On the Influence of Supernova Remnant Thermal Energy in Powe

The fundamental tenet of the classical supernovae-driven wind model of elliptical galaxies is that the residual thermal energy of all supernovae remnants (SNRs) provide sufficient energy to overcome the binding energy of the remaining interstellar gas, the

astro-ph/9410031 11 Oct 1994

The fundamental tenet of the classical supernovae-driven wind model of elliptical galaxies is that the residual thermal energy of all supernovae remnants (SNRs) provide sufficient energy to overcome the binding energy of the remaining interstellar gas, the

1. Introduction. It has long been recognised that the colours of elliptical galaxies become increasingly red with decreasing magnitudes, or conversely, increasing mass. This e ect has been commonly attributed to an increasing average galactic metal content with increasing galactic mass (e.g. Faber 1977, for an early review). The key to understanding the origin of these correlations was provided by Mathews& Baker (1971), but not fully appreciated until Larson (1974). In order to explain the paucity of interstellar gas in most ellipticals Mathews& Baker (1971) postulated that much of it had been strongly heated by supernovae (SNe) explosions and driven out by a hot galactic wind once the residual thermal energy of all SNe remnants exceeded the binding energy of the remaining gas, thereby bringing to a halt the bulk of active star formation. Subsequent evolution would then be regulated by the gas returned to the interstellar medium (ISM) from dying stars. It was left to Larson (1974) to recognise that the binding energy per unit mass of gas is higher in the more massive galaxies, and thus these systems would retain their gas for longer initial periods before reaching this epoch of galactic wind tGW, thereby attaining higher metallicities in a manner consistent with the observed mass-metallicity relationship. Further developments over the past decade can be attributed to Saito (1979), Arimoto& Yoshii (1987), Matteucci& Tornambe (1987), Angeletti& Giannone (1990), Bressan, Chiosi& Fagotto (1994), Elbaz, Arnaud& Vangioni-Flam (1994), and Gibson (

1995). It is generally accepted that wind models of this nature may be inadequate in some details, but are still the framework of choice for modeling the early evolution of spheroids (Renzini et al. 1993). Determining the epoch of global gas ejection is an imperative aspect of these wind models as tGW governs the cessation of the bulk of star formation, as well as the amount and metallicity of expelled gas, and the current spectrophotometric properties of ellipticals. Angeletti& Giannone (1991) have discussed the sensitivity of tGW predictions to the assumed initial proto-galactic radius (contributing to the binding energy of the spheroid), and Matteucci (1994) has explored recently the importance of the astration parameter (contributing to the timescale for star formation). Our plan herein is to re-examine brie y one of the fundamental ingredients to all supernovae-powered wind models, speci cally, the formalism adopted to represent the evolution of a supernova remnant's (SNR) internal thermal energy"th(t), and the availability of such energy for driving a galactic wind. In Section 2 we outline the basic chemical evolution and wind model framework used in our study. We present the classic Cox (1972) and Chevalier (1974) formalism used in each of the post-Larson (1974) papers listed above, highlighting an oversight which has lead, in some cases, to an overestimation of the gas ejection time tGW . Following Cio, McKee& Bertschinger (1988), we discuss their alternative formalism for the evolution of the SNR thermal energy"th (t), superseding the earlier Cox and Chevalier work with its more sophisticated treatment of radiative cooling in the hot SNR interior. Sections 3 and 4 provide the relevant equations governing the evolution of"th (t) set by these competing formalisms. A direct comparison of the di erences in some of the model predictions based upon the selection of thermal energy formalism is given in Section 5 and summarised in Section 6. Our aim is not to analyse each and every consequence of this selection, but only to highlight a few important ones, and in particular, to demonstrate the in uence of

The fundamental tenet of the classical supernovae-driven wind model of elliptical galaxies is that the residual thermal energy of all supernovae remnants (SNRs) provide sufficient energy to overcome the binding energy of the remaining interstellar gas, the

"th (t) upon tGW predictions. This is su cient for our purposes as many of the predictions (e.g. mass and metallicity of gas ejected) are related in a simple manner to tGW .2. The Classical Wind Model of Ellipticals. For convenience we have adopted the classical one-zone wind model of ellipticals as presented by Matteucci& Greggio (1986) and Matteucci& Tornambe (1987). A brief outline follows, with a more detailed accounting of the relevant equations and input ingredients pertaining to our package (entitled MEGaW Metallicity Evolution with Galactic Winds) to be presented elsewhere (Gibson 1995), although the reader is directed to the above references, as well as those of Arimoto& Yoshii (1987) and Angeletti& Giannone (1990), for a complementary introduction to the subject. The gas mass Mg in the ISM is depleted by star formation

and replenished through ejection from stars, and is governed by dMg (t)= (t)+ E (t); (1) dt where (t) is the star formation rate and E (t) is the total gas ejection rate from all stars. Coupled to the gas mass equation 1, the mass of metals MZ ZMg in the ISM evolves as

dMZ (t)= Z (t) (t)+ E (t); (2) Z dt where EZ (t) is the total ejection rate of both processed and unprocessed metals. The relations for E (t) and EZ (t) are adapted from Greggio& Renzini (1983) and Matteucci& Greggio (1986). T …… 此处隐藏：46503字，全部文档内容请下载后查看。喜欢就下载吧 ……