Hubble’s Galaxies With Knots, Bursts

NGC 4858, NGC 4860

Credit: ESA/Hubble & NASA

In the northern constellation of Coma Berenices (Berenice's Hair) lies the impressive Coma Cluster —  a structure of over a thousand galaxies bound together by gravity. Many of these galaxies are elliptical types, as is the brighter of the two galaxies dominating this image: NGC 4860 (center).

 However, the outskirts of the cluster also host younger spiral galaxies that proudly display their swirling arms. Again, this image shows a wonderful example of such a galaxy in the shape of the beautiful NGC 4858, which can be seen to the left of its bright neighbor and which stands out on account of its unusual, tangled, fiery appearance.

NGC 4858 is special. Rather than being a simple spiral, it is something called a “galaxy aggregate,” which is as the name suggests a central galaxy surrounded by a handful of luminous knots of material that seem to stem from it, extending and tearing away and adding to or altering its overall structure. It is also experiencing an extremely high rate of star formation, possibly triggered by an earlier interaction with another galaxy. As we see it, NGC 4858 is forming stars so frantically that it will use up all of its gas long before it reaches the end of its life. The color of its bright knots indicates that they are formed of hydrogen, which glows in various shades of bright red as it is energized by the many young, hot stars lurking within.

This scene was captured by the NASA/ESA Hubble Space Telescope’s Wide Field Camera 3 (WFC3), a powerful camera designed to explore the evolution of stars and galaxies in the early universe.

Source: NASA/Hubble

---

A subtle swarm

NGC 4789A

Credit:  ESA/Hubble & NASA

Acknowledgements: Judy Schmidt (Geckzilla)

This Hubble image shows NGC 4789A, a dwarf irregular galaxy in the constellation of Coma Berenices. It certainly lives up to its name — the stars that call this galaxy home are smeared out across the sky in an apparently disorderly and irregular jumble, giving NGC 4789A a far more subtle and abstract appearance than its glitzy spiral and elliptical cousins.

These stars may look as if they have been randomly sprinkled on the sky, but they are all held together by gravity. The colours in this image have been deliberately exaggerated to emphasise the mix of blue and red stars. The blue stars are bright, hot and massive stars that have formed relatively recently, whereas the red stars are much older. The presence of both tells us that stars have been forming in this galaxy throughout its history.

At a distance of just over 14 million light-years away NGC 4789A is relatively close to us, allowing us to see many of the individual stars within its bounds. This image also reveals numerous other galaxies, far more distant, that appear as fuzzy shapes spread across the image.

Source: ESA/Hubble/Images

Dead galaxies in Coma Cluster may be packed with dark matter

This artist's impression of the ‘quenching’ process shows how a normal blue (star-forming) galaxy lost its gas while falling into the Coma Cluster very early on in its formation. Credit: Cameron Yozin, ICRAR/UW. Hi-res image

The Coma Galaxy Cluster is a massive cluster of galaxies in the constellation Coma Berenices. Each point of light in this image may look like a star but in fact they are, mostly galaxies. With over 650 galaxies in the cluster, Abell 1656 is one of the densest collections of galaxies in the entire sky. Credit: Greg Parker, New Forest Observatory.

Galaxies in a cluster roughly 300 million light years from Earth could contain as much as 100 times more dark matter than visible matter, according to an Australian study.

The research, published today, used powerful computer simulations to study galaxies that have fallen into the Coma Cluster, one of the largest structures in the Universe in which thousands of galaxies are bound together by gravity.

"It found the galaxies could have fallen into the cluster as early as seven billion years ago, which, if our current theories of galaxies evolution are correct, suggests they must have lots of dark matter protecting the visible matter from being ripped apart by the cluster.”

Dark matter cannot be seen directly but the mysterious substance is thought to make up about 84 per cent of the matter in the Universe.

International Centre for Radio Astronomy Research PhD student Cameron Yozin, who led the study, says the paper demonstrates for the first time that some galaxies that have fallen into the cluster could plausibly have as much as 100 times more dark matter than visible matter.

Yozin, who is based at The University of Western Australia, says the galaxies he studied in the Coma Cluster are about the same size as our own Milky Way but contain only one per cent of the stars.

He says the galaxies appear to have stopped making new stars when they first fell into the cluster between seven and ten billion years ago and have been dead ever since, leading astrophysicists to label them “failed” galaxies.

This end to star formation is known as “quenching”.

“Galaxies originally form when large clouds of hydrogen gas collapse and are converted to stars—if you remove that gas, the galaxy cannot grow further,” Yozin says.

“
Falling into a cluster is one way in which this can happen. The immense gravitational force of the cluster pulls in the galaxy, but its gas is pushed out and essentially stolen by hot gas in the cluster itself.

“For the first time, my simulations have demonstrated that these galaxies could have been quenched by the cluster as early as seven billion years ago.

“They have however avoided being ripped apart completely in this environment because they fell in with enough dark matter to protect their visible matter.”

This research was motivated by the recent observational discovery of these galaxies by an American and Canadian team led Professor Pieter van Dokkum of Yale University. 

Using the data the North American team published last year, Yozin was able to create computer simulations to model how the galaxies evolved into what we can see today.

The study was released in the journal Monthly Notices of the Royal Astronomical Society, published by Oxford University Press.

Further Information  

ICRAR is a joint venture between Curtin University and The University of Western Australia with support and funding from the State Government of Western Australia.


Original publication details

'The quenching and survival of ultra-diffuse galaxies in the Coma cluster’ in Monthly Notices of the Royal Astronomical Society. Published online on 20/7/2015 at the MNRAS website.

Contact Details  

Cameron Yozin (ICRAR – UWA)
Ph: +61 8 6488 3819
E: cameron.yozin-smith@icrar.org
M: +61 423 941 128  

Pete Wheeler (Media Contact, ICRAR)
Ph: +61 8 6488 7758
E: pete.wheeler@icrar.org
M: +61 423 982 018

UWA Media Office
Ph: +61 8 6488 3229
E: uwamedia@uwa.edu.au

Source: ICRAR - International Centre for Radio Astronomy Research