When Theory Meets Observations

This summer around 30 astronomers met for the CANDELS Theory Workshop, held from August 8-10 at the University of California, Santa Cruz. This was a smaller event than the recent CANDELS team meeting, with most researchers working in one or two subfields in extragalactic astronomy. The meeting wasn’t limited to just theorists however; in fact much of the discussion centered around how we could use CANDELS observations to better constrain theoretical models of galaxy formation.

Most of the presentations centered around two theoretical tools: semi-analytic models and hydrodynamical simulations. While both of these are computerized models that predict the properties of galaxies, they have vastly different approaches.

Hydrodynamical simulations 

Hydrodynamical (‘hydro’) simulations are high-resolution, detailed simulations of the formation of galaxies. While stars and dark matter are simulated with particles, we use a technique known as Adaptive Mesh Refinement to trace the movement of gas, dust, and metals throughout a galaxy. Areas of greater density – those that are more likely to have interesting physics going on – are simulated in greater detail while regions with little gas or stars are treated with less refinement.

One of the major discoveries from these hydro simulations has been the formation of stellar clumps in high redshift galaxies. Most of the ‘classical’ images we have of disk galaxies such as our Milky Way or the nearby Andromeda Galaxy show regular spiral structures. At higher redshifts however, the picture is murkier. Galaxies seem to have large clumpy regions embedded within their disks.

Galaxies at high redshifts tend to have clumpy structures. Since these galaxies are far away, individual features of the galaxy are harder to resolve. Shown here are images of 6 galaxies taken with two CANDELS filters. Image credit: CANDELS collaboration, http://candels.ucolick.org. 

Naturally, both theorists and observers would like to understand how these clumps form. Are they remnants of small galaxies swallowed up in mergers, were they accreted from the cosmic web, or do they form within the disks themselves?

An advantage of hydro simulations is that we can study these processes directly and watch them evolve over time. A team of theorists, led by Professor Avishai Dekel has been doing just that. Dekel’s team has found that about 2/3 these clumps formed in-situ, while the rest joined the galaxy through a merger. Furthermore, clumps that formed in-situ tend to be less massive and contain younger stars – all tantalizing predictions that may be confirmed with CANDELS data.

A high-redshift galaxy from a hydrodynamical simulation. Regions with
redder colors have greater densities, and clumps have been outlined in
circles. The labels on the clumps indicate whether the clump formed
in-situ (is) or ex-situ (es). 
Image credit: Dylan Tweed, Hebrew University of Jerusalem

While hydrodynamical simulations can produce detailed images of galaxies, in some instances the simulations are actually too detailed. Real high-redshift galaxies are billions of light-years away from Earth and appear only as specks of light on even the largest telescopes. Furthermore, these galaxies tend to have a large amount of dust that scatters and absorbs their light, much like a car’s headlights are diffused by fog at night.

To compare theory and observations directly, we must mimic the effects of dust and simulate the blurriness and uncertainties introduced by a real telescope. To do this we use a tool called SUNRISE, which takes the raw data from hydro simulations and reprocesses it, projecting the information from three dimensions down to two and allowing for dust emission and absorption. We then create mock ‘observations,’ using simulated filters that match the real ones on Hubble.

This process, which we’re terming ‘Candelization’, is still a work in progress. The images we have so far however are strikingly realistic. In many cases, it’s hard to tell the difference between simulated galaxies and the real thing! Even though the hydro models only simulate dozens of galaxies, between the hundreds of possible camera angles and dozens of simulated filters, we can create a suite of thousands of images that can be directly compared to CANDELS observations.

A 'Candelized' simulated galaxy in three projections at redshift z = 1.70.  Note the clumpy substructure, and the red dusty region in the center of the galaxy.  Image credit: Christopher Moody, University of California, Santa Cruz).

Semi-analytic modeling

Instead of making a handful of galaxies in great detail, semi-analytic models (SAMs) focus on simulating thousands or millions of galaxies with very little detail. These two methods are often complimentary, and indeed many of the physical properties included in SAMs were first studied in hydro simulations.

Semi-analytic modeling uses simple physical approximations to predict the statistical properties of hundreds of thousands of galaxies. The first step is to construct a high-resolution simulation of the way dark matter forms structure. Since most of the matter in the Universe is actually dark matter, the galaxies we see are all embedded in large dark matter halos. These halos grow and merge over time, condensing along filaments and leaving voids where there is not enough dark matter to gravitationally collapse.

