Photometry of Partially Overlapping Galaxies
- use non-overlapping parts & symmetry to estimate
- how much light from background galaxy is lost
- in passing through foreground spiral
--> DIRECT measure of opacity in foreground spiral
Benefits
- direct (non-statistical)
- no selection against high opacity regions
- purely differential photometry (no calibrations)
- large area coverage
- need no corrections for:
- internal extinction of background galaxy
- extinction of Milky Way
Disadvantages
- few reasonable objects
- dependent on galaxy symmetry