arXiv subjects

A. Zavagno

Publications and source records attributed to A. Zavagno.

At least 19 recordsLinked to original sources

arXiv2026

Young star clusters in the extended UV disk of M83

The process of star formation in a low-metallicity environment and whether it differs from star formation in the solar neighbourhood is an open topic. Recently, CO clumps were identified within the extended ultraviolet (XUV) disk of M83 despite the low metallicity and distance from the galaxy center which allows a search for any recent star formation in the clumps. We aim to probe whether active star formation is occurring within the CO clumps in the XUV disk, and to assess its implications for star formation in such environments. We analyse deep Subaru Suprime-Cam Halpha, Hyper Suprime-Cam g, r, & i, and Gemini/FLAMINGOS 2 J and Ks band imaging to search for evidence of star formation within the ALMA-identified CO clumps. We identify sources within the CO clump contours, and we evaluate the probability that these sources are associated with the CO clumps rather than being chance alignments. Based on their magnitudes and adopting single-age stellar population models, we estimate their masses. Four of the clumps have an associated near-infrared counterpart. Based on their magnitude, color, and the general source density in the field, two of these could be chance alignments. One counterpart is associated with the most massive clump in the sample, while another is an unresolved cluster near-infrared source with an estimated age of 5 Myr and a mass of 2000 Msun. The other, an extended complex, is consistent with an age of 6Myr and a mass of 700Msun. The near-infrared photometry is sensitive to young clusters with masses down to a few hundred of Msun for a fully sampled IMF. Star formation is ongoing in a few of the CO clumps, and despite their location on the outskirts of M83, favourable conditions for star formation persist in at least a few clusters. One of the detected sources appears to be interacting with an adjacent molecular clump, which could trigger further star formation.

astro-ph.GA↗

arXiv2026

The 10-15 GHz radio continuum survey of the Galactic Plane with SKAO

Star formation emerges from the complex interplay between gravity, turbulence, magnetic fields, and stellar feedback, all of which vary across spatial scales and Galactic environments. Over the past decades, extensive multiwavelength surveys of the Galactic Plane have progressively unveiled this complexity. Far-infrared and sub-millimetre surveys have identified and characterized tens of thousands of star-forming regions, revealing their mass, temperature, and evolutionary stage. Complementary molecular-line surveys, spanning several CO transitions and isotopologues, have mapped the gas kinematics from giant molecular clouds down to sub-parsec structures. The advent of interferometers such as ALMA has revolutionized this field, enabling systematic studies of gas dynamics, fragmentation, and collapse in dense clumps at scales of a few thousand astronomical units. At the same time, mid-infrared and radio surveys at frequencies 0.8 <= nu <= 5 GHz have traced ionised gas associated with the earliest and latest phases of massive-star evolution, including thermal radio jets, hypercompact and ultracompact HII regions, supernova remnants, planetary nebulae, and evolved massive stars. Yet, a uniform, Galaxy-wide census of ionised structures and feedback processes remains elusive. A transformational leap forward requires a sensitive, high-resolution radio survey of the Galactic Plane at 10-15 GHz, capable of resolving physical scales smaller than 0.05 pc at distances up to 20 kpc. This is precisely the goal of the SKA-Mid Galactic Plane survey, which will, with its unprecedented sensitivity, angular resolution, and mapping speed, provide the first panoptic view of ionised gas and stellar feedback across the Milky Way.

astro-ph.GA↗

arXiv2026

B-Fields and Star Formation across Scales with TRAO (B-FROST): CO Abundances, Dynamics and Relative Orientations in the Translucent High Latitude Cloud MBM12

