Tag Archive | Mergers

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.

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….

Galaxy Zoo: Mergers – A personal perspective

Now that the launch of Galaxy Zoo: Understanding Cosmic Mergers has been completed, I wanted to give a personal perspective on this project.

For me, this project started twenty years ago  when I was in graduate school.    In my dissertation work, I  modeling the tidal features of interacting galaxies.  I wrote a Fortran code for doing some of this modeling work.   You would set up a run, and then wait hours to see the result.   If it didn’t match, you had to wait hours for the next attempt.


The worst part about the modeling process was getting the “final” result.   Even if you got a close match, you never knew if you had actually found the best match.  It was always possible that a completely different set of parameters was the real solution, and you had just made a mistake.    Even with good fits, you couldn’t tell if you really had arrived at the ‘right’ solution.

Our understanding of galaxy collisions has been limited by the lack of dynamical models.  For example, we know that some galaxy collisions have very high star formation rates.   We also know that almost all extreme star burst galaxies (Ultra-luminous infrared galaxies) have undergone some type of collision.   Why isn’t this sort of reaction the inevitable result of a merger?   It seemed like the answer was always out of reach – unless we can understand the dynamics of lots of collisions.

The java applet developed for Mergers by Anthony Holincheck is the direct descendent of the old Fortran code.  Now you can run the same kind of simulations I ran for my dissertation in fractions of a second.    When Anthony and I first resurrected this code, we immediately tried using a Genetic Algorithm help us converge on the final solution.   It didn’t work.   We couldn’t reliably teach the computers how to recognize a good match.   We could run a few hundred thousand simulations per day, but we never knew if we got the right results.

The idea of using volunteers to help us happened a few years ago.   It was crazy and impractical to imagine volunteers helping out with a project like this.   Even so, a group of us proposed to do.  Of course, our proposal got shot down.  After all, there was no way that this type of thing would work.  How would you recruit such volunteers?

About a year later, I started talking with some of the team from Galaxy Zoo.    You – the volunteers of Galaxy Zoo-  have made the impossible possible.   With your help, we can create the models we need to understand the histories of hundreds of galaxy collisions.   These models will be more reliable than any a single scientist could create.    This result alone would incredibly important.   However, by carefully analyzing your inputs, we eventually hope to train the computers to do thousands of more models.   This kind of man/machine partnership is being planned for a number of future data projects, where computers need help learning how to be scientists.     We will never discover future Voorwerpen or new Peas without your help.   However, in return, we will also never make you do busy work that a machine can do.

Your efforts on the Zoo projects have created a new the way to do science.     This is nothing less than a transformation in how we look at data, analysis, and computing.

Of course, that’s just a personal perspective.

I just posted a new target for you to try.  We are going to be doing updates at 1600 GMT everyday. even Thanksgiving.  Of course, we will keep the old targets live for a week so you can go and revisit them.   This one is a repeat from some of the beta tests.   Getting a perfect model is hard, but getting close is easy.  We didn’t want to make things too difficult – at least for now.   Be assured, we will be kicking up a notch over the next days and weeks.


Mergers Update

We have just changed the target on the Galaxy Zoo Mergers page (http://mergers.galaxyzoo.org).  The new system has a broken ring and a nearby companion.  It’s a very pretty system, and it seems to be a bit easier to model than the first one we posted.  For all the systems we are putting up as challenges, we do a quick run ourselves to see if we can find any solutions that might be on-track.   Although we found a few solutions right away, we don’t know if they are the best ones or if they are unique.  Of course, that’s why we need your help.

We are going to be updating the target daily.  Every day, we should will have a new cosmic collision for you to help us model.

If you can spend 10 minutes to quickly weed out the obvious bad ones on 20-30 screens, it would be a great help to us!   The more clicks we have, the better we constrain the collision.   Make sure you hit save when you are done looking at the images!  Although we automatically back up some clicks, we don’t want to lose any of your data.

Thanks for all you do.

– John Wallin, Computational Scientist/Astronomer

Galaxy Zoo: Understanding Cosmic Mergers

Starting at midnight 11/24, our new site ‘Galaxy Zoo: Understanding Cosmic Mergers’ went on-line as a new project in Galaxy Zoo. In Mergers, we are working to understand the cosmic collisions that lead to galaxy mergers. Every day we will have a new target galaxy that we need your help to model. Based on the basic input parameters that we provide, a Java applet running in your browser will simulate some possible collision scenarios. Computers don’t do a good job comparing simulations and real astronomical images, so we need your help to find out which simulations are the most similar to the real galaxy collision.

Working on Mergers will require some patience. Some of the collisions we are trying to model are rarer than others, so don’t get discouraged. In some cases, you will need to look at a few hundred images to get your first close match. Just remember, you aren’t looking for perfection. Just try to find a simulation that has some of the unusual and unique tidal features of the target galaxy. When you found something close, you might want to go further and “enhance” the image to make even a better match. The more data we have on these galactic collisions, the more we can narrow down the input parameters that caused these systems to form. You can be the most helpful by looking at a lot of images and then select the best of the best through the evaluate mode of the applet. This will happen automatically when you have selected eight possible merger images.

My graduate student Anthony Holincheck and I have been working on this project for a long time, and are very excited to see it see it launch today. We want to thank all the Zooites that participated in our beta test. Zooites rock! Of course, thanks also go out to Arfon, Chris, Lucy, Nancy, Geza, and Mark in their work in the development. Without all of your help, this project would not be possible. Our team will be adding more features in the coming weeks and months, so please stay tuned.

As I write this blog, we are T-5 hours before the full launch of our site. I cannot help but be humbled by the incredible dedication of the Zooites. With your help, we are going to model the dynamics of hundreds of galaxy collisions. This effort will help us connect the dynamics of galaxy collision to the star formation rates in galaxies. Thank you for your on-going support Galaxy Zoo!

– John Wallin – Computational Scientist/Astronomer

Galaxy Zoo featured on Astronomy Picture of the Day!

Check it out: http://apod.nasa.gov/apod/ap091026.html

Thanks to all of you who submitted entries, your creativity amazes us every day.

Merger Papers Accepted for Publication in MNRAS

Thanks for everyone’s work – both papers should soon be appearing in the Monthly Notices of the Royal Astronomical Society 🙂