I am trying to understand some maps of radio emission in e.g the Milky Way. I continue to see in papers that these radio maps report negative values of the flux in Jansky units, although no explanation is given as to why.

For example Figure 1 here: The 1.28 GHz MeerKAT Galactic Center Mosaic and here: Towards a More Complex Understanding of Natal Super Star Clusters with Multiwavelength Observations

enter image description here I am wondering if the negative values are simply due to background subtraction, or if there is something more complicated going on.

If it's just background subtraction, a simple reference explainaing how the background subtraction is done in general would be useful.



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