Deanne B. Fisher

Small-scale multiphase structure plays a central role in galactic-wind evolution, yet the parsec-scale morphology and excitation of the warm ionized gas remain poorly constrained. We present deep Hubble Space Telescope (HST) narrow-band imaging of the southern wind of Messier 82 (M82) in H α , [O iii ], [S ii ], and [N ii ], designed to resolve the warm ionized phase on parsec scales. The H α emission is detected to ≈2.1 kpc above the disk, while the fainter emission lines are detected over smaller radial extents, with [O iii ] reaching ≈1.5 kpc. We develop a filament-finding pipeline for the H α image and construct a quantitative catalogue of the filamentary structures. The wind forms a highly connected network of strands and knots, dominated by compact filaments with typical projected widths of ≃5.3 pc and lengths of ≃9.5 pc. Both the projected covering fraction and the line-flux contribution of the filamentary component decline with height, showing that the outer wind becomes increasingly dominated by diffuse emission. Optical line-ratio diagnostics indicate that the warm ionized gas occupies an intermediate excitation regime: photoionization by the central starburst can energetically power the observed H α luminosity, while the systematic separation between filamentary and diffuse emission, together with the evolution of the line ratios with vertical distance, suggests an increasing contribution from shocks or other similar heating in the diffuse outer wind. These results show that separating filamentary and diffuse emission in high-resolution imaging provides a powerful way to connect the morphology, excitation, and multiphase structure of galactic winds.

We present high-resolution (0 . ″ 94 ≈ 55 pc) Atacama Large Millimeter/submillimeter Array (ALMA) CO(2–1) and ¹³ CO(2–1) observations of the highly inclined ( i ∼ 87 . ° 5 ) galaxy NGC 4565 covering out to galactocentric radius R _gal ≳ ± 17 kpc. The combination of sensitivity and resolution enables the detection of CO emission well into the H i -dominated outer disk while isolating individual molecular clouds across the full extent of the galaxy. Although often described as an edge-on Milky Way analog, the molecular gas profile of NGC 4565 has a central gap that is more similar to M31. The ¹³ CO/ ¹² CO ratio remains consistent at 0.086 ± 0.009 from R _gal = 5–13 kpc. Based on fits to position–velocity slices, the molecular disk remains thin, with an FWHM scale height of 79.1 ± 1.6 pc measured from the vertical intensity profile with little evidence for vertical flaring. Molecular clouds in NGC 4565 show sizes, linewidths, and surface densities consistent with those found in similar environments in PHANGS-ALMA galaxies and in M31. We identify a prominent star-forming complex on the ring—an overdensity of molecular gas we term the “East Ring Pileup.” This feature hosts a compact, multiwavelength-bright region, which we call “the Jewel.” Effects of galaxy inclination on molecular cloud radius, velocity dispersion, surface density, and virial parameter appear as second-order effects that are strongest in velocity dispersion. At this resolution, GMCs are preferentially aligned with the disk of the galaxy and horizontally elongated by a factor of ∼2.

Emission from the pure rotational transitions of H ₂ traces warm molecular gas, providing insight into its temperature distribution and local heating conditions. We have extended previous power-law H ₂ temperature models to account for differential extinction by dust as well as nonequilibrium ortho-to-para-H ₂ ratios (OPR). The turbulent environment of the M82 starburst offers a unique opportunity to study H ₂ out of equilibrium conditions, using ∼15 pc spatially resolved measurements from MIRI/MRS on JWST. With extensive detections of H ₂ S(1)–S(7), we use our model to assess spatial variations in local heating conditions of molecular gas across a ∼500 pc region of the M82 central starburst. The average slope of the recovered H ₂ power-law temperature distribution is consistent with prior studies, and the slope strongly anticorrelates with relative [Fe ii ]/H ₂ S(1)–S(2) strength, pointing to the importance of shock heating. Our models indicate that the OPR is, on average, about half of its equilibrium value. This suppression is attributed to cloud mixing timescales, which are short compared to timescales for spin conversion, with molecular gas remembering its “cooler past.” By accounting for OPR disequilibrium, we can identify instances of recent and rapid heating to better understand the flow of energy through the interstellar medium and track its thermal history.

We present a Bayesian analysis of star clusters in the dwarf starburst galaxy NGC 1569 based on high-resolution Hubble Space Telescope (HST) imaging combined with integral-field spectroscopy from the Keck Cosmic Web Imager, obtained as part of the DUVET survey. For each cluster identified, we infer posterior probability distributions for mass and age using a forward modelling method that properly accounts for uncertainties due to stochastic sampling of the initial mass function (IMF). We investigate how the inferred properties depend on photometric coverage by repeating the analysis with different filter combinations, including mock extensions to the ultraviolet (UV) and near-infrared that emulate the addition of HST UV bands and James Webb Space Telescope imaging. We find that, while inclusion of these wavelength regimes further breaks age and mass degeneracies, the currently available data yield reasonably strong constraints on cluster parameters. We compare inferred cluster properties to the conditions of the local interstellar medium, and find evidence for multiple interesting correlations. The truncation mass of the cluster mass function varies with galactocentric distance, particularly moving off the disc, consistent with a dependence on the density of the interstellar medium. Cluster mass positively correlates with metallicity, suggesting that massive clusters preferentially form in pre-enriched gas, and the ionization state of the gas, reflecting the increased prevalence of high-mass stars in high-mass clusters. These results demonstrate the power of Bayesian, IMF-aware modelling for resolving cluster populations in nearby starburst dwarfs and provide new insight into how cluster formation and feedback respond to local galactic conditions.

