The ISO-2MASS AGN survey: on the type-1 sources

We combined the ISOCAM Parallel Mode Survey at 6.7 μ m ($LW2$ filter) with the Two Micron All Sky Survey in order to obtain a powerful tool to search for AGN independent of dust extinction. Using moderate colour criteria $H-K>0.5$ and $K-LW2>2.7$ we have selected a sample of 77 AGN candidates in an effective area of ~10 square degrees. By means of optical spectroscopy we find 24 (~$30\%$) type-1 QSOs at redshifts $0.1 0.8$. About one third of the ISO-2MASS QSOs show so red optical colours, that they are missed in optical and UV AGN surveys like SDSS, 2DF, or HES. With a surface density of about 2 deg$^{\rm - 2}$ down to $R -2 . Since only two of the ISO-2MASS QSOs have also $J-K>2$, the inclusion of the ISO mid-infrared photometry significantly extends the capabilities of the pure 2MASS red AGN survey. We suggest that the newly found red AGN resemble young members of the quasar population, and that quasars spend much of their lifetime in a dust enshrouded phase.