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Using the Global Magneto-Ionic Medium Survey (GMIMS) Low-Band South (LBS) southern sky polarization survey, covering 300 to 480 MHz at 81 arcmin resolution, we reveal the brightest region in the Southern polarized sky at these frequencies. The region, G150-50, covers nearly 20deg$^2$, near (l,b)~(150 deg,-50 deg). Using GMIMS-LBS and complementary data at higher frequencies (~0.6--30 GHz), we apply Faraday tomography and Stokes QU-fitting techniques. We find that the magnetic field associated with G150-50 is both coherent and primarily in the plane of the sky, and indications that the region is associated with Radio Loop II. The Faraday depth spectra across G150-50 are broad and contain a large-scale spatial gradient. We model the magnetic field in the region as an expanding shell, and we can reproduce both the observed Faraday rotation and the synchrotron emission in the GMIMS-LBS band. Using QU-fitting, we find that the Faraday spectra are produced by several Faraday dispersive sources along the line-of-sight. Alternatively, polarization horizon effects that we cannot model are adding complexity to the high-frequency polarized spectra. The magnetic field structure of Loop II dominates a large fraction of the sky, and studies of the large-scale polarized sky will need to account for this object. Studies of G150-50 with high angular resolution could mitigate polarization horizon effects, and clarify the nature of G150-50., 25 pages, 14 figures. Accepted for publication in MNRAS

24 pags., 32 figs., 3 tabs., Context. The [CII] 158 μm far-infrared fine-structure line is one of the dominant cooling lines of the star-forming interstellar medium. Hence [CII] emission originates in and thus can be used to trace a range of ISM processes. Velocity-resolved large-scale mapping of [CII] in star-forming regions provides a unique perspective of the kinematics of these regions and their interactions with the exciting source of radiation. Aims. We explore the scientific applications of large-scale mapping of velocity-resolved [CII] observations. With the [CII] observations, we investigate the effect of stellar feedback on the ISM. We present the details of observation, calibration, and data reduction using a heterodyne array receiver mounted on an airborne observatory. Methods. A 1.15 square degree velocity-resolved map of the Orion molecular cloud centred on the bar region was observed using the German REceiver for Astronomy at Terahertz Frequencies (upGREAT) heterodyne receiver flying on board the Stratospheric Observatory for Infrared Astronomy. The data were acquired using the 14 pixels of the German REceiver for Astronomy at Terahertz Frequencies that were observed in an on-the-fly mapping mode. 2.4 million spectra were taken in total. These spectra were gridded into a three-dimensional cube with a spatial resolution of 14.1 arcseconds and a spectral resolution of 0.3 km s-1. Results. A square-degree [CII] map with a spectral resolution of 0.3 km s-1 is presented. The scientific potential of this data is summarized with discussion of mechanical and radiative stellar feedback, filament tracing using [CII], [CII] opacity effects, [CII] and carbon recombination lines, and [CII] interaction with the large molecular cloud. The data quality and calibration is discussed in detail, and new techniques are presented to mitigate the effects of unavoidable instrument deficiencies (e.g. baseline stability) and thus to improve the data quality. A comparison with a smaller [CII] map taken with the Herschel/Heterodyne Instrument for the Far-Infrared spectrometer is presented. Conclusions. Large-scale [CII] mapping provides new insight into the kinematics of the ISM. The interaction between massive stars and the ISM is probed through [CII] observations. Spectrally resolving the [CII] emission is necessary to probe the microphysics induced by the feedback of massive stars. We show that certain heterodyne instrument data quality issues can be resolved using a spline-based technique, and better data correction routines allow for more efficient observing strategies., This work is based on observations made with the NASA/DLR Stratospheric Observatory for Infrared Astronomy (SOFIA). SOFIA is jointly operated by the Universities Space Research Association, Inc.(USRA), under NASA contract NAS2-97001, and the Deutsches SOFIA Institut (DSI) under DLR contract 50 OK 0901 to the University of Stuttgart. This work is carried out within the Collaborative Research Centre 956, subproject [A4], funded by the Deutsche Forschungsgemeinschaft (DFG) – project ID 184018867. We thank the Spanish MICIU for funding support under grant AYA2017-85111-P.

We present Multi-Unit Spectroscopic Explorer (MUSE) integral-field spectroscopy of ESO 253-G003, which hosts a known active galactic nucleus (AGN) and the periodic nuclear transient ASASSN-14ko, observed as part of the All-weather MUse Supernova Integral-field of Nearby Galaxies survey. The MUSE observations reveal that the inner region hosts two AGN separated by 1.4±0.1 kpc (≍1 ′′. 7). The brighter nucleus has asymmetric broad permitted emission-line profiles and is associated with the archival AGN designation. The fainter nucleus does not have a broad emission-line component but exhibits other AGN characteristics, including vFWHM≈700 km~s−1 forbidden line emission, log10([OIII]/Hβ)≈1.1 , and high-excitation potential emission lines, such as [Fe VII] λ6086 and He II λ4686. The host galaxy exhibits a disturbed morphology with large kpc-scale tidal features, potential outflows from both nuclei, and a likely superbubble. A circular relativistic disc model cannot reproduce the asymmetric broad emission-line profiles in the brighter nucleus, but two non-axisymmetric disc models provide good fits to the broad emission-line profiles: an elliptical disc model and a circular disc + spiral arm model. Implications for the periodic nuclear transient ASASSN-14ko are discussed., MAT acknowledges support from the DOE CSGF through grant no. DE-SC0019323. BJS and CSK are supported by NSF grant no. AST-1907570. BJS is also supported by NASA grant no. 80NSSC19K1717 and NSF grants AST-1920392 and AST-1911074. CSK is supported by NSF grant no. AST-181440. KAA is supported by the Danish National Research Foundation (DNRF132). Support for JLP is provided in part by FONDECYT through grant n.1191038 and by the Ministry for the Economy, Development, and Tourism’s Millennium Science Initiative through grant no. IC120009, awarded to The Millennium Institute of Astrophysics, MAS. LG acknowledges financial support from the Spanish Ministry of Science, Innovation and Universities (MICIU) under the 2019 Ramón y Cajal program RYC2019-027683 and from the Spanish MICIU project PID2020-115253GA-I00. Parts of this research were supported by the Australian Research Council Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), through project number CE170100013. LG was funded by the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 839090, and partially supported by the Spanish grant no. PGC2018-095317-B-C21 within the European Funds for Regional Development (FEDER). Support for TW-SH was provided by NASA through the NASA Hubble Fellowship grant no. #HST-HF2-51458.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555. Based on observations collected at the European Organization for Astronomical Research in the Southern Hemisphere under ESO programme 096.D-0296(A).

