arXiv subjects

Jiayi Sun

Publications and source records attributed to Jiayi Sun.

At least 37 records · Page 2Linked to original sources

arXiv2026

The impact of ram pressure on the radio spectral index and magnetic field of NGC 4522: A high-resolution VLA continuum study

We present high-resolution Very Large Array (VLA) continuum observations at S-band ($3$ GHz, $560$ pc scale) and X-band ($10$ GHz, $200$ pc scale) of the ram-pressure-stripped Virgo galaxy NGC 4522, to investigate the characteristics of its radio continuum, spectral index, and magnetic field under the influence of the intracluster medium (ICM). The total radio continuum shows an asymmetry that extends northwest, mirroring the HI gas distribution, but showing distinct features in the extraplanar regions. The spectral index steepens systematically from $α\sim-0.6$ in the main disk to $α\sim-1.1$ in the outer disk. We find that the spectral index behavior of the outer disk is mainly due to an ICM shock that can re-accelerate electrons and a significant reduction of thermal emission. Intriguingly, extraplanar clouds exhibit exceptionally flat spectral indices ($α\sim-0.2$ to $0$), resulting from a combination of significantly enhanced thermal emission and pronounced spectral aging of the non-thermal component. Although some of these regions correlate with H$α$, others do not. We propose that the mixing between the ICM and interstellar medium (ISM) is an alternative mechanism that enhances thermal emission independently of star formation. Polarized continuum emissions are highly asymmetric, preferentially distributed along the ICM wind side, and the polarization fraction increases radially outward from the galactic midplane, indicating that the polarized emission is strongly influenced by the ICM wind. Our results show how and where the ICM substantially affects the ISM, and also demonstrate that high-frequency observations are crucial for analyzing the radio continuum of ram pressure stripping galaxies.

astro-ph.GA↗

arXiv2025

Evolved Supergiants in PHANGS I: Red Supergiants in 19 Galaxies between 5-20 Mpc with HST and JWST

Red supergiants (RSGs) are important for our understanding of supernova progenitors, stellar populations, stellar evolution, mass loss and dust production. Extragalactic surveys of RSGs have a long history in the Local Group, but few studies exist beyond that due to the limited resolution and sensitivity of ground-based and previous space-based infrared observatories. Here we demonstrate the combined power of HST and JWST to push systematic searches of RSGs out to $\sim$20 Mpc. We introduce a catalog of 97057 RSGs -- the largest single-survey release of RSGs -- with masses $\gtrsim$10 M$_{\odot}$ in 19 galaxies from the PHANGS HST+JWST Treasury program. We use HST F814W and JWST F200W photometry to select stars as RSGs based on predicted colors and magnitudes from PARSEC isochrones. The spatial distribution of our recovered RSGs follow the familiar pattern of mostly being concentrated in active star-forming regions such as spiral arms and central starburst rings. The RSG number density on kpc-scales is strongly correlated ($r_s$$\sim$0.82) with local star-formation rate density ($Σ_{SFR}$) traced by extinction-corrected far-ultraviolet (FUV) from GALEX+WISE, and weakly correlated ($r_s$$\sim$0.57) with the total stellar mass density ($Σ_*$), traced by near-infrared emission from WISE+Spitzer. The number of RSGs per mass of stellar populations with ages 6-30 Myr (the likely age range of RSGs $>$10 M$_{\odot}$) is $\sim$1 per 10$^{3.77\pm0.27}$ M$_{\odot}$, assuming constant star-formation rates from FUV+W4. Our sample will be a useful resource for tracking progenitors and feedback sites of future supernovae in PHANGS, age-dating stellar populations, and more.

astro-ph.GA↗

arXiv2025

Duration and properties of the embedded phase of star formation in 37 nearby galaxies from PHANGS-JWST

