EDP Sciences
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Volume 415, Number 2, February IV 2004
Page(s) 509 - 520
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20034635

A&A 415, 509-520 (2004)
DOI: 10.1051/0004-6361:20034635

Dust and super star clusters in NGC 5253

L. Vanzi1 and M. Sauvage2

1  ESO - European Southern Observatory Alonso de Cordova, 3107 Santiago, Chile
2  Service d'Astrophysique, CEA/DSM/DAPNIA, Centre d'Études de Saclay, 91191 Gif-sur-Yvette Cedex, France
    e-mail: msauvage@cea.fr

(Received 8 July 2003 / Accepted 14 November 2003)

We present new observations of the famous starburst galaxy NGC 5253 which owes its celebrity to possibly being the youngest and closest starburst galaxy known. Our observations in the infrared and millimeter contribute to shed light on the properties of this interesting object. We have used our new data along with data from the literature to study the properties of the young stellar clusters present in NGC 5253. We find that the brightest optical clusters are all characterized by a near-infrared excess that is explained by the combined effect of extinction and emission by dust. For the brightest infrared cluster we model the spectral energy distribution from the optical to the radio. We find that this cluster dominates the galaxy emission longward of 3 $\mu$m, that it has a bolometric luminosity of $1.2\times 10^9~L_{\odot}$ and a mass of $1.2\times 10^6~M_{\odot}$, giving $L/M\approx10^3$. The cluster is obscured by 7 mag of optical extinction produced by about $1.5\times 10^{5}$  $M_{\odot}$ of dust. The dust properties are peculiar with respect to the dust properties in the solar neighbourhood with a composition characterized by a lack of silicates and a flatter size distribution than the standard one, i.e. a bias toward larger grains. We find that NGC 5253 is a striking example of a galaxy where the infrared-submillimeter and ultraviolet-optical emissions originate in totally decoupled regions of vastly different physical sizes.

Key words: galaxies: starburst -- dust, extinction -- infrared -- super-star clusters -- galaxies: individual: NGC 5253

Offprint request: L. Vanzi, lvanzi@eso.org

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