AAS 205th Meeting, 9-13 January 2005
Session 163 New Results from the Great Observatories Origins Deep Survey
Special Session, Thursday, January 13, 2005, 2:00-3:30pm, Town and Country

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[163.08] GOODS Optically Variable Galaxy Nuclei and Their Multiwavelength Properties

N. A. Grogin (JHU), A. T. Steffen, W. N. Brandt (PSU), M. Paolillo (U. of Naples), A. M. Koekemoer (STScI), E. J. Schreier (AUI)

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.

We compare the overlap of GOODS OVs with known Chandra sources; present the X-ray properties, including X-ray variability, of Chandra-detected OVs; and comment on X-ray stacking analyses of Chandra-undetected OVs to investigate the nature of these potentially X-ray underluminous AGN. We discuss future prospects, including the extension of the z-band light-curves to > 1yr baselines with existing and upcoming post-GOODS SNe-search epochs, and the potential detection of rest-frame NIR variability with SST/IRAC re-visits of the GOODS fields.

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© 2004. The American Astronomical Society.