A grid of 20 millions 3-1100$\mu$m SED models is presented for synthetic young clusters embedded in dense clumps. The models depend on four primary parameters: the clump mass M$_{ clump}$ and dust temperature T$_{ dust}$, the fraction of mass f$_{ core}$ locked in dense cores, and the age of the clump t$_{ SF}$. We populate the YSO clusters using the IMF from Kroupa(2001) and the YSOs SED models grid of Robitaille et al. (2006). We conduct extensive testing of SED fitting using a simulated dataset and we find that M$_{ clump}$ essentially depends on the submillimeter portion of the SED, while T$_{ dust}$ is mostly determined from the shape of the SED in the 70-350$\mu$m range. Thanks to the large number of models computed we verify that the combined analysis of L/M, [8-24] and [24-70] colours removes much of the SEDs f$_{ core}$-t$_{ SF}$ degeneracy. The L/M values are particularly useful to diagnose f$_{ core}$. L/M$\leq$1 identifies protoclusters with f$_{ core}\leq$0.1 and t$_{ SF} \leq 10^5$ years, while L/M$\geq$10 excludes f$_{ core}\leq$0.1. We characterize lower limits of L/M where ZAMS stars are not found in models, and we also find models with L/M $\geq$10 and no ZAMS stars, in which [8-24]$\geq0.8\pm 0.1$ independently from M$_{ clump}$, temperature and luminosity. This is the first set of synthesis SED models suited to model for embedded and unresolved clusters of YSOs. A set of new evolutionary tracks in the L/M diagram is also presented.
Categories: astro-ph.SR astro-ph.GA