In our Galaxy, the average star formation efficiency is of the order of a few percent. We investigated the high-latitude molecular cloud MBM12 as part of the B-fields and star formation across scales (B-FROST) survey with the Taeduk Radio Astronomical Observatory (TRAO) to assess why star formation activity in MBM12 is low. We combine {\it Herschel}-based, locally $κ_ν$-calibrated $N$(H$_2$) estimates with $^{12}$CO and $^{13}$CO ($J=1-0$) observations (2.5$^\circ \times$3$^\circ$ at 48$''$) to map $N$(CO), $X$(CO), and [CO/H$_2$], compute multi-scale $α_{\rm vir}$ and mass-size scaling laws from dendrograms, and derive the histogram of relative orientations from {\it Planck} dust polarisation. We identify four main regions based on velocities that have H$_2$ column densities ranging from $2\times10^{20}$ cm$^{-2} - 1.3\times10^{22}$ cm$^{-2}$. The average $X$(CO) is close to the galactic average, with variations below $X_{\rm Gal}$ from collisional de-excitation in low-density gas, and above $X_{\rm Gal}$ from CO photodissociation at cloud edges. The hierarchical structures follow a broken power law mass-size relation $M=AR^α$. The values of $α_{\rm vir}$ ranged from $3-60$, with the smallest values at 0.1 pc scales. The mass-size relations for the structures with the lowest $α_{\rm vir}$ have scaling factors $A$ three times larger than those of high $α_{\rm vir}$ structures, indicating external pressure one order of magnitude larger. We found a transition of parallel to perpendicular between column density structures and magnetic field orientations at $N$(H$_2$) $= 4.5 \times 10^{21}$ cm$^{-2}$. We provide the first integrated chemical, dynamical, and magnetic field analysis of MBM12. Scale-dependent mass-size and virial analysis can further constrain the role of external pressure in regulating the star formation efficiency.

astro-ph.GA↗

arXiv2026

Kinematics of the HII region NGC 7538 from study of the Ha line

Aims. Massive stars impact their surrounding initiating star-formation along their photo-dissociation region. Once the HII region is formed it is unclear if and how the second generation of stars impacts its aspect and evolution. Methods. We performed high spectral resolution (R ~ 23400) Ha Fabry-Perot observations in five fields covering the Galactic HII region NGC 7538 and lead profiles multi-gaussian fitting to extract the parameters as peak intensity, width and velocity. We then analyse the kinematics of the ionised gas building kinematic diagrams and second order structure functions for every field. Results. The observations reveal a general blue-shifted ionised gas flow larger than 11 km s-1 in NGC 7538, consistent with previous studies. Profiles originating from features that are dark in Ha due to extinction or from outside the region show velocity dispersion larger than the one typically found for the Warm Interstellar Medium. The analysis of kinematic diagrams and second-order structure functions reveals non-thermal motions attributed to turbulence and large-scale velocity gradients. In the direction of the HII region itself the turbulence seems to be shock-dominated, with a characteristic scale length between ~ 0.72 and 1.46 pc. In this context, we propose that the kinematics of the central part of the region could be explained by the superposition of the outflow coming from IRS1 and a wind bow shock formed ahead IRS6.

astro-ph.GA↗

arXiv2025

FIRESTORM I: Stellar Feedback and Gas Kinematics in the Evolved W40 Hub-Filament System

The FIRESTORM project--Feedback-Induced Regions and Emission from Star-forming Tracers of ObseRvable Molecular Gas--has targeted four star-forming regions to quantify the impact of stellar feedback on star formation. In this paper, we present multiwavelength results for one of the targets, the nearby high-mass star-forming region W40. Using dense-gas tracers C$^{18}$O(1--0) and H$^{13}$CO$^+$(1--0), we identified six velocity-coherent filaments: five at \vlsr $\sim$\,7.5\kms\! and one at \vlsr $\sim$\,5\kms. Four of these converge towards an infrared-bright cluster hosting the most massive star of the region (IRS 1A South, O9.5V), forming a hub-filament system (HFS). Key physical parameters, including filament lengths, widths, masses, velocity dispersions, and line masses, are derived. Five dense clumps traced by N$_2$H$^+$(1--0) exhibit subsonic to transonic turbulence, contrasting with the supersonic motions of their parental filaments, indicating turbulence dissipation. A deficit of emission at \vlsr $\sim$\,7\kms\! in several molecular lines, along with a blueshifted absorption dip in the HCN(1--0) profile, suggests that emission from OB-heated gas is being absorbed by a cold foreground cloud. A bridge-like feature in position-velocity space connects the \vlsr $\sim$\,5 and $\sim$\,7.5\kms\! filaments, and spatially coinciding with dense condensations and radio continuum peaks. These findings suggest that a past interaction--likely a cloud-cloud collision--triggered the formation of HFS and ultimately the central massive cluster.

