BA: Galaxy cluster at the edge of the Universe

[bystander]

Galaxy cluster at the edge of the Universe
Bad Astronomy - 10 May 2010

Astronomers have found the most distant galaxy cluster ever seen: the sexily-named SXDF-XCLJ0218-0510.

First, the picture, then the words:

Invisible light discovers the most distant cluster of galaxies (Subaru/XMM-Newton Deep Field)

Yikes! What’s all that then?

Okay, first, this picture is littered with stars and galaxies. The galaxies are so far away they’re hard to distinguish from the stars! The dots that have arrows pointing to them are the galaxies that are most likely part of the cluster. The ones with circles have had their distance measured and are known to be part of the cluster for sure. The contour lines represent the detection of very hot gas, which is a dead giveaway that we’re dealing with a cluster here; all big clusters have gas swirling around them that gives off X-rays; the lines are like a topographic map telling you where the (otherwise invisible) gas is in the picture.

"So what?", you might say. We’ve seen lots of clusters before. Ah, but this one is different: it’s a whopping 9.6 billion light years away.

Invisible light discovers the most distant cluster of galaxies
Institute for the Physics and Mathematics of the Universe (IPMU) - 10 May 2010

Dr. Masayuki Tanaka of the Institute for the Physics and Mathematics of the Universe (IPMU), Dr. Alexis Finoguenov of the Max Planck Institute for Extraterrestrial Physics, and Dr. Yoshihiro Ueda of Kyoto University discovered the most distant cluster of galaxies in the universe 9.6 billion light years away using light invisible to our eyes.

The universe hosts a multitude of galaxies. Galaxies are not uniformly distributed in the universe, but are arrayed in filamentary structures. Filaments permeate the universe and form a gigantic cosmic spider web. Galaxies clusters, where many galaxies live together, are often located at the knots of the filaments. The most distant cluster known – at least until now – is located some 9.2 billion light years away. A team of astronomers from Japan and Germany has discovered an even more distant cluster of galaxies using light invisible to human eyes.

Most distant galaxy cluster revealed by invisible light
Max Plank Institute for Extraterrestrial Physics (MPE) - 10 May 2010

An international team of astronomers from Germany and Japan has discovered the most distant cluster of galaxies known so far - 9.6 billion light years away. The X-ray and infrared observations showed that the cluster hosts predominantly old, massive galaxies, demonstrating that the galaxies formed when the universe was still very young. These and similar observations therefore provide new information not only about early galaxy evolution but also about history of the universe as a whole.

Clusters of galaxies are the largest building blocks in the universe. Our galaxy, the Milky Way, is part of the Virgo cluster, comprising some 1000-2000 galaxies. By observing galaxies and clusters that are very distant from Earth, astronomers can look back in time, as their light was sent out a long time ago and took millions or billions of light-years to reach the astronomers´ telescopes.

An international team of astronomers from the Max Planck Institute for Extraterrestrial Physics, the University of Tokyo and the Kyoto University has now discovered the most distant cluster of galaxies observed so far. X-ray observations in the Subaru XMM Deep Field helped to identify the candidates, and infrared observations using the Subaru telescope provided the distance information. A particularity of this discovery consists in using infrared wavelengths, invisible to the naked eye. This is dictated by the expansion of the universe, which forces distant galaxies to have large velocities, shifting their light away from visible to infrared wavelengths. The Multi-Object Infrared Camera and Spectrometer (MOIRCS) at the Subaru telescope works at near-infrared wavelengths, where the galaxies are most luminous.

The spectroscopically confirmed X-ray cluster at z=1.62 with
a possible companion in the Subaru/XMM-Newton deep field

• arXiv.org > astro-ph > arXiv:1004.3606 > 21 Apr 2010
  Accepted for publication in The Astrophysical Journal Letters

http://asterisk.apod.com/vie ... 31&t=19363

[rstevenson]

About the colours of those galaxies...

1. Some of the arrowed galaxies are not deep orange in colour -- most are.
2. All but one of the circled galaxies are deep orange -- the odd one is somewhat reddish in tone.

So... does the colour of a galaxy at that distance come mostly from red-shift of its "natural" colour? Or is the natural colour what we're seeing?

Rob

[Chris Peterson]

So... does the colour of a galaxy at that distance come mostly from red-shift of its "natural" colour? Or is the natural colour what we're seeing?

I assume you're actually talking about the color? <g>

I don't think any semblance of "natural" color is possible in a raw image like this. Of course, color could be reconstructed mathematically by careful image processing, but pretty clearly that hasn't been done. So I'd go along with your suggestion that we are seeing the redshifted version of the natural colors (including wavelengths that aren't even part of visible light). The fact that this actually comes out red, however, is probably a coincidence.

[rstevenson]

I assume you're actually talking about the color? <g>

Nah, colour is so much more, um, expressive.

I was wondering if the redshift at about 9.6 billion light years was sufficient to shift a normally white galaxy image (I think I recall you saying here that most galaxies were pretty much white overall) to the orange we're seeing in that image. And also, if that is so, why some of those pointed out as being part of the group were not as orange as others.

Rob

PS
Learn more than you ever wanted to know about the differences between 'Murican and Canajun spelling here.

[wonderboy]

I learned about redshift the other day, if not all of the galaxies are similar in colour or exactly the same then surely the different coloured galaxies are not part of the cluster but much closer than the other red shifted galaxies.

What confuses me is what direction are we looking in. If these galaxies are closer to the origin of the big bang, i.e. younger, then they should be closer together as the expansion theory has not had time to push them apart.

However if they are further away from the big bang than us, then surely this would make them much further apart, as expansion theories suggest that they would be getting further away from each other.

Maybe expansion has taken place in my head and I am talking rubbish, I'm not an expert and don't make myself out to be, I just think a lot lol.


Paul.

[Chris Peterson]

I learned about redshift the other day, if not all of the galaxies are similar in colour or exactly the same then surely the different coloured galaxies are not part of the cluster but much closer than the other red shifted galaxies.

Galaxies tend to be similar in color, but certainly not identical. They have a thermal contribution from their stars as well as a variety of emission contributions. So galaxies with different apparent colors will maintain a difference as they are redshifted. The difference may even increase as short wavelengths are shifted into the visible range.

What confuses me is what direction are we looking in.

There's nothing magic about direction. The idea of "looking back towards the Big Bang" probably causes all sorts of confusion. But really, we see a 3D universe and the direction we look is just a normal direction. Look around your room- do you find the idea of north and south walls confusing? Of course, when you look at those walls, you are seeing them as they were a little while ago, not now. But that doesn't change their direction at all. Likewise for looking at distant galaxies.

If these galaxies are closer to the origin of the big bang, i.e. younger, then they should be closer together as the expansion theory has not had time to push them apart.

These galaxies are closer to the Big Bang in time, but not in space. The Big Bang didn't occur at a specific place, and nothing is getting farther from the Big Bang (except in time). The Universe itself is stretching out, but that stretching can't overcome gravitational attraction. Galaxy clusters maintain their member spacing as the Universe expands around them. The galaxies aren't getting larger, and the space between them isn't increasing, because gravity is holding these structures together.