A SINFONI view of the nuclear activity and circumnuclear star formation in NGC4303-II. Spatially resolved stellar populations

Abstract

We present a spatially resolved stellar population study of the inner∼200 pc radius ofNGC 4303 based on near-infrared integral field spectroscopy with SINFONI/VLT at a spatial resolution of 40–80 pc and using the STARLIGHT code. We found that the distribution of thestellar populations presents a spatial variation, suggesting an age stratification. Three main structures stand out. Two nuclear blobs, one composed by young stars (t≤50 Myr) and onewith intermediate-age stars (50 Myr<t≤2 Gyr), both shifted from the centre. The third oneis an internal intermediate-age spiral arm-like structure, surrounding the blob of young stars.Our results indicate that star formation has occurred through multiple bursts in this source. Furthermore, the youngest stellar populations (t 2 Gyr) are distributed along a circumnu-clear star-forming ring withr∼250 pc. The ring displays star formation rates (SFRs) in therange of 0.002–0.14 M yr−1, favouring the ‘pearls-on-a-string’ scenario. The old underlyingbulge stellar population component (t>2 Gyr) is distributed outside the two blob structures.For the nuclear region (inner∼60 pc radius) we derived an SFR of 0.43 M yr−1and foundno signatures of non-thermal featureless continuum and hot dust emission, supporting thescenario in which an LLAGN/LINER-like source is hidden in the centre of NGC 4303. Thus, our results reveal a rather complex star formation history in NGC 4303, with different stellar population components coexisting with a low efficiency accreting black hole in its centre.