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We present high-resolution (10243) simulations of super-/hypersonic isothermal hydrodynamic turbulence inside an interstellar molecular cloud (resolving scales of typically 20–100 au), including a multidisperse population of dust grains, i.e. a range of grain sizes is considered. Due to inertia, large grains (typical radius |$a \gtrsim 1.0\, \mu$| m) will decouple from the gas flow, while small grains (⁠|$a\lesssim 0.1\, \mu$| m) will tend to better trace the motions of the gas. We note that simulations with purely solenoidal forcing show somewhat more pronounced decoupling and less clustering compared to simulations with purely compressive forcing. Overall, small and large grains tend to cluster, while intermediate-size grains show essentially a random isotropic distribution. As a consequence of increased clustering, the grain–grain interaction rate is locally elevated; but since small and large grains are often not spatially correlated, it is unclear what effect this clustering would have on the coagulation rate. Due to spatial separation of dust and gas, a diffuse upper limit to the grain sizes obtained by condensational growth is also expected, since large (decoupled) grains are not necessarily located where the growth species in the molecular gas is. [ABSTRACT FROM AUTHOR]

We explore how the velocity gradient technique (VGT) can be applied to absorbing media in the case of 13CO 2–1 emission. The VGT is a new way to trace magnetic fields in the plane of the sky using only spectroscopic observations. We apply the VGT to magnetohydrodynamic turbulence simulations that have been post-processed to include 13CO 2–1 emission and we calculate the velocity centroid gradients. We find that the velocity centroid gradients trace the projected magnetic field in media with different 13CO abundances, densities and optical depths. Our study opens up the possibility of using velocity centroid gradients to trace magnetic fields in molecular clouds using 13CO emission. [ABSTRACT FROM AUTHOR]

We detected OH 18 cm main line emission from 5 of 7 positions in the intermediate-velocity molecular cloud (IVMC) G211+63. These are the first detections of hydroxyl in IVMCs. Our OH detections at AV levels ranging from 0.24 to 0.27 mag reinforce the notion that these lines can efficiently trace diffuse, low-extinction molecular gas. N (OH) is derived for a range of excitation temperatures (5–30 K) and likely falls between 1 and 16 × 10 $$^{13}\, {\rm cm}^{-2}$$. The corresponding N (H2) values are consistent both with estimates derived from E (B − V) and CO data. Estimates of the cloud mass from the OH data range from 26 to 820 M⊙ for distances from 100 to 400 pc and T ex from 5 to 10 K. These values are 3–20 times less than the virial mass of the cloud. It is likely IVMCs resemble high-latitude clouds in this respect. If so, they are transient structures breaking up on time-scales of $${\sim }10^6\, {\rm yr}$$. [ABSTRACT FROM AUTHOR]

We explore the structure of magnetic field lines in and around filaments in simulations of molecular clouds undergoing global, multiscale gravitational collapse. In these simulations, filaments are not in a static equilibrium, but are long-lived flow structures that accrete gas from their environment and direct it towards clumps embedded in the filament or at the nodes at the conjunction with other filaments. In this context, the magnetic field is dragged by the collapsing gas, so its structure must reflect the flow that generates the filament. Around the filament, the gas is accreted on to it, and the magnetic lines must then be perpendicular to the filament. As the gas density increases, the gas flow changes direction, becoming almost parallel to the filament, and magnetic lines also tend to align with it. At the spine of the filament, however, magnetic lines become perpendicular again since they must connect to lines on the opposite side of the filament, resulting in 'U'-shaped magnetic structures, which tend to be stretched by the longitudinal flow along the filament. Magnetic diffusive processes, however, allow the gas to continue to flow. Assuming a stationary state in which the ram pressure of the flow balances the magnetic tension, the curvature of the field lines is determined by the diffusion rate. We derive an expression relating the curvature of the field lines to the diffusive coefficient, which may be used to observationally determine the nature of the diffusive process. [ABSTRACT FROM AUTHOR]

A semiempirical model of single differential cross sections (SDCS) for ionization of water vapor by fast electrons and bare ions is presented. At low secondary-electron energy, the model is based on an asymptotic expansion of the first Born approximation with coefficients, that are independent of projectile properties, evaluated from experimental photoabsorption and proton-impact ionization data. As the secondary-electron energy increases, the model converges to a binary-encounter approximation. Comparisons with measured differential, total, and dissociative cross sections for ionization of water by fast electrons are used to test the model. For primary electrons with energy greater than about 500 eV, agreement with these data is generally within experimental uncertainty; however, some discrepancies of uncertain origin exist. [ABSTRACT FROM AUTHOR]

In previous contributions, we have presented an analytical model describing the evolution and star formation rate (SFR) of molecular clouds (MCs) undergoing hierarchical gravitational contraction. The cloud's evolution is characterized by an initial increase in its mass, density, SFR, and star formation efficiency (SFE), as it contracts, followed by a decrease of these quantities as newly formed massive stars begin to disrupt the cloud. The main parameter of the model is the maximum mass reached by the cloud during its evolution. Thus, specifying the instantaneous mass and some other variable completely determines the cloud's evolutionary stage. We apply the model to interpret the observed scatter in SFEs of the cloud sample compiled by Lada et al. as an evolutionary effect so that, although clouds such as California and Orion A have similar masses, they are in very different evolutionary stages, causing their very different observed SFRs and SFEs. The model predicts that the California cloud will eventually reach a significantly larger total mass than the Orion A cloud. Next, we apply the model to derive estimated ages of the clouds since the time when approximately 25 per cent of their mass had become molecular. We find ages from ∼1.5 to 27 Myr, with the most inactive clouds being the youngest. Further predictions of the model are that clouds with very low SFEs should have massive atomic envelopes constituting the majority of their gravitational mass, and that low-mass clouds (M ∼ 103–104M⊙) end their lives with a mini-burst of star formation, reaching SFRs ∼300–500M⊙ Myr−1. By this time, they have contracted to become compact (∼1 pc) massive star-forming clumps, in general embedded within larger giant molecular clouds. [ABSTRACT FROM AUTHOR]

