Update on the "Violin Clef" merger: redshifts and Merger Zoo
Since I haven’t posted here before, I’d like to introduce myself. My name is Kyle Willett, and I’m a postdoc working at the University of Minnesota in Lucy Fortson’s group. My work for Galaxy Zoo includes development of the next generation of tools that Zooites can use to explore galaxies and conduct their own research. My own scientific focus is on high-energy active galaxies, for which our group is using Sloan and Galaxy Zoo data to try and quantify the environmental properties.
For this post, I’d like to talk about follow-up work we’ve been doing on a recent discovery. About a month ago, Galaxy Zoo contributor Bruno discovered an example of a spectacular merger in the Sloan DR8 data that looked like a triple, or possibly quadruple system. It’s been informally dubbed the “Violin Clef” or the “Integral” based on its shape:
This system is scientifically interesting for several reasons. While merging galaxies are common throughout the universe, the merging process is relatively quick compared to the total lifetime of a galaxy. Catching a system with long tails and multiple companions is rarer, and gives us the chance to match our models of galaxy interaction against a system “caught in the act”. This is one of the main drivers of Merger Zoo, and a system like this is a good test to see if we can reproduce the tidal features. If so, then we can start to think about the bigger picture, and predict how often you’d expect a multi-galaxy merger like this to occur.
We’re also interested in the gas and stellar content of the galaxies and their tails. In most merging systems, gas in the galaxies is gravitationally compressed, which leads to a burst of new star formation in the galaxies and their tails. Since this results in more young and hot stars, the colors of these galaxies are typically blue in the Sloan bands. However, all four galaxies and the tidal tails in this system are red. If that’s the case, then we want to estimate the current age of the system. Were the galaxies all red ellipticals to begin with, with very little gas that could form new stars? Or has the starburst already come and gone – and if so, how long-lived are these tidal tails going to be?
After Bruno’s discovery, the team started by looking at what other archived observations could tell us. An ultraviolet image from the GALEX satellite showed no strong UV source in the system. Radio observations showed a point source in the system that might be consistent with weak star formation. This convinced us that we needed an optical spectrum of the system.
Spectra give several crucial pieces of information – first, by measuring redshifts we can determine an accurate distance. This tells us whether all four galaxies genuinely belong to a single interacting group, or whether some appear in projection. Knowing the distance, we can also use the UV and radio flux measurements as diagnostics of the total star formation rate. Finally, with really accurate spectroscopy, we might be able to measure the kinematics of the galaxies, and measure the velocities to get a 3-D picture of how the four members are interacting.
Since Sloan doesn’t have a spectrum of this system, we needed more observations. Danielle Berg, a graduate student at the University of Minnesota, observed the Violin Clef in September using the 6.5-meter Multiple Mirror Telescope in Arizona and obtained two optical spectra.
The analysis has shown that all four galaxies lie at the same redshift (z=0.0956 +- 0.002), and are likely all genuine members of the same group. None of the galaxies show evidence of strong star formation, confirming the red colors that we see in the Sloan data.
The next step in the analysis will be working with simulations like the ones in Merger Zoo. Having confirmed that this really is a quadruple merger will significantly constrain the merger models, and hopefully give us well-defined parameters for the age and history of the system. This is a step that Zooites can help with – if you go to http://mergers.galaxyzoo.org/merger_wars, you can identify simulations that resemble the Violin Clef. We need more clicks at this point, so please consider going to Merger Zoo and helping out! We hope that this will result in another scientific publication soon for the Galaxy Zoo team, and it’s been an exciting project to work on.
This Week’s OOTW features Budgieye’s OOTD posted on the 1st of April 2011.
These two objects, called CFBDSIR J1458+101 A and B, lurk 75 light years away in the constellation Bootes just below Arcturus; a star marking one of the constellation’s knee. Both objects – called Brown Dwarfs – are locked in orbit with each other, with the distance between them about 2.6 AU or 388, 954, 800 Kilometres.
Brown Dwarfs are often known as ‘failed stars’. They’re objects not much bigger than a gas giant, with the smaller dwarfs weighing in at 13 times the mass of Jupiter and the largest just below 0.08 solar masses; the mass of the smallest main sequence stars. They aren’t planets however, as, unlike planets, they form just like any other star – out of the interstellar medium, but because of their low mass they can never undergo any sustainable fusion.
The object of interest in Budgie’s OOTD is the dimmest object of the pair. With a meagre temperature of 370 K (about 96 Centigrade) it’s as hot as a fresh cup of tea, making it the coolest brown dwarf on record!
The paper on the discovery of this dwarf is here.
