Star Formation, Stellar Feedback, and the Ecology of Galaxies

Official opening of the conference

Introductory remarks

Starting as an amateur in my teen years, I became fascinated by the beauty and nature of the cosmos. During my career I've witnessed the amazing transformation of astronomy from a mostly visual-wavelength endeavor into the multi-spectral and multi-messenger discipline of today. After a short personal "history", I will review the "feedback ladder" of ever-more powerful mechanisms in the self-regulation of star formation and the "Galactic ecology" - the cycling of atoms through the phases of the interstellar medium (ISM), into stars, and back into the ISM. Feedback and N-body dynamics play important roles in establishing stellar masses, the Initial Mass Function (IMF), and the formation of star clusters. I will comment on current challenges and the importance of physics and astrophysics to our technology and economy.

We search for potential "birthmarks'' left from the formation of filamentary molecular clouds in the Ophiuchus, Lupus, Pipe Nebula complexes. We find two distinct types of filaments based on their orientation relative to nearby massive stars: radial (R-type) and tangential (T-type). R-type filaments exhibit decreasing mass profiles away from massive stars, while T-type filaments show flat but structured profiles. We propose a scenario where both filament types originate from the dynamic interplay of compression and stretching forces exerted by a fast outflow emanating from the OB association. The two formation mechanisms leave distinct observable "birthmarks'' (namely, filament orientation, mass distribution, and star formation location) on each filament type. Our results illustrate a complex phase in molecular cloud evolution with two simultaneous yet contrasting processes: the formation of filaments and stars via the dispersal of residual gas from a previous massive star formation event. We will also present preliminary analysis of the Taurus cloud complex.

The ALMA large program ALMAGAL has surveyed more then 1000 candidate high-mass star-forming regions in our Galaxy, based on properties revealed by the Herschel survey of the Milky Way, Hi-GAL. This large data set allows to derive statistically robust properties of a representative sample. I will present first results on the impact of radiative and mechanical feedback by discussing statistics on temperature distributions, the correlation with HII regions and outflow properties.

Accretion driven outflows play a fundament role in star formation, reducing the star formation efficiency, shaping the initial mass function, and regulating the rate of star formation in clouds. Despite the importance of this mode of feedback, substantial questions remain, particular for the deeply embedded phases of star formation. Questions such as what is the nature of the wide angle wind component of the outflows, how is the momentum from the outflows coupled to the surrounding envelopes, and how do the outflows vary in time and with stellar mass?

JWST, with its ability to obtain 2.9-27 micron IFU spectral imaging, is now detecting warm gas in jets and winds via ionic, atomic and molecular tracers. We will present observations made in the Cycle 1 Investigating Protostellar Accretion (IPA) program, a 65 hour program observing five Class 0 protostars with keplerian masses of 0.12 to 12 solar masses.

For the 0.12 to 2.5 solar masses protostars, these observations show high velocity jets (150 km s-1) in lines of shocked ionized gas such as [FeII]. Although the jets are primarily traced in ionic lines, they contain knots or regions of molecular emission indicating molecules can be launched, entrained, or formed in the jets. Surrounding the jets are lower velocity winds (20 km s-1) traced in molecular hydrogen and other molecules such CO, CO2 and H2O. Using 1D shock models, we are constraining the mass, momentum and energy flows of the jets/winds as a function of the stellar mass and luminosity.

We will also discuss the Cycle 3 program High angular resolution observations of stellar Emergence in Filamentary Environments (HEFE), a 180 hour program targeting the OMC2/3 region of Orion with a combination of NIRCam imaging and NIRSpec and MIRI IFU observations, merged with ground-based data, to provide a comprehensive portrait of accretion and feedback in this highly active SFR. Observations are scheduled for this winter, and we will show initial results.

Precise large-scale astrometric data have provided a fresh perspective of star forming regions, which encode key information on cloud formation processes and stellar evolution. We can now resolve their non-trivial star formation histories in great detail for the first time. The well-studied Orion star forming region is a prime example of the complexity associated with the star forming process. However, despite its importance, a comprehensive mapping and characterization of its stellar populations, including the embedded Young Stellar Objects (YSOs), is still lacking.
In my talk, I will present a homogeneous, holistic spatio-kinematic analysis of the Orion region based on Gaia mDR3 data. Leveraging the Significance Mode Analysis (SigMA) clustering algorithm, specifically tailored to 5D positional and kinematic phase-space data, I aim to contribute to a deeper understanding of Orion’s complex structure and evolution. We find that the region separates into ~40 co-spatial and co-moving stellar groups (> 15,000 stars). Compared to other works, we validate most previously found groups, but often reach 50-100% richer member counts, and also discover ~8 new groups. Estimating the age of each group, we discuss possible coherent age-position patterns, as were found for the Sco-Cen OB association.
Orion also comprises active star forming sites with extended nebulosity, such as the Flame Nebula. The YSOs embedded there are excellent gas motion tracers, but are mainly visible in the Infrared. Using ESO data from three surveys, we successfully calculate proper motions on the order of 1 mas/yr for the YSOs at ~400 pc and perform a kinematic analysis for the Flame Nebula.
I will conclude with a high-resolution star formation history of Orion, revealing a rich tapestry of sub-populations with distinct kinematics and ages. I will also summarize and discuss the motion trends we find for different YSO classes in the Flame Nebula and their implications on the evolution of the cluster.

The sensitivity upgrades of both the NRAO Very Large Array (VLA) and the Very Long Baseline Array (VLBA) have begun to provide us with a much improved perspective on stellar centimeter radio emission, particularly concerning young stellar objects (YSOs), in ideal preparation for ngVLA and SKA science. For the first time we now have systematic access to the cm-radio time domain on short timescales and the possibility to disentangle thermal and nonthermal emission. I will mainly present an update on the Orion Radio All-Stars, an ongoing project targeting the star-forming Orion Nebula Cluster (ONC) with the VLA, VLBA, and ALMA, including a radio perspective of the Orion explosion and John's related work. I will first present the increasingly well-characterized ONC radio sample, including first constraints on YSO radio flares and their relation with X-ray flares, as well as on the resulting high-energy irradiation of their surroundings. I will then focus on a VLBA non-thermal variability survey of all identified VLA targets in Orion in the largest such survey of YSO emission to date, enabled by software correlation - currently in a coordinated joint VLBA-Chandra large program to look for radio emission from coronal mass ejections following X-ray megaflares. Other than providing a nonthermal census, I will additionally discuss the use of the VLBA for precision stellar astrometry in the Gaia era. I will conclude with a complementary look at variable YSO millimeter continuum emission in the ONC, targeting synchrotron flares in this new window on high-energy processes in YSOs, using ALMA.

Giant Herbig-Haro jets have parsec-scale dimensions and thus provide a fossil record of the accretion history of their sources. The
morphology of these major outflows is well explained as the result of a newborn triple system that breaks up, leading to an eccentric binary that spirals in, with accretion and outflow events at each
increasingly close periastron passage. The end result is likely a
spectroscopic binary, but if enough dissipation occurs, the binary
components may merge in a major explosion. I will present evidence for the first such case of a merger event in young low mass stars and discuss the properties of the peculiar star that has resulted. The dynamical interactions that lead to such events play a major role in determining the final masses of the stars involved. Given the ubiquity of young multiple stars, this supports the idea that such processes have an important impact on the shape of the IMF.

The Orion Nebula forms a cornerstone of our understanding of star formation, and it rightly is the first region we look at when commissioning almost any new telescope or instrument. The BN/KL nebula is the infrared nebula bright in lines of molecular hydrogen that lies behind the ionized Orion Nebula along the line of sight. John has led observations of this unique explosive source for several decades, and he proposed the leading models that challenge our ideas of how stars form. The current best model is that, around 500 years ago, three stars coexisted in a non-hierarchical multiple system that underwent a cataclysmic decay, which flung out both the stars and the nebula. I'll describe the observations, the proper motion measurements, the modeling work that justifies the hierarchical decay model, the hydrodynamics of the 'bullet' system, and the broader implications of this one dynamical interaction for theories of star formation.

