共查询到20条相似文献，搜索用时 15 毫秒
1.
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Peter Berczik Gerhard Hensler Christian Theis Rainer Spurzem 《Astrophysics and Space Science》2002,281(1-2):297-300
We present our recently developed 3-dimensional chemodynamical code for galaxy evolution. This code follows the evolution
of different galactic components like stars, dark matter and different components of the interstellar medium (ISM), i.e. a
diffuse gaseous phase and the molecular clouds. Stars and dark matter are treated as collisionless N-body systems. The ISM
is numerically described by a smoothed particle hydrodynamics (SPH) approach for the diffuse gas and a sticky particle scheme
for the molecular clouds. Additionally, the galactic components are coupled by several phase transitions like star formation,
stellar death or condensation and evaporation processes within the ISM. As an example we show the dynamical and chemical evolution
of a star forming dwarf galaxy with a total baryonic mass of 2 ċ 109 M⊙. After a moderate collapse phase the stars and the molecular clouds follow an exponential radial distribution, whereas the
diffuse gas shows a central depression as a result of stellar feedback. The metallicities of the galactic components behave
quite differently with respect to their temporal evolution as well as their radial distribution. Especially, the ISM is at
no stage well mixed.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
3.
We present a 3d code for the dynamical evolution of a multi-phase interstellar medium (ISM) coupled to stars via star formation
(SF) and feedback processes. The multi-phase ISM consists of clouds (sticky particles) and diffuse gas (SPH): exchange of
matter, energy and momentum is achieved by drag (due to ram pressure) and condensation or evaporation processes. The cycle
of matter is completed by SF and feedback by SNe and PNe. A SF scheme based on a variable SF efficiency as proposed by Elmegreen
and Efremov (1997) is presented. For a Milky Way type galaxy we get a SF rate of ∼1 M⊙ yr-1 with an average SF efficiency of ∼5%.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
4.
2D hydrodynamical simulations are performed to examine the evaporation and condensation processes of giant molecular clouds
in the hot phase of the interstellar medium. The evolution of cold and dense clouds (T = 1000 K, n
H = 3 cm-3,M = 6·104 M⊙) is calculated in the subsonic stream of a hot tenuous plasma (T = 5 ·106 K, n
H = 6·10-4cm-3). Our code includes self-gravity, heating and cooling processes and heat conduction by electrons. The thermal conductivity
of a fully ionized hydrogen plasma (κ ∝ T5/2) is applied as well as a saturated heat flux in regions where the mean free path of the electrons is large compared to the
temperature scaleheight. Significant differences occur between simulations with and without heat conduction. In the simulations
without heat conduction, the clouds outermost regions is stired up by Kelvin-Helmholtz (KH) instability after only a few dynamical
times. This prevents an infiltration of a significant amount of hot gas into the cloud before its destruction. In contrast,
models including heat conduction evolve less violently. The boundary of the cloud remains nearly unsusceptible to KH instabilities.
In this scenario it is possible to mix the formerly hot streaming gas very effectively with the cloud material.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
5.
6.
K. Tainaka S. Fukazawa H. Nishimori M. Yokosawa S. Mineshige 《Astrophysics and Space Science》1993,210(1-2):117-120
Population dynamics of multi-phased interstellar medium (ISM) is investigated by using the lattice model in position-fixed reaction. Interactions between three distinct phases of gas, cold clouds, warm gas, and hot gas give rise to cyclic phase changes in ISM. Such local phase changes are propagated in space, and stochastic steady-state spatial pattern is finally achieved. We obtain the following two characteristic patterns:
- When the sweeping rate of a warm gas into a cold component is relatively high, cold clouds associated with warm gas form small-scale clumps and are dispersively distributed, whereas hot gas covers large fraction of space.
- When the sweeping rate is relatively low, in contrast, warm gas and cold clouds are diffusively and equally distributed, while hot gas component is substantially localized.
7.
