Ultraviolet detection of very low-surface-brightness objects

The night-sky surface brightness at excellent ground-based sites is compared to the sky background in space. In directions typical of extragalactic pointings, the background in the space ultraviolet reaches 26 mag/sq arcsec for the wavelength 2000 A, which is a factor of 40 darker than at any wavelength on the ground. This represents an important new 'window' for the study of extragalactic systems with low surface brightness. Taking into account the UV/V energy distributions of potential targets, it is found that in certain favorable circumstances UV photometry may permit the detection of regions with equivalent V band surface brightness as low as 35 mag/sq arcsec, or over 100,000 times fainter than the ground-based sky.