THE EXCITATION MECHANISM OF [FE-II] 1.644 MICRON EMISSION IN SEYFERT AND STARBURST GALAXIES REVISITED

In a previous paper (Mouri et al. 1990), we studied the origin of [Fe II] 1.644 mum emission in galaxies with starburst nuclei (SBNs) and active galactic nuclei (AGNs), by comparing the intensity ratio of [Fe II]/Brgamma with those of optical emission lines. A linear correlation was found between [Fe II]/Brgamma and [O I] lambda6300/Halpha. Since the [O I] line is excited in partly ionized regions which are created by shocks in SBNs and by X-rays from Seyfert nuclei in AGNs, it was suggested that (1) [Fe II]/Brgamma is determined by the volume ratio of partly ionized to fully ionized regions, (2) the [Fe II] emission in SBNs is powered by shocks, and (3) the [Fe II] emission in AGNs is due to photoionization by the nonthermal sources. However, it is also argued that [Fe II]/Brgamma is controlled by the fraction of iron depleted into dust grains. Some researchers claim that the [Fe II] emission in SBNs comes from photodissociation regions situated near OB stars, while others claim that the [Fe II] emission in AGNs comes from circumnuclear starburst regions. Taking account of this situation, we reexamine the observational properties of [Fe II] in SBNs and AGNs in detail. It is concluded that (1) the grain depletion effect is unimportant to the observed [Fe II]/Brgamma ratio, (2) the contribution of [Fe II] from photodissociation regions is negligible in SBNs, and (3) the [Fe II] emission in AGNs is in principle associated with the nuclear activity.