26 pags., 33 figs., 10 tabs., Context. The Orion Molecular Cloud is the nearest massive-star forming region. Massive stars have profound effects on their environment due to their strong radiation fields and stellar winds. Stellar feedback is one of the most crucial cosmological parameters that determine the properties and evolution of the interstellar medium in galaxies. Aims. We aim to understand the role that feedback by stellar winds and radiation play in the evolution of the interstellar medium. Velocity-resolved observations of the [C » II] 158 μm fine-structure line allow us to study the kinematics of UV-illuminated gas. Here, we present a square-degree-sized map of [C » II] emission from the Orion Nebula complex at a spatial resolution of 16′′ and high spectral resolution of 0.2 km s-1, covering the entire Orion Nebula (M 42) plus M 43 and the nebulae NGC 1973, 1975, and 1977 to the north. We compare the stellar characteristics of these three regions with the kinematics of the expanding bubbles surrounding them. Methods. We use [C » II] 158 μm line observations over an area of 1.2 deg2 in the Orion Nebula complex obtained by the upGREAT instrument onboard SOFIA. Results. The bubble blown by the O7V star θ1 Ori C in the Orion Nebula expands rapidly, at 13 km s-1. Simple analytical models reproduce the characteristics of the hot interior gas and the neutral shell of this wind-blown bubble and give us an estimate of the expansion time of 0.2 Myr. M 43 with the B0.5V star NU Ori also exhibits an expanding bubble structure, with an expansion velocity of 6 km s-1. Comparison with analytical models for the pressure-driven expansion of H » II regions gives an age estimate of 0.02 Myr. The bubble surrounding NGC 1973, 1975, and 1977 with the central B1V star 42 Orionis expands at 1.5 km s-1, likely due to the over-pressurized ionized gas as in the case of M 43. We derive an age of 0.4 Myr for this structure. Conclusions. We conclude that the bubble of the Orion Nebula is driven by the mechanical energy input by the strong stellar wind from θ1 Ori C, while the bubbles associated with M 43 and NGC 1977 are caused by the thermal expansion of the gas ionized by their central later-type massive stars., This work is based on observations made with the NASA/DLR Stratospheric Observatory for Infrared Astronomy (SOFIA). SOFIA is jointly operated by the Universities Space Research Association, Inc. (USRA), under NASA contract NNA17BF53C, and the Deutsches SOFIA Institut (DSI) under DLR contract 50 OK 0901 to the University of Stuttgart. J.R.G. thanks the ERC and the Spanish MCIU for funding support under grants ERC-2013- Syg-610256-NANOCOSMOS and AYA2017-85111-P, respectively. Research on the interstellar medium at Leiden Observatory is supported through a Spinoza award of the Dutch Science Organisation (NWO).

18 pags., 21 figs., 5 tabs, 1 app., Strong winds and ultraviolet (UV) radiation from O-type stars disrupt and ionize their molecular core birthplaces, sweeping up material into parsec-size shells. Owing to dissociation by starlight, the thinnest shells are expected to host low molecular abundances and therefore little star formation. Here, we expand previous maps made with observations using the IRAM 30 m telescope (at 11″ ≃ 4500 AU resolution) and present square-degree 12CO and 13CO (J = 2-1) maps of the wind-driven "Veil bubble"that surrounds the Trapezium cluster and its natal Orion molecular core (OMC). Although widespread and extended CO emission is largely absent from the Veil, we show that several CO "globules"exist that are blueshifted in velocity with respect to OMC and are embedded in the [C » II] 158 μm-bright shell that confines the bubble. This includes the first detection of quiescent CO at negative local standard of rest velocities in Orion. Given the harsh UV irradiation conditions in this translucent material, the detection of CO globules is surprising. These globules are small (Rg = 7100 AU), not massive (Mg = 0.3 M⊙ ), and are moderately dense: nH = 4 × 104 cm-3 (median values). They are confined by the external pressure of the shell, Pext∕ k ≳ 107 cm-3 K, and are likely magnetically supported. They are either transient objects formed by instabilities or have detached from pre-existing molecular structures, sculpted by the passing shock associated with the expanding shell and by UV radiation from the Trapezium. Some represent the first stages in the formation of small pillars, others of isolated small globules. Although their masses (Mg, We warmly thank the operators, AoDs, and chefs at the IRAM 30 m telescope for their support while the CO observations were conducted. This work is also based on observations made with the NASA/DLR Stratospheric Observatory for Infrared Astronomy (SOFIA). SOFIA is jointly operated by the Universities Space Research Association, Inc. (USRA), under NASA contract NNA17BF53C, and the Deutsches SOFIA Institut (DSI) under DLR contract 50 OK 0901 to the University of Stuttgart. We acknowledge the work, during the C+ upGREAT square degree survey of Orion, of the USRA and NASA staff of the Armstrong Flight Research Center in Palmdale, the Ames Research Center in Mountain View (California), and the Deutsches SOFIA Institut. We thank the Spanish MICIU for funding support under grant AYA2017-85111-P. Research on the ISM at Leiden Observatory is supported through a Spinoza award.

Some ultraluminous X-ray sources (ULXs) are surrounded by collisionally ionized bubbles, larger and more energetic than supernova remnants: they are evidence of the powerful outflows associated with super-Eddington X-ray sources. We illustrate the most recent addition to this class: a huge (350 pc x 220 pc in diameter) bubble around a ULX in NGC 5585. We modelled the X-ray properties of the ULX (a broadened-disc source with L_X ~ 2-4 x 10^{39} erg/s) from Chandra and XMM-Newton, and identified its likely optical counterpart in Hubble Space Telescope images. We used the Large Binocular Telescope to study the optical emission from the ionized bubble. We show that the line emission spectrum is indicative of collisional ionization. We refine the method for inferring the shock velocity from the width of the optical lines. We derive an average shock velocity ~125 km/s, which corresponds to a dynamical age of ~600,000 years for the bubble, and an average mechanical power P_w ~ 10^{40} erg/s; thus, the mechanical power is a few times higher than the current photon luminosity. With Very Large Array observations, we discovered and resolved a powerful radio bubble with the same size as the optical bubble, and a 1.4-GHz luminosity ~10^{35} erg/s, at the upper end of the luminosity range for this type of source. We explain why ULX bubbles tend to become more radio luminous as they expand while radio supernova remnants tend to fade., Comment: Accepted by MNRAS on 2020 Dec 4. Nineteen pages, 7.9 MB

Aims: We use new deep XMM-Newton observations of the northern disk of M 31 to trace the hot interstellar medium (ISM) in unprecedented detail and to characterise the physical properties of the X-ray emitting plasmas. Methods: We used all XMM-Newton data up to and including our new observations to produce the most detailed image yet of the hot ISM plasma in a grand design spiral galaxy such as our own. We compared the X-ray morphology to multi-wavelength studies in the literature to set it in the context of the multi-phase ISM. We performed spectral analyses on the extended emission using our new observations as they offer sufficient depth and count statistics to constrain the plasma properties. Data from the Panchromatic Hubble Andromeda Treasury were used to estimate the energy injected by massive stars and their supernovae. We compared these results to the hot gas properties. Results: The brightest emission regions were found to be correlated with populations of massive stars, notably in the 10 kpc star-forming ring. The plasma temperatures in the ring regions are ~0.2 keV up to ~0.6 keV. We suggest this emission is hot ISM heated in massive stellar clusters and superbubbles. We derived X-ray luminosities, densities, and pressures for the gas in each region. We also found large extended emission filling low density gaps in the dust morphology of the northern disk, notably between the 5 kpc and 10 kpc star-forming rings. We propose that the hot gas was heated and expelled into the gaps by the populations of massive stars in the rings. Conclusions. It is clear that the massive stellar populations are responsible for heating the ISM to X-ray emitting temperatures, filling their surroundings, and possibly driving the hot gas into the low density regions. Overall, the morphology and spectra of the hot gas in the northern disk of M 31 is similar to other galaxy disks., 23 pages, 14 figures, accepted for publication in Astronomy & Astrophysics

