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The cosmic evolution of the chemical elements from the Big Bang to the present time is driven by nuclear fusion reactions inside stars and stellar explosions. A cycle of matter recurrently re-processes metal-enriched stellar ejecta into the next generation of stars. The study of cosmic nucleosynthesis and of this matter cycle requires the understanding of the physics of nuclear reactions, of the conditions at which the nuclear reactions are activated inside the stars and stellar explosions, of the stellar ejection mechanisms through winds and explosions, and of the transport of the ejecta towards the next cycle, from hot plasma to cold, star-forming gas. Due to the long timescales of stellar evolution, and because of the infrequent occurrence of stellar explosions, observational studies are challenging. Due to their radioactive lifetime of million years, the 26Al and 60Fe isotopes are suitable to characterise simultaneously the processes of nuclear fusion reactions and of interstellar transport. We describe and discuss the nuclear reactions involved in the production and destruction of 26Al and 60Fe, the key characteristics of the stellar sites of their nucleosynthesis and their interstellar journey after ejection from the nucleosynthesis sites. We connect the theoretical astrophysical aspects to the variety of astronomical messengers, from stardust and cosmic-ray composition measurements, through observation of gamma rays produced by radioactivity, to material deposited in deep-sea ocean crusts and to the inferred composition of the first solids that have formed in the Solar System. We show that considering measurements of the isotopic ratio of 26Al to 60Fe eliminate some of the unknowns when interpreting astronomical results, and discuss the lessons learned from these two isotopes on cosmic chemical evolution., 51 pages, 44 figures; review from an ISSI workshop series; accepted for publication in PASA

Star clusters are fundamental units of stellar feedback and unique tracers of their host galactic properties. In this review, we will first focus on their constituents, i.e. detailed insight into their stellar populations and their surrounding ionised, warm, neutral, and molecular gas. We, then, move beyond the Local Group to review star cluster populations at various evolutionary stages, and in diverse galactic environmental conditions accessible in the local Universe. At high redshift, where conditions for cluster formation and evolution are more extreme, we are only able to observe the integrated light of a handful of objects that we believe will become globular clusters. We therefore discuss how numerical and analytical methods, informed by the observed properties of cluster populations in the local Universe, are used to develop sophisticated simulations potentially capable of disentangling the genetic map of galaxy formation and assembly that is carried by globular cluster populations., Open access funding provided by Stockholm University. We thank the anonymous referee for a constructive and careful revision of this work. We thank the staff at ISSI for their generous hospitality, and the editors to invite us to contribute to this topic collection. We are grateful to Hui Li and Joel Pfeffer for sharing their data and Nate Bastian for providing comments on the manuscript. A.A. thanks Matteo Messa, Katie Hollyhead and the LEGUS and HiPEEC teams for support with the analyses showed in this review. A.A. acknowledges the support of the Swedish Research Council, Vetenskapsrådet, and the Swedish National Space Agency (SNSA). P.Z. acknowledges support by the Forschungsstipendium (grant number ZE 1159/1-1) of the German Research Foundation (DFG). J.M.D.K. and M.C. gratefully acknowledge funding from the German Research Foundation (DFG) in the form of an Emmy Noether Research Group (grant number KR4801/1-1) and a DFG Sachbeihilfe Grant (grant number KR4801/2-1). J.M.D.K. gratefully acknowledges funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme via the ERC Starting Grant MUSTANG (grant agreement number 714907), and from Sonderforschungsbereich SFB 881 “The Milky Way System” (subproject B2) of the DFG. C.C.acknowledges funding from the Swiss National Foundation (SNF grants 200021_169125 and 200020_192039).

The 511 keV line from positron annihilation in the Galaxy was the first $\gamma$-ray line detected to originate from outside our solar system. Going into the fifth decade since the discovery, the source of positrons is still unconfirmed and remains one of the enduring mysteries in $\gamma$-ray astronomy. With a large flux of $\sim$10$^{-3}$ $\gamma$/cm$^{2}$/s, after 15 years in operation INTEGRAL/SPI has detected the 511 keV line at $>50\sigma$ and has performed high-resolution spectral studies which conclude that Galactic positrons predominantly annihilate at low energies in warm phases of the interstellar medium. The results from imaging are less certain, but show a spatial distribution with a strong concentration in the center of the Galaxy. The observed emission from the Galactic disk has low surface brightness and the scale height is poorly constrained, therefore, the shear number of annihilating positrons in our Galaxy is still not well know. Positrons produced in $\beta^+$-decay of nucleosynthesis products, such as $^{26}$Al, can account for some of the annihilation emission in the disk, but the observed spatial distribution, in particular the excess in the Galactic bulge, remains difficult to explain. Additionally, one of the largest uncertainties in these studies is the unknown distance that positrons propagate before annihilation. In this paper, we will summarize the current knowledge base of Galactic positrons, and discuss how next-generation instruments could finally provide the answers., Comment: 10 pages including 3 figures. Science White paper submitted to Astro2020

