  We compute the equation of state in the confining phase of SU(N) Yang-Mills
theories with N=2, 3, 4, 5 and 6 colors in 2+1 dimensions, via lattice
simulations. At low enough temperatures, the results are accurately described
by a gas of glueballs, including all known states below the two-particle
threshold. Close to the deconfinement temperature, however, this prediction
underestimates the numerical results, and the contribution from heavier
glueballs has to be included. We show that the spectral density of the latter
can be accurately described using a simple bosonic string model.

High Energy Physics - Lattice;High Energy Physics - Theory;Nuclear Theory