Subject: Astronomers discover new galaxy in the Local Group (Forwarded)
Date: Wed, 6 Jan 1999 23:04:55 -0500
From: Andrew Yee <ayee@nova.astro.utoronto.ca>
Organization: UTCC Campus Access
National Optical Astronomy Observatories
Tucson, Arizona

EMBARGOED FOR RELEASE: 9:20 a.m. EST, JANUARY 6, 1999

RELEASE NO: NOAO 99-01

ASTRONOMERS DISCOVER NEW GALAXY IN THE LOCAL GROUP

Astronomers George H. Jacoby and Taft E. Armandroff of the National Optical
Astronomy Observatories in Tucson, Arizona, and James E. Davies of The Johns
Hopkins University announced today their discovery of a new galaxy in The
Local Group, the group of galaxies within 4 million light-years of our own
Milky Way. The new galaxy is the second one that the team has found in the
past year by using new computer enhancement techniques applied to 10-year
old photographs of the sky. Small galaxies of the type found by Jacoby and
collaborators are the most common type of galaxy in the universe, yet the
region around the Milky Way Galaxy's big brother, the spiral galaxy in
Andromeda, had been thought to be highly deficient of these "dwarf" galaxies
before the team began their search. The census of the Local Group, though,
is now as high as 43 galaxies, meaning that our neighborhood may not be as
unusual as was previously thought.

The newest member of the Local Group, named And VI (as the 6th dwarf galaxy
candidate associated with the spiral galaxy in the constellation of
Andromeda) is about 27 degrees on the sky south of the Andromeda Galaxy.
This position places it about 900,000 light-years from the Andromeda Galaxy
and 2.6 million light-years from Earth. And VI was identified as one of
roughly 100 candidate Local Group dwarf galaxies by computer enhancement of
a large region of the sky near Andromeda using the Digital Sky Survey (see
figure below). To verify its nature as a galaxy, And VI was observed
initially with the 4-m (158-inch) telescope at the National Science
Foundation's Kitt Peak National Observatory near Tucson. Once the galaxy was
confirmed as a likely Local Group member, it was studied in detail with the
3.5-m (138-inch) WIYN, also at the Kitt Peak National Observatory (see
attached figure).

[Image: http://www.noao.edu/outreach/press/9901.html]

The two galaxies discovered by Jacoby, Armandroff and Davies, And V (upper
pair of panels; shown as a negative image) and And VI (lower pair) were
extremely difficult to identify. The lefthand images are from the Digital
Sky Survey. The righthand images show how computer enhancement reveals these
faint dwarf galaxies against the background of stars in our own Milky Way
Galaxy. The dark regions in the center of the righthand panels are the
signatures of the dwarf galaxy candidate. While And VI can be seen faintly
in the original (lower left panel) before computer enhancement, And V is
completely invisible to the eye (upper left panel). The technique used by
Jacoby and collaborators promises to identify the faintest dwarf galaxies in
the Local Group from existing Sky Survey photographs. Sidney van den Bergh
(Dominion Astrophysical Observatory in Victoria, Canada) discovered the
dwarf galaxies And I, II and III associated with the Andromeda Galaxy in
1972, but no additional dwarfs were found during the next 26 years. The
identification of And VI as a new Andromeda dwarf, along with 2 others
recently discovered (And V by Armandroff, Davies, and Jacoby last year, and
Cas dSph by Karachentsev and Karachentseva this past summer), are vital
clues to the way that galaxies and clusters of galaxies form. The
identification of some 30 additional dwarf galaxies are required in our
Local Group to make the census of dwarf galaxies in our cluster of galaxies
comparable to rich clusters of galaxies. Dwarf galaxies like And VI are
thought by many to be the building blocks of bigger galaxies through a
mechanism referred to as "cannibalism". If true, then the kinds of stars
found in dwarfs should be reflected in the kinds of stars found in big
galaxies. To test this hypothesis, Jacoby's team, as well as others (see the
press release by Grebel and Guhathakurta at this meeting, paper 8.02;
http://www.ucolick.org/~raja/pressrel.html) have been measuring the chemical
compositions of the stars in the dwarfs around Andromeda.

Is our Local Group really special, or have astronomers not looked hard
enough for these extremely faint and elusive galaxies? The recent discovery
by Jacoby and his collaborators suggests that hard work may rectify the
apparently unusual status of the Local Group. The team has another 65
candidate galaxies to check into; future work may reveal additional dwarf
galaxies to add to the Local Group inventory over the next few years.

The National Optical Astronomy Observatories are operated by the Association
of Universities for Research in Astronomy (AURA), Inc., under Cooperative
Agreement with the National Science Foundation.

For more information:

Dr. George H. Jacoby (1-520-318-8292; gjacoby@noao.edu)
Dr. Taft E. Armandroff (1-520-318-8382; tarmandroff@noao.edu)
Suzanne H. Jacoby (1-520-318-8364; sjacoby@noao.edu)

                  #####

EDITORS: High resolution versions of the illustrations are available via the
internet at http://www.noao.edu/outreach/press/9901image.html

Image Caption: [http://www.noao.edu/outreach/press/9901image.html]

The discovery of the new dwarf galaxy by Jacoby and collaborators runs
counter to the suggestion that the Local Group is deficient in dwarf
galaxies.
The census of dwarf galaxies is important because they are thought to be the
building blocks of larger galaxies through "cannibalism". The new dwarf
galaxy is the second the team has found in the past year through innovative
computer techniques. The image is a true color image of the new dwarf
galaxy,
And VI, obtained with the 3.5-m WIYN telescope at the National Science
Foundation's Kitt Peak National Observatory. Most of the stars are slightly
red in color. A few very evolved stars are extremely red, while some blue
stars (probably foreground stars in our own Milky Way) are present. The
right
panel is an enlarged view of the center of And VI showing the tight packing
of stars in this high resolution image.

Photo Credit: National Optical Astronomy Observatories/National Science
Foundation

---
Andrew Yee
ayee@nova.astro.utoronto.ca