This week’s OOTW features an OOTD posted by Lightbulb500 on the 22nd of February 2011.
Lurking in the constellation Pegasus is this beautiful pair of active galaxies. Their catalogue names are UGC 12914 and UGC 12915, and their more imaginative name is the Taffy Galaxies.
In the words of Lightbulb:
The galaxies are located around 60 megaparsecs from Earth (or 196 million light years).
Both were once normal spiral galaxies, but are now in the midst of a high speed collision that has already stripped them of most of their hydrogen gas.
The pair will likely merge together at some point in the future.
What earns this pair their ‘Taffy’ designation is quite unusual. There is a bridge of hydrogen gas linking the two galaxies that is emitting large quantities of radio waves and is also producing at least a few stars. It is the presence of this intergalatic gas bridge that makes these Taffy galaxies.
While searching around for info I came across an interesting paper on this galaxy pair by J Braine et al (PDF here); it’s well worth a read. According to the paper, the galaxies collided more or less head on 20 million years ago, creating that widening bridge composed of anything between 2-9 x 10^9 solar masses of interstellar gas! The green tint in between the galaxies would be from H-alpha emissions, showing where the bridge is churning out newborn stars, or, where the collision sent out shockwaves, ionizing parts of the bridge.
This week’s OOTW features an OOTD by Alice, which was posted on the 27th of January 2011.
Today’s OOTW is a lovely silly one; here’s a screenshot:
Most of the images came from the pure art thread, a place full of fun pictures made from images from the SDSS!
Alice also mentioned a survey of our experiences on the Zooniverse for us all to do. It’s a citizen science research project by Peter Darch! There’s more info here 🙂
And also a congratulations to Half65, who through his work in the overlapping galaxies project is now a co-author of a galaxy zoo paper!
Astrophotography 365 – Completed!
This week’s OOTW features an OOTD by Jules, posted on the 7th of January 2011.
Jules, at the end of 2009, had the idea of an ‘Astrophotography 365’ challenge, where at least one astronomically themed image gets posted on the Galaxy Zoo forum each day in 2010. And it went down extremely well, with just over a thousand images posted!
In the words of Jules:
The level of interest in the thread was unexpected and the contributions came thick and fast. On cloudy nights we had photos of astronomy themed gadgets, toys, books and jewellery! There were several photos posted for each day and the project grew bigger than I had anticipated. I had originally intended to put all the photos into a montage at the end of the year but we had so many contributions that I opted for monthly montages instead in order to make the final one manageable.
The 365 is now complete. We more than met the challenge and here is the result:
We had pictures of deep sky treasures such as star clusters, nebulae and galaxies as well as comets stars, planets and the Sun (including its spectrum) and the Moon. Equipment ranged from mobile phones to DSLRs and webcams to remotely controlled scopes like SLOOH and SARA-S. Some contributors had never taken an astrophoto before and produced some amazing results. We also braved all weathers to meet the challenge. I hope we kept people entertained – the thread has had over 42,000 views.
Thanks to everyone who took part. It was huge fun. Maybe we can have a year off and do it all over again! Meanwhile let’s resurrect Alexandre’s old thread and keep clicking in 2011!
A Spindle in the Dragon
This week’s OOTW features Alice’s OOTD posted on the 30th of December 2010.
This is the Spindle Galaxy, otherwise known as NGC 5866. It’s a beautiful lenticular that lurks 44 million light years away from us in the constellation Draco.
Lenticular galaxies are a bit like spiral galaxies in the fact that the main part of the galaxy is a flattened disk of stars, but like an elliptical galaxy they have no arms. The star forming material in lenticulars is mostly used up, so these galaxies mostly consist of old stars rather than new ones.
NGC 5866, unlike most of the galaxies that share its morphology, has a dust line stretching through its galactic plane – its disk – and as the dust lane is perfect for churning out stars, it has a string of hot, young, blue stars accompanying it.
The images on MAST and the Hubble Legacy Archive are certainly worth a look too!
Happy New year! 🙂
A Dark Secret in Virgo
This week’s OOTW features my OOTD ‘A Dark Secret in Virgo‘ posted on the 11th of December 2010.
