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Abstracts for the oral presentations
Day1 (Monday, August 25)
| Time | Name | Affiliation | Title & Abstract |
|---|---|---|---|
| 08:30-09:20 | Registration | ||
| 09:20-09:30 | Opening remarks | ||
| 09:30-10:15 | Ralf S. Klessen | Heidelberg University |
The physics of early star and galaxy formation The emergence of the first stars and galaxies marks an important transition phase in cosmic evolution. I review some of the key physical processes and environmental parameters that govern the formation of the first and second generations of stars, and I discuss current theoretical models and observational constraints for the assembly and early evolution of galaxies in the high-redshift Universe. |
| 10:15-10:35 | Fabian Walter | Max Planck Institute for Astronomy Heidelberg |
The multi-phase ISM in the most distant quasar host galaxies Quasars are the brightest, non-transient objects observed at the highest redshifts, z>7, which makes them unique probes of the evolution of the earliest massive galaxies. Observations in the (sub)millimeter (with ALMA and NOEMA) constrain the gas and dust content, star formation rate and masses of the galaxies hosting these luminous accreting supermassive black holes. Observations with MUSE reveal large-scale ionized structures around many of these quasar host galaxies. New JWST observations now provide further insight into the ionized medium of these actively star forming systems, and in some cases reveal the stellar hosts of the quasars. I will present the results of various multi-wavelength follow-up programmes of the most distant quasars currently known, focusing on our recent very high-resolution (few 100pc) ALMA observations of quasar host galaxies at z~7. I will discuss the implications of the findings on massive galaxy formation, the interplay of their multi-phase ISM, and their relation to cosmic reionization. |
| 10:35-10:55 | Lucy Ivey | Kavli Institute for Cosmology, University of Cambridge |
The Role of AGN feedback at z~7 with JWST/NIRSpec IFS Discovery of quiescent galaxies up to z～7 show AGN feedback is needed earlier than expected. While JWST has now revealed a large population of AGN at z>4, the influence on their host galaxies’ evolution remains debated. I will present results from the analysis of new, deeper JWST/NIRSpec data on two z∼7.6 AGN host galaxies, illustrating spatially-resolved ionised gas kinematics via [O III]5007 emission. Furthermore, we identify faint broad wings in the [O III]λ5007 profile, indicating galaxy-wide outflows, and present spatially-resolved outflow properties of moderate-luminosity AGN at z>7 for the very first time. I will discuss the impact of feedback on the evolution of these high-z galaxies, with the aim of situating our results in a wider context. |
| 10:55-11:20 | Break / Poster viewing | ||
| 11:20-11:40 | Kejian Chen | KIAA, Peking University |
Quantifying the Coupling Effects of Supernova Feedback on Black Hole Accretion in Galactic Nuclei Growth of massive black holes (BHs) in the galactic centers are regulated by the environment. Modern cosmological galaxy-formation simulations suggest that supernova (SN) feedback evacuates the gas in galactic center, suppressing the BH growth until the host galaxies have grown sufficiently to develop a deep gravitational potential, leading to under-massive growth track relative to the local relationship. However, this scenario does not explain the over-massive nature of BHs observed at high redshift through JWST. In this work, we perform a suite of 3D high-resolution hydrodynamical simulations that investigate the properties of turbulent, multi-phase gas driven by individual SN explosions, and the dynamics of accreting gas onto a BH through its gravitational influence radius. We explore a broad parameter space of the BH mass (~ 10^4 - 10^7 Msun), density of the surrounding gas (~ 1-10^5 cm^-3), and frequency of explosions (given by star-formation timescale, tau ~ 10-10^4 Myr). When the density in the nucleus is as high as > 10^3 cm^-3 (tau / 10^2 Myr)^(-2), where the volume filling factor of SN bubbles within the BH influence radius is less than 0.1, the BH is fed at a high rate comparable to the Bondi accretion rate by dense cold gas formed between SN bubbles. This result, unlike most large-scale galaxy simulations that hardly resolve the nucleus, suggests that SN feedback is inefficient to expel the gas and prevent the BH from growing. These high-resolution simulations enable us to provide a physically motivated subgrid feedback model, which can be applied to large-scale simulations. |
| 11:40-12:00 | Vinny D’Onofrio | Texas A&M University |
Investigating Star Formation Suppression via the ISM of Higher-Redshift Post-Starburst Galaxies Post-starburst galaxies offer a critical window into quenching, shutting down star formation despite retaining massive molecular gas reservoirs. Using the SQuIGGLE sample of PSBs at z~0.7, we investigate their ISM properties across a range of tracers. ALMA CO(2-1) and new CO(5-4) observations suggest that distant gas-rich PSBs host dense, excited gas - different to the diffuse gas found in low-z systems. Our VLA program of ~50 PSBs reveals that radio detections are most common in the youngest (<200 Myr) PSBs, with radio-mode feedback playing a role in maintaining suppression during early quiescence. In some cases star-forming gas is displaced into tidal tails on >50 kpc scales, indicating tidal removal of ISM gas may be a relevant quenching mechanism at high-z. Together, these multiwavelength results highlight the complexity of ISM evolution and the varied pathways to star formation shutdown. |
| 12:00-12:20 | Gabriel Maheson | University of Cambridge |
Big, Dusty Galaxies: Dust Attenuation and Morphology in Massive Galaxies at Cosmic Noon with Blue Jay Dust attenuation in galaxies exhibit variability due to factors such as metallicity, redshift, and whether it is a quenched or star-forming galaxy. Using observations with both NIRSpec and NIRCam aboard JWST from the Blue Jay survey, a mass-selected sample of 145 galaxies in the COSMOS field at cosmic noon (1.7 < z < 1.3) was compiled to connect the enigmatic nature of the dust attenuation law with the physical parameters of the galaxy. These deep spectroscopic and photometric observations were fit simultaneously using the SED fitting tool Prospector, which implemented a non-parametric star-forming history and a flexible attenuation curve. For the first time, we find evidence of the dust attenuation vs stellar mass relationship holding for starbursts, star-forming galaxies, and quenched galaxies. Using size measurements, we can show that the star formation rate and stellar mass surface densities are more strongly correlated with the dust attenuation than the global parameters. We find a size-mass relation in the rest-frame optical; however, this flattens when we observe in the rest-frame near infrared. We find a colour gradient in the sizes of these galaxies, with the higher mass galaxies ($\rm M_{\star}\gtrsim10^{10}\rm M_{\odot}$) appearing more extended in the red than the blue due to an excess in central dust attenuation. At low masses, we see a large variation in this size gradient, likely due to the galaxies' assembly history. |
| 12:20-14:20 | Lunch | ||
| 14:20-15:05 | Florent Renaud | Strasbourg Observatory / CNRS |
From intergalactic to interstellar: the (not so trivial) role of mergers on the ISM and star formation From the injection of turbulence to the alteration of the gravitational potential, galaxy interactions are known to play an important role in shaping the interstellar medium and influencing star formation. The detection of starbursts is one of the most spectacular manifestations of this coupling. However, the underlying multi-physics processes of this multi-scale problem seems to be a very complex interplay of mechanisms, each with their own time and spatial scales. In this talk, I will review the recent results from theoretical works in this field. I will attempt to connect the conclusions from controlled experiments of isolated interacting systems with that from large-volume cosmological simulations, and show where differences arise. I will conclude by presenting what, in my opinion, constitutes the biggest challenges for the next generation of simulations aiming at capturing the physics of star forming sites in their galactic and cosmological context. |
