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The study of dynamic properties of bubbles in the interstellar medium is important for understanding the feedback mechanisms from star-formation processes in galaxies. The ongoing integral field spectroscopy of nearby star-forming galaxies reveals many expanding bubbles and superbubbles identified by the local increase in gas velocity dispersion. The limited angular resolution often prevents bona fide measures of the expansion velocities in galaxies outside the Local Group, even despite sufficient spectroscopic resolution. We present a method that makes it possible to measure the expansion velocity of bubbles surrounding massive stars and clusters based on the data about local variations in gas velocity dispersion. We adapt the method for the Fabry–Perot interferometers used with the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences, as well as for any integral field spectrograph with a Gaussian line spread function. We apply the method described to analyze the kinematics of ionized superbubbles gas and the only known supernova remnant in the IC 1613 galaxy. The estimate of the kinematic age of the supernova remnant (on the order of 3100 years) agrees well with the previously obtained independent estimate based on X-ray data. [ABSTRACT FROM AUTHOR]

Massive stellar clusters inject significant mass and energy into their surroundings driving superbubbles, 100–1000 pc diameter shells of swept-up interstellar material that contain a hot ( 10 6 K), shock-heated gas. Analytically, the evolution of these objects is usually described as an expanding, pressure-driven bubble. However, in the 90s discrepancies between predictions of the pressure-driven model and X-ray observations of superbubbles were observed. Resolutions to these discrepancies were proposed, mainly through modifications to the model, though it wasn't until the advent of Chandra, XMM-Newton, and Suzaku that these could be observationally tested, with advances in numerical modelling also providing valuable insight. Here I review X-ray observations of superbubbles and their massive stellar clusters and describe how their thermal and non-thermal X-ray emission have helped the understanding of the physical properties and evolution of these objects. Future prospects with the next generation of X-ray observatories are also discussed. [ABSTRACT FROM AUTHOR]

We present multi-wavelength analysis for four bipolar bubbles (G045.386-0.726, G049.998-0.125, G050.489+0.993, and G051.610-0.357) to probe the structure and dynamics of their surrounding gas. The CO $J=1\mbox{-}0$ , CO $J=1\mbox{-}0$ and CO $J=1\mbox{-}0$ observations are made with the Purple Mountain Observation (PMO) 13.7 m radio telescope. For the four bipolar bubbles, the bright 8.0 μm emission shows the bipolar structure. Each bipolar bubble is associated with an H ii region. From CO observations we find that G045.386-0.726 is composed of two bubbles with different distances, not a bipolar bubble. Each of G049.998-0.125 and G051.610-0.357 is associated with a filament. The filaments in CO emission divide G049.998-0.125 and G051.610-0.357 into two lobes. We suggest that the exciting stars of both G049.998-0.125 and G051.610-0.357 form in a sheet-like structure clouds. Furthermore, G050.489+0.993 is associated with a clump, which shows a triangle-like shape with a steep integrated intensity gradient towards the two lobes of G050.489+0.993. We suggest that the two lobes of G050.489+0.993 have simultaneously expanded into the clump. [ABSTRACT FROM AUTHOR]

A disconcerting mismatch of thermal pressures for two media in contact with each other, (1) the warm, Circum-Heliospheric Interstellar Medium (CHISM) and (2) the very hot material within a much larger region called the Local Bubble (LB), has troubled astronomers for over two decades. A possible resolution of this problem, at least in part, now seems possible. We now understand that earlier estimates for the average electron density in the very hot LB plasma were inflated by an unrecognized foreground contamination to the low energy diffuse X-ray background measurements. This foreground illumination arises from photons emitted by charge exchange reactions between solar wind ions and neutral atoms from the interstellar medium that enter into the heliosphere. However, with the resolution of this problem comes a new one. The high ionization fraction of helium in the CHISM, relative to that of hydrogen, could be understood in terms of the effects from a strong flux of EUV and X-ray radiation coming from both the Local Bubble and a conductive interface around the CHISM. A revision of this interpretation may now be in order, now that the photoionization rate from radiation emitted by hot gas the Local Bubble is lower than previously assumed. [ABSTRACT FROM AUTHOR]

The differences between the composition of Galactic cosmic rays and that of the interstellar medium are manifold, and they contain a wealth of information about the varying processes that created them. These differences reveal much about the initial mixing of freshly synthesized matter, the chemistry and differentiation of the interstellar medium, and the mechanisms and environment of ion injection and acceleration. Here we briefly explore these processes and show how they combine to create the peculiar, but potentially universal, composition of the cosmic rays and how measurements of the composition can provide a unique measure of the mixing ratio of the fresh supernova ejecta and the old interstellar medium in this initial phase of interstellar mixing. In particular, we show that the major abundance differences between the cosmic rays and the average interstellar medium can all result from cosmic ray ion injection by sputtering and scattering from fast refractory oxide grains in a mix of fresh supernova ejecta and old interstellar material. Since the bulk of the Galactic supernovae occur in the cores of superbubbles, the bulk of the cosmic rays are accelerated there out of such a mix. We show that the major abundance differences all imply a mixing ratio of the total masses of fresh supernova ejecta and old interstellar material in such cores is roughly 1 to 4. That means that the metallicity of ∼3 times solar, since the ejecta has a metallicity of ∼8 times that of the present interstellar medium. [ABSTRACT FROM AUTHOR]

Mechanical feedback from massive stars, primarily from supernovae, can dominate ISM structuring and phase balance, thereby profoundly affecting galactic evolutionary processes. Our understanding of mechanical feedback is based on the adiabatic, wind-driven bubble model, applied on size scales ranging over three decades. Tests of the model, and our consequent understanding of feedback, are reviewed. While the model is broadly successful, critical unknowns still prevent a comprehensive understanding of the consequences of feedback. [ABSTRACT FROM AUTHOR]

The gravitational instability of expanding shells evolving in a homogeneous and static medium is discussed. In the low density environment (n = 1 cm-3), the fragmentation starts in shells with diameters of a few 100 pc and fragment masses are in the range of 5 × 10³ - 106M[This symbol cannot be presented in ASCII format]. In the high density environment (n = 105 - 107 cm-3), shells fragment at diameters of ∼ 1 pc producing clumps of stellar masses. The mass spectrum in both environments is approximated by a power law dN/dm ∼ m-2.3. This is close to the slope of the stellar IMF. To reproduce the observed mass spectrum of clouds (the spectral index close to ∼ −2.0) we have to assume, that the cloud formation time is independent of the cloud size, similarly to the Jeans unstable medium. [ABSTRACT FROM AUTHOR]

The gravitational instability of expanding shells triggering the formation of clouds and stars is analyzed. Disks with different scale-heights, ambient and shell velocity dispersions, mid-plane densities, rotation rates and shear rates are explored with three dimensional numerical simulations in the thin shell approximation. Three conditions for the shell collapse are specified: the first is that it happens before a significant blow-out, the second requires that the shell collapses before it is distorted by Coriolis forces and shear, and the third requires that the internal pressure in the accumulated gas is small and the fragmentation is achieved within the expansion time. The gas-rich and slowly rotating galaxies are the best sites of the triggered star formation, concluding that its importance has been much larger at the times of galaxy formation compared to the present epoch. [ABSTRACT FROM AUTHOR]