Protostellar jets play a pivotal role in injecting matter and momentum into their environment, influencing regions several parsecs in size. This feedback mechanism significantly impacts the dynamics, morphology, and fragmentation of molecular clouds, which in turn, affects the formation of subsequent protostars. Understanding how jets regulate accretion processes and filamentary structures is critical for accurately modelling star formation. In this submission we present a novel subgrid model within the widely-used hydrodynamic simulation code, AREPO, to simulate protostellar jet feedback. Our approach injects mass and momentum into conical volumes near the sink particles, with adaptive mesh refinement ensuring numerical consistency. This methodology enables an investigation of the interplay between jet-driven feedback and filamentary evolution. Areas of particular interest include the alignment between the jets and the filaments; the impact on the lifetime of the filaments by the jets; and measuring the correlation between the abundance and strength of the jets with the star formation efficiency. Ultimately, this work aims to enhance the predictive power of simulations, bridging the gap between theoretical models and observations.

Protostellar outflows originate within a few au (or less) of the forming star and may reach linear sizes of a few parsecs. As they travel through the dense infalling envelope, they push and accelerate the ambient gas, thereby injecting energy and momentum into their surroundings. This feedback may have its most important effect on the star formation process in regions within about 10,000 au of the protostar, where most of the forming star's mass reservoir resides. We present results from an ongoing survey of the environment surrounding a large sample of protostars at different evolutionary stages in the Orion A molecular cloud. This study uses new multi-line ALMA data to probe the envelope scales, and data from the CARMA-NRO Orion survey to study the larger (core and cloud) scales. We use the molecular line data to derive the angular distribution of molecular outflow momentum and energy, and obtain two-dimensional instantaneous mass, momentum, and energy ejection rate maps using a novel approach. Our results indicate that by the end of the protostellar phase, outflows will remove about 3 to 4 solar masses from the surrounding low-mass core. These high values indicate that outflows remove a significant amount of gas from their parent envelopes and cores and continuous core accretion from larger scales is needed to replenish material for star formation. Furthermore, we show that cavity opening angles, as well as the angular distribution of outflow momentum and energy increase with the protostars' evolutionary stage. This is clear evidence that protostellar outflows significantly disrupt their natal cores, ejecting a large fraction of the mass that would have otherwise fed the nascent star. Our results support the conclusion that protostellar outflows have a direct impact on how stars get their mass, and that the natal sites of individual low-mass star formation are far more dynamic than commonly accepted theoretical paradigms.

Massive stars play an essential role in the Universe. They are rare, yet the energy and momentum they inject into the interstellar medium (i.e., stellar feedback) dominate the energetics of star-forming regions, impacting both star and galaxy formation. Massive stars form from the gravitational collapse of magnetized, dense, and turbulent molecular gas in Giant Molecular Clouds (GMCs). During their formation, feedback mechanisms – including intense radiation fields, collimated protostellar outflows, and fast stellar winds – may limit their growth by accretion. Understanding this complex interplay requires detailed radiation magnetohydrodynamic (RMHD) simulations. In this talk, I will present how simulations have advanced our understanding of massive star formation and describe the impact and importance of these feedback processes. Additionally, I will discuss how such simulations can help interpret multi-wavelength observations and motivate how massive stars most likely form in regions within GMCs that are supplied mass via large-scale, high ram-pressure dynamical inflows in agreement with observations of massive star-forming regions.

Most stars and planets form in clusters/associations with hundreds of low-mass stars and their associated planetary systems forming alongside each high-mass star. UV radiation from the highest mass stars permeates these regions and will illuminate, heat, and evaporate the planet-forming disks around nearby low-mass stars from the outside-in. This reduces the time and materials available to make planets. By removing this reservoir of planet building blocks, external UV irradiation may lead to lower final planet masses and more compact orbital architectures built out of disks with markedly different chemistry. Detailed observations of a few objects demonstrate the profound effect that external photoevaporation can have on disks, but not the scope or scale of its impact more generally. Fortunately, new instruments have unlocked the high-mass star-forming environment, permitting observations of thousands of low-mass stars in a wide range of UV environments. In the coming years, these studies will transform the landscape, providing detailed constraints on how external UV affects the disk lifetime, the chemistry in disks, and ultimately the demographics and habitability of planets.

In order to quantify how a molecular cloud responds on subarcsecond scales when subjected to a powerful radiation front in a region of massive star formation we have acquired high-resolution ALMA maps of the continuum and 12CO, 13CO, C18O, and CI line emission in a portion of Carina's iconic Western Wall (G287.38-0.62; Car 1-E), situated near Trumpler 14 and well-known as the brightest H2-fluorescence source in the region. In addition to clearly demonstrating the physics within a PDR front, these data allow us to separate the Wall from foreground and background clouds. Within the Wall we identify coherent gas 'droplets' on small scales and compare their mass and virial distributions with those of cores located in less-irradiated environments. The observations are ideal for studies of turbulence, and make it possible to investigate correlation lengths and driving scales. There is no direct evidence for triggering of star formation in the Western Wall in that its C18O clumps and continuum cores appear starless, with no pillars present. However, radiation helps create conditions more suitable for star formation, in that the densest portion of the cloud lies closest to the PDR, and the C18O emission flattens along the radiation front.

The Carina Nebula Complex (CNC) is a spectacular star-forming region located at 2.3 kpc, which is close enough to observe different size scales in detail. With more than 65 O-stars and more than 900 young stellar objects identified it is also the nearest analogue of more extreme star forming regions, such as 30 Doradus. In this talk I will present the results of a major effort to study the relationship between the different gas phases in the Carina region from 100 pc to 0.01 pc using the Australia Telescope Compact Array (ATCA), the Mopra telescope and ALMA.  At large scales, CO image combined with far-infrared data from Herschel revealed the overall molecular mass and its distribution across the CNC (Rebolledo et al. 2016).  An extremely detailed map of the HI 21-cm line across the whole nebula revealed a complex filamentary structure in the atomic gas, which allowed the identification of regions where phase transition between atomic and molecular gas is happening (Rebolledo et al. 2017). An ATCA 1-3 GHz radio continuum image across the whole Carina region revealed a complete and spectacular view of the ionized gas in the region (Rebolledo et al. 2021).  At small scales, ALMA high spatial resolution observations of molecular line tracers and dust showed that the level of stellar feedback effectively influences the fragmentation process in clumps, and provides further evidence for a higher level of turbulence in the material with a higher level of massive stellar feedback (Rebolledo et al. 2020). Recent Cycle 10 ALMA observations have complemented this view with information of the denser gas distribution, temperature, level of photo-dissociation and chemistry of the molecular gas. Additionally, I will be reporting a recent all-CNC survey of dense clumps with ALMA which will shed light on the dependence of the star-formation threshold on the level of turbulence and external pressure across the whole molecular complex.

The interaction of massive stars with their environments regulates the evolution of galaxies. Specifically, through their radiation and their winds, massive stars disrupt their environment and disturb their nascent molecular cloud.

The combination of the sensitive THz heterodyne receiver arrays upGREAT with a nimble telescope on SOFIA enabled large-scale [CII] 158 μm surveys of regions of massive star formation. This line is the main cooling line of neutral gas in the interstellar medium and therefore a key diagnostic of the interstellar gas energy balance. It also provides a unique window on stellar feedback. The high spectral resolution inherent to heterodyne techniques allows a detailed study of the kinematics of photodissociation regions, which separate ionized from molecular gas.

