Is the (J-Ks) excess in the nuclear region of NGC 1241 due to dust or to C-stars?

Abstract

Abstract. NGC 1241 is a Sy 2 galaxy with a 1.4 kpc circumnuclear ring (CNR) of star formation revealed in Paα. A 0.3 kpc long Paα emitting bar centered on the nucleus is present, apparently without associated absorption features. GEMINI (+QUIRC+Hokupa) IR pixel-photometry reveals instead an azimuthally symmetric (J − Ks) color which is redder at the nucleus than at the CNR. This property may well be due to the increasing importance of dust when going from the ring inward into the nucleus. Nevertheless the (V − H) color does not indicate special absorption conditions in the nucleus with respect to the CNR, and no absorption features are evident, as normally expected near emitting bars. Then, we propose as an alternative explanation an excess of C-stars in the nuclear region which decreases outwards until reaching the CNR and its colors. We have compared the pixel color-magnitude diagram with the 2-MASS (J − K s ) vs. Ks diagram for the Large Magellanic Cloud: about 5 × 10 2 C-stars and 2.5 × 10 4 AGB Oxygen-rich stars inside r ∼ 50 pc, are enough to reproduce the observed nuclear tip in the diagram. This stars would release gas that, gravitationally bounded, pollutes the nuclear environment and could amount 10 −2 to 10 −1 M yr −1 of fuel for the central engine during the lifetime of stars with masses 2 M < MCStars < 6 M . This scenario may also explain the observed increased strength of the CN-bands in the stellar populations of Sy 2 nuclei, and the recent claim of a significant contribution of intermediate age stars to the optical continuum of low luminosity AGNs.