| 15:05-15:25 | Maritza A. Lara-López | Universidad Complutense de Madrid |
A multiwavelength perspective of galaxy evolution What are the main drivers in the evolution of galaxies? is one of the biggest open questions in Astronomy to date even though it is critical in every aspect of the evolving universe. This is because galaxy evolution is driven by a complex interplay of various processes and factors that affect the baryon cycle and shape the properties of galaxies over cosmic time. The interplay between several properties at multiple wavelengths, metals, cold gas, dust, environment, star formation rate in galaxies, and even magnetic fields, is mandatory to have a comprehensive understanding on how galaxies evolve. I will introduce the Metal-THINGS survey, which is obtaining IFU spectroscopy of a unique sample of 34 nearby galaxies from The HI Nearby Galaxy Survey (THINGS, Walter et al. 2008). One of the main characteristics of the THINGS galaxies is that they have been observed by multiple wavelengths (see Fig. 1). Metal-THINGS has already observed more than 130 nights with VIRUS-P (GCMS), and has fully mapped 23 galaxies from the THINGS survey. I will present the latest results of the Metal-THINGS survey focussing in the analysis of gas metallicity gradients (Vale et al. 2025, submitted), the reconstruction of the resolved Spectral Energy Distribution (SED) from UV to FIR (Garduño et al. 2023), effects of Ultra Luminous X-ray sources in galaxies (Lara-López et al., 2021), and the star formation rate in the rims of HI holes (Lara-López et al. 2023). |
| 15:25-15:45 | Alex Wagner | University of Tsukuba |
Interactions of AGN jets with the interstellar medium AGN jets are powerful enough to disrupt the inner regions of galaxies by dispersing, heating, and possibly blowing out dense gas. Due to the lightness of the jets, they couple surprisingly strongy with the clumpy ISM, imparting substantial momentum and energy on scales of at least kpcs, that are likely to contribute to establishing and maintaining the M-sigma relation and lead to modifications of the star formation rate. We have been performing relativistic hydrodynamic simulations to investigate the interactions of AGN jets and the clumpy interstellar medium of gas-rich galaxies. In this talk, I will present a series of studies on how the efficiency of the momentum and energy feedback by jets depends on both jet properties and ISM properties, how star formation may be affected, and how the simulations have been compared to observations. |
| 15:45-16:20 | Poster flash talk | ||
| 16:20-16:40 | Break / Poster viewing | ||
| 16:40-17:00 | Lingyu Wang | Kapteyn Astronomical Institute / The University of Groningen (RuG) |
A first look into evolution of star formation along statistical merger sequence Galaxy mergers are violent cosmic collisions and impact on many aspects of galaxy evolution. For example, they are known to trigger starburst and active galactic nuclei (AGN) activity. However, to date we have very little idea of when these crucial phases in the evolutionary history of galaxies preferentially occur along the merging sequence. One of the main difficulties is that identification of mergers and merger stages (e.g., pre-merger and post-merger) is very challenging with traditional methods. Additionally, mergers are relatively rare, often leading to very incomplete and unreliable samples. To address this, we train state-of-the-art deep learning model on large samples of mock JWST and Euclid galaxies generated from the latest cosmological hydrodynamical simulations. These extensive samples capture the full range of variations in merger morphologies arising from different stages along the Gyr-long merging sequences. In addition, a unique advantage of our approach is that our model can be trained with accurate ground-truth labels indicating the merger status and merger stage of a galaxy. We apply our trained model to the JWST survey in the COSMOS field and the Euclid survey in the three deep fields (Euclid Deep Field North, Euclid Deep Field South and Euclid Deep Field Fornax) to obtain reliable samples of pre-mergers, post-mergers, and non-mergers up to redshift around 3 (in the case of JWST) and 2 (in the case of Euclid). This allows us to analyse how mergers and the different merger stages are connected with starbursts. Our findings indicate that mergers play a significant role in the most extreme starbursts. At lower redshifts (z<1), pre-mergers and post-mergers have similar relevance, potentially indicating a stochastic nature of starburst activity along the merger sequence. However, at higher redshifts (z>1), our preliminary analysis shows that starbursts are preferentially triggered in the post-merger phase. |
| 17:00-17:20 | Zongnan Li | National Astronomical Observatory of Japan |
Understanding circumnuclear environments in M31 and M81 with spatially-resolved multiphase gas Galactic circumnuclear regions, where stars and supermassive black holes interact with the interstellar medium, are crucial for understanding black hole feeding, feedback, and galaxy co-evolution. However, the connection between black hole feedback and the surrounding interstellar medium remains elusive. We utilizes multiwavelength observations of nearby galaxies (M31 and M81) to investigate the interaction between the multiphase interstellar medium and supermassive black holes in circumnuclear regions. Millimeter and infrared observations reveal a deficiency of cold gas in the circumnuclear region of M31 compared to the Milky Way, but with higher temperatures possibly linked to past nuclear activity. Additionally, optical spectroscopic observations uncover a biconical ionized gas outflow structure located at around 200 pc from the center of M81, likely associated with the low luminosity active galactic nucleus. We also addresses the long-standing puzzle of the origin of low-ionization nuclear emission-line regions (LINERs) in both galaxies. Using the CLOUDY photoionization code, the model incorporating contributions from inactive nuclei and stellar populations fails to fully explain the observed radial distribution of emission-line intensity within 1 kpc. This discrepancy suggests the presence of additional mechanisms, such as shocks or previous nuclear activity, in the ionization processes of these nearest LINERs. |
| 17:20-17:40 | Mikhail de Villiers | University of Cape Town / South African Astronomical Observatory |
Diffuse gas in MHONGOOSE galaxies NGC 3511 and NGC 3513 NGC 3511 and NGC 3513 are a pair of spiral galaxies with undisturbed stellar disks but show clear signs of interaction in their neutral atomic hydrogen (HI) distribution. This is evident from the presence of an HI bridge between the two galaxies as well as peculiar morphologies in the HI of either galaxy. We aim to understand the origins of this gas by analysing the dynamics of the HI disks and the extended HI distribution through both internal processes like stellar feedback and external processes such as tidal interactions. The result showcases how extremely sensitive HI observations of galaxies provide insight on the circulation of neutral atomic gas in an environment of galaxies with interacting HI, broadening the picture of the baryon cycle and large-scale gas flows between galaxies. |
| 17:40-18:00 | Poster viewing |
Day2 (Tuesday, August 26)
| Time | Name | Affiliation | Title & Abstract |
|---|---|---|---|
| 09:00-09:30 | Hsi-An Pan | Tamkang University |
