Massive Star Formation in AGN Host Galaxies Observed by the Ultraviolet Imaging Telescope

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Session 46 -- Seyfert Galaxies and LINERS
Display presentation, Thursday, January 13, 9:30-6:45, Salons I/II Room (Crystal Gateway)

[46.10] Massive Star Formation in AGN Host Galaxies Observed by the Ultraviolet Imaging Telescope

N.R. Collins (Hughes STX), M.N. Fanelli (NRC / LASP / GSFC), G.S. Hennessy (USNO), R.W.O'Connell (UVa), R.Bohlin (STScI), M.S.Roberts (NRAO), S.G. Neff, A.M.Smith, T.P.Stecher (LASP/GSFC/NASA)

We present ultraviolet images of four Seyfert galaxies observed with the Ultraviolet Imaging Telescope (UIT) and compare their off-nuclear UV morphology and colors. Images were obtained at far-UV (FUV), $\lambda_{eff} \sim 1520$ \AA, and near-UV (NUV), $\lambda_{eff} \sim 2490$ \AA, wavelengths for NGC~1068 (Sy~2), NGC~2992 (Sy~2), NGC~4151 (Sy~1), and MRK~335 (Sy~1). UV imagery permits detection of recent high-mass star formation in AGN host galaxies since the cool stars which dominate the light at optical wavelengths contribute minimal light in the vacumn UV.

The host galaxies span a broad range in UV morphology. NGC~1068 contains multiple components at UV wavelengths: the central AGN; a population of luminous starburst knots; a bright oval inner disk; and a fainter, more circular outer disk. The brightest knot gives NGC~1068 a `double nucleus' appearance in the UV and is $\sim 80$ times the luminosity of 30~Doradus. The UV flux is dominated by the disk $+$ knot component, the AGN produces 17\% of the total flux in the NUV and 29\% in the FUV. In contrast to NGC~1068, the unresolved bright nucleus dominates the UV light distribution in NGC~4151. Two lobes of emission are observed bracketing the nucleus extending to $\sim 6$ kpc (Hennessy et~al. 1992, BAAS 24, 1274). The AGN comprises 76\% of the total flux in the NUV and 81\% in the FUV. The active nucleus in MRK~335, the most distant object in our sample ($D \sim 105$ Mpc), appears as a point source in both bandpasses with a FWHM of $\sim 3.4^{\prime\prime}$, which corresponds to a linear distance of 1.7 kpc. After subtraction of the AGN light distribution, no additional UV emission is observed. NGC~2992 is detected at NUV wavelengths only. The data reveal diffuse (perhaps dust-scattered) light at the position of the optically-defined bulge, but no bright nuclear source. We use these data to estimate the massive star formation rate in the AGN host galaxies.

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