We have isolated a sample of 14 candidate variable objects with extended image structure to B _ { J } = 22.5 in 0.284 deg ^ { 2 } of Selected Area 57 .
The majority of candidates are blue ( U - B < 0 ) and relatively compact .
At fainter magnitudes , there is a steep rise in the number of variable objects .
These objects are also compact and blue , and some of them are likely to be truly stellar .
Twelve of the B _ { J } \leq 22.5 candidates have been observed spectroscopically over limited ranges of wavelength and a variety of resulting signal-to-noise .
Three of the four brightest have broad emission lines characteristic of Seyfert 1 galaxies .
The fourth has a highly variable spectrum consistent with Seyfert-like activity .
A fifth candidate has emission line ratios nominally consistent with a Seyfert 2 galaxy .
In most cases where we have not been able to confirm a Seyfert spectroscopic type , the spectra are of insufficient quality or coverage to rule out such a classification .
Based on spectroscopic and photometric redshift information , the majority of candidates have luminosities less than 10 % of the nominal demarkation between QSOs and AGN ( M _ { B } = -23 , H _ { 0 } = 50 km s ^ { -1 } Mpc ^ { -1 } , q _ { 0 } = 0.5 ) .
The surface density of confirmed M _ { B } > -23 AGN to B _ { J } = 22 , including stellar sources , is \sim 40 deg ^ { -2 } , in good agreement with other surveys at this depth .
The confirmed AGN in extended sources make up 36 % of this population .
Thus , the application of a variability criterion to images with extended structure enhances the completeness of the census of active nuclei .
If the majority of our candidates are bona fide AGN , the surface density could be as high as 82 deg ^ { -2 } for M _ { B } > -23 , and 162 deg ^ { -2 } for all luminosities to B _ { J } = 22 , with extended sources contributing up to 33 % of the total .