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News Release 74 of 85

July 24, 1995 12:00 AM (EDT)

News Release Number: STScI-1995-08

Hubble Sheds Light on the "Faint Blue Galaxy" Mystery

Background information useful for exploring this news release:

"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).

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