arXiv subjects

Davide Elia

Publications and source records attributed to Davide Elia.

At least 19 recordsLinked to original sources

arXiv2026

What sets the star-formation rate in the Milky Way? I. A multi-scale view of the star-formation rate

Context. The star-formation rate (SFR) is one of the key quantities that characterizes the star formation process and has been extensively investigated both observationally and theoretically. Aims. We aim to provide a coherent multi-scale view of star formation by connecting Galactic-scale conditions (kpc) to the properties of individual star-forming clumps at sub-parsec scales. Methods. We perform a set of numerical simulations with large-scale turbulent forcing designed to reproduce physical conditions typical of the solar neighbourhood. Using adaptive zooming down to 0.03 pc, we obtain a population of star-forming clumps that is analyzed and compared with observational catalogues in a companion paper. Results. For column densities and velocity dispersions consistent with Galactic values, the resulting SFR is close to the rate inferred for the Milky Way. Comparing this value with the SFR expected from pure free-fall collapse shows that turbulence provides multiscale support that lowers the SFR by more than an order of magnitude. Additional regulation by stellar feedback, including ionizing radiation and protostellar outflows, likely reduces the SFR by an additional factor of 3-10. Comparisons with observations across multiple spatial scales show good overall agreement with this model. Conclusions. These results support a picture in which turbulence plays a central role in regulating star formation in the Milky Way. In combination with stellar feedback, it limits the star formation efficiency to only a few percent. Key words. stars: formation -- ISM: clouds -- physical processes: turbulence

astro-ph.GA↗

arXiv2026

What sets the star-formation rate in the Milky Way?. II. Comparing the star-forming clumps from simulations and observations

Context. Linking the star formation (SF) properties of dense clumps to their parent large-scale environment is a key step to interpret Galactic surveys. Achieving a consistent, multi-scale picture of SF requires a comparative analysis of observations and simulations. Aims. We exploit kiloparsec-scale magneto-hydrodynamic simulations designed to reproduce local Milky Way conditions. Leveraging the wide range of scales covered by the simulations (reaching a resolution of 0.03 pc), we aim to compare the properties of the simulated population of star-forming clumps with observational catalogues. Methods. After extracting the star-forming structures with the HOP clump-finding algorithm, we compare their physical (mass and size) and SF properties (SF rate and efficiency) with those of the Hi-GAL compact source catalogue. Results. Despite the different methodologies and the three-dimensional nature of our clump extraction, the simulated clumps show good agreement with the observed sample in their mass and size distributions. We discover a consistently linear relation between mass and SF rate (SFR) for the simulated clumps, which is remarkably independent of the initial conditions of the boxes. Using scaling relations to distinguish between turbulence- and gravity-regulated gas inflow onto the clump scales, we find tentative evidence in favour of a gravity-regulated regime of SF at the probed sub-parsec scales. Key words. methods: numerical - stars: formation - ISM: clouds

astro-ph.GA↗

arXiv2026

A clump population framework for star formation across galactic scales

Whether star formation across different spatial scales and galactic environments follows universal laws remains poorly understood. We investigate cloud-scale star formation in 30 dwarf and disk galaxies. Molecular clouds are identified using a dendrogram algorithm, and their molecular gas masses ($M_{\rm H_2}$) and star formation rates (SFRs) are derived from integrated CO and mid-infrared emission, respectively. We find a consistent $M_{\rm H_2}$--SFR relation across all galaxies, with little sensitivity to galactic environment. Extending the analysis to Milky Way cloud substructures down to sub-parsec scales and 311 diverse nearby galaxies, we find that this relation persists across ten orders of magnitude in molecular gas mass and SFR. A theoretical model in which star formation occurs within dense clumps embedded in molecular clouds reproduces this observed relation. The weak environmental dependence of star formation at the clump scale provides a possible explanation for the nearly universal $M_{\rm H_2}$--SFR relation across galaxies. This framework establishes an observationally grounded connection between star formation in the Milky Way and external galaxies.

