Photometric properties of the Arp 220 super star clusters

We investigate the photometric properties of six super stellar clusters (SS Cs) seen in both the optical and near-infrared Hubble Space Telescope image s of the local ultraluminous starburst galaxy Arp 220. Three of the SSCs ar e located in the central 0.5-kpc region. The remaining three are in the cir cumnuclear region between 0.5 and 2.5 kpc from the centre. Comparing the ob served spectral energy distributions (SEDs) of the SSCs with the Starburst9 9 models of Leitherer et al., we confirm that all three nuclear SSCs are he avily obscured (A(V)similar to 10 mag). Considering the results from this c omparison in conjunction with measurements of the near-infrared CO absorpti on index and of millimetre CO linewidths and luminosities, we estimate the ages of the nuclear SSCs to be 10(7)-10(8) yr. The bolometric luminosity of the three nuclear SSCs is at most one-fifth of the total bolometric lumino sity of Arp 220. On the other hand, the circumnuclear SSCs have little inte rnal extinction (A(V)less than or equal to1 mag). These contribute negligib ly to the total bolometric luminosity.