Infrared Photometric Study for the IRAS 1 Jy Sample of Ultraluminous Infrared Galaxies

The Two Micron All Sky Survey observation of the IRAS 1 Jy sample of ultraluminous infrared galaxies (ULIRGs) is presented in this paper. Together with the IRAS photometric data, the properties and energy sources of the IRAS 1 Jy sample of ULIRGs in the near- and far-infrared are discussed. It is shown that most sources, not only Seyfert galaxies but also H II and LINER galaxies, have a radiation mechanism with a power-law continuum in the near-infrared. All Seyfert 1 sources and some Seyfert 2 sources with hidden broad-line regions (BLRs) have much redder colors and steeper spectral indices in the near-infrared, indicative of an extremely strong energy source from the central active galactic nucleus. Almost all sources have thermal radiation indicative of starburst domination in the IRAS region; in particular, all Seyfert 1 sources and many Seyfert 2 sources with hidden BLRs have lower [25]-[60] colors, indicative of a flatter spectral continuum and a rather warm color temperature in the 25-60 μm region. However, all kinds of sources have similar [60]-[100] color distributions, indicative of similar energy sources from the enhanced heating in active star-forming regions and very cold material and also indicative of the quite small influence from the central activity in the 60-100 μm region. In addition, all Seyfert 1 sources and some Seyfert 2 sources with hidden BLRs have much larger absolute magnitudes in the K band compared with other sources. The results presented in this paper may further help us to understand the physical properties of ULIRGs.

This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center, funded by the National Aeronautics and Space Administration and the National Science Foundation.