We’re Observing at the Very Large Array!
I’m really excited to be able to post that galaxies selected with the help of Galaxy Zoo classifications are being observed at the VLA (Very Large Array) in New Mexico, possibly right now.
The funny thing about observing at the VLA is that you do all of the work for the actual observations in advance.
The VLA runs in queue mode – as an observer you have to submit very (very) detailed information about what you want the telescope to do during your session (called a “scheduling block”) and a set of constraints about when it’s OK to run that (for example you tell them when the galaxy is actually up in the sky above the telescope!). Then the telescope operators pick from the available pool of scheduling blocks at any time to make best use of the array.
This means after you submit the scheduling blocks you just have to sit and wait until you start getting notifications from VLA that your galaxies have been observed. The observing semester for the B-array configuration started on 4th October (had a pause for the US shutdown) and runs until the 13th January 2014. I’m happy to report that we started getting notifications in late November of the first of our 2 hour scheduling blocks having been observed. At the time of writing four of our galaxies have each been observed at least once (we need six repeat visits to each one to get the depth of data we’d like) for a total of 16 hours of VLA time. I’ve been getting notifications every couple of days – which means that as I write this the VLA could be observing one of our galaxies!
Since making these very detailed observation files is the observing prodecure at the VLA – it takes the length of time you’d expect given that…..
So, in September in-between a crazy travel schedule, and with a lot of help from our collaborator Kelley Hess at Cape Town, I spent a lot of time scheduling VLA observations of some very interesting very gas rich and very strongly barred galaxies we identified in the Galaxy Zoo 2 sample (the bit which overlaps with the ALFALFA survey which measures total HI gas in each galaxy).
We have been granted time to observe up to 7 of these fascinating objects (depending on scheduling constraints at the VLA) which I think may reveal some really interesting physics about how bars drive gas around in the discs of galaxies.
You might notice from the picture (and the name) that the VLA is not a “normal telescope”. It’s what astronomers call a radio interferometer. Signals are collected from 27 separate antennas and combined in a computer. This means that as well as observing sources for flux calibration (so we can link how bright our target is through the telescope with physical units) we also have to observe, roughly every 20 minutes or so a “phase calibrator” to be able to know how to correctly add the signals together from each of the antennae (to add them “in phase”).
So a single scheduling block lasting 2 hours for one of our sources comprises:
1. Information to tell the VLA where to slew initially and what instrumentation to use (how to “tune” it to the frequency we know the HI in the galaxy will emit at).
2. A short observation of a known bright source for flux calibration.
Then there’s a loop of
a. Phase calibration
b. Source observation
c. Phase calibration
d. Source observation
and so on – ending with a Phase calibration (on Kelley’s advice we’ll do 5 source observations, and 6 phase calibrations). We have a total of 6 of these blocks for each galaxy, that makes 12 hours of telescope resulting in about 10 hours of collecting 21cm photons per galaxy.
We have to check which times all these sources are visible to the VLA, and set durations for each part which give enough slew time and on source time wherever the sources are on the sky. And this all has to add up exactly to 2 hours to fit the scheduling block.
The benefit of this though is a telescope which acts like it’s much larger than you could ever physically build. We’re trying to detect emission from atomic hydrogen in these galaxies which emits at 21cm. So we need a really large telescope to get a sharp picture.
And just to end, because they’re lovely, here are the four galaxies the VLA has observed so far in the Sloan Digital Sky Survey visible light images.
Thanks again for your help finding these rare and interesting galaxies. They’re rare, because they’re so gas rich and strongly barred – we have previously posted about how we showed strong bars are rare in galaxies with lots of atomic hydrogen. Hopefully we’ll have some exciting results to share once we’ve analysed these data.
(PS. That takes a lot of time too – it’ll be almost 1TB of data to process in total!).
Good Things come at the same time
AAS meeting update!
The last 24 hours have been good for Zoo team member Bill Keel (@ngc3314) is based at the University of Alabama. Not only did his University football team win some sort of championship (they all look the same to Europeans) last night, but the Hubble Space Telescope observed the final Voorwerpje in our approved programme! That means Bill was probably glued to the TV and downloading and reducing the data at the same time!
He’ll add the reduced image to his poster at the AAS meeting, so if you want to see the image, come join us at the poster tomorrow! He may also blog it some time later, but for the FIRST look, you’ll have to come to the poster! There may be chocolates too….
The poster is: 339.47. HST Imaging of Giant Ionized Clouds Around Fading AGN, up all of Wednesday from 9-6.
XMM-Newton time granted to observe the Voorwerpjes!
Quick note to let you know that we’ve been granted time on XMM-Newton to observe three of the “top” Voorwerpjes. This follows the proposal we submitted earlier this year. The allocation is for priority “C” which means that they will take our observations if they fit into the schedule, but there is no guarantee.
First X-ray Data of the Mergers with Chandra
I just got notice from the people at the Chandra Science Center that Chandra has executed the observation of the first Galaxy Zoo merger – part of our study to understand black holes in mergers. This is the first of twelve such observations that should take place over the next year or so. The main science question we have that this program will help us answer is: in how many mergers do both black holes feed?
All I have at the moment are the quick-look data that that they sent me. They are more or less raw images. Here is the full frame:
And here is a zoom-in:
This is raw data, rather than properly analyzed data, so we can’t really draw any firm conclusions based on it yet, but it seems like there is no significant source detected. What does that mean? Assuming that there really is no source after we properly analyze the data, then the black hole(s) in this particular merger are either not feeding very much, or they are hidden behind lots of gas and dust.
For now, we will wait for the actual data to fully analyze it, and for the remaining 11 targets to be observed.