astro-ph.GA↗

arXiv2026

The Milky Way Joins the Extragalactic World: I. PHANGS

Complete catalogs of molecular clouds in the Milky Way allow analysis of the molecular medium and the star formation properties of the Milky Way that closely follows the method used for nearby galaxies, in particular in the PHANGS project. The dependencies of the depletion time on other properties of molecular gas in the Milky Way are similar to those of other galaxies when analyzed in an analogous way. They exhibit a large scatter and relatively weak correlations. The strongest correlation is a decrease in depletion time with increasing velocity dispersion. We explore the effects of spatial resolution, sensitivity, cloud identificaton method, averaging method, and tracer choice on our results. Metallicity effects in converting observations to mass can have a substantial impact. Somewhat fortuitously, differences in conversion methods between PHANGS and the Milky Way do not affect the current comparison. Inadequate spatial resolution, resulting in unresolved cloud structure, has the most important effect on interpretation of both extragalactic observations and existing catalogs of Milky Way clouds.

astro-ph.GA↗

arXiv2026

ALMAGAL VII. Cataloging Hierarchical Mass Structure from Cores to Clumps across the Galactic Disk

Investigating the multi-scale fragmentation of dense clumps into compact cores is essential for understanding the processes that govern the initial distribution of mass in stellar clusters and how high-mass stars ($>8~M_{\odot}$) form. We present a catalog of the hierarchical continuum structure from 904 clumps observed in the ALMAGAL program, a high resolution ($0.15-0.8$\arcsec) 1.38 mm Atacama Large Millimeter/submillimeter Array (ALMA) large program targeting dense clumps capable of high-mass star formation throughout the Galactic disk. We use \verb|astrodendro|, a dendrogram-based algorithm, on a uniform linear resolution (2000 au) version of the data to extract 5160 continuum structures with effective radii spanning $800-42000$ au and estimated masses between $~0.05-670~M_{\odot}$. With our large sample, we statistically examine differences in clump properties for regions with varying levels of hierarchical complexity. We find that clumps exhibiting the richest hierarchical morphology have distributions with higher dust temperatures, surface densities, luminosity-to-mass (\textit{L/M}) ratios, and most massive core (MMC) masses, indicating that these regions tend to be at later evolutionary stages. We find a positive correlation between the mass of cores from the ALMAGAL core catalog and the surface density of their surrounding structures identified in this work. However, this correlation is weaker for cores in more evolved clumps, where lower mass cores can be found at higher local surface densities. This could indicate that some cores accrete mass less efficiently from the intra-clump reservoir than others, despite the total available mass increasing over time, a scenario that is congruent with a clump-fed core accretion model.

astro-ph.GA↗

arXiv2026

Molecular Gas Morphological Analogues for the Milky Way

Complete catalogs of molecular clouds in the Milky Way allow analysis of the molecular medium and the star formation properties of the Milky Way that closely follows the method used for nearby galaxies. We explore whether the big dip in the radial distribution of molecular gas in the Milky Way is peculiar and find several other galaxies with similar patterns, all with similar morphological classifications of YClxxGnR, indicating a clearly defined, long bar leading to a grand-design spiral. This category is fairly rare among galaxies in the PHANGS sample, but all galaxies with this classification have some evidence for dips in the radial distribution of CO emission. The lengths of the bars correlate with the extents of the dips. The Milky Way and the other galaxies with dips have similar stellar masses and star formation rates, both lying near the high ends of the distributions for all PHANGS galaxies.

astro-ph.GA↗

arXiv2025

The Rosetta Stone Project. II. The correlation between star formation efficiency and L/M indicator for the evolutionary stages of star-forming clumps in post-processed radiative magnetohydrodynamics simulations