Light reprocessed by dust grains emitting in the infrared allows the study of the physics at play in dusty, embedded regions, where ultraviolet and optical wavelengths are attenuated. Infrared telescopes such as JWST have made it possible to study the earliest feedback phases, when stars are shielded by cocoons of gas and dust. This phase is crucial for unravelling the effects of feedback from young stars, leading to their emergence and the dispersal of their host molecular clouds. Here we show that the transition from the embedded to the exposed phase of star formation is short (< 4 Myr) and sometimes almost absent (< 1 Myr), across a sample of 37 nearby star-forming galaxies, covering a wide range of morphologies from massive barred spirals to irregular dwarfs. The short duration of the dust-clearing timescales suggests a predominant role of pre-supernova feedback mechanisms in revealing newborn stars, confirming previous results on smaller samples and allowing, for the first time, a statistical analysis of their dependencies. We find that the timescales associated with mid-infrared emission at 21 μm, tracing a dust-embedded feedback phase, are controlled by a complex interplay between giant molecular cloud properties (masses and velocity dispersions) and galaxy morphology. We report relatively longer durations of the embedded phase of star formation in barred spiral galaxies, while this phase is significantly reduced in low-mass irregular dwarf galaxies. We discuss tentative trends with gas-phase metallicity, which may favor faster cloud dispersal at low metallicities.

astro-ph.GA↗

arXiv2025

Multiphase Astrophysics to Unveil the Virgo Environment (MAUVE)

The Multiphase Astrophysics to Unveil the Virgo Environment (MAUVE) project is a multi-facility programme exploring how dense environments transform galaxies. Combining a VLT/MUSE P110 Large Programme and ALMA observations of 40 late-type Virgo Cluster galaxies, MAUVE resolves star formation, kinematics, and chemical enrichment within their molecular gas discs. A key goal is to track the evolution of cold gas that survives in the inner regions of satellites after entering the cluster, and how it evolves across different infall stages. With its high spatial resolution -- probing down to the physical scales of giant molecular cloud complexes -- and multiphase synergy, MAUVE aims to offer a time-resolved view of environmental quenching and set a new benchmark for cluster galaxy studies.

astro-ph.GA↗

arXiv2025

The Hierarchical Dynamical State of Molecular Gas from 3 to 300 pc in NGC 253

Understanding how the dynamical state of the interstellar medium (ISM) changes across spatial scales can provide important insights into how the gas is organized and ultimately collapses to form stars. To this end, we present ALMA $^{12}\mathrm{CO}(2-1)$ observations at $7$ pc ($0''.4$) spatial resolution across a $1.4~\mathrm{kpc}\times5.6~\mathrm{kpc}$ ($1'.3\times1'.3$) region located in the disk of the nearby ($D = 3.5$ Mpc), massive, star-forming galaxy NGC 253. We decompose this emission with a hierarchical, multiscale dendrogram algorithm to identify 2463 structures with deconvolved sizes ranging from $\sim3$ to $300$ pc, complete to a limiting mass of $10^4~M_\odot$. By comparing the virial parameter of these structures against physical properties including size, mass, surface density, velocity dispersion, and hierarchical position, we carry out a comprehensive search for a preferred scale at which gravitationally bound structures emerge. Ultimately, we do not identify evidence of an emergent scale for bound objects in our data, nor do we find a significant correlation between the virial parameter and structure sizes. These findings suggest that simple observational estimates of gravitational binding cannot be used to define molecular clouds and emphasize the need for multiscale approaches to characterize the ISM.

astro-ph.GA↗

arXiv2025

Stability and slow dynamics of an interior spiky pattern in a one-dimensional spatial Solow model with capital-induced labor migration

One of the most significant findings in the study of spatial Solow-Swan models is the emergence of economic agglomeration, in which economic activities concentrate in specific regions. Such agglomeration provides a fundamental mechanism driving the spatial patterns of urbanization, labor migration, productivity growth, and resource allocation. In this paper, we consider the one-dimensional spatial Solow-Swan model with capital-induced labor migration, which captures the dynamic interaction between labor and capital through migration and accumulation. Focusing on the regime of sufficiently small capital diffusivity, we first construct an interior spike (spiky economic agglomeration) quasi-equilibrium. Next, we perform the linear stability of the corresponding spike equilibrium by using a hybrid asymptotic and numerical method. We show that a single interior spike remains stable for small reaction-time constants but undergoes a Hopf bifurcation when the constant is sufficiently large, leading to oscillations in spike height (economic fluctuation). Finally, we derive a differential-algebraic system to capture the slow drift motion of quasi-equilibrium (core-periphery shift). Numerical simulations are carried out to support our theoretical studies and reveal some intriguing yet unexplained dynamics.