Galaxy Interactions as Drivers of Star Formation, Metallicity Evolution, and Molecular Gas Redistribution Galaxy interactions are powerful drivers of transformation, triggering starbursts, altering chemical enrichment, and redistributing interstellar gas. With recent IFU surveys, the spatially resolved impact of interactions can now be studied across large galaxy samples. This talk explores how gravitational encounters influence star formation in both central and disk regions, and how they reshape gas-phase metallicity. I will also discuss changes in molecular gas concentration and distribution based on recent CO observations. Combining results from multiple surveys, the talk offers an overview of how interactions shape the baryonic structure of galaxies. |
| 09:30-09:50 | Zein Bazzi | Argelander Institute for Astronomy |
Mapping the Cold ISM with JWST PAH Emission: The Largest Molecular Cloud Catalog to Date Recent JWST/MIRI imaging of nearby galaxies, particularly using the F770W filter, has revealed a strong correlation between polycyclic aromatic hydrocarbon (PAH) emission and carbon monoxide (CO) emission across 70 galaxies on tens-of-parsec scales (Leroy et al. 2023; Chown et al. 2025). This finding allows PAHs to serve as high-resolution, high-sensitivity tracers of molecular gas, making it possible to detect and study low-mass molecular clouds currently undetectable in CO observations. Building on this result, we analyze 7.7 micron PAH maps of 66 nearby galaxies from the PHANGS survey, homogenized to a spatial resolution of 30 pc. Using the machine learning algorithm SCIMES (Colombo et al. 2015), we identify 108,466 PAH clouds, assembling the largest cloud catalog to date. We then convert the PAH flux into CO-intensity based on a calibration (Chown et al. 2025), allowing us to derive cloud properties, including mass, surface density, and size. We validate our PAH-based cloud catalog by cross-matching it with ALMA-resolved CO cloud catalogs (Hughes et al., in preparation). Across galaxy disks, we find a strong correspondence between PAH-derived and CO-derived gas surface densities, confirming that PAH emission is a potent tracer of the molecular interstellar medium. Using our large statistical sample, we fit the molecular cloud mass spectra with a lognormal function, reaching an unprecedented completeness limit of 10^3 Msun, a 2.4 dex improvement over ALMA-CO thresholds (Rosolowsky et al. 2021). The strong preference for a lognormal shape, as opposed to a power-law, implies a suppressed high-mass tail, indicating that extremely massive clouds are intrinsically rare. We find that the mean of the lognormal mass distribution positively correlates with the galaxy-specific star formation rate (sSFR) and atomic hydrogen (HI) mass, suggesting that in environments with more intense star formation and/or greater HI reservoirs, the molecular cloud population shifts toward higher masses. These results support a scenario where more massive clouds are more efficient at forming stars, while HI supplies the raw material required for molecular cloud formation. This catalog highlights that individual galaxy mass spectra reflect the physical conditions of the interstellar medium. However, when all clouds are combined from all galaxies and analyzed by the galactic environment, global environmental differences become apparent, with spiral arms hosting more massive clouds than interarm regions. Additionally, we find that positive molecular mass correlations with SFR only become prominent after 10^4 Msun, underlining that star formation occurs and is concentrated in the more massive clouds. Our results demonstrate the utility of PAH emission in tracing molecular clouds in the JWST era and provide new empirical constraints for models of cloud formation and destruction. By extending the observable dynamic range, particularly in the low-mass regime, this work deepens our understanding of how clouds form and fuel star formation across galactic environments. The resulting catalog serves as an observational benchmark for simulations of the turbulent interstellar medium, cloud evolution, and feedback, while also paving the way for synergy between JWST, ALMA, and future HI surveys. |
| 09:50-10:10 | Kirsten Larson | ESA / Space Telescope Science Institute |
The Interplay between Stars, Dust, and the ISM Shaping the Environments of Stellar Associations in NGC 4826 with PHANGS In order to better understand star formation and the coevolution of ISM structures, we have to trace the star formation on scales of individual stars and clusters. In the Physics at High Angular Resolution in Nearby Galaxies surveys (PHANGS), stellar associations trace loosely bound young stars in recent star formation sites. Using new HST H-alpha, and JWST Paschen-alpha, we measure the complex dust morphology and extinctions of stellar associations in NGC 4826 using the H-alpha to Pa-alpha decrement. We investigate the H-alpha and Pa-alpha morphology and its potential impact on the accuracy of the dust extinction estimation and use this to refine the stellar age and mass estimates in these young star-forming regions. We further correlate the H II emission to the dust emission from PAHs as revealed by JWST to study the effect of the young stars on the surrounding ISM. Through these means, our study refines measured properties of stellar associations, connects stars to the interstellar medium, and reveals their mutual influence on each other. |
| 10:10-10:40 | Break / Poster viewing | ||
| 10:40-11:10 | Kisetsu Tsuge | Gifu University |
High-Mass Star Formation Triggered by Colliding HI Flows and Its Relation to the Metallicity Distribution in the Large Magellanic Cloud Tidal interactions between galaxies are thought to trigger active star formation. Using HI data of the Large Magellanic Cloud (LMC), we found evidence that a tidally induced HI stream (L-component) collides with the LMC disk gas (D-component), driving massive star formation in regions such as R136 and N44. To evaluate the galaxy-wide impact, we examined the collisionally compressed gas (I-component) across the LMC disk and found that about 74% of O-type and Wolf Rayet stars are located within it, suggesting their formation in the colliding gas. A comparison of four major regions—R136, N44, N11, and the N77 N79 N83 complex—revealed a positive correlation between the number of high-mass stars and the pressure of the compressed gas, indicating that pressure is a key factor in star formation. Numerical simulations further show that HI collisions can produce dense molecular clouds capable of forming young massive clusters. This provides quantitative support for a starburst-triggering mechanism previously discussed only qualitatively. I will present a framework linking small-scale star formation with galaxy-scale gas dynamics, highlighting new results from the ALMA LMC survey and the Antennae galaxies. |
| 11:10-11:30 | Kengo Tachihara | Nagoya University |
Triggered Formation of Massive Stars in the Large Magellanic Cloud and Their Kinematic Properties The formation of massive stars, which play an important role in the galaxy evolution, requires some kind of trigger, but this process is poorly understood to date. Statistical approaches are particularly useful for observational study of this process as it takes place in giant molecular clouds in a short timescale. For sampling massive stars uniformly and at sufficient depth, the best target is the Large Magellanic Cloud, where we identified massive star candidates from the Gaia DR3 data. Their proper motions relative to the galaxy are also investigated. The results show that the massive stars have very non-uniform distributions forming many clusters. The positional correlation with the low-velocity component of HI gas and the stellar kinematics suggest that large-scale gas collisions have triggered the formation of massive stars and clusters. |
| 11:30-11:50 | Kazuki Tokuda | Kagawa University |
Formation and Evolution of Filamentary Clouds Associated with High-Mass Star Formation in the Magellanic Clouds Recent ALMA observations have achieved ~0.1 pc resolution in the Large and Small Magellanic Clouds (LMC and SMC), enabling the identification of filamentary molecular structures that are thought to be ubiquitous in Galactic star-forming regions. We find that the most luminous high-mass protostars (> 5 × 10^4 L_sun) in the LMC are often embedded in hub-filament systems, and some exhibit coherent, asymmetric head-tail structures extending beyond a single GMC, suggesting triggering by global-scale gas flows. In contrast, high-mass star-forming clouds in the SMC are not always filamentary. This morphological diversity may arise from thermal properties specific to the low-metallicity environment, highlighting the role of metallicity in shaping molecular cloud structures. |