Comparing and contrasting three regions with different types of stellar feedback allows to identify universal and environment-specific features of stellar feedback: The Horsehead Nebula in the Orion B molecular cloud is being compressed and evaporated by a previously-formed nearby massive star (Bally et al. 2018), while the Orion Nebula, the closest region of massive star formation, situated in the Orion A molecular cloud, contains multiple nested expanding shells being blown by a single massive star in its core. 30 Doradus in the LMC, on the other hand, is the nearest birth site of a super star cluster, where ~1000 OB stars are disrupting the molecular cloud in which they were formed. The [CII]-emitting structures in Orion can be studied in large spatial detail, while in 30 Doradus, a significant amount of the input mechanic and radiative energy is dissipated on scales smaller than 14” (3.4 pc at a distance of 50 kpc), the resolution of SOFIA at 158 μm, as has previously been suggested by observations of the ionized gas. This renders the lines broader than expected from observations of Orion. In my talk I will review differences and similarities in these regions.

FEEDBACK was a legacy program conducted with SOFIA, targeting 11 high-mass star-forming regions through observations of the [CII] 158 μm and [OI] 63 μm emission lines. Here, we highlight key findings from the FEEDBACK survey, with a focus on ongoing and future projects.

Spectrally resolved [CII] observations of HII region bubbles confirmed the detection of fast-expanding (v>10 km/s) [CII] shells driven by stellar winds (e.g., Luisi et al. 2021). More recently, we identified a slowly expanding (v<3 km/s) [CII] shell and a ring, respectively, associated with both the earliest (Keilmann et al. 2025) and terminal (Dannhauer et al., in prep) evolutionary stages of [CII] bubbles. Current work is focused on establishing an evolutionary sequence of [CII] bubbles, exploring their dependence on environmental properties, and investigating the physical processes driving their expansion.
We will also demonstrate the usefulness of the CII line to trace CO-dark, large-scale colliding flows of atomic and molecular gas that built up molecular clouds (Schneider et al. 2023).

We propose new projects aimed at addressing critical questions, including:
- Determining the factors that govern whether a molecular cloud is dispersed or new star formation is triggered.
- Developing sophisticated models of photo-dissociated gas using additional, unpublished SOFIA data, including high-J CO transitions and the CI 1–0 lines.
- Assessing the heating efficiency of gas traced by the [CII] and [OI] lines to test theoretical models of gas heating mechanisms.

To support these efforts, the newly established SOFIA Data Center in Stuttgart, which we present shortly, will provide high-quality data products from most SOFIA instruments.

The PhotoDissociation Region Toolbox is an open-source, science-enabling tool for the community, designed to help astronomers determine the physical parameters of photodissociation regions (PDRs) from observations. It is written in Python, using packages familiar to most astronomers, such as astropy, numpy, and matplotlib, with ease-of-use as a key goal. As such, it has become an essential tool for assessing feedback in Galactic and extragalactic star-forming regions. In this talk, I will review the tools and models currently available in the Toolbox and preview some upcoming features. http://dustem.astro.umd.edu

Massive stars strongly impact their environment, shaping structures on all scales throughout the universe and impacting subsequent generations of star formation, in a process known as feedback. Since most massive stars form in binary systems, it is crucial to understand how binary interactions modify the feedback properties of stellar populations, both before and during their supernova (SN) phase. The energy, momentum, and mass returns—key components in models of galaxy formation and dynamics—are heavily dependent on the evolutionary pathways a binary system may follow and on metallicity. This highlights the importance of studying not only individual stars or binary systems but also how feedback operates collectively across entire stellar populations in galaxies. To address this, we conduct a binary population synthesis study using the next generation POSYDON code, built on high-precision MESA binary models, to quantify the energy, momentum, and mass ejected by stellar populations across a wide range of metallicities and over time. This study accounts for all possible evolutionary channels and incorporates various updated SN prescriptions. Our findings reveal that a significant fraction of stars are able to explode much earlier or later in time through binary interactions compared to a single-star population, significantly altering the SN feedback in high-metallicity environments. At lower metallicities, these interactions delay the timing of pulsational pair-instability and pair-instability SNe, influencing early energetic outputs. Binary systems also greatly enhance pre-SN feedback, increasing the mechanical energy budget and mass loss, particularly at low metallicities. This enhancement is primarily driven by delayed winds from merged products and mass transfer processes. Comparing our results with prior studies, we highlight how binary evolution fundamentally reshapes energy, momentum, timing, and mass yields, profoundly impacting their host galaxies/enviroments

Galaxies are in constant evolution, under the influence of the gas-star matter cycle within them. However, the exact physical mechanisms driving this multi-scale cycle remain elusive, due to a lack of observational constraints. By combining high-resolution, multi-wavelength observations from a broad range of galactic environments, I will present how we can characterise for the first time the successive steps of this cycle, from the assembly of dense gas clouds from the diffuse interstellar medium, to the successive collapse, star formation and dispersal by stellar feedback redistributing matter and energy back into the diffuse medium. I will show that molecular clouds are rapidly destroyed by pre-supernova stellar feedback (within 1-5 Myr), which drastically limit their star formation efficiency to 2 to 10%, depending on the galactic environment. The vast majority of momentum and energy emitted by the young stellar populations escapes the parent cloud, affecting galaxies on large scales. This comprehensive analysis sheds new light on the matter cycle within galaxies, revealing its underlying processes and quantitative characteristics. I will conclude by showing how these measurements provide critical constrains to improve the description of the unresolved processes of star formation and feedback in galaxy formation and evolution simulations.

Stellar feedback plays a crucial role in shaping the structure and evolution of galaxies, influencing star formation, interstellar medium (ISM) dynamics, and large-scale galactic outflows. This review examines recent advancements in numerical simulations of stellar feedback and their implications for the ecology of galaxies.

We discuss key feedback mechanisms, including supernovae explosions, stellar winds, (ionising) radiation and radiation pressure, as well as the role of cosmic rays, and touch upon common implementations in state-of-the-art simulations. The review highlights the challenges in modeling feedback across multiple scales, from resolving individual star-forming regions to capturing global galactic flows.

The wavelengths and sensitivity of JWST have opened a unique window to study the emergence phases of star clusters, as stellar feedback rapidly disrupts the natal molecular clouds—at physical scales previously inaccessible beyond our Galaxy. I will review recent results obtained from combined JWST and HST observations of galaxies spanning the full range of star-forming environments observed in the local universe. Embedded star clusters are now routinely detected in association with 3.3 µm PAH emission and exhibit physical properties indicative of an evolutionary sequence linking them to optically visible star clusters. From the earliest embedded stages, star clusters appear to follow a power-law mass distribution with a slope of –2, consistent with that of optical counterparts.

I will discuss the emerging picture of an evolutionary sequence in which photodissociation regions rapidly fade, giving way to classical H II regions driven by stellar feedback form star clusters. The 3.3 and 7.7 µm polycyclic aromatic hydrocarbon (PAH) bands are found to be sensitive tracers of the earliest phases and typically vanish within ~4 Myr at the locations of emerging star clusters. Evidence suggests that the timescale for emergence varies across galactic environments, with an average of ~6 Myr. This implies that supernovae (SNe) are likely to explode in a medium already shaped by photoionization and stellar winds, potentially exerting a significant impact on the galactic-scale interstellar medium (ISM). Using the FUV spectra of the intervening ISM absorption lines of star clusters in local galaxies, we see: 1. varying coupling efficiency between stellar feedback and surrounding gas, 2. a clear link between cluster mass and the outflow velocities powered by star cluster feedback, 3. and bubbles driven by SNe feedback in line with several studies conducted in the literature.

Feedback from massive stars plays a central role in shaping the evolution of galaxies. Conversely, different galactic environments play a central role in regulating the impact of massive stars. Yet, despite a solid qualitative understanding of feedback, our quantitative knowledge remains poor. Until recently, only a few star-forming regions had adequate observational information on gas and stars needed for detailed stellar feedback studies.
Over the past decade, integral field units (IFUs) have revolutionized our approach to resolved stellar feedback studies in nearby galaxies. In this talk, I will present recent results of large IFU nearby galaxy surveys and discuss how these enable an empirical quantification of the interdependence between stellar feedback and the environments massive stars form in. They also allowquantifying the importance of pre-supernova feedback in regulating the impact of subsequent SN explosions.

