Emission-line diagnostics of the central engines of weak-line radio galaxies

Karen T. Lewis, Michael Eracleous, Rita M. Sambruna

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25 Scopus citations


A handful of well-studied weak-line radio galaxies (WLRGs) have been traditionally classified as lowionization nuclear emission-line regions (LINERs), suggesting that these two groups of active galactic nuclei (AGNs) might be related. In this paper, we present new optical emission-line measurements for 20 WLRGs, which we supplement with measurements for an additional four from the literature. Classifying these objects by their emission-line ratios, we find that 50% of the objects are robustly classified as LINERs, while an additional 25% are likely to be LINERs. Photoionization calculations show that the spectral energy distribution of the well-studied WLRG 3C 270 (NGC 4261) is able to produce the observed emission-line ratios, but only if the UV emission seen by the narrow emission line gas is significantly higher than that observed, implying AV = 2.5-4.2 mag along our line of sight to the nucleus. From the photoionization calculations, we find that the emission-line gas must have an ionization parameter between 10-3.5 and 10-4.0 and a wide range in hydrogen density (102-106 cm-3) to reproduce the measured emission-line ratios, similar to the properties inferred for the emission-line gas in LINERs. Thus, we find that properties of the emission-line gas as well as the underlying excitation mechanism are indeed similar in LINERs and WLRGs. By extension, the central engines of accretion-powered LINERs and WLRGs, which do host an accreting black hole, may be qualitatively similar.

Original languageEnglish (US)
Pages (from-to)115-126
Number of pages12
JournalAstrophysical Journal
Issue number1 I
StatePublished - Aug 10 2003

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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