The avian song system is a group of brain areas specialized for vocal learning and production of song. A major cortical control area, HVC, projects both to a motor output circuit and to a striatal area in the anterior forebrain pathway. These projections are made by two groups of neurons, with mainly distinct roles in either programming vocal production or regulating vocal plasticity. In order to distinguish these two types of projection neurons in singing birds, we recorded unit activity in HVC of anesthetized birds, while stimulating in the anterior forebrain nucleus Area X. HVC units identified in this way had a distinct spike waveform, with a much longer duration positive peak than an initial negative one. We further found that units with a very similar spike waveform were phasically active during singing, firing at specific points of a limited number of song syllables. These units were also less active when birds only heard their own song, during the same syllables. While similar results from anesthetized and awake recordings have been reported in previous studies, the combination of both types of experiments here may be useful as a basis for identifying HVC neurons projecting to Area X based on their spike waveforms, and aid further study of their role in song learning and control. [ABSTRACT FROM AUTHOR]

High-velocity clouds (HVCs) are interstellar clouds of atomic hydrogen that do not follow normal Galactic rotation and have velocities of a several hundred kilometres per second. A considerable number of these clouds are falling down towards the Galactic disc. HVCs form large and massive complexes, so if they collide with the disc a great amount of energy would be released into the interstellar medium. The cloud-disc interaction produces two shocks: one propagates through the cloud and the other through the disc. The properties of these shocks depend mainly on the cloud velocity and the disc-cloud density ratio. In this work, we study the conditions necessary for these shocks to accelerate particles by diffusive shock acceleration and we study the non-thermal radiation that is produced. We analyse particle acceleration in both the cloud and disc shocks. Solving a time-dependent two-dimensional transport equation for both relativistic electrons and protons, we obtain particle distributions and non-thermal spectral energy distributions. In a shocked cloud, significant synchrotron radio emission is produced along with soft gamma rays. In the case of acceleration in the shocked disc, the non-thermal radiation is stronger; the gamma rays, of leptonic origin, might be detectable with current instruments. A large number of protons are injected into the Galactic interstellar medium, and locally exceed the cosmic ray background. We conclude that under adequate conditions the contribution from HVC-disc collisions to the galactic population of relativistic particles and the associated extended non-thermal radiation might be important. [ABSTRACT FROM AUTHOR]

The [C2H]/[C2D] abundance ratio is a useful tool to explore the physical and chemical conditions of cold molecular clouds. Hence, an accurate determination of both the C2H and C2D abundances is of fundamental interest. Due to the low density of the interstellar medium, the population of the energy levels of the molecules is not at local thermodynamical equilibrium. Thus, the accurate modelling of the emission spectra requires the calculation of collisional rate coefficients with the most abundant interstellar species. Hence, we provide rate coefficients for the hyperfine excitation of C2H and C2D by para-H2(j=0), the most abundant collisional partner in coldmolecular clouds. State-to-state rate coefficients between the lowest levels were computed for temperatures ranging from 5 to 80 K. For both isotopologues, the Λj = ΛF propensity rule is observed. The comparison between C2H and C2D rate coefficients shows that differences by up to a factor of two exist, mainly for Λj = ΛN = 1 transitions. The new rate coefficients will significantly help in the interpretation of recent observed spectra. [ABSTRACT FROM AUTHOR]

The [C2H]/[C2D] abundance ratio is a useful tool to explore the physical and chemical conditions of cold molecular clouds. Hence, an accurate determination of both the C2H and C2D abundances is of fundamental interest. Due to the low density of the interstellar medium, the population of the energy levels of the molecules is not at local thermodynamical equilibrium. Thus, the accurate modelling of the emission spectra requires the calculation of collisional rate coefficients with the most abundant interstellar species. Hence, we provide rate coefficients for the hyperfine excitation of C2H and C2D by para-H2(j=0), the most abundant collisional partner in coldmolecular clouds. State-to-state rate coefficients between the lowest levels were computed for temperatures ranging from 5 to 80 K. For both isotopologues, the Λj = ΛF propensity rule is observed. The comparison between C2H and C2D rate coefficients shows that differences by up to a factor of two exist, mainly for Λj = ΛN = 1 transitions. The new rate coefficients will significantly help in the interpretation of recent observed spectra. [ABSTRACT FROM AUTHOR]

We report high angular resolution (4.9" × 3.0") images of reactive ions SH+, HOC+, and SO+ toward the Orion Bar photodissociation region (PDR). We used ALMA-ACA to map several rotational lines at 0.8mm, complemented with multi-line observations obtained with the IRAM30m telescope. The SH+ and HOC+ emission is restricted to a narrow layer of 2"- to 10"-width (≈800 to 4000AU depending on the assumed PDR geometry) that follows the vibrationally excited H2* emission. Both ions efficiently form very close to the H/H2 transition zone, at a depth of AV ≲ 1mag into the neutral cloud, where abundant C+, S2* coexist. SO+ peaks slightly deeper into the cloud. The observed ions have low rotational temperatures (Trot ≈ 10-30 K « Tk) and narrow line-widths (~2-3kms-1), a factor of ≃2 narrower that those of the lighter reactive ion CH+. This is consistent with the higher reactivity and faster radiative pumping rates of CH+ compared to the heavier ions, which are driven relatively more quickly toward smaller velocity dispersion by elastic collisions and toward lower Trot by inelastic collisions. We estimate column densities and average physical conditions from an excitation model (n(H2) ≈ 105-106cm-3, n(e-) ≈ 10cm-3, and Tk ≈ 200K). Regardless of the excitation details, SH+ and HOC+ clearly trace the most exposed layers of the UV-irradiated molecular cloud surface, whereas SO+ arises from slightly more shielded layers. [ABSTRACT FROM AUTHOR]

We present an analysis of the diffuse ultraviolet emission near the Taurus Molecular Cloud based on observations made by the Galaxy Evolution Explorer. We used a Monte Carlo dust scattering model to show that about half of the scattered flux originates in the molecular cloud with 25 per cent arising in the foreground and 25 per cent behind the cloud. The best-fitting albedo of the dust grains is 0.3, but the geometry is such that we could not constrain the phase function asymmetry factor (g). [ABSTRACT FROM AUTHOR]

