Spectrograph spectroscopy of two active galactic nucleus sight lines passing through the Sextans B CGM at small impact parameters of 4 and 8 kpc (≈0.04–0.08 R ₂₀₀ ), we detect the CGM in Si ii , Si iii , Si iv , and C ii absorption. All four ions show a column-density profile that declines with radius. The profiles fall below the average CGM profiles of other nearby dwarfs (by ≈0.3–0.6 dex, depending on the ion), likely due to the low halo mass and low metallicity of Sextans B. Using Cloudy photoionization models and interferometric measurements of the H i column density, we find gas-phase silicon and carbon abundances in the Sextans B CGM of [Si/H] = −1.7 ± 0.2 and [C/H] = −2.1 ± 0.2, respectively, among the lowest gas-phase abundances anywhere in the LG. We calculate a cool CGM gas mass within 8 kpc of ≈4 × 10 ⁷ M _⊙ , comparable to the H i mass and the stellar mass of Sextans B.

The inner circumgalactic medium (CGM) of galaxies, where disk and halo processes intersect, remains poorly characterized despite its critical role in regulating galaxy evolution. We present results from Project AMIGA Insider, mapping Andromeda’s (M31) inner CGM within 0.25 R _vir (∼75 kpc) using 11 QSO sightlines, bringing our total sample to 54 sightlines from the disk to 2 R _vir . We detect a clear transition between M31’s thick disk and CGM at R ≲ 30 kpc, where low/intermediate ions show thick-disk corotating components with higher column densities than the CGM ones, while high ions exhibit similar column densities in both the CGM and thick disk. Beyond this region, all ion column densities decrease with impact parameter, with steeper gradients for low ions than high ions. The inner CGM ( R ≲ 100 kpc) shows more complex gas phases and multicomponent absorption compared to the predominantly single-component outer CGM. We find no significant azimuthal dependence for any observed ions, suggesting M31’s CGM is shaped by radial processes (e.g., cooling flows, precipitation) rather than disk-aligned outflows. We estimate the total metal mass in M31’s cool (Si ii , Si iii , Si iv ) CGM within R _vir to be (1.9 ± 0. 3 _stat ± 0. 7 _sys ) × 10 ⁷ M _⊙ , leading to a cool gas mass of ≈ 6 × 1 0 9 ( Z / 0.3 Z ⊙ ) − 1 M _⊙ . The warmer O vi gas may contain at least 10 times more metal and gas mass. Compared to the COS-Halos L *galaxies, M31’s cool CGM shows lower Si column densities at R ≲ 0.4 R ₂₀₀ and overall lower cool CGM masses, likely reflecting differences in galaxy mass and environment.

The Large Magellanic Cloud (LMC) has experienced disruption from tidal and ram-pressure forces as it travels through the halo of the Milky Way. In this project, we combine radio emission-line observations from the Galactic All Sky Survey and Galactic Australian Square Kilometre Array Pathfinder surveys with UV absorption-line observations from the Hubble Space Telescope Ultraviolet Legacy Library of Young Stars as Essential Standards (ULLYSES) program to trace the material in front of the LMC. Along our eight stellar sight lines near 30 Doradus, we observe gaseous structures likely associated with two arm-like features flowing in and around the LMC’s disk. We detect the nearside gas in neutral, low-, and medium-ionization species. The lower-ionization species likely undergo both thermal and nonthermal broadening while the moderately ionized phase is influenced by more nonthermal processes. The total integrated column density of Al iii decreases with increasing angular offset from 30 Doradus, with sight lines within Δ θ ≲ 0 . ° 25 containing more moderately ionized gas. We demonstrate from a Gaussian decomposition technique on the H i emission that both arms likely trace an additional ∼ 1 . ° 0 in Galactic longitude toward the 30 Doradus region than previously predicted. We constrain the orientation of the arms by suggesting that they likely converge around ( l , b ) = ( 280 . ° 5 , − 31 . ° 2 ) and at least partially cross in front of the LMC. Our observations are consistent with two competing origins of the arms: (1) outflowing material is swept back by tidal and ram-pressure forces or (2) tidally stripped inflows fuel the ongoing stellar activity inside the LMC. Future studies are needed to distinguish between these scenarios.

One of the main unknowns in galaxy evolution is how gas flows into and out of galaxies in the circumgalactic medium (CGM). Studies observing the CGM in absorption using multiple or extended background objects suggest a high degree of variation on relatively small (≲1 kpc) spatial scales. Similarly, high-resolution simulations generally exhibit small-scale substructure in the gas around galaxies. We examine the small-scale structure of the z = 1 CGM using simulations from the Figuring Out Gas and Galaxies in Enzo (FOGGIE) project. We select gaseous substructures (“clumps”) by their local overdensity and investigate their physical properties, including temperature, metallicity, and kinematics with respect to the galaxy and the nearby surroundings. FOGGIE resolves clumps down to sphericalized radii R ∼ 0.25 kpc at z = 1. The distribution of clumps peaks at ∼10 ⁵ M _⊙ and 10 ⁴ K, consistent with relatively condensed, cool gas with a slight preference for inflow-like velocities. Many clumps show internal temperature and density variations, and thus internally varying ionization levels for key diagnostic ions such as H i , Mg ii , and O vi . The average metallicity in clumps is about a factor 1.5–2× lower in metallicity than nearby gas, suggesting that the metals are not well mixed between structured and diffuse CGMs, which may have implications for observational metallicity estimations of dense CGM clouds. We estimate the survivability of CGM clumps and find that structures larger than 0.5 kpc are generally long-lived. Finally, we qualitatively compare the simulated cloud properties to Milky Way high-velocity clouds.