| 11:50-12:10 | Notahiana Ranaivoharimina | University of Cape Town |
Refining HI scale heights: kinematic analysis of MHONGOOSE galaxies ESO 362-G011 and IC 4951 The HI thickness of disc galaxies offers a unique perspective in understanding the evolution of galaxies as energy injections influence the HI vertical morphology directly revealing the physics at play within those systems. We first examine the HI scale heights $h$ of four edge-on MHONGOOSE galaxies at $z \sim 0$ using a purely photometric method to avoid degeneracy from complex, multicomponent kinematic fits. This technique also allows a consistent evaluation of the scale heights of other wavelengths. This morphological analysis reveals the presence of both an HI thin and thick disc with typical values of $\bar{h}{\rm thin} = 0.7 - 1.4$ kpc and $\bar{h}{\rm thick} = 1.4 - 3.6$ kpc and a good correlation between the HI scale heights and the SFR surface density. However, the photometric scale heights are biased due to projection effects and line-of-sight warps. In this project, we will present the HI scale height results from 3D kinematic modelling for ESO 362-G011 and IC 4951 with a comparison of the photometric and kinematic scale heights of the two galaxies as well as those of UGCA 250 and UGCA 320 in an effort to correct the photometric biases. Additionally, we will discuss the effect of spatial resolution on the HI scale height results. The anticipated findings aim to essentially achieve more accurate thicknesses and help verify the scale height-$\rm \Sigma_{SFR}$ relation that suggests evidence in favor of the galactic fountain model as the main mechanism of HI thick disc formation. |
| 12:10-12:30 | Gundo Madiba | University of Cape Town / South African Astronomical Observatory |
Imaging Polarised Radio Emission in and around Nearby Galaxies within the MHONGOOSE survey Sensitive, high-resolution polarimetric radio imaging offers valuable insights into galaxies and their internal environments such as their projected magnetic field morphologies and large rotation measure (RM) regions within their discs, as well as in their circumgalactic and interstellar medium. We present results from the processing of the full-depth, 55 hour 4k-wideband radio continuum and polarisation data collected by MeerKAT as part of the MHONGOOSE(MeerKAT H i Observations of Nearby Galactic Objects: Observing Southern Emitters) survey with the aim to study the magnetized, ionized gas local to the target galaxies using rotation measure synthesis. |
| 12:30-14:30 | Lunch + conference photo | ||
| 14:30-15:00 | Masato Kobayashi | University of Cologne |
Molecular cloud formation in large-scale colliding gas flows and its metallicity dependence Colliding gas flow and associated shocks are key to lead the formation and evolution of molecular clouds from galactic scales to individual molecular cloud scales. In particular, I will first introduce latest status of magnetohydrodynamics numerical simulations, with particular attention to why galaxy-galaxy interactions are important for molecular cloud formation and subsequent star formation in low-metallicity environments. I will then briefly discuss how molecular cloud evolution is impacted by multiple supernovae and how that impact can be observed in various lines from Halpha to CO. |
| 15:00-15:20 | Rin I. Yamada | Gifu university / NAOJ |
Gas ionization driven by the intermediate velocity clouds falling onto the Galactic disk High-velocity clouds (HVCs), characterized by velocities exceeding –100 km/s as they fall toward the Galactic plane, have been suggested to originate from gas accreting from the intergalactic medium. In contrast, intermediate-velocity clouds (IVCs), which have velocities around –50 km/s—between those of HVCs and local gas—have traditionally been interpreted as gas blown out by past events such as supernova explosions and now falling back onto the Galactic disk as part of a galactic fountain cycle (fountain cycle; Shapiro & Field 1976;Bregman 1989). However, Hayakawa & Fukui (2024), based on a comparison of τ₃₅₃ and HI, pointed out that a significant fraction of IVCs consists of low-metallicity gas. They argued that IVCs may be decelerated components of HVCs interacting with halo or local gas, highlighting the growing importance of IVCs in the process of gas accretion onto the Galactic disk. In our study, we found that in the cases of IVC86–36 and IVC 75, Hα emission aligns well with an HI filament falling toward the Galactic plane at a relative velocity of ~50 km/s. The HI filament has a density of approximately 1cm⁻³, suggesting that the gas may be ionized as a result of this high-velocity collision. |
| 15:20-15:40 | Maki Nagata | The University of Tokyo |
High-Velocity Molecular Clouds in M83 High-velocity clouds (HVCs), which are gas clouds moving at high velocity relative to the galactic disk, may play a critical role in galaxy evolution, potentially supplying gas to the disk and triggering star formation. In this study, we focus on the nearby face-on barred spiral galaxy M83, where high spatial resolution, high-sensitivity CO (1–0) data are available. We identified molecular clouds and searched for clouds with velocities deviating by more than 50 km/s from the disk velocity field as HVCs. We identified 10 HVCs with radius of 30–80 pc, masses on the order of 10^5 Msun, and velocity dispersions of 3–20 km/s, indicating higher dispersions than disk clouds. Most do not coincide with supernova remnants, and the energy needed to drive HVCs at such high velocities exceed supernova energy. we thus conclude that most of the HVCs found in this study are inflow from outside the M83’s disk. |
| 15:40-16:10 | Lori Porter | Columbia University |
Simulating High-Velocity Clouds in the Observational Plane: An Initial Study with the Smith Cloud High-velocity clouds (HVCs) have the potential to fuel future star formation in the Galaxy, but to do so, they must survive their passage through the hot halo. While recent work has improved our understanding of the survival criterion for cloud-wind interactions, few observational comparisons exist that explore this criterion. We therefore present an initial comparison of simulations with the Smith Cloud (SC; 𝑑 = 12.4 kpc, 𝑙, 𝑏 = 40◦, −13◦), recently mapped with neutral hydrogen observations from the high-resolution GALFA-HI survey. We use observed properties of the Smith Cloud to motivate simulations of comparable clouds in wind tunnel simulations with Enzo-E, an adaptive mesh refinement MHD code. For both observations and simulations, we utilize moment maps and characterize turbulence through a projected first-order velocity structure function and do the same for HI column density with a normalized autocovariance function. Using these properties as common comparison metrics, we evaluate how well simulations replicate observations, show the relevance of turbulent radiative mixing layer (TRML) entrainment to HVCs, and investigate how various initial cloud conditions (such as radius, metallicity, thermal pressure, viewing angle, and distance) affect the presented statistics. We also make suggestions on how to further improve such simulations to better match observed HVCs and predict future star formation. |
| 16:10-16:30 | Break / Poster viewing | ||
| 16:30-16:50 | Rei Enokiya | NAOJ |