math.AP↗

arXiv2025

Resolved Profiles of Stellar Mass, Star Formation Rate, and Predicted CO-to-H$_2$ Conversion Factor Across Thousands of Local Galaxies

We present radial profiles of surface brightness in UV and IR bands, estimate stellar mass surface density ($Σ_\star$) and star formation rate surface density ($Σ_\mathrm{SFR}$), and predict the CO-to-H$_2$ conversion factor ($α_\mathrm{CO}$) for over 5,000 local galaxies with stellar mass $M_\star\,{\geq}\,10^{9.3}\rm\,M_\odot$. We build these profiles and measure galaxy half-light radii using GALEX and WISE images from the $z$0MGS program, with special care given to highly inclined galaxies. From the UV and IR surface brightness profiles, we estimate $Σ_\star$ and $Σ_\mathrm{SFR}$ and use them to predict $α_\mathrm{CO}$ with state-of-the-art empirical prescriptions. We validate our (kpc-scale) $α_\mathrm{CO}$ predictions against observational estimates, finding the best agreement when accounting for CO-dark gas as well as CO emissivity and excitation effects. The CO-dark correction plays a primary role in lower-mass galaxies, whereas CO emissivity and excitation effects become more important in higher-mass and more actively star-forming galaxies, respectively. We compare our estimated $α_\mathrm{CO}$ to observed galaxy-integrated SFR to CO luminosity ratio as a function of $M_\star$. A large compilation of literature data suggests that star-forming galaxies with $M_\star = 10^{9.5{-}11}\,M_\odot$ show strong anti-correlations of SFR/$L^\prime_\mathrm{CO(1{-}0)} \propto M_\star^{-0.29}$ and SFR/$L^\prime_\mathrm{CO(2{-}1)} \propto M_\star^{-0.40}$. The estimated $α_\mathrm{CO}$ trends, when combined with a constant molecular gas depletion time $t_\mathrm{dep}$, can only explain ${\approx}1/3$ of these SFR/$L^\prime_\mathrm{CO}$ trends. This suggests that $t_\mathrm{dep}$ being systematically shorter in lower-mass star-forming galaxies is the main cause of the observed SFR/$L^\prime_\mathrm{CO}$ variations. (Abridged)

astro-ph.GA↗

arXiv2025

Masses, Star-Formation Efficiencies, and Dynamical Evolution of 18,000 HII Regions

We present measurements of the masses associated with $\sim18,000$ HII regions across 19 nearby star-forming galaxies by combining data from JWST, HST, MUSE, ALMA, VLA, and MeerKAT from the multi-wavelength PHANGS survey. We report 10 pc-scale measurements of the mass of young stars, ionized gas, and older disk stars coincident with each HII region, as well as the initial and current mass of molecular gas, atomic gas, and swept-up shell material, estimated from lower resolution data. We find that the mass of older stars dominates over young stars at $\gtrsim10\rm\,pc$ scales, and ionized gas exceeds the stellar mass in most optically bright HII regions. Combining our mass measurements for a statistically large sample of HII regions, we derive 10 pc scale star-formation efficiencies $\approx6{-}17\%$ for individual HII regions. Comparing each region's self-gravity with the ambient ISM pressure and total pressure from pre-supernova stellar feedback, we show that most optically bright HII regions are over-pressured relative to their own self-gravity and the ambient ISM pressure, and that they are hence likely expanding into their surroundings. Larger HII regions in galaxy centers approach dynamical equilibrium. The self-gravity of regions is expected to dominate over pre-supernova stellar feedback pressure at $\gtrsim130\rm\,pc$ and $60\rm\,pc$ scales in galaxy disks and centers, respectively, but is always sub-dominant to the ambient ISM pressure on HII region scales. Our measurements have direct implications for the dynamical evolution of star-forming regions and the efficiency of stellar feedback in ionizing and clearing cold gas.

