Spectral line variability amplitudes in active galactic nuclei

Abstract

We present the results of a long-term variability campaign of very broad-line AGNs with line widths broader than FWHM > 5000 km s −1 . The main goal of our investigation was to study whether the widths of the optical broad emission lines are correlated with the optical intensity variations on timescales of years. Our AGN sample consisted of 10 objects. We detected a significant correlation between optical continuum variability amplitudes and Hβ emission line widths (FWHM) and, to a lesser degree, between Hβ line intensity variations and Hβ equivalent widths. We add the spectroscopic data of variable AGNs from the literature to supplement our sample. The AGNs from other optical variability campaigns with different line-widths helped to improve the statistical significance of our very broad-line AGN sample. After including the data on 35 additional galaxies, the correlation between optical continuum variability amplitudes and Hβ emission line widths becomes even more significant and the probability that this is a random correlation drops to 0.7 percent.

Line profile and continuum variability in the very broad-line Seyfert galaxy Mrk 926

“…All spectra were calibrated to the same absolute [O iii] λ5007 flux of 3.14 ×10 −13 erg s −1 cm −2 . This flux value were used in Kollatschny et al (2006). Durret & Bergeron (1988) and Morris & Ward (1988) all forbidden emission lines in the spectra.…”

“…Osterbrock & Shuder (1982) published emission-line profiles of Mrk 926, reporting that the lines did not vary between July 1978 and December 1979. Kollatschny et al (2006) demonstrated that both continuum and Balmer lines of Mrk 926 varied strongly over a period of eight years between 1990 and 1997.…”

“…Mrk 926 is a Seyfert 1 galaxy with very broad emission lines, its Balmer and helium lines having widths (FWHM) of more than 10 000 km s −1 . In their study of the long-term variability of very broad-line AGNs, Kollatschny et al (2006) demonstrated Mrk 926 has strong Hβ line variability amplitudes.…”

Line and continuum variability in active galaxies

“…For our sample, of the order of 50% of the continuum flux density is likely to be due to the stellar continuum, which is not variable on the time scales discussed here. For more luminous objects this may be of the order of 20% (Kollatschny, Zetzl & Dietrich 2006b). This indicates that the pure nuclear continuum variability which is not contaminated by stellar flux may in general be larger by up to 50%.…”

“…The data for the NLS1 sources ESO 012-G21, NGC 1365, and MKN 1044 are taken from Giannuzzo & Stirpe (1996). The data for the BLS1 sources NGC 7603 and PKS 2349-14 are based on spectra from Kollatschny et al (2000) and Kollatschny et al (2006a), respectively.…”