Dwarf galaxies are the most abundant galaxies in the universe. Yet understanding how these systems behave in galaxy group environments is still a mystery.
These objects are notoriously difficult to study because they are very small relative to classic spiral galaxies. They also have low mass and a low surface brightness, which means that, to date, we have only studied the dwarf galaxies in the nearby universe, out to about 35 million light years away.
My collaborators and I have been studying a dwarf galaxy named ESO 324-G024 and its connection to the northern radio lobe of a galaxy known as Centaurus A (Cen A).
The giant radio lobes are comprised of high energy charged particles, mostly made up of protons and electrons, that are moving at extremely high speeds. The lobes were created from the relativistic jet (shown in the image at the top) that is blasting out of the central core of Cen A.
These energetic particles glow at radio frequencies and can be seen as the fuzzy yellow lobes in the centre of the image (above), together with the neutral hydrogen intensity (HI) maps of its companion galaxies. The lobes now occupy a volume more than 1,000 times that of the host galaxy shown in the image at the top, assuming the lobes are as deep as they are wide.
These HI intensity maps are part of a large HI survey of nearby galaxies called the Local Volume HI Survey (LVHIS). These maps have been magnified in size by a factor of 10 so that they can be seen on such a large scale and are coloured by their relative distances to the centre of Cen A.
A green galaxy is at virtually the same distance from Earth as Cen A, while blue galaxies are in front of Cen A (closer to us) and red galaxies are behind it (farther away).
One of the striking things about this image is that out of the 17 galaxies overlaid onto the Cen A field, 14 are dwarf galaxies.
An interesting dwarf
The one object that really interested me after making this image was the dwarf irregular galaxy ESO 324-G024 (just above the black box). It has a long HI gaseous tail that extends roughly 6,500 light years to the northeast of its main body and it is at nearly the same distance as Cen A.
These two pieces of information right away made this a system worthy of investigation because we thought that perhaps there is a connection between this dwarf galaxy and the northern radio lobe of Cen A.
Nothing like this has ever been seen before, probably because galaxies that have giant radio lobes like Cen A are usually hundreds of millions to billions of light years away. Cen A is a special galaxy because it’s only about 12 million light years from Earth.
This was an interesting result and it told us that the northern radio lobe must be inclined toward our line of sight, because ESO 324-G024 was at nearly the same distance as Cen A. This had previously been suggested by studying the jet way down in the core of the host galaxy, but it had never been confirmed in this way before.
A wind in the tail
Next we investigated the mechanism responsible for creating the HI tail in ESO 324-G024. We looked at the likelihood of gravitational forces from the large, central host galaxy of Cen A as a potential culprit for ripping out ESO 324-G024’s gas. But we determined that it is simply too far away from the central gravitational potential for gravity to have created the tail.
So we explored ram pressure stripping, which is thought to be a dominant force for removing gas in galaxies within these kinds of groups. Ram pressure is a force created when a galaxy moves through a dense medium, and thus experiences a wind in its “face”.
It’s similar to holding a dandelion in your hand and then running as fast as you can go and watching the seeds blow away in the wind. At rest, the dandelion feels no wind and the seeds stay intact. But when you run, all of a sudden, the dandelion feels the wind created from your running and this wind blows away the seeds.
In this scenario, ESO 324-G024 is the dandelion and you represent gravity carrying the galaxy through space. We calculated the wind speed required to blow the gas out of ESO 324-G024 and compared this speed to the speed of ESO 324-G024 moving through space. It turns out that the two speeds did not match.
ESO 324-G024 seemed to be moving too slow for all of its gas to have been blown into its long tail. So we went back to our first conclusion about ESO 324-G024 being behind the radio lobe and surmised what may be happening.
We know that the charged particles inside the northern radio lobe of Cen A are moving extremely fast. If ESO 324-G024 is just now coming into contact with the posterior outer edge of the radio lobe of Cen A, which is likely due to its proximity to Cen A, then it is possible that ESO 324-G024 is not only feeling the wind generated from its own motion through space, but also the wind from the charged particles in the radio lobe itself.
