Wild Early Lives of Massive Galaxies: Dramatic star formation cut short

The LABOCA camera on the ESO-operated 12-meter Atacama Pathfinder Experiment (APEX) telescope reveals distant galaxies undergoing the most intense type of star formation activity known, called a starburst. This image shows these distant galaxies, found in a region of sky known as the Extended Chandra Deep Field South, in the constellation of Fornax (The Furnace). The galaxies seen by LABOCA are shown in red, overlaid on an infrared view of the region as seen by the IRAC camera on the Spitzer Space Telescope. Courtesy of ESO, APEX (MPIfR/ESO/OSO), A. Weiss et al., NASA Spitzer Science Center

Using the APEX telescope, a team of astronomers has found the strongest link so far between the most powerful bursts of star formation in the early Universe, and the most massive galaxies found today. The galaxies, flowering with dramatic starbursts in the early Universe, saw the birth of new stars abruptly cut short, leaving them as massive — but passive — galaxies of aging stars in the present day. The astronomers also have a likely culprit for the sudden end to the starbursts: the emergence of supermassive black holes.

Astronomers have combined observations from the LABOCA camera on the ESO-operated 12-meter Atacama Pathfinder Experiment (APEX) telescope with measurements made with ESO’s Very Large Telescope, NASA’s Spitzer Space Telescope, and others, to look at the way that bright, distant galaxies are gathered together in groups or clusters.

The 12-meter-diameter APEX telescope is located on the Chajnantor plateau in the foothills of the Chilean Andes. APEX is a pathfinder for ALMA, the Atacama Large Millimeter/ submillimeter Array, a revolutionary new telescope that ESO, together with its international partners, is building and operating, also on the Chajnantor plateau. APEX is itself based on a single prototype antenna constructed for the ALMA project. The two telescopes are complementary: for example, APEX can find many targets across wide areas of sky, which ALMA will be able to study in great detail.

The more closely the galaxies are clustered, the more massive are their halos of dark matter — the invisible material that makes up the vast majority of a galaxy’s mass. The new results are the most accurate clustering measurements ever made for this type of galaxy.

The galaxies are so distant that their light has taken around 10 billion years to reach us, so we see them as they were about 10 billion years ago. These distant galaxies are known as submillimeter galaxies. They are very bright galaxies in the distant Universe in which intense star formation occurs. Because of this extreme distance, their infrared light from dust grains heated by starlight is redshifted into longer wavelengths, and the dusty galaxies are, therefore, best observed in submillimeter wavelengths of light.

In these snapshots from the early Universe, the galaxies are undergoing the most intense type of star formation activity known, called a starburst. By measuring the masses of the dark matter halos around the galaxies, and using computer simulations to study how these halos grow over time, the astronomers found that these distant starburst galaxies from the early cosmos eventually become giant elliptical galaxies — the most massive galaxies in today’s Universe.

“This is the first time that we’ve been able to show this clear link between the most energetic starbursting galaxies in the early Universe, and the most massive galaxies in the present day,” explains Ryan Hickox (Dartmouth College, USA and Durham University, UK), the lead scientist of the team.

Furthermore, the new observations indicate that the bright starbursts in these distant galaxies last for a mere 100 million years — a very short time in cosmological terms — yet, in this brief time, they are able to double the quantity of stars in the galaxies. The sudden end to this rapid growth is another episode in the history of galaxies that astronomers do not yet fully understand.

“We know that massive elliptical galaxies stopped producing stars rather suddenly a long time ago, and are now passive. And scientists are wondering what could possibly be powerful enough to shut down an entire galaxy’s starburst,” says Julie Wardlow (University of California at Irvine, USA and Durham University, UK), a member of the team.

The team’s results provide a possible explanation: at that stage in the history of the cosmos, the starburst galaxies are clustered in a very similar way to quasars, indicating that they are found in the same dark matter halos. Quasars are among the most energetic objects in the Universe — galactic beacons that emit intense radiation, powered by a supermassive black hole at their center.

There is mounting evidence to suggest the intense starburst also powers the quasar by feeding enormous quantities of material into the black hole. The quasar, in turn, emits powerful bursts of energy that are believed to blow away the galaxy’s remaining gas — the raw material for new stars — and this effectively shuts down the star formation phase.

“In short, the galaxies’ glory days of intense star formation also doom them by feeding the giant black hole at their centre, which then rapidly blows away or destroys the star-forming clouds,” explains David Alexander (Durham University, UK), a member of the team.

Citation: This research is presented in a paper that appeared in the journal Monthly Notices of the Royal Astronomical Society on 26 January 2012. http://www.eso.org/public/archives/releases/sciencepapers/eso1206/eso1206.pdf

The team is composed of Ryan C. Hickox (Dartmouth College, Hanover, USA; Department of Physics, Durham University (DU); STFC Postdoctoral Fellow, UK), J. L. Wardlow (Department of Physics & Astronomy, University of California at Irvine, USA; Department of Physics, DU, UK), Ian Smail (Institute for Computational Cosmology, DU, UK), A. D. Myers (Department of Physics and Astronomy, University of Wyoming, USA), D. M. Alexander (Department of Physics, DU, UK), A. M. Swinbank (Institute for Computational Cosmology, DU, UK), A. L. R. Danielson (Institute for Computational Cosmology, DU, UK), J. P. Stott (Department of Physics, DU, UK), S. C. Chapman (Institute of Astronomy, Cambridge, UK), K. E. K. Coppin (Department of Physics, McGill University, Canada), J. S. Dunlop (Institute for Astronomy, University of Edinburgh, UK), E. Gawiser (Department of Physics and Astronomy, The State University of New Jersey, USA), D. Lutz (Max-Planck-Institut fur extraterrestrische Physik, Germany), P. van der Werf (Leiden Observatory, Leiden University, The Netherlands), A. Weiß (Max-Planck-Institut fur Radioastronomie, Germany).