The Purpose of this work is to study the evolution of magnetized rotating filamentary molecular clouds. We consider cylindrical symmetric filamentary molecular clouds at an early stage of evolution. For the first time we consider the rotation of filamentary molecular in the presence of an axial and azimuthal magnetic field without any assumption of density and magnetic functions. We show that in addition to decreasing the radial collapse velocity, the rotational velocity is also affected by the magnetic field. The existence of rotation yields fragmentation of filaments. Moreover, we show that the magnetic field has a significant effect on the fragmentation of filamentary molecular clouds. [ABSTRACT FROM AUTHOR]

The dependence of the current in the measurement circuit of a high-velocity microparticle detector on the parameters of these particles is found. The Ramo-Shockley theorem is used to derive an analytic expression for the current in a series RC circuit. [ABSTRACT FROM AUTHOR]

Numerical simulations of the motions of stars in the gravitational fields of binary black holes with various component mass ratios have been carried out. Two models are considered: (1) the two-body problem with two fixed centers; (2) the general three-body problem. The first model is applicable only over short times Δ t ≫ T, where T is the period of the binary system. The second model is applicable at all times except for during close encounters of stars with one of the binary components, r ≤ 0.00002 pc, where r is the distance from the star to the nearer black hole. In very close passages, relativistic corrections must be taken into account. Estimates of the probability of formation of high-velocity stars as a result of such interactions are obtained. It is shown that this mechanism is not suitable for the nucleus of our Galaxy due to the probable absence of a second massive black hole in the central region of the Galaxy. [ABSTRACT FROM AUTHOR]

We present a high-resolution study of five high-velocity clouds in the Magellanic Leading Arm region. This is a follow-up study of our widefield Parkes survey of the region in order to probe the multiphase structures of the clouds and to give an insight to their origin, evolution and distance. High-resolution data were obtained from the Australia Telescope Compact Array. By combining with single-dish data from the Galactic All-Sky Survey, we are able to probe compact and diffuse emission simultaneously. We identify resolved and unresolved clumps. Physical parameters were derived for both diffuse structure and compact clumps. The latter are cold with typical velocity linewidths of 5 km s-1.We find a gradient in thermal halo pressure, hydrogen density and HI column density of high-velocity clouds as a function of Galactic latitude. This is possibly the first observational evidence of varying distance in the Leading Arm region, with the leading part of the Leading Arm (LA II and III) probably being closer to the Galactic disc than the trailing end (LA I). [ABSTRACT FROM AUTHOR]

Drag from hydrogen in the interstellar cloud which formed Gould’s Belt may have sent interplanetary dust particle (IDPs) and small meteoroids with embedded helium to the Earth, perhaps explaining part the helium-3 flux increase seen in the sedimentary record near the Eocene–Oligocene transition. Assuming the Solar System passed through part of the cloud, IDPs in the inner Solar System may have been dragged to Earth, while dust and small meteoroids in the asteroid belt up to centimeter size may have been dragged to the resonances, where their orbital eccentricities were pumped up into Earth-crossing orbits; however, this hypotheses does not explain the Popigai and Chesapeake Bay impacts. [ABSTRACT FROM AUTHOR]

The physical origin of high-velocity cool gas seen in galactic winds remains unknown. Following work by B. Wang, we argue that radiative cooling in initially hot thermally-driven outflows can produce fast neutral atomic and photoionized cool gas. The inevitability of adiabatic cooling from the flow's initial 107-108 K temperature and the shape of the cooling function for T ≾ 107 K imply that outflows with hot gas mass-loss rate relative to star formation rate β of = Mhot/M*≿ 0.5 cool radiatively on scales ranging from the size of the energy injection region to tens of kpc. We highlight the β and star formation rate surface density dependence of the column density, emission measure, radiative efficiency, and velocity. At rcool, the gas produces X-ray and then UV/optical line emission with a total power bounded by ~10-2 L* if the flow is powered by steady-state star formation with luminosity L*. The wind is thermally unstable at rcool, potentially leading to a multiphase medium. Cooled winds decelerate significantly in the extended gravitational potential of galaxies. The cool gas precipitated from hot outflows may explain its prevalence in galactic haloes. We forward a picture of winds whereby cool clouds are initially accelerated by the ram pressure of the hot flow, but are rapidly shredded by hydrodynamical instabilities, thereby increasing β, seeding radiative and thermal instability, and cool gas rebirth. If the cooled wind shocks as it sweeps up the circumgalactic medium, its cooling time is short, thus depositing cool gas far out into the halo. Finally, conduction can dominate energy transport in low-β hot winds, leading to flatter temperature profiles than otherwise expected, potentially consistent with X-ray observations of some starbursts. [ABSTRACT FROM AUTHOR]

Observations show the presence, in the halo of our Galaxy, of stars moving at velocities so high to require an acceleration mechanism involving the presence of a massive central black hole. Thus, in the frame of a galaxy hosting a supermassive black hole (108M⊙) we investigated a mechanism for the production of high-velocity stars, which was suggested by the results of N-body simulations of the close interaction between a massive, orbitally decayed, globular cluster and the supermassive black hole. The high velocity acquired by some stars of the cluster comes from the transfer of gravitational binding energy into kinetic energy of the escaping star originally orbiting around the cluster. After the close interaction with the massive black hole, stars could reach a velocity sufficient to travel in the halo and even overcome the galactic gravitational well, while some of them are just stripped from the globular cluster and start orbiting on precessing loops around the galactic centre. [ABSTRACT FROM AUTHOR]