MeerKAT reveals substructures of atomic gas in the Galactic Center Since the atomic gas in galactic centers—where strong frozen-in magnetic fields exist—is often driven by the fields, resulting supersonic flows can enhance molecular gas and star formation. Magnetic fields are thus one of the fundamental factors advancing the evolution of a galaxy. Molecular loops 1 and 2, located ~600 pc from the Galactic Center, are thought to be gas flows shaped by magnetic field lines. To investigate the origin of these loops, we conducted high-resolution HI observations with the MeerKAT telescope operated by SARAO. More than 10 pc above the top of molecular loop 2, we identified a thin HI filament, with a width of a few parsecs and a length of a few tens of parsecs, oriented nearly perpendicular to the loop. This structure suggests shock-compressed atomic gas. We also found many small HI clumps, each a few parsecs in size. By comparing our results with simulations, we discuss the origin of the loop and the formation of molecular gas from these HI substructures. |
| 16:50-17:10 | Kensuke Kakiuchi | Kyusyu Sangyo University |
The Magnetized Interstellar Medium in the Galactic Center Region: Effects of Radiative Heating and Cooling We investigate the role of magnetic fields on gas dynamics in a galactic bulge region using 3D simulations with radiative cooling and heating. A high-temperature corona (T > 10⁶ K) forms in halo regions, while the gas near the mid-plane stays ≲10⁴ K, following the thermal equilibrium curve determined by these processes. The magnetic field amplifies to about 10 μG on average, reaching several hundred μG locally. Magnetically dominated regions form at midlatitudes with radiative effects, which are absent without them. These regions are 50–150 pc thick at 0.4–0.8 kpc from the Galactic center, consistent with the observed distribution of neutral atomic gas. Averaging over the entire bulge region, the magnetic energy density is comparable to the thermal energy density, indicating that magnetic fields significantly influence the dynamical and thermal structure of the bulge. |
| 17:10-17:30 | Kyra L. Kummer | Department of Astronomy, University of Cape Town |
IC 5332 as a Laboratory for Probing Outer-Disk Star Formation & HI Gas Properties Understanding how outer-disk star formation is triggered and fuelled in low-mass galaxies, and low-density environments, is a key challenge for galaxy evolution models. IC 5332, a nearby, nearly face-on SABc galaxy with a putative Type 2 XUV disk offers an opportunity to study this phenomenon. We combine new high resolution MeerKAT HI data with FUV, IR, and Ha observations to explore the multiphase properties of its outer disk. We find evidence for an extended, warped HI disk coincident with its XUV disk, hosting low rates of star-formation. We test prevailing star-formation models and explore the correlation between IC 5332’s HI and star-formation properties. We will discuss our results, and their implications on understanding the evolution and star-formation of extended disk galaxies. |
| 17:30-17:50 | Izumi Seno | Nagoya University |
Thermal Instability of Circum-Galactic Medium as The Fuels for Star Formation in The Galactic Disks The total gas mass in the galactic disk is about 10^9 solar masses, with a star formation rate of several solar masses per year. This suggests depletion within 1 Gyr, yet observations indicate that star formation has persisted for ~10 Gyr. Recent studies reveal ionized, metal-rich halo gas extending over 100 kpc, with a mass exceeding 10^10 solar masses, suggesting that halo inflows sustain star formation. We investigate thermal instability as a key mechanism, analyzing halo gas stability under gravity, radiative cooling, and cosmic rays. Our results indicate that cold HI clouds can be formed primarily in the lower halo and may appear as Intermediate-/High-Velocity Clouds, playing a role in the galactic gas supply. |
Day3 (Wednesday, August 27)
| Time | Name | Affiliation | Title & Abstract |
|---|---|---|---|
| 09:00-09:45 | Eve Ostriker | Princeton University |
Feedback and the Multiphase, Multicomponent ISM: Theory It is well known that star formation and the interstellar medium (ISM) are intimately connected: new stars form out of the densest portion of interstellar gas, and the immediate impact of stellar feedback has been evident to astronomers since the first observations of HII regions. But stellar feedback also profoundly impacts ISM gas on larger spatial and temporal scales. Ionizing and non-ionizing UV are the most important sources of heating in the warm ionized and neutral phases and cold atomic phase, while shocks from (clustered) supernovae create the hot phase, and cosmic rays accelerated in those shocks are the source of much of the ISM's ionization as well as heating of shielded molecular gas. Additionally, pressure forces that owe to these localized inputs of feedback energy are responsible for much of the dynamics in the ISM, including turbulence, galactic fountain flows, and galactic winds. In recent years, theory and simulations have "closed the loop" to identify how the ISM acts back on star formation on large spatio-temporal scales, with the star formation rate regulated such that the combined total pressure derived from feedback balances the weight of the ISM. In this talk, I will review the concept of co-regulation between the ISM and star formation, as embodied in the pressure-regulated, feedback-modulated theory. I will also summarize the latest results from numerical simulations on the feedback yield in different ISM components, where this yield is defined as the ratio between mean pressure and the mean star formation rate per unit area. With numerical calibrations of thermal, turbulent, and magnetic feedback yields, and most recently cosmic ray feedback yield, we now have the ingredients to build predictive theoretical models of the multiphase, multi-component ISM -- from our own back yard in the Milky Way to the distant realms of the universe. |
| 09:45-10:05 | Aurelien Piluso | Observatoire de Paris (FRANCE) |
Unveiling physical and microphysical process in Photo-Dominated Regions with H2 ro-vibrational lines from IGRINS observations H₂ emission lines are powerful tools for investigating star-forming regions and young stars radiative feedback. JWST enabled the detection of hundreds of ro-vibrational lines. IGRINS, a high-resolution ground-based spectrometer, expands this detection to higher ro-vibrational levels (v=1 to 13, J up to 10). Five emblematic PDRs (Orion Bar, Horsehead) were observed, offering a unique opportunity to study the action of O/B stars on their parent clouds. These data, combined with the Meudon PDR code, new molecular data, and an innovative inference bayesian method, allow to constrain physical conditions (Pressure, UV intensity) induced by the feedback as never before. Also, for the first time, they allow to study key processes such as H₂ formation levels and ortho-para conversion. |
| 10:05-10:25 | Yuankang Liu | Durham University |
Emission line diagnostics in H II regions: a non-equilibrium perspective Recent advancements in instrumentation have enabled the investigation of interstellar medium with unprecedented spatial resolution. To facilitate detailed comparisons between simulations and observations, we generate mock emission line maps based on a state-of-the-art simulation of an H II region, utilizing a novel post-processing pipeline. In this talk, I will introduce a new atomic model that accurately predicts hydrogen recombination line emissivity. This model is computationally efficient and can be seamlessly integrated into post-processing workflows for hydrodynamic simulations. By applying it to our new simulation, we gain new insights into emission line diagnostics in a non-equilibrium setting, which was previously unattainable. I will then explore widely used diagnostic tools in the ISM community, highlighting their deviations from traditional equilibrium-based predictions. The atomic model, together with the pipeline, steps towards bridging the gap between simulations and observations, providing insights into the physical conditions of star-forming regions and contributing to the refinement of theoretical models. |
| 10:25-10:55 | Break / Poster viewing | ||
| 10:55-11:40 | Janice C. Lee | Space Telescope Science Institute |
