The Superbubble Power Problem: Overview and Recent Developments. S. Oey

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1 The Superbubble Power Problem: Overview and Recent Developments S. Oey It has been known for decades that superbubbles generated by massive star winds and supernovae are smaller than expected based on presumed adiabatic growth due to the input mechanical power from the parent massive star cluster. Many possible solutions have been proposed over the years, suggesting unaccounted-for effects relating to the driving power, ambient environment, and energy losses. I will review the status of this problem, including recent focus on catastrophically suppressed feedback in the most massive, compact clusters.

2 Environmental effects on growing superbubbles Y. Shchekinov Dynamical structures growing under merging of multiple supernova (SN) remnants, their morphology and observational appearance are sensitive to the large scale density distribution of ambient gas. While such merging remnants in gaseous disks of dwarf galaxies (like Holmberg II) form extended superbubbles (supergiant HI shells), in thinner disks of spirals they tend to superbubbles outflowing in the vertical direction (galactic winds like in M82). The two regimes are determined by the interrelation between the SN rate, gas density and its scale height. Their contributions to chemical enrichment of circumgalactic gas are briefly discussed.

3 Hydrodynamic simulations of superbubbles M. Krause The last decades have seen impressive improvements in superbubble simulations.superbubbles have now been simulated, e.g., in 3D, with magnetic fields and in structured environments. The higher resolution available now allows to resolve important hydrodynamic instabilities and to model the evolutionary phases of individual massive stars in a superbubble with high accuracy. These developments have allowed to better understand for example the power problem, the X-ray dichotomy, high energy tracers like 26Al and cosmic ray acceleration in superbubbles, and the conditions for galactic outflows. I will review the simulation work and implications for observations.

4 The interstellar bubbles and the impact of stellar feedback on star formation J. Jose Feedback from massive stars has far-reaching effects on a galaxys interstellar medium and is thought to play a crucial role in the life cycle of molecular material in the Galaxy and the regulation of star formation on global scales. Ionizing radiation and stellar winds from massive stars and clusters carve out lowdensity bubbles and shells and these bubbles are thus ideal laboratories for studying the effects of massive stellar feedback on the surrounding material. An overdensity of massive cold clumps and young stellar objects has been observed at the edges of the expanding bubbles but the mechanisms that give rise to this phenomenon are not clearly identified. We present our recent observational analysis on a few selected Galactic bubbles and the ongoing star formation activities at their edges. The main goals are to detect the young stellar objects, derive their properties and their evolutionary stages in these regions in order to understand the feedback mechanisms and its possible outcome on the subsequent star formation properties, such as, IMF, star formation efficiency and star formation rate.

5 How superbubble powered entropy-driven outflows regulate galaxy formation B. Keller Galaxies like our own, with halo masses M, live in an interesting part of parameter space. Not only are they the turnover in the galaxy mass Schecter function, they also have the highest stellar mass (and baryon) fraction, very low bulgeto-disk ratios, and dominate the star formation of the epoch they live in. In this talk I will present the results of a sample of 18 cosmological M* galaxies, simulated using the state-ofthe-art superbubble method for handling feedback from Type II Supernovae. I will show that the key to obtaining a realistic stellar mass to halo mass relation (SMHMR) is preventing the runaway growth of a massive bulge by driving outflows with large mass-loadings. When, SN feedback alone can no longer effectively drive outflows from the galaxy, and star formation becomes unregulated. In addition, I will show how the buoyancy of outflowing material from feedback-regulated galaxies governs how it circulates through the CGM, resulting in entropy-driven winds and fountains.

6 Cosmic rays from young star clusters S. Gupta High energy observations show the presence of cosmic rays (CR) in OB associations, and it is also expected since massive stars are usually born in such associations. We have studied various aspects of CR acceleration in these star clusters using an analytical method and 1-D/3-D two-fluid CR hydrodynamic simulations. We investigate CR injection scenarios, the dynamical impact of CRs and their imprints on luminosities in different wavebands. We find that the thermal profile of a bubble can be significantly affected by CRs when (i) the Mach number of the shock exceeds M th 12 and (ii) the dynamical time is longer than the CR acceleration time scale τ acc κ cr /v 2 (κ cr is the CR diffusion coefficient and v is the upstream velocity). We estimate the gamma-ray, X-ray and radio luminosities, and show how multi-wavelength observation can constrain the CR injection parameters. Our analysis indicates that the reverse shock (wind-termination shock) is the main CR acceleration site in compact star clusters.

7 Infrared dust bubble CS51 and its interaction with the surrounding interstellar medium S. R. Das A multiwavelength investigation of the southern infrared dust bubble CS51 is presented in this work. We probe the associated ionized, cold dust, molecular and stellar components. Radio continuum emission mapped at 610 and 1300 MHz, using the Giant Metrewave Radio Telescope, India, reveals the presence of three compact emission components (A, B, and C) apart from large-scale diffuse emission within the bubble interior. Radio spectral index map shows the co-existence of thermal and non-thermal emission components. Modified blackbody fits to the thermal dust emission using Herschel Photodetector Array Camera and Spectrometer and Spectral and Photometric Imaging Receiver data is performed to generate dust temperature and column density maps. We identify five dust clumps associated with CS51 with masses and radius in the range M and pc, respectively. We further construct the column density probability distribution functions of the surrounding cold dust which display t he impact of ionization feedback from high-mass stars. The estimated dynamical and fragmentation time-scales indicate the possibility of collect and collapse mechanism in play at the bubble border. Molecular line emission from the Millimeter Astronomy Legacy Team 90 GHz survey is used to understand the nature of two clumps which show signatures of expansion of CS51.