The Nature of LINERS
Abstract
We present J-band (1.15-1.35 μm) spectroscopy of a sample of nine galaxies showing some degree of LINER activity (classical LINERs, weak-[O 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 II] 1.2567 μm/Paβ line ratios. We conclude that different types of LINERs (i.e., photoionized by a stellar continuum or by an active galactic nucleus) cannot be easily distinguished based solely on the [Fe II] 1.2567 μm/Paβ 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 II region component photoionized with a single stellar temperature T*=38,000 K, plus a supernova remnant (SNR) component. The [Fe II] line is predominantly excited by shocks produced by SNRs in starbursts and starburst-dominated LINERs, while Paβ tracks H II regions ionized by massive young stars. The contribution from SNRs to the overall emission-line spectrum is constrained by the [Fe II] 1.2567 μm/Paβ 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 (Lion) to the supernova rate (SNr), Lion/(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. Observations reported in this paper were obtained with the Multiple Mirror Telescope, which is operated jointly by the Smithsonian Astrophysical Observatory and the University of Arizona.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- February 2000
- DOI:
- 10.1086/308388
- arXiv:
- arXiv:astro-ph/9909316
- Bibcode:
- 2000ApJ...530..688A
- Keywords:
-
- GALAXIES: ACTIVE;
- GALAXIES: NUCLEI;
- GALAXIES: STELLAR CONTENT;
- INFRARED: GALAXIES;
- Astrophysics
- E-Print:
- Accepted in ApJ (19 pages, 8 figures, uses emulateapj.sty)