Decoding Galaxies & Star Formation Feedback with 100,000 Star Clusters: PHANGS-HST & JWST today, HWO tomorrow Our PHANGS surveys with HST and JWST have produced the most extensive inventories to date of both optically visible and dust-embedded star clusters in nearby galaxies. A consistent picture is now emerging of the early phases of cluster evolution, built from complementary tracers and methods of analysis, and confirming the short dust-clearing timescales (<3 Myr) indicated by earlier optical studies. These results highlight the critical role of early, pre-supernova feedback in regulating the star formation cycle. Drawing on the statistical power of tens of thousands of clusters across dozens of galaxies, I will synthesize what has been learned from PHANGS and related programs about cluster formation, evolution, and feedback. I will highlight new findings from our resolved stellar population analysis using the unique combination of Hubble and Webb imaging, and despite this progress, make the case for the Habitable Worlds Observatory, NASA’s next flagship astrophysics mission and a true “Super-Hubble” with capabilities out to the far ultra-violet. |
| 11:40-12:00 | You-Hua Chu | National Sun Yet-sen University |
High-Resolution Views of the Multiphase ISM of the Magellanic Clouds The Large and Small Magellanic Clouds (LMC and SMC) at 50 and 60 kpc distances, respectively, are the only galaxies with substantial amounts of ISM that can be viewed with sub-pc resolution using ground-based telescopes. Multiwavelength surveys of the ISM as well as optical surveys of the stars in the MCs make it possible to quantitatively study the interplay between the ISM and stars at scales from a few to 1000 pc. Optical surveys of the ionized ISM provide excellent fiducials for the multiphase ISM. Previously, the Magellanic Cloud Emission-Line Survey (MCELS) of the LMC and SMC have been widely used to search for nebulae and to compare with the distribution of not only the neutral atomic and molecular interstellar gas but also the hot coronal gas. MCELS is now replaced by DeMCELS, a new emission-line survey of the MCs using the Dark Energy Camera on the Blanco 4m telescope. The angular resolution of DeMCELS is 3-5 times better than that of MCELS. At radio wavelengths, the ASKAP and MeerKAT surveys of the MCs offer exquisite high-resolution images to search for nonthermal emission. Gaia survey further provides photometric data and radial velocities of stars. The available multiwavelength surveys of the ISM and stars have been used to investigate energy feedback in interstellar structures and characterize the first massive stars formed in molecular clouds. |
| 12:00-12:20 | Manami Sasaki | Dr. Karl Remeis Observatory, Friedrich-Alexander-University Erlangen-Nürnberg |
The hot phase of the interstellar medium The interstellar medium (ISM) is ionized and heated by radiation, by stellar winds, and finally, by supernova explosions. Since these processes are often correlated in space and time, the combination of stellar winds and supernova remnants (SNRs) can form large interstellar structures called superbubbles, which are filled with hot thin plasma. If superbubbles expand and break, the hot plasma will escape into the galactic disk and also out of the disk, forming galactic winds and fountains. The hot plasma in SNRs and superbubbles can be studied best in X-rays due to its high temperature (10^6 − 10^7 K), while particles are also accelerated in the shock waves. We will present the results of X-ray studies of the hot phase of the ISM in the Milky Way and the nearby galaxies and discuss the physics of the hot plasma, the evolution and energetics of SNRs and superbubbles, and the implications for the star formation history of galaxies. |
| 12:20-12:40 | Slawa Kabanovic | Physikalisches Institut, Universität zu Köln |
Probing the Multi-Phase ISM: From Expanding [C II] Bubbles to Cold Absorbing Gas As part of the SOFIA Legacy Program FEEDBACK (PIs N. Schneider and A. Tielens), we observed various evolutionary stages of stellar wind-driven bubbles characterized by fast-expanding [C II] shells. An analysis of these bubbles indicates that, while the initial expansion compresses the surrounding medium - triggering star formation, we also observe streams of gas escaping from the molecular cloud. This outflow effectively removes material and halts further star formation as the region evolves. The variety of sources observed allowed us to study these expanding bubbles at different stages of evolution: from compact, [C II]-filled bubbles such as those in RCW 79 to highly evolved regions like Cygnus X where the shell has burst out of the sheet-like parental molecular cloud. However, the remaining torus - visible as a ring in the plane of the sky - is still slowly expanding. The observed [C II] emission is not free from optical depth effects. To disentangle self-absorption from kinematic features, we developed a model that solves a set of radiative transfer equations. This model separates the warm, emitting gas from the cold, absorbing material and reveals that substantial amounts of ionized carbon are located in a cold atomic layer. To better understand the physical conditions of this cold absorbing gas, we applied the model to [C II], [O I], and CO observations from the Orion Legacy Project (PI: S. Kabanovic), enabling us to determine the spatial distribution and physical properties of the gas. |
| 12:40-14:15 | Lunch | ||
| 14:15-14:45 | Oleg Egorov | Heidelberg University |
A multi-scale and multi-wavelength perspective on stellar feedback in nearby galaxies Feedback from massive stars plays a fundamental role in shaping the ISM across a vast range of scales and influences the evolution of galaxies. Current instruments can resolve star-forming regions at the energy injection scales, enabling empirical characterization of HII regions and allowing constraints on stellar feedback to be derived directly from observations. In my talk, I will provide a brief overview of the ongoing surveys of the Milky Way and nearby galaxies (namely PHANGS and especially SDSS-V/LVM), and highlight selected results that focus on linking massive stars and the ISM at resolved scales, from ~100 pc down to ~1pc. I will also overview the future prospects for the LVM survey beyond SDSS-V. |
| 14:45-15:05 | Nushkia Chamba | NASA Ames Research Center |
Signatures of Star Formation, Feedback and Mergers in the Multi-phase Interstellar Medium of Galaxies The multi-phase interstellar medium (ISM) of galaxies, from X-rays to the neutral atomic hydrogen (HI) component, regulates galaxy growth via star formation, feedback and mergers. However, the signatures of these processes can be faint and irregular in shape, making characterization difficult. We present new tools for the detection and analysis of ultra-faint, diffuse ISM components in galaxies from X-ray to radio frequencies. Considering dwarf and disk galaxies, we discuss how their stellar and HI edges, i.e. the outermost radial location where in situ star formation significantly drops, is a sensitive tracer of stellar feedback and environmental processes. At the edges of more massive galaxies, we present new asymmetric features in X-ray and star light, demonstrating the impact of feedback and mergers on their hot plasma. Our tools enable multi-scale, multi-frequency studies on the processes impacting the ISM of galaxies. |
| 15:05-15:25 | Juhi Tiwari | The University of Alabama in Huntsville, USA |
Gone Without a Glow?: Hot-phase X-ray Thermal Coronae in Low-Mass Cluster Galaxies In many galaxies residing within galaxy clusters, centrally concentrated, hot X-ray-emitting gas (thermal coronae; ~a few million Kelvins), representing the innermost hot phase of the multi-phase ISM, is commonly detected. These coronae are heated by shock processes, and stellar and AGN feedback, and are commonly detected in massive galaxies. Although simulations suggest that X-ray coronae are unlikely to survive in low-mass cluster galaxies, this prediction remains largely untested observationally. In this work, we investigate the potential presence of thermal X-ray coronae in dwarf galaxies located within a large sample of rich galaxy clusters. Leveraging over two decades of archival observations, we aim to place the most robust observational constraints to date on the hot-phase X-ray emission in these dwarf galaxies and to examine the environmental and intrinsic factors that may govern their survival. |
