IRAS FSC 15307+3252 -- Gravitationally Lensed Seyfert or Cannibal Elliptical at z = 0.93?
Abstract
We present the highest spatial and spectral resolution near-infrared data to date of the ~1013~h-2~L IRAS source FSC 15307+3252 at z = 0.93, apparently the most luminous galaxy in the known Universe. Deep K-band (2.2 ) images taken in 04 seeing at the W.\ M.\ Keck Telescope reveal three components within 2. The dominant component has a surface brightness profile well-characterized by an r1/4 law and a nucleus which is stellar in appearance with extended structure, possibly a second nucleus ~05 away. Our 1.1--1.4~\ spectrum shows strong emission lines of \ 6300, 6364; blended ~+~\ 6548, 6583; and \ 6716, 6731 with characteristics of Seyfert 2 galaxies. The \ line also has a broad (1900 km~s-1) component. In light of the recent discovery that FSC 10214+4724, previously the most luminous known galaxy, is a gravitationally-lensed system, we explore the possibility that F15307 is also lensed. Quantitative arguments are inconclusive, but aspects of F15307's morphology do suggest lensing; the system bears a strong resemblance to quadruple-image gravitational lenses. On the other hand, given the r1/4 profile, the close companions, and the active nucleus, F15307 may in fact be a giant elliptical galaxy caught in the act of galactic cannibalism, a scenario which could also account for its unparalleled luminosity.
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