astro-ph.GA↗

arXiv2025

Azimuthal offsets in spiral arms of nearby galaxies

Spiral arms play a central role in disc galaxies, but their dynamical nature remains a long-standing open question. Azimuthal offsets between molecular gas and star formation are expected if gas crosses spiral arms, as predicted by quasi-stationary density wave theory. In this work, we measure offsets between CO and Halpha peaks in radial bins for 24 galaxies from the PHANGS survey that display a well-delineated spiral structure. The offsets exhibit substantial scatter, implying that star formation is not exclusively initiated at a coherent spiral shock. We define offsets such that positive values mean Halpha peaks lie ahead of CO peaks in the direction of galactic rotation. With this convention, 14 galaxies show mean positive CO-Halpha offsets, typically of a few hundred parsecs. In four of these 14 galaxies (17% of the total), offsets become smaller with increasing radius, as expected for a single quasi-stationary spiral density wave. Ten galaxies (42%) show positive mean offsets but no clear correlation with radius, which is compatible with multiple overlapping modes. In the remaining ten galaxies (42%), we find no significantly positive offsets, which could point to transient dynamical spirals or material arms, where gas and stars co-rotate with the spiral perturbation. Across the full sample, we find mostly positive offsets between CO peaks and the gravitational potential minimum, confirming that gas often crosses the spiral perturbation. For the four galaxies with clear positive offsets and a radial trend, we derived pattern speeds in good agreement with the literature. Overall, our results suggest that even well-delineated spirals in the local Universe can arise from a variety of underlying dynamical mechanisms.

astro-ph.GA↗

arXiv2025

The SWAN view of dense gas in the Whirlpool -- A cloud-scale comparison of N2H+, HCO+, HNC and HCN emission in M51

Tracing dense molecular gas, the fuel for star formation, is essential for the understanding of the evolution of molecular clouds and star formation processes. We compare the emission of HCN(1-0), HNC(1-0) and HCO+(1-0) with the emission of N2H+(1-0) at cloud-scales (125 pc) across the central 5x7 kpc of the Whirlpool galaxy, M51a, from "Surveying the Whirlpool galaxy at Arcseconds with NOEMA" (SWAN). We find that the integrated intensities of HCN, HNC and HCO+ are more steeply correlated with N2H+ emission compared to the bulk molecular gas tracer CO, and we find variations in this relation across the center, molecular ring, northern and southern disk of M51. Compared to HCN and HNC emission, the HCO+ emission follows the N2H+ emission more similarly across the environments and physical conditions such as surface densities of molecular gas, stellar mass, star-formation rate, dynamical equilibrium pressure and radius. Under the assumption that N2H+ is a fair tracer of dense gas at these scales, this makes HCO+ a more favorable dense gas tracer than HCN within the inner disk of M51. In all environments within our field of view, even when removing the central 2 kpc, HCN/CO, commonly used to trace average cloud density, is only weakly depending on molecular gas mass surface density. While ratios of other dense gas lines to CO show a steeper dependency on the surface density of molecular gas, it is still shallow in comparison to other nearby star-forming disk galaxies. The reasons might be physical conditions in M51 that are different from other normal star-forming galaxies. Increased ionization rates, increased dynamical equilibrium pressure in the central few kpc and the impact of the dwarf companion galaxy NGC 5195 are proposed mechanisms that might enhance HCN and HNC emission over HCO+ and N2H+ emission at larger-scale environments and cloud scales.

