UK-led team unveil more about today's most massive galaxies

Distant star forming galaxies
Credit: ESO

A UK-led 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. Using the European Southern Observatory’s (ESO’s) Atacama Pathfinder Experiment (APEX) telescope, the astronomers have found that the lives of new stars, abundant in galaxies in the early Universe,  were dramatically cut short, leaving them in the present day, as massive (though passive) galaxies of aging stars. The team led by Durham University has also predicted that the likely culprit for the sudden end to the starbursts is the emergence of supermassive black holes.

The work, a combination of observations from the LABOCA camera on APEX and measurements made with ESO’s Very Large Telescope, NASA’s Spitzer Space Telescope, and others, looks at the way that bright, distant galaxies are gathered in groups or clusters. 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. By measuring the masses of their dark matter halos, 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 (Durham University, UK and Dartmouth College, USA), 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. What causes the abrupt end to their rapid growth is not yet fully understood but the team’s results offer 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 centre.

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.

STFC is the UK sponsor of astronomy and allows UK astronomers access to ESO’s telescopes through a subscription. The Universities of Edinburgh and Cambridge were also involved with the work. For more details see the press release issued by ESO (link opens in a new window).