Circumnuclear Star Forming Activity in NGC 3982

Abstract

We present a study of the nearby Seyfert galaxy NGC 3982 using optical, infrared and X-ray data acquired by SDSS, Spitzer and Chandra. Our main results are as follows: (1) A simple stellar population synthesis on the nuclear and circumnuclear SDSS spectra gives unambiguous evidence of young stellar components in both the nuclear and circumnuclear regions. (2) The Spitzer Infrared Spectrograph (IRS) spectrum of the central region (~3'') shows a power-law continuum, a silicate emission feature at 9.7 μm, and significant PAH emission features at 7.7, 8.6, 11.3 and 12.7 μm, suggesting the coexistence of AGN and starburst activities in the central region of NGC 3982. (3) We estimate the star formation rate (SFR) of the circumnuclear (~5''−20'') region from the Hα luminosity to be SFRHα = 0.52 M⊙ yr−1, which is consistent with the result from the Spitzer IRAC 8 μm luminosity, SFR8.0 μm = 0.57 M⊙ yr−1. (4) We measure the spectral energy distribution for the active nucleus of NGC 3982 from radio to X-ray, and obtain a bolometric luminosity of Lbol = 4.5×1042 erg s−1, corresponding to an Eddington ratio (Lbol/LEdd) of 0.014. The HST image of NGC 3982 shows a nuclear mini-spiral between the circumnuclear star-forming region and the nucleus, which could be the channel through which gas is transported to the supermassive black hole from the circumnuclear star-forming region.