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

A Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE) XVII. Statistical properties of individual HII regions in unperturbed systems

The Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE) is a blind narrow-band Halpha+[NII] imaging survey of the Virgo cluster carried out with MegaCam at the CFHT telescope. The survey provides deep narrow-band images for 385 galaxies hosting star forming HII regions. We identify individual HII regions and measure their main physical properties such as Halpha luminosity, equivalent diameter, and electron density with the purpose of deriving standard relations as reference for future local and high-z studies of HII regions in star forming systems in different environments. For this purpose we use a complete sample of ~ 13.000 HII regions of luminosity L(Halpha)>= 10^37 erg s^-1 to derive the main statistical properties of HII regions in unperturbed systems, identified as those galaxies with a normal HI gas content (64 objects). These are the composite Halpha luminosity function, equivalent diameter and electron density distribution, and luminosity-size relation. We also derive the main scaling relations between several parameters representative of the HII regions properties (total number, luminosity of the first ranked regions, fraction of the diffuse component, best fit parameters of the Schechter luminosity function measured for individual galaxies) and those characterising the properties of the host galaxies (stellar mass, star formation rate and specific star formation rate, stellar mass and star formation rate surface density, metallicity, molecular-to-atomic gas ratio, total gas-to-dust mass ratio). We briefly discuss the results of this analysis and their implications in the study of the star formation process in galaxy discs.

astro-ph.GA↗

arXiv2024

Understanding the Star Formation Efficiency in Dense Gas: Initial Results from the CAFFEINE Survey with ArTéMiS

Despite recent progress, the question of what regulates the star formation efficiency in galaxies remains one of the most debated problems in astrophysics. According to the dominant picture, star formation (SF) is regulated by turbulence and feedback, and the SFE is 1-2% per local free-fall time. In an alternate scenario, the SF rate in galactic disks is linearly proportional to the mass of dense gas above a critical density threshold. We aim to discriminate between these two pictures thanks to high-resolution observations tracing dense gas and young stellar objects (YSOs) for a comprehensive sample of 49 nearby massive SF complexes out to d < 3 kpc in the Galactic disk. We use data from CAFFEINE, a 350/450 $μ$m survey with APEX/ArTéMiS of the densest portions of all southern molecular clouds, in combination with Herschel data to produce column density maps at 8" resolution. Our maps are free of saturation and resolve the structure of dense gas and the typical 0.1 pc width of molecular filaments at 3 kpc, which is impossible with Herschel data alone. Coupled with SFR estimates derived from Spitzer observations of the YSO content of the same clouds, this allows us to study the dependence of the SFE with density in the CAFFEINE clouds. We also combine our findings with existing SFE measurements in nearby clouds to extend our analysis down to lower column densities. Our results suggest that the SFE does not increase with density above the critical threshold and support a scenario in which the SFE in dense gas is approximately constant. However, the SFE measurements traced by Class I YSOs in nearby clouds are more inconclusive, since they are consistent with both the presence of a density threshold and a dependence on density above the threshold. Overall, we suggest that the SFE in dense gas is primarily governed by the physics of filament fragmentation into protostellar cores.