Javier Ballesteros-Paredes 《Astrophysics and Space Science》2004,289(3-4):243-254
Molecular clouds (MC) are the densest and coldestcomponent of the interstellar gas, and the sites of starformation. They are also turbulent and fractaland theirmasses and sizes span several orders of magnitude. It is also generally believed that they are close to Virial equilibrium (VE).Since this statement has beenquestioned by a number of authors, with important implicationson molecular clouds’ lifetimes, we will review this subjectwithin the context of a turbulent ISM. In this framework, there issignificant numerical evidence that MCs are not in VE, that there is a strong exchange of mass, momentum and energy between clouds and their surrounding medium, andthat it is difficult (if not impossible) to form quasistatic coresinside MCs, suggesting that they must be transient, short-livedphenomena. Thus, their formation and disruption must be primarily dynamical, and probably not due tojust a single mechanism, but rather to the combination of severalprocesses. This picture seems consistent withrecent estimates of ages of stars in the solar neighborhood. 相似文献
8.
A model of supernova feedback in galaxy formation 总被引：3，自引：0，他引：3
G. Efstathiou 《Monthly notices of the Royal Astronomical Society》2000,317(3):697-719
A model of supernova feedback during disc galaxy formation is developed. The model incorporates infall of cooling gas from a halo, and outflow of hot gas from a multiphase interstellar medium (ISM). The star formation rate is determined by balancing the energy dissipated in collisions between cold gas clouds with that supplied by supernovae in a disc marginally unstable to axisymmetric instabilities. Hot gas is created by thermal evaporation of cold gas clouds in supernova remnants, and criteria are derived to estimate the characteristic temperature and density of the hot component and hence the net mass outflow rate. A number of refinements of the model are investigated, including a simple model of a galactic fountain, the response of the cold component to the pressure of the hot gas, pressure-induced star formation and chemical evolution. The main conclusion of this paper is that low rates of star formation can expel a large fraction of the gas from a dwarf galaxy. For example, a galaxy with circular speed 50 km s1 can expel 6080 per cent of its gas over a time-scale of 1 Gyr, with a star formation rate that never exceeds 0.1 M1 . Effective feedback can therefore take place in a quiescent mode and does not require strong bursts of star formation. Even a large galaxy, such as the Milky Way, might have lost as much as 20 per cent of its mass in a supernova-driven wind. The models developed here suggest that dwarf galaxies at high redshifts will have low average star formation rates and may contain extended gaseous discs of largely unprocessed gas. Such extended gaseous discs might explain the numbers, metallicities and metallicity dispersions of damped Lyman systems. 相似文献
9.
Nicole St-Louis 《Astrophysics and Space Science》1998,260(1-2):161-171
In this paper, I present a brief overview of the observational evidence for the interaction between the winds of hot stars
and their surrounding interstellar medium (ISM). As the star evolves, it will impinge on the gas in different ways depending
on the nature of its wind and on the physical state of the interstellar gas. The three main evolutionary phases of massive
stars, the main sequence O phase, the intermediate red supergiant or luminous blue variable phase and finally the Wolf-Rayet
phase are discussed. The study of the ISM in the vicinity of hot stars is shown to be a powerful tool to study the history
of the gas and gain more insight into the evolution of the star.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
10.
