The Interstellar Medium White Paper (original) (raw)
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The Evolution of the Interstellar Medium Around Young Stellar Clusters
1999
The interplay between the ISM and the massive stars formed in clusters and, more generally, in recent events of star formation is reviewed via the global effects each has on the other. The pre-existing environment affects the properties of the massive stars, the duration of the star-forming event and could potentially affect the IMF. The collective effect of massive-star winds and supernova explosions creates a structured ISM by forming bubbles, supershells and, in more extreme cases, by inducing large-scale gas outflows. Gas/dust removal may quench star formation in young stellar clusters. Conversely, supernova-driven shocks may trigger star formation in molecular clouds surrounding the stellar clusters. Metal ejection from the massive stars is responsible for the pollution of the ISM and, if the metal-rich gas can escape the galaxy's gravitational potential, of the IGM. The environment where stellar clusters form is populated by a diffuse stellar population which contributes ...
Stellar sources of the interstellar medium
2002
With the exception of the Big Bang, responsible for 1,2 H, 3,4 He, and 7 Li, stars act as sources for the composition of the interstellar medium. Cosmic rays are related to the latter and very probably due to acceleration of the mixed interstellar medium by shock waves from supernova remnants. Thus, the understanding of the abundance evolution in the interstellar medium and especially the enrichment of heavy elements, as a function of space and time, is essential. It reflects the history of star formation and the lifetimes of the diverse contributing stellar objects. Therefore, the understanding of the endpoints of stellar evolution is essential as well. These are mainly planetary nebulae and type II/Ib/Ic supernovae as evolutionary endpoints of single stars, but also events in binary systems can contribute, like e.g. supernovae of type Ia, novae and possibly X-ray bursts and neutron star or neutron star -black hole mergers. Despite many efforts, a full and self-consistent understanding of supernovae (the main contributors to nucleosynthesis in galaxies) is not existing, yet. Their fingerprints, however, seen either in spectra, lightcurves, radioactivities/decay gammarays or in galactic evolution, can help to constrain the composition of their ejecta and related model uncertainties.
Composition and evolution of interstellar clouds
Comets II, 2004
In this chapter we describe how elements have been and are still being formed in the galaxy and how they are transformed into the reservoir of materials present in protostellar environments. We discuss the global cycle of matter from stars, where nucleosynthesis produces heavy elements that are ejected through explosions and winds into the interstellar medium (ISM), through the formation and evolution of interstellar cloud material. In diffuse clouds, low-energy cosmic rays impact silicate grains, amorphizing crystals, and UV photons easily penetrate, sponsoring a simple photochemistry. In dense cold molecular clouds, cosmic rays penetrate, driving a chemistry where neutral-neutral reactions and ion-molecule reactions increase the complexity of molecules in icy grain mantles. In the coldest, densest prestellar cores within molecular clouds, all available heavy elements are depleted onto grains. Dense cores collapse to form protostars and the protostars heat the surrounding infalling matter and release molecules previously frozen in ices into the gas phase, sponsoring a rich gas-phase chemistry. Some material from the cold regions and from hot or warm cores within molecular clouds probably survives to be incorporated into the protoplanetary disks as interstellar matter. For diffuse clouds, for molecular clouds, and for dense hot cores and dense warm cores, the physiochemical processes that occur within the gas and solid state materials are discussed in detail.
Division VI: Interstellar Matter: (Matière Interstellaire)
Transactions of the International Astronomical Union, 2000
Division VI of the International Astronomical Union deals with Interstellar Matter, and incorporates Commission 34. It gathers astronomers studying the diffuse matter in space between the stars, ranging from primordial intergalactic clouds via dust and neutral and ionised gas in galaxies to the densest molecular clouds and the processes by which stars are formed. There are approximately 730 members. The working groups in Planetary Nebulae and Cosmochemistry have served us well in organising periodic seminars in these subject areas. However, the Organising Committee has recognised that other developing areas of the ISM are not properly represented in the current organisation. In January 1997, the Division formed a new ISM working group on Star Forming Regions including cross-divisional representation to monitor progress in their fields and to help develop proposals for future IAU Symposia or Colloquia. In the future, especially in view of the rapid developments in spaceborne X-ray an...
Solar System - Interstellar Medium
Astrochemistry of Cosmic Phenomena, 1992
The growing body of data on solar system objects and interstellar space provides us with new tests of the connection between the two. We emphasize here the role played by the study of comets through the properties of the dust, the chemical composition of volatiles and the elemental abundances. These data inform us on cometary matter formation, and hence on conditions in the protosolar nebula. Under the adopted scenario of formation in a cold environment, with little further processing, cometary abundances are even new constraints to interstellar (gas and solid phase) abundances. Several points specific to the chemical modelling of the collapsing cloud and of the protosolar nebula are listed.
