2014MNRAS.441..513C

In this paper, we present the Spitzer Infrared Spectrograph (IRS) low-resolution spectra of ultraluminous infrared galaxies with Seyfert spectral types from the 1-Jy sample. Among these sources, nine type 1 Seyfert galaxies and 17 type 2 Seyfert galaxies have Spitzer IRS low-resolution observations. For Seyfert 1 sources, we find that all sources have [Nev] and/or [Siv] features, indicating an active galactic nucleus (AGN) nature, while many sources show polycyclic aromatic hydrocarbon (PAH) features, indicative of starburst activity. It is also found that most Seyfert 2 sources have mid-infrared spectra similar to that for Seyfert 1 sources, also indicating an AGN nature, and thus these could be classified as Seyfert 1-like sources. However, only a few sources have a normal Seyfert 2 nature and can be considered to be `pure' Seyfert 2 sources. In addition, it is found that more prominent PAH features are found for Seyfert 2 sources, indicating strong star formation activity.