  We report on a search for the optical counterparts of 175 um - selected
sources from the Far-Infrared Background (FIRBACK) survey in the European Large
Area ISO Survey (ELAIS) N2 field. Applying a likelihood ratio technique to
optical catalogues from the Isaac Newton Telescope - Wide Field Survey
(INT--WFS), we found optical identifications for 33 out of 55 FIRBACK sources
in this field. These were then reassessed in the light of associations with the
ELAIS final catalogue for the the N2 field, to yield a final set of 31
associations. We have investigated the nature of this population through a
comparison of their observed spectral energy distributions with predictions
from radiative transfer models which simulate the emission from both cirrus and
starburst components. We find the far-infrared sources to be 80 per cent star
bursting galaxies with their starburst component at a high optical depth. The
resulting SEDs were used to estimate far-infrared luminosities, star formation
rates, dust temperatures and dust masses. The N2 FIRBACK population is found to
consist of four suspected ULIRGs, a number of LIRGs and a population of low
redshift quiescently star forming galaxies. We also discuss the implications of
these results for current evolutionary models.

Astrophysics