Are elliptical galaxies much younger than previously thought?

The new age estimate is based on the presence of ultra-faint filaments in the distant outskirts of two galaxies.

By Canada-France-Hawaii Corp., Kamuela, Hawaii — Published: July 22, 2011

Galaxy NGC 5557 exhibits extremely extended and faint tidal streams spanning more than 1.2 million light-years from left to right on this image from the MegaCam mounted on the Canada-France-Hawaii Telescope. Image credit: P.-A. Duc 2011 (c) CEA/CFHT

The standard model for elliptical galaxy formation is challenged by a new result uncovered by an international team of astronomers from the Atlas3D collaboration. The first results from the group’s study on two elliptical galaxies exhibiting features characteristic of a fairly recent merger, suggest they are 5 times younger than commonly thought.

The accepted belief on the mass assembly history of massive elliptical galaxies based on their stellar population leads to an age between 7 and 10 billion years old. A different story is shaping up based on ultra-deep images of two galaxies observed with the MegaCam camera mounted on the Canada-France-Hawaii Telescope (CFHT).

A sample of elliptical galaxies from the Atlas3D survey's current collection, all showing clear signs of a recent collision. Image credit: P.-A. Duc 2011 (c) CEA/CFHT

The astronomers established that the formation of the two elliptical galaxies, NGC 680 and NGC 5557, originated from a merger of two giant spiral galaxies that took place only 1 to 3 billion years ago. The age estimate is based on the presence of ultra-faint filaments in the distant outskirts of the galaxies. These features called tidal streams are typical residuals from a galaxy merger. They are known not to survive in this shape and brightness for more than a few billion years, hence the new age estimate of the resulting elliptical galaxies. These structures were detected for the first time thanks to an imaging technique boosting the capabilities of CFHT's wide-field optical imager MegaCam.

The Atlas3D team conducts a systematic survey of more than 100 nearby elliptical galaxies. If the current result based on the first two galaxies is confirmed on the larger sample, i.e. if faint extended features are frequently detected, the standard model for elliptical galaxies formation should be revisited.

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ROBERT BOWERS from FLORIDA said:

At the risk of sounding ignorant, are we assuming that the universe is expanding at a uniform rate?

Submitted: 7/31/2011 6:24:11 PM (CST)

CHRIS R BAKER from CALIFORNIA said:

Absolutely! Although I'd want a way back too.

Submitted: 7/31/2011 12:05:51 AM (CST)

BILL SIMPSON from LOUISIANA said:

Well, a portion of the elliptical galaxies might be younger than previously thought. You have got to figure that the galaxies we see may be the result of multiple mergers early in the history of the Universe. Mathematical modeling might be able to explain their shapes, but that would seem far from certain to me. It would be interesting to know how fast the rate of galaxy merger is slowing, as they get farther apart with the expansion of the Universe. Are more than a few still merging today? You would need to find some nearby mergers to be sure that it hasn't nearly ended, unless math could be used to do a calculation with a high degree of certainty. Then again, since Andromeda is heading right to us, it seems likely that mergers are still common. It would be strange if big groups of galaxies are coming together as the Universe expands. Can that be tested, or would the expansion of the Universe distort the measurements? I thought they had all this stuff figured out. I guess not. Not for a long time. Maybe never. Can it be infinitely complex? Think how boring life would be if we knew everything. They keep making more discoveries about these galaxies and you are going to need more staff. I liked the words 'fairly recent' when talking about between 1 to 3 BILLION years ago. Three billion years ago bacteria was the highest life form on Earth. The tides were 300 feet high. And the weather was REALLY bad. And 3 billion years from now Andromeda still won't be here. But any intelligent life that may have escaped to some nearby planet won't need a star chart to find it. So if you had a time machine and could jump 3 billion years into some future civilization that evolved from Earth today, would you do it? You go first.

Submitted: 7/23/2011 1:27:34 AM (CST)

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Are elliptical galaxies much younger than previously thought?

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