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

The SOFIA FEEDBACK Legacy Survey: Rapid molecular cloud dispersal in RCW 79

It has long been discussed whether stellar feedback in the form of winds and/or radiation can shred the nascent molecular cloud, thereby controlling the star formation rate. However, directly probing and quantifying the impact of stellar feedback on the neutral gas of the nascent clouds is challenging. We present an investigation doing exactly that toward the RCW 79 HII region using the ionized carbon line at 158 $μ$m ([CII]) from the FEEDBACK Legacy Survey. We combine this data with information on the dozen ionizing O stars responsible for the evolution of the region, and observe in [CII] for the first time both blue- and red-shifted mostly neutral high-velocity gas which reaches velocities up to 25 km s$^{-1}$ relative to the bulk emission of the molecular cloud. This high-velocity gas mostly contains neutral gas and partly forms a fragmented shell, similar to recently found shells in a few Galactic HII regions. However, this shell does not account for all of the observed neutral high-velocity gas. We also find high-velocity gas streaming out of the nascent cloud through holes and obtain a range of dynamical timescales below 1.0 Myr for the high-velocity gas which is well below the 2.3$\pm$0.5 Myr age of the OB cluster. This suggests a different scenario for the evolution of RCW 79, where the high-velocity gas is not solely stemming from a spherical expanding bubble, but also from gas recently ablated at the edge of the turbulent molecular cloud into the surrounding interstellar medium through low-pressure holes or chimneys. The resulting mass ejection rate estimate for the cloud is 0.9-3.5$\times$10$^{-2}$ M$_{\odot}$~yr$^{-1}$, which leads to short erosion timescales, i.e. $<$5 Myr, for the nascent molecular cloud. This finding provides direct observational evidence of rapid molecular cloud dispersal.

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↗

arXiv2023

ATOMS: ALMA Three-millimeter Observations of Massive Star-forming regions -XIII. Ongoing triggered star formation within clump-fed scenario found in the massive ($\sim1500$ $\rm M_\odot$) clump

Whether ionization feedback triggers the formation of massive stars is highly debated. Using ALMA 3 mm observations with a spatial resolution of $\sim 0.05$ pc and a mass sensitivity of 1.1 $\rm M_\odot$ beam$^{-1}$ at 20 K, we investigate the star formation and gas flow structures within the ionizing feedback-driven structure, a clump-scale massive ($\gtrsim 1500$ $\rm M_\odot$) bright-rimmed cloud (BRC) associated with IRAS 18290-0924. This BRC is bound only if external compression from ionized gas is considered. A small-scale ($\lesssim1$ pc) age sequence along the direction of ionizing radiation is revealed for the embedded cores and protostars, which suggests triggered star formation via radiation-driven implosion (RDI). Furthermore, filamentary gas structures converge towards the cores located in the BRC's center, indicating that these filaments are fueling mass towards cores. The local core-scale mass infall rate derived from H$^{13}$CO$^+$ $J=1-0$ blue profile is of the same order of magnitude as the filamentary mass inflow rate, approximately 1 $\rm M_\odot$ kyr$^{-1}$. A photodissociation region (PDR) covering the irradiated clump surface is detected in several molecules, such as CCH, HCO$^+$, and CS whereas the spatial distribution stratification of these molecules is indistinct. CCH spectra of the PDR possibly indicate a photoevaporation flow leaving the clump surface with a projected velocity of $\sim2$ km s$^{-1}$. Our new observations show that RDI accompanied by a clump-fed process is operating in this massive BRC. Whether this combined process works in other massive BRCs is worth exploring with dedicated surveys.

astro-ph.GA↗

arXiv2022

Supervised machine learning on Galactic filaments Revealing the filamentary structure of the Galactic interstellar medium

Context. Filaments are ubiquitous in the Galaxy, and they host star formation. Detecting them in a reliable way is therefore key towards our understanding of the star formation process. Aims. We explore whether supervised machine learning can identify filamentary structures on the whole Galactic plane. Methods. We used two versions of UNet-based networks for image segmentation.We used H2 column density images of the Galactic plane obtained with Herschel Hi-GAL data as input data. We trained the UNet-based networks with skeletons (spine plus branches) of filaments that were extracted from these images, together with background and missing data masks that we produced. We tested eight training scenarios to determine the best scenario for our astrophysical purpose of classifying pixels as filaments. Results. The training of the UNets allows us to create a new image of the Galactic plane by segmentation in which pixels belonging to filamentary structures are identified. With this new method, we classify more pixels (more by a factor of 2 to 7, depending on the classification threshold used) as belonging to filaments than the spine plus branches structures we used as input. New structures are revealed, which are mainly low-contrast filaments that were not detected before.We use standard metrics to evaluate the performances of the different training scenarios. This allows us to demonstrate the robustness of the method and to determine an optimal threshold value that maximizes the recovery of the input labelled pixel classification. Conclusions. This proof-of-concept study shows that supervised machine learning can reveal filamentary structures that are present throughout the Galactic plane. The detection of these structures, including low-density and low-contrast structures that have never been seen before, offers important perspectives for the study of these filaments.

