|
I have found an early mention of the intracluster light (= ICL) by Fritz Zwicky in 1951. He was well aware that inter-galactic stars most probably do exist within clusters of galaxies, stars that do not belong to any of the galaxies in a cluster. (I believe that Zwicky plainly saw the inter-galactic light in an image of the Coma Cluster)
As with his discoveries of dark matter and many other things, Zwicky was far ahead of his time;
so far ahead, in fact, that some of his major discoveries were virtually ignored for decades...... simply because they seemed at the time to be 'too far out'.
(of course, Zwicky was also often wrong about things; but that is the occupational hazard if you are creative enough to come up with wild ideas that are not part of the current paradigm)
Intergalactic red giant stars & Planetary Nebulae & Globular Clusters have been detected within clusters of galaxies, objects that do not belong to any specific galaxy within a cluster of galaxies. The orbits and velocities of these intracluster (inter-galaxy) objects are very distinct from the orbital structures of objects belonging to the cluster galaxies.
I suspect that the actual proof that the intracluster light is composed of stars that move in such a way that they cannot be associated with any of the cluster galaxies, may have come very late in the 90 year history of extragalactic astronomy (with Time = 0 being the year of Hubble's first resolution of an external galaxy!)
For instance, in a 1996 paper , Arnaboldi and Freeman et al., ApJ, 472, 145,
were studying the planetary nebulae that belong to Messier 86 , which is a giant elliptical galaxy in the Virgo Cluster of Galaxies, and they found that three of their studied planetaries actually had redshifts similar to that of the Virgo Cluster Core rather than the redshift of M86.
[[ M86 actually has a velocity of approach (!!)(V equals
minus 240 km/s) due (it is believed) to the fact that it is falling into the Virgo Cluster Core. In contrast, the three planetaries with the anomalous velocities had an average recession velocity of 1573 km/s ! ]]
|