This would be like you running with the dandelion and at the same time blowing on it. Therefore, we concluded that ESO 324-G024 is most likely experiencing ram pressure stripping of its gas as it passes close to the posterior edge of the northern radio lobe.
This means that these types of radio lobes must have wreaked havoc on their dwarf galaxy companions in the distant past. This is an interesting case study that showcases how dwarf galaxies may have been knocked about, blasted, by their larger companion galaxies.
Just how common are situations like this and how have they influenced dwarf galaxies over cosmic time? The answer is that we simply don’t know, but I look forward to exploring these questions.
Claire-Elise Green wants to time travel. She wants to peer into the stellar nursery of the cosmos and understand how stars are formed, in their infancy, billions of years ago. To do this she needs access to multi-billion dollar telescopes, astronomical amounts of data and the time to work with the best and brightest in the field. Not something you can just Google.
This is why she is heading to the Max Planck Institute for Radio Astronomy in Bonn, Germany to work with the equipment, data and experts needed to further her PhD research. This isn’t a cheap European getaway by any stretch of the imagination.
But Claire-Elise took a big step towards financing this journey when she was selected as the first ever recipient of the CSIRO Alumni 2015 Scholarship in Physics award.
The award was setup in honour of the four physicists who sadly lost their lives – two years ago – in a tragic accident, with a view to helping young Australians finance their projects and research in physics.
After beating out 14 other entries, Claire-Elise was handed the award and the $5000 scholarship fund at a ceremony in Lindfield, NSW.
Before she heads off to Germany with her novelty over-sized cheque, we had a chance to sit down and speak with Claire-Elise about her research, her time with us and her passion for science.
Claire-Elise’s scholarship winning project seeks to understand the birth of stars. So she scours the sky, looking for ancient molecular clouds in the deep dark recesses of space. These clouds play the role of stellar nurseries and look like large blobs with a radio telescope, so naturally she refers to this area of research as blob-ology.
Deep within the blob (and with the help of incredibly sensitive high resolution telescopes) you can find strings of gas and dust which appear within the cloud. These strings, called filaments, are the focus of Claire-Elise’s PhD, supervised by Dr. Maria Cunningham at UNSW, and our very own Dr Joanne Dawson.
In the process of star formation, dense regions of gas and dust within the molecular cloud collapse under gravity to form star forming cores. Most of these star forming cores have been found to lie on these dense filaments of gas like beads on a string. The role of these filaments in the star formation process, however, is currently unknown.
While she has had access to the Australian Compact Telescope Array near Narribri, and the Mopra Telescope, near Coonabarabran there is still lots of work to be done in this relatively new field of astrophysics and the time she will spend at the Max Planck Institute will further her understanding of the cosmic cabbage patch.
This PhD research into star formation is the culmination of many years of study back here on Earth.
A passionate scientist from a young age, Claire-Elise cites our Double Helix magazine as an early inspiration for all things scientific (please excuse the shameless self-promotion).
As she moved into high school she was fortunate enough to be part of a program designed to encourage young women to engage with science. Indeed, she chose to complete a Bachelor of Advanced Science majoring in Physics at University. And even though she was considering a double major including chemistry, we won’t fault her for taking the easy road and sticking to a single major!
In order to get some real world experience she completed two summer programs with our scientists where she collected her own data with the telescope at Parkes and the array of telescopes at Narrabri, she even used this opportunity to be get published.
Not only did she spend valuable time in the field where she could get her hands dirty and experience the realities of modern research, she also had the opportunity to rub shoulders with inspirational scientists like our own Dr Julie Banfield and Dr Jill Rathborne. Oh and she got to take a hayride on the world famous ‘Dish’ and take some memorable pictures.
Through all these experiences and with the example set by her mentors like Dr Cunningham, Dr Dawson and Dr Rathborne, Claire-Elise developed into a scientist with a passion for encouraging more women to try science, as she says – they tend to “rock at it”.
Before she departs for Europe and the next stage of her research career, she hopes to find some time to indulge in her favourite pastimes: tending her vegetable and herb gardens and enjoying a bit of the old ‘Crafternoon tea’ (that’s an afternoon tea coupled with crafts if you are unfamiliar with the term). When you are searching for the answers to the some of the universe’s biggest questions, it pays to stay grounded.