Context. The evolution of massive star-forming clumps that are progenitors of high-mass young stellar objects are often classified based on a variety of observational indicators ranging from near-infrared to radio wavelengths. Among them, the ratio of the bolometric luminosity to the mass of their envelope, $L/M$, has been observationally diagnosed as a good indicator for the evolutionary classification of parsec-scale star-forming clumps in the Galaxy. Aims. We developed the Rosetta Stone project$\unicode{x2013}$an end-to-end framework designed to enable an accurate comparison between simulations and observations for investigating the formation and evolution of massive clumps. In this study, we calibrate the $L/M$ indicator in relation to the star formation efficiency (SFE) and the clump age, as derived from our suite of simulations. Methods. We performed multi-wavelength radiative transfer post-processing of radiative magnetohydrodynamics (RMHD) simulations of the collapse of star-forming clumps fragmenting into protostars. We generated synthetic observations to obtain far-infrared emission from $70$ to $500\,μ$m, as was done in the Hi-GAL survey, and at $24\,μ$m in the MIPSGAL survey, which were then used to build the spectral energy distributions (SEDs) and estimate the $L/M$ parameter. An additional $1.3\,$mm wavelength in ALMA Band 6 was also produced for the comparison with observational data. We applied observational techniques$\unicode{x2013}$commonly employed by observers$\unicode{x2013}$to the synthetic data in order to derive the corresponding physical parameters. Results. We find a correlation between $L/M$ and the SFE, with a power-law form $L/M\propto {\rm SFE}^{1.20^{+0.02}_{-0.02}}$. This correlation is independent of the mass of the clumps and the choice of initial conditions of the simulations in which they formed. (Abridged)

astro-ph.GA↗

arXiv2025

The Rosetta Stone Project. I. A suite of radiative magnetohydrodynamics simulations of high-mass star-forming clumps

Context. Star formation and, in particular, high-mass star formation are key astrophysical processes that are far from being fully understood. Unfortunately, progress in these fields is slow because observations are hard to interpret as they cannot be directly compared to numerical simulations. Synthetic observations are therefore necessary to better constrain the models. Aims. With the Rosetta Stone project, we aim to develop an end-to-end pipeline to compare star formation simulations with observations as accurately as possible in order to study the evolution from clumps scales to stars. Methods. Using the adaptive mesh-refinement code RAMSES, we computed a first grid of model of star-forming clumps to develop our pipeline and explore the impact of the clump initial conditions on their evolution. The main purpose of this set of simulations is to be converted into synthetic observations to enable a direct comparison with real star-forming clumps observed with Herschel and ALMA. Results. The Rosetta Stone simulations presented here provide a catalog available for full post-processing and subsequent comparison with observations (RS1). Among all the parameters explored here, the strength of the magnetic field has the strongest influence on the clump evolution (fragmentation, star formation, global collapse) at both large and small scales. Numerical parameters such as the resolution per Jeans length or the threshold for accretion onto sink particles affects the formation of low-mass sinks. Finally, the widely used L/M ratio is found to be a good indicator of the clump evolutionary state regardless of its initial condition, but this could change when more feedback processes (jets, HII regions) are included. Conclusions. We now have a new suite of simulations of star-forming clumps that is available for full post-processing and subsequent comparison with the observations,

astro-ph.SR↗

arXiv2025

The Rosetta Stone project. III. ALMA synthetic observations of fragmentation in high-mass star-forming clumps

