- dust opacity is concentrated in spiral arms
- spiral interarm regions are ~transparent
- since most blue disk emission comes from arms as well . . .
- => ABSORPTION is CORRELATED with EMISSION
- => disk surface brightness can be
- ~independent of inclination
- WITHOUT high optical depth
- throughout whole disk!
- this is contrary to the results of most surface brightness-inclination
statistical tests, which conclude that disks are generally opaque
- our results are area-weighted, rather than intensity-weighted
- most of the area beyond ~0.5 R 25B
in our grand design spirals
is nearly transparent interarm material