The starburst phenomenon from the opticalnear-IR perspective.pdf

a r X i v : a s t r o - p h / 0 4 1 2 1 1 9 v 1 6 D e c 2 0 0 4 THE STARBURST PHENOMENON FROM THE OPTICAL/NEAR-IR PERSPECTIVE Nils Bergvall,1 Thomas Marquart,1 Go?ran O?stlin,2 Erik Zackrisson1 1Uppsala Astronomical Observatory Box 515, SE-751 20 Uppsala, Sweden nils.bergvall@astro.uu.se, thomas.marquart@astro.uu.se, ez@astro.uu.se 2Stockholm Observatory AlbaNova University Center, Roslagstullsbacken 21, SE-106 91 Stockholm, Sweden ostlin@astro.su.se Abstract The optical/near-IR stellar continuum carries unique information about the stellar population in a galaxy, its mass function and star-formation history. Star-forming regions display rich emission-line spectra from which we can derive the dust and gas distribution, map velocity fields, metallicities and young massive stars and locate shocks and stellar winds. All this information is very useful in the dissection of the star- burst phenomenon. We discuss a few of the advantages and limitations of observations in the optical/near-IR region and focus on some results. Special attention is given to the role of interactions and mergers and observations of the relatively dust-free starburst dwarfs. In the future we expect new and refined diagnostic tools to provide us with more de- tailed information about the IMF, strength and duration of the burst and its triggering mechanisms. Keywords: galaxies:dwarfs, galaxies:evolution, galaxies:interactions, galaxies:starburst, infrared:galaxies 1. Introduction Optical/near-IR broadband photometry of a starburst galaxy gives a first indication of burst strength, age and distribution of the young and old populations and their basic morphological structure parameters. Model based spectrophotometric tools are provided for more detailed analysis. A rich set of emission lines are used for analysis of kinematics, chemical abundance, shocks, stellar upper mass limit and distribution of dust and molecular gas. Absorption line indices provide estimates of age 2and IMF of the evolved