The λ21-cm line is an excellent tracer of the neutral interstellar medium (ISM). Atomic hydrogen (HI) is found in a variety of environments, from dense clouds to the diffuse galactic halo, and its filling factor is often high, so structures with sizes over a wide range of scales can be mapped with this line. Galactic HI surveys show small scale structure that is consistent with a spectrum of interstellar turbulence similar to what is measured in the ionized component of the ISM. But our sampling of the spectrum of this turbulence is limited to a few size ranges, based on the sensitivities of existing telescopes for emission and absorption studies. The Square Kilometer Array (SKA) will provide the sensitivity and resolution to give continuous coverage of the turbulence spectrum from hundreds of parsecs to a few tens of Astronomical Units. By showing us the full spectrum of interstellar turbulence in the neutral medium, the physical processes driving hydrodynamic and magneto-hydrodynamic instabilities will be illuminated. Ultimately the turbulence governs the passage of the gas from the warm phases of the medium to the cold phases where gravitational collapse can initiate star formation. The SKA is needed to fill in this missing link in the cycle of star formation and chemical enrichment that drives the evolution of galaxies. In the Milky Way halo, SKA mapping of HI high velocity clouds will trace the structure and motion of both the warm phase gas and the hot medium. The interaction between these two phases of halo gas is a great unsolved problem in Galactic astrophysics. 相似文献
11.
R.M. Hueckstaedt J.H. HunterJr 《Monthly notices of the Royal Astronomical Society》2001,327(4):1097-1102
The evolution of the interstellar medium (ISM) is driven by a variety of phenomena, including turbulence, shearing flows, magnetic fields and the thermal properties of the gas. Among the most important forces at work is self-gravity, which ultimately drives protostellar collapse. As part of an ongoing study of instabilities in the ISM, Hunter, Whitaker & Lovelace have discovered another process driven by self-gravity: the instability of an interface of discontinuous density. Theory predicts that this self-gravity driven interfacial instability persists in the static limit and in the absence of a constant background acceleration. Disturbances to a density interface are found to grow on a time-scale of the order of the free-fall time, even when the perturbation wavelength is much less than the Jeans length. Here we present the first numerical simulations of this instability. The theoretical growth rate is confirmed and the non-linear morphology displayed. The self-gravity interfacial instability is shown to be fundamentally different from the Rayleigh–Taylor instability, although both exhibit similar morphologies under the condition of a high density contrast, such as is commonly found in the ISM. Such instabilities are a possible mechanism by which observed features, such as the pillars of gas seen near the boundaries of interstellar clouds, are formed. 相似文献
12.
Joel N. Bregman 《Astrophysics and Space Science》2004,289(3-4):181-192
The interstellar medium of the Milky Way possesses a remarkable rangeof components, which have individual lifetimes considerably less than aHubble time. Consequently, there has been a major effort inunderstanding the properties of these components, their heating andcooling mechanisms, and the process by which one component istransformed into another. We review several of the issues in an effort tohighlight controversies that are under study presently. One of the centraldebates involves star formation, where there are two general andconflicting theoretical models. Another issue deals with the efforts tounderstand the fractional amounts of gas in the various phases, whichbrings together star formation with global gas dynamical reactions. Thisinteraction is responsible for heating of the gas by supernovae, causingsuperbubbles, and subsequently, either galactic winds or galacticfountains. The relative amounts of material in the hot and cold phasesnot only depends upon the supernova rate, it also depends upon details ofinterstellar models, such as whether thermal conduction is an importantprocess. We review the progress that people have made onself-consistent modeling of the ISM. The constraints on such models comefrom a wide variety of observations of molecular, neutral atomic, warmionized, and X-ray gas. Both observations and theory are represented atthis meeting and we highlight areas in which contributions are likely toresolve the existing controversies. 相似文献
13.
Numerical simulations of two-component (stars + gas) self-gravitating galactic disks show that the interstellar gas can significantly affect the dynamical evolution of the disk even if its mass fraction (relative to the total galaxy mass) is as low as several percent. Aided by efficient energy dissipation, the gas becomes gravitationally unstable onlocal scale and forms massive clumps. Gravitational scattering of stars by these clumps leads to suppression of bar instability usually seen in heavy stellar disks. In this case, gas inflow towards the galactic center is driven by dynamical friction which gas clumps suffer instead of bar forcing. 相似文献
14.
