Evolution of gaseous disk viscosity driven by supernova explosion. II. Structure and emissions from star-forming galaxies at high redshift

Abstract

High spatial resolution observations show that high-redshift galaxies are undergoing intensive evolution of dynamical structure and morphologies displayed by the Hα, Hβ, [Oiii], and [N ii] images. It has been shown that supernova explosion (SNexp) of young massive stars during the star formation epoch, as kinetic feedback to host galaxies, can efficiently excite the turbulent viscosity. We incorporate the feedback into the dynamical equations through mass dropout and angular momentum transportation driven by the SNexp-excited turbulent viscosity. The empirical Kennicutt-Schmidt law is used for star formation rates (SFRs). We numerically solve the equations and show that there can be intensive evolution of structure of the gaseous disk. Secular evolution of the disk shows interesting characteristics: (1) high viscosity excited by SNexp can efficiently transport the gas from 10 kpc to ∼1 kpc forming a stellar disk whereas a stellar ring forms for the case with low viscosity; (2) starbursts trigger SMBH activity with a lag of ∼10 8 yr depending on SFRs, prompting the joint evolution of SMBHs and bulges; and (3) the velocity dispersion is as high as ∼100 km s-1 in the gaseous disk. These results are likely to vary with the initial mass function (IMF) that the SNexp rates rely on. Given the IMF, we use the GALAXEV code to compute the spectral evolution of stellar populations based on the dynamical structure. In order to compare the present models with the observed dynamical structure and images, we use the incident continuum from the simple stellar synthesis and CLOUDY to calculate emission line ratios of Hα, Hβ, [Oiii], and [N ii], and Hα brightness of gas photoionized by young massive stars formed on the disks. The models can produce the main features of emission from star-forming galaxies. We apply the present model to two galaxies, BX 389 and BX 482 observed in the SINS high-z sample, which are bulge and disk-dominated, respectively. Two successive rings independently evolving are able to reproduce the main dynamical and emission properties of the two galaxies, such as the Baldwin-Phillips-Terlevich diagram, the relation between line ratios, and Hα brightness. The observed relation between turbulent velocity and the Hα brightness can be explained by the present model. High viscosity excited by SNexp is able to efficiently transport the gas into a bulge to maintain high SFRs or to form a stellar ring close enough to the bulge so that it immigrates into the bulge of its host galaxy. This leads to a fast growing bulge. Implications and future work of the present models have been extensively discussed for galaxy formation in high-z universe. © 2010. The American Astronomical Society. All rights reserved.