Monday, November 10, 2014

ESO VLT: MUSE reveals true story behind galactic crash

The MUSE instrument on ESO's Very Large Telescope has provided researchers with the best view yet of a spectacular cosmic crash. 

Observations reveal for the first time the motion of gas as it is ripped out of the galaxy ESO 137-001 as it ploughs at high speed into a vast galaxy cluster. 

The results are the key to the solution of a long-standing mystery, why star formation switches off in galaxy clusters. 

In this picture the colours show the motions of the gas filaments, red means the material is moving away from Earth compared to the galaxy and blue that it is approaching. 

Note that the upper-left and lower-right parts of this picture have been filled in using the Hubble image of this object. 

Credit: ESO/M. Fumagalli

A team of researchers led by Michele Fumagalli from the Extragalactic Astronomy Group and the Institute for Computational Cosmology at Durham University, were among the first to use ESO's Multi Unit Spectroscopic Explorer (MUSE) instrument on the VLT.

Observing ESO 137-001, a spiral galaxy 200 million light-years away in the southern constellation of Triangulum Australe (The Southern Triangle), they were able to get the best view so far of exactly what is happening to the galaxy as it hurtles into the Norma Cluster.

MUSE gives astronomers not just a picture, but provides a spectrum, or a band of colours, for each pixel in the frame.

With this instrument researchers collect about 90 000 spectra every time they look at an object, and thereby record a staggeringly detailed map of the motions and other properties of the observed objects.

ESO 137-001 is being robbed of its raw materials by a process called ram-pressure stripping, which happens when an object moves at high speed through a liquid or gas.

This is similar to how air blows a dog's hair back when it sticks its head out of the window of a moving car.

In this case the gas is part of the vast cloud of very thin hot gas that is enveloping the galaxy cluster into which ESO 137-001 is falling at several million kilometres per hour.

The galaxy is being stripped of most of its gas, the fuel needed to make the next generations of young blue stars.

ESO 137-001 is in the midst of this galactic makeover, and is being transformed from a blue gas-rich galaxy to a gas-poor red one. Scientists propose that the observed process will help to solve a long-standing scientific riddle.

"It is one of the major tasks of modern astronomy to find out how and why galaxies in clusters evolve from blue to red over a very short period of time," says Fumagalli.

"Catching a galaxy right when it switches from one to the other allows us to investigate how this happens."

Observing this cosmic spectacle, however, is no mean feat. The Norma Cluster lies close to the plane of our own galaxy, the Milky Way, so it is hidden behind copious amounts of galactic dust and gas.

With the help of MUSE, which is mounted on one of the VLT's 8-metre Unit Telescopes at the Paranal Observatory in Chile, scientists could not only detect the gas in and around the galaxy, but were able to see how it moves.

The new instrument is so efficient that a single hour of observing time was sufficient to obtain a high resolution image of the galaxy as well as the distribution and motion of its gas.

More information: Research paper (PDF):… eso1437/eso1437a.pdf

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