Observations challenge standing view of how and when galaxies formed

A rare glimpse back in time into the universe’s early
evolution has revealed something startling: mature, fully formed
galaxies where scientists expected to discover little more than
infants.

“Up until now, we assumed that galaxies were just beginning to
form between 8 and 11 billion years ago, but what we found suggests that
that is not the case,” said Karl Glazebrook, associate professor of
physics and astronomy in the Krieger School of Arts and Sciences at The
Johns Hopkins University in Baltimore and co-principal author of a paper
in the July 8 issue of Nature. “It seems that an unexpectedly large
fraction of stars in big galaxies were already in place early in the
universe’s formation, and that challenges what we’ve believed. We
thought massive galaxies came much later.”

Using the Frederick C. Gillett Gemini North Telescope in Mauna
Kea, Hawaii, Glazebrook and a multinational team of researchers called
the Gemini Deep Deep Survey (GDDS) employed a special technique called
the “Nod and Shuffle” to peer into what had traditionally been a
cosmological blind spot. Called “the Redshift Desert,” this era – 8
billion to 11 billion years ago, when the universe was only 3 billion to
6 billion years old – has remained relatively unexplored until now,
mainly because of the challenges inherent in collecting data from the
faintest galactic light ever to be dissected into the rainbow of colors
called a spectrum. In all, the team collected and analyzed spectra from
300 galaxies, making it the most complete sample ever taken from the
Redshift Desert.

“This was the most comprehensive survey ever done covering the
bulk of the galaxies that represent conditions in the early universe,”
Glazebrook said. “We expected to find basically zero massive galaxies
beyond about 9 billion years ago, because theoretical models predict
that massive galaxies form last. Instead, we found highly developed
galaxies that just shouldn’t have been there, but are.”

These findings challenge the dominant theory of galactic
evolution, which posits that at this early stage, galaxies should have
formed from the bottom up, with small pieces crashing together to build
small and then ever larger galaxies. Called the “hierarchical
model,” this scenario predicts that normal-to-large galaxies such
as those studied by GDDS would not yet exist.

“There are obviously some aspects of the early lives of
galaxies that we don’t yet completely understand, Glazebrook said.
“We do find fewer massive galaxies in the past, but there are still
more than we expected. This result is giving us a big clue as to how
stars form from invisible gas in the hierarchical model, which is
something not well understood under current theories. Some new
ingredient is required to make more stars form earlier in the big
galaxies. But what that ingredient is, we don’t yet know.”

The GDDS team, which included Nature paper co-authors Roberto
Abraham from the University of Toronto, Patrick McCarthy from the
Observatories of the Carnegie Institution of Washington and David
Crampton of the National Research Council of Canada’s Herzberg
Institute of Astrophysics, was supported by a grant from the Packard
Foundation and by institutional support from the National Science
Foundation, Canada’s National Research Council, the Natural Sciences
and Engineering Research Council of Canada and the United Kingdom’s
Particle Physics and Research Council, among others.

Related Web site:

Karl Glazebrook: http://www.pha.jhu.edu/people/faculty/kgb.html