# Galactic cirri in deep optical imaging

## TL;DR

This study characterizes Galactic cirri in deep optical images using SDSS data, revealing their optical colors, relation to dust, and potential for high-resolution dust mapping with future surveys.

## Contribution

It introduces a novel method to isolate and analyze Galactic cirri in optical images, demonstrating their color properties and distinguishing them from extragalactic sources.

## Key findings

- Cirri become redder with increased 100 μm emission.
- Optical colors of cirri differ from extragalactic sources, with bluer r-i colors.
- Deep multi-band photometry can identify cirri at high resolution.

## Abstract

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.