The physical mechanisms that regulate the collapse of high-mass parsec-scale clumps and allow them to form clusters of new stars represent a crucial aspect of star formation. To investigate these mechanisms, we developed the Rosetta Stone project: an end-to-end (simulations-observations) framework that is based on the systematic production of realistic synthetic observations of clump fragmentation and their comparison with real data. In this work, we compare ALMA 1.3mm continuum dust emission observations from the SQUALO survey with a new set of 24 radiative magnetohydrodynamical simulations of high-mass clump fragmentation, post-processed using the CASA software to mimic the observing strategy of SQUALO. The simulations were initialized combining typical values of clump mass (500,1000 solar masses) and radius (~0.4pc) with two levels of turbulence (Mach number of 7,10) and three levels of magnetization (mass-to-flux ratio of ~3,10,100). Following the clump evolution over time with two random seeds projected along three orthogonal directions, we produced a collection of 732 synthetic fields. The synthetic observations of clump fragmentation at ~7000AU revealed between 2 and 14 fragments per field. Among the initial conditions of the simulations, magnetic fields have the largest impact on the fragment multiplicity at these scales. In advanced stages of clump evolution, a lower number of fragments is preferentially associated with magnetized clumps. Fragments identified at ~7000AU correspond to individual or multiple sink particles in ~75% of the cases, suggesting that not all fragments are actively forming stars. Both sinks and fragments accrete mass throughout the whole clump evolution, favoring a scenario in which fragments are not isolated from the environment. Our study demonstrates the importance of synthetic observations in interpreting results from interferometric observations.

astro-ph.SR↗

arXiv2025

The Evolutionary Path of Star-Forming Clumps in Hi-GAL

Star formation (SF) studies are benefiting from the huge amount of data made available by recent large-area Galactic plane surveys conducted between 2 μm and 3 mm. Fully characterizing SF demands integrating far-infrared/sub-millimetre (FIR/sub-mm) data, tracing the earliest phases, with near-/mid-infrared (NIR/MIR) observations, revealing later stages characterized by YSOs just before main sequence star appearance. However, the resulting dataset is often a complex mix of heterogeneous and intricate features, limiting the effectiveness of traditional analysis in uncovering hidden patterns and relationships. In this framework, machine learning emerges as a powerful tool to handle the complexity of feature-rich datasets and investigate potential physical connections between the cold dust component traced by FIR/sub-mm emission and the presence of YSOs. We present a study on the evolutionary path of star forming clumps in the Hi-GAL survey through a multi-step approach, with the final aims of (a) obtaining a robust and accurate set of features able to well classify the star forming clumps in Hi-GAL based on their evolutionary properties, (b) establishing whether a connection exists between the cold material reservoir in clumps, traced by FIR/sub-mm emission, and the already formed YSOs, precursors of stars. For these purposes, our designed experiments aim at testing whether the FIR/sub-mm properties related to clumps are sufficient to predict the clump evolutionary stage, without considering the direct information about the embedded YSOs at NIR/MIR. Our machine learning-based method involves a four-step approach, based on feature engineering, data handling, feature selection and classification. Our findings suggest that FIR/sub-mm and NIR/MIR emissions trace different evolutionary phases of star forming clumps, highlighting the complex and asynchronous nature of the SF process.

astro-ph.GA↗

arXiv2025

Star formation efficiency and scaling relations in parsec-scale cluster-forming clumps

Numerical simulations predict that clumps ($\sim$1 pc) should form stars at high efficiency to produce bound star clusters. We conducted a statistical study of 17 nearby cluster-forming clumps to examine the star formation rate and gas mass surface density relations (i.e. $Σ_{\rm{SFR}}$ vs. $Σ_{\rm{gas}}$) at the clump scale. Using near-infrared point sources and Herschel dust continuum analysis, we obtained the radius, age, and stellar mass for most clusters in the ranges 0.5$-$1.6 pc, 0.5$-$1.5 Myr, 40$-$500 M$_\odot$, respectively, and also found that they are associated with $Σ_{\rm{gas}}$ values ranging from 80$-$600 M$_\odot$ pc$^{-2}$. We obtained the best-fit scaling relations as $Σ_{\rm{SFR}}$ $\propto$ $Σ_{\rm{gas}}^{1.46}$ and $Σ_{\rm{SFR}}$ $\propto$ $(Σ_{\rm{gas}}/t_{\rm{ff}})^{0.80}$ for the studied sample of clumps. Comparing our results with existing scaling relations at cloud and extragalactic scales, we found that while the power-law exponent obtained in this work is similar to those found at these scales, the star formation rate surface densities are relatively higher for similar gas mass surface densities. From this work, we obtained instantaneous median star formation efficiency (SFE) and efficiency per free-fall time ($ε_{\rm{ff}}$) of $\sim$20% and $\sim$13%, respectively, for the studied clumps. We discuss the cause of the obtained high SFE and $ε_{\rm{ff}}$ in the studied clumps and also discuss the results in the context of bound cluster formation within molecular clouds. We conclude that our results do not favour a universal scaling law with a constant value of $ε_{\rm{ff}}$ in star-forming systems across different scales.