In the extragalactic sky, microquasars and ultra-luminous X-ray sources (ULXs) are known as energetic compact objects locating at off-nucleus positions in galaxies. Some of these objects are associated with expanding bubbles with a velocity of 80-250 ${\rm km~s^{-1}}$. We investigate the shock acceleration of particles in those expanding nebulae. The nebulae having fast expansion velocity $\gtrsim120~{\rm km~s^{-1}}$ are able to accelerate cosmic rays up to $\sim100$ TeV. If 10% of the shock kinetic energy goes into particle acceleration, powerful nebulae such as the microquasar S26 in NGC 7793 would emit gamma rays up to several tens TeV with a photon index of $\sim2$. These nebulae will be good targets for future Cherenkov Telescope Array observations given its sensitivity and angular resolution. They would also contribute to $\sim7$% of the unresolved cosmic gamma-ray background radiation at $\ge0.1~{\rm GeV}$. In contrast, particle acceleration in slowly expanding nebulae $\lesssim120~{\rm km~s^{-1}}$ would be less efficient due to ion-neutral collisions and result in softer spectra at $\gtrsim10$ GeV., Comment: 7 pages, 2 figures, Accepted for publication in Astroparticle Physics

We report the results of spectroscopic observations and numerical modelling of the H II region IRAS 18153-1651. Our study was motivated by the discovery of an optical arc and two main-sequence stars of spectral type B1 and B3 near the centre of IRAS 18153-1651. We interpret the arc as the edge of the wind bubble (blown by the B1 star), whose brightness is enhanced by the interaction with a photoevaporation flow from a nearby molecular cloud. This interpretation implies that we deal with a unique case of a young massive star (the most massive member of a recently formed low-mass star cluster) caught just tens of thousands of years after its stellar wind has begun to blow a bubble into the surrounding dense medium. Our two-dimensional, radiation-hydrodynamics simulations of the wind bubble and the H II region around the B1 star provide a reasonable match to observations, both in terms of morphology and absolute brightness of the optical and mid-infrared emission, and verify the young age of IRAS 18153-1651. Taken together our results strongly suggest that we have revealed the first example of a wind bubble blown by a main-sequence B star., Comment: 12 pages, 10 figures, accepted for publication in MNRAS

Young stars typically form in star clusters, so the supernovae (SNe) they produce are clustered in space and time. This clustering of SNe may alter the momentum per SN deposited in the interstellar medium (ISM) by affecting the local ISM density, which in turn affects the cooling rate. We study the effect of multiple SNe using idealized 1D hydrodynamic simulations which explore a large parameter space of the number of SNe, and the background gas density and metallicity. The results are provided as a table and an analytic fitting formula. We find that for clusters with up to ~100 SNe the asymptotic momentum scales super-linearly with the number of SNe, resulting in a momentum per SN that can be an order of magnitude larger than for a single SN, with a maximum efficiency for clusters with 10-100 SNe. We argue that additional physical processes not included in our simulations -- self-gravity, breakout from a galactic disk, and galactic shear -- can slightly reduce the momentum enhancement from clustering, but the average momentum per SN still remains a factor of 4 larger than the isolated SN value when averaged over a realistic cluster mass function for a star-forming galaxy. We conclude with a discussion of the possible role of mixing between hot and cold gas, induced by multi-dimensional instabilities or preexisting density variations, as a limiting factor in the buildup of momentum by clustered SNe, and suggest future numerical experiments to explore these effects., Comment: 19 pages, 26 figures, revised to reflect accepted version. Discussion regarding resolution effects has changed; additional analysis into galactic and gravitational effects has been added

The properties of dust in the interstellar medium (ISM) nearest the Sun are poorly understood because the low column densities of dust toward nearby stars induce little photometric reddening, rendering the grains largely undetectable. Stellar polarimetry offers one pathway to deducing the properties of this diffuse material. Here we present multi-wavelength aperture polarimetry measurements of seven bright stars chosen to probe interstellar polarization near the edge of the Local Hot Bubble (LHB) - an amorphous region of relatively low density interstellar gas and dust extending ~70-150 pc from the Sun. The measurements were taken using the HIgh Precision Polarimetric Instrument (HIPPI) on the 3.9-m Anglo-Australian Telescope. HIPPI is an aperture stellar polarimeter with a demonstrated sensitivity of 4.3 parts-per-million (ppm). Of the stars observed two are polarized to a much greater degree than the others; they have a wavelength of maximum polarization ($\lambda_{max}$) of ~550 $\pm$ 20 nm - similar to that of stars beyond the LHB - and we conclude that they are in the wall of the LHB. The remaining five stars have polarizations of ~70 to 160 ppm, of these four have a much bluer $\lambda_{max}$, ~350 $\pm$ 50 nm. Bluer values of $\lambda_{max}$ may indicate grains shocked during the evolution of the Loop I Superbubble. The remaining star, HD 4150 is not well fit by a Serkowski curve, and may be intrinsically polarized., Comment: 12 pages, 2 figures, 6 tables, accepted to MNRAS

The Bubble Nebula (or NGC 7635) is a parsec-scale seemingly spherical wind-blown bubble around the relatively unevolved O star BD+60$^\circ$2522. The small dynamical age of the nebula and significant space velocity of the star suggest that the Bubble Nebula might be a bow shock. We have run 2D hydrodynamic simulations to model the interaction of the central star's wind with the interstellar medium (ISM). The models cover a range of possible ISM number densities of $n=50-200 {\rm cm}^{-3}$ and stellar velocities of $v_{\star}=20-40$ km s$^{-1}$. Synthetic H$\alpha$ and 24 $\mu$m emission maps predict the same apparent spherical bubble shape with quantitative properties similar to observations. The synthetic maps also predict a maximum brightness similar to that from the observations and agree that the maximum brightness is at the apex of the bow shock. The best-matching simulation had $v_{\star}\approx20$ km s$^{-1}$ into an ISM with $n\sim100 {\rm cm}^{-3}$, at an angle of 60$^\circ$ with respect to the line of sight. Synthetic maps of soft ($0.3-2$ keV) and hard ($2-10$ keV) X-ray emission show that the brightest region is in the wake behind the star and not at the bow shock itself. The unabsorbed soft X-rays have luminosity $\sim10^{32}-10^{33}$ erg s$^{-1}$. The hard X-rays are fainter, luminosity $\sim 10^{30} - 10^{31}$ erg s$^{-1}$, and may be too faint for current X-ray instruments to successfully observe. Our results imply that the O star creates a bow shock as it moves through the ISM and in turn creates an asymmetric bubble visible at optical and infrared wavelengths, and predicted to be visible in X-rays. The Bubble Nebula does not appear to be unique, it could be just a favourably oriented very dense bow shock. The dense ISM surrounding BD+60$^\circ$2522 and its strong wind suggest that it could be a good candidate for detecting non-thermal emission., Comment: Accepted for publication in Astronomy & Astrophysics