 

Visualization of dark matter structure formation from the Bolshoi Simulation.  The brighter regions have more dark matter, and are the regions where galaxies will eventually form.  Image credit: Chris Henze, NASA Ames Research Center.

Even though dark matter is only subject to the force of gravity, the sheer size of the simulation requires billions of particles each representing millions of solar masses. The CANDELS SAMs all are based off the results of the Bolshoi Simulation, which took over 6 million processor hours to run on a NASA supercomputer. 

The next step is taking all of the information from the Bolshoi Simulation and condensing it into a simple form for the SAMs to use. To do this, we construct ‘merger trees’ that record the masses, sizes, and positions of dark matter halos when they merge together. This retains much of the statistical information about dark matter structure – for example, how it clusters in space, how larger halos form from smaller ones – without having to keep information about every particle of dark matter.

Once we have a merger tree we take all of the dark matter halos at high redshift and ‘seed’ them with a galaxy. We then follow the merger tree over time. Whenever two dark matter halos merge we allow their host galaxies to merge as well, until the simulation reaches redshift zero. We then compare to well-known observational relations such as the galactic stellar luminosity function, which describes how many galaxies there are of a given luminosity within a chosen volume of the Universe.

As with most things, the devil is in the details. SAMs include prescriptions for most of the physical interactions galaxies are thought to undergo, such as the growth of black holes, reionization, the blowout of gas due to supernovae, and the formation of galactic disks and bulges. Since all of these areas are still the subjects of active research, many of the formulas SAMs use are educated guesses at best. 

Furthermore, to use a quote from Einstein, SAMs try to “Make things as simple as possible, but not simpler.” In contrast to the Bolshoi Simulation, which generated terabytes of data and took months to run, SAMs can simulate the evolution of hundreds of thousands of galaxies over all 13.7 billion years of the Universe overnight on a consumer-grade laptop! 

The advantage of being able to run so quickly is that SAMs can try out many different physical models in a relatively short period of time. We can pose simple questions – what if the star formation rate is dependent on the amount of metals in a galaxy? How does removing supernovae affect the stellar masses of galaxies? – modify the SAMs accordingly, and see what the results are.

The relationship between hydro simulations and SAMs. Plotted
is the correlation between galaxy mass ratio and the amount of star
formation in a merger.  Each point represents a measurement from a
different simulation of two galaxies merging, while the black solid and
dotted lines represent approximations used by many modern SAMs.
Image credit: Cox et al. (2008), MNRAS 384, 386

There is a tradeoff, however – you won’t see pretty pictures of galaxies generated from SAMs. Every ‘galaxy’ exists as a single line in a spreadsheet, detailing the general properties such as its size and its mass. But for questions where you need to simulate large numbers of galaxies to get an answer, SAMs are the way to go.

While these two approaches – hydrodynamical and semi-analytical – may seem to have nothing in common, many of the equations used in SAMs were derived from approximations to hydro simulations.  The physical processes that we can study in great detail in the hydro simulations should apply to galaxies in SAMs as well.

One of the major themes of the Theory Workshop was how to continue this interplay between hydro simulations and SAMs, and between theory and observations.  After all, at the end of the day we're all looking at the same fundamental questions: How do galaxies form, and how do they evolve over time?  We don't have all the answers, but with CANDELS the picture is becoming a little bit clearer.

The REU Experience and Working with CANDELS

My name is Erin O’Leary and I am an undergraduate student pursuing my bachelors in physics and astronomy. This summer I had the opportunity to join the CANDELS team working with Jeyhan Kartaltepe as part of the National Optical AstronomyObservatory’s (NOAO) Research Experience for Undergraduates (REU) program at Kitt Peak National Observatory. I thought I would take the opportunity to share with everyone the story of my summer and the experience I had working with CANDELS.

I am an undergraduate in my senior year finishing my astronomy degree at Macalester College, a small liberal arts school in Saint Paul, MN. Astronomy has been an interest of mine since I could check out stacks of space books at the public library. In high school when I realized I could make a career out of my interest in astronomy, my path was pretty much set.