Massive star clusters are fundamentally important sources of stellar feedback and chemical enrichment in galaxies. They regulate star formation, drive galactic outflows and may even be significant sources of ionizing radiation during the epoch of cosmic reionization. In the GRIFFIN project (Galaxy Realizations Including Feedback From INdividual massive stars) we examine the formation and evolution of resolved star clusters up to the mass range of globular clusters using high-resolution (sub-parsec, star-by-star) hydrodynamical simulations of low-metallicity dwarf galaxies. The simulations account for the radiation, stellar winds and supernovae of individually realized stars. We have shown that massive star clusters form hierarchically and rapidly over time-scales of less than 10 Myr. During formation, the clusters can be self-enriched in light-element-rich stellar winds of very massive stars, while supernova ejecta escape in metal-enriched outflows. Recently, we supplemented the methodology with a regularized integrator to accurately solve the stellar gravitational dynamics on small spatial scales. This was shown to be critically important for the modelling of more realistic star cluster life cycles from formation until disruption in the tidal field of the host galaxy. In this talk, I will discuss some of the key results of GRIFFIN and future avenues toward unravelling the cosmic origin and role of globular clusters.

Molecular clouds (MCs) are known to be supersonically turbulent, and this turbulence has long been associated with maintaining the clouds in near virial equilibrium with their self-gravity. However, recent observations and simulations indicate that MCs lie at the intersections of shells, suggesting that they are actually formed by the collision of the shells. But clearly this mechanism cannot apply to the first generation of stars that formed the shells. In this contribution, I will discuss the evolution of molecular clouds and their star formation activity in the galactic context from the standpoint of a continuous gas flow entering the gravitational potential of a stellar spiral arm. Warm atomic gas entering the arm suffers a phase transition to the cold phase, and continues to be compressed to become molecular and gravitationally contracting. As a consequence, the star formation rate increases and massive stars begin to form after a few Myr. The virial parameter is of order unity during the contraction stage. The feedback is capable of dispersing the remaining gas, pushing the virial parameter to large values, and reducing or stopping the local star formation episode, while collecting the dense gas somewhere else. This reinitiates the cycle somewhere else, possibly with weakening strength, until the gas leaves the spiral arm, leaving behind some molecular shreds that may survive into the interarm region.

Galactic-scale simulations rely on sub-grid models to provide prescriptions for the coupling between supernova (SN) feedback and the interstellar medium (ISM). Many of these models are computed in 1-D to allow for an efficient way to account for the variability of properties of their local environment. However, small-scale simulations revealed that the release of energy from SNe within molecular clouds can be highly asymmetrical. This is largely due to the presence of pre-SN feedback, such as ionizing radiation, that are able to carve cavities and channels around the progenitors prior to their detonation. Being partially confined, the SN energy escapes into the outer ISM preferentially through these channels, departing from the spherically symmetric 1-D descriptions. In this talk, I will present our novel analytical and numerical models for a semi-confined SN. I will show that this mode of energy release increases the local dynamical impact of the outflows, and extends the timescales over which the SN is energetically coupled to the surrounding matter.

Molecular gas is a cornerstone of the star formation cycle in galaxies, yet mapping its distribution and properties remains a significant challenge. In this talk, I will present new JWST observations of 55 nearby galaxies obtained as part of the PHANGS-JWST survey, bringing the total coverage to 74 galaxies. I will show new results leveraging the unparalleled sensitivity and resolution of these new JWST data to trace cold gas through infrared emission from polycyclic aromatic hydrocarbons (PAHs). This approach offers a powerful alternative to traditional tracers like CO, particularly in terms of sensitivity and resolution, and possibly even in regions where CO cannot be used as a gas tracer.

I will highlight two key outcomes of this research: First, I will showcase results from Chown et al. (2025), where we demonstrate a strong correlation between JWST PAH emission and ALMA CO(2-1) observations at ~100 pc resolution across 70 nearby star-forming galaxies from the PHANGS sample. This work establishes PAH emission as a robust tracer of cold gas, revealing filaments, shells and other structures in this gas with sharper resolution and better sensitivity than ALMA. PAH emission also traces HI gas, opening exciting new avenues for studying the interstellar medium. Second, I will present ongoing efforts to measure how regional variations in the radiation field, dust to gas ratio, and PAH abundance modulate the PAH-vs-gas relation.

This work not only advances our understanding of the cold gas content in galaxies but also paves the way for future JWST observations to map the gas in the universe with unprecedented detail. I will conclude by discussing the broader implications of this approach for studies of star formation, feedback, and galaxy evolution.

We investigate the kinematics and star formation history of Scorpius-Centaurus (Sco-Cen), the nearest OB association to Earth, using Gaia DR3, APOGEE-2 DR17, and GALAH DR3 data. We focus on the sequentially aligned chains of clusters within Sco-Cen, including the Corona Australis (CrA), Lower Centaurus Crux (LCC), and Upper Scorpius (Upper Sco) chains. Our study reveals that all three cluster chains exhibit distinct patterns in 3D spatial alignment, ages, relative velocities, and masses. We propose a scenario where stellar feedback from the most massive star formation episode 15 Myr ago initiated the formation of these spatio-temporal cluster sequences. Their well-defined physical properties can be explained by their progenitor molecular clouds being continuously affected by feedback over 5–10 Myr. Approximately 40% of the stellar population in Sco-Cen formed through triggered star formation, with 35% forming along the three observed cluster chains. We propose that cluster chains are common structures in OB associations like Sco-Cen. Finally, we can isolate the feedback-induced acceleration of the CrA molecular cloud beyond the acceleration caused by the Galactic gravitational potential. This represents a first data-based measurement of molecular cloud acceleration driven by stellar feedback. Our results show the significant impact of stellar feedback on the spatial distribution and kinematics of OB associations like Sco-Cen.

How does exploring the boundaries of human knowledge of space bring us closer together as humans on earth?

From the New Horizon's Pluto and extend mission to more recent launch of the Lucy spacecraft to study to the Trojan Asteroids, amateurs have supported science both in the field and off the field. Our joint and fundamentally human quest to explore and understand not only provides the science critical for steering spacecraft, but brings together communities across the globe.

The MDW H-alpha Survey

Amateur Contributions to Astronomy

Star formation is a fundamental astrophysical process, influencing phenomena at many different scales. In turn, star formation is driven by a wide range of physical mechanisms: stars form in the cold, dense gas of molecular clouds, and this gas is self-gravitating, turbulent, and magnetized. Newly forming stars then produce stellar feedback in the form of protostellar jets, which alter the properties of the star-forming region and subsequent star formation. As stars progress to the main sequence, they produce radiative feedback and stellar wind feedback, which drastically alter the properties of the interstellar medium. Finally, stars reaching the end of their lives explode as supernovae, which can halt local star formation, form large bubbles in the interstellar medium, and drive interstellar turbulence at large spatial scales and longer time scales. Out of this turbulent interstellar medium, new self-gravitating and turbulent molecular clouds form, collapse, and begin to form another generation of stars. In this talk, I will explore what we know from both observations and simulations about how each of these different feedback mechanisms drive interstellar turbulence - and how this turbulence in turn shapes star formation.

Significant progress has been made in characterizing the star formation (SF) timeline in Giant Molecular Clouds (GMCs), taking advantage of high-resolution multi-wavelength observations and robust statistical methods that contrast tracers of molecular gas (e.g., CO) with tracers of SF (e.g., Ha). However, our understanding of the early feedback phase, when stars are still embedded in gas and dust, has been so far limited by the lack of high-resolution infrared data. This is now possible with the spatial resolution and sensitivity provided by JWST.

