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Title:
Clues to Active Galactic Nucleus Growth from Optically Variable Objects in the Hubble Ultra Deep Field
Authors:
Cohen, S. H.; Ryan, R. E., Jr.; Straughn, A. N.; Hathi, N. P.; Windhorst, R. A.; Koekemoer, A. M.; Pirzkal, N.; Xu, C.; Mobasher, B.; Malhotra, S.; Strolger, L.-G.; Rhoads, J. E.
Affiliation:
AA(Department of Physics and Astronomy, Arizona State University, Tempe, AZ 85287-1504 ), AB(Department of Physics and Astronomy, Arizona State University, Tempe, AZ 85287-1504), AC(Department of Physics and Astronomy, Arizona State University, Tempe, AZ 85287-1504), AD(Department of Physics and Astronomy, Arizona State University, Tempe, AZ 85287-1504), AE(Department of Physics and Astronomy, Arizona State University, Tempe, AZ 85287-1504), AF(Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218), AG(Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218), AH(Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218), AI(Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218), AJ(Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218), AK(Space Telescope Science), AI(Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218), AJ(Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218), AK(Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218), AL(Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218)
Publication:
The Astrophysical Journal, Volume 639, Issue 2, pp. 731-739. (ApJ Homepage)
Publication Date:
03/2006
Origin:
UCP
ApJ Keywords:
Black Hole Physics, Galaxies: Active, Galaxies: Formation, Galaxies: Nuclei
DOI:
10.1086/499577
Bibliographic Code:
2006ApJ...639..731C

Abstract

We present a photometric search for objects with point-source components that are optically variable on timescales of weeks to months in the Hubble Ultra Deep Field (HUDF) to i'AB=28.0 mag. The data are split into four substacks of approximately equal exposure times. Objects exhibiting the signature of optical variability are selected by studying the photometric error distribution between the four different epochs and selecting 622 candidates as 3.0 σ outliers from the original catalog of 4644 objects. Of these, 45 are visually confirmed as free of contamination from close neighbors or various types of image defects. Four lie within the positional error boxes of Chandra X-ray sources, and two of these are spectroscopically confirmed AGNs. The photometric redshift distribution of the selected variable sample is compared to that of field galaxies, and we find that a constant fraction of ~1% of all field objects show variability over the range of 0.1<~z<~4.5. Combined with other recent HUDF results, as well as those of recent state-of-the-art numerical simulations, we discuss a potential link between the hierarchical merging of galaxies and the growth of AGNs.
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