Other
Scientific paper
Aug 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003basbr..23..149c&link_type=abstract
Boletim da Sociedade Astronômica Brasileira (ISSN 0101-3440), vol.23, no.1, p.149-150
Other
Scientific paper
We present a spectroscopic study of the stellar populations of LINERs and LINER/HII Transition Objects (TOs). Our main goal is to determine whether the stars who live in the innermost regions of these low luminosity active galaxies are in some way related to their emission line properties, which would imply in a link between the stellar population and the gas excitation mechanism. High sinal to noise long-slit spectra in the 3500-5400 Å interval were collected for over 50 galaxies. The sample was selected out of the magnitude limited survey of ~ 500 galaxies of Ho et al (1997), which provides a representative sample of the local universe. The stellar content of these galaxies was examined in entirely empirical terms, both by the measurement of colors and absorption features and by a comparison with non-active galaxies spanning a wide range of stellar populations, from young starbursts to old elliptical galaxies. Our main findings are: No features due to Wolf-Rayet stars were detected in either LINERs or TOs. On the other hand, strong High order Balmer lines (HOBLs) of HI in absorption are ubiquitous in TOs but not in LINERs. About 50% of the TOs exihibit these features, which indicate the presence of 108-109 yr populations. These TOs also have diluted metal absorption lines and somewhat bluer colors than other objects in the sample. Most LINERs and the remaining 50% TOs, on the other hand, have deep metal lines typical of old stellar populations. The presence of intermediate age populations anti-correlates strongly with [OI]/Ha, a critical diagnostic line ratio. For instance, over 90% of nuclei with conspicuous intermediate age populations are weak [OI]-emitters. These findings strongly suggest a link between the stellar populations and the ionization mechanism in TOs. Possible scenarios, including weak circumnuclear starbursts, supernova-remnannts and evolved post-starburst populations, are being examined. By analogy with previous work on starburst + Seyfert 2 composites, we conclude that weak starbursts are the most likely contenders to explain these findings. These starbursts are directly detected in at least a a few cases.
Cid Fernandes Roberto
Gonzalez-Delgado Rosa
Martins Lucimara P.
Schmitt Henrique
Storchi-Bergmann Thaisa
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