Using 30 galaxies from the PHANGS-JWST survey, we aim to derive new constraints on the physical mechanisms associated with early feedback and the emergence of clusters from their birth clouds. We derive the total duration of the dust-emitted 21um emission and find that it correlates with the averaged mass and velocity dispersion of the GMCs, with evidence for secondary dependencies on galactic morphological type and metallicity. Regardless of these variations, we find that the deeply embedded phase of the SF is short in all galaxies in our sample, with a maximum of only 5 Myr in the most metal-rich environments.

Our results indicate a rapid - sometimes absent - transition from the embedded to the exposed phase of SF in a sample of nearby star-forming galaxies covering a wide range of physical conditions. I will discuss what physical processes could be responsible for these short timescales, and how additional spectroscopic information can help to disentangle different scenarios.

Although substantial progress has been made in our understanding of star formation, the impacts of environment is still of great debate. The intricate interplay of infall, outflows, stellar winds etc. could strongly affect the final outcomes of the star formation processes. In particular, does the environment have an impact on the Initial Mass Function, the binary fraction produced, and the evolution of circumstellar disks? The answers have profound implications for our understanding of planet formation, the mass to light ratios of stellar populations, and the dynamics of star clusters.
To push the studies to more extreme (and more distant) regions than the typical low-mass star forming regions near the sun, sensitivity and spatial resolution is paramount to resolve the cluster content to low mass.
Here we present observations of young massive clusters in the Milky way and the Large Magellanic Cloud using a combination of adaptive optics ground-based observations, HST, and JWST observations. Covering a range in cluster mass of over 10 and a factor of over three in metallicity, we have derived mass functions and disk fractions, reaching well into the brown dwarf regime within the Galaxy. We discuss the IMF as a function of cluster metallicity, the disk fraction as a function of metallicity, cluster mass, and age and show the effects of environment through comparison with nearby regions.

Outflowing gas driven by star formation plays a critical role regulating star formation and contributing to the baryon cycle. However the details of this stellar feedback process are still unclear, particularly in starbursting environments. To better constrain feedback models used to understand galaxy evolution, high resolution IFU observations are needed to spatially resolve star formation-driven outflow properties and link these to co-located galaxy properties. I will present results from the DUVET survey of starbursting galaxies observed using the IFU KCWI. We measure outflows in 10 face-on local galaxies with ~1000 lines of sight of individual outflow measurements at 500pc resolution. Using our observations, we are able to discriminate between widely used models of the launching mechanism of the outflow. We derive much needed scaling relations for the relationship between star formation and outflow properties across a range of star-forming environments, and compare these to simulations. We compare to observations from NOEMA, and connect the outflows with location in the resolved Kennicutt-Schmidt relation to find that starburst regions remove more gas via the outflow than they convert into stars. This directly measures how outflows regulate star formation and contribute to the baryon cycle. DUVET's unprecedented sample of resolved outflows provides a new perspective to make ground-breaking constraints on how stellar feedback regulates star formation, contributes to the baryon cycle, and drives galaxy evolution.

Galaxies and clusters of galaxies show remarkably tight scaling relations between their global properties. These cannot be explained by purely gravitational processes, and are instead attributed to the feedback effects of massive stars and supermassive black holes on the surrounding baryons. In this talk I will summarize how stars and black holes provide feedback. I will then outline the construction of a global inventory of the amount of energy released by massive stars and supermassive black holes over cosmic time. Finally, I will assess the impacts of these two energy sources, identifying which one is most important for the specific observed scaling relations.

We exploit the unprecedented capabilities of JWST in the MIR, using the MIRI/MRS, performing a spatially-resolved study of the multi-phase ISM in the heart of the face-on spiral galaxy M83. Our detailed analysis probing the distribution of the multi-phase gas on spatial scales ~5 pc, is uncovering the effect recently-formed massive stars, observed with HST/COS, have on the reservoirs of gas and active star formation. We will report on the intriguing first detections of [Ne V] 14.3 micron and [Ne VI] 7.7 micron in this starburst region. We find that photoionization models of fast radiative shocks are able to reproduce the observed emission line fluxes only for the lowest preshock density available in the library. Additionally, comparison with tailored active galactic nuclei (AGN) photoionization models assuming a two-zone structure confirm that the observed high ionization fluxes are also compatible with emission expected from a cloud ionized by the radiation cone of an AGN. Previously known as a purely starburst system, these new findings on M83 demand a reassessment of its nature, and of objects similar to it, particularly now that we have access to the unparalleled infrared sensitivity and spatial resolution of JWST.

We ask the question whether supernovae created by young and massive stars within Nuclear Star Clusters (NSCs) can feed Supermassive Black Holes (SMBHs) at the centers of galaxies. We use numerical simulations showing that supernovae occurring near the galaxy rotational axis or inside Circum Nuclear Disk (CND) supply to the vicinity of the central accretion disk surrounding the SMBH the supernova ejecta combined with the mass collected from the interstellar medium by the expnading supernova expanding shells. The mass deposited by individual supernovae varies between 1 and a few 100 solar masses depending on the position of the supernova and on the density of the ambient medium. Supernovae occurring in the aftermath of a starburst event can deposit 10^3 - 10^6 Msun into the vicinity of the accretion disk within 30 Myrs. The fate of that mass is split between the growth of the SMBH and outflow from the nuclear accretion disk.

According to the Jeans Criterion, the temperature of the dense gas, from which stars form, has a major impact on the masses of the cores (and stars) that result from the fragmentation of the gas. Feedback from the massive star population of freshly formed massive young clusters could be expected to have a significant impact on the dense gas physical properties surrounding these clusters and skew the stellar mass function resulting from star formation in such an environment. Star formation in the early Universe and around cosmic noon proceeded with a much more significant share of stars formed in starburst environments involving the formation of massive clusters, hence we could expect differences in the resulting stellar mass spectrum, if compared to, e.g., local Universe galaxies such as our Milky Way, which features hardly any objects that could be termed young massive clusters.

We here explore to which extent thermal feedback from the massive star population in young massive clusters could potentially affect the outcome of further star formation in adjacent clouds due to heating the dense gas forming the next generation of stars. We use H2CO to measure the dense gas temperature distribution around a small sample of galactic young massive clusters. We find clear gradients - temperature falling with distance over scales of several parsecs - for NGC3603, RCW38, and DBS[2003]179, indicating that indeed feedback can have a profound impact on the dense gas temperature. To complicate the picture, however, we also find evidence for very cold (20K) gas even in the massive, 60K warm clumps directly exposed to the NGC3603 starburst cluster from N2H+ observations! This finding calls for a discussion on whether or not cold, dense gas or rather warm gas forms the next generation of stars in starburst environments, and whether this could have an effect on the resulting stellar initial mass function.

I will give an introduction to star formation and gas dynamics in the central regions of the Milky Way. This region hosts a complex dynamical ecosystem that is continually exchanging matter with the rest of the Galaxy through inflows and outflows. The Galactic bar efficiently transports gas from the Galactic disc towards the centre at a rate of ~1 Msun/yr, creating a ring-like accumulation of molecular gas known as the Central Molecular Zone (CMZ) at a radius R=120pc. The CMZ is the local analog of the star-forming nuclear rings commonly found at the centre of external barred galaxies. Once in the ring, approximately 10% of the gas is consumed by intense star formation activity. Star formation does not occur uniformly throughout the CMZ ring, but is more likely to occur near the sites where the bar-driven inflow is deposited. The star formation rate of the CMZ varies as a function of time, but it is currently debated whether this is due to an internal feedback cycle or to external variations in the bar-driven inflow rate. The radius of the CMZ gas ring slowly grows over Gyr timescales, and its star formation activity builds up a flattened stellar system known as the nuclear stellar disc, which currently dominates the gravitational potential of the Milky Way at 30pc<R<300pc. Most of the gas not consumed by star formation in the CMZ is ejected perpendicularly to the plane by a Galactic outflow powered either by stellar feedback and/or AGN activity, while a tiny fraction continues moving radially inward towards the circum-nuclear disc at R=few pc, and eventually into the sphere of influence of the central black hole SgrA* at R<1pc.