| 15:25-15:45 | Martin Mayer | Dr. Karl Remeis Observatory, Friedrich-Alexander-University Erlangen-Nürnberg |
X-raying the multi-phase interstellar medium of the LMC with eROSITA Much of the interstellar space of galaxies is occupied by hot plasma energized through stellar feedback, which provides significant pressure to the multi-phase ISM. X-ray observations allow us to map the distribution of the hot ISM phase in nearby galaxies, e.g., the LMC. We will present our study of the ISM in the LMC, based on the eROSITA all-sky X-ray survey combined with multiwavelength data. We show that the distribution hot gas (T ~ 3*10^6 K, P ~ 10^4-10^5 K/cm^3) anticorrelates with that of cold gas on 100-1000 pc scales. By comparing ISM pressure with predictions of stellar feedback, we identify regions of excess energy input, e.g. from tidally driven collisions. Finally, we find a global gradient in the alpha-element enrichment of the ISM, tracing the impact of massive stars. |
| 15:45-16:15 | Break / Poster viewing | ||
| 16:15-16:35 | Eva Schinnerer | MPIA |
Gas-rich galaxy centers as extreme environments for star formation Gas-rich galaxy centers like the Central Molecular Zone in our own Galaxy are extreme, yet poorly understood environments for the formation of massive stars. The combination of ALMA and JWST observations is ideal to study the molecular gas—star formation—stellar feedback cycle in these regions with high surface density of stellar mass, gas density, and often star formation rate, and short dynamic timescales. I will present results from recent ALMA CO and JWST dust observations of a selected set of gas-rich centers from the PHANGS sample at ~20pc resolution and place them into the context of expectations for the evolution of such centers in barred galaxies. Further I will briefly discuss the opportunities provided by a next generation ALMA in this research area. |
| 16:35-16:55 | Takuto Ito | Nagoya University |
Filament and star formation triggered by stellar feedback probed by the dynamics of young stellar objects in the Perseus cloud Shock waves by stellar feedback are thought to make important effects, such as accumulating surrounding gas and induce star formation. We focused on the Perseus molecular cloud, including NGC 1333 and IC 348 star forming regions, located on the surface of an expanding HI shell with a diameter of 150 pc. Using CO data from the Nobeyama 45m telescope, we identified 40 and 20 filamentary structures in NGC 1333 and IC 348, respectively. Gaia DR3 and APOGEE-2 data show that the associated young stellar objects show radially outward motions from the shell center, with their radial velocities matching the CO filaments. The CO data also reveal that two diffuse clouds with distinct velocities are colliding, and the filaments are formed in the compressed layer with intermediate velocity of the two clouds. These results suggest that a cloud-cloud collision driven by the expanding shell triggered both filament and star formation in the Perseus cloud. |
| 16:55-17:15 | Kenshin Onogawa | Nagoya University |
Histogram of Bubbles in Spiral Arms The bubble-filament paradigm (Inutsuka+2015, Pineda+2023) was proposed for describing the cloud formation in magnetized interstellar medium is supposed to explain many features of observations of interstellar medium and star formation. A resemblance of the observation of bubbles in NGC628 by JWST (Watkins+2023) to the basic picture of the paradigm is remarkable.. In this contribution we calculate the evolutions of super nova remnants and theoretically provide bubble size histogram using numerical simulations and analytical considerations. By comparing our results with observations, we can determine the various quantities in each spiral galaxy, such as the mean volume density and the degree of density fluctuations in the disk midplane. |
| 17:15-18:00 | Poster viewing | ||
| 18:00~ | Conference Dinner |
Day4 (Thursday, August 28)
| Time | Name | Affiliation | Title & Abstract |
|---|---|---|---|
| 09:00-09:45 | Tsuyoshi Inoue | Konan University |
Effects of Shock–Cloud Interactions on the Evolution of Supernova Remnants Interaction between supernova blast wave shock and molecular clouds causes so many effects in the evolution of young supernova remnants. In this talk, I particularly focus on the shock-cloud interaction in clumpy ISM. There are three important effects: i) magnetic field amplification, which enhances x-ray emissions through particle acceleration at reflection shocks induced by the interaction. ii) diffusive penetration of CRs into clumpy clouds, which modifies hadronic gamma-ray spectrum and has a big impact on observed character of the SNR. iii) shock propagation velocity through clumpy medium, which gives a clue to measure volume filling factor of dense clumps around the SNR. All these effects make it possible to understand the CR acceleration in the young SNR interacting with molecular clouds. |
| 09:45-10:30 | Hidetoshi Sano | Gifu university |
Origin of Cosmic Rays in the Galaxy The origin of cosmic rays in our Galaxy has remained a fundamental question in astrophysics since their discovery in 1912. In this review talk, I will present an overview of recent observational advances concerning shocked interstellar clouds associated with supernova remnants (SNRs), which play a key role in probing the acceleration and energetics of cosmic rays. I will begin with a summary of our current understanding of Galactic cosmic rays, followed by a review of progress made over the past two decades, driven by advances in X-ray and gamma-ray observations. I will then highlight how precise measurements of the interstellar medium, based on recent radio-line observations combined with high-energy data, have provided compelling evidence for the acceleration of cosmic-ray protons in SNRs. Finally, I will discuss new insights from sub-PeV gamma-ray observations, particularly those from LHAASO, and offer perspectives on future observational approaches to studying the origin and propagation of Galactic cosmic rays. |
| 10:30-11:00 | Break / Poster viewing | ||
| 11:00-11:20 | Knox S. Long | STScI |
Integral Field Spectroscopy of Galactic and Magellanic Cloud Supernova Remnants with the SDSS-V Local Volume Mapper With a 30′ field of view and spectral coverage from 3600–9800 Å at ~75 km/s resolution, the SDSS-V Local Volume Mapper enables high-quality optical spectroscopy of entire supernova remnants (SNRs) in the Milky Way and a uniform spectroscopic survey of all SNRs in the Magellanic Clouds. In the Galaxy, we can resolve the diverse shocks produced as supernovae interact with the surrounding medium. In the Magellanic Clouds, integrated spectra of many SNRs allow us to study shocks in varied environments and compare with SNRs in more distant galaxies, where multi-wavelength data are limited. I will present early results from both surveys. |
| 11:20-11:40 | Federico Zangrandi | Dr. Karl Remeis Observatory, Friedrich-Alexander-University Erlangen-Nürnberg |
Supernova remnant population in the Large Magellanic Cloud A statistical study of supernova remnants (SNRs) inside a galaxy is important for the understanding of the chemical enrichment and the energy budget inside a galaxy. The complete coverage of the Large Magellanic Cloud (LMC) and its surroundings provided by eROSITA allows us to investigate the SNR candidates proposed in radio and optical and to detect new SNR candidates never observed by another X-ray telescope before. Of particular interest is the increasing population of SNRs detected in the outskirts of the LMC. We present the most updated catalog of SNRs in the LMC. We compare the X-ray luminosity function (XLF) of the SNRs in the LMC with the XLF in the Local Group galaxies. Furthermore, we perform a morphology study on the X-ray SNRs in the LMC. |
| 11:40-13:40 | Lunch + conference photo | ||
| 13:40-14:10 | Tsunefumi Mizuno | Hiroshima University |
