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H.M.L.G. Flohic, M. Eracleous, G. Chartas (Pennsylvania State University), J.C. Shields (Ohio University), E.C. Moran (Wesleyan University)
We have used archival Chandra observations of 19 galaxies hosting Low-Ionization Nuclear Emission Regions (LINERs) to explore the morphology and source populations of their inner kiloparsec. The vast majority of these galaxies were originally observed for reasons unrelated to the presence of a LINER. Our ultimate goal was, in general, to determine the power source behind their nuclear X-ray emission, and, in particular, to investigate the presence of an Active Galactic Nucleus (AGN). The galaxies in our sample span a wide range of morphological and comprise relative numbers of LINER very similar to those found among nearby galaxies studies in large, optical, spectroscopic surveys.
We find that diffuse, thermal emission is very common in these galaxies and is typically concentrated within the central few hundred parsec. The average spectra of the hot gas (stacked separately for spirals and ellipticals) can be fitted with a model consisting of a thermal plasma (kT~ 0.6 keV) plus a power law (photon index around 1.3-1.5), very similar to what is found in normal galaxies. The sample galaxies have on average 3 point sources in their inner kiloparsec (up to 12 in the most extreme case). Constructing luminosity functions for sources in spirals and ellipticals separately, we find these to be identical to those of normal galaxies. Focusing on the innermost circle of 2.5 arcsecond radius in each galaxy (120-300 pc in linear radius, comparable to the area of typical optical spectroscopic apertures), we find that an AGN is present in 12 of the 19 galaxies; in the others the central X-ray source is powered by stellar processes or its nature is ambiguous. These AGNs contribute between 20 and 90% of the total 0.5-10 keV luminosity of the central 2.5 arcsecond region (a median of ~ 60%), they have typical luminosities of order 1038 - 1039 erg/s, and they are all radio-loud.
This work was supported by NASA through grant AR4-5010A from Smithsonian Astrophysical Observatory.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.