You can hear more about Claire-Elise’s research in her own words on Thinkable.org. Don’t forget to vote for her while you are there.
By Emily Lehmann
There’s a new star in the making in the world of astronomy, with our Australian Square Kilometre Array Pathfinder (ASKAP) named as a finalist in The Australian Innovation Challenge’s Manufacturing, Construction and Infrastructure category*.
We recently shared some of the first images produced by the amazing ASKAP telescope. It comprises a cluster of 36 radio dishes that work in conjunction with a powerful supercomputer to form what is, in effect, a single composite radio telescope a massive six kilometres across.
This allows it to survey the night sky very quickly, taking panoramic snapshots over 100 times the size of the full moon (as viewed from Earth, of course!).
The world-leading facility is revolutionising astronomy, and this award nomination is a welcome recognition. You can vote for it here – just scroll down to the bottom of the page.
Now, for all you space cadets, here’s five astronomical facts about why ASKAP is out of this world and a sure-fire winner:
- ASKAP’s 36 radio dishes, each 12 metres in diameter, give it the capacity to scan the whole sky and make it sensitive to whisper-quiet signals from the Milky Way.
- ASKAP is an outstanding telescope in its own right, as well as a technology demonstrator for the Square Kilometre Array (SKA). This pioneering technology will make ASKAP the fastest radio telescope in the world for surveying the sky.
- Once built, the SKA will comprise of a vast army of radio receivers distributed over tens to hundreds of kilometres in remote areas of Western Australia and Africa.
- The SKA will generate five million million bytes of information in its first day. That’s almost as many grains of sand on all of the world’s beaches.
- ASKAP is located in the remote Murchison Shire of Western Australia, which was chosen because there is hardly any human activity and so little background radio noise.
ASKAP is one of four CSIRO projects already in the running for different categories in the Oz’s Innovation Challenge (we’ve also written about swarm sensing and Direct Nickel). You can #voteCSIRO for any and all of them – just follow the links from the Challenge’s home page!
By Nola Wilkinson
Ever wondered what there is between the stars? Dr Naomi McClure-Griffiths not only wonders about it, she’s on a mission to find out.
Naomi is fascinated with the life of stars, the behaviour of interstellar gas, and how gas and stars interact. “As an astronomer, I’d like to understand how the galaxy formed and how it’s living its life,” she says.
“The galaxy is much more frothy and bubbly than we ever thought. It looks like the head on a glass of beer.”
Very large stars, 8-20 times the size of our sun, experience dramatic supernova explosions that push gas out of the galaxy via solar winds travelling at up to 1000 kilometres a second.
It is these solar winds that blow bubbles in the gas between the stars, creating a frothy, foamy appearance.
Watch this video to find out more about Naomi and her amazing work:
By Lisa Harvey-Smith, CSIRO
The first images from Australia’s Square Kilometre Array Pathfinder (ASKAP) telescope have given scientists a sneak peek at the potential images to come from the much larger Square Kilometre Array (SKA) telescope currently being developed.
ASKAP comprises a cluster of 36 large radio dishes that work together with a powerful supercomputer to form (in effect) a single composite radio telescope 6km across.
What makes ASKAP truly special is the wide-angle “radio cameras”, known as phased array feeds, which can take up to 36 images of the sky simultaneously and stitch them together to generate a panoramic image.
Why panoramic vision?
Traditional radio telescope arrays such as the Australia Telescope Compact Array near Narrabri, NSW, are powerful probes of deep-space objects. But their limited field of view (approximately equivalent to the full moon) means that undertaking major research projects such as studying the structure of the Milky Way, or carrying out a census of millions of galaxies, is slow, painstaking work that can take many years to realise.
The special wide-angle radio receivers on ASKAP will increase the telescope’s field of vision 30 times, allowing astronomers to build up an encyclopedic knowledge of the sky.
This technological leap will enable us to study many astrophysical phenomena that are currently out of reach, including the evolution of galaxies and cosmic magnetism over billions of years.
For the past 12 months a team of CSIRO astronomers has been testing these novel radio cameras fitted on a test array of six antennas.