We report new Chandra hard X-ray ($>2\rm~keV$) and JVLA C-band observations of the nuclear superbubble of NGC 3079, an analog of the "Fermi bubble" in our Milky Way. We detect extended hard X-ray emission on the SW side of the galactic nucleus with coherent multi-wavelength features in radio, H$\alpha$, and soft X-ray. The hard X-ray feature has a cone shape with possibly a weak cap, forming a bubble-like structure with a diameter of $\sim1.1\rm~kpc$. A similar extended feature, however, is not detected on the NE side, which is brighter in all other wavelengths such as radio, H$\alpha$, and soft X-ray. Scattered photons from the nuclear region or other nearby point-like X-ray bright sources, inverse Compton emission from cosmic ray electrons via interaction with the cosmic microwave background, or any individually faint stellar X-ray source populations, cannot explain the extended hard X-ray emission on the SW side and the strongly NE/SW asymmetry. A synchrotron emission model, plus a thermal component accounting for the excess at $\sim1\rm~keV$, can well characterize the broadband radio/hard X-ray spectra. The broadband synchrotron spectra do not show any significant cutoff, and even possibly slightly flatten at higher energy. This rules out a loss-limited scenario in the acceleration of the cosmic ray electrons in or around this superbubble. As the first detection of kpc-scale extended hard X-ray emission associated with a galactic nuclear superbubble, the spatial and spectral properties of the multi-wavelength emissions indicate that the cosmic ray leptons responsible for the broad-band synchrotron emission from the SW bubble must be accelerated in situ, instead of transported from the nuclear region of the galaxy., Comment: 7 pages, 3 figures, ApJ in press

International audience; A solution of the transport equation for cosmic rays in turbulent magnetic fields in a spherically symmetric geometry is presented. The results are applied to particle propagation in superbubbles. In the fully analytical calculation, various energy-loss processes are considered. From the distribution function of the cosmic-ray particles, the distribution for pions from continuous losses is computed. Folding with the appropriate cross section yields the gamma-ray distribution. It is shown that in the case of efficient acceleration the volume-integrated π 0-decay gamma-ray emission from the superbubble exhibits the characteristic hard differential number density spectrum at large gamma-ray energies, E γ ≫ 70 MeV. This prediction is useful for identifying efficient superbubble cosmic-ray accelerators from gamma-ray observations.

The 30 Dor C superbubble is unique for its synchrotron X-ray shell, as well as being the first superbubble to be detected in TeV $\gamma$-rays, though the dominant TeV emission mechanism, i.e., leptonic or hadronic, is still unclear. We aim to use new Chandra observations of 30 Dor C to resolve the synchrotron shell in unprecedented detail and to estimate the magnetic ($B$) field in the postshock region, a key discriminator between TeV $\gamma$-ray emission mechanisms. We extracted radial profiles in the 1.5-8 keV range from various sectors around the synchrotron shell and fitted these with a projected and point spread function convolved postshock volumetric emissivity model to determine the filament widths. We then calculated the postshock magnetic field strength from these widths. We found that most of the sectors were well fitted with our postshock model and the determined $B$-field values were low, all with best fits $\lesssim 20~\mu$G. Upper limits on the confidence intervals of three sectors reached $\gtrsim 30~\mu$G though these were poorly constrained. The generally low $B$-field values suggests a leptonic-dominated origin for the TeV $\gamma$-rays. Our postshock model did not provide adequate fits to two sectors. We found that one sector simply did not provide a clean enough radial profile, while the other could be fitted with a modified model where the projected profile falls off abruptly below $\sim0.8$ times the shell radius, yielding a postshock $B$-field of 4.8 (3.7-11.8) $\mu$G which is again consistent with the leptonic TeV $\gamma$-ray mechanism. Alternatively, the observed profiles in these sectors could result from enhancements around a shock-cloud interaction as suggested in previous works. The average $B$-field determined around the X-ray synchrotron shell of 30 Dor C suggests the leptonic scenario as the dominant emission mechanism for the TeV $\gamma$-rays., Comment: 16 pages, 14 figures, accepted for publication in Astronomy & Astrophysics

The nearby Orion-Eridanus superbubble, which was blown by multiple supernovae several Myr ago, has likely produced cosmic rays. Its turbulent medium, still energised by massive stars, can impact cosmic-ray transport locally. The gamma rays produced in cosmic-ray interactions with interstellar gas were used to compare the GeV to TeV cosmic-ray spectrum in the superbubble and in other regions near the Sun. We used ten years of Fermi-LAT data in the 0.25-63 GeV energy range to study the closer (Eridanus) end of the superbubble. We modelled the spatial and spectral distributions of the gamma rays produced in the different gas phases of the clouds found in this direction. We found that the gamma-ray emissivity spectrum of the gas along the outer rim and in a shell inside the superbubble is consistent with the average spectrum measured in the solar neighbourhood. This result calls for a detailed assessment of the recent supernova rate and census of massive stellar winds in the superbubble in order to estimate the epoch and rate of cosmic-ray production and to constrain the transport conditions that can lead to such homogeneity and little re-acceleration. We also found significant evidence that a diffuse cloud lying outside the superbubble, at a height of 200-250 pc below the Galactic plane, is pervaded by a 34\% lower cosmic-ray flux, but with the same particle energy distribution as the local one. Super-GeV cosmic rays should freely cross such a diffuse atomic cloud without significant loss or spectral distorsion. We tentatively propose that the cosmic-ray loss relates to the orientation of the magnetic field lines threading the cirrus, which point towards the halo according to the dust polarisation data. We gathered past and present emissivity measurements near the Sun to show how the local cosmic-ray flux decreases with Galactic height and to compare this trend with model predictions., Comment: 20 pages, 17 figures, accepted for publication in Astronomy & Astrophysics