We exploited observational constraints on stars, gas and nucleosynthesis ashes for the closest region of recent massive-star formation, Scorpius-Centaurus OB2, and combined them with 3D hydrodynamical simulations, in order to address physics and history for the case of the Scorpius-Centaurus superbubble. We used published cold gas observations through PLANCK survey data processing, HERSCHEL and APEX, continuum and molecular line observations. We analysed the Galactic All Sky Survey (GASS) to investigate shell structures in atomic hydrogen, and used HIPPARCOS and Gaia data in combination with interstellar absorption against stars to obtain new constraints for the distance to the Hi features. Hot gas is traced in soft X-rays via the ROSAT all sky survey. Nucleosynthesis ejecta from massive stars were traced with new INTEGRAL spectrometer observations via 26Al radioactivity. We also performed 3D hydrodynamical simulations for the Sco-Cen superbubble. To investigate the impact of massive star feedback on extended clouds, we simulate the interaction of a turbulent cloud with the hot, pressurised gas in a superbubble. The hot gas fills the tenuous regions of the cloud and compresses the denser parts. Stars formed in these dense clumps would have distinct spatial and kinematic distributions. The combined results from observations and simulations are consistent with a scenario where dense gas was initially distributed in a band elongated in the direction now occupied by the OB association. Superbubbles powered by massive stars would then repeatedly break out of the elongated parent cloud, surround and squash the denser parts of the gas sheet and thus induce more star formation. The expected spatial and kinematic distribution of stars is consistent with observations of Sco-Cen. The scenario might apply to many similar regions in the Galaxy and also to AGN-related superbubbles., 14 pages, 11 figures, accepted by Astronomy & Astrophysics

Early on, extragalactic radio sources have pointed to a cosmologically evolving Universe. They were also an important piece of evidence for the existence of supermassive black holes, now thought to be a key component of galaxies. The observation that the power of radio sources increases with redshift, whereas the cosmological assembly of mass proceeds vice versa means that radio sources have their strongest impact in the early Universe. Our simulations suggest that radio sources heat hot halo gas, boost star formation in disc galaxies and other cold gas in the vicinity, possibly filaments, by a surround and squash mechanism. They might cause gaseous outflows in connection with stellar feedback. This might be an important mode of star formation for forming massive galaxies. Analysis of the jet-environment interaction may provide insights into black-hole physics and jet formation, e.g., rotational energy extraction (Blandford-Znajek) or how frequent black-hole binaries or multiple systems are. The former relates to fundamental questions about the nature of black holes. The latter is expected from hierarchical cosmology. Extragalactic radio sources thus continue to corroborate the cosmological picture and lead the way towards new, exciting discoveries., Invited review given at the international conference "The Physical Universe" in Nagpur, India, 26 Feb - 1 March 2018. Minor style adaptation and a clarification in Sect. 4.2 compared to the version printed in the conference book

Type-Ia supernovae result from binary systems that include a carbon-oxygen white dwarf, and these thermonuclear explosions typically produce 0.5 M☉ of radioactive (56)Ni. The (56)Ni is commonly believed to be buried deeply in the expanding supernova cloud. Surprisingly, in SN2014J we detected the lines at 158 and 812 keV from (56)Ni decay (τ~8.8 days) earlier than the expected several-week time scale, only ~20 days after the explosion, and with flux levels corresponding to roughly 10% of the total expected amount of (56)Ni. Some mechanism must break the spherical symmetry of the supernova, and at the same time create a major amount of (56)Ni at the outskirts. A plausible explanation is that a belt of helium from the companion star is accreted by the white dwarf, where this material explodes and then triggers the supernova event., 「目に見えない光」でIa型超新星の爆発機構を探る-予想外に早かったガンマ線放出をとらえた-.京都大学プレスリリース. 2014-08-01.

