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Issue A&A
Volume 436, Number 2, June III 2005
Page(s) 417 - 426
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20042014



A&A 436, 417-426 (2005)
DOI: 10.1051/0004-6361:20042014

Variability of optical Fe II complex in narrow-line Seyfert 1 galaxy NGC 4051

J. Wang1, J. Y. Wei2 and X. T. He3

1  National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China
    e-mail: wjy@bao.ac.cn
2  National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China
3  Department of Astronomy, Beijing Normal University, Beijing 100875, China
    e-mail: xthe@bun.edu.cn

(Received 15 September 2004 / Accepted 24 January 2005)

Abstract
The variability of optical $\ion{Fe}{ii}$ blends in NGC 4051 is examined from spectra extracted from the AGN Watch program. In our analysis, the $\ion{Fe}{ii}$ complex are subtracted and measured, with the following results. Firstly, the $\ion{Fe}{ii}$ variations were detected in NGC 4051 during a 3-year period. The identified $\ion{Fe}{ii}$ variations followed the variations in continuum closely. Secondly, the EW of $\ion{Fe}{ii}$ is reported to increase with rising continuum flux, which is consistent with previous claims that there is no convincing Baldwin Effect in optical $\ion{Fe}{ii}$. Thirdly, by comparing the variations of H$\beta$ and $\ion{Fe}{ii}$, we find that ${R_{\rm Fe}}$ scales with continuum flux as ${R_{\rm Fe}\propto (5.0\pm0.8) \log(L/M)}$, which is significantly different from the theoretical expectations. Finally, in six selected Seyferts, four out of five Narrow-Line Seyfert 1 galaxies present positive correlation between ${R_{\rm Fe}}$ and the continuum flux. The negative correlations are identified in the remaining two objects that have relatively broad profiles of H$\beta$ ( ${\it FWHM}>1500\rm ~ km\ s^{-1}$). We argue that the difference of electron density of broad line clouds and/or variability behavior of incident high-energy radiation can explain the dichotomy in variability behavior of ${R_{\rm Fe}}$.


Key words: galaxies: active -- galaxies: individual: NGC 4051 -- galaxies: quasars: emission lines

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© ESO 2005


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