Little is known about how high-mass stars form. Around 30\% of the young high-mass stars in the Galaxy are observed at the edges of ionized (HII) regions. Therefore these are places of choice to study the earliest stages of high-mass star formation, especially towards the most massive condensations. High-spatial resolution observations in the millimeter range might reveal how these stars form and how they assemble their mass. We want to study the fragmentation process down to the 0.01~pc scale in the most massive condensation observed at the south-western edge of the HII region RCW~120 where the most massive Herschel cores ($\sim$124~$M_{\odot}$ in average) could form high-mass stars. Using ALMA 3~mm continuum observations towards the densest and most massive millimetric condensation (Condensation 1) of RCW~120, we used the getimages and getsources algorithms to extract the sources detected with ALMA and obtained their physical parameters. The fragmentation of the hersche cores is discussed through their Jeans mass to understand the properties of the future stars. We extracted 18 fragments from the ALMA continuum observation at 3~mm towards 8 cores detected with Herschel, whose mass and deconvolved size range from 2~$M_{\odot}$ to 32~$M_{\odot}$ and from 1.6~mpc to 28.8~mpc, respectively. The low degree of fragmentation observed, regarding to the thermal Jeans fragmentation, suggests that the observed fragmentation is inconsistent with ideal gravitational fragmentation and other ingredients such as turbulence or magnetic fields should be added in order to explain it. Finally, the range of fragments' mass indicates that the densest condensation of RCW~120 is a favourable place for the formation of high-mass stars with the presence of a probable UCHII region associated with the 27~$M_{\odot}$ Fragment 1 of Core 2., 7 pages, 4 figures

Context. Recent observations of unexpected structures in the Galactic Cosmic Ray (GCR) spectrum and composition, as well as growing evidence for episodes of intense dynamical activity in the inner regions of the Galaxy, call for an evaluation of the high-energy particle acceleration associated with such activity and its potential impact on the global GCR phenomenology. Aims. We investigate whether particles accelerated during high-power episodes around the Galactic center can account for a significant fraction of the observed GCRs, or conversely what constraints can be derived regarding their Galactic transport if their contributions are negligible. Methods. We address these questions by studying the contribution of a continuous source of energetic particles at the Galactic center to the local GCRs. Particle transport in the Galaxy is described with a two-zone analytical model. We solve for the contribution of a Galactic Center Cosmic-Ray (GCCR) source using Green functions and Bessel expansion, and discuss the required injection power for these GCCRs to influence the global GCR phenomenology at Earth. Results. We find that, with standard parameters for particle propagation in the galactic disk and halo, the GCCRs can make a significant or even dominant contribution to the total CR flux observed at Earth. Depending on the parameters, such a source can account for both the observed proton flux and B-to-C ratio (in the case of a Kraichnan-like scaling of the diffusion coefficient), or potentially produce spectral and composition features. Conclusions. Our results show that the contribution of GCCRs cannot be neglected a priori, and that they can influence the global GCR phenomenology significantly, thereby calling for a reassessement of the standard inferences from a scenario where GCRs are entirely dominated by a single type of sources distributed throughout the Galactic disk., Comment: 10 pages, 13 figures, 1 table, accepted for publication in Astronomy and Astrophysics

The magnetic field in the local interstellar medium does not follow the large-scale Galactic magnetic field. The local magnetic field has probably been distorted by the Local Bubble, a cavity of hot ionized gas extending all around the Sun and surrounded by a shell of cold neutral gas and dust. However, so far no conclusive association between the local magnetic field and the Local Bubble has been established. Here we develop an analytical model for the magnetic field in the shell of the Local Bubble, which we represent as an inclined spheroid, off-centred from the Sun. We fit the model to Planck dust polarized emission observations within 30 deg of the Galactic poles. We find a solution that is consistent with a highly deformed magnetic field, with significantly different directions towards the north and south Galactic poles. This work sets a methodological framework for modelling the three-dimensional (3D) structure of the magnetic field in the local interstellar medium, which is a most awaited input for large-scale Galactic magnetic field models., Comment: 5 pages (plus 1 page Appendix), 2 figures, Accepted for publications in A&A Letters

We report the detection of a new Galactic bubble at the interface between the halo and the Galactic disc. We suggest that the nearby Lupus complex and parts of the Ophiuchus complex constitute the denser parts of the structure. This young bubble, < 3 Myr old, could be the remnant of a supernova and expands inside a larger HI loop that has been created by the outflows of the Upper Scorpius OB association. An HI cavity filled with hot X-ray gas is associated with the structure, which is consistent with the Galactic chimney scenario. The X-ray emission extends beyond the west and north-west edges of the bubble, suggesting that hot gas outflows are breaching the cavity, possibly through the fragmented Lupus complex. Analyses of the polarised radio synchrotron and of the polarised dust emission of the region suggest the connection of the Galactic centre spur with the young Galactic bubble. A distribution of HI clumps that spatially corresponds well to the cavity boundaries was found at V_LSR ~ -100 km/s. Some of these HI clumps are forming jets, which may arise from the fragmented part of the bubble. We suggest that these clumps might be `dripping' cold clouds from the shell walls inside the cavity that is filled with hot ionised gas. It is possible that some of these clumps are magnetised and were then accelerated by the compressed magnetic field at the edge of the cavity. Such a mechanism would challenge the Galactic accretion and fountain model, where high-velocity clouds are considered to be formed at high Galactic latitude from hot gas flows from the Galactic plane., 16 pages, 16 figures

The recent discovery of an enriched metallicity for the Smith high-velocity HI cloud (SC) lends support to a Galactic origin for this system. We use a dynamical model of the galactic fountain to reproduce the observed properties of the SC. In our model, fountain clouds are ejected from the region of the disc spiral arms and move through the halo interacting with a pre-existing hot corona. We find that a simple model where cold gas outflows vertically from the Perseus spiral arm reproduces the kinematics and the distance of the SC, but is in disagreement with the cloud's cometary morphology, if this is produced by ram-pressure stripping by the ambient gas. To explain the cloud morphology we explore two scenarios: a) the outflow is inclined with respect to the vertical direction; b) the cloud is entrained by a fast wind that escapes an underlying superbubble. Solutions in agreement with all observational constraints can be found for both cases, the former requires outflow angles >40 deg while the latter requires >1000 km/s winds. All scenarios predict that the SC is in the ascending phase of its trajectory and have large - but not implausible - energy requirements., Submitted to MNRAS letters, revised after referee's comments. Comments are welcome

We study the propagation of cosmic rays generated by sources residing inside superbubbles. We show that the enhanced magnetic field in the bubble wall leads to an increase of the interior cosmic ray density. Because of the large matter density in the wall, the probability for cosmic ray interactions on gas peaks there. As a result, the walls of superbubbles located near young cosmic ray sources emit efficiently neutrinos. We apply this scenario to the Loop~I and Local Superbubble: These bubbles are sufficiently near such that cosmic rays from a young source as Vela interacting in the bubble wall can generate a substantial fraction of the observed astrophysical high-energy neutrino flux below $\sim$ few $\times 100$ TeV., Comment: 5 pages, 3 eps figures; v2: explanations and 2 figures added, to appear in ApJL