I will summarise recent advances in our understanding of star formation in the CMZ from an observational perspective.

The growth of galaxies in the local Universe is fundamentally influenced by the physical conditions of the hot phase of the interstellar and circumgalactic medium, as well as its dynamic interactions with other phases through processes such as outflows and re-condensation. X-ray data from the eROSITA All-Sky Survey is providing an unprecedented view of the hot plasma within the Galactic ecosystem. These data capture emission from the hot interstellar medium to the hot circumgalactic medium, extending from the disk-halo interface to regions beyond the virial radius of the Milky Way.

In addition, deep X-ray observations of the Galactic center with XMM-Newton and Chandra have revealed evidence of energetic activity within the central degree of the Milky Way, including signatures of an outflow on scales of hundreds of parsecs. This localized activity appears to be linked to a larger-scale Galactic outflow extending over tens of kiloparsecs.

This review highlights recent advancements in our understanding of the hot phase of the Milky Way, emphasizing the role of Galactic outflows in shaping the hot circumgalactic medium and their broader implications for galaxy evolution.

Star formation and stellar feedback in extreme environments like the Central Molecular Zone (CMZ) are important yet poorly constrained. Here we present JWST-NIRCam observations of the CMZ molecular cloud Sagittarius C (Sgr C) in order to take a census of its star formation activity. In conjunction with ancillary NIR, MIR, FIR, and sub-mm data from Spitzer, SOFIA, Herschel, and ALMA, we characterise the massive protostars G359.44a and G359.44b via SED fitting as well as their neighbouring cores. The NIRCam data reveals in high resolution the outflows from these protostellar sources in the form of atomic and molecular hydrogen-shocked material. Outflows are widespread throughout the entire Sgr C cloud, corroborating previous observations with ALMA, and tracing both low- and high-mass star formation. Overall, these observations paint a picture of star formation in Sgr C that is largely similar to the solar neighbourhood, despite the extreme environment of the CMZ. We also report the discovery of a new star-forming region ~1' to the west of the main protocluster, hosting two prominent bow shocks visible in H2 emission driven by at least two actively forming YSOs. We speculate on the locations of further YSOs in the region, as well as whether the entire star-forming region is in the CMZ or foreground. Finally, we discuss the extended, often filamentary molecular hydrogen shocks around Sgr C that do not appear to be associated with protostellar outflows.

We present evidence that the Sagittarius C (Sgr C) HII region, located in the Central Molecular Zone (CMZ) and spatially associated with the Sgr C star-forming region, is evolving under magnetically dominated conditions. Unlike any HII region in the Solar vicinity, the Sgr C plasma displays a remarkably filamentary structure in JWST-NIRCam Brα observations. The brightest of these filaments are also visible in the radio continuum with ALMA and MeerKAT, and 1 to 100 GHz spectral index measurements indicate thermal free-free emission. However, in-band 1 to 2 GHz spectral index measurements from MeerKAT alone imply the presence of a non-thermal synchrotron component across the entire HII region. We argue that the strong (~1 mG) CMZ magnetic fields have confined the plasma flow in Sgr C to rope-like filaments or sheets. This results in the measured non-thermal component of low-frequency radio emission, as well as a plasma β (thermal pressure divided by magnetic pressure) below 1, even in the densest regions. Corroborating this claim, we observe a statistically significant peak in the distribution of Brα filament orientations perpendicular to the galactic plane, or along the poloidal component of the global CMZ magnetic field. We speculate that all mature HII regions in the CMZ, and galactic nuclei in general, evolve in a magnetically dominated, low plasma β regime. Therefore, there is a pressing need to incorporate the impact of strong magnetic fields into the ‘standard’ models of HII region evolution, with potential consequences for our understanding of stellar feedback in extreme environments.

The central 500 pc of our Galaxy, known as the Central Molecular Zone (CMZ), contains a huge reservior of dense molecular gas. Due to the extreme physical conditions around the Galactic Center, star formation in the CMZ exhibits characteristics distinct from those in the solar neighborhood, such as a star formation efficiency approximately ten times lower, and a potentially top-heavy initial mass function (IMF). To explore the origins of these peculiar star formation activities, we have initiated an ALMA observational campaign, termed CONCERT, which peers into molecular clouds, dense cores, and accretion disks in the CMZ. In this talk, I will highlight recent findings from our studies of 0.01-pc dense cores and pc-scale filaments within molecular clouds in the CMZ. Key results include: i) The cores are primarily bound by external pressure, contrasting with their counterparts in Galactic disk clouds, which are predominatly bound by self gravity. ii) Spectral indices derived from 1.3 mm and 3 mm continuum emission of the cores are intriguingly low, a feature not observed in Galactic disk clouds (e.g., those studied in the ALMA-IMF project), suggesting beam-diluted optically thick substructures or the presence of large dust grains. iii) A unique class of slim filaments seen in several shock tracers and complex organic molecules but not in dust continuum are found to be in dynamically inequilibrium and could dissipate soon, which may be related to the widespread emission of SiO and complex organic molecules in the CMZ. iv) Intriguing absorption filaments, which are discovered by Bally et al. (2014) using two molecular lines in one cloud, are revealed in more molecules and toward more clouds, whose nature is still uncertain.

The Galactic Bar is the link between the Milky Way disk and the Galaxy's nuclear environment that is characterized by the Central Molecular Zone (CMZ). Gas in the CMZ is much more dense and abundant as compared to the disk, and it is undergoing extreme physical forces such as shear due to bar motions, a high flux of ionizing radiation and cosmic rays, as well as strong magnetic fields and outflows. John Bally was one of the pioneers to bring all the different phenomena together and to build up a model that describes the CMZ as a whole. Such models are crucial in for the understanding of the formation and processes of the gas flow and the inner workings of the CMZ. I will present a study of a number of clouds that are not part of the regular, bulk bar flow, but are at a much higher velocity dispersion along the same line of sight. We obtained ALMA data in a number of molecular tracers to characterize those clouds. We find strong collisions between gas clouds at about 5deg in Galactic longitude. In addition, we find that some of the clouds have elevated internal Mach numbers. These turbulent clouds show the increase in temperature and they exhibit suppressed star formation. The turbulent clouds almost certainly are in the bar, and they have properties that are typical for the CMZ (including a lower Xco-H2 conversion ratio). This indicates that at least some gas is energized before it reaches the inner Galactic Center. The best physical model is that these clouds are related to material that is overshooting accretion on the inner 100pc cloud only to collide with gas on the opposite Bar side. The loss of angular momentum will eventually drive them back to the CMZ.

The circumgalactic medium (CGM) plays a pivotal role in galaxy formation, primarily characterized by its hot, diffuse nature, which necessitates X-ray observations for detailed study. As inhabitants of the Milky Way, we are uniquely positioned to examine the CGM of our own spiral galaxy. Recent discoveries have overturned traditional views of the CGM's thermal structure, unveiling a complex model of X-ray emissions that includes temperatures near the galaxy’s virial temperature (~0.18 keV), as well as a super-virial range (0.4–1.2 keV). Even more striking is the newfound evidence of significantly enhanced abundances of nitrogen, neon, and magnesium in the Milky Way’s CGM—particularly an abundance of nitrogen detected throughout the sky.
This super-solar nitrogen abundance, along with the super-virial temperature gas, is likely shaped by hot outflows driven by ongoing star formation across the Galactic disk. Notably, the CGM in the direction of the Galactic center interacts with the X-ray Galactic bubbles, providing clear evidence of Galactic Center feedback that injects both energy and momentum into the extended CGM.
In my presentation, I will explore these latest findings on the thermal structure of the extended Milky Way CGM, focusing on the surprising nitrogen abundance and its implications for Galactic evolution.

