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Title:
A Reevaluation of the Excitation Mechanism of LINERs
Authors:
Ho, Luis C.; Filippenko, Alexei V.; Sargent, Wallace L. W.
Publication:
Astrophysical Journal v.417, p.63 (ApJ Homepage)
Publication Date:
11/1993
Origin:
APJ; KNUDSEN
Astronomy Keywords:
GALAXIES: ACTIVE, GALAXIES: ISM, GALAXIES: NUCLEI, GALAXIES: SEYFERT
DOI:
10.1086/173291
Bibliographic Code:
1993ApJ...417...63H

Abstract

We present high-quality spectra of a sample of 13 low-ionization nuclear emission-line regions (LINERs) observed in the range ˜3400-9800 Å at ˜5-8 Å resolution. Starlight removal is achieved by the subtraction of a suitable absorption-line "template" galaxy, allowing accurate measurement of emission lines. We use the line fluxes to examine several candidates for the excitation mechanism of those LINERs whose emission-line gas is largely confined to radii ≲200 pc. We find that photoionization by a nonstellar ionizing continuum provides the best overall explanation for the spectra over the optical-to near-infrared region. This is supported by the detection of broad Halpha emission, a correlation between line width and critical density of the forbidden lines, and pointlike X-ray emission in several of these objects. Wolf-Rayet stars or unusually hot O stars are less probable photoionization sources, especially for LINERs which exhibit broad Halpha emission. The prevalence of shock heating in galactic nuclei cannot be readily evaluated with the present plane-parallel shock models, although it is likely to be an important excitation mechanism for LINERs with spatially extended emission. A small fraction of objects previously classified as LINERs may be undergoing active star formation in or near their nuclei.

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