Type-Ia supernovae result from binary systems that include a carbon-oxygen white dwarf, and these thermonuclear explosions typically produce 0.5 M_solar of radioactive 56Ni. The 56Ni is commonly believed to be buried deeply in the expanding supernova cloud. Surprisingly, in SN2014J we detected the lines at 158 and 812 keV from 56Ni decay (��~8.8 days) earlier than the expected several-week time scale, only ~20 days after the explosion, and with flux levels corresponding to roughly 10% of the total expected amount of 56Ni. Some mechanism must break the spherical symmetry of the supernova, and at the same time create a major amount of 56Ni at the outskirts. A plausible explanation is that a belt of helium from the companion star is accreted by the white dwarf, where this material explodes and then triggers the supernova event., 7 pages, 3 figures; submitted 10 Apr 2014; accepted 21 Jul 2014 (www.sciencemag.org)

Feedback from active galactic nuclei (AGN) has become a major component in simulations of galaxy evolution, in particular for massive galaxies. AGN jets have been shown to provide a large amount of energy and are capable of quenching cooling flows. Their impact on the host galaxy, however, is still not understood. Subgrid models of AGN activity in a galaxy evolution context so far have been mostly focused on the quenching of star formation. To shed more light on the actual physics of the "radio mode" part of AGN activity, we have performed simulations of the interaction of a powerful AGN jet with the massive gaseous disc (10^11 solar masses) of a high-redshift galaxy. We spatially resolve both the jet and the clumpy, multi-phase interstellar medium (ISM) and include an explicit star formation model in the simulation. Following the system over more than 10^7 years, we find that the jet activity excavates the central region, but overall causes a significant change to the shape of the density probability distribution function and hence the star formation rate due to the formation of a blast wave with strong compression and cooling in the ISM. This results in a ring- or disc-shaped population of young stars. At later times, the increase in star formation rate also occurs in the disc regions further out since the jet cocoon pressurizes the ISM. The total mass of the additionally formed stars may be up to 10^10 solar masses for one duty cycle. We discuss the details of this jet-induced star formation (positive feedback) and its potential consequences for galaxy evolution and observable signatures., Comment: 14 pages, 10 figures. Accepted for publication in MNRAS. Added more details and clarifications after referee report. For associated movies, see http://www.mpe.mpg.de/~vgaibler/jet-disk-sf/

Hydrodynamic stability has been a longstanding issue for the cloud model of the broad line region in active galactic nuclei. We argue that the clouds may be gravitationally bound to the supermassive black hole. If true, stabilisation by thermal pressure alone becomes even more difficult. We further argue that if magnetic fields should be present in such clouds at a level that could affect the stability properties, they need to be strong enough to compete with the radiation pressure on the cloud. This would imply magnetic field values of a few Gauss for a sample of Active Galactic Nuclei we draw from the literature. We then investigate the effect of several magnetic configurations on cloud stability in axi-symmetric magnetohydrodynamic simulations. For a purely azimuthal magnetic field which provides the dominant pressure support, the cloud first gets compressed by the opposing radiative and gravitational forces. The pressure inside the cloud then increases, and it expands vertically. Kelvin-Helmholtz and column density instability lead to a filamentary fragmentation of the cloud. This radiative dispersion continues until the cloud is shredded down to the resolution level. For a helical magnetic field configuration, a much more stable cloud core survives with a stationary density histogram which takes the form of a power law. Our simulated clouds develop sub-Alfvenic internal motions on the level of a few hundred km/s., 16 pages, 11 figures, accepted by MNRAS, Figure 6 updated due to inconsistent linestyles, corrected mistake in Alfven speed formula, some very minor language corrections. The definitive version is available at www.blackwell- synergy.com