Interstellar Gas Properties in the Solar Neighborhood Revealed by Diffuse Gamma Rays Galactic cosmic rays interact with interstellar gas and produce diffuse gamma ray emission, making it a powerful probe of gas in all phases. To investigate the interstellar gas and cosmic rays in the solar neighborhood, we analyzed Fermi-LAT data of five nearby molecular cloud regions. We constructed the interstellar gas templates by a component decomposition of the 21 cm HI line, the Planck dust emission model, and the CO 2.6 mm line. Through gamma-ray data analysis, we successfully decomposed the interstellar gas into narrow-line and optically thick HI, broad-line and optically thin HI, CO-bright H2, and CO-dark H2. We found that thick HI clouds exhibit filamentary structure and surround H2 clouds, and the ratio of CO-dark H2 to CO-bright H2 anti-correlates with the H2 mass traced by the CO 2.6 mm line. This contribution will present our analysis and discuss the implications for the interstellar gas and cosmic rays. |
| 14:10-14:30 | Nick Indriolo | Space Telescope Science Institute |
Mapping the Cosmic-Ray Ionization Rate in the Solar Neighborhood Chemical complexity in the molecular interstellar medium (ISM) is driven by fast ion-molecule reactions, and cosmic rays are the dominant mechanism for ionization of H and H2. Observations of H3+, a molecule with very simple formation and destruction pathways, can be used to infer the cosmic-ray ionization rate (CRIR) via chemical modeling. Using extinction maps derived from Gaia, we can now link molecular absorption features to specific clouds in the local (1 kpc) ISM, and build the first 3D map of CRIRs in the solar neighborhood. Here, I will present the results of our recent H3+ survey using IRTF/iSHELL, which has more than doubled the number of sight lines where we have precision estimates of the CRIR, and enabled the investigation of spatial variations in the cosmic-ray flux. |
| 14:30-14:50 | Ellis Owen | RIKEN |
Probing the physics of cosmic rays in molecular clouds Recent high-energy observations and ionization rate measurements of nearby Galactic molecular clouds suggest that cosmic ray (CR) transport in dense clumps deviates from both purely ballistic and purely diffusive behavior. To investigate this, we present a self-consistent model of CR transport and interactions in magnetized molecular clouds, testing three CR propagation regimes: ballistic, diffusive, and a hybrid configuration featuring a diffusive envelope with a ballistic core. By computing ionization rates and multi-wavelength signatures of nearby molecular cloud complexes, we show CR transport in these environments is best explained by a combination of diffusive transport in turbulent envelopes and a transition to ballistic propagation in dense cores. Moreover, we find that the structure of the diffusive envelope must vary between individual clouds to consistently account for both the gamma-ray and ionization constraints. Our results establish an efficient new framework for interpreting multi-wavelength observations of CR interactions in molecular clouds and offer a path toward systematically constraining the physics of CR transport in dense ISM environments and its environmental dependence throughout the Galaxy. |
| 14:50-15:20 | Break / Poster viewing | ||
| 15:20-15:50 | Robert Brose | University of Potsdam |
Supernova Remnants as Accelerators of Galactic Cosmic Rays For over five decades, supernova remnants (SNRs) have been extensively studied as potential sources of Galactic cosmic rays (CRs). While they provide enough energy to sustain the Galactic CR spectrum at the low energies, their ability to accelerate particles to the knee of the CR spectrum at PeV-energies is lacking observational evidence. Many aspects regarding the microphysics of the acceleration process that would facilitate them to reach PeV-energies are not well understood to this day. However, these details are crucial for understanding which SNRs are potential CR factories and how the accelerated CRs might impact the interstellar medium in the vicinity of the SNRs. This presentation will focus on the recent developments of two aspects of CR-acceleration, a) the ability of SNRs to accelerate CRs to the highest energies and thus qualifying SNRs the primary accelerators of the Galactic CR spectrum and b) the inevitable escape of particles from the SNRs deep-downstream over their lifetime and the observable signatures this will leave in the surrounding medium. |
| 15:50-16:10 | Jason Alford | NYU Abu Dhabi |
Cosmic Ray Leptons Escaping from CTA 1? Many Galactic TeV sources are associated with middle-aged (~10^4-5) pulsar wind nebulae (PWNe), with the γ-ray emission extending beyond the X-rays. This suggests that high-energy $e^pm$ first escape from the PWN, and then produce the γ-rays through inverse Compton (IC) scattering. However, how they escape from the PWN and enter the ISM is poorly understood, in part because there are very few examples of systems where the particles are 'caught in the act' of escaping from the PWN. Understanding this process requires spatially-resolved measurements of the diffuse, X-ray spectrum of the extended TeV source. Spatially resolved spectral measurements of the PWN in CTA 1 are suggestive of high-energy e^pm 'caught in the act' of escaping into the ISM. We have analyzed a new 150 ks NuSTAR observation of the PWN in CTA 1, as well as an archival 120 ks XMM observation, and will present initial results from our analyses. |
| 16:10-16:30 | Ryosuke Kobashi | University of Tokyo |
Environment of Tycho's SNR inferred from shock-dynamics and gamma-ray spectrum Recent analysis of Chandra data has revealed the substantial deceleration of the forward shock of Tycho's supernova remnant (SNR), which suggests recent shock interactions with a cavity-wall environment. We characterize this cavity-wall environment in term of shock-expansion dynamics and show that the existence of dense molecular cloud surrounding the rarefied wind-like circumstellar matter (CSM) can well explain this observation. As for non-thermal emission, we investigate whether such environment is consistent with the multi-wavelength spectrum. We find that such an environment predicts a harder gamma-ray spectrum than observed. This difference can be due to the limitation in the present one-dimensional model which does not consider (multi-dimensional) clumpy structure. |
| 16:30-16:50 | Shuta Tanaka | Aoyama Gakuin University |
The Origin of Filamentary Structures in the Crab Nebula: A Unified Solution to the Sigma and Kappa Problems The Crab Nebula, a remnant of the 1054 supernova, is a pulsar wind nebula (PWN) powered by the Crab Pulsar. It shows a multi-phase structure: relativistic electron-positron plasma from the pulsar produces non-thermal emission up to PeV gamma rays, while non-relativistic filaments emit optical lines from heavy elements. These filaments, composed of cool material with molecular lines, clearly originate from sources other than the pulsar. We investigate their origin, focusing on a possible link to molecular cloud filaments that may have formed the progenitor star. We also discuss how these filaments, though apparently unrelated to the PWN, may help resolve long-standing issues regarding the PWN’s magnetization and particle content. |
| 16:50-17:10 | Yasuo Fukui | Nagoya University |
Cosmic ray acceleration in a microquasar candidate TeV γ ray source HESS J1023-57 (Westerlund 2) Fukui et al. 2009 discovered Jet and Arc CO clouds toward Westerlund 2 which accompanies a TeV gamma ray source HESS J1023-575. We have made CO observations with ALMA at five time higher resolution than the single dish data. The new CO image has revealed that the clouds consist of numerous CO filamentary features with 0.5 pc width and 10-20 pc length. Surprisingly, all the features are well lined up along the axis of the Jet and Arc which are connected with HESS J 1023-575. We propose an interpretation that the Jet and Arc clouds were formed by the interaction between a microquasar jet similar to SS433 with the ambient Hi gas. HESS J1023-575 is therefore a good candidate of very powerful cosmic ray acceleration overwhelming SNRs. |
| 17:10-17:30 | Poster viewing | ||
| 17:30-18:20 | Discussion | ||
| 18:20-18:30 | Closing remarks |