The physical connections among infrared QSOs, palomar-green QSOs, and narrow-line Seyfert 1 galaxies

We study the properties of infrared- selected QSOs ( IR QSOs), optically selected Palomar- Green QSOs ( PGQSOs), and narrow- line Seyfert 1 galaxies ( NLS1s). We compare their properties from the IR to the optical and examine various correlations among the black hole mass, accretion rate, star formation rate, and optical and IR luminosities. We find that the IR excess in IR QSOs is mostly in the far- IR, and their IR spectral indices suggest that the excess emission is from low- temperature dust heated by starbursts rather than active galactic nuclei ( AGNs). The IR excess is therefore a useful criterion to separate the relative contributions of starbursts and AGNs. We further find a tight correlation between the star formation rate and the accretion rate of central AGNs for IR QSOs. The ratio of the star formation rate and the accretion rate is about several hundred for IR QSOs but decreases with the central black hole mass. This shows that the tight correlation between the stellar mass and the central black hole mass is preserved in massive starbursts during violent mergers. We suggest that the higher Eddington ratios of NLS1s and IR QSOs imply that they are in the early stage of evolution toward classical Seyfert 1 galaxies and QSOs, respectively.