The first task for the team was to test the ability of the cameras to image wide fields-of-view and thus demonstrate ASKAP’s main competitive advantage. The results were impressive!
One of the first test images from the ASKAP test array is seen above. The hundreds of star-like points are actually galaxies, each containing billions of stars, seen in radio waves. Using CSIRO’s new radio cameras, nine overlapping images were taken simultaneously and stitched together.
The resulting image covers an area of sky more than five times greater than is normally visible with a radio telescope. The information contained in such images will help us to rapidly build up a picture of the evolution of galaxies over several billion years.
Where next for ASKAP to look
On the back of this success, the commissioning team turned the telescope to the Sculptor or “silver coin” galaxy to test its ability to study deep-space objects.
Sculptor is a spiral galaxy like our own Milky Way, but appears elongated as it is seen almost edge-on from earth.
This image (above) shows the radio waves emitted by hydrogen gas that is swirling in an almost circular motion around the galaxy as it rotates.
The red side of the galaxy is moving away from us and the blue side is moving towards us. The speed of rotation tells us the galaxy’s mass.
The team has also tested the ability of the telescope to “weigh” the gas in very distant galaxies. The image (below) shows a grouping of overlapping galaxies called a gravitational lens.
Seven billion years ago, radio waves from a distant galaxy were absorbed by a foreground galaxy in this group. That signal was processed by ASKAP to form the spectrum (top right in the above image).
Although not visually pretty, this type of observation has enormous scientific value, allowing astronomers to understand how quickly galaxies use up their star-forming fuel.
The latest demonstration with the ASKAP test array is a movie (below) of layers through a cloud of gas in our Milky Way.
This series of images – similar to an MRI scan imaging slices through the human body – demonstrates the ability of the telescope to measure the intricate motions of the spiral arms of the Milky Way and other galaxies.
Building to the bigger array
These images are just the beginning of a new era in radio astronomy, starting with SKA pathfinders like ASKAP and culminating in the construction of the SKA radio telescope.
Once built, the SKA will comprise a vast army of radio receivers distributed over tens to hundreds of kilometres in remote areas of Western Australia and South Africa.
Just like ASKAP combines signals from several dishes, the SKA will use a supercomputer to build up a composite image of the sky.
Each ensemble of antennas will work together to photograph distant astronomical objects that are so faint, that they can’t be seen at all with current technology.
The SKA will thereby open up vast tracts of unexplored space to scientific study, making it a game-changer in astrophysical and cosmological research.
Where does our Galaxy get the fuel to keep forming stars? The answer may lie in thousands of gas clouds flying around the outskirts of our Galaxy.
Originally posted on Universe @ CSIRO:
“Food pills” were a staple of science fiction for decades. For our Galaxy, they may be real.
The Galaxy has been making stars for the last 8 billion years. What’s kept it going all that time?
When old stars die, some of their gas goes back into the galactic “soup” for star making. But in the long run a lot of it gets locked up in long-lived dwarf stars.
So the Galaxy needs fresh supplies of gas.
Astronomer think that gas rains in from, probably in the form of “clouds”, and that this fuels the star-making.
But there’s a problem.
If a regular gas cloud were to hit the warm outer parts of the Galaxy — the halo — the gas would dissipate, and not reach the Galaxy’s starry disk where the party is going on.
Something must hold the gas clouds together on their way to the…
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Some exciting news from ‘The Dish’ today.
Originally posted on Universe @ CSIRO:
In the journal Science today, astronomers using our Parkes telescope have revealed signs of cataclysms in the distant Universe.
They’ve found four ‘bursts’ or ‘flashes’ of radio waves, the furthest one coming from about 11 billion light-years away. And, they say, if you had ‘radio eyes’ — eyes that could detect radio waves — you’d see one of these ‘bursts’ going off somewhere in the sky every ten seconds. It would be like a continuous show of distant fireworks.
What is a ‘burst’? It’s a spike in the radio energy the telescope receives. Here, from the Science paper, is what the astronomers found. (‘Flux density’ means signal strength.)
‘FRB’ stands for Fast Radio Burst. Because they really are very fast, lasting for only a couple of milliseconds.
The speed of the bursts, their strength, and other characteristics of the radio signal, all help to show what the bursts…
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