Ultra-deep Large Binocular Camera U-band Imaging of the GOODS-North Field: Depth Versus Resolution

Abstract

We present a study of the trade-off between depth and resolution using a large number of U-band imaging observations in the GOODS-North field from the Large Binocular Camera (LBC) on the Large Binocular Telescope (LBT). Having acquired over 30 hr of data (315 images with 5-6 minutes exposures), we generated multiple image mosaics, starting with the best atmospheric seeing images (FWHM ≲ 0.″8), which constitute ∼10% of the total data set. For subsequent mosaics, we added in data with larger seeing values until the final, deepest mosaic included all images with FWHM ≲ 1.″8 (∼94% of the total data set). From the mosaics, we made object catalogs to compare the optimal-resolution, yet shallower image to the lower-resolution but deeper image. We show that the number counts for both images are ∼90% complete to U <SUB> AB </SUB> ≲ 26 mag. Fainter than U <SUB> AB </SUB> ∼ 27 mag, the object counts from the optimal-resolution image start to drop-off dramatically (90% between U <SUB> AB </SUB> = 27 and 28 mag), while the deepest image with better surface-brightness sensitivity ({μ }<SUB>U</SUB><SUP>{AB</SUP>} ≲ 32 mag arcsec<SUP>-2</SUP>) show a more gradual drop (10% between U <SUB> AB </SUB> ≃ 27 and 28 mag). For the brightest galaxies within the GOODS-N field, structure and clumpy features within the galaxies are more prominent in the optimal-resolution image compared to the deeper mosaics. We conclude that for studies of brighter galaxies and features within them, the optimal-resolution image should be used. However, to fully explore and understand the faintest objects, the deeper imaging with lower resolution are also required. Finally, we find—for 220 brighter galaxies with U <SUB> AB </SUB> ≲ 23 mag—only marginal differences in total flux between the optimal-resolution and lower-resolution light-profiles to {μ }<SUB>U</SUB><SUP>{AB</SUP>} ≲ 32 mag arcsec<SUP>-2</SUP>. In only 10% of the cases are the total-flux differences larger than 0.5 mag. This helps constrain how much flux can be missed from galaxy outskirts, which is important for studies of the Extragalactic Background Light. <P />Based on data acquired using the Large Binocular Telescope (LBT).