We present a new method to model an HST/COS (Hubble Space Telescope/Cosmic Origins Spectrograph) spectrum, aimed to analyse intrinsic UV absorption from the outflow of Mrk 290, a Seyfert I galaxy. We use newly updated xstar to generate photoionization models for the intrinsic absorption from the active galactic nuclei (AGN) outflow, the line emission from the AGN broad- and narrow-line regions, and the local absorption from high-velocity clouds and Galactic interstellar medium. The combination of these physical models accurately fits the COS spectrum. Three intrinsic absorbers outflowing with velocities ∼500 km s− 1 are identified, two of which are found directly from two velocity components of the N v and C iv doublets, while the third is required by the extra absorption in the Lyα. Their outflow velocities, ionization states and column densities are consistent with the lowest and moderate ionization warm absorbers (WAs) in the X-ray domain found by Chandra observations, suggesting a one-to-one correspondence between the absorbing gas in the UV and X-ray bands. The small turbulent velocities of the WAs (vturb ≲ 100 km s− 1) support our previous argument from the X-ray study that the absorbers originate from the inner side of the torus due to thermal evaporation. Given the covering fractions of ∼65 per cent for the three WAs, we deduce that the lengths and the thicknesses of the WAs are comparable, which indicates that the geometry of WAs are more likely clouds rather than flat and thin layers. In addition, the modelling of the broad-line emission suggests a higher covering fraction of clouds when they are very closer to the black hole. [ABSTRACT FROM AUTHOR]

Context. Given the current and past star-formation in the Milky Way in combination with the limited gas supply, the re-fuelling of the reservoir of cool gas is an important aspect of Galactic astrophysics. The infall of Hi halo clouds can, among other mechanisms, contribute to solving this problem. Aims. We study the intermediate-velocity cloud IVC135+54 and its spatially associated high-velocity counterpart to look for signs of a past or ongoing interaction. Methods. Using the Effelsberg-Bonn Hi Survey data, we investigated the interplay of gas at different velocities. In combination with far-infrared Planck and IRIS data, we extended this study to interstellar dust and used the correlation of the data sets to infer information on the dark gas. Results. The velocity structure indicates a strong compression and deceleration of the infalling high-velocity cloud (HVC), associated with far-infrared excess emission in the intermediate-velocity cloud. This excess emission traces molecular hydrogen, confirming that IVC135+54 is one of the very few molecular halo clouds. The high dust emissivity of IVC135+54 with respect to the local gas implies that it consists of disk material and does not, unlike the HVC, have an extragalactic origin. Conclusions. Based on the velocity structure of the HVC and the dust content of the IVC, a physical connection between them appears to be the logical conclusion. Since this is not compatible with the distance difference between the two objects, we conclude that this particular HVC might be much closer to us than complex C. Alternatively, the indicators for an interaction are misleading and have another origin. [ABSTRACT FROM AUTHOR]

High-velocity lower crust (HVLC) and seaward-dipping reflector (SDR) sequences are typical features of volcanic rifted margins. However, the nature and origin of HVLC is under discussion. Here we provide a comprehensive analysis of deep crustal structures in the southern segment of the South Atlantic and an assessment of HVLC along the margins. Two new seismic refraction lines off South America fill a gap in the data coverage and together with five existing velocity models allow for a detailed investigation of the lower crustal properties on both margins. An important finding is the major asymmetry in volumes of HVLC on the conjugate margins. The seismic refraction lines across the South African margin reveal cross-sectional areas of HVLC 4 times larger than at the South American margin, a finding that is opposite to the asymmetric distribution of the flood basalts in the Paraná-Etendeka Large Igneous Province. Also, the position of the HVLC with respect to the SDR sequences varies consistently along both margins. Close to the Falkland-Agulhas Fracture Zone in the south, a small body of HVLC is not accompanied by SDRs. In the central portion of both margins, the HVLC is below the inner SDR wedges while in the northern area, closer to the Rio Grande Rise-Walvis Ridge, large volumes of HVLC extend far seaward of the inner SDRs. This challenges the concept of a simple extrusive/intrusive relationship between SDR sequences and HVLC, and it provides evidence for formation of the HVLC at different times during the rifting and breakup process. We suggest that the drastically different HVLC volumes are caused by asymmetric rifting in a simple-shear-dominated extension. [ABSTRACT FROM AUTHOR]

Context. We present deep Hi observations of three compact high-velocity clouds (CHVCs). Aims. The main goal is to study their diffuse warm gas and compact cold cores. We use both low- and high-resolution data obtained with the 100 m Effelsberg telescope and the Westerbork Synthesis Radio Telescope (WSRT). The combination is essential in order to study the morphological properties of the clouds since the single-dish telescope lacks a sufficient angular resolution while the interferometer misses a large portion of the diffuse gas. Methods. Here single-dish and interferometer data are combined in the image domain with a new combination pipeline. The combination makes it possible to examine interactions between the clouds and their surrounding environment in great detail. Results. The apparent difference between single-dish and radio interferometer total flux densities shows that the CHVCs contain a considerable amount of diffuse gas with low brightness temperatures. A Gaussian decomposition indicates that the clouds consist predominantly of warm gas. [ABSTRACT FROM AUTHOR]

We report the detection of extremely broad emission toward two molecular clumps in the Galactic central molecular zone. We have mapped the Sagittarius C complex (–0.°61 < l < –0.°27, –0.°29 < b < 0.°04) in the HCN J = 4-3, 13CO J = 3-2, and H13CN J = 1-0 lines with the ASTE 10 m and NRO 45 m telescopes, detecting bright emission with 80-120 km s–1 velocity width (in full-width at zero intensity) toward CO–0.30–0.07 and CO–0.40–0.22, which are high velocity compact clouds (HVCCs) identified with our previous CO J = 3-2 survey. Our data reveal an interesting internal structure of CO–0.30–0.07 comprising a pair of high velocity lobes. The spatial-velocity structure of CO–0.40–0.22 can be also understood as a multiple velocity component, or a velocity gradient across the cloud. They are both located on the rims of two molecular shells of about 10 pc in radius. Kinetic energies of CO–0.30–0.07 and CO–0.40–0.22 are (0.8-2) × 1049 erg and (1-4) × 1049 erg, respectively. We propose several interpretations of their broad emission: collision between clouds associated with the shells, bipolar outflow, expansion driven by supernovae (SNe), and rotation around a dark massive object. These scenarios cannot be discriminated because of the insufficient angular resolution of our data, though the absence of a visible energy source associated with the HVCCs seems to favor the cloud-cloud collision scenario. Kinetic energies of the two molecular shells are 1 × 1051 erg and 0.7 × 1051 erg, which can be furnished by multiple SN or hypernova explosions in 2 × 105 yr. These shells are candidates of molecular superbubbles created after past active star formation. [ABSTRACT FROM AUTHOR]

