Association of galaxies at disparate redshifts. There are some amazing cases of objects with wildly different redshifts but showing the appearance of direct interaction. No two seem to be of the same kind, and there are more or less plausible ad hoc conventional interpretations depending on how much of a statistical fluke one is willing to believe out of a given number of galaxies. Some of the most notorious cases are Stephan's Quintet, NGC 4319/Mkn 205, and NGC 7603. Stephan's Quintet is a compact group (probably the first to be found) in which four of the members have redshifts cz = 5700 - 6700 km/s, while the remaining member NGC 7320 has redshift only 800 km/s, close to that of the bright spiral NGC 7331 only abour 1/2° away. NGC 7320 is of larger angular size than the other members, but only less than a factor 2. NGC 7320 shows a low-surface-brightness tail approximately opposite the other group members. Detection of even fainter structure is thwarted by especially strong galactic "cirrus" reflection in this area. Sizes of H II regions have been used to argue for various distances, but as Kennicutt has shown,
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This note was uploaded on 11/10/2011 for the course AST AST1002 taught by Professor Emilyhoward during the Fall '10 term at Broward College.