astro-ph.GA↗

arXiv2025

Multi-Agent Synergy-Driven Iterative Visual Narrative Synthesis

Automated generation of high-quality media presentations is challenging, requiring robust content extraction, narrative planning, visual design, and overall quality optimization. Existing methods often produce presentations with logical inconsistencies and suboptimal layouts, thereby struggling to meet professional standards. To address these challenges, we introduce RCPS (Reflective Coherent Presentation Synthesis), a novel framework integrating three key components: (1) Deep Structured Narrative Planning; (2) Adaptive Layout Generation; (3) an Iterative Optimization Loop. Additionally, we propose PREVAL, a preference-based evaluation framework employing rationale-enhanced multi-dimensional models to assess presentation quality across Content, Coherence, and Design. Experimental results demonstrate that RCPS significantly outperforms baseline methods across all quality dimensions, producing presentations that closely approximate human expert standards. PREVAL shows strong correlation with human judgments, validating it as a reliable automated tool for assessing presentation quality.

cs.CL↗

arXiv2025

Modeling the Mass Distribution and Gravitational Potential of Nearby Disk Galaxies: Implications for the ISM Dynamical Equilibrium

We characterize stellar, gas, and dark matter mass distributions for 17 nearby massive disk galaxies from the PHANGS sample. This allows us to compute the gravitational potential that vertically confines the interstellar gas and determines its equilibrium scale height and weight. We first combine dynamical mass constraints from existing CO and HI rotation curves together with stellar and gas mass estimates from near-infrared, CO, and HI data. These estimates incorporate current best practices in modeling stellar mass-to-light ratios and CO-to-H2 conversion factor variations. Then, we fit joint stellar--gas--dark matter mass models to the rotation curves, adopting the classic maximal disk assumption to account for remaining zero-point uncertainties on the stellar mass-to-light ratio. After obtaining three-component radial mass profiles, we calculate the vertical equilibrium gas scale height and ISM weight in the combined gravitational potential. We find the gas scale height $H_\text{gas}$ increases from ${\lesssim}100$pc in the inner disks to ${>}500$pc at large radii, consistent with observations of our Galaxy and other edge-on galaxies. The gas weight is dominated by stellar gravity at small radii, but the gas and dark matter gravity often become important beyond 3-6 times the stellar disk radial scale length. Both our gas scale height and weight estimates are dependent on the treatment of stellar disk scale height $H_\star$, with $H_\text{gas}$ varying by 30-40% when $H_\star$ varies by a factor of 3. The relationship between our refined ISM weight estimates and local star formation surface density generally agrees with previous observations and predictions from theory and simulations.

astro-ph.GA↗

arXiv2025

The Karl G. Jansky Very Large Array Local Group L-band Survey (LGLBS)

We present the Local Group L-Band Survey (LGLBS), a Karl G. Jansky Very Large Array (VLA) survey producing the highest quality 21-cm and 1-2 GHz radio continuum images to date for the six VLA-accessible, star-forming, Local Group galaxies. Leveraging the VLA's spectral multiplexing power, we simultaneously survey the 21-cm line at high 0.4 km/s velocity resolution, the 1-2 GHz polarized continuum, and four OH lines. For the massive spiral M31, the dwarf spiral M33, and the dwarf irregular galaxies NGC6822, IC10, IC1613, and the Wolf-Lundmark-Melotte Galaxy (WLM), we use all four VLA configurations and the Green Bank Telescope to reach angular resolutions of $< 5''$ ($10{-}20$~pc) for the 21-cm line with $<10^{20}$~cm$^{-2}$ column density sensitivity, and even sharper views ($< 2''$; $5{-}10$~pc) of the continuum. Targeting these nearby galaxies ($D\lesssim1$ Mpc) reveals a sharp, resolved view of the atomic gas, including 21-cm absorption, and continuum emission from supernova remnants and HII regions. These datasets can be used to test theories of the abundance and formation of cold clouds, the driving and dissipation of interstellar turbulence, and the impact of feedback from massive stars and supernovae. Here, we describe the survey design and execution, scientific motivation, data processing, and quality assurance. We provide a first look at and publicly release the wide-field 21-cm HI data products for M31, M33, and four dwarf irregular targets in the survey, which represent some of the highest physical resolution 21-cm observations of any external galaxies beyond the LMC and SMC.

