The Caldwell Objects

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NGC 4697
Type: Elliptical Galaxy (E6)
/ Lenticular Galaxy (SO)
Con: Virgo
RA:12 h 48.6 m
Dec:-05° 48'
Mag: 9.2; 9.0 (O'Meara)
Dim: 7.1' x 5.4'
SB: 11.6
Dist: 76 million light-years
Disc: William Herschel, 1784
W. H ERSCHEL: [Observed 24
April 1784] Very bright, very
large, suddenly much brighter
in the middle. Resolvable
nucleus. (Η I-39)
GC/NGC: Very bright, large,
little extended toward position
angle ~45°, suddenly much
brighter in the middle to a
nucleus.
NGC 4697 is AN ENORMOUS ELLIPTICAL
system in the southern extension of the Virgo
Cluster and somewhat of a problem child. The
problem is its morphology. In 1925 Edwin
Hubble introduced a system for categorizing
galaxy types, in which he recognized three main
varieties: ellipticals, "normal" spirals, and barred
spirals (see the discussion on page 139).
Ellipticals, Hubble said, were amorphous objects
"ranging from globular to discus shaped," and he
organized them according to their flatness. The
most spherical galaxies he called E0, and the
most flattened ones he called E7. Hubble's
scheme has been slightly revised today, but the
framework is essentially
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the same. Until recently astronomers recognized
NGC 4697 as a typical elliptical system, though
they disagreed on its exact shape; various sources
still list the galaxy as either an E4, an E5, or an E6
system. Recent observations have upped the ante,
suggesting that NGC 4697 is an early-type disk
galaxy with a lenticular (lens-shaped) body — an
S0, in short (see Caldwell 53 for another
example).
Both ellipticals and lenticulars can be lensshaped,
and both have very little gas and dust (in
fact, some ellipticals may have none). Unlike
lenticulars, however, ellipticals show no central
bulges, nor structures like disks or spiral arms. A
classical elliptical galaxy is simply
The Caldwell Objects 207