ASCAObservations of “Type 2” LINERs: Evidence for a Stellar Source of Ionization

We present ASCA observations of LINERs without broad H$\alpha$ emission intheir optical spectra. The sample of "type 2" LINERs consists of NGC 404, 4111,4192, 4457, and 4569. We have detected X-ray emission from all the objectsexcept for NGC 404; among the detected objects are two so-called transitionobjects (NGC 4192 and NGC 4569), which have been postulated to be compositenuclei having both an HII region and a LINER component. The images of NGC 4111and NGC 4569 in the soft (0.5-2 keV) and hard (2-7 keV) X-ray bands areextended on scales of several kpc. The X-ray spectra of NGC 4111, NGC 4457 andNGC 4569 are well fitted by a two-component model that consists of soft thermalemission with $kT\sim0.65$ keV and a hard component represented by a power law(photon index $\sim$ 2) or by thermal bremsstrahlung emission ($kT\sim$ severalkeV). The extended hard X-rays probably come from discrete sources, while thesoft emission most likely originates from hot gas produced by active starformation in the host galaxy. We have found no clear evidence for the presenceof active galactic nuclei (AGNs) in the sample. If an AGN component is theprimary ionization source of the optical emission lines, then it must beheavily obscured with a column density significantly larger than $10^{23}$cm$^{-2}$. Alternatively, the optical emission could be ionized by a populationof exceptionally hot stars.Comment: 13 pages, 5 figures, emulateapj.sty, Accepted for publication in the Astrophysical Journa