Working with scientists in India, we have been awarded time on the Giant Metrewave Radio Telescope (GMRT) to study the radio properties of the Green Pea galaxies discovered by Galaxy Zoo users. We hope to use this telescope to detect the first signs of radio emission from the Peas, establishing them as a new class of radio sources.
Why do we want to search for radio signals from the Peas? The radio emission comes from remnant supernovae which can accelerate relativistic electrons that emit synchrotron radiation. So when we are detecting star forming galaxies in radio emission, we are finding signatures from these supernovae, which tell us about the stars that live (or lived) in the galaxy. Therefore, using the radio emission we can trace recent star formation activity in the galaxy.
We are particularly interested in these Green Peas, because they are the closest analogues to a class of vigorously star forming galaxies found in the early universe (known as Lyman Break Galaxies). These galaxies behaved very differently from star forming galaxies in the present day universe, and can help us to understand how galaxies formed in the early universe. Because Lyman Break Galaxies are so far away, Astronomers have not yet been able to detect radio emission from any of these galaxies individually. In contrast, the Peas are much closer and we have a good chance of being able to directly detect them in radio emission. Detecting this radio emission, and determining whether or not the radio emission from the Peas is like that in nearby star forming galaxies will help us to understand the nature of star formation in the youngest galaxies.
Chandra Program to study Galaxy Zoo Mergers approved
Good news, everyone!
Earlier this year we submitted a proposal to use the Chandra X-ray Observatory to observe a set of merging galaxies in X-rays. The target list for Cycle 12 has just been released, and with a bit of scanning, you can find a set of targets with names like “GZ_Merger_AGN_1”. These targets are a set of beautiful merging galaxies discovered by YOU as part of Galaxy Zoo 1 and the Merger Hunt. The 12 approved targets are here:
These 12 mergers are all very pretty, but they have something else in common: they all host active galactic nuclei (AGN) – feeding supermassive black holes at their centers. X-rays are great for finding such hungry black holes, but we already know that all 12 of these mergers are AGN, so why observe them again? We’re looking for a mythical rare beast: the binary AGN!
Only a handful of these objects are known and they were discovered by chance. We believe that every massive galaxy has a supermassive black hole at its center and so when two galaxies merge, then there should be two black holes around for a while, that is, until they merge. The goal of our Chandra study of these 12 mergers is to systematically search for binary AGN in merging galaxies to work out what fraction of them feature two feeding black holes. Knowing whether such phases are common or not is important for understanding how black holes interact with galaxies in mergers and what exactly happens to them as they plunge towards the center of the new galaxies where they are doomed to merge and form a single supermassive black hole.
As usual, it may be quite a while before we get the data. The observing cycle won’t start for a while and takes about a year. Since our observations are short and we don’t have any time constraints (they’re galaxies, they don’t move!) the Chandra operators will most likely schedule our observations in between longer projects and time sensitive observations and so we won’t know when they will happen. Of course, once we do get the data, we’ll definitely update you.
Oh and you might notice some of the targets in the Merger Zoo in the near future. We’ll need your help to fully understand them….
Dust in the Zoo – chapters opening, continuing, and closing
Anna Manning and I are back at Kitt Peak, using the 3.5m WIYN telescope for
more observations of overlapping-galaxy systems from the Galaxy Zoo sample.
This trip started with an unexpected dust encounter. Indulging my fascination with some of the technological excesses of the Cold War, I dragged Anna (and my mother-in-law as well) to Tucson’s Pima Air and Space Museum. I particularly wanted to see their newly-restored B-36 aircraft, one of only 4 of these vintage giants left. The wind had been high already, but really whipped up and caught us in a dust storm (with added rain so it was like tiny mud droplets stinging the skin). Anna pointed out the irony, especially since I had announced on Twitter that “dust will be revealed, in detail”. Maybe next time it is I who should be more detailed.
Leaving La Silla
Our pea hunting observing run is over and, as you will have gathered from previous posts, it has gone very well. We travelled back from La Silla to Santiago last night, for another brief stay at the ESO Guesthouse. Now I’m about to get on the plane back to the UK.
We are thrilled with how well the run has gone. I’ve done a rough analysis of the data already and we’ve already started drafting the paper presenting the results! I’ll do a more careful analysis once I get back to the office, but early indications are that we’ve got a nice collection of higher redshift objects that are very similar to the fascinating SDSS Peas that were discovered on the Galaxy Zoo forum, and an almost perfect technique for finding more! I’ll keep you posted as our work progresses.
The Chilean Pea hunt continues…
You may have noticed the Galaxy Zoo blog was down over the weekend. Well, it wasn’t the only one to be experiencing technical difficulties. On Sunday night we unfortunately lost four hours of observing time to technical gremlins. First we tried to use a new filter, which resulted in a nice 10 minute exposure of nothing. After a trip to the telescope to look around inside the instrument, the support staff worked out the problem: the filter was mislabelled on the computer. With that figured out, we changed to the correct filter and carried on – only to be stopped in our tracks again a couple of hours later by the whole telescope control system crashing! This time it took three hours of methodical troubleshooting to fix the problem, apparently some problem with a power lead. By then the night was almost over.
Peas please me
Well, at the start of the night we were a bit nervous that none of our objects would turn out to be Peas. Fortunately, by the end of the night our quick looks at the data indicate that four of the seven i-Pea candidates that we managed to observe are emission line objects at the redshift we expected our selection to give, i.e. they are Peas! That’s about as good a success rate as we dared hope for.
The night hasn’t been without its difficulties. The seeing (how blurry the atmosphere makes our images) wasn’t great for most of the night, and it has turned out to be hard to actually find our targets because they are so faint. Those issues combined meant that we didn’t get through as many candidates as we hoped for, but we are still happy with the collection we got.
Right now, time for a quick breakfast then some sleep before trying to net some more Peas tomorrow night.