January 2014 – Carolin Villforth on merger rates in X-ray selected AGN

In quasar science, the birth of an AGN is a hotly studied topic. That is because of two reasons. For one it takes a violent or turbulent event for the particles in a galaxy to move to its center and make the black hole there active. Think of it this way, it would need something quite radical for the earth to move away from its current orbit and suddenly fall into the sun, even though it has about 99.8% of the Solar System’s mass. Angular momentum conservation is just too hard to break.

The other reason AGN triggering is important is that we think that the active galaxy has a big impact on the rest of the galaxy. We see this by the close correlations between the black hole mass and the host galaxy properties However, by the time we observe the galaxies this close relationship is already established, so studying the birth of AGN might bring us clues to the mechanisms that establish this relationship.

In the 1980’s aided by the great work of the IRAS satellite, David Sanders proposed that quasars are triggered by major mergers between galaxies – that’s what he saw in the ULIRGs (Ultraluminous Infrared Galaxies) with the IRAS satellite. At a certain infrared luminosity all ULIRGs were mergers and nearly all of them contained an active galaxy in their centers (summary work here)


The picture became much more muddled in the 2000s, though. The theorists could explain the formation of elliptical galaxies, their bulges, the close relationship between the black hole mass and the host’s properties, the triggering of the AGN and many more phenomena with ever improving simulations (see Phil Hopkins’ great summary in the picture above).

However, the observational picture showed various results. Optically selected hosts showed no excess of mergers when compared to quiescent (non-AGN) galaxies and only showed about merger signatures in about 30% of the quasars (Dunlop et al. 2003, Guyon et al. 2006). At redshifts below 1 they did see an increase in elliptical host galaxy with luminosity, though. X-ray selected quasars also show no excess in merger fraction when compared to quiescent galaxies either at low or high redshift (Cisternas et al. 2011, Kocevski et al. 2012). At high redshift and high luminosity their host galaxies are disks rather than ellipticals (Schawinski et al. 2012). Our work however has shown that red or infrared selected quasars, DO show a high incidence of mergers (or their signatures) up to moderate redshifts (Canalizo & Stockton 2001, Urrutia et al. 2008). Also, low surface brightness features that could be indicative of past mergers were found in many luminous quasars (Bennert et al. 2008), however, these could also be mergers with satellite galaxies, so not as wild and destructive as expected.

With that in mind, I would like to present Carolin Villforth’s recent paper: “Morphologies of z~0.7 AGN Host Galaxies in CANDELS: No trend of merger incidence with AGN luminosity” posted on astro-ph recently (1401.5477). She takes X-ray selected AGN and not only investigates the merger fraction, but also tries to see if it increases with luminosity when compared to a control sample. For that she uses the very deep data of the CANDELS survey using Hubble’s new camera in the infrared. By the way, if you are interested in CANDELS, its blog is really great and you can learn a lot from it.


Rather than simple visual classification, she used the quantifiable asymmetry index as a tracer for mergers as you can see in the picture. She found no higher incidence of mergers when compared to ellipticals and also didn’t find any increase of merger fraction with luminosity, which leaves us a bit head-scratching, but science isn’t always neat and easily explained. I sat down with Carolin and talked with her about her paper and speculated a bit on her research. Download or take a listen below!

MUSE becoming reality and seeing first light soon

I was hired in 2011 at the Leibniz Institute for Astrophysics to help write the pipeline of the MUSE instrument. Back then it seemed so distant that the instrument would actually collect photons one day. In September of that year, we were so excited to test our pipeline on lab photons and to work with the first simulated data. This year in 2014 MUSE will begin actual astronomical observations, first light is only a few day away!


It has been quite exciting to slowly integrate myself within the MUSE team. While I have not done any hardcore programming on the pipeline itself (my colleague Peter Weilbacher did the excellent work of building the core and framework of the program), we have been testing, adjusting and writing lots of technical reports relating to the pipeline. Furthermore, as part of the science team, we have run many simulations, feasibility studies to test whether the science vision of our team members will be possible. Over the last 2 years, I have also written the User Manual for the pipeline, so if you are interested in MUSE data reduction, I am your gal (hint, hint for all you science collaborators out there).