We report the first detection of magnetic fields associated with the Smith High Velocity Cloud. We use a catalog of Faraday rotation measures toward extragalactic radio sources behind the Smith Cloud, new H I observations from the Robert C. Byrd Green Bank Telescope, and a spectroscopic map of Hα from the Wisconsin H-Alpha Mapper Northern Sky Survey. There are enhancements in rotation measure (RM) of ≈100 rad m–2 which are generally well correlated with decelerated Hα emission. We estimate a lower limit on the line-of-sight component of the field of ≈8 μG along a decelerated filament; this is a lower limit due to our assumptions about the geometry. No RM excess is evident in sightlines dominated by H I or Hα at the velocity of the Smith Cloud. The smooth Hα morphology of the emission at the Smith Cloud velocity suggests photoionization by the Galactic ionizing radiation field as the dominant ionization mechanism, while the filamentary morphology and high (≈1 Rayleigh) Hα intensity of the lower-velocity magnetized ionized gas suggests an ionization process associated with shocks due to interaction with the Galactic interstellar medium. The presence of the magnetic field may contribute to the survival of high velocity clouds like the Smith Cloud as they move from the Galactic halo to the disk. We expect these data to provide a test for magnetohydrodynamic simulations of infalling gas. [ABSTRACT FROM AUTHOR]

Two impulsive limb coronal mass ejections (CMEs), one of which was accompanied by an active prominence and the other by a flare, are analyzed using AIA/SDO solar data. The analysis leads to the conclusion that, in both cases, the sources of the CME formation were magnetic tubes rising from beneath the photosphere at high velocity. One or more arch structures can be located in the path of the magnetic tube, which it influences and drags along with it. The arch structures may then participate in the formation of the future CME, whose main basis is the magnetic tube itself. [ABSTRACT FROM AUTHOR]

Star formation in molecular clouds is intimately linked to their internal mass distribution. We present an unprecedentedly detailed analysis of the column density structure of a high-mass, filamentary molecular cloud, namely IRDC G11.11-0.12 (G11). We use two novel column density mapping techniques: high-resolution (FWHM = 2", or ~0.035 pc) dust extinction mapping in near- and midinfrared, and dust emission mapping with the Herschel satellite. These two completely independent techniques yield a strikingly good agreement, highlighting their complementarity and robustness. We first analyze the dense gas mass fraction and linear mass density of G11. We show that G11 has a top heavy mass distribution and has a linear mass density (Ml ~ 600 M☉ pc-1) that greatly exceeds the critical value of a self-gravitating, non-turbulent cylinder. These properties make G11 analogous to the Orion A cloud, despite its low star-forming activity. This suggests that the amount of dense gas in molecular clouds is more closely connected to environmental parameters or global processes than to the star-forming efficiency of the cloud. We then examine hierarchical fragmentation in G11 over a wide range of size-scales and densities. We show that at scales 0.5 pc ☉ l ☉ 8 pc, the fragmentation of G11 is in agreement with that of a self-gravitating cylinder. At scales smaller than l ☉ 0.5 pc, the results agree better with spherical Jeans' fragmentation. One possible explanation for the change in fragmentation characteristics is the size-scale-dependent collapse time-scale that results from the finite size of real molecular clouds: at scales l ☉ 0.5 pc, fragmentation becomes sufficiently rapid to be unaffected by global instabilities. [ABSTRACT FROM AUTHOR]

The central parsec of the Milky Way is a very special region of our Galaxy; it contains the supermassive black hole associated with Sgr A* as well as a significant number of early-type stars and a complex structure of streamers of neutral and ionized gas, within two parsec from the centre, representing a unique laboratory. We report the identification of a high velocity compact nebular filament 2.2 arcsec south of Sgr A*. The structure extends over ∼1 arcsec and presents a strong velocity gradient of ∼200 km s−1 arcsec−1. The peak of maximum emission, seen in [Fe iii] and He i lines, is located at dα = +0.20 ± 0.06 arcsec and dδ = −2.20 ± 0.06 arcsec with respect to Sgr A*. This position is near the star IRS 33N. The velocity at the emission peak is Vr = −267 km s−1. The filament has a position angle of PA = 115° ± 10°, similar to that of the Bar and of the Eastern Arm at that position. The peak position is located 0.7 arcsec north of the binary X-ray and radio transient CXOGX J174540.0−290031, a low-mass X-ray binary (LMXB) with an orbital period of 7.9 h. The [Fe iii] line emission is strong in the filament and its vicinity. These lines are probably produced by shock heating but we cannot exclude some X-ray photoionization from the LMXB. Although we cannot rule out the idea of a compact nebular jet, we interpret this filament as a possible shock between the Northern and the Eastern Arm or between the Northern Arm and the mini-spiral ‘Bar’. [ABSTRACT FROM AUTHOR]

Aims. Stars twinkle because their light propagates through the atmosphere. The same phenomenon is expected on a longer time scale when the light of remote stars crosses an interstellar turbulent molecular cloud, but it has never been observed at optical wavelengths. The aim of the study described in this paper is to fully simulate the scintillation process, starting from the molecular cloud description as a fractal object, ending with the simulations of fluctuating stellar light curves. Methods. Fast Fourier transforms are first used to simulate fractal clouds. Then, the illumination pattern resulting from the crossing of background star light through these refractive clouds is calculated from a Fresnel integral that also uses fast Fourier transform techniques. Regularisation procedure and computing limitations are discussed, along with the effect of spatial and temporal coherency (source size and wavelength passband). Results. We quantify the expected modulation index of stellar light curves as a function of the turbulence strength - characterised by the diffraction radius Rdiff - and the projected source size, introduce the timing aspects, and establish connections between the light curve observables and the refractive cloud. We extend our discussion to clouds with different structure functions from Kolmogorov-type turbulence. Conclusions. Our study confirms that current telescopes of ~4 m with fast-readout, wide-field detectors have the capability of discovering the first interstellar optical scintillation effects. We also show that this effect should be unambiguously distinguished from any other type of variability through the observation of desynchronised light curves, simultaneously measured by two distant telescopes. [ABSTRACT FROM AUTHOR]

