Formation and evolution of dusty starburst galaxies. I. A new method for deriving a spectral energy distribution

We present a new numerical code that is designed to derive a spectral energ y distribution (SED) for an arbitrary spatial distribution of stellar and g aseous components in a dusty starburst galaxy. We apply a ray-tracing metho d to numerical simulations and thereby estimate extinction and reemission o f stellar light by dusty gas in an explicitly self-consistent manner. By us ing this code, we can investigate simultaneously dynamical and photometric evolution of a dusty galaxy based on stellar and gaseous dynamical simulati ons. As an example, we demonstrate when and how a major galaxy merger with dusty starburst becomes an ultraluminous infrared galaxy owing to strong in ternal dust extinction. We furthermore discuss advantages and disadvantages of the present new code in clarifying the nature and the origin of low- an d high-redshift dusty starburst galaxies.