astro-ph.GA↗

arXiv2025

Variation of Dense Gas Mass-Luminosity conversion factor with metallicity in the Milky Way

HCN and HCO$^+$ are the most common dense gas tracers used both in the Milky Way and external galaxies. The luminosity of HCN and HCO$^+$ $J = 1-0$ lines are converted to a dense gas mass by the conversion factor, $α_{Q}$. Traditionally, this $α_{Q}$ has been considered constant throughout the Galaxy and in other galaxies, regardless of the environment. We analyzed 17 outer Galaxy clouds and 5 inner Galaxy clouds with metallicities ranging from 0.38 Z$_{\odot}$ to 1.29 Z$_{\odot}$. Our analysis indicates that $α_{Q}$ is not constant; instead, it varies with metallicity. The metallicity-corrected $α_{Q}$ derived from the HCN luminosity of the entire cloud is almost three times higher in the outer Galaxy than in the inner galaxy. In contrast, HCO$^+$ seems less sensitive to metallicity. We recommend using the metallicity-corrected dense gas conversion factors $α^{'}_{\rm tot, Gas}(\rm HCN) = 19.5^{+5.6}_{-4.4} Z^{(-1.53 \pm 0.59)}$ and $α^{'}_{\rm tot, Gas}(\rm HCO^{+}) = 21.4^{+5.5}_{-4.4} Z^{(-1.32\pm0.55)}$ for extragalactic studies. Radiation from nearby stars has an effect on the conversion factor of similar magnitude as that of the metallicity. If we extend the metallicity-corrected scaling relation for HCN to the Central Molecular Zone, the value of $α(\rm HCN)$ becomes $1/3$ to $1/2$ of the local values. This effect could partially account for the low star formation rate per dense gas mass observed in the CMZ.

astro-ph.GA↗

arXiv2024

The Giant Molecular Cloud G148.24+00.41: Gas Properties, Kinematics, and Cluster Formation at the Nexus of Filamentary Flows

Filamentary flows toward the centre of molecular clouds have been recognized as a crucial process in the formation and evolution of stellar clusters. In this paper, we present a comprehensive observational study that investigates the gas properties and kinematics of the Giant Molecular Cloud G148.24+00.41 using the observations of CO (1-0) isotopologues. We find that the cloud is massive (10$^5$ M$_\odot$) and is one of the most massive clouds of the outer Galaxy. We identified six likely velocity coherent filaments in the cloud having length, width, and mass in the range of 14$-$38 pc, 2.5$-$4.2 pc, and (1.3$-$6.9) $\times$ 10$^3$ M$_\odot$, respectively. We find that the filaments are converging towards the central area of the cloud, and the longitudinal accretion flows along the filaments are in the range of $\sim$ 26$-$264 M$_\odot$ Myr$^{-1}$. The cloud has fragmented into 7 clumps having mass in the range of $\sim$ 260$-$2100 M$_\odot$ and average size around $\sim$ 1.4 pc, out of which the most massive clump is located at the hub of the filamentary structures, near the geometric centre of the cloud. Three filaments are found to be directly connected to the massive clump and transferring matter at a rate of $\sim$ 675 M$_\odot$ Myr$^{-1}$. The clump hosts a near-infrared cluster. Our results show that large-scale filamentary accretion flows towards the central region of the collapsing cloud is an important mechanism for supplying the matter necessary to form the central high-mass clump and subsequent stellar cluster.

