The Nature of Submm-Detected Galaxies

The submm detected sources at high redshifts are believed to comprise a class of objects which are highly luminous dusty sources, emitting most of their luminosity at FIR wavelengths (see review by I. Smail in these proceedings). It is presently unclear what is the most common dominative power source: star formation or AGN activity? In the case of star formation, the implied star formation rates exceed 1000 M⊙/yr. Combined with a large gas reservoir, this SFR can be sustained for relatively long time periods (~ 108 years) and the end result is a massive galaxy, created at high redshift in a short time period. If AGN activity is the power source, however, the observed redshifted FIR and molecular gas may not directly probe the star formation properties. In order to study two of the identified submm sources in more detail we have observed SMM J14011+0252 at z = 2.565 and SMM J02399-0136 at z = 2.808 with the VLT/FORS2 (longslit), with an observed spectral resolution of 1.06 A. This is 15 times better than anything achieved previously. The goal was to search for diagnostic stellar absorption lines, giving information about the massive stellar population.