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Register a new userAstro2020: The Cycling of Matter from the Interstellar Medium to Stars and back
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Understanding the matter cycle in the interstellar medium of galaxies from the assembly of clouds to star formation and stellar feedback remains an important and exciting field in comtemporary astrophysics. Many open questions regarding cloud and structure formation, the role of turbulence, and the relative importance of the various feedback processes can only be addressed with observations of spectrally resolved lines. We here stress the importance of two specific sets of lines: the finestructure lines of atomic carbon as a tracer of the dark molecular gas and mid-J CO lines as tracers of the warm, active molecular gas in regions of turbulence dissipation and feedback. The observations must cover a wide range of environments (i.e., physical conditions), which will be achieved by large scale surveys of Galactic molecular clouds, the Galactic Center, the Magellanic clouds, and nearby galaxies. To date, such surveys are completely missing and thus constitute an important science opportunity for the next decade and beyond. For the successful interpretation of the observations, it will be essential to combine them with results from (chemical) modelling and simulations of the interstellar medium.
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Magnetism is one of the most important forces on the interstellar medium (ISM), anisotropically regulating the structure and star formation that drive galactic evolution. Recent high dynamic range observations of diffuse gas and molecular clouds have revealed new links between interstellar structures and the ambient magnetic field. ISM morphology encodes rich physical information, but deciphering it requires high-resolution measurements of the magnetic field: linear polarization of starlight and dust emission, and Zeeman splitting. These measure different components of the magnetic field, and crucially, Zeeman splitting is the only way to directly measure the field strength in the ISM. We advocate a statistically meaningful survey of magnetic field strengths using the 21-cm line in absorption, as well as an observational test of the link between structure formation and field strength using the 21-cm line in emission. Finally, we report on the serendipitous discovery of linear polarization of the 21-cm line, which demands both theoretical and observational follow-up.
The interstellar medium (ISM) is a very complex medium which contains the matter needed to form stars and planets. The ISM is in permanent interaction with radiation, turbulence, magnetic and gravitational fields, and accelerated particles. Everything that happens in this medium has consequences on the dynamics and evolution of the Galaxy, resulting the link that relates the stellar scale with the galactic one. Thus, the study of the ISM is crucial to advance in the knowledge of stellar and galactic astrophysics. In this article I present a summary of what we know about the physics and chemistry of this medium, giving an special emphasis on star formation, and how the processes related to the stars birth and evolution interrelate with the environment that surrounds them.
I review (1) Physics of Star Formation & Open Questions; (2) Structure & Dynamics of Star-Forming Clouds & Young Clusters; (3) Star Formation Rates: Observations & Theoretical Implications.
Employing the the stellar evolution code (Modules for Experiments in Stellar Astrophysics), we calculate yields of heavy elements from massive stars via stellar wind and core-collapse supernovae (CCSN) ejecta to interstellar medium (ISM). In our models, the initial masses ($M_{rm ini}$) of massive stars are taken from 13 to 80 $M_odot$, their initial rotational velocities (V) are 0, 300 and 500 km s$^{-1}$, and their metallicities are [Fe/H] = -3, -2, -1, and 0. The yields of heavy elements coming from stellar winds are mainly affected by the stellar rotation which changes the chemical abundances of stellar surfaces via chemically homogeneous evolution, and enhances mass-loss rate. We estimate that the stellar wind can produce heavy element yields of about $10^{-2}$ (for low metallicity models) to several $M_odot$ (for low metallicity and rapid rotation models) mass. The yields of heavy element produced by CCSN ejecta also depend on the remnant mass of massive mass which is mainly determined by the mass of CO-core. Our models calculate that the yields of heavy elements produced by CCSN ejecta can get up to several $M_odot$. Compared with stellar wind, CCSN ejecta has a greater contribution to the heavy elements in ISM. We also compare the $^{56}$Ni yields by calculated in this work with observational estimate. Our models only explain the $^{56}$Ni masses produced by faint SNe or normal SNe with progenitor mass lower than about 25 $M_odot$, and greatly underestimate the $^{56}$Ni masses produced by stars with masses higher than about 30 $M_odot$.
We developed a new population synthesis code for groups of massive stars, where we model the emission of different forms of energy and matter from the stars of the association. In particular, the ejection of the two radioactive isotopes 26Al and 60Fe is followed, as well as the emission of hydrogen ionizing photons, and the kinetic energy of the stellar winds and supernova explosions. We investigate various alternative astrophysical inputs and the resulting output sensitivities, especially effects due to the inclusion of rotation in stellar models. As the aim of the code is the application to relatively small populations of massive stars, special care is taken to address their statistical properties. Our code incorporates both analytical statistical methods applicable to small populations, as well as extensive Monte Carlo simulations. We find that the inclusion of rotation in the stellar models has a large impact on the interactions between OB associations and their surrounding interstellar medium. The emission of 26Al in the stellar winds is strongly enhanced, compared to non-rotating models with the same mass-loss prescription. This compensates the recent reductions in the estimates of mass-loss rates of massive stars due to the effects of clumping. Despite the lower mass-loss rates, the power of the winds is actually enhanced for rotating stellar models. The supernova power (kinetic energy of their ejecta) is decreased due to longer lifetimes of rotating stars, and therefore the wind power dominates over supernova power for the first 6 Myr after a burst of star-formation. For populations typical of nearby star-forming regions, the statistical uncertainties are large and clearly non-Gaussian.
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