astro-ph.GA↗

arXiv2024

Understanding the relative importance of magnetic field, gravity, and turbulence in star formation at the hub of the giant molecular cloud G148.24+00.41

The relative importance of magnetic fields, turbulence, and gravity in the early phases of star formation is still not well understood. We report the first high-resolution dust polarization observations at 850 $μ$m around the most massive clump, located at the hub of the Giant Molecular Cloud G148.24+00.41, using SCUBA-2/POL-2 at the James Clerk Maxwell Telescope. We find that the degree of polarization decreases steadily towards the denser portion of the cloud. Comparing the intensity gradients and local gravity with the magnetic field orientations, we find that local gravity plays a dominant role in driving the gas collapse as the magnetic field orientations and gravity vectors seem to point towards the dense clumps. We also find evidence of U-shaped magnetic field morphology towards a small-scale elongated structure associated with the central clump, hinting at converging accretion flows towards the clump. Our observation has resolved the massive clump into multiple substructures. We study the magnetic field properties of two regions, central clump (CC) and northeastern elongated structure (NES). Using the modified Davis-Chandrasekhar Fermi method, we determine that the magnetic field strengths of CC and NES are $\sim$24.0 $\pm$ 6.0 $μ$G and 20.0 $\pm$ 5.0 $μ$G, respectively. The mass-to-flux ratios are found to be magnetically transcritical/supercritical, while the Alfv$\acute{\text{e}}$n Mach number indicates a trans-Alfv$\acute{\text{e}}$nic state in both regions. These results, along with Virial analysis, suggest that at the hub of G148.24+00.41, gravitational energy has an edge over magnetic and kinetic energies.

astro-ph.GA↗

arXiv2023

Probing the Global Dust Properties and Cluster Formation Potential of the Giant Molecular Cloud G148.24+00.41

Clouds more massive than about $10^5$ M$_\odot$ are potential sites of massive cluster formation. Studying the properties of such clouds in the early stages of their evolution offers an opportunity to test various cluster formation processes. We make use of CO, Herschel, and UKIDSS observations to study one such cloud, G148.24+00.41. Our results show the cloud to be of high mass ($\sim$ $1.1\times10^5$ M$_\odot$), low dust temperature ($\sim$ 14.5 K), nearly circular (projected radius $\sim$ 26 pc), and gravitationally bound with a dense gas fraction of $\sim 18$% and a density profile with a power-law index of $\sim -1.5$. Comparing its properties with those of nearby molecular clouds, we find that G148.24+00.41 is comparable to the Orion-A molecular cloud in terms of mass, size, and dense gas fraction. From our analyses, we find that the central area of the cloud is actively forming protostars and is moderately fractal with a Q-value of $\sim$ 0.66. We also find evidence of global mass-segregation in the cloud, with a degree of mass-segregation ($Λ_{MSR}) \approx3.2$. We discuss these results along with the structure and compactness of the cloud, the spatial and temporal distribution of embedded stellar population, and their correlation with the cold dust distribution, in the context of high-mass cluster formation. Comparing our results with models of star cluster formation, we conclude that the cloud has the potential to form a cluster in the mass range $\sim$ 2000--3000 M$_\odot$ through dynamical hierarchical collapse and assembly of both gas and stars.

astro-ph.GA↗

arXiv2022

How magnetic field and stellar radiative feedback influences the collapse and the stellar mass spectrum of a massive star forming clump

