The Caldwell Objects

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Now, if you push your telescope 35' due east of
the center point between NGC 3607 and 3608,
you will encounter a 10th-magnitude star. NGC
3626 sits alone just about 15' northeast of that
star. NGC 3626 is only 0.2 magnitude (20 percent)
fainter than NGC 3608, so look for something
similarly bright when you search for the
Caldwell galaxy.
NGC 3626 is inclined 48° from face on. With
the 4-inch at 23x and averted vision it looks like a
slightly out-of-focus star south of a flattened
keystone of dim suns. (With direct vision the
galaxy just looks like another star.) Lenticular
galaxies are known for being small and bright,
packing a lot of light into their lens-shaped
bodies. NGC 3626 is no exception, though its
distance places it at a disadvantage. The galaxy is
three and a half times farther from Earth than
Leo's celebrated M65. If NGC 3626 were at M65's
distance it would blaze at magnitude 8.3 (a full
magnitude brighter than M65) and be a truly
stunning sight, even outperforming the lenticular
wonder NGC 5866 in Draco (see page 432). NGC
3626 is a large system, with a physical diameter
of 70,000 light-years and a total mass of 120
billion Suns.
Alas, even at 130x the galaxy shows very
little detail in the 4-inch. A dim outer halo surrounds
a brighter lens-shaped oval that hugs the
galaxy's needle-sharp nucleus. With a long,
intense look I convinced myself that the inner
lens's light distribution is not entirely uniform,
though the slight intensity differences are fleeting
at best. If yours is a small telescope, do not
fret. Most lenticular galaxies are notoriously
bland. Even with her 20-inch reflector Barbara
Wilson saw no outstanding details in NGC 3626.
Indeed, even in the plates taken with the 48-inch
Schmidt telescope atop Palomar Mountain (one
of which is reproduced on page 159), the galaxy
looks like three gray ovals of varying intensity
superimposed on one
160
another; the brightest oval is skewed counterclockwise
with respect to the smooth, symmetrical
outer envelope. CCD images can
penetrate the core that so often is burned out in
photographs, and they reveal a pinpoint nucleus
as well as a suggestive hint of obscuring dust in
the eastern half of the inner lens.
In a 1998 Astrophysical Journal paper, Daniela
Bettoni (Astronomical Observatory of Padova,
Italy) and her colleagues reported a massive
counter-rotating disk of molecular gas in NGC
3626. The gas is swimming against the tide, so to
speak, of the stars in the galaxy's disk. This
finding is not unprecedented. In 1992 Vera Rubin
(Carnegie Institute of Washington) discovered
that almost half of the stars in the disk of Virgo's
NGC 4550 were orbiting in the direction opposite
that of the galaxy's other stars. In other words,
NGC 4550 appears to contain two disks, one
spinning clockwise as seen from Earth, the other
counterclockwise. (Anyone who has been to the
Vatican will appreciate this discovery, for the
Vatican has an intricate double-spiral staircase in
which ascending visitors never meet descending
ones, even though the spirals are concentric.)
Other galaxies that show this cospatial counterrotation
are NGC 4826 in Coma Berenices, NGC
7217 and NGC 7332 in Pegasus,
Deep-Sky Companions: The Caldwell Objects