Building-block process in evolution of massive galaxy clusters revealed

Apr 05, 2006
galaxy cluster
The distant, massive galaxy cluster as it existed when the Universe was less than five billion years old, or one third its present age. Credit: ESO/ESA/Mullis et al.

A study of the Universe’s most massive galaxy clusters has shown that mergers play a vital role in their evolution.

Astronomers at Oxford University and the Gemini Observatory used a combination of data from the twin Gemini Telescopes, located in Hawaii and Chile, and the Hubble Space Telescope (HST) to study populations of stars in the Universe’s most massive galaxy clusters over a range of epochs – the earliest being half the age of the Universe. The HST images were used to map the light distribution of the galaxies in the cluster. Data from the Gemini Multi-Object Spectrograph allowed the team to analyse the light from galaxies to determine their masses, ages and chemical compositions.

“We still don’t have a clear picture of how galaxies develop over the history of the Universe. The strength of this study is that we are able to look at galaxy clusters over a range of epochs,” said Dr Jordi Barr of Oxford University, who is presenting some of the first results of the Gemini/HST Galaxy Cluster Project at the RAS National Astronomy Meeting on 5th April.

Galaxy clusters contain the most massive galaxies in the Universe. Until recently, astronomers believed that all galaxies in the centres of clusters formed rapidly and then aged without any further changes to their structure in a process known as “Passive Evolution”. Results from the Gemini/HST Galaxy Cluster Project now show that this cannot be the case.

Dr Barr explained, “When we’re looking at the most distant galaxy clusters, we are looking back in time to clusters that are in early stages of their formation. The young galaxies in distant clusters appear to be very different from those in the mature clusters that we see in the local Universe. We found the earliest galaxy clusters have a huge variation in the abundances of elements such as oxygen and magnesium, whereas the chemistry of galaxies in the sample of closer clusters appears to be much more homogenous. This difference in chemistry proves that the clusters must actively change over time. If the galaxies in the old clusters have acquired a complete ‘set’ of elements, it’s most likely that they have formed from the mergers of several young galaxies”.

The group found that the star-formation in galaxies is dependent on mass and that in lower mass galaxies star-formation continues for longer. The most massive galaxies in clusters appear to have formed all their stars by the time the universe is just over a billion years old, whereas the lower mass galaxies finish forming their stars some 4 billion years later.

“We see the effects of star-formation in low mass galaxies but are unsure about why it’s happening. It’s possible that star-formation can be shut down very rapidly in dense environments and that the lower mass galaxies are recent arrivals that are forming stars over a longer period outside the cluster, then falling in. But we are still speculating...” said Dr Barr.

The group’s observations of merging galaxy clusters showed that a large proportion of the galaxies in those clusters have undergone recent bursts of star formation. This indicates that star formation may be triggered if galaxies are thrown, during the course of a merger, into contact with the gaseous medium pervading the cluster.

Future observations are planned at X-ray wavelengths to study the interactions between galaxies and the distribution and temperature of the surrounding gas.

Source: Royal Astronomical Society

Explore further: Full lunar eclipse delights Americas, first of year

add to favorites email to friend print save as pdf

Related Stories

Chance meeting creates celestial diamond ring

Apr 09, 2014

Astronomers using ESO's Very Large Telescope in Chile have captured this eye-catching image of planetary nebula PN A66 33—usually known as Abell 33. Created when an aging star blew off its outer layers, ...

Astronomers challenge Cosmological Model

Apr 03, 2014

(Phys.org) —Astronomers Professor Chris Collins and Dr Ian McCarthy from LJMU's Astrophysics Research Institute are challenging the view that the currently preferred cosmological model of the Universe is ...

Image: Magnifying the distant universe

Apr 01, 2014

(Phys.org) —Galaxy clusters are some of the most massive structures that can be found in the Universe—large groups of galaxies bound together by gravity. This image from the NASA/ESA Hubble Space Telescope ...

Black hole makes 'String of Pearls' clusters

Apr 01, 2014

(Phys.org) —Huge young star clusters resembling a string of pearls around a black hole in the centre of a galaxy 120 million light-years away have been discovered by researchers at Swinburne University ...

Recommended for you

Astronomers: 'Tilt-a-worlds' could harbor life

11 hours ago

A fluctuating tilt in a planet's orbit does not preclude the possibility of life, according to new research by astronomers at the University of Washington, Utah's Weber State University and NASA. In fact, ...

Vegetables on Mars within ten years?

17 hours ago

The soil on Mars may be suitable for cultivating food crops – this is the prognosis of a study by plant ecologist Wieger Wamelink of Wageningen UR. This would prove highly practical if we ever decide to ...

NASA Cassini images may reveal birth of a Saturn moon

17 hours ago

(Phys.org) —NASA's Cassini spacecraft has documented the formation of a small icy object within the rings of Saturn that may be a new moon, and may also provide clues to the formation of the planet's known ...

User comments : 0

More news stories

Astronomers: 'Tilt-a-worlds' could harbor life

A fluctuating tilt in a planet's orbit does not preclude the possibility of life, according to new research by astronomers at the University of Washington, Utah's Weber State University and NASA. In fact, ...

NASA Cassini images may reveal birth of a Saturn moon

(Phys.org) —NASA's Cassini spacecraft has documented the formation of a small icy object within the rings of Saturn that may be a new moon, and may also provide clues to the formation of the planet's known ...

Vegetables on Mars within ten years?

The soil on Mars may be suitable for cultivating food crops – this is the prognosis of a study by plant ecologist Wieger Wamelink of Wageningen UR. This would prove highly practical if we ever decide to ...

Low Vitamin D may not be a culprit in menopause symptoms

A new study from the Women's Health Initiative (WHI) shows no significant connection between vitamin D levels and menopause symptoms. The study was published online today in Menopause, the journal of The North American Menopa ...