Separating c-Stars from dust in the central region of the Seyfert 2 galaxy NGC 1241

Abstract

The Seyfert 2 galaxy NGC 1241 presents a 1.5 kpc large circumnuclear ring (CNR) of star formation embracing a small bar plus leading arms. Those structures are Paα emitters but barely seen in Haα. It also presents stellar trailing arms inside the CNR. Gemini and HST imagery allow the construction of high-resolution (V−H) and (J−K) color maps, as well as a (J−K) versus K color-magnitude diagram of this complex region. The CNR s s is heavily obscured in V, but a fairly transparent window appears in the direction of the nucleus. Nonetheless, the nucleus presents a (J−K) color that is redder than the CNR. The CNR is composed of extremely young s H II regions still enshrouded in their dust cocoons. However, the nuclear (J−K) color cannot be explained in s this manner. Therefore, we propose the contribution of C stars as the most feasible mechanism for explaining the colors. If the nuclear stellar population is comparable to that of the Large Magellanic Cloud bar, 500 C stars and 25,000 asymptotic giant branch O-rich stars inside 50 pc may reproduce the observed colors. C stars release enriched material to the nuclear environment, probably fueling the central engine of this Seyfert 2 galaxy during the lifetime of stars with masses in the range 2 Mʘ < M cstar < 6 Mʘ (C-star phase). The ejected material that , C star, remains trapped in the central potential might also explain the systematically observed increased strength of the optical CN bands in Seyfert 2 galaxies and is consistent with the significant contribution of intermediate age stars to the optical continuum of low-luminosity active galactic nuclei.