astro-ph.GA↗

arXiv2025

Time-scales of polycyclic aromatic hydrocarbon and dust continuum emission from gas clouds compared to molecular gas cloud lifetimes in PHANGS-JWST galaxies

Recent JWST mid-infrared (mid-IR) images, tracing polycyclic aromatic hydrocarbons (PAHs) and dust continuum emission, provide detailed views of the interstellar medium (ISM) in nearby galaxies. Leveraging PHANGS-JWST Cycle 1 and PHANGS-MUSE data, we measure the PAH and dust continuum emission lifetimes of gas clouds across 17 nearby star-forming galaxies by analyzing the relative spatial distributions of mid-IR (7.7-11.3$μ$m) and H$α$ emission at various scales. We find that the mid-IR emitting time-scale of gas clouds in galaxy disks (excluding centers) ranges from 10 to 30Myr. After star formation is detected in H$α$, mid-IR emission persists for 3-7Myr during the stellar feedback phase, covering 70-80% of the H$α$ emission. This significant overlap is due to intense radiation from star-forming regions, illuminating the surrounding PAHs and dust grains. In most galaxies, the mid-IR time-scale closely matches the molecular cloud lifetime measured with CO. Although mid-IR emission is complex as influenced by ISM distribution, radiation, and abundances of dust and PAHs, the similarity between the two time-scales suggests that once gas clouds form with compact mid-IR emission, they quickly provide sufficient shielding for stable CO formation. This is likely due to our focus on molecular gas-rich regions of galaxies with near-solar metallicity. Finally, we find that the mid-IR emitting time-scale is longer in galaxies with well-defined HII regions and less structured backgrounds, allowing photons to more efficiently heat the ambient ISM surrounding the HII regions, rather than contributing to diffuse emission. This suggests that the shape of the ISM also influences mid-IR emission.

astro-ph.GA↗

arXiv2025

Constraining resolved extragalactic $R_{21}$ variation with well calibrated ALMA observations

CO(1-0) and CO(2-1) are commonly used as bulk molecular gas tracers. The CO line ratios (especially CO(2-1)/CO(1-0) - $R_{21}$) vary within and among galaxies, yet previous studies on $R_{21}$ and alike often rely on measurements constructed by combining data from facilities with substantial relative calibration uncertainties that have the same order as physical line ratio variations. Hence robustly determining systematic $R_{21}$ variations is challenging. Here, we compare CO(1-0) and CO(2-1) mapping data from ALMA for 14 nearby galaxies, at a common physical resolution of 1.7 kpc. Our dataset includes new ALMA (7m+TP) CO(1-0) maps of 12 galaxies. We investigate $R_{21}$ variation to understand its dependence on global galaxy properties, kpc-scale environmental factors, and its correlation with star formation rate (SFR) surface density and metallicity. We find that the galaxy-to-galaxy scatter is 0.05 dex. This is lower than previous studies which reported over 0.1 dex variation, likely reflecting significant flux calibration uncertainties in single-dish surveys. Within individual galaxies, $R_{21}$ has a typical mean value of ~0.64 and 0.1 dex variation, with an increase to ~0.75 towards galactic centers. We find strong correlations between $R_{21}$ and various galactic parameters, particularly SFR surface density, which shows a power-law slope of 0.10-0.11 depending on the adopted binning/fitting methods. Our findings suggest that, for studies covering main sequence galaxy samples, assuming a fixed $R_{21}$=0.64 does not significantly bias kpc-scale molecular gas mass estimates from CO(2-1). Instead, systematic uncertainties from flux calibration and the CO-to-H$_2$ conversion factor account for more systematic scatter of CO-derived molecular gas properties.

astro-ph.GA↗

arXiv2025

Reconciling extragalactic star formation efficiencies with theory: insights from PHANGS

