Around a Galaxy, A Pocket Full of Stars...
Zoom from a Digitized
Sky Survey color image of the field
around the ring galaxy AM 0644-741
and dissolve into the Hubble Advanced
Camera for Surveys image. A pan
along the star-forming regions of
the bright ring is also included.
HST ACS Image of AM 0644-741
NASA, ESA, and The Hubble Heritage
NASA, Z. Levay and G. Bacon (STScI)
to know the Lindsay-Shapley Ring
Higdon (Cornell University) and Ian
as "AM0644-741" in the Catalog
of "Southern Peculiar Galaxies and
Associations" by Halton Arp and Barry
Madore, this beautiful system is also
known as the "Lindsay-Shapley Ring"
after its discoverers. Eric
Lindsay, a student under Harlow
Shapley, was the first to publish
on the existence of the eccentric elliptical
ring in 1960. AM 0644-741 is situated
in the southern sky close to the Large
Magellanic Cloud (LMC), a close companion
galaxy of the Milky Way. As a result,
it was at first unclear if AM0644-741
was a distant background object. Because
of its proximity to the LMC and the lack
of confirming radial velocity data, Lindsay
and Shapley suggested it might be some
sort of stellar remnant. Astronomer John
A. Graham first positively identified
it as "a peculiar southern ring galaxy"
in 1974 by observing the object spectroscopically.
Later known as "Graham's Ring Galaxy,"
AM 0644-741 resides nearly 300 million
light-years away, and is over 150,000
light years in diameter, making it larger
than our home galaxy.
is not the first time that Hubble has
captured a ring galaxy. In 1995, Hubble's
Wide Field Planetary Camera 2 imaged The
Cartwheel ring galaxy. They have several
conspicuous differences which can be attributed
to differences in the pre-interaction
"target" galaxies and details
in the collisions. For example, AM0644-741's
nucleus is displaced far from the ring's
center, whereas the Cartwheel's nucleus
is very nearly at the center. This is
from the "intruder" galaxies
impacting the "target" disks
at slightly different radii. In the Cartwheel,
the "intruder" scored a nearly
perfect hit on the center of the "target".
In AM 0644-741, the "intruder"
passed through the disk roughly half-way
out. Note that unlike AM0644-741 the Cartwheel
has a small second ring close to its nucleus.
But unlike the Cartwheel, AM0644-741's
large outer ring resembles a coiled rope
wrapped around the nucleus.
collection of imaging data shows the
environment around AM 0644-741 in ground-based
radio, IR, and optical wavelengths. Just
as color photographs provide much more
information about a scene than does a
black-and-white photo, by examining a
region of the sky in more than one wavelength,
much can be gleaned about what is going
on. A brief tour of the region around
AM0644-741 is given by successively stepping
through multi-wavelength data collected
from various astronomical facilities starting
at very long wavelengths (radio), and
proceed on up through the optical.
other groundbased images of AM 0644-74