Dynamical evolution and molecular abundances of interstellar clouds

Prasad, S. S.; Heere, Karen R.; Tarafdar, S. P.

doi:10.1086/170031

Cited by 27 publications

(12 citation statements)

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“…These cores would take as long as 10 Myr to reach equilibrium, which could still occur in the standard model. However, Prasad, Heere, & Tarafdar (1991) demonstrated that the abundances of the different species agreed much better with the results at times of less than 1 Myr from time-dependent models of the chemical evolution of collapsing cores (also see Section III.D.2.d). Bergin & Langer (1997), Bergin et al (1997), Pratap et al (1997), and Aikawa et al (2001) came to similar conclusions from careful comparison of several different cloud cores to extensive chemical model networks.…”

Section: A Formation and Lifetime Of Molecular Cloudsmentioning

confidence: 55%

Control of star formation by supersonic turbulence

2004

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Understanding the formation of stars in galaxies is central to much of modern astrophysics. However, a quantitative prediction of the star formation rate and the initial distribution of stellar masses remains elusive. For several decades it has been thought that the star formation process is primarily controlled by the interplay between gravity and magnetostatic support, modulated by neutral-ion drift (known as ambipolar diffusion in astrophysics). Recently, however, both observational and numerical work has begun to suggest that supersonic turbulent flows rather than static magnetic fields control star formation. To some extent, this represents a return to ideas popular before the importance of magnetic fields to the interstellar gas was fully appreciated. This review gives a historical overview of the successes and problems of both the classical dynamical theory, and the standard theory of magnetostatic support from both observational and theoretical perspectives. The outline of a new theory relying on control by driven supersonic turbulence is then presented. Numerical models demonstrate that although supersonic turbulence can provide global support, it nevertheless produces density enhancements that allow local collapse. Inefficient, isolated star formation is a hallmark of turbulent support, while efficient, clustered star formation occurs in its absence. The consequences of this theory are then explored for both local star formation and galactic scale star formation. It suggests that individual star-forming cores are likely not quasi-static objects, but dynamically collapsing. Accretion onto these objects varies depending on the properties of the surrounding turbulent flow; numerical models agree with observations showing decreasing rates. The initial mass distribution of stars may also be determined by the turbulent flow. Molecular clouds appear to be transient objects forming and dissolving in the larger-scale turbulent flow, or else quickly collapsing into regions of violent star formation. We suggest that global star formation in galaxies is controlled by the same balance between gravity and turbulence as small-scale star formation, although modulated by cooling and differential rotation. The dominant driving mechanism in star-forming regions of galaxies appears to be supernovae, while elsewhere coupling of rotation to the gas through magnetic fields or gravity may be important.

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Section: A Formation and Lifetime Of Molecular Cloudsmentioning

confidence: 55%

Control of star formation by supersonic turbulence

2004

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“…Monteiro (1991) finds a similar enhancement for rotating clumps in PDRs. Gerola and Glassgold (1978), Tarafdar et al (1985), Prasad et al (1991), Heck et al (1992), Lee et al (1996), Nelson andLanger (1997), andShematovich et al (1997) examine the time-dependent evolution of diffuse atomic clouds into molecular clouds and the collapse toward star formation. Lee et al (1996) also study the time-dependent chemistry of an inhomogeneous molecular cloud suddenly exposed to far-ultraviolet radiation.…”

Section: B Time-dependent and Nonstationary Pdrsmentioning

confidence: 99%

Photodissociation regions in the interstellar medium of galaxies

Hollenbach

Tielens²

1999

Rev. Mod. Phys.

737

712

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The interstellar medium of galaxies is the reservoir out of which stars are born and into which stars inject newly created elements as they age. The physical properties of the interstellar medium are governed in part by the radiation emitted by these stars. Far-ultraviolet (6 eVϽh Ͻ13.6 eV) photons from massive stars dominate the heating and influence the chemistry of the neutral atomic gas and much of the molecular gas in galaxies. Predominantly neutral regions of the interstellar medium in which the heating and chemistry are regulated by far ultraviolet photons are termed PhotoDissociation Regions (PDRs). These regions are the origin of most of the non-stellar infrared (IR) and the millimeter and submillimeter CO emission from galaxies. The importance of PDRs has become increasingly apparent with advances in IR and submillimeter astronomy. The IR emission from PDRs includes fine structure lines of C, C ϩ , and O; rovibrational lines of H 2 ; rotational lines of CO; broad mid-IR features of polycyclic aromatic hydrocarbons; and a luminous underlying IR continuum from interstellar dust. The transition of H to H 2 and C ϩ to CO occurs within PDRs. Comparison of observations with theoretical models of PDRs enables one to determine the density and temperature structure, the elemental abundances, the level of ionization, and the radiation field. PDR models have been applied to interstellar clouds near massive stars, planetary nebulae, red giant outflows, photoevaporating planetary disks around newly formed stars, diffuse clouds, the neutral intercloud medium, and molecular clouds in the interstellar radiation field-in summary, much of the interstellar medium in galaxies. Theoretical PDR models explain the observed correlations of the [CII] 158 m with the CO Jϭ1 -0 emission, the CO Jϭ1 -0 luminosity with the interstellar molecular mass, and the [CII] 158 m plus [OI] 63 m luminosity with the IR continuum luminosity. On a more global scale, PDR models predict the existence of two stable neutral phases of the interstellar medium, elucidate the formation and destruction of star-forming molecular clouds, and suggest radiation-induced feedback mechanisms that may regulate star formation rates and the column density of gas through giant molecular clouds. [S0034-6861(99)01001-6] CONTENTS

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“…Such complete chemical-hydrodynamical codes are not yet feasible computationally, so current models make simplifications on either the chemical or the dynamical side. Early dynamical models with limited chemistry include those of Gerola & Glassgold (1978), Tarafdar et al (1985), Umebayashi & Nakano (1990), and Prasad et al (1991). Examples of more recent work are by Nelson & Langer (1997) and Shematovich et al (1997).…”

Section: Gas-phase Modelsmentioning

confidence: 99%

Chemical Evolution of Star-Forming Regions

Dishoeck

Blake

1998

Annu. Rev. Astron. Astrophys.

452

241

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Recent advances in the understanding of the chemical processes that occur during all stages of the formation of stars, from the collapse of molecular clouds to the assemblage of icy planetesimals in protoplanetary accretion disks, are reviewed. Observational studies of the circumstellar material within 100-10,000 AU of the young star with (sub)millimeter single-dish telescopes, millimeter interferometers, and ground-based as well as space-borne infrared observatories have only become possible within the past few years. Results are compared with detailed chemical models that emphasize the coupling of gas-phase and grain-surface chemistry. Molecules that are particularly sensitive to different routes of formation and that may be useful in distinguishing between a variety of environments and histories are outlined. In the cold, low-density prestellar cores, radicals and long unsaturated carbon chains are enhanced. During the cold collapse phase, most species freeze out onto the grains in the high-density inner region. Once young stars ignite, their surroundings are heated through radiation and/or shocks, whereupon new chemical characteristics appear. Evaporation of ices drives a "hot core" chemistry rich in organic molecules, whereas shocks propagating through the dense envelope release both refractory and volatile grain material, resulting in prominent SiO, OH, and H 2 O emission. The role of future instrumentation in further developing these chemical and temporal diagnostics is discussed. 317

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Dynamical evolution and molecular abundances of interstellar clouds

Cited by 27 publications

References 0 publications

Control of star formation by supersonic turbulence

Control of star formation by supersonic turbulence

Photodissociation regions in the interstellar medium of galaxies

Chemical Evolution of Star-Forming Regions

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