The Blanco telescope from CTIO,
and the sky as it would appear if your eye could see both optical and
radio wavelengths. Blue and purple nebulosity shows hydrogen gas, which
connects the Small Magellanic Cloud (at top right) and the Large
Magellanic Cloud (middle right) and also stretches across the sky. Green
circles show some of the DECam pointings of the SMASH survey,
indicating the area over which Magellanic Cloud stars have been found.
Image Credit: K. Olsen (NOAO/AURA/NSF), SMASH team, Roger Smith, and
McClure-Griffiths.
DECam on the Blanco 4-m Telescope at CTIO.
SMASH DECam image in the Small Magellanic Cloud with moon for scale.
The Magellanic Clouds are the two brightest nearby satellite galaxies
to our own Milky Way galaxy. From a new study it appears that not only
are they much bigger than astronomers calculated, but also have
non-uniform structure at their outer edge, hinting at a rich and complex
field of debris left over from their formation and interaction. This is
an early result from a survey called SMASH, for “Survey of the
MAgellanic Stellar History”, carried out by an international team of
astronomers using telescopes that include the Blanco 4-meter at Cerro
Tololo Inter-American Observatory (CTIO) in Chile and presented today at
the 225th meeting of the American Astronomical Society in Seattle,
Washington.
The Large and Small Magellanic Clouds are dominant features in the
Southern hemisphere sky. Although named after explorer Ferdinand
Magellan who brought them to the attention of Europeans, they were
already known to every early culture in the Southern hemisphere. The
Large Cloud (LMC), covering about 5 degrees in angular size (10 lunar
diameters), appears to the naked eye like a detached piece of the Milky
Way. At a distance from us of about 160 thousand light years, even the
brightest stars in these galaxies can’t be seen without a telescope.
As principal investigator Dr. David Nidever (University of Michigan)
says, “We have a decent understanding of how large galaxies like the
Milky Way form, but most galaxies in the universe are faint, distant,
dwarf galaxies. The Magellanic Clouds are two of the few nearby dwarf
galaxies, and SMASH is able to map out and study the structures in them
like no other survey has been able to do before.”
“We knew from the earlier work of SMASH team
members that the LMC was larger than we thought, but those observations
probed only 1 percent of the area that we need to explore. SMASH is
probing an area 20 times larger, and is confirming beyond doubt that the
LMC is really large while also giving us a chance to map its structure
in detail.” said Dr. Knut Olsen (National Optical Astronomy Observatory)
one of the leaders of the SMASH team. The team has identified stars
belonging to the LMC at angular distances up to 20 degrees away,
corresponding to 55 thousand light years. This was done using a new
camera, dubbed DECam, mounted on the CTIO Blanco 4-meter telescope,
which allows the SMASH team to identify faint stars over a much larger
area than ever before.
With the Blanco telescope, SMASH can detect exceptionally diffuse
stellar structures – up to 400,000 times fainter than the appearance of
the faint band of the Milky Way in the night sky. This is possible
because DECam can distinguish individual faint Magellanic stars over a
huge area. (In astronomical parlance, the survey can reach a surface
brightness limit of ~35 magnitudes per square arc second). That allows
the team to detect stellar structures that were previously much too
faint to see.
The team is also exploring the Magellanic Stream, a gaseous structure
that connects the two Clouds and extends in front and behind them. The
existence of the Magellanic Stream, first detected with radio telescopes
over 30 years ago, clearly indicates that the two galaxies are
interacting with each other and with our Milky Way. Astronomers have
long expected to also find stars in the Stream but so far none have been
detected. It’s likely this is because the stellar component of the
Stream is too faint to have been detected until the availability of the
new camera. As Dr. Nidever said, “SMASH’s ability to reveal super-faint
stellar structures should not only allow us to finally detect the
stellar component of the Magellanic Stream but also map out its
structure which will give us a much better understanding of the
Magellanic Clouds’ interaction history.”
Cerro Tololo Inter-American Observatory is managed by National
Optical Astronomy Observatory which is operated by Association of
Universities for Research in Astronomy Inc. under a cooperative
agreement with the National Science Foundation.
Science Contacts
Dr. David Lee Nidever
University of Michigan, Ann Arbor
Department of Astronomy
dnidever@umich.edu
astro.lsa.umich.edu/~dnidever
434.249.6845
Dr Knut Olsen
National Optical Astronomy Observatory
950 N Cherry Ave, Tucson AZ 85719 USA
kolsen@noao.edu