I spent my previous summer conducting astronomy research at Macalester with Professor John Cannon. I analyzed the stellar populations within a nearby low mass galaxy. This was my first real taste of the research world, and I loved it! I thrived on the independence and the sense of depth that so is different from coursework. I decided I wanted to spend my next summer carrying out astronomy research at a larger science institution. Galaxies in particular piqued my interest and I sought a research experience where I could explore the topic further. I applied to many NSF funded REU programs across the country, and to my excitement, I was offered my top choice position at the KPNO REU!

2012 KPNO and NSO REU students at Kitt Peak

For twelve weeks I lived in Tucson, AZ (quite different than Minnesota!). I spent my time engaging in the undergraduate research experience, which included - yes - lots of research hours spent in front of a computer writing and debugging programs. But what is so great about REU programs like the one I experienced are the vast opportunities to gain exposure to other areas of astronomy and meet cool people. Tucson is a huge hub for astronomy, making it a great place to see all the areas of astronomy in action. Weekly we heard from NOAO or visiting scientists about their area of research. My fellow students and I had tours of the University of AZ mirror lab, NOAO’s optics lab, the McMath-Pierce, 2.1-meter, and the Mayall 4-meter telescopes on Kitt Peak, as well as a week of travel to New Mexico to visit the Very Large Array, the Sloan Digital Sky Survey, and the National Solar Observatory Sacramento Peak facilities. I also spent four nights observing on the 2.1-meter on Kitt Peak. Being able to see (and use) these instruments and then hear about the science resulting from these observations was truly inspiring! I gained so much insight into where my astronomy career can take me. 

Sunset over Kit Peak National Observatory this summer. 

Now onto my work with CANDELS! Before this summer, I had not heard of CANDELS. I was quickly amazed by the quantity of data and science coming out of this project, which made me even more excited to be part of it! 

As I mentioned above, my summer research focused on understanding the role that galaxy mergers and interactions played in galaxy evolution. A few related posts are here and here. Galaxy mergers are beautiful and dynamic phenomena and seen as important drivers of galaxy evolution. Merging galaxies are rare now, but are believed to have played a larger role earlier in the universe. My work involved identifying these galaxy mergers.

CANDELS data are unique and exciting in that they probe higher redshift objects allowing us to view light whose wavelength has been stretched in the expanding universe. What was once visible as optical light is now observable in the infrared. This is essential for accurate galaxy morphology classification. My project was a first look at galaxy mergers at higher redshift (greater than z ~ 1). This can also raise some difficulties in merger identification. As we look at higher redshift galaxies, signature merger features can become faint and more difficult to detect.

I began my work familiarizing myself with the mechanisms of galaxy evolution, galaxy morphology classification, and the scheme that CANDELS has adapted in classifying morphologies. It was a flood of new concepts to me. I spent a fair amount of time classifying these galaxies and debating with myself whether something constituted a merging system. Simply the number of galaxies we were dealing with and the uniqueness of each galaxy blew me away. 

CANDELS images showing a sample of visually identified galaxy mergers.

I then set to work on analyzing the results of the visual morphology classifications of the CANDELS data covering the GOODS-South field. This is a catalog of 7,628 galaxies, each classified visually by about 3-6 people, which means a lot of things to keep track of! Sorting through the data, it was fascinating yet frustrating to compare the classifications that each person had assigned to a given galaxy. 

From this data set, I created selection criteria to choose systems that were merging. Visually, mergers appear to have undergone an interaction evident by an irregular structure, tidal features, double nuclei, or asymmetries. We selected a conservative catalog of galaxies we were pretty certain were mergers. For each identified galaxy merger we collected additional information by matching them to their redshift and mass. We looked for trends in the mass, mass ratio (for interacting pairs), and redshift to tell us about our merger sample.

It is satisfying to look back and see how much I learned this past summer. I felt that my work was just a tip of the iceberg. It was difficult to part ways with my project after those 12 weeks when I knew there exists so much more data and discovery on the horizon. With four more CANDELS fields, it will be very exciting to hear about future outcomes!

So what’s next for me? I am spending my current semester studying abroad at the University of Oslo in Norway and using the opportunity to squeeze extra astrophysics courses into my undergraduate years. When I return in January, I will present my summer research at the AAS meeting in Long Beach, CA. This will be followed by graduation in the spring of 2013. My future plans certainly involve attending graduate school for astronomy. 