Galactic outflows and evolution of the interstellar medium
Monthly Notices of the Royal Astronomical Society, 2012
We present a model to self-consistently describe the joint evolution of starburst galaxies and the galactic wind resulting from this evolution. This model will eventually be used to provide a subgrid treatment of galactic outflows in cosmological simulations of galaxy formation and the evolution of the intergalactic medium (IGM). We combine the population synthesis code Starburst99 with a semi-analytical model of galactic outflows and a model for the distribution and abundances of chemical elements inside the outflows. Starting with a galaxy mass, formation redshift, and adopting a particular form for the star formation rate, we describe the evolution of the stellar populations in the galaxy, the evolution of the metallicity and chemical composition of the interstellar medium (ISM), the propagation of the galactic wind, and the metal-enrichment of the intergalactic medium. The model takes into account the full energetics of the supernovae and stellar winds and their impact on the propagation of the galactic wind, the depletion of the ISM by the galactic wind and its impact on the subsequent evolution of the galaxy, as well as the evolving distributions and abundances of metals in the galactic wind. In this paper, we study the properties of the model, by varying the mass of the galaxy, the star formation rate, and the efficiency of star formation. Our main results are the following: (1) For a given star formation efficiency f * , a more extended period of active star formation tends to produce a galactic wind that reaches a larger extent. If f * is sufficiently large, the energy deposited by the stars completely expels the ISM. Eventually, the ISM is being replenished by mass loss from supernovae and stellar winds. (2) For galaxies with masses above 10 11 M ⊙ , the material ejected in the IGM always falls back onto the galaxy. Hence lower-mass galaxies are the ones responsible for enriching the IGM. (3) Stellar winds play a minor role in the dynamical evolution of the galactic wind, because their energy input is small compared to supernovae. However, they contribute significantly to the chemical composition of the galactic wind. We conclude that the history of the ISM enrichment plays a determinant role in the chemical composition and extent of the galactic wind, and therefore its ability to enrich the IGM.
Self-regulated star formation and the evolution of the interstellar medium
Astrophysics and Space Science, 1990
Calculations of the evolution of the interstellar medium (ISM) in a one-zone model are presented. The purpose is to study the influences of different processes on the evolution of the ISM and the star-formation rate by applying a detailed description of the stars and the ISM as weI1 as their interactions. Different processes and timescales are taken into account: stellar evolutionary timescales and nneleosynthesis, stellar mass loss and energy release to the ISM by means of both supernovae and stellar winds, and a multi-component ISM with phase transitions by means of condensation, evaporation, and ionization as well as metal-dependent heating and cooling of the different phases. Moreover, we allow for intrinsic heating of the cool star-forming clouds. The results show that in addition to the heating by means of supernovae that represents the global star-formation regulation mechanism young stars act predominantly already locally within the star-forming sites. Open-box models allowing for inflow of all existing gas phases with similar physical states but restricting the outflow to the hot phase only are able to explain successfully the dilution of metallicity and large fluctuations of the star-formation rate, of the volume-filling factors, and of the amounts of different gas phases.
In the Diffuse Interstellar Medium
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2006
Three forms of solely hydrogen-bearing molecules—H 2 , HD and —are observed in diffuse or optically transparent interstellar clouds. Although no comprehensive theory exists for the diffuse interstellar medium or its chemistry, the abundances of these species can generally be accommodated locally within the existing static equilibrium frameworks for heating/cooling, H 2 -formation on large grains, etc. with one modification demanded equally by observations of HD and , i.e. a pervasive low-level source of H and H 2 ionization ca 10 times faster than the usual cosmic ray ionization rate ζ H ≈10 −17 s −1 per free H-atom. We discuss this situation with reference to observation and time-dependent modelling of H 2 and formation. While not wishing to appear ungrateful for the success of what are very simplistic notions of the interstellar medium, we point out several reasons not to feel smug. The equilibrium conditions which foster high H 2 and abundances are very slow to appear and these ...
Astronomy and Astrophysics Review, 1999
Substantial progress in the field of the Local Interstellar Medium has been largely due to recent launches of space missions, mostly in the UV and X-ray domains, but also to ground-based observations, mainly in high resolution spectroscopy. However, a clear gap seems to remain between the wealth of new data and the theoretical understanding. This paper gives an overview of some observational aspects, with no attempt of completeness or doing justice to all the people involved in the field. As progress rarely evolves in straight paths, we can expect that our present picture of the solar system surroundings is not definitive.