The Nature of LINERs

Almudena Alonso-Herrero; Marcia J. Rieke; George H. Rieke; Joseph C. Shields

doi:10.1086/308388

paper

The Nature of LINERs

arXiv:astro-ph/9909316 · doi:10.1086/308388

Abstract

We present $J$ -band ( $1.15 - 1.35 μ$ m) spectroscopy of a sample of nine galaxies showing some degree of LINER activity (classical LINERs, weak-[O {\sc i}] LINERs and transition objects), together with $H$ -band spectroscopy for some of them. A careful subtraction of the stellar continuum allows us to obtain reliable [Fe {\sc ii}] $1.2567 μ$ m/Pa $β$ line ratios. We conclude that different types of LINERs (i.e., photoionized by a stellar continuum or by an AGN) cannot be easily distinguished based solely on the [Fe {\sc ii}] $1.2567 μ$ m/Pa $β$ line ratio. The emission line properties of many LINERs can be explained in terms of an aging starburst. The optical line ratios of these LINERs are reproduced by a model with a metal-rich H {\sc ii} region component photoionized with a single stellar temperature $T_{*} = 38, 000$ K, plus a supernova remnant (SNR) component. The [Fe {\sc ii}] line is predominantly excited by shocks produced by SNRs in starbursts and starburst-dominated LINERs, while Pa $β$ tracks H {\sc ii} regions ionized by massive young stars. The contribution from SNRs to the overall emission line spectrum is constrained by the [Fe {\sc ii}] $1.2567 μ$ m/Pa $β$ line ratio. Although our models for aging starbursts are constrained only by these infrared lines, they consistently explain the optical spectra of the galaxies also. The LINER-starburst connection is tested by predicting the time dependence of the ratio of the ionizing luminosity ( $L_{ion}$ ) to the supernova rate (SNr), $L_{ion}$ /(SNr). We predict the relative number of starbursts to starburst-dominated LINERs (aging starbursts) and show that it is in approximate agreement with survey findings for nearby galaxies.

Accepted in ApJ (19 pages, 8 figures, uses emulateapj.sty)

The Nature of LINERs

Abstract

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