Now the instrument is becoming a reality. We are already working on data taken at the VLT UT 4 telescope! They are only flats and arc lamp exposures, no on-sky data yet, but it is exciting that the mounting of the instrument went so smoothly and that data is actually coming in from Chile. Nevertheless, there are some kinks to be worked out. Beginning of February there will be a 2 week commisioning run testing out the instrument’s performance on different (calibration) objects on the sky – bright stars, galaxies and other objects.

If you are interested in this stage of the MUSE development, either because you may be interested in proposing to observe with MUSE or just because of general astronomical interest, I suggest you follow the blog over at http://muse-vlt.eu/blog/MUSE-Comm/Blog/Blog.html. We plan on being very community conscious and want to release as much information to the scientific community as possible. The intent of the blog is geared towards the professional astronomer or the very interested amateur, hopefully you will find it helpful and will propose to observe with MUSE! In the future, we plan not only to write about the instrument’s progress, but to show behind the scenes reduction and new science results relating to MUSE. Stay tuned, 2014 will be an exciting year for large datasets related to integral field (3D) astronomy!

So what do I want this blog to be in 2014?

In my last blog post I wrote that I wanted to get back to the saddle of blogging, that I always had fun writing my thoughts down. While I may not have some earth shattering insights, it really helped my order my feelings on what was happening in astronomy. But up until now, it has been sort of random ramblings. I had been pondering if maybe there should be some more structure to this blog, if it should have a theme. There are several things I have been thinking sort of formalizing this blog.

a) I’ve always wanted a more thorough look-in on some paper that was on astro-ph. Of course, I would be mostly selfish and it would be on some AGN related science most of the time. But sometimes, I find other things in astronomy really fascinating (you can’t help but be awed by the pace exoplanet science has evolved in the last 10 years, for example). So the thought was to really go in depth into one paper on astro-ph per week, maybe contact the author, make an informal interview and provide a summary of the paper – sort of like astrobites. However, this is too much work, there are only so many hours in the day. I can hardly keep up with astro-ph at all, although I really did in December and really liked it.

b) I want to become better at programming. Not because I think I am a bad programmer, but because I think I have the wrong approach. Often I program inefficiently. My mindset is often: “It works, so what if it takes 3 times as long, it is a matter of 30 seconds versus 10 seconds, I’ve got the time”. This is clearly the wrong approach and it is a detriment of the ultra-fast computers we have nowadays that we don’t learn to program memory saving and efficiently. So while vowing to delve more deeply into python, I wanted to put myself out there and just put my code out there and my thinking behind it. Maybe somebody can use the code, but mostly I would be looking for feedback on the code. I obviously would be doing some things wrong, but if I don’t put them out there, I would be doing them wrong forever, all in the name of “it works!”. However, even though I do quite a bit of coding, it could be difficult to put it in sort of blog post and I couldn’t do it quite as often.

c) I’ve been reading some astronomy and general physics books lately. I wanted to review them. Most of them aren’t in the too technical “Binney and Tremaine” formalism, but are more towards popular science. Still, I think some are quite interesting even to professional astronomers. A book review is work, often books are long and it is impossible to read one per week, sometimes even per month.

d) I enjoyed writing about the conferences I attended very much, providing some sort of summary and the take home message of the conference. Maybe highlight the motivation for organizing this conference. Or the friendships and collaborations made. Or the interesting venue. However, with the new baby, there will hardly be any travel. It is hard with breasfeeding, even with pumping milk.

e) Maybe that’s what I should write about – just the trials and tribulations now with the new baby. I wish, I had written down stuff, when my daughter was born, perhaps I am painting a rosy picture of what it was back then, maybe I am not. Just right now, I had to get up about 5 times because the little one was crying in his crib. There is this facebook group called “AWM: Astronomer, Woman, Mom” and the group is so different from other mom’s groups I have joined (either on FB or in real life). We do seem to be some weird species these astronomer moms.

So – main take-home point: I’ll just keep writing random stuff. I definitely want to write some of all of the above. But it won’t be a formalized approach or anything. Just what is passing through my head. Let’s see how it goes!