Supernova Hunting

Somewhere in the observable universe, a star is exploding right now. Actually, something like 30 stars are exploding right this second, adding up to 2.5 million supernovae each day. That may sound like a ridiculously high number of exploding stars (If the universe is popping off supernovae so fast, then how do we have any stars left!?). Lets see if we can unpack it a bit. 

An average galaxy like our own produces roughly one supernova per century (I'll explain where this number comes from below). There are roughly 100 billion galaxies near enough to be observed by the Hubble Space Telescope (HST). If each of those observable galaxies gives us one supernova each century, then we expect about 100 billion supernovae every hundred years. One century is equal to about 3.15 billion seconds (that's about π x 10⁹ seconds per year, as a handy way to remember it). So we divide those 100 billion supernovae over 3 billion seconds, and get roughly 30 supernovae per second.

August, 2010 (pre-Supernova) 

With so many supernovae blinking on every night, it is actually not too hard to find one of these objects. The three-step process is simple:

1. take a picture of the sky 

2. wait a few days or weeks, and take another picture

3. look for any new "stars" that weren't in the first picture

October, 2010 (see anything new?)

Subtracting off the August image
reveals the newly arrived SN Primo.

Stars and galaxies don't appear or disappear on the timescale of weeks (or years or centuries...) so there are very few astronomical objects that can appear so suddenly in between two pairs of images like that. Fast moving objects (like asteroids and comets) might move into your frame, but these are easy to sort out: take a third picture and you'll see that they keep moving. Anything that blinks on, stays in place, and then shows a steady rise and fall in brightness is most probably a supernova. The figure below shows two infrared images from HST.  The first was taken in early August, 2010, and the second was taken two months later, in October, 2010. The third image shows what happens when we subtract off the September picture: all the galaxies and stars are unchanged, so they get subtracted cleanly away, and we're left with just one new star. This particular supernova was the first one discovered in the CANDELS survey. Nicknamed "SN Primo,"  it is currently the most distant supernova of its kind. SN Primo and other stellar explosions we find with CANDELS will eventually be used to measure distances in the universe, helping us to understand the nature of the mysterious dark energy that is driving the accelerated expansion of space.

Supernova hunting is not limited to the professional astronomers with access to multi-million dollar observatories. Unlike many areas of physics, dedicated amateurs can and do make significant contributions to astronomy - especially in this sub-field of supernova science. The renowned Australian amateur Robert Evans has discovered over 40 supernovae himself, primarily using his own visual memory of the sky.  Lets take a moment to consider that, because this is really quite extraordinary: Rev. Evans was able to discover dozens of supernovae without using any of the careful image subtraction that astronomers rely on. He simply scanned the sky each night with his telescope, and looked for the single new pinpoint of light around a familiar galaxy that signals the death of another star and the start of a new supernova. We professional astronomers didn't get to be as efficient as Evans until the advent of robotic telescopes in the mid 90's.

Young amateurs are in on the supernova hunt, too. The unique object SN 2008ha was discovered by 14-year old Caroline Moore in upstate New York. In recent years this object has become a prototype for a whole new class of supernovae, which are still puzzling astronomers today. Alas, Caroline's record as the youngest person to find a supernova didn't last too long:  two years later SN 2010lt was discovered by Kathryn Gray, a 10 year old girl from Fredericton, New Brunswick in Canada.  

SN 2008ha was discovered by a 14-year-old amateur, and
astronomers now believe it to be the prototype of a new 
class of supernovae.  This picture was taken with the 2.2m
Telescope of the Calar Alto Observatory in southern Spain.
Image credit: Stefan Taubenberger, MPA

So there are 30 new supernovae every second, and we've got world-class telescopes and dedicated backyard astronomers on the hunt... but unfortunately we still don't actually see most of those supernovae. Some fraction are screened by dust, or hidden behind millions of other stars in the bright cores of their host galaxies. But most of the easily observable supernovae are missed simply because we aren't looking for them. To catch them all, we'd need a few million telescopes like HST observing every corner of the sky every day around the clock. We'll never have that, but there are some exciting new telescopes on the ground that can observe the sky much more efficiently than HST - although they don't go as deep or as distant. Amid the alphabet soup of astronomical acronyms, there's Pan-STARRS, PTF, and LSST, just to name a few. Eventually these wide-field surveys will really clean up in the local universe, detecting basically all the nearby supernova explosions.