New extragalactic measurements of the cloud population-averaged star formation (SF) efficiency per freefall time $\rmε_{\rm ff}$ from PHANGS show little sign of theoretically predicted dependencies on cloud-scale virial level or velocity dispersion. We explore ways to bring theory into consistency with observations, highlighting systematic variations in internal density structure that must happen together with an increase in virial level typical towards galaxy centers. To introduce these variations into conventional turbulence-regulated SF models we adopt three adjustments motivated by the host galaxy's influence on the cloud-scale: we incorporate self-gravity and a gas density distribution that contains a broad power-law (PL) component and resembles the structure observed in local resolved clouds, we let the internal gas kinematics include motion in the background potential and let this regulate the onset of self-gravitation, and we assume that the gas density distribution is in a steady-state for only a fraction of a freefall time. The combined result is a strong reduction to $\rmε_{\rm ff}$ predicted in multi-freefall (MFF) scenarios compared to purely lognormal probability density functions and variations that are tied to the PL slope $α$. The $α$ needed to match PHANGS $\rmε_{\rm ff}$'s vary systematically with environment in the sense that gas sitting furthest from virial balance contains more gas at high density. With this `galaxy regulation' behavior included, our `self-gravitating' sgMFF models function similar to the original, roughly `virialized cloud' single-freefall models. However, outside disks with their characteristic regulation, the flexible MFF models may be better suited.

astro-ph.GA↗

arXiv2025

The impact of spiral arms on the star formation life cycle

The matter cycle between gas clouds and stars in galaxies plays a crucial role in regulating galaxy evolution through feedback mechanisms. In turn, the local and global galactic environments shape the interstellar medium and provide the initial conditions for star formation, potentially affecting the properties of this small-scale matter cycle. In particular, spiral arms have been proposed to play a pivotal role in the star formation life cycle, by enhancing the gas density and triggering star formation. However, their exact role is still debated. In this paper, we investigate the role of spiral arms in the giant molecular cloud evolutionary life cycle and on the star formation process in a sample of 22 nearby spiral galaxies from the PHANGS survey. We measure the cloud lifetime, the feedback timescale, the typical distance between independent regions and the star formation efficiency in spiral arms and inter-arm regions separately. We find that the distributions of the cloud lifetime as well as the feedback timescale are similar in both environments. This result suggests that spiral arms are unlikely to play a dominant role in triggering star formation. By contrast, the star formation efficiency appears to be slightly higher in inter-arm regions compared to spiral arms.

astro-ph.GA↗

arXiv2025

Linking stellar populations to HII regions across nearby galaxies. II. Infrared Reprocessed and UV Direct Radiation Pressure in HII Regions

Radiation pressure is a key mechanism by which stellar feedback disrupts molecular clouds and drives HII region expansion. This includes direct radiation pressure exerted by UV photons on dust grains, pressure associated with photoionization, and infrared (IR) radiation pressure on grains due to dust-reprocessed IR photons. We present a new method that combines high resolution mid-IR luminosities from JWST-MIRI, optical attenuation and nebular line measurements from VLT-MUSE, and HST H$α$-based region sizes to estimate the strength of radiation pressure in $\approx 18,000$ HII regions across 19 nearby star-forming galaxies. This is the most extensive and direct estimate of these terms beyond the Local Group to date. In the disks of galaxies, we find that the total reprocessed IR pressure is on average 5% of the direct UV radiation pressure. This fraction rises to 10% in galaxy centers. We expect reprocessed IR radiation pressure to dominate over UV radiation pressure in regions where $L_{\rm F2100W}/L_{\rm Hα}^{\rm corr} \gtrsim 75$. Radiation pressure due to H ionizations is lower than pressure on dust in our sample, but appears likely to dominate the radiation pressure budget in dwarf galaxies similar to the Small Magellanic Cloud. The contribution from all radiation pressure terms appears to be subdominant compared to thermal pressure from ionized gas, reinforcing the view that radiation pressure is most important in compact, heavily embedded, and young regions.

astro-ph.GA↗