  We have recorded fluorescence spectra of the atomic rubidium D-lines in the
presence of several hundreds of bars buffer gas pressure. With additional
saturation broadening a spectral linewidth comparable to the thermal energy of
the atoms in the heated gas cell is achieved. An intensity-dependent blue
asymmetry of the spectra is observed, which becomes increasingly pronounced
when extrapolating to infinitely high light intensity. We interpret our results
as evidence for the dressed (coupled atom-light) states to approach thermal
equilibrium.
