Astrophysics (index)about

foreground subtraction

(removing unwanted sources of EMR in intensity mapping)

Foreground subtraction is removing nearer sources of electromagnetic radiation when more distant sources are what is of interest. This can be necessary in intensity mapping (e.g., 21cm experiments or CMB surveys) that have the intention of studying long-term, cosmological effects, given that nearer sources are producing the same wavelength of interest through completely different means, e.g., thermal radiation from nearby sources producing some of the same wavelength of an emission line being mapped.

For cosmological studies, it may be that sources from within the Milky Way are unwanted, and sometimes more distant sources or influences from known structures.

One means determining the likely amount of competing radiation is through correlation of the intensity map data with data from surveys covering sources likely to compete.