In spite of decades of theoretical efforts, the physical origin of the stellar initial mass function (IMF) is still debated. We aim at understanding the influence of various physical processes such as radiative stellar feedback, magnetic field and non-ideal magneto-hydrodynamics on the IMF. We present a series of numerical simulations of collapsing 1000 M$_\odot$ clumps taking into account radiative feedback and magnetic field with spatial resolution down to 1 AU. Both ideal and non-ideal MHD runs are performed and various radiative feedback efficiencies are considered. We also develop analytical models that we confront to the numerical results. The sum of the luminosities produced by the stars in the calculations is computed and it compares well with the bolometric luminosities reported in observations of massive star forming clumps. The temperatures, velocities and densities are also found to be in good agreement with recent observations. The stellar mass spectrum inferred for the simulations is, generally speaking, not strictly universal and in particular varies with magnetic intensity. It is also influenced by the choice of the radiative feedback efficiency. In all simulations, a sharp drop in the stellar distribution is found at about $M_{min} \simeq$ 0.1 M$_\odot$, which is likely a consequence of the adiabatic behaviour induced by dust opacities at high densities. As a consequence, when the combination of magnetic and thermal support is not too large, the mass distribution presents a peak located at 0.3-0.5 M$_\odot$. When magnetic and thermal support are large, the mass distribution is better described by a plateau, i.e. $d N / d \log M \propto M^{-Γ}$, $Γ\simeq 0$. Abridged

astro-ph.GA↗

arXiv2022

The signature of large scale turbulence driving on the structure of the interstellar medium

The mechanisms that maintain turbulence in the interstellar medium (ISM) are still not identified. This work investigates how we can distinguish between two fundamental driving mechanisms: the accumulated effect of stellar feedback versus the energy injection from Galactic scales. We perform a series of numerical simulations describing a stratified star forming ISM subject to self-consistent stellar feedback. Large scale external turbulent driving of various intensities is added to mimic galactic driving mechanisms. We analyse the resulting column density maps with a technique called Multi-scale non-Gaussian segmentation that separates the coherent structures and the Gaussian background. This effectively discriminates between the various simulations and is a promising method to understand the ISM structure. In particular the power spectrum of the coherent structures flattens above 60 pc when turbulence is driven only by stellar feedback. When large-scale driving is applied, the turn-over shifts to larger scales. A systematic comparison with the Large Magellanic Cloud (LMC) is then performed. Only 1 out of 25 regions has a coherent power spectrum which is consistent with the feedback-only simulation. A detailed study of the turn-over scale leads us to conclude that regular stellar feedback is not enough to explain the observed ISM structure on scales larger than 60 pc. Extreme feedback in the form of supergiant shells likely plays an important role but cannot explain all the regions of the LMC. If we assume ISM structure is generated by turbulence, another large scale driving mechanism is needed to explain the entirety of the observations.

astro-ph.GA↗

arXiv2022

The Galactic dynamics revealed by the filamentary structure in atomic hydrogen emission

We present a study of the filamentary structure in the atomic hydrogen (HI) emission at the 21 cm wavelength toward the Galactic plane using the observations in the HI4PI survey. Using the Hessian matrix method across radial velocity channels, we identified the filamentary structures and quantified their orientations using circular statistics. We found that the regions of the Milky Way's disk beyond 10 kpc and up to roughly 18 kpc from the Galactic center display HI filamentary structures predominantly parallel to the Galactic plane. For regions at lower Galactocentric radii, we found that the HI filaments are mostly perpendicular or do not have a preferred orientation with respect to the Galactic plane. We interpret these results as the imprint of supernova feedback in the inner Galaxy and Galactic rotation in the outer Milky Way. We found that the HI filamentary structures follow the Galactic warp and that they highlight some of the variations interpreted as the effect of the gravitational interaction with satellite galaxies. In addition, the mean scale height of the filamentary structures is lower than that sampled by the bulk of the HI emission, thus indicating that the cold and warm atomic hydrogen phases have different scale heights in the outer galaxy. Finally, we found that the fraction of the column density in HI filaments is almost constant up to approximately 18 kpc from the Galactic center. This is possibly a result of the roughly constant ratio between the cold and warm atomic hydrogen phases inferred from the HI absorption studies. Our results indicate that the HI filamentary structures provide insight into the dynamical processes shaping the Galactic disk. Their orientations record how and where the stellar energy input, the Galactic fountain process, the cosmic ray diffusion, and the gas accretion have molded the diffuse interstellar medium in the Galactic plane.

astro-ph.GA↗