We present three dimensional simulations of the interaction of a light hypersonic jet with an inhomogeneous thermal and turbulently supported disk in an elliptical galaxy. These simulations are applicable to the GPS/CSS phase of some extragalactic radio sources. We identify four generic phases in the evolution of such a jet with the interstellar medium. The first is a “flood and channel” phase, dominated by complex jet interactions with the dense cloudy medium close to the nucleus. This is characterized by high pressure jet gas finding changing weak points in the ISM and flowing through channels that form and reform over time. A spherical, energy driven, bubble phase ensues, wherein the bubble is larger than the disk scale, but the jet remains fully disrupted close to the nucleus, so that the jet flux is thermalised and generates a smooth isotropic energy-driven bubble. In the subsequent, rapid, jet break-out phase the jet breaks free of the last obstructing dense clouds, becomes collimated and pierces the more or less spherical bubble. In the final classical phase, the jet propagates in a momentum-dominated fashion similar to jets in single component hot haloes, leading to the classical jet–cocoon–bow-shock structure. 相似文献
15.
Michael Dahlem 《Astrophysics and Space Science》2004,289(3-4):405-414
Starbursts are the most efficient producers of metals in the Universe at low redshifts. They produce enough energy to driveoutflows of material from their disks.This makes them important objects to study in order to understand the chemical evolution not only of the interstellar medium (ISM) in the starburst galaxies themselves, but also of the intergalactic medium (IGM) in their vicinity. However, several key quantities of starbursts that are neededas input to models of their ISM are still ill-constrained. Some of these critical parameters are e.g. the metalabundances of hot ionized gas, the ionization state ofwarm ionized gas, the amount of energy deposited intothe ambient by a starburst, the efficiency of itsconversion into mechanical energy and thus the totalkinetic energy of the star formation-driven outflowsand their kinematics. The latter are important when considering under whichcircumstances matter energized by a starburst will reach the so-called ‘blowout’ condition, i.e. supersede the threshold energy starting at which local energy injection into the ISM can drive an outflow first into the halo (where metal re-distribution might be very efficient) and eventually out into intergalactic space. I will discuss here a few of these quantities, how we canmeasure them better than in the past, and in which way some of our observing techniques need to be improved in order toobtain better constraints from the data. 相似文献
16.
Charge‐transfer is the main process linking neutrals and charged particles in the interaction regions of neutral (or partly ionized) gas with a plasma. In this paper we illustrate the importance of charge‐transfer with respect to the dynamics and the structure of neutral gas‐plasma interfaces. We consider the following phenomena: (1) the heliospheric interface ‐ region where the solar wind plasma interacts with the partly‐ionized local interstellar medium (LISM) and (2) neutral interstellar clouds embedded in a hot, tenuous plasma such as the million degree gas that fills the so‐called “Local Bubble”. In (1), we discuss several effects in the outer heliosphere caused by charge exchange of interstellar neutral atoms and plasma protons. In (2) we describe the role of charge exchange in the formation of a transition region between the cloud and the surrounding plasma based on a two‐component model of the cloud‐plasma interaction. In the model the cloud consists of relatively cold and dense atomic hydrogen gas, surrounded by hot, low density, fully ionized plasma. We discuss the structure of the cloud‐plasma interface and the effect of charge exchange on the lifetime of interstellar clouds. Charge transfer between neutral atoms and minor ions in the plasma produces X‐ray emission. Assuming standard abundances of minor ions in the hot gas surrounding the cold interstellar cloud, we estimate the X‐ray emissivity consecutive to the charge transfer reactions. Our model shows that the charge‐transfer X‐ray emission from the neutral cloud‐plasma interface may be comparable to the diffuse thermal X‐ray emission from the million degree gas cavity itself (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
17.