Galactic winds powered by star formation are a ubiquitous multiphase phenomenon associated with concentrated starbursts. These winds, particularly their cool phases, remove material from the starburst region and drive it into the circumgalactic medium, affecting the duration of the star formation episode. At their base there are massive clusters, injecting energy and momentum that act as feedback, sometimes driving their own winds. I will briefly discuss the view of the phenomenon afforded by observations by ALMA and JWST, and discuss the prospects for future observatories.

I will present a new suite of cosmological zoom-in simulations of galaxy formation and evolution containing a novel set of subgrid models for stellar feedback and star cluster formation and evolution. These EMP simulations (for “Empirically Motivated Physics”) provide a solution to the stellar feedback "recipe" problem by adopting a model that uses feedback momentum input rates directly obtained from the observed molecular cloud lifecycle. Instead of attempting to solve the immensely complex nature of multi-mechanism, multi-scale stellar feedback from the bottom up, it applies the emergent, macroscopic "right answer" as observed in the real Universe. This new feedback model is combined with a model for the multi-phase interstellar medium, abundance tracking of 36 chemical elements and their isotopes, and a state-of-the-art model for the formation and evolution of the entire star cluster population (an evolution of the E-MOSAICS star cluster model). I will show how the physics contained in the EMP simulations change the baryon cycle in simulated galaxies relative to older feedback models. These simulations provide an important step forward by allowing us to obtain a detailed understanding of the star formation-feedback cycle on molecular cloud scales, from nearby galaxies out to the extreme formation environments of globular clusters at high redshift.

I will present a series of recent results from ALMA and IRAM campaigns targeting -in particular density-sensitive- molecular line ensembles like HCN, HCO+, HNC, CS or N2H+ and low-J CO, but also a range of faint CO isotopologues like 13CO or C18O across and among nearby spiral galaxies. The data situation of resolved "mm-spectroscopy" across nearby galaxies has improved dramatically over the last ~10 years and significant progress was made probing canonical, extragalactic, density-sensitive line ratios like HCN/CO or HCO+/CO and their relation with star formation in diverse samples of around 30 nearby galaxies. I will introduce a comprehensive kpc-scale ALMA ACA survey (ALMOND), targeted higher-resolution ALMA follow-up and the NOEMA Large Program SWAN, mapping these molecular lines directly at cloud scales across M51. In this talk, I will synthesize the key results from these campaigns and what they tell us about dense gas fractions and star formation efficiencies from larger scales to cloud scales across local galaxies, how the various canonical extragalactic tracers compare and outline intriguing links to cloud-scale work in the Milky Way.

In this talk, I will present the most recent chemical evolution models of the Milky Way. The SDSS-V Milky Way Mapper (MWM) survey will create the largest chemical map of our Galaxy by observing 5 million stars by 2027. MWM has observed 2 million stars to date, about 1 million will be made public in the first data release of MWM (DR19) in the Summer of 2025. Our group is not only leading the calibration/validation effort within SDSS for the first data release of MWM, but also uses its private data of nearly 400,000 stars to create an accurate history of the formation of our Galaxy, which consisted of a collision with another galaxy in the past. We modelled the evolution of 15 elements (Fe, Mg, O, Si, S, Ca, Ti, Na, Al, K, V, Cr, Mn, Co, Ni) in the entire Milky Way and divided the Galaxy into six regions based on the distance from the galactic center and modeled each of them separately. Within the six modelled regions the time of the second infall event ranges between 2.7 Gyr and 4.5 Gyr. The collision with the other galaxy happened earlier at the outermost regions, and as time elapsed it succesively reached the regions closer to the Galactic center. This means that the gravitational interaction between the potentially accreted dwarf galaxy and the early Milky Way started about 11.4 Gyr ago at the distance of R=14 kpc and finished about 2 billion years later, 9.5 Gyr ago at R=4 kpc.

We study the physical origins of outflowing cold clouds in a sample of 14 low-redshift dwarf ($M_{\ast} \lesssim 10^{10} \ M_{\odot}$) galaxies from the COS Legacy Archive Spectroscopic SurveY (CLASSY) using Keck/ESI data. Outflows are traced by broad (FWHM ~ 260 km s−1) and very-broad (VB; FWHM ~ 1200 km s−1) velocity components in strong emission lines like [O III] λ5007 and Hα. The maximum velocities (vmax) of broad components correlate positively with SFR, unlike the anti-correlation observed for VB components, and are consistent with superbubble models. In contrast, supernova-driven galactic wind models better reproduce the vmax of VB components. Direct radiative cooling from a hot wind significantly underestimates the luminosities of both broad and VB components. A multi-phase wind model with turbulent radiative mixing reduces this discrepancy to at least one dex for most VB components. Stellar photoionization likely provides additional energy since broad components lie in the starburst locus of excitation diagnostic diagrams. We propose a novel interpretation of outflow origins in star-forming dwarf galaxies−broad components trace expanding superbubble shells, while VB components originate from galactic winds. One-zone photoionization models fail to explain the low-ionization lines ([S II] and [O I]) of broad components near the maximal starburst regime, which two-zone photoionization models with density-bounded channels instead reproduce. These two-zone models indicate anisotropic leakage of Lyman continuum photons through low-density channels formed by expanding superbubbles. Our study highlights extreme outflows (vmax ≳ 1000 km s−1) in 9 out of 14 star-forming dwarf galaxies, comparable to AGN-driven winds.

Two mechanisms compete for each parcel of gas in a starforming molecular cloud. Young stars try to accrete gas with gravitational attraction, while at the same time generating powerful outflows that can drive the gas away. If gravity wins, the cloud can collapse to a massive bound cluster; if the outflows dominate the stars will be unbound and the cluster disperse. The dwarf starburst galaxy He2-10 is a nearby laboratory for cluster formation. He2-10 holds two starforming clouds, each ~10 times the mass of W49 and each actively forming clusters of 10^(5-6) Mo. Infrared and millimeter observations of the ionized and molecular gas show that the clouds are in very different stages of evolution. In one, the clusters are actively accreting molecular gas; in the other, clusters are driving away molecular and ionized gas. Our observations and computer simulations show how each cloud may develop and how this activity may relate to ionized shells and bubbles seen in He2-10 on large scales.

The formation of massive star clusters containing massive stars is thought to require some kind of triggering. The Large Magellanic Cloud (LMC) is one of the best sites to study this mechanism as we can observe the entire galactic disk without contamination and small distance uncertainty. For a statistical approach, a uniformly sampled massive star catalog is essential, but it is far from complete.
To overcome this situation, we identified massive stars in the LMC from the Gaia DR3 catalog, taking full advantage of its accurate optical photometry and color indices. Also star clusters are identified from their non-uniform distributions. As a result, we have identified more than 12,000 massive (> 8 Mo) star candidates and about 300 clusters. We then derived their age and Av by fitting to theoretical isochrone. Another notable advantage of the Gaia catalog is their high-precision proper motions. We subtracted the the galaxy bulk motion and rotation from each stellar motion and derived the internal proper motions of the clusters.
Thus derived massive star clusters exhibit highly non-uniform distributions, as several clusters are associated with major large HII regions such as N11, and N158. There are also numerous clusters distributed inside the Super Giant Shell LMC 4. Also we see a clear trend that neighboring clusters within a few 100 pc have similar proper motions and ages. This indicate that formation of those clusters did not occur independently, but rather have triggered by a common large-scale phenomena.
In the LMC, infalling HI clouds are suggested as a possible triggering mechanism to form the R136 cluster in 30 Dor (Fukui et al. 2017), and also in N44 (Tsuge et al. 2019). This is also supported by the existence of molecular filaments and their velocity structures (Wong et al. 2022; Maity et al. 2024). Our results provide another piece of evidence of the collisions of HI clouds on the LMC disk that triggered massive star formations in the entire LMC.