This brings us back to the question of how do we know just how many supernovae are exploding each second. One critical piece of information is the rate of supernova explosions in an average galaxy. I stated at the top that this rate is about one supernova per century in a galaxy like our own Milky Way. We could measure that number by observing our own galaxy over a century and counting up the number of supernova explosions. That is painfully slow, and rather imprecise, but we can do effectively the same thing by watching a hundred galaxies for one year. But why stop there? It's far better to watch thousands or tens of thousands of galaxies over several years. Then we count up a large number of supernova detections, divide by the number of galaxies and the number of years and come up with the observed rate of one supernova per galaxy per century.   

This is precisely what we are doing with the CANDELS supernova survey - but with an important twist. The other wide-field surveys I mentioned above (like Pan-STARRS and PTF) are observing many thousands of galaxies each night, but they are limited to (relatively) nearby galaxies that are bright enough to observe in short exposures from the ground. The unique difference in the CANDELS survey is that we use very deep infrared imaging from HST. This allows us to look to higher redshifts (farther back in time) and catch supernova explosions within very distant galaxies in the early universe. Right now, our HST survey is the only program able to measure the supernova rate at a time when the universe was only about 3 billion years old. We can compare that observed rate from the early universe with the observed rate in the present-day universe to learn something about how the supernova population has changed. Do these early universe supernovae look the same as local supernovae? Are they exploding at the same rate as they do locally? These are the first questions that we're beginning to address with the CANDELS supernova program, and we hope the answers will help us understand more about these extraordinary events. 

Surfing the High-Redshift Universe in Santa Cruz

I was waiting all week long for the last day of the CANDELS team meeting, not to go home, but because on that day we finally had the high-redshift sessions!  We had two sessions devoted wholly to high-redshift science, split with some science talks, and some discussion sessions.  My primary goal for these sessions was to get our group to work together - we have high-redshift experts in CANDELS spread not only throughout the US, but around the world, with large groups in Edinburgh and Rome.  Each of these groups sent representatives to Santa Cruz, so it was a great opportunity for the team to catch up on the goings on around the high-redshift team.

We also got updates on some of the papers in progress.  One of the most interesting results came from Vithal Tilvi, who is a postdoc at my old stomping grounds, Texas A&M.  He has been combining CANDELS data with some ground-based medium-band images (meaning he's using some filters narrower than those we've been using on HST to isolate specific wavelengths).  His primary goal was to find distant galaxies.  But in an ironic twist, he thinks he might have found an extremely nearby object; a very low-mass star known as a Y-dwarf (these are so small they are not undergoing any fusion, and thus are known as brown dwarfs, and this particular flavor of brown dwarfs are barely larger than Jupiter).  Brown dwarfs have colors similar to high-redshift galaxies, thus they can hide in our samples.  Typically they're thought of as contaminants, but this particular type of star is rare, so its more like a diamond in the rough!  We also heard some updates by Giovanni Fazio on the status of his deep Spitzer Space Telescope program which is imaging the CANDELS field in the infrared, and I updated the team on my ongoing work measuring the luminosity functions of distant galaxies (which is a measure of the distribution of galaxy brightnesses).

An image of the field with the Y-dwarf, with the box highlighting the brown dwarf.  The inset shows an image of a Jupiter-like planet, which likely doesn't look much different from this brown dwarf.

We had some interesting discussion sessions as well.  We made a lot of progress on a project we're doing to create a catalog of "CANDELS-approved" very distant galaxies.  We also discussed how best to proceed with measuring galaxy clustering, which is a highly interesting yet extremely difficult way to measure the cosmic structure from the positions of galaxies.  And we had a great session where we interfaced with our fantastic theory group, working with them to identify the key problems we should be focussing on.  So now its back to work for all of us, but it won't be too long until we get together again - we're planning for our next high-redshift meeting to be in the scenic city of Sesto, Italy in January.  Sesto is like the Aspen of Italy, so don't forget your snow pants!

Uncovering the Role of Black Holes in Galaxy Evolution

Artist impression of a supermassive black hole 
surrounded by an accretion disk of infalling gas 
and twin, highly-collimated plasma jets. 
Credit: Aurore Simonnet (Sonoma State University

Although Active Galactic Nuclei (AGN), and the supermassive black holes (SMBH) that power them, have been studied for more than half a century, their potential importance to the evolution of galaxies has only recently become evident. Observations over the last decade indicate an intimate connection exists between the growth of galaxies and their central SMBHs. Furthermore, computer simulations have shown that highly energetic AGN can drive outflows that disrupt the star formation activity of the AGN's host galaxy.  For these reasons, AGN have become central figures in Astronomy's attempt to understand the evolution of galaxies from star forming to passively evolving systems. However, despite our increasing focus on AGN, it is still unknown how the connection between black holes and their host galaxies is established and maintained. This issue remains one of the key unanswered questions in Astrophysics today.

