FOR RELEASE: 9:20 AM EST, JANUARY 8, 2004
`INFANT GALAXIES' DISCOVERED IN NEARBY GALAXY GROUP
A team of astronomers have discovered objects in the nearby M81 Galaxy Group
that may be small, young galaxies that have only recently formed. If
confirmed, these objects would be among the nearest examples of tidal dwarf
galaxies--small galaxies formed from gas expelled from a larger galaxy due
to gravitational interactions with other galaxies in the group. A report
of their work is being presented today at the American Astronomical Society
meeting in Atlanta, Georgia.
The team members presenting the report at the meeting include Megan DeCesar,
an undergraduate student at Penn State University in University Park, Pennsylvania;
Patrick Durrell, a research associate at Penn State; and John Feldmeier,
a research associate at Case Western Reserve University in Cleveland, Ohio,
and a National Science Foundation Astronomy and Astrophysics Postdoctoral
Fellow. Other team members include Robin Ciardullo, professor of astronomy
and astrophysics at Penn State; and Denise Hurley-Keller, research associate
at Case Western Reserve University and a National Science Foundation Astronomy
and Astrophysics Postdoctoral Fellow.
To find these curious objects, the team used the 100-Megapixel CCD camera
of the Canada-France-Hawaii Telescope
(CFHT), which can image a area of the sky 1.5 times the area of the Full
Moon. In their search of the "empty'' regions between the galaxies
M81 and NGC 3077, the team found two small clumps of bright blue stars.
These clumps, each of which are over 3000 light years across, have never
been observed before and may reflect the initial burst of star formation
in newly formed galaxies.
Figure 1 : An optical image of the galaxies NGC 3077 (left)
and M81 (right), showing the field covered by the survey. The area
is a degree across. The original goal of the project was to look for
old stars between these galaxies. Unexpectedly, newly formed stars
were discovered in intergalactic space. This material was presented
to the American Astronomical Society meeting in Atlanta, Georgia on January
8, 2004.
PHOTO CREDIT: Image from the Digitized Sky Survey. The DSS was produced
at the Space Telescope Science Institute under U.S. Government grant NAG
W-2166. The images of these surveys are based on photographic data
obtained using the Oschin Schmidt Telescope on Palomar Mountain and the UK
Schmidt Telescope. The plates were processed into the present compressed
digital form with the permission of these institutions. The Second
Palomar Observatory Sky Survey (POSS-II) was made by the California Institute
of Technology with funds from the National Science Foundation, the National
Aeronautics and Space Administration, the National Geographic Society, the
Sloan Foundation, the Samuel Oschin Foundation, and the Eastman Kodak Corporation.
High-resolution TIFF image (2.2M)
Lower-resolution JPG image (43k)
The M81 group of galaxies, named for its largest member,
lies about 12 million light years from us. Like the Local Group of
galaxies, home to the Milky Way, the M81 Group consists of a few large spirals
and a few dozen small dwarfs. However, the large spirals in the M81
group have passed close to each other recently--about 200 to 300 million
years ago according to computer simulations. This close encounter caused
large streams of hydrogen gas to be ripped out into intergalactic space.
The clumps of young blue stars discovered by DeCesar and her collaborators
lie inside these regions of stripped gas. Says Durrell, "These stars
have almost certainly been formed inside the gas clouds. It gives us
a close-up view of how star formation can occur when two galaxies pass close
to each other.''
What these new objects truly are is unclear. They
may well be tiny young galaxies which have just begun to form stars, each
with less than 0.1 percent as many stars as our own Milky Way galaxy. Alternatively,
these stars may not be bound to any galaxy, and may be destined to live their
lives in intracluster space. What is clear, however, is that these
stars did not form inside any of the large galaxies. Because hot blue
stars live only a short time, their presence implies that the clumps cannot
be more than 100 million years old, which is extremely young compared to
most galaxies. Moreover, the new stars must have formed outside of
the larger galaxies because the M81 group gas was stripped from its parent
galaxies during the interaction over 200 million years ago. Hurley-Keller
adds, "If these stars had formed inside the large galaxies, and then simply
got ripped out, they would have expired long ago, before we could detect
them."
Figure 2: A false-color radio image (data supplied
by Dr. Min Yun, University of Massachusetts) of the hydrogen gas in the M81
Group. While much of the gas is bound to M81, a tidal stream linking
M81 to NGC 3077 is also seen. This gas was pulled into intergalactic
space when the galaxies interacted about 300 million years ago. The
blue points show the locations of young stars discovered in the survey (the
survey region is outlined in yellow); these stars are coincident with the
gas. The inset shows a color close up of one of the 'tidal dwarf' candidates
(indicated by the white box), where the greatest concentration of blue stars
is found. These stars are believed to have formed from the gas less
than 100 million years ago. This material was presented to the American
Astronomical Society meeting in Atlanta, Georgia on January 8, 2004.
PHOTO CREDIT : Patrick Durrell and Megan DeCesar (Penn State University),
based on HI data from Dr. Min Yun (University of Massachusetts), originally
published by him in 1994.
High-resolution TIFF image (both) - 2.7M
Lower-resolution JPG image (both) - 43k
High-resolution TIFF image (HI image) - 2.5M
High resolution TIFF image (inset) - 1.4M
If the young star clumps are indeed 'infant' dwarf galaxies,
they would be among the closest examples of tidal dwarf galaxies. But
even if these objects are not dwarf galaxies, their existence still proves
that star formation can take place without a parent galaxy if there is a
sufficient amount of gas around to make the process work. Says Feldmeier,
"We have plenty of evidence that large galaxy clusters have stars outside
the galaxies, but in this nearby, less dense group, we are seeing stars actually
form in intergalactic space.''
CONTACT INFORMATION
For more information:
Dr. Patrick Durrell (814-865-2918; pdurrell@astro.psu.edu)
Dr. Denise Hurley-Keller (216-368-6699; denise@smaug.astr.cwru.edu)
Dr. Robin Ciardullo (814-865-6601; rbc@astro.psu.edu)
Dr. John Feldmeier (216-368-0310; johnf@bottom.astr.cwru.edu)