University Communications
New Mexico State Univeristy
Las Cruces, New Mexico

Astronomers discover galaxy in our cosmic back yard
By Karl Hill

Two New Mexico State University astronomers teamed up with colleagues in
the Netherlands to discover a large galaxy in the immediate neighborhood of
our own Milky Way galaxy.

Rene Walterbos, head of the astronomy department at NMSU, said the
previously undetected galaxy is only about 20 million light years away -- a
very close neighbor by galactic standards.

"It is surprising that we apparently have not found all the large nearby
galaxies," Walterbos said. "Astronomers have been finding a lot of dwarf
galaxies, but this is a fairly substantial galaxy."

Several large nearby galaxies lurking behind the dusty absorbing band of the
Milky Way have also been discovered over the past decade, but this is the
first large nearby galaxy found in the modern astronomical era that is only
mildly obscured in this way.

Because it is the first nearby galaxy discovered in the constellation
Cepheus, the newly discovered galaxy was named Cepheus 1. It belongs to a
class known as Low Surface Brightness (LSB) galaxies, in which stars are
spread further apart than in most galaxies.

Signs of Cepheus 1 were first noticed in observations made with the
Dwingeloo 25-meter radio telescope in the Netherlands. Robert Braun of the
Netherlands Foundation for Research in Astronomy and Butler Burton of Leiden
University had been using that telescope to study compact clouds of hydrogen
gas found swarming around the Milky Way. The motions of these gas clouds
could be measured by their Doppler shifts -- changes in the wavelengths of
the signals coming from the clouds -- and one was seen to move differently
from the others.

Braun and Burton contacted Walterbos and Charles Hoopes, a doctoral student
in astronomy at NMSU, who used the 3.5-meter optical telescope at Apache
Point Observatory to verify that the hydrogen gas signature corresponded to
a new galaxy. Apache Point, high in the Sacramento Mountains on one of the
best observing sites in North America, is operated by NMSU for the
Astrophysical Research Consortium, a group of seven universities and
research institutions.

"This demonstrates very well the capabilities of Apache Point," Walterbos
said. "It required a rapid response and it involved three different
observational techniques."

The optical picture obtained by Apache Point showed what the astronomers
described as a "rather anemic-looking galaxy" with only a few sites of
recent star formation scattered across a large area. Further radio
observations from the Dominion Radio Astrophysical Observatory in British
Columbia revealed that the weak optical signal was embedded in a much larger
and rapidly rotating disk of hydrogen gas, characteristic of a robust spiral
galaxy.

Walterbos said Cepheus 1 is one of the dozen largest nearby spiral galaxies,
"and one of only two large Low Surface Brightness spirals that we know of in
the nearby universe."

LSB galaxies can be massive, with copious amounts of gas within them, but
the gas is evolving to form stars very slowly compared with other galaxies,
the astronomers said. Most galaxies occur in large clusters or groups and
interact with each other gravitationally. The largest galaxies are believed
to evolve by cannibalizing smaller ones. The Milky Way and its nearest large
neighbor, the Andromeda galaxy, are on a collision course and probably will
merge dramatically in a few billion years.

LSB galaxies, on the other hand, are commonly found in quite empty regions
of space. With little external influence on their internal circumstances,
the process of star formation is not triggered efficiently, leaving vast
reservoirs of gas but only a few young, bright stars.

Discovery of Cepheus 1 gives astronomers a nearby example of LSB galaxies to
study in detail. It also represents another step in completing the census of
galaxies in the local neighborhood, which is important to determining the
mass and luminosity characteristics of these fundamental building blocks of
the universe.

A scientific article on the discovery by the four astronomers will appear in
the January 1999 issue of the "Astronomical Journal," published by the
American Astronomical Society.

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