GOODS Optically Variable Galaxy Nuclei and Their Multiwavelength Properties

In both GOODS fields, the survey's HST/ACS observations were taken in five epochs with uniform ˜ 45-day spacing, for the primary purpose of high-z supernova detection and follow-up. However, this combination of sensitivity, high resolution, and time spacing is also well-suited to detecting optical variables (OVs) among ˜ 50000 moderate-z galaxy nuclei on rest-frame timescales of weeks to months. The overwhelming majority of these variable galaxy nuclei will be AGN; the small fraction arising from SNe have already been meticulously culled by the high-z SNe search effort. Previous OV studies in the HDF-N have shown relatively poor overlap with X-ray-identified AGN from CXO 2-Msec observations. Thus OV galaxy nuclei potentially represent a significant addition to the census of distant AGN subject to multiwavelength scrutiny with GOODS. We present the results of our z-band variability analysis, including the discovery of ˜ 170 ``significantly variable'' galaxy nuclei at z850 < 24.5AB whose light-curve excess variance is statistically inconsistent with non-variability at the 10-4 level or better. Although the GOODS sensitivity is less than previous two-epoch OV searches in the HDF-N, the much larger GOODS area compared to HDF-N results in a several-fold increase to the number of known OV AGN in the Chandra Deep Fields. Moreover, the GOODS OVs are broadly distributed in redshift out to z ˜ 1.3, comparable to the redshift distribution of the Chandra Deep Field sources.