Galactic cirri in deep optical imaging
  The ubiquitous presence of Galactic cirri in deep optical images represents a
major obstacle to study the low surface brightness features of extragalactic
sources. To address this issue, we have explored the optical properties of
cirri using g, r, i and z bands in the Sloan Digital Sky Survey (SDSS) Stripe82
region. Using state-of-the-art, custom made, image processing techniques,
including the modeling and removal of the instrumental scattered light produced
by the stars, we managed to isolate the optical diffuse emission by the cirri,
allowing their photometric characterization. We find that their optical colors
are driven by the dust column density: The cirri become redder as their 100
$\mu$m emission increases. Remarkably, the optical colors of the Galactic cirri
differ significantly from those of extragalactic sources, with a characteristic
bluer r-i color for a given g-r, allowing one to detect these by using a simple
color relation. Our results show the high potential of deep multi-band optical
photometry, on its own, identifying the presence of cirri at a higher spatial
resolution than those provided by far-infrared observations. The combination of
very deep data and multi-band photometry (as the one produced by LSST and
Euclid) would make it possible to build dust maps of unprecedented quality.