Large-scale shocks formed by clustered feedback of young OB stars are considered an important source of mechanical energy for the ISM and a trigger of molecular cloud formation. Their interaction sites are locations where kinetic energy and magnetic fields are redistributed between ISM phases. In this work we study the effect of the magnetic field on the expansion and fragmentation of supershells and look for the signatures of supershell collisions on dense structures and on the kinetic and magnetic energy distribution of the ISM. We performed a series of high-resolution, three-dimensional simulations of colliding supershells. The shocks are created by time-dependent feedback and evolve in a diffuse turbulent environment that is either unmagnetized or has different initial magnetic field configurations. In the hydrodynamical situation, the expansion law of the superbubbles is consistent with the radius-time relation that is theoretically predicted for wind-blown bubbles. The supershells fragment over their entire surface into small dense clumps that carry more than half of the total kinetic energy in the volume. However, this is not the case when a magnetic field is introduced, either in the direction of the collision or perpendicular to the collision. In magnetized situations, the shell surfaces are more stable to dynamical instabilities. When the magnetic field opposes the collision, the expansion law of the supershells also becomes significantly flatter than in the hydrodynamical case. Although a two-phase medium arises in all cases, in the MHD simulations the cold phase is limited to lower densities., Comment: to appear in A&A Section 6: Interstellar and circumstellar matter

Most models identify the X-ray bright North Polar Spur (NPS) with a hot interstellar (IS) bubble in the Sco-Cen star-forming region at $\simeq$130 pc. An opposite view considers the NPS as a distant structure associated with Galactic nuclear outflows. Constraints on the NPS distance can be obtained by comparing the foreground IS gas column inferred from X-ray absorption to the distribution of gas and dust along the line of sight. Absorbing columns towards shadowing molecular clouds simultaneously constrain the CO-H$_{2}$ conversion factor. We derived the columns of X-ray absorbing matter NH(abs) from spectral fitting of dedicated XMM-Newton observations towards the NPS southern terminus (l=29{\deg}, b=+5 to +11{\deg}). The IS matter distribution was obtained from absorption lines in stellar spectra, 3D dust maps and emission data, including high spatial resolution CO measurements recorded for this purpose. NH(abs) varies from $\simeq$ 4.3 to $\simeq$ 1.3 x 10$^{21}$ cm$^{-2}$ along the 19 fields. Relationships between X-ray brightness, absorbing column and hardness ratio demonstrate a brightness decrease with latitude governed by increasing absorption. The comparison with absorption data, local and large-scale dust maps rules out a NPS near side closer than 300 pc. The correlation between NH(abs) and the reddening increases with the sightline length from 300 pc to 4 kpc and is the tightest with Planck $\tau_{353}$-based reddening, suggesting a much larger distance. N(H)/E(B-V) $\simeq$ 4.1 x 10$^{21}$ cm$^{-2}$ mag$^{-1}$. NH(abs) absolute values are compatible with HI-CO clouds at -5 $\leq$ V(LSR) $\leq$ +25 to +45 km s$^{-1}$ and a NPS potentially far beyond the Local Arm. A molecular cloud shadow at b=+9deg constrains X$_{CO}$ to $\leq$ 1.0 x 10$^{20}$ cm$^{-2}$ K$^{-1}$ km$^{-1}$ s. The average X$_{CO}$ is $\leq$ 0.75 x 10$^{20}$ cm$^{-2}$ K$^{-1}$ km$^{-1}$ s., Comment: 15 pages, 26 figures, accepted for publication in Astronomy & Astrophysics

Context. The infrared emission (IR) of the interstellar dust has been claimed to be a tracer of the star formation rate. However, the conversion of the IR emission into star formation rate can be strongly dependent on the physical properties of the dust, which are a ected by the environmental conditions where the dust is embedded. Aims. We study here the dust properties of a set of Hii regions in the Local Group galaxy M33 presenting different spatial configurations between the stars, gas, and dust to understand the dust evolution indierent environments. Methods. We modelled the spectral energy distribution (SED) of each region using the DustEM tool and obtained the mass relative to hydrogen for very small grains (VSG, YVSG), polycyclic aromatic hydrocarbons (YPAH), and big grains (BG, YBG). We furthermore performed a pixel-by-pixel SED modelling and derived maps of the relative mass of each grain type for the whole surface of the two most luminous Hii regions in M33, NGC 604 and NGC 595. Results. The relative mass of the VSGs (YVSG/YTOTAL) changes with the morphology of the region: YVSG/YTOTAL is a factor of ∼1.7 higher for Hii regions classified as filled and mixed than for regions presenting a shell structure. The enhancement in VSGs within NGC 604 and NGC 595 is correlated to expansive gas structures with velocities ≥50 km s. The gas-to-dust ratio derived for the Hii regions in our sample exhibits two regimes related to the Hi.H2 transition of the interstellar medium (ISM). Regions corresponding to the Hi diffuse regime present a gas-to-dust ratio compatible with the expected value if we assume that the gas-to-dust ratio scales linearly with metallicity, while regions corresponding to a H2 molecular phase present a flatter dust-gas surface density distribution. Conclusions. The fraction of VSGs can be affected by the conditions of the interstellar environment: strong shocks of ∼5090km s existing in the interior of the most luminous Hii regions can lead to fragmentation of BGs into smaller ones, while the more evolved shell and clear shell objects provide a more quiescent environment where reformation of dust BGs might occur. The gas-to-dust variations found in this analysis might imply that grain coagulation and/or gas-phase metal incorporation into the dust mass is occurring in the interior of the Hii regions in M33. © 2016 ESO., Part of this research has been supported by the PERG08-GA-2010-276813 from the EC. This work was partially supported by the Junta de Andalucia Grant FQM108 and Spanish MEC Grants, AYA-2011-24728 and AYA-2014-53506-P. EPM thanks Spanish MINECO grant AYA-2013-47742-C4-1-P of the Spanish Plan for Astronomy and Astrophysics. This work was in part supported through NSF ATI grant 1106284.

The efforts for comparing dust polarization measurements with synthetic observations from MHD models have previously concentrated on the scale of molecular clouds. Here we extend the model comparisons to kiloparsec scales, taking into account hot shocked gas generated by supernovae, and a non-uniform dynamo-generated magnetic field at both large and small scales down to 4 pc spatial resolution. Radiative transfer calculations are used to model dust emission and polarization on the top of MHD simulations. We compute synthetic maps of column density $N_H$, polarization fraction $p$, and polarization angle dispersion $S$, and study their dependencies on the important properties of the MHD simulations. These include the large-scale magnetic field and its orientation, the small-scale magnetic field, and supernova-driven shocks. Similar filament-like structures of $S$ as seen in the Planck all-sky maps are visible in our synthetic results, although the smallest scale structures are absent from our maps. Supernova-driven shock fronts and $S$ do not show significant correlation. Instead, $S$ can clearly be attributed to the distribution of the small-scale magnetic field. We also find that the large-scale magnetic field influences the polarization properties, such that, for a given strength of magnetic fluctuation, a strong plane-of-the-sky mean field weakens the observed $S$, while strengthening $p$. The anticorrelation of $p$ and $S$, and decreasing $p$ as a function of $N_H$ are consistent across all synthetic observations. The magnetic fluctuations follow an exponential distribution, rather than Gaussian, characteristic of flows with intermittent repetitive shocks. The observed polarization properties and column densities are sensitive to the line of sight distance over which the emission is integrated., Comment: 21 pages, 18 figures, 2 tables, accepted by Astronomy & Astrophysics

