Multiwavelength study of the star-formation in the bar of NGC 2903

Abstract

Aims. NGC 2903 is a nearby barred spiral with an active starburst in the center and H ii regions distributed along its bar. We aim to analyse the star formation properties in the bar region of NGC 2903 and study the links with the typical bar morphological features.

Methods. A combination of space and ground–based data from the far–ultraviolet to the sub–millimeter spectral ranges is used to create a panchromatic view of the NGC 2903 bar. We produce two catalogues: one for the current star formation regions, as traced by the Hα compact emission, and a second one for the ultraviolet (UV) emitting knots, containing positions and luminosities. From them we have obtained ultraviolet colours, star formation rates, dust attenuation and Hα EWs, and their spatial distribution have been analysed. Stellar cluster ages have been estimated using stellar population synthesis models (Starburst99).

Results. NGC 2903 is a complex galaxy, with a very different morphology on each spectral band. The CO (J=1-0) and the 3.6 µm emission trace each other in a clear barred structure, while the Hα leads both components and it has an s–shape distribution. The UV emission is patchy and does not resemble a bar. The UV emission is also characterised by a number of regions located symmetrically with respect to the galaxy center, almost perpendicular to the bar, in a spiral shape covering the inner ∼ 2.5kpc. These regions do not show a significant Hα nor 24 µm emission. We have estimated ages for these regions ranging from 150 to 320 Myr, being older than the rest of the UV knots, which have ages lower than 10 Myr. The SFR calculated from the UV emission is ∼0.4 M⊙ yr−1 , compatible with the SFR as derived from Hα calibrations (∼1 M⊙ yr−1 ).