astro-ph.GA↗

arXiv2022

The Star Formation Rate of the Milky Way as seen by Herschel

We present a new derivation of the Milky Way's current star formation rate (SFR) based on the data of the Hi-GAL Galactic plane survey. We estimate the distribution of the SFR across the Galactic plane from the star-forming clumps identified in the Hi-GAL survey and calculate the total SFR from the sum of their contributions. The estimate of the global SFR amounts to $2.0 \pm 0.7$~M$_{\odot}$~yr$^{-1}$, of which $1.7 \pm 0.6$~M$_{\odot}$~yr$^{-1}$ coming from clumps with reliable heliocentric distance assignment. This value is in general agreement with estimates found in the literature of last decades. The profile of SFR density averaged in Galactocentric rings is found to be qualitatively similar to others previously computed, with a peak corresponding to the Central Molecular Zone and another one around Galactocentric radius $R_\mathrm{gal} \sim 5$~kpc, followed by an exponential decrease as $\log(Σ_\mathrm{SFR}/[\mathrm{M}_\odot~\mathrm{yr}^{-1}~\mathrm{kpc}^{-2}])=a\,R_\mathrm{gal}/[\mathrm{kpc}]+b $, with $a=-0.28 \pm 0.01$. In this regard, the fraction of SFR produced within and outside the Solar circle is 84\% and 16\%, respectively; the fraction corresponding to the far outer Galaxy ($R_\mathrm{gal} > 13.5$~kpc) is only 1\%. We also find that, for $R_\mathrm{gal}>3$~kpc, our data follow a power law as a function of density, similarly to the Kennicutt-Schmidt relation. Finally, we compare the distribution of the SFR density across the face-on Galactic plane and those of median parameters, such as temperature, luminosity/mass ratio and bolometric temperature, describing the evolutionary stage of Hi-GAL clumps. We found no clear correlation between the SFR and the clump evolutionary stage.

astro-ph.GA↗

arXiv2022

The SOFIA FEEDBACK Legacy Survey: Dynamics and mass ejection in the bipolar HII region RCW 36

We present [CII] 158 $μ$m and [OI] 63 $μ$m observations of the bipolar HII region RCW 36 in the Vela C molecular cloud, obtained within the SOFIA legacy project FEEDBACK, which is complemented with APEX $^{12/13}$CO(3-2) and Chandra X-ray (0.5-7 keV) data. This shows that the molecular ring, forming the waist of the bipolar nebula, expands with a velocity of 1 - 1.9 km s$^{-1}$. We also observe an increased linewidth in the ring indicating that turbulence is driven by energy injection from the stellar feedback. The bipolar cavity hosts blue-shifted expanding [CII] shells at 5.2$\pm$0.5$\pm$0.5 km s$^{-1}$ (statistical and systematic uncertainty) which indicates that expansion out of the dense gas happens non-uniformly and that the observed bipolar phase might be relatively short ($\sim$0.2 Myr). The X-ray observations show diffuse emission that traces a hot plasma, created by stellar winds, in and around RCW 36. At least 50 \% of the stellar wind energy is missing in RCW 36. This is likely due to leakage which is clearing even larger cavities around the bipolar RCW 36 region. Lastly, the cavities host high-velocity wings in [CII] which indicates relatively high mass ejection rates ($\sim$5$\times$10$^{-4}$ M$_{\odot}$ yr$^{-1}$). This could be driven by stellar winds and/or radiation pressure, but remains difficult to constrain. This local mass ejection, which can remove all mass within 1 pc of RCW 36 in 1-2 Myr, and the large-scale clearing of ambient gas in the Vela C cloud indicates that stellar feedback plays a significant role in suppressing the star formation efficiency (SFE).