On the 17th of March 1781, Pierre Méchain discovered this beautiful galaxy. NGC4254 lurks 50 million light years away in the constellation Coma Berenices. It’s a disturbed spiral, with its right arm jutting out further than the other. So what’s caused this? Let’s zoom out…
There’s nothing to see that could have caused the disruption, right? Well, let’s zoom into this patch of sky in Coma Berenices’ next door neighbour, Virgo:
Is it a black hole? No. Is it a gigantic cloaked alien ship that tugs galaxies?! Nope. It is in fact VIRGOHI21; a HI region 50 million light years away that was first detected by the Lovell telescope. A HI region is a mass of neutral hydrogen, and in this case it has hardly any or no stars. But there’s something more to this object than meets the eye…
This is a screenshot of an animation (my attempts at posting the animation here failed!) which shows a map of VIRGOHI21. According to this website here the larger brighter mass is NGC 4254, and you can see the cloud is cascading down from the disturbed spiral arm in a stream of neutral hydrogen to the centre of the image. Astronomers have calculated that the total mass of this HI region is 2×10^8 Mʘ (solar masses), but the velocity and spin of this object indicates that there is more mass than we can detect and so the object actually has a mass of 10^11 Mʘ! So where does the rest of the mass come from…?
Dark matter! It is currently thought that VIRGOHI21 is a dark galaxy, which is a starless galaxy made up of mostly dark matter with little else apart from dust and hydrogen. This dark galaxy is interacting with NGC 4254 like any other normal galaxy would!
VIRGOHI21 is currently the best dark galaxy candidate out there, but others include HE0450-2958 which is a quasar that appears to be galaxy-less! Usually quasars have a host galaxy, but this one doesn’t appear to have one that we can see, so it has been proposed that the Quasar is actually part of a dark galaxy.
A survey called AGES uses the Arecibo observatory to find HI regions that are in connection with dark galaxies: http://www.naic.edu/~ages/
A Universe Brimming with Red Dwarfs
This week’s OOTW features Lightbulb500’s OOTD posted on the 4th of December 2010.
This star, with a mass of around half of that of our own star and a temperature many degrees cooler; is a red dwarf. They are the most common stars in the universe, 85% of our galaxy’s stellar population is composed of red dwarfs and it was thought that there was 1×10^23 (or 100 sextillion) in the universe. They are also the longest lived with a lifespan of up to ten trillion years!
The number of red dwarfs in the universe has been recently changed to a much higher number, as Lightbulb500 writes:
[…] New data that confirms the presence of red dwarfs in eight elliptical galaxies between 50,000 and 3 million light years distant. As well as confirming their presence the number of red dwarfs per galaxy has been calculated and reveals that these elliptical galaxies contain 20 times the number of red dwarfs as the Milky Way!
Such a large jump in the number of red dwarfs in elliptical galaxies has necessitated a ‘slight’ revision to the number of stars inhabiting our universe.
The figure has been revised from 100 sextillion or (if I may have an infant moment) 100,000,000,000,000,000,000,000, or 1×10^23 if you like standard form to 300 sextillion – It has been tripled!
Such an increase has other knock on effects – more stars means more ‘normal’ matter so the universe would ‘need’ less dark matter to ‘work’.
It could also have an effect on how dark matter is concentrated around galaxies.
Birthday Wishes and NGC 3169
This week’s OOTW features Alice’s OOTD posted on the 25th of November 2010.
This beauty is NGC 3169. It’s a spiral galaxy 55.3 million light years away in the constellation Sextans. It’s part of a group of two other spiral galaxies: NGC 3166 and NGC 3165. The nearest galaxy to it – NGC 3166 – is tugging at it, causing its spiral arms to distort.
NGC 3169 also happens to be a nomination for this:
“Today’s Object of the Day is not an object, but a request for some. Zookeeper Rob is looking for an “Object of the Day” for a Zoo Advent Calendar, which should be interesting (open up this pocket of space and – oops, a black hole! ). Want to help?
From now until Monday, please post your favourite galaxy, either from Hubble Zoo or from SDSS. On Monday we will have a poll, closing on Tuesday night.”
(Post the galaxies in Alice’s OOTD)
Also, Happy Birthday Zookeeper Chris!
NGC7252: The Atoms-For-Peace Galaxy
This OOTW features Budgieye’s OOTD posted on the 18th of November 2010.
This is NGC 7252, or the Atoms-For-Peace galaxy. This beautiful merger lurks in the constellation Aquarius 220 million light years away. It’s a beautiful example of a galaxy interacting with another, with both galaxies twisting round each other as they are caught up in each others gravitational pull. As this happens over a course of millions and billions of years tidal tails are thrown out, creating streamers of stars stretching for thousands of light years. As well as beautiful streamers the collision has created hundreds of new stars from the disruption, and many new star clusters only 50-500 million years old are now spread out across the galaxy.
And what of the name?
The galaxy – which looks rather like a diagram of an atom – was named after a lecture called Atoms for Peace, which was given by the US president Dwight D. Eisenhower in 1953. In his lecture, he called for nuclear power to be used for peaceful rather than destructive purposes.
There’s more info on the galaxy at ESO!