SCIENCE BACKGROUND

"THE FAINT BLUE GALAXY MYSTERY"
A CENSUS OF GALAXIES 

In the 1920s, when Edwin Hubble first discovered that the universe
contained countless "island universes" called galaxies, astronomers
believed that giant spiral galaxies, such as our own Milky Way and
nearby Andromeda, as well as luminous elliptical galaxies, such as
Messier 87 in the Virgo cluster, dominated the vast volume of space.

However, since the 1970s astronomers have been perplexed by the
enormous numbers of "faint blue galaxies" seen in the deepest images
gathered by the world's largest telescopes.  Several Hubble Medium Deep
Survey team members including David Koo of Lick Observatory, Richard
Ellis of the Institute of Astronomy at Cambridge University, England,
and Tony Tyson of AT&T Bell Laboratories, have grappled with this
problem over the last two decades.  In recent years, some hints to the
nature of the faint blue galaxies also have come from ground-based
surveys of nearby galaxies, including work done by John Huchra and
colleagues at the Center for Astrophysics in Cambridge, MA.  Due to
distortion by Earth's atmosphere, these mysterious objects have
remained murky blobs seen against the background glow of the
ground-based night sky.

"The clue to further progress lies in extensive spectroscopic studies
of these remarkable galaxies using ground-based telescopes," concluded
Ellis.  Ellis, Karl Glazebrook (Institute of Astronomy at Cambridge
University, England) and colleagues have pioneered the construction of
multiple object spectrographs precisely for this purpose on Britain's
large telescopes.  "Thus far we can say that many of these peculiar
systems are being seen during an unusually active stage of star
formation.  Finding the cause of this activity is the remaining
puzzle."


INTERNATIONAL TEAMS PURSUE THE FAINT BLUE GALAXY MYSTERY

Initial results and images from Wide Field and Planetary Camera 2 were
published in the Astrophysical Journal Letters at the end of last year
by Griffiths and co-investigators, and Duncan Forbes and
co-investigators (Lick Observatory).  The present results (Simon Driver
of Arizona State University, Windhorst and Griffiths) are scheduled to
be published in the Astrophysical Journal this summer.  These results
were independently and simultaneously found by Glazebrook (Glazebrook,
Ellis, Santiago and Griffiths published in the Monthly Notices of the
Royal Astronomical Society on July 15, 1995).  Both Driver and
Glazebrook based their results directly on the extensive Medium Deep
Survey database built by Kavan Ratnatunga and colleagues at Johns
Hopkins University in Baltimore, MD.  The new results from the deeper
survey are scheduled for publication in the Astronomical Journal
Letters in August by Driver, et al.

The excellent new data have absolutely confirmed the initial hints in
data taken before the HST servicing mission in December 1993, that the
faint population was intrinsically small systems (papers in the
Astrophysical Journal and Letters by Myungshin Im, et al., and by
Stefano Casertano, et al. of the Johns Hopkins team, the latter to be
published this summer).

The Medium Deep Survey is led by R. Griffiths at the Johns Hopkins
University in the United States, in collaboration with eight other co-
 investigators in the USA and the United Kingdom, including R. S. Ellis
and G. F. Gilmore (University of Cambridge), R. F. Green (National
Optical Astronomical Observatories), J. P. Huchra (Harvard-Smithsonian
Center for Astrophysics), G. D.Illingworth and D. C. Koo (Lick
Observatory, University of California at Santa Cruz), K. Ratnatunga
(Johns Hopkins University), A. J. Tyson (AT&T Bell Laboratories, New
Jersey), and R. A. Windhorst (Arizona State University).