We study the evolution of isolated and merging interstellar bubbles of three stars (25, 32 and 60 M\odot) in a homogeneous background medium with a density of 10 mp /ccm via 3D-hydrodynamic simulations with standard ISM thermodynamics (optically thin radiative cooling and photo-electric heating) and time dependent energy and mass input according to stellar evolutionary tracks. We vary the position of the three stars relative to each other to compare the energy response for cases of isolated, merging and initially cospatial bubbles. Due to mainly the Vishniac instability, our simulated bubbles develop thick shells and filamentary internal structures in column density. The shell widths reach tens of per cent of the outer bubble radius, which compares favourably to observations. More energy is retained in the ISM for more closely packed groups, by up to a factor of three and typically a factor of two for intermediate times after the first supernova. Once the superbubble is established, different positions of the contained stars make only a minor difference to the energy tracks. For our case of three massive stars, the energy deposition varies only very little for distances up to about 30 pc between the stars. Energy injected by supernovae is entirely dissipated in a superbubble on a timescale of about 1 Myr, which increases slightly with the superbubble size at the time of the explosion. The Vishniac instability may be responsible for the broadening of the shells of interstellar bubbles. Massive star winds are significant energetically due to their - in the long run - more efficient, steady energy injection and because they evacuate the space around the massive stars. For larger scale simulations, the feedback effect of close groups of stars or clusters may be subsumed into one effective energy input with insignificant loss of energy accuracy., 14 pages, 15 figures, accepted by A&A, shortened, different code test

We investigate the evolution of dusty gas clouds falling into the centre of an active Seyfert nucleus. Two-dimensional high-resolution radiation hydrodynamics simulations are performed to study the fate of single clouds and the interaction between two clouds approaching the Active Galactic Nucleus. We find three distinct phases of the evolution of the cloud: (i) formation of a lenticular shape with dense inner rim caused by the interaction of gravity and radiation pressure (the lense phase), (ii) formation of a clumpy sickle-shaped structure as the result of a converging flow (the clumpy sickle phase) and (iii) a filamentary phase caused by a rapidly varying optical depth along the sickle. Depending on the column density of the cloud, it will either be pushed outwards or its central (highest column density) parts move inwards, while there is always some material pushed outwards by radiation pressure effects. The general dynamical evolution of the cloud can approximately be described by a simple analytical model., Comment: 13 pages, 18 figures, accepted by MNRAS

Observational and theoretical studies of extragalactic radio sources have suggested that an inhomogeneous environment may be responsible for observed arm length asymmetries of jets and the properties of extended emission line regions in high redshift radio galaxies. We perform 3D hydrodynamic simulations of the interaction of a powerful extragalactic bipolar jet with a disc-shaped clumpy interstellar medium of log-normal density distribution and analyze the asymmetry. Furthermore, we compute the relation between jet asymmetry and the ISM properties by means of Monte Carlo simulations based on a 1D propagation model for the jet through the dense medium. We find that the properties of the ISM can be related to a probability distribution of jet arm length asymmetries: Disc density and height are found to have the largest effect on the asymmetry for realistic parameter ranges, while the Fourier energy spectrum of the ISM and turbulent Mach number only have a smaller effect. The hydrodynamic simulations show that asymmetries generally may be even larger than expected from the 1D model due to the complex interaction of the jet and its bow shock with gaseous clumps, which goes much beyond simple energy disposal. From our results, observed asymmetries of medium-sized local radio galaxies may be explained by gas masses of 10^9 to 10^10 solar masses in massive elliptical galaxies. Furthermore, the simulations provide a theoretical basis for the observed correlation that emission line nebulae are generally found to be brighter on the side of the shorter lobe in high redshift radio galaxies (McCarthy et al. 1991). This interaction of jets with the cold gas phase suggests that star formation in evolving high redshift galaxies may be affected considerably by jet activity., 8 pages, 9 figures. Submitted to MNRAS. For associated movies, see http://www.mpe.mpg.de/~vgaibler/jet-disk/

We investigate the global dynamic stability of spherical clouds in the Broad Line Region (BLR) of Active Galactic Nuclei (AGN), exposed to radial radiation pressure, gravity of the central black hole (BH), and centrifugal forces assuming the clouds adapt their size according to the local pressure. We consider both, isotropic and anisotropic light sources. In both cases, stable orbits exist also for very sub-Keplerian rotation for which the radiation pressure contributes substantially to the force budget. We demonstrate that highly eccentric, very sub-Keplerian stable orbits may be found. This gives further support for the model of Marconi et al. 2008, who pointed out that black hole masses might be significantly underestimated if radiation pressure is neglected. That model improved the agreement between black hole masses derived in certain active galaxies based on BLR dynamics, and black hole masses derived by other means in other galaxies by inclusion of a luminosity dependent term. For anisotropic illumination, energy is conserved for averages over long time intervals, only, but not for individual orbits. This leads to Rosetta orbits that are systematically less extended in the direction of maximum radiation force. Initially isotropic relatively low column density systems would therefore turn into a disk when an anisotropic AGN is switched on., Comment: 7 pages, 4 fig.s, accepted by MNRAS, some text was missing - corrected