Brainstorming session during the third annual CANDELS team
meeting recently held at the University of California at Santa Cruz.
Image Credit: Dale Kocevski

One of the goals of the CANDELS AGN working group is to determine how our remaining questions about AGN can be best answered given our current observations and to identify promising directions for future research. Recently the AGN working group gathered to discuss these very issues at the third annual CANDELS team meeting at the University of California at Santa Cruz.  During the meeting, members of the working group not only presented their recent findings to the team, but we also spent a considerable amount of time discussing which areas of AGN-related science still require further study and worked to chart a course for our future work.  Although it may seem odd that scientists would gather to discuss what we don't know about a particular topic, identifying which aspects of AGN are still poorly understood and what areas require further study is key to advancing our understanding of AGN.  The team identified the following three open questions that we believe we now have the potential to answer in the near future with the help of the CANDELS survey.

What Mechanisms Trigger AGN Activity in Galaxies?

Although it is thought that all massive galaxies have a SMBH at their center, only about 10% appear to be experiencing an AGN growth phase at any given time.  The majority of SMBHs simply lie dormant in their host galaxies.  What mechanisms fuel SMBH growth and turn a dormant black hole into an AGN has remained an enduring mystery.  The collision of two galaxies has long been espoused as a possible triggering mechanism since computer simulations have shown that these violent interactions can be extremely effective at funneling gas to the center of a galaxy and into the central black hole.  However our very own research conducted by the CANDELS team suggests galaxy mergers can not be the sole explanation.  Additional work is needed studying the morphologies and environments of galaxies hosting AGN to determine what distinguishes them from non-active galaxies in the hopes of pin-pointing the mechanism that initiates black hole growth in certain galaxies.

What is the Nature of Heavily Obscured AGN?

Artist impression of a thick dust torus surrounding an obscured
supermassive black hole.  When seen edge-on, as in this case,
much of the light emitted by the AGN is blocked from view.
Credit: ESA / V. Beckmann (NASA)

When gas spirals into a black hole, it forms an accretion disk and rapidly heats up. As it does so, it emits immense amounts of energy at optical, ultraviolet and X-ray wavelengths. Since galaxies themselves do not produce strong X-ray emission, X-ray observations have become the most common method that astronomers use to find AGN. However, if the black hole's accretion disk is obscured by interstellar gas and dust, some or all of the emitted X-ray radiation will be absorbed by the surrounding gas.  The AGN will then no longer be visible at X-ray wavelengths and will be missed by AGN surveys relying solely on X-ray observations.  That said, these so-called obscured AGN can be found since the absorbed X-ray emission will be re-radiated at infrared wavelengths.  Only recently have studies starting examining the properties of this population of obscured AGN.  It may be that this long-lost set of AGN are the missing link between dormant SMBHs and X-ray bright AGN and therefore might provide a clue as to what activates AGN activity in galaxies in the first place.

Do AGN Turn Off Star Formation within Galaxies?

The accretion events that power AGN can be extremely energetic and this can have profound effects on a galaxy that harbors a growing SMBH. Computer simulations have shown that a sufficiently energetic AGN can drive outflows that can effectively suppress the surrounding galaxy's star formation activity.  In this way, SMBHs can regulate the growth of their host galaxies by limiting the amount of stars they form.  This scenario has been widely adopted such that most cosmological models of galaxy evolution now invoke feedback from an AGN as the primary mechanism to terminate the star formation activity of massive galaxies. However, observational evidence that this suppression actually occurs in AGN host galaxies is still tenuous at best.  One of the goals identified by the CANDELS AGN working group is a better understanding of the connection between star formation activity and AGN activity in galaxies.  This may soon be possible as infrared observations from the Herschel Space Observatory are now allowing us to measure the star formation rates of active galaxies far better than previously possible.  This will provide the first clues as to whether star formation activity is indeed suppressed in galaxies harboring highly energetic AGN.