The other side – serving on a Telescope Time Allocation Committee

This week I want to talk a bit about observing and TACs (Time Allocation Committees). Usually, when you want to observe at a big telescope, you must submit a proposal for your program. In that proposal you have to explain in detail what you want to observe and the scientific merits of your program among other things. Some telescopes (especially of the space variety) want to include how your program might relate to public outreach activities, other telescopes require an extensive list of your previous work, so that high quality and timely output is ensured.

All these things are graded by a group of people called the TAC. It is usually a group of people familiar with the facility and the scientific field of the proposal. However, large leeway can be made in either of these directions. If there is a time oversubscription, that is if the number of proposed observing hours exceed the number of available hours, then only the highest graded proposals will get any observing time. For highly sought after telescopes, such as the Hubble Space Telescope, the oversubscription rate can be as high as 10:1. Considering that only very few outright unfeasible or unscientific (aehm, bad) proposals get submitted, that is a lot of pressure on the TAC, making sure that only the best programs are selected. Every member has to carefully read the proposal and make personal notes, grades and comments, but each proposal gets discussed by the time the panel meets, to make sure that there are no conflicts of interest, personal vendettas or even to clear out some potential misunderstandings. The TAC then sends the recommendations and grades to the telescope scheduler, who actually has final say which programs get chosen. The proposer then gets the comments back with a likelihood with which the program will actually be observed.

During the last few years all of this was pretty much a black box to me. I submitted and submitted proposals. Sometimes I got the time, sometimes I didn’t. Sometimes the negative feedback was extremely helpful, sometimes… well, it really wasn’t and actually made me angry. Sometimes the feedback was a bit bizarre. A few examples (paraphrasing to make shorter): “This program is great, but the proposers should have asked for more time, so we chose to not give any time”, “This program is great, but the proposer is not senior enough”, “You have convinced us that red quasars are young, but we don’t think the young phase is really interesting”. And of course, there is the flattering comments: “This was the best proposal in its category, it should definitely be awarded time!” ha! Also, it seemed some telescopes were, hmmm, how to put this delicately, fairer than others, it was about the science and not about who you knew at the TAC.

In the last year I have now been part of the LBT TAC relating to the german time allocated. The AIP gets about 5% of the total observing time, since it is building the PEPSI high resolution spectrograph. Because the amount of time is so small, about 40 hours of observing time divided into 20 hours good time and 20 hours doubtful time, the TAC has to actually evaluate every science category and not just your field of expertise (which would be extragalactic science for me).

It has been an interesting experience to be sitting on the other side of the process (similar to being referee for a paper). As usual, I am always very impressed with all the good work that my colleagues are doing in astronomy. The following are a few things, I kind of picked up these last 3 TAC meetings and evaluations:

It is not necessary to go for the home run (“this will fundamentally change our understanding in galaxy evolution”) – in baseball, as in science OBP – on base percentage (projects to work on) are the meat and potatoes. Describe to me your project in context of other work going on. It’s ok if your result will be just a grain of salt within a big field, but be sure to thoroughly make me understand that grain of salt and why it is important.

Be very aware of the telescope / instrument you are applying for. Look, we all recycle our proposals for different telescopes, but you need to at least address why this instrument is best suited for your science. Otherwise, since I am trying to cut time among a lot of good projects, I will just tell you to propose at that other instrument (that you have access to), which is better suited. This is just like applying for a job and just replacing the name and institution in your cover letter – don’t! At least change your proposal somewhat to tailor it for the facility.

This relates very much to the first point above, try to write a proposal without too much jargon in it. I know this is difficult, especially for graduate students. Believe me, practice makes perfect and you will become much better at it explaining you research to all different levels of an audience. For example, instead of saying “the M-sigma relation” write that the mass of the central supermassive black hole is related to many properties of its host galaxy. An expert will know what you mean with both statements, but a stellar astronomer might not have known everything about it.

I think those are the most important points. Of course, the actual process of the proposal (e.g. simulations or previous work) should be careful, precise and honest, but I assume that as a given. The actual TAC meetings are always fun. We are genuinely sad, even though we were looking for them, when points come up, that make your proposal unfeasible. I am definitely looking forward to continuing the work in the next few semesters.