Could galactic find be Andromeda's food? (Forwarded)

Sloan Digital Sky Survey

CONTACTS:
Daniel Zucker, Max Planck Institute for Astronomy


Eric Bell, Max Planck Institute for Astronomy

(Zucker and Bell will be attending the AMERICAN ASTRONOMICAL SOCIETY
meeting in Atlanta and can be reached immediately following their panel
presentation through the AAS Press Room at the Hyatt Regency Hotel --
404-577-1234, fax 404-588-4137).

Michael A. Strauss, SDSS Scientific Spokesman
(609) 258-3808,

Gary S. Ruderman, SDSS Public Information Officer
(312)-320-4794,

January 5, 2004

COULD GALACTIC FIND BE ANDROMEDA'S FOOD?

SLOAN DIGITAL SKY SURVEY REVEALS GIANT CLUMP OF STARS NEAR THE ANDROMEDA
GALAXY

ATLANTA -- A international team of astronomers from the Sloan Digital Sky
Survey collaboration has discovered a giant clump of stars near the
Andromeda Galaxy that could be a previously unknown satellite galaxy of
Andromeda or could be the last remnants of a galaxy torn apart by
Andromeda's tidal forces.

The clump of stars, named Andromeda NE by the researchers for its
location to the northeast of the Andromeda Galaxy, is enormous. It covers
a larger area on the sky than the full Moon. If added together the total
light from the stars in Andromeda NE would rival many nearby galaxies in
brightness. Yet because these stars are so spread out, Andromeda NE
appears 10 times dimmer than the faintest known galaxy."This helps to
explain why it remained undiscovered," said Daniel Zucker, one of the
Sloan Digital Sky Survey (SDSS) researchers. "The quality of the SDSS
data allowed us to find this elusive object close to Andromeda, one of
the best-studied galaxies in the sky," added team member Eva Grebel of
the University of Basel. More than 2 million light years away, the
Andromeda Galaxy or M31 is the nearest spiral galaxy, and is one of a
handful of galaxies (besides our own Milky Way) that can be seen with the
naked eye.

Zucker and Eric Bell from the Max Planck Institute for Astronomy (MPIA)
in Heidelberg, Germany presented these findings today (January 5, 2004)
at the American Astronomical Society meeting in Atlanta.

While analyzing data from an SDSS scan of Andromeda, Zucker and his team
used special filtering techniques to select objects with specific colors
and brightness typical of Andromeda's stars. When the SDSS team mapped
the distribution of these stars they detected a number of features
previously noted by other astronomers. But SDSS researchers didn't know
what to make of a large concentration of stars -- what they described at
first as a giant, ghostly shape -- that appeared to the northeast of
Andromeda.

"At first we thought it was some sort of artifact, some kind of problem
with our filtering technique," says Zucker. "But test after test showed
that it was really there."

Having determined that the stellar structure was real, the SDSS team
members from MPIA, the University of Washington in Seattle, the
University of Basel in Switzerland and New Mexico State University in Las
Cruces worked to find out what it was.

"One of the most important questions about Andromeda NE is its distance.
Although our findings don't allow us to measure this precisely, our data
indicate that it is roughly at the same distance as the Andromeda
Galaxy," said Bell.

That means that the clump of stars is gravitationally bound to the
Andromeda Galaxy, in orbit around its larger neighbor and possibly is in
the process of being torn apart by Andromeda's tidal forces. These forces
arise because Andromeda's gravitational pull is stronger on the near side
of Andromeda NE than on the far side, pulling the stars away from each
other. "For most small companion galaxies it is ultimately only a matter
of time until they are shredded by the tides of the parent galaxy,"
explained Hans-Walter Rix, director of MPIA.

Over the past decade astronomers have found increasing evidence that the
distant, outer reaches of normal spiral galaxies like Andromeda and the
Milky Way are not quiet backwaters, but rather arenas of ongoing galaxy
disruption. As satellite galaxies are ripped apart by tidal forces, they
lose stars in great streams along their orbital paths. Researchers have
detected such stellar streams around both the Milky Way and Andromeda,
suggesting that this kind of galactic cannibalism is commonplace.

"SDSS data have been used to study the destruction of satellites by our
galaxy, and now they are adding to our knowledge of Andromeda's eating
habits," observed Alexei Kniazev, an SDSS collaboration member and a
researcher at MPIA.

In 2003, a team of SDSS scientists found what is believed to be the
remnants of a galaxy pulled apart by the Milky Way. The SDSS's ability to
do three-dimensional mapping revealed that the concentration of stars of
a certain color and brightness were actually parts of a separate
structure outside of the Milky Way.

So far the exact nature of Andromeda NE remains a mystery. It could be a
satellite galaxy of Andromeda, perhaps one so stretched out by
Andromeda's tides that it has become the enormous, remarkably diffuse
structure seen today. Or it could be part of a giant stream of stars, all
that remains of a satellite that was completely disrupted by Andromeda's
tidal forces in the distant past. "But we'll need more data to determine
which it is," said Zucker.

AUTHORS:

Daniel Zucker
Max Planck Institute for Astronomy
Konigstuhl 17, D-69117
Heidelberg, Germany


Alexei Kniazev
Max Planck Institute for Astronomy


Eric Bell
Max Planck Institute for Astronomy


David Martinez-Delgado
Max Planck Institute for Astronomy


Hans-Walter Rix
Max Planck Institute for Astronomy


Eva Grebel
Astronomical Institute of the University of Basel
Venusstrasse 7, CH-4102 Basel, Switzerland


Connie Rockosi
Department of Astronomy, P.O. Box 351580
University of Washington
Seattle, WA 98195


Jon Holtzman
Astronomy Department
New Mexico State University
Box 30001, Department 4500
Las Cruces, NM 88003


Rene Walterbos
New Mexico State University


Zeljko Ivezic
Princeton University Observatory
Princeton, NJ 08544


Jonathan Brinkmann
Apache Point Observatory, P.O. Box 59
Sunspot, NM 88349


IMAGE CAPTION:
[http://www.sdss.org/news/releases/AndNEandmoon2.jpg (35KB)]
This composite illustration shows the location of Andromeda NE (arrow),
the complicated stellar structures in the halo of the Andromeda Galaxy
(inset image to scale) and a scaled photo of the moon as a size reference
(to the right). The colors in the image reflect the relative colors of
stars that are predominantly red giants at the distance of the Andromeda
Galaxy. Bluer and whiter colors generally indicate lower metallicity
(elemental abundances) and yellow and red stars indicate increasing
elemental abundances. (Except for Andromeda NE, most of the major
structures shown here were also seen by Ferguson et al as noted in
Astronomical Journal, vol. 124, p. 1452, Sept. 2002, although the
representation of SDSS data is more informative.)

SOURCES: Sloan Digital Sky Survey; Inset of M31 from Bill Schoening,
Vanessa Harvey/REU program/NOAO/AURA/NSF; Photo of full moon from
Lick Observatory.