Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011aas...21734709w&link_type=abstract
American Astronomical Society, AAS Meeting #217, #347.09; Bulletin of the American Astronomical Society, Vol. 43, 2011
Astronomy and Astrophysics
Astronomy
Scientific paper
We review the instrumental and natural confusion limits for the 6.5m James Webb Space Telescope (JWST), which apply to mostly unresolved or mostly resolved objects, resp. For ultradeep JWST surveys with 0.08" FWHM resolution, the natural confusion limit may become more important for the definition of faint object samples than the survey surface brightness (SB) limit. This effect may already be visible in the deepest HUDF images for AB>25 mag. This does, however, not mean that the deepest JWST samples will be fundamentally limited by natural confusion. Instead, from hierarchical simulations we argue that for AB>28 mag, faint objects seen by JWST are likely mostly unresolved at 0.08" FWHM. For these objects, instrumental confusion doesn't set in until AB>33.5 mag, a limit which even JWST will not reach. Does this therefore mean that the confusion limit is irrelevant for JWST?
We show that gravitational lensing will lead to a correlation between the sky positions of high redshift candidates and bright foreground galaxies, and present evidence for this correlation among a sample tentatively identified at z 10.6. By extrapolating the evolution of the galaxy LF-slope and amplitude to z>8, we suggest that gravitational lensing may dominate the observed properties of galaxies at z>10 discovered by JWST. The observed surface density of galaxies at z 12-15 will likely be boosted by an order of magnitude, and most z>12-15 galaxies may well be part of a multiply-imaged system, located less than 1 arc-second from a brighter foreground galaxy.
This means that deep JWST surveys of the First Light epoch at z>10 may be limited by "gravitational" confusion, where a good part of the First Light "forest" may be gravitationally amplified by the foreground galaxy "trees". Lensing bias will therefore need to be carefully considered for First Light studies with JWST.
Mao Shijun
Windhorst Rogier A.
Wyithe Stuart J. B.
Yan Hui
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