Strong Evidence for a Buried AGN in UGC 5101: Implications for
LINER-Type Ultra-Luminous Infrared Galaxies
release_uzn2hgfkknb2hbbuvgpocdzi5a
by
Masatoshi Imanishi
NAO,
Japan
2001
Abstract
We report on the results of 3--4 μm spectroscopy of the ultra-luminous
infrared galaxy (ULIRG) UGC 5101. It has a cool far-infrared color and a
LINER-type optical spectrum, and so, based on a view gaining some currency,
would be regarded as dominated by star formation. However, we find that it has
strong 3.4 μm carbonaceous dust absorption, low-equivalent-width 3.3 μm
polycyclic aromatic hydrocarbon (PAH) emission, and a small 3.3 μm PAH to
far-infrared luminosity ratio. This favors an alternative scenario, in which an
energetically dominant AGN is present behind obscuring dust. The AGN is
plausibly obscured along all lines of sight (a `buried AGN'), rather than
merely obscured along our particular line of sight. Such buried AGNs have
previously been found in thermal infrared studies of the ULIRGs IRAS 08572+3915
and IRAS F00183-7111, both classified optically as LINERs. We argue that
buried AGNs can produce LINER-type optical spectra, and that at least some
fraction of LINER-type ULIRGs are predominantly powered by buried AGNs.
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astro-ph/0108156v2
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