We present first results from the Herschel Gould Belt survey for the B211/L1495 region in the Taurus molecular cloud. Thanks to their high sensitivity and dynamic range, the Herschel images reveal the structure of the dense, star-forming filament B211 with unprecedented detail, along with the presence of striations perpendicular to the filament and generally oriented along the magnetic field direction as traced by optical polarization vectors. Based on the column density and dust temperature maps derived from the Herschel data, we find that the radial density profile of the B211 filament approaches power-law behavior, ρ α r-2:0 ± 0.4, at large radii and that the temperature profile exhibits a marked drop at small radii. The observed density and temperature profiles of the B211 filament are in good agreement with a theoretical model of a cylindrical filament undergoing gravitational contraction with a polytropic equation ofz state: P α γ and T α ρ γ-1, with = 0:97 ± 0:01 < 1 (i.e., not strictly isothermal). The morphology of the column density map, where some of the perpendicular striations are apparently connected to the B211 filament, further suggests that the material may be accreting along the striations onto the main filament. The typical velocities expected for the infalling material in this picture are ~0.5-1 km s-1, which are consistent with the existing kinematical constraints from previous CO observations. [ABSTRACT FROM AUTHOR]

We present WHAM observations of Hα, [N II], and [S II] in the Smith Cloud. A map of Ha emission from the cloud shows ionized gas coincident with the brightest H I emission, but nearly-as-bright Ha in some regions with faint H I. The ionized mass of the cloud is at least as large as the neutral mass, >106 M⊙. Ionized gas in the core of the Smith Cloud has an electron temperature 6000 K < T < 16 000 K. The observed ratio [N II]/Hα = 0.39 ± 0.09 shows that the cloud has a non-primordial nitrogen abundance, 0.1 - 1 x solar. [ABSTRACT FROM AUTHOR]

Over the last few years, evidence that nearby spiral galaxies are surrounded by massive halos of cold gas has been accumulating. This extra-planar cold gas, rotating more slowly than the disk gas, is observed in galaxies with a range of different properties (such as mass and star formation rate, SFR) and it appears analogous to the Intermediate and High Velocity Clouds of the Milky Way. Models for the origin of extra-planar gas have been proposed taking into account the effects of supernova feedback (galactic fountain), cooling flow accretion and hydrostatic equilibrium. Several techniques have been used from analytical treatments and ballistic orbit integration to hydrodynamical simulations. I present a new model where a galactic fountain sweeps up ambient medium as it travels through the halo. This seems to give the best results in reproducing the kinematics of the extra-planar gas and it implies a gas accretion rate of the order of the SFR of the host galaxy. [ABSTRACT FROM AUTHOR]

There exist many physical processes that may contribute to the driving of turbulence in galactic disks. Some of them could drive turbulence even in the absence of star formation. For example, hydrodynamic (HD) or magnetohydrodynamic (MHD) instabilities, frequent mergers of small satellite clumps, ram pressure, or infalling gas clouds. In this work we present numerical simulations to study the interaction of compact high velocity clouds (CHVC) with the outskirts of magnetized gaseous disks. With our numerical simulations we show that the rain of small HVCs onto the disk is a potential source of random motions in the outer parts of HI disks. [ABSTRACT FROM AUTHOR]

Indirect evidence from detailed chemical evolution studies shows that infall of low metallicity gas appears to have proceeded at a rather constant rate during the lifetime of the Galactic disk. We explore two possible implications: (a) the effect of an infalling high velocity cloud (HVC) on interstellar cloud stability leading to enhanced star formation, and (b) the presence of these HVC's around neighbouring galaxies, which would generalize this aspect of the evolution of galaxies in groups. (a) Using a simple analytical model we show how the overpressure produced in the galactic plane by HVC infall reduces the effective Jeans mass of the existing clouds, thus tending to enhance the SFR. (b) Using HI data from the THINGS survey we detect HI "fluff" around 4 galaxies of a total sample of 32 observed. Projecting some of the largest Galactic HVC's to the distances of the THINGS galaxies we produce a useful estimate of the fraction of the HVC masses that we can detect at these distances, finding a value of order 10%, and go on to make tentative estimates about infall rates for nearby galaxies. [ABSTRACT FROM AUTHOR]

Hα emission from neutral halo clouds probes the radiation and hydrodynamic conditions in the halo. Armed with such measurements, we can explore how radiation escapes from the Galactic plane and how infalling gas can survive a trip through the halo. The Wisconsin H-Alpha Mapper (WHAM) is one of the most sensitive instruments for detecting and mapping optical emission from the ISM. Here, we present recent results exploring the ionization of two infalling high-velocity complexes. First, we report on our progress mapping Hα emission covering the full extent of Complex A. Intensities are faint (100 mR; EM 0.2 pc cm-6) but correlate on the sky and in velocity with 21-cm emission. Second, we explore the ionized component of some Anti-Center Complex clouds studied by Peek et al. (2007) that show dynamic shaping from interaction with the Galactic halo. [ABSTRACT FROM AUTHOR]

We have detected hundreds of HI clouds in the lower Galactic halo within the Galactic All-Sky Survey pilot region, a region spanning 325° ≤ l ≤ 343° and |b| ≤ 20°. The motions of these clouds are governed by Galactic rotation, they are seen within the disk and up to heights of 2.5 kpc, and they span a wide range of Galactocentric radii. However, these clouds are not uniformly distributed and appear to be associated with Galactic structures such as spiral arms or superbubbles. [ABSTRACT FROM AUTHOR]

We report on new optical emission line observations toward the northern part of the Magellanic Stream. Using the Wisconsin H-Alpha Mapper (WHAM), we have detected Ha emission toward 17 directions spread across 50° of the Stream. We find strong variation in the Ha surface brightness with no significant correlation with Magellanic longitude. We compare our data with HI observations and briefly discuss the implications for the physical conditions of the Stream. [ABSTRACT FROM AUTHOR]

