The IRAC Ultradeep Field (IUDF) combines all ultradeep data ever taken with the Spitzer Infrared Array Camera (IRAC) at 3.6μm and 4.5μm over GOODS-South and the HUDF (+ parallels). The deepest observations come from the IRAC Ultra Deep Field (IUDF, ID 70145, PI Labbé) and IRAC Legacy over GOODS (IGOODS, PID 10076, PI Oesch) programs, combined with archival data from GOODS (PID 194, PI Dickinson), S-CANDELS (PID 70204, PI Fazio), ERS (PID 80217, PI Fazio), and UDF2 (PID 30866, PI Bouwens).
Data Release v0.9
- The combined IRAC images in this data release amount to 1500 hour total integration time. The coverage at 3.6μm and 4.5μm is unprecedented: ranging from >50 hour over 150 arcmin2, and >100 hour over 60 sq arcmin2, to ∼200 hour over 5 − 10 arcmin2. The increase in sensitivity compared to 25 hour data is about a factor of 3 in the deepest parts of the image. The images are drizzled on a 0.3" arcsec grid and the image quality is a constant FWHM=1.49" over the field. The background is flat to AB 31 mag / arcsec2 over scales of ~ arcminutes.
- To facilitate prior-based WFC3+IRAC photometry, we introduce a new procedure to create very high signal-to-noise PSFs from the IRAC data and to reconstruct the complex spatial variation due to survey geometry. We publicly release the PSF maps.
- Simulations using WFC3 priors to extract IRAC fluxes show that the point source sensitivity in the ultradeep IRAC images decreases approximately as the square root of integration time over the range 20 − 200 hours, reaching 1σ point source sensitivities as faint as of 15 nJy (28.5 AB) at 3.6μm and 19 nJy (28.2 AB) at 4.5μm.
- The primary aim of the ultradeep observations is to directly detect the infrared light of reionization epoch galaxies at z > 7 and to constrain their stellar populations. The value of such ultradeep IRAC data is illustrated by direct detections of z = 7 − 8 galaxies as faint as HAB = 28.