AAS 201st Meeting, January, 2003
Session 32. Galaxy Evolution and Surveys: ``Far Away"
Oral, Monday, January 6, 2003, 2:00-3:30pm, 608-609

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[32.07] Object Sizes from Reionization to the Present, and the Natural Confusion Limit Expected in Ultradeep Surveys

R. Windhorst, S. Cohen, R. Jansen, S. Odewahn (ASU), S. Driver (ANU), D. Kawata, B. Gibson (Swinburne), J. P. Gardner (GSFC), A. Hopkins (U. Pittsburgh)

We discuss the {\emph natural} confusion limit for the 6m James Webb Space Telescope (JWST; launch planned in 2010), and for the Square Kilometer Array (SKA; becoming reality in a decade). First, we summarize the observed half-light radius vs. flux relation for the galaxy population from the RC3 level to the HDF limit. Together with size estimates from hierarchical models fainter than J(1.35\mu)AB~q28 mag and model extrapolations of the faint galaxy counts from JAB~q28 to 34 mag, we estimate the {\emph natural} confusion limit for JWST due to the finite object sizes.

A rather unexpected result is that for ultradeep surveys with ~q0.1" FWHM resolution, the {\emph natural} confusion limit may become {\emph more} important in the definition of faint source samples than the traditional surface brightness (SB) limits. This may already be somewhat visible in the deepest HDF images for AB\ge25 mag. This does, however, {\emph not} mean that the deepest JWST samples will be fundamentally limited by {\emph natural} confusion. Instead, for JAB\ge28--30 mag, faint objects seen by JWST are likely mostly unresolved at 0.08" FWHM. In this case, the deepest JWST images will be limited only by {\emph instrumental} confusion (i.e., by the telescope FWHM), which doesn't set in until around JAB\ge33.5 mag.

Last, we compute the SKA {\emph natural} confusion limit from the JWST results, assuming that the same population of faint irregular, peculiar and merging/star-forming objects that dominates the faint galaxy counts likely dominates the radio source counts at nanoJansky levels. The SKA will need to have resolutions better than 50--100 m.a.s. (FWHM) to not run into the {\emph instrumental} confusion limit at nanoJy levels. At S1.4~q10 nanoJy, the SKA will likely not run into the {\emph natural} confusion limit, {\emph if} the slope of the nanoJy counts remains below \gamma\le1.7 {\emph and if} the ratio of radio to optical--near-IR sizes remains close to unity.

We acknowledge funding from NASA Grant NAG5-12460.

If you would like more information about this abstract, please follow the link to http://www.stsci.edu/ngst/science/simulations/. This link was provided by the author. When you follow it, you will leave the Web site for this meeting; to return, you should use the Back comand on your browser.

The author(s) of this abstract have provided an email address for comments about the abstract: Rogier.Windhorst@asu.edu

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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.