2009MNRAS.392L..16F

Very Large Telescope adaptive optics images of NGC 253 with resolutions down to 200mas resolve the central 300pc of this galaxy in ∼37 infrared (IR) bright knots, a factor of 3 larger than previously reported and extended diffuse emission. The angular resolution, comparable to that of available Very Large Array 2cm maps, permits us a very accurate IR-radio registration. Eight radio sources are found to have an IR counterpart. The knots have Hα equivalent width of about 80Å, sizes of ∼ 3pc, magnitudes in L band of about 12mag and relatively high extinction, A_V ∼ 7mag. Their spectral energy distributions (SEDs) look very similar, characterized by a maximum at 20µm and a gentle bump in the 1-2µm range. These features can be well reproduced by considering an important contribution of very young stellar objects to the IR, efficiently heating their dust envelope. The evidence indicates that these are young massive clusters bursting from their dust cocoons. A median SED of the knots is provided, which may represent one of the most genuine templates of an extragalactic circumnuclear star-forming region. The lack of any optical or IR counterpart for the previously identified radio core calls into question its supposed active nucleus nature. This source may instead represent a scaled up version of Sgr A* at the Galactic Centre.