astro-ph.GA↗

arXiv2022

Filamentary structures of ionized gas in Cygnus X

Ionized gas probes the influence of massive stars on their environment. The Cygnus X region (d~1.5 kpc) is one of the most massive star forming complexes in our Galaxy, in which the Cyg OB2 association (age of 3-5 Myr and stellar mass $2 \times 10^{4}$ M$_{\odot}$) has a dominant influence. We observe the Cygnus X region at 148 MHz using the Low Frequency Array (LOFAR) and take into account short-spacing information during image deconvolution. Together with data from the Canadian Galactic Plane Survey, we investigate the morphology, distribution, and physical conditions of low-density ionized gas in a $4^{\circ} \times 4^{\circ}$ (100 pc $\times$ 100 pc) region at a resolution of 2' (0.9 pc). The Galactic radio emission in the region analyzed is almost entirely thermal (free-free) at 148 MHz, with emission measures of $10^3 < EM~{\rm[pc~cm^{-6}]} < 10^6$. As filamentary structure is a prominent feature of the emission, we use DisPerSE and FilChap to identify filamentary ridges and characterize their radial ($EM$) profiles. The distribution of radial profiles has a characteristic width of 4.3 pc and a power-law distribution ($β= -1.8 \pm 0.1$) in peak $EM$ down to our completeness limit of 4200 pc cm$^{-6}$. The electron densities of the filamentary structure range from $10 < n_e~{\rm[cm^{-3}]} < 400$ with a median value of 35 cm$^{-3}$, remarkably similar to [N II] surveys of ionized gas. Cyg OB2 may ionize at most two-thirds of the total ionized gas and the ionized gas in filaments. More than half of the filamentary structures are likely photoevaporating surfaces flowing into a surrounding diffuse (~5 cm$^{-3}$) medium. However, this is likely not the case for all ionized gas ridges. A characteristic width in the distribution of ionized gas points to the stellar winds of Cyg OB2 creating a fraction of the ionized filaments through swept-up ionized gas or dissipated turbulence.

astro-ph.GA↗

arXiv2022

Self-absorption in [CII], $^{12}$CO, and HI in RCW120. Building up a geometrical and physical model of the region

Revealing the 3D dynamics of HII regions and their associated molecular clouds is important for understanding the longstanding problem as to how stellar feedback affects the density structure and kinematics of the interstellar medium. We employed observations of the HII region RCW 120 in [CII], observed within the SOFIA legacy program FEEDBACK, and the $^{12}$CO and $^{13}$CO (3$\to$2) lines, obtained with APEX. In addition we used HI data from the Southern Galactic Plane Survey. Two radiative transfer models were used to fit the observed data. A line profile analysis with the 1D non-LTE radiative transfer code SimLine proves that the CO emission cannot stem from a spherically symmetric molecular cloud configuration. With a two-layer multicomponent model, we then quantified the amount of warm background and cold foreground gas. There is a deficit of CO emission along the line-of-sight toward the center of the HII region which indicates that the HII region is associated with a flattened molecular cloud. Self-absorption in the CO line may hide signatures of infalling and expanding molecular gas. The [CII] emission arises from an expanding [CII] bubble and from the PDRs. A significant part of [CII] emission is absorbed in a cool (~60-100 K), low-density (<500 cm$^{-3}$) atomic foreground layer with a thickness of a few parsec. We propose that the RCW 120 HII region formed in a flattened molecular cloud and is now bursting out of its parental cloud. The compressed surrounding molecular layer formed a torus around the spherically expanding HII bubble. This scenario can possibly be generalized for other HII bubbles and would explain the observed "flat" structure of molecular clouds associated with HII bubbles. We suggest that the [CII] absorption observed in many star-forming regions is at least partly caused by low-density, cool, HI-envelopes surrounding the molecular clouds.

astro-ph.GA↗