anemic spiral galaxy
A galaxy with characteristics that are intermediate between
those of a normal spiral galaxy and a lenticular galaxy. Anemic spirals
have smooth, weak spiral arms and a reduced rate of star
formation linked to their deficiency in neutral hydrogen gas. They tend
to occur in rich clusters of galaxies,
suggesting that they may have been stripped of interstellar material through
multiple encounters with other galaxies. This raises the question of whether
anemic spirals mark both a morphological and an evolutionary transition
between normal spirals and lenticulars.
|NGC 4145, an anemic spiral in the Ursa Major cluster
of galaxies. While the spiral arms of this galaxy are punctuated by
some activity, the rest of the galaxy is quite quiet. The likelihood
is that a galaxy like this will soon (in galactic terms) lose the
impetus to form stars and settle down to become a lenticular galaxy.
Image credit : NOAO