We present near-infrared spectroscopic observations for a sample of ten optically faint luminous infrared galaxies ( R - [ 24 ] \geq 14 ) using Keck NIRSPEC and Gemini NIRI .
The sample is selected from a 24 \mu m Spitzer MIPS imaging survey of the NDWFS Boötes field .
We measure accurate redshifts in the range 1.3 \raisebox { -2.58 pt } { $ \stackrel { \raisebox { -0.86 pt } { $ \textstyle < $ } } { \sim } $% } z \raisebox { -2.58 pt } { $ \stackrel { \raisebox { -0.86 pt } { $ \textstyle < $ } } { \sim } $ } % 3.4 .
Based on either emission line widths or line diagnostics , we find that all ten galaxies harbor luminous AGN .
Seven sources are type I AGN , exhibiting broad ( > 1900 km s ^ { -1 } ) H \alpha or H \beta emission lines ; the remaining three are type II AGN .
Given their large mid-IR luminosities and faint optical magnitudes , we might expect these sources to be heavily extincted quasars , and therefore only visible as type II AGN .
The visibility of broad lines in 70 % of the sources suggests that it is unlikely that these AGN are being viewed through the mid-plane of a dusty torus .
For four of the sources we constrain the H \alpha /H \beta Balmer decrement and estimate the extinction to the emission line region to be large for both type I and type II AGN , with A _ { H \alpha } \raisebox { -2.58 pt } { $ \stackrel { \raisebox { -0.86 pt } { $ \textstyle > % $ } } { \sim } $ } 2.4 - 5 mag .
Since the narrow-line region is also extincted and the UV continuum emission from the host galaxies is extremely faint , this suggests that much of the obscuration is contributed by dust on large ( \sim kpc ) scales within the host galaxies .
These sources may be examples of `` host-obscured '' AGN which could have space densities comparable or greater to that of optically luminous type I AGN with similar bolometric luminosities .