This contribution summarizes some recent results concerning gas in Galaxy halos. In the past few years, distances have been determined for six high-velocity clouds (HVCs), including the second largest, complex C. The derived distances range from about 2 to 10 kpc, placing these HVCs in the near Galactic halo, but far above the Galactic plane. Distances of ~10 kpc were determined to three different concentrations in Complex C, implying a mass of ~5 x 107 M⊙; this cloud is known to have a metallicity of ~0.15 solar, and represents an inflow of 0.15-0.25 M⊙ yr-1 of low-metallicity material. A statistical analysis of the sky and velocity distribution of the ~200 small HVCs shows that they probably form a population of clouds orbiting the Milky Way, with distances up to 80 kpc, and a radial inflow component of 50 km s-1. A study of 115 Lyα and 14 O VI absorption lines at redshifts z < 0.017 (v < 5000 km s-1) in the spectra of 76 AGNs shows that half of the intergalactic Lyα absorption lines originate within 450 kpc of galaxies. The amount of gas inside this distance is a factor 2-4 more than the total amount of mass inside the galaxies. [ABSTRACT FROM AUTHOR]

ABSTRACT High-velocity clouds (HVCs), fast-moving ionized and neutral gas clouds found at high galactic latitudes, may play an important role in the evolution of the Milky Way. The extent of this role depends sensitively on their distances and total sky covering factor. We search for HVC absorption in Hubble Space Telescope high-resolution ultraviolet (UV) spectra of a carefully selected sample of 133 active galactic nuclei (AGN) using a range of atomic species in different ionization stages (e.g. O i, C ii, C iv, Si ii, Si iii, Si iv). This allows us to identify neutral, weakly ionized or highly ionized HVCs over several decades in H i column densities. The sky covering factor of UV-selected HVCs with | vLSR| ≥ 90 km s−1 is about 68 per cent for the Galactic sky at [ABSTRACT FROM AUTHOR]

Context. High-velocity halo stars provide important information about the properties of the extreme Galactic halo. The study of unbound and bound Population II stars permits us to better estimate the mass of the halo. Aims. We carried out a detailed spectroscopic and kinematic study and have significantly refined the distance and the evolutionary state of the star. Methods. Its atmospheric parameters, chemical abundances and kinematical properties were determined using high-resolution optical spectroscopy and employing the local-thermodynamic-equilibrium model atmospheres of Kurucz and the spectral analysis code moog. Results. We found that CD-62°1346 is a metal-poor ([Fe/H] = -1.6) evolved giant star with Teff = 5300 K and log g = 1.7. The star exhibits high carbon and s-element abundances typical of CH stars. It is also a lead star. Our kinematic analysis of its 3D space motions shows that this star has a highly eccentric (e = 0.91) retrograde orbit with an apogalactic distance of ∼100 kpc, exceeding by a factor of two the distance of the Magellanic Clouds. The star travels with very high velocity relative to the Galactocentric reference frame (VGRF = 570 km s-1). Conclusions. CD-62°1346 is an evolved giant star and not a subgiant star, as was considered earlier. Whether it is bound or unbound to the Galaxy depends on the assumed mass and on the adopted Galactic potential. We also show that the star HD5223 is another example of a high-velocity CH star that exceeds the Galactic escape velocity. Possible origins of these two high-velocity stars are briefly discussed. CD-62°1346 and HD5223 are the first red giant stars to join the restricted group of hypervelocity stars. [ABSTRACT FROM AUTHOR]

We present an analysis of a systematic CO(2-1) survey at 12″ resolution covering most of the Local Group spiral M 33, which, at a distance of 840 kpc, is close enough for individual giant molecular clouds (GMCs) to be identified. The goal of this work is to study the properties of the GMCs in this subsolar metallicity galaxy. The CPROPS (Cloud PROPertieS) algorithm was used to identify 337 GMCs in M 33, the largest sample to date for an external galaxy. The sample is used to study the GMC luminosity function, or mass spectrum under the assumption of a constant N(H2) /ICO ratio. We find that n(L)dL ∝ L-2.0±0.1 for the entire sample. However, when the sample is divided into inner and outer disk samples, the exponent changes from 1.6 ± 0.2 in the center 2 kpc to 2.3 ± 0.2 for galactocentric distances larger than 2 kpc. On the basis of the emission in the FUV, Hα, 8 μm, and 24 μm bands, each cloud was classified in terms of its star-forming activity - no star formation or either embedded or exposed star formation (visible in FUV and Hα). At least one sixth of the clouds had no (massive) star formation, suggesting that the average time required for star formation to start is about one sixth of the total time for which the object is identifiable as a GMC. The clouds without star formation have significantly lower CO luminosities than those with star formation, whether embedded or exposed, a result that is presumably related to the lack of heating sources. Taking the cloud sample as a whole, the main non-trivial correlation is the decrease in cloud CO brightness (or luminosity) with galactocentric radius. The complete cloud catalog, including the CO and HI spectra and the CO contours overlaid on the FUV, Hα, 8 μm, and 24 μm images is presented in the appendix. [ABSTRACT FROM AUTHOR]

BSTRACT We present optical spectra of 403 stars and quasi-stellar objects in order to obtain distance limits towards intermediate- and high-velocity clouds (IHVCs), including new Fibre-fed Extended Range Optical Spectrograph (FEROS) observations plus archival ELODIE, FEROS, High Resolution Echelle Spectrometer (HIRES) and Ultraviolet and Visual Echelle Spectrograph (UVES) data. The non-detection of Ca ii K interstellar (IS) absorption at a velocity of −130 to −60 km s−1 towards HDE 248894 ( d∼ 3 kpc) and HDE 256725 ( d∼ 8 kpc) in data at signal-to-noise ratio (S/N) > 450 provides a new firm lower distance limit of 8 kpc for the anti-centre shell HVC. Similarly, the non-detection of Ca ii K IS absorption towards HD 86248 at S/N ∼ 500 places a lower distance limit of 7.6 kpc for Complex EP, unsurprising since this feature is probably related to the Magellanic System. The lack of detection of Na i D at S/N = 35 towards Mrk 595 puts an improved upper limit for the Na i column density of log ( NNaD <) 10.95 cm−2 towards this part of the Cohen Stream where Ca ii was detected by Wakker et al. Absorption at ∼−40 km s−1 is detected in Na i D towards the Galactic star PG 0039+049 at S/N = 75, placing a firm upper distance limit of 1 kpc for the intermediate-velocity cloud south (IVS), where a tentative detection had previously been obtained by Centurión et al. Ca ii K and Na i D absorption is detected at −53 km s−1 towards HD 93521, which confirms the upper distance limit of 2.4 kpc for part of the IV arch complex obtained using the International Ultraviolet Explorer ( IUE) data by Danly. Towards HD 216411 in Complex H a non-detection in Na D towards gas with log() = 20.69 cm−2 puts a lower distance limit of 6.6 kpc towards this HVC complex. Additionally, Na i D absorption is detected at −43.7 km s−1 in the star HD 218915 at a distance of 5.0 kpc in gas in the same region of the sky as Complex H. Finally, the Na i/Ca ii and Ca ii/H i ratios of the current sample are found to lie in the range observed for previous studies of IHVCs. [ABSTRACT FROM AUTHOR]