The paper assumes radiation forces proportional to distance between equal temperature clouds. However, we assume there are clouds in any direction. The forces then cancel almost entirely, besides small velocity effects. Therefore, the presented theory is inadequate., 10 pages, 5 figures, accepted by MNRAS, this paper has been withdrawn by the authors due to an essential flaw in the assumptions

At high redshift, extragalactic jets are associated with extended emission line regions. We present global and local hydrodynamic simulations of the interaction of jets with their environment relevant to this phenomenon. We determine the fraction of kinetic energy and momentum of the jet that should appear in the emission line gas. From momentum considerations, we argue that the gas seen in outward motion in many examples must to a large part originate from within the galaxy. The host galaxies should have been massive, gas rich and heavily star forming galaxies. The expelled gas is not expected to return to the galaxy quickly. The observed kinetic energy in the emission line gas constrains the jet powers to be greater than 10^47 erg/s., Comment: 12 pages, 5 figures

Jets are observed to stir up multi-phase turbulence in the inter-stellar medium as well as far beyond the host galaxy. Here we present detailed simulations of this process. We evolve the hydrodynamics equations with optically thin cooling for a 3D Kelvin Helmholtz setup with one initial cold cloud. The cloud is quickly disrupted, but the fragments remain cold and are spread throughout our simulation box. A scale free isotropic Kolmogorov power spectrum is built up first on the large scales, and reaches almost down to the grid scale after the simulation time of ten million years. We find a pronounced peak in the temperature distribution at 14,000K. The luminosity of the gas in this peak is correlated with the energy. We interpret this as a realisation of the shock ionisation scenario. The interplay between shock heating and radiative cooling establishes the equilibrium temperature. This is close to the observed emission in some Narrow Line Regions. We also confirm the shift of the phase equilibrium, i.e. a lower (higher) level of turbulence produces a higher (lower) abundance of cold gas. The effect could plausibly lead to a high level of cold gas condensation in the cocoons of extragalactic jets, explaining the so called Alignment Effect., 4 pages, 3 figures, conference: "The central kpc", Crete, June 2008, Volume 79 of the Memorie della Societa Astronomica Italiana

A comparison is drawn between jet propagation in molecular clouds and jets launched by galaxies in clusters. The biggest difference between the two types of jets is found in the density contrast. While the cocoon plasma in extragalactic jets has now been detected in X-rays, the corresponding cocoon gas for Herbig-Haro flows is barely visible.

We report two simulations that have been carried out at the SX-5 at HLRS (Stuttgart). One simulation is axisymmetric and purely hydrodynamic, but with a resolution of 20 points per beam-radius (ppb). The bipolar jet is injected in the center of a spherically symmetric King profile, initially underdense to its environment by a factor of 10,000. As expected from our previous work, the jet starts with producing a spherical bubble around it, bounded by the bow shock. The bubble slowly elongates, first with roughly elliptical shape, and then forms narrower extensions in beam direction. The final aspect ratio of the bow shock is 1.8. We have transformed the results on a 3D-rectangular grid and integrated the emission properties to compare the results with observed central cluster radio galaxies. In the particular case of Cygnus A, we come to convincing consistency, morphologically, regarding the size of the influenced region by the jet, size, and cylindrical shape of the radio cocoon, and source age. This strongly supports our earlier hypothesis on the nature of the jet in Cygnus A, and the derived constraints on other jet parameters like a power of $8 \times 10^{46}$ erg/s and an age of 27 Myr. But, the simulation also clearly shows the shortcoming of the model: The jet's beam is very unstable, reaching the tip of the bow shock only very seldom. Also, the contact discontinuity between shocked beam plasma and shocked ambient gas is quite disrupted by the action of the Kelvin-Helmholtz-instability. This is not seen in observations, and necessitates the presence of dynamically important magnetic fields or an at least moderately relativistic flow, or both. [abridged], Comment: accepted for publication in the transactions of the HLRS 2003, Springer lecture notes Replacement due to a few minor orthographic mistakes