Deep-sea archives all over the world show an enhanced concentration of the radionuclide $^{60}$Fe, isolated in layers dating from about 2.2 Myr ago. Since this comparatively long-lived isotope is not naturally produced on Earth, such an enhancement can only be attributed to extraterrestrial sources, particularly one or several nearby supernovae in the recent past. It has been speculated that these supernovae might have been involved in the formation of the Local Superbubble, our Galactic habitat. Here, we summarize our efforts in giving a quantitative evidence for this scenario. Besides analytical calculations, we present results from high-resolution hydrodynamical simulations of the Local Superbubble and its presumptive neighbor Loop I in different environments, including a self-consistently evolved supernova-driven interstellar medium. For the superbubble modeling, the time sequence and locations of the generating core-collapse supernova explosions are taken into account, which are derived from the mass spectrum of the perished members of certain, carefully preselected stellar moving groups. The release and turbulent mixing of $^{60}$Fe is followed via passive scalars, where the yields of the decaying radioisotope were adjusted according to recent stellar evolution calculations. The models are able to reproduce both the timing and the intensity of the $^{60}$Fe excess observed with rather high precision. We close with a discussion of recent developments and give future perspectives., 10 pages, 3 figures, published in the special issue of Galaxies: "Searching for Connections among the Fermi Bubbles, the Galactic Center GeV Excess, and Loop I"

The 21 cm emission of neutral hydrogen is the most promising probe of the epoch of reionization(EoR). In the next few years, the SKA pathfinders will provide statistical measurements of this signal. Numerical simulations predicting these observations are necessary to optimize the design of the instruments. The main difficulty is the computation of the spin temperature of neutral hydrogen which depends on the gas kinetic temperature and on the level of the local Lyman-alpha flux. A T_s >> T_cmb assumption is usual. However, this assumption does not apply early in the reionization history, or even later in the history as long as the sources of X-rays are too weak to heat the intergalactic medium significantly. This work presents the first EoR numerical simulations including, beside dynamics and ionizing continuum radiative transfer, a self-consistent treatment of the Ly-alpha radiative transfer. This allows us to compute the spin temperature more accurately. We use two different box sizes, 20 Mpc/h and 100 Mpc/h, and a star source model. Using the redshift dependence of average quantities, maps, and power spectra, we quantify the effect of using different assumptions to compute the spin temperature and the influence of the box size. The first effect comes from allowing for a signal in absorption. The magnitude of this effect depends on the amount of heating by hydrodynamic shocks and X-rays in the intergalactic medium(IGM). The second effects comes from using the real, local, Lyman-alpha flux. This effect is important for an average ionization fraction of less than 10%: it changes the overall amplitude of the 21 cm signal, and adds its own fluctuations to the power spectrum., 20 pages, 16 figures, 2 tables, To be publish A&A. High resolution version available at http://aramis.obspm.fr/~baek/21cm_Lya.pdf

Massive stars with strong stellar winds are expected to have a huge impact on their interstellar surroundings, an effect which, in a surprisingly large number of cases, is not observed. This work is part of a concerted effort to obtain a better and more homogeneous observational data base with which to test the predictions of theoretical models. Analysis of the interstellar medium around the Of star HD 229196 shows that it coincides (in projection) with a region of lower radio continuum emission. This suggests that the star has shaped the surrounding interstellar medium via its ionizing flux and stellar wind. However, we find no clear evidence of the star's action in atomic hydrogen images. The radio continuum morphology and absence of a clear expanding H i shell are consistent with the possibility that the star, which is travelling supersonically at ∼30 km s-1 with respect to its local interstellar medium, is creating a weak bow shock. We cannot however rule out the possibility that the observed asymmetry is due to an inhomogeneous interstellar density distribution. We use data from the Canadian Galactic Plane Survey to carry out this study., Facultad de Ciencias Astronómicas y Geofísicas, Instituto Argentino de Radioastronomía

Aims: We present very large array (VLA) and Effelsberg radio continuum and 21 cm Hi line observations of the interstellar medium (ISM) surrounding the runaway star WR 124 and the nebula M 1-67. The HI data have been used to investigate the effects that a star with a strong stellar wind and a high peculiar velocity has on the ISM. Methods: The VLA 21 cm HI observations were combined with single-dish Effelsberg observations to produce a series of HI images sensitive to all angular scales from the VLA resolution limit (∼46") up to the primary field of individual VLA antennae (FWHM = 36'). MSX and IRIS images were used to analyze the infrared emission around the star. Because the star is highly supersonic with respect to its local ISM, the observed HI distribution around the star is interpreted in terms of a simple bow shock model. Results: The analysis of the HI data reveals the presence of a cavity centered on the star at an LSR velocity of ∼60 km s-1, consistent with a distance estimate of 5 kpc for WR124. A second HI cavity is observed located 10' to the north of the stellar position, consistent with the direction of motion of WR 124. The VLA continuum image at 8.5 GHz shows a remarkable resemblance to the optical images. All available radio continuum data suggest a purely thermal spectrum for the nebula. The MSX and IRIS infrared data show a changing morphology with wavelength. The dust temperature deduced from the infrared luminosities is in agreement with previous observations of bow shocks., Facultad de Ciencias Astronómicas y Geofísicas, Instituto Argentino de Radioastronomía

International audience; The Local Leo Cold Cloud (LLCC, at a distance of 11–24 pc) was studied in its relation to the Local Hot Bubble (LHB) and the result suggested that much of the observed $1/4$ keV emission in that direction originates in front of the cloud. This placed a strong constraint on the distribution of X-ray emission within the LHB and called into question the assumption of a uniform distribution of X-ray emitting plasma within the Local Cavity. However, recent work has quantified the contribution of heliospheric solar wind charge exchange (SWCX) emission to the diffuse X-ray background measured by the ROSAT All-Sky Survey (RASS) at $1/4$ keV, and led to the consistency of pressure measurements between the LHB and the local cloud component of the complex of local interstellar clouds (CLICs) surrounding the Sun. In this paper we revisit the LLCC and improve the previous analysis by using higher resolution RASS data, a serendipitous ROSAT pointed observation, a rigorous treatment of the band-averaged X-ray absorption cross section, and models for the heliospheric and magnetospheric SWCX contributions. We find that the foreground emission to the cloud is in excess of the expected heliospheric (interplanetary plus near Earth) SWCX contribution but that it is marginally consistent with the range of possible LHB plasma path lengths between the LLCC and the CLICs given the currently understood plasma emissivity.

