Understanding the AGN-Host Connection in Broad Mgii Emission Selected
  AGN-Host Hybrid Qausars
  We study the issue of AGN-host connection in intermediate-z (1.2>z>0.4)
galaxies with hybrid spectra (hybrid QSOs for short). The observed spectra
redward of the Balmer limit are dominated by starlight, and the spectra at blue
end by both an AGN continuum and a MgII broad emission line. Such unique
property allows us to examine both AGN and its host galaxy in individual galaxy
simultaneously. At first, 15 hybrid QSOs are selected from the Sloan Digital
Sky Survey Data Release 6. The spectra are then analyzed in detail in three
objects: SDSS J162446.49+461946.7, SDSS J102633.32+103443.8 and SDSS
J090036.44+381353.0. Our spectral analyzing shows that the current star
formation activities are strongly suppressed, and that the latest burst ages
range from ~400Myr to 1Gyr. Basing upon the MgII-based black hole masses, the
three hybrid QSOs are consistent with the D_n(4000)-L/L_{Edd} sequence that was
previously established in local AGNs. The three hybrid QSOs are located in the
middle range of the sequence, which implies that the hybrid QSOs are at the
transition stage not only from young to old AGN, but also from host-dominated
phase to AGN-dominated phase.