Galactic winds are considered a likely driver of rapid quenching in early massive galaxies, but until now there has been no direct evidence that such systems drive winds powerful enough to meaningfully suppress their star formation. We present resolved cold gas and ionized gas observations of a powerful supernova-driven wind in a massive galaxy 1.1 billion years after the Big Bang (at z = 5.3). The outflow, likely triggered by ongoing merger activity, is removing gas at twice the rate of star formation and could plausibly eject all the cold gas from the galaxy within 100 Myr. Our results suggest that powerful merger-driven outflows may be a key mechanism to produce abundant massive quiescent galaxies in the early Universe when a large fraction of massive galaxies is interacting. The mass and energetics of this distant outflow are consistent with nearby starburst-driven superwinds, suggesting that the efficiency of stellar feedback has remained relatively constant over the last 12 billion years of cosmic history.

We present JWST MIRI and NIRCam imaging of the inner ∼5 kpc of the M82 superwind at ∼ 0 . ″ 05 − 0 . ″ 375 (∼0.9–6.5 pc) resolution. Targeted filters probe emission from polycyclic aromatic hydrocarbons (PAHs; F335M, F360M , F770W, F1130W) and continuum (F250M, F360M) The images reveal a network of cool wind filaments traced by PAHs. PAH surface brightness declines with the inverse square of distance to the midplane, suggesting that the incident radiation field from the starburst drives the observed PAH intensity out to ±2.5 kpc. The 3.3/11.3 and 3.3/7.7 μ m band ratios show uniformity with distance from the starburst, though comparisons with mid-IR dust emission models indicate a modest shift toward larger PAHs. Outside the disk, 11.3/7.7 μ m increases moderately, reflecting that PAHs become more neutral with distance from the starburst as they are exposed to a declining radiation field and ionization parameter. Overall, PAHs in the wind are consistent with standard-to-large sizes and standard-to-high ionization states. Including Spitzer and Herschel data, PAH abundance ( q _PAH ) is set at ∼1% in the starburst and remains unchanging out to ±5 kpc off the disk. This flat q _PAH profile suggests that PAHs are shielded from the hot wind, perhaps residing in the surface layers of cool clouds, with possible replenishment from cloud interiors and enrichment of the halo from previous bursts. In this picture, clouds are not dense enough to promote PAH growth, and they likely undergo radiative cooling and mixing with the hot phase to survive the gauntlet for at least ∼20 Myr.

We map the extraplanar gas, with ∼50-200 pc resolution, in nine star-forming galaxies using Multi-Unit Spectroscopic Explorer (MUSE) observations from the GECKOS VLT Large Program targeting edge-on galaxies with similar stellar mass as the Milky Way. The narrow range in stellar mass (±0.35 dex) of the GECKOS sample makes it ideal for studying trends with star formation rate (SFR). We find strong extraplanar emission reaching ∼2-8 kpc from the disk midplane in all targets with $\rm {SFR}\ge$1 M⊙ yr−1. Targets with SFR ≥ 5 M⊙ yr−1 have brighter, more extended Hα emission compared to lower SFR targets. In high-SFR systems, the gas velocity dispersion (σHα) shows a biconical morphology, consistent with the expectation of outflows. This agrees with previous works suggesting high velocity dispersion in a biconical shape is a good means to identify outflows. We find mixed results using line diagnostics ([OIII]5007/Hβ - [NII]/Hα and σHα - [SII]/Hα) to spatially resolve ionisation mechanisms across the extraplanar gas. The highest [NII]/Hα are found in the extraplanar gas of the highest SFR systems , yet main-sequence galaxies have the highest [OIII]/Hβ. While the morphology of [NII]/Hα may be useful to identify outflows, the absolute value of the line ratio alone may not distinguish strong outflows from extraplanar gas of main-sequence galaxies. The ubiquitous extraplanar emission can be interpreted as the result of feedback, in the form of large-scale winds for starbursts or smaller-scale galactic fountains for main-sequence galaxies. Moreover, shock-heating may ionise gas at the interface of the disk and the circumgalactic medium, independent of the source of the gas.

Stellar feedback drives multiphase gas outflows from starburst galaxies, but the interpretation of dust emission in these winds remains uncertain. To investigate this, we analyze new JWST mid-infrared images tracing polycyclic aromatic hydrocarbon (PAH) emission at 7.7 and 11.3 μ m from the outflow of the prototypical starburst M82 out to 3.2 kpc. We find that PAH emission shows significant correlations with CO, H α , and X-ray emission within the outflow, though the strengths and behaviors of these correlations vary with gas phase and distance from the starburst. PAH emission correlates strongly with cold molecular gas, with PAH–CO scaling relations in the wind nearly identical to those in galaxy disks despite the very different conditions. The H α –PAH correlation indicates that H α traces the surfaces of PAH-bearing clouds, consistent with arising from ionized layers produced by shocks. Meanwhile, the PAH–X-ray correlation disappears once distance effects are controlled for past 2 kpc, suggesting that PAHs are decoupled from the hot gas and the global correlation merely reflects the large-scale structure of the outflow. The PAH-to-neutral gas ratio remains nearly flat to 2 kpc, with variations following changes in the radiation field. This implies that the product of PAH abundance and dust-to-gas ratio does not change significantly over the inner portion of the outflow. Together, these results demonstrate that PAHs robustly trace the cold phase of M82’s wind, surviving well beyond the starburst and providing a powerful, high-resolution proxy for mapping the life cycle of entrained cold material in galactic outflows.