We report the detection of O and N absorption in a system of 'mini-broad' absorption lines (mini-BALs) previously reported to have variable C in the quasar PG0935+417. The formation of these lines in an extremely high velocity outflow (with km s) is confirmed by the line variability, broad smooth absorption profiles and partial covering of the background light source. H and lower-ionization metals are not clearly present. The line profiles are complex and asymmetric, with full widths at half-minimum (FWHM) of different components in the range 660 to 2510 km s. The resolved O doublet indicates that these lines are moderately saturated, with the absorber covering 80 per cent of the quasar continuum source . We derive ionic column densities of the order of 10 cm in C and several times larger in O , indicating an ionization parameter of . Assuming solar abundances, we estimate a total column density of cm. Comparisons to data in the literature show that this outflow emerged sometime between 1982 when it was clearly not present and 1993 when it was first detected. Our examination of the C data from 1993 to 2007 shows that there is variable complex absorption across a range of velocities from to km s. There is no clear evidence for acceleration or deceleration of the outflow gas. The observed line variations are consistent with either changes in the ionization state of the gas or clouds crossing our lines of sight to the continuum source. In the former case, the recombination times constrain the location of outflow to be at a radial distance of 1.2 kpc with density of cm. In the latter case, the nominal transit times of moving clouds indicate pc. Outflows are common in active galactic nuclei (AGN), but extreme speeds such as those reported here are extremely rare. It is not clear what properties of PG 0935+417 might produce this unusual outflow. The quasar is exceptionally luminous, with erg s, but it has just a modest Eddington ratio, , and no apparent unusual properties compared to other quasars. In fact, PG 0935+417 has significantly less X-ray absorption than typical BAL quasars even though its outflow has a degree of ionization typical of BALs at speeds that are 2-3 times larger than most BALs. These results present a challenge to theoretical models that invoke strong radiative shielding in the X-rays/far-UV to moderate the outflow ionization and thus enable its radiative acceleration to high speeds. [ABSTRACT FROM AUTHOR]

ABSTRACT We report on the discovery of a high-velocity narrow absorption line outflow in the redshift 2.3 quasar J 212329.46 − 005052.9. Five distinct outflow systems are detected with velocity shifts from −9710 to −14 050 km s −1 and C iv λλ1548, 1551 linewidths of FWHM ≈ 62-164 km s −1. This outflow is remarkable for having high speeds and a degree of ionization similar to broad absorption line (BAL) flows, but linewidths roughly 100 times narrower than BALs and no apparent X-ray absorption. This is also, to our knowledge, the highest-velocity narrow absorption line system confirmed to be in a quasar outflow by all three indicators of line variability, smooth superthermal line profiles and doublet ratios that require partial covering of the quasar continuum source. All five systems have stronger absorption in O vi λλ1032, 1038 than C iv with no lower ionization metal lines detected. Their line variabilities also appear coordinated, with each system showing larger changes in C iv than O vi and line strength variations accompanied by nearly commensurate changes in the absorber covering fractions. The metallicity is approximately twice solar. These data require five distinct outflow structures with similar kinematics, physical conditions and characteristic sizes of order 0.01-0.02 pc (based on partial covering). The coordinated line variations, occurring on time-scales ≤0.63 yr (quasar frame), are best explained by global changes in the outflow ionization caused by changes in the quasar's ionizing flux. An upper limit on the acceleration, ≲3 km s −1 yr −1, is consistent with blobs of gas that are gravitationally unbound and coasting freely ≳5 pc from the central black hole. Additional constraints from the variability time indicate that the full range of plausible distances is 5 ≲ R ≲ 1100 pc. However, if these small absorbing structures were created in the inner flow, they should be near the ∼5 pc minimum radius because they can travel just a few pc before dissipating (without external confinement). An apparent double line-lock in C iv suggests that the flow was radiatively accelerated and its present trajectory is within ∼16 ° of the radial (line-of-sight) direction. The absence of strong X-ray absorption shows that radiative shielding in the far-UV and X-rays is not needed to maintain moderate BAL-like ionizations and therefore, apparently, it is not needed to facilitate the radiative acceleration to high speeds. We argue that the ionization is moderated, instead, by high gas densities in small outflow substructures. Finally, we estimate that the kinetic energy yield from this outflow is at least 2 orders of magnitude too low to be important for feedback to the host galaxy's evolution. [ABSTRACT FROM AUTHOR]

The Gould Belt Legacy Survey on the James Clerk Maxwell Telescope's has observed a region of 260 arcmin in CO emission, and a 190 arcmin subset of this in CO and towards the Serpens molecular cloud. We examine the global velocity structure of the non-outflowing gas, and calculate excitation temperatures and opacities. The large-scale mass and energetics of the region are evaluated, with special consideration for high-velocity gas. We find the cloud to have a mass of 203 M, and to be gravitationally bound, and that the kinetic energy of the outflowing gas is approximately 70 per cent of the turbulent kinetic energy of the cloud. We identify compact outflows towards some of the submillimetre Class 0/I sources in the region. [ABSTRACT FROM AUTHOR]