Findings related to the puzzle as to how galaxies were formed about 9 billion years ago were announced at the American Astronomical Society meeting held in Toronto, Ontario, Canada, in January. The work was done by a research group headed by astronomers at the University of California (UC) Observatories/Lick Observatories (Santa Cruz, CA) using the Low-Resolution Imaging Spectrograph on the Keck I Telescope (Mauna Kea, HI).
The effort was a tandem telescope project, starting with Hubble Space Telescope Deep Field images that directed the researchers to 24 galaxies in the "preadolescent" stage prior to maturing into structures like our own Milky Way galaxy (see figure). Spectra from the images were examined with the Keck instrument, with exposure times varying from two to four hours for each of the 24 galaxies. The team was able to use the spectra to determine the distances to about half of these galaxies. Doppler redshifts observed ranged, on the nonlinear scale, from 2.2 to 3.4. A redshift of 3 would mean a galaxy existed at a time roughly 90% of the way back to the Big Bang, which is now put at 8 to 12 billion years ago. "We pushed the limit to among the faintest galaxies for which anyone has attempted to obtain spectra," says investigator David Koo.
Conclusions reached by the group show that, with so many distant objects across the Deep Field, probably they all could not have grown uniformly into future massive galaxies. The variance in shape and size points to many of them merging to evolve into a smaller number of "grand design" galaxies observed at this time in cosmological history. Others may have faded into dwarf galaxies, unobtrusive and scattered throughout the universe. Researcher James Lowenthal notes, "If these galaxies didn`t merge together, they would build up into far too many bright galaxies as the universe evolved, many more galaxies than we see around the Milky Way today."
The distant galaxies were at least as luminous as the Milky Way but only a tenth as large. They gave birth to new stars at rates comparable to starbirth today, which is much less prolific than in galaxies that produced tremendous numbers of stars billions of years later. The researchers say this is strong evidence that stellar formation rates have flowed and ebbed significantly as the universe has aged. The spectra also show evidence of the elements carbon, oxygen, silicon, and metals, as opposed to exclusively primordial hydrogen and helium, indicating that generations of star births and deaths had occurred, even at the universe`s young age of just a couple of billion years.
Other evidence
In a related development, University of California Observatories/Lick Observatories also used the Keck I and II telescopes to obtain detailed spectra of discrete nebulous structures surrounding most observed quasars. The spectra, according to the investigators, clearly indicate that these objects are galaxies full of normal stars with ages ranging from 1 to 10 billion years. The observations also suggest that galaxies in collision fuel the energy output of some of the quasars by hurling stellar debris into black holes at the cores of the galaxies.
"The evidence is extraordinarily strong that quasars live in host galaxies as we expected," says observatory director and team leader Joseph Miller. "This is consistent with the hypothesis that quasars are natural features of massive galaxies . . . not freaks of nature."