Astronomy and Astrophysics – Astrophysics
Scientific paper
Jan 2012
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2012aas...21940307y&link_type=abstract
American Astronomical Society, AAS Meeting #219, #403.07
Astronomy and Astrophysics
Astrophysics
Scientific paper
Ever since their discovery, the nature of low ionization nuclear emission-line regions (LINERs) has been hotly debated. Some authors treat them as AGNs, others argue they are not AGNs but powered by shocks or hot old stars. No universal agreement has been reached. On the other hand, early-type galaxies frequently contain spatially extended warm ionized gas and have spectra similar to LINERs. How is this large-scale emission related to the nuclear LINERs? Because LINER-like spectrum is the most common spectral type found in early-type galaxies in both nuclear and integrated spectra, understanding its nature is important to numerous topics in astrophysics.
By comparing nuclear aperture spectroscopy from the Palomar survey with larger scale data from the Sloan Digital Sky Survey, we find the line emission in the majority of passive red galaxies is spatially extended. We detect strong line ratio gradients with radius in [NII]/Halpha, [SII]/Halpha, and [OIII]/[SII], requiring the ionization parameter to increase outwards. Combined with a realistic gas density profile, this outward increasing ionization parameter convincingly rules out AGN as the dominant ionizing source, and strongly favors distributed ionizing sources. Sources that follow the stellar density profile can additionally reproduce the observed luminosity-dependence of the line ratio gradient. Post-AGB stars provide a natural ionization source candidate, though they have an ionization parameter deficit. Velocity width differences among different emission lines disfavor shocks as the dominant ionization mechanism, and suggest that the interstellar medium in these galaxies contains multiple components. We conclude that the line emission in most LINER-like galaxies found in large aperture (>100pc) spectroscopy is not primarily powered by AGN activity and thus does not trace the AGN bolometric luminosity. However, they can be used to trace warm gas in these early-type galaxies.
Blanton Michael R.
Yan Renbin
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