The structure and kinematics of the ISM on the scale of individual clouds is a powerful probe of
stellar feedback. However, isolating the very local effects of feedback requires removing the bulk
velocity structure of the gas, which is shaped more by the gravitational potential and possible
large scale gas accretion. Given the high spatial and kinematic resolution needed to measure
signatures of feedback, such an experiment requires data of exceptionally high quality in the
closest star forming galaxies. Here we show first results for global kinematic modeling of Local
Group star-forming galaxies, using new data from the Local Group L-band Survey (LGLBS).
LGLBS comprises approximately 1800 hours of observations using all available configurations
of the Karl G. Jansky Very Large Array (VLA), targeting NGC6822, WLM, M33, M31, IC10,
and IC1613. We focus on 21-cm line emission to map the atomic-dominated diffuse interstellar
medium (ISM). The proximity of the observed galaxies (500 kpc -1 Mpc), along with the
unprecedented resolution (<10 to 100 pc, and ~0.42 km/s velocity resolution), allows for detailed
studies of the atomic gas kinematics on both global and highly-local scales. The high-resolution
2-dimensional velocity fields we present here offer the best measurements of gas motion in
nearby galaxies to date, providing new insights into the relationship between gas dynamics and
stellar feedback in the Local Group.

I will discuss the evolution of molecular gas and subsequent star formation/feedback across the entire disk of the barred spiral galaxy M83. I will show an analysis of the ALMA CO J=1-0 and 2-1 line maps, which have x10 higher sensitivity (10^4Msun) and x2-3 higher resolution (40pc) than the target sensitivity and resolution of PHANGS. The CO 2-1/1-0 ratio map clearly shows the large-scale variations of gas physical conditions as a function of galactic structures. The density and temperature of the bulk gas systematically increase by a factor of 2-3 from the interarm regions to the bar and spiral arms. This gas evolution occurs even without (massive) star formation and is likely controlled by large-scale galactic dynamics. HII regions appear as a consequence of this evolution, and their feedback appears to push the gas density and temperature even higher. However, the impacts of the feedback is localized to their vicinity, and therefore, it role is limited in the galaxy-scale gas evolution. A similar evolutionary sequence is seen in an analysis of molecular clouds. Low-mass, unbound clouds without star formation are abundant in the interarm regions. They become more massive and bounds in the bar and spiral arms and form stars. These results suggest that both stellar feedback and galactic dynamics should be considered as the energy sources for ISM evolution, star formation, and galaxy evolution (Koda et al. submitted). M83 is the closest morphological analog of the Milky Way at the very close distance (4.5 Mpc), and thus, is an important prototype of MW-type galaxies. The similar evolutionary trends are also being confirmed in other spiral galaxies in our on-going ALMA survey.

The chemical enrichment state and dust attenuation of galaxies, their redshift evolution, and their dependence on stellar mass, star-formation rate, and environment are some of the most readily testable predictions of theoretical models of galaxy formation. The complex interplay between the processes that regulate chemical enrichment, including mergers, accretion, star-formation, and feedback-driven outflows is expected to become simpler at early times and easier to model. Hence, high-z constraints on the gas-phase metallicity and dust attenuation of galaxies are crucial for informing the theoretical models. I will present these measurements based on a large compilation of NIRSpec data, containing more than 2000 galaxies at 3 < z < 14. I will highlight established correlations, including the mass-metallicity relation and its redshift evolution, as well as the fundamental metallicity relation. Moreover, I will highlight new findings concerning the cosmic buildup of interstellar dust. The revolutionary combination of depth, wavelength coverage, and spatial resolution afforded by JWST has brought morphological and chemical analysis to the forefront of high-z studies. However, we are already facing the limitations of space telescopes: i) their limited spatial resolution, and ii) the high exposure times required to acquire deep high-spectral-resolution spectra. I will discuss these in light of the upcoming class of ELTs, highlighting the improvements expected in the coming decade.

Modern galaxy simulations routinely reach parsec resolution, thus unlocking a more self-consistent treatment for ISM-scale physics while being able to capture galactic-scale gas flows. In this context, I will present the latest results from my model INFERNO, focusing on star formation regulated by stellar feedback from individual stars in a multi-phase ISM with accurate tracking of chemical enrichment. My results include parsec-resolution cosmological simulations resolving the evolution of all observable stars on a star-by-star basis, making available, e.g., the observable color-magnitude diagram directly from the cosmological initial conditions. I will emphasize its importance for the robust interpretation of dwarf galaxy data. Furthermore, I will discuss how lingering uncertainties in model choices affect simulation outcomes, particularly concerning stellar evolution. For example, the co-evolution of binary stars determining the timing for type Ia supernovae is now relevant for modern simulations, highlighting how galaxy formation has entered an era of precise modeling.

In this talk I will present results from the FIRE cosmological zoom-in simulations exploring the (un)changing properties of the ISM through cosmic time, from redshift three to zero. I will highlight how on (sub)kiloparsec scales, several important properties of the ISM do not change as the galaxies grow and evolve from dispersion-supported, star-bursting objects to rotation-supported, smoothly star-forming disks. In particular, the importance of equilibria and stability against gravitational fragmentation and collapse on the gas scale height will be discussed. Intriguingly, gas appears to arrange itself in a manner so as to maintain marginal stability, regardless of the large-scale galaxy morphology, provided the entire gas reservoir is not being affected by a major merger. For this reason, I will show how though many variables are changing across the history of these galaxies, e.g., star formation rates, gas fractions, turbulent gas velocity dispersions, cold gas fractions, the underlying (dynamic) equilibrium of the ISM is not. Lastly, I will point to observational consequences of this underlying dynamical equilibrium that will be testable by the current and next generation of IFU surveys of extragalactic gas and star formation on the sub-kiloparsec scale.

Reflections on the conference

High-angular resolution X-ray observations provide an important view of stellar feedback processes, probing the energetics of stellar winds and supernovae in massive star clusters as well as allowing direct imaging of the hot gas that drives superwinds. This presentation will discuss the future of these studies that will be enabled by the Advanced X-ray Imaging Satellite (AXIS), a NASA probe-class concept currently in Phase A study. AXIS provides high-angular resolution (1.5-2.0" half-power diameter) across a large 24 arcminute field of view with an effective collecting area 5-10x that of Chandra. In addition to the stellar-feedback work included in the PI-led science program, I will highlight the possibilities enabled by the large General Observer component of this program.

I review the current state of theoretical work on star formation and feedback, with an eye toward identifying the most significant outstanding theoretical problems that seem ripe for progress in the coming years. I focus in particular on two outstanding questions. First, can we understand the formation and dissolution of star clusters in a full galactic context, so as to be able predict stellar clustering statistics as a function of age and environment? Second, can we understand the generation of galactic winds and their implications for the metal content of galaxies?

This talk provides a summary of the conference and describes the PRobe far-Infrared Mission for Astrophysics (PRIMA) which is a proposed mission to NASA’s Astrophysics Probe Explorer (APEX) call. PRIMA answers fundamental questions about our cosmic origins by investigating the role of water in planet assembly, the co-evolution of galaxies and their supermassive black holes, and the changing properties of dust and metal building blocks over cosmic time. As NASA’s first astrophysics probe and only far-infrared (far-IR) observatory for the next generation, PRIMA provides a scientific leap with broad continuous spectral coverage in the far-IR (24–261 μm), unprecedented sensitivity, polarimetry, and 3–5 orders of magnitude improvement in spectral mapping speed compared to previous far-IR missions. JPL and GSFC, NASA’s two leading centers for astrophysics, partner to develop PRIMA with its cold telescope and two far-IR instruments, enabled by innovative detectors. The majority of PRIMA’s time (>75%) is general observer time and all of data is available for archival research by the community.