C23 UV spectroscopy of the PG1159-type star NGC7094 C26 Variations of the radio synchrotron spectral index in the interstellar medium of M33 C38 Angular Momentum Evolution of Young Brown Dwarfs and Low Mass Stars C48 The radio halo of the nearby starburst galaxy NGC 253 C95 Signatures of early metal enrichment in Damped-Lyman Alpha systems C113 CO 4 → 3 and [CI] 1 → 0 in the centers of NGC4945 and Circinus C115 Ratio of atomic and molecular gas and gravitational stabilty in the disk of M51 C130 The Interstellar Mediumat Early Cosmic Times: Molecular Gas in Distant Quasar Host Galaxies C188 Probing the interstellar medium in distant galaxies with SPICA/ESI C191 The evolution of spectral energy distributions of galaxies over cosmic times C197 Observations of 60Fe in the Galaxy with INTEGRAL/SPI C204 Evolution of Interstellar Clouds in a hot Gas Environment C205 The effect of clouds in a galactic wind on the evolution of gas-rich dwarf galaxies C206 Energy and element deposit into the interstellar medium during the lives of massive stars C209 The distribution and kinematics of massive stars in the inner Galaxy mapped with SPI/INTEGRAL 26Al 1.8 MeV line observations C213 PDR modelling of the Galactic FIR line emission C239 Towards a complete picture of the molecular ISM in local Luminous Infrared Galaxies: first results from the JCMT/IRAM line survey C242 The Search for the Very High-redshift Tail of Submillimeter Galaxies 相似文献
18.
J. Martí D. Pérez-Ramírez P. Luque-Escamilla J. L. Garrido J. M. Paredes A. Muñoz-Arjonilla J. R. Sánchez-Sutil 《Astrophysics and Space Science》2007,309(1-4):309-313
We report and shortly discuss here the observational work carried out in order to test the possibility that two previously
detected radio sources, in the vicinity of the well known microquasar Cygnus X-3, could be hot spot tracers of interaction
between its relativistic jet and the interstellar medium (ISM). The motivation behind this search is in part justified considering
recent theoretical models of high energy γ-ray emission which strongly rely on the interaction sites of galactic relativistic jets with nearby ISM clouds.
The results presented in this paper include an improved radio exploration of the several arc-minute field around Cygnus X-3
using the Very Large Array (VLA), as well as deep near infrared (NIR) imaging with the Calar Alto 3.5 m telescope. We anticipate
here that our observations do not appear to support the initial hot spot hypothesis. Instead, the resulting images suggest
that the two radio sources, originally believed to be hot spot candidates, are most likely background or foreground objects. 相似文献
19.
We investigate with 3D hydrodynamical simulations the role played by thermal processes in the dynamical evolution of the interstellarmedium (ISM). A parametric approach of the coolingprocess shows that the observed mass fraction of the cold (< 300 K)and unstable gas (300K < T < 6000K) can not be produced by turbulentcompression or background heating of the medium alone. An analysis of theproperties of the clouds that are formed by the combined effect of the thermal and gravitational instability shows that the cloud’s scaling relations imprinted by the thermal instability (TI) are in good agreementwith observational values. 相似文献
20.
Philip R. Maloney 《Astrophysics and Space Science》1999,266(1-2):207-230
The energy input into the interstellar medium in UltraluminousInfrared Galaxies (ULIRGs) is enormous, regardless of the nature ofthe power source. I discuss some of the major consequences for thestructure and energetics of the ISM in these galaxies. Observationally, the column densities in the nuclear regions of ULIRGsare known to be very high, which makes distinguishing starbursts fromAGN quite difficult. The level of energy and momentum injection meansthat the pressure in the ISM must be extremely high, at least 3-4orders of magnitude larger than in the local ISM or typical giantmolecular clouds. It also means that the luminosity of GMCs in ULIRGsmust be very high, as they must radiate many times their bindingenergy over their lifetimes. I briefly review the influence whichX-ray irradiation can have on the ISM in AGN-powered ULIRGs. Finally,I show that the presence of PAH features in ULIRGs does not imply thatthey must be starburst-dominated, since at the column densities andpressures typical of the ISM in ULIRGs PAHs can survive even at tensof parsec distances from the AGN. 相似文献