ترغب بنشر مسار تعليمي؟ اضغط هنا

139 - Hugo Martel , Andrea Urban , 2012
Dust and gas energetics are incorporated into a cluster-scale simulation of star formation in order to study the effect of heating and cooling on the star formation process. We build on our previous work by calculating separately the dust and gas tem peratures. The dust temperature is set by radiative equilibrium between heating by embedded stars and radiation from dust. The gas temperature is determined using an energy-rate balance algorithm which includes molecular cooling, dust-gas collisional energy transfer, and cosmic-ray ionization. The fragmentation proceeds roughly similarly to simulations in which the gas temperature is set to the dust temperature, but there are differences. The structure of regions around sink particles have properties similar to those of Class 0 objects, but the infall speeds and mass accretion rates were, on average, higher than those seen for regions forming only low-mass stars. The gas and dust temperature have complex distributions not well modeled by approximations that ignore the detailed thermal physics. There is no simple relationship between density and kinetic temperature. In particular, high density regions have a large range of temperatures, determined by their location relative to heating sources. The total luminosity underestimates the star formation rate at these early stages, before ionizing sources are included, by an order of magnitude. As predicted in our previous work, a larger number of intermediate mass objects form when improved thermal physics is included, but the resulting IMF still has too few low mass stars. However, if we consider recent evidence on core-to-star efficiencies, the match to the IMF is improved.
We present a model to self-consistently describe the joint evolution of starburst galaxies and the galactic wind resulting from this evolution. 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 (IGM). 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 Msun, 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.
mircosoft-partner

هل ترغب بارسال اشعارات عن اخر التحديثات في شمرا-اكاديميا