High energy resolution spectroscopy of the 1.8 MeV radioactive decay line of 26Al with the SPI instrument on board the INTEGRAL satellite has recently revealed that diffuse 26Al has large velocities in comparison to other components of the interstellar medium in the Milky Way. 26Al shows Galactic rotation in the same sense as the stars and other gas tracers, but reaches excess velocities up to 300 km/s. We investigate if this result can be understood in the context of superbubbles, taking into account the statistics of young star clusters and H I supershells, as well as the association of young star clusters with spiral arms. We derive energy output and 26Al mass of star clusters as a function of the cluster mass via population synthesis from stellar evolutionary tracks of massive stars. [...] We link this to the size distribution of HI supershells and assess the properties of likely 26Al-carrying superbubbles. 26Al is produced by star clusters of all masses above about 200 solar masses, roughly equally contributed over a logarithmic star cluster mass scale, and strongly linked to the injection of feedback energy. The observed superbubble size distribution cannot be related to the star cluster mass function in a straight forward manner. In order to avoid that the added volume of all superbubbles exceeds the volume of the Milky Way, individual superbubbles have to merge frequently. If any two superbubbles merge, or if 26Al is injected off-centre in a bigger HI supershell we expect the hot 26Al-carrying gas to obtain velocities of the order of the typical sound speed in superbubbles, about 300 km/s before decay. [...], 6 pages, 5 figures, accepted for A&A

We present a study of the molecular CO gas and mid/far-infrared radiation arising from the environment surrounding the Wolf-Rayet (WR) star 130. We use the multiwavelength data to analyse the properties of the dense gas and dust, and its possible spatial correlation with that of young stellar objects (YSOs). We use 12CO J=1-0 data from the Five College Radio Astronomy Observatory survey as tracer of the molecular gas, and mid/far-infrared data from the recent Wide-Field Infrared Survey Explorer (WISE) and Herschel space surveys to study the dust continuum radiation and to identify a population of associated candidate YSOs. The spatial distribution of the molecular gas shows a ring-like structure very similar to that observed in the H I gas, and over the same velocity interval. The relative spatial distribution of the H I and CO components is consistent with a photodissociation region. We have identified and characterized four main and distinct molecular clouds that create this structure. Cold dust is coincident with the dense gas shown in the CO measurements. We have found several young stellar object candidates that lie along the regions with the highest gas column density, and suggest that they are spatially correlated with the shell. These are indicative of regions of star formation induced by the strong wind and ionization of the WR star., Facultad de Ciencias Astronómicas y Geofísicas, Instituto Argentino de Radioastronomía

High-velocity clouds consist of cold gas that appears to be raining down from the halo to the disc of the Milky Way. Over the past 50 years, two competing scenarios have attributed their origin either to gas accretion from outside the Galaxy or to circulation of gas from the Galactic disc powered by supernova feedback (galactic fountain). Here, we show that both mechanisms are simultaneously at work. We use a new galactic fountain model combined with high-resolution hydrodynamical simulations. We focus on the prototypical cloud complex C and show that it was produced by an explosion that occurred in the Cygnus-Outer spiral arm about 150 Myr ago. The ejected material has triggered the condensation of a large portion of the circumgalactic medium and caused its subsequent accretion on to the disc. This fountain-driven cooling of the lower Galactic corona provides the low-metallicity gas required by chemical evolution models of the Milky Way's disc.

Aims. We present here a study of the cold dust in the close environs of the ring nebula Gum 31. We aim at deriving the physical properties of the molecular gas and dust associated with the nebula, and investigating its correlation with the star formation in the region, which was probably triggered by the expansion of the ionization front against its environment. Methods. We make use of 870 μm emission data obtained with the Large APEX Bolometer Camera (LABOCA) to map the dust emission. The 870 μm emission provides an excellent probe of mass and density of dense molecular clouds. The obtained LABOCA image was compared to archival infrared, radio continuum, and optical images. Results. The 870 μm emission follows the 8 μm (Spitzer), 250 μm, and 500 μm (Herschel) emission distributions showing the classical morphology of a two-dimensional projection of a spherical shell. We use the 870 μm and 250 μm images to identify 60 dust clumps in the collected layers of molecular gas using the Gaussclumps algorithm. The clumps have effective deconvolved radii between 0.16 pc and 1.35 pc, masses between 70 M⊙ and 2800 M⊙, and volume densities between 1.1 × 103 cm-3 and ~2.04 × 105 cm-3. The total mass of the clumps is ~37 600 M⊙. The dust temperature of the clumps is in the range from 21 K to 32 K, while inside the Hii region it reaches ~40 K. The clump mass distribution for the sample is fitted by a power law dN/dlog (M/M⊙) ∝ M-α, with α = 0.93 ± 0.28. The slope differs from those obtained for the stellar IMF in the solar neighborhood, suggesting that the clumps are not direct progenitors of single stars/protostars. The mass-radius relationship for the 41 clumps detected in the 870 μm emission shows that only 37% of them lie in or above the high-mass star formation threshold. Most of this 37% have candidate YSOs projected inside their limits. A comparison of the dynamical age of the Hii region with the fragmentation time, allowed us to conclude that the collect-and-collapse mechanism may be important for the star formation at the edge of Gum 31, although other processes may be acting simultaneously. The position of the identified young stellar objects in the region is also a strong indicator that the collect-and-collapse process is acting., Facultad de Ciencias Astronómicas y Geofísicas, Instituto Argentino de Radioastronomía

Aims. We carry out a multiwavelength study to characterize the H I supershell designated GS118+01-44, and to analyse its possible origin. Methods. A multiwavelength study has been carried out to study the supershell and its environs. We performed an analysis of the H I, CO, radio continuum, and infrared emission distributions. Results. The Canadian Galactic Plane Survey (CGPS) H I data reveals that GS118+01-44 is centred at (l,b) = (117°.7, 1°.4) with a systemic velocity of -44.3 km s-1. According to Galactic rotation models this structure is located at 3.0 ± 0.6 kpc from the Sun. There are several H II regions and three supernova remnants (SNRs) catalogued in the region. On the other hand, the analysis of the temperature spectral index distribution shows that in the region there is a predominance of non-thermal emission. Infrared emission shows that cool temperatures dominate the area of the supershell. Concerning the origin of the structure, we found that even though several OB stars belonging to CasOB5 are located in the interior of GS118+01-44, an analysis of the energy injected by these stars through their stellar winds indicates that they do not have sufficient energy to create GS118+01-44. Therefore, an additional energy source is needed to explain the genesis of GS118+01-44. On the other hand, the presence of several H II regions and young stellar object candidates in the edges of GS118+01-44 shows that the region is still active in forming new stars., Facultad de Ciencias Astronómicas y Geofísicas, Instituto Argentino de Radioastronomía

We use 3D numerical simulations to study the evolution of the Hα intensity and velocity dispersion for single and multiple supernova (SN) explosions. We find that the IHα– σ diagram obtained for simulated gas flows is similar in shape to that observed in dwarf galaxies. We conclude that colliding SN shells with significant difference in age are responsible for high velocity dispersion that reaches up to ≳ 100 km s−1. Such a high velocity dispersion could be hardly obtained for a single SN remnant. Peaks of velocity dispersion in the IHα– σ diagram may correspond to several isolated or merged SN remnants with moderately different ages. Degrading the spatial resolution in the Hα intensity and velocity dispersion maps makes the simulated IHα– σ diagrams close to those observed in dwarf galaxies not only in shape, but also quantitatively.