Friday, September 28, 2012

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. 

Wednesday, September 26, 2012

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!

Monday, September 24, 2012

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.

Friday, September 21, 2012

Endeavour's Last Adventure

Endeavour's first launch in 1992
image credit: NASA
In today's post I'd like to tell you about a little piece of history that I witnessed yesterday and although it seems like this has nothing to do with CANDELS, let me tell you otherwise. 

Yesterday, the space shuttle Endeavour flew piggyback on a special Boeing 747 over Tucson, AZ, at a height of about only 1500 feet (yes, that's pretty low!). This fly-by is one of many that Endeavour has made and will make on its way across the country from Houston to its final destination at the California Science Center.

Fly-by of Endeavour over Tucson, AZ
image credit: Janine Pforr
The Endeavour is one of the 5 NASA orbiters that ever made it into space. The others are Discovery, Atlantis, Challenger and Columbia. The Endeavour was built in 1987 (and 1988, '89, '90, and '91, as it took some years to built it) after the loss of Challenger during a launch accident. In May 1992 it took off for its first flight into space. Between then and its last flight in May 2011, Endeavour spent nearly 300 days in space while carrying out 25 missions. During this time, Endeavour orbited the earth 4671 times and traveled for 122,883,151 miles. In comparison, if you were to drive once around the Earth in your car (if that were possible), you would have only traveled 24,901 miles and would have to make the same journey another 4934 times to reach the same mileage. Or in other words Endeavour traveled 1.3 times the distance between the Earth and the Sun in its 19 years of service. It was planned that the last ever space shuttle mission would be carried out by Endeavour, but then it was beat by Atlantis and one last mission. During its time in space Endeavour met the MIR, the Russian Space Station, and helped transport men and material to built the International Space Station (ISS). It also carried the first female African-American astronaut Mae Jemison.

But there are a lot of other special facts about Endeavour. It was the first space shuttle that received its name from school children through a naming contest. They chose the name of Captain James Cook's ship "Endeavour" with which he crossed the South Pacific in the 18th century to observe the Transit of Venus in Tahiti. James Cook was not only an explorer by sea, but also an explorer of space as an amateur astronomer!

Endeavour piggyback on the special Boeing 747, Tucson, AZ
image credit: Janine Pforr
But I promised you at the beginning of this post that I would tell you the connection between Endeavour and CANDELS. Although Endeavour did not take the Hubble Space Telescope, with which CANDELS observes the night sky, into space it was the space shuttle that carried out the first servicing mission for Hubble. During this mission in 1993 the astronauts on board of Endeavour repaired the famous mirror problem which had left the HST's performance well below optimal. The astronaut crew installed a new wide field camera (number 2) which corrected the problem and in essence provided Hubble with a pair of glasses. So if it weren't for Endeavour and the other space shuttles (and of course the many astronauts, ground personell and scientists), we might not be able to carry out the research that we do with CANDELS and which relies on the excellent images taken with a space-based telescope!

So you can imagine that I was pretty excited to learn that Endeavour will fly over my head, also because I have never seen a space shuttle this close or on the back of a Boeing 747 for that matter. Many people assembled on the outside grounds of the University of Arizona to witness this spectacle around 11:15 am local time and everyone applauded the shuttle on its last travel. Today, the 747+Endeavour package will do several fly-overs across California, for example NASA's Jet Propulsion Laboratory and the San Francisco Bay area, before landing around noon in LA from where it will make a road trip to the California Science Center. Save final travels to you Endeavour and a well-deserved retirement!

Wednesday, September 19, 2012

The Dawn of Galaxies

One of the most exciting areas of astrophysics today is understanding how the very first stars and galaxies lit up the Universe.  This happened during the Epoch of Reionization (EoR), which was highlighted in the latest Astronomy Decadal Survey report New Worlds, New Horizons as the area of astronomy with the greatest discover potential in the next decade.  It is a central goal of CANDELS to probe galaxies in the EoR.

The Universe began in a hot Big Bang.  Early on, it was too hot for the protons and electrons to combine into atoms, because the high temperature made particles smash into each other too often.  So the Universe after about three minutes consisted of a fully ionized plasma -- that is, an admixture of positively-charged hydrogen and helium nuclei, and negatively-charged electrons.  Finally, after about 380,000 years, the Universe became cool enough that protons and electrons could bind together into neutral hydrogen atoms.  Thus began the Cosmic Dark Ages, so called because no sources of light were present, and all of the cosmos was enshrouded in a fog of neutral hydrogen and helium gas.

The Dark Ages lasted until a few hundred million years after the Big Bang.  It was then that the very first sources of light appeared, providing energy that ate away at the neutral hydrogen fog.  And so the Universe became ionized again, slowly and inhomogeneously, with electrons and protons being separated by energetic photons emitted by the earliest stars and galaxies.  We call this process cosmic re-ionization.  The Epoch of Reionization lasted until about one billion years after the Big Bang, and left the bulk of the Universe fully ionized and transparent as we see it today.  The EoR is the last major phase transition that the Universe undergoes, and it is the frontier of galaxy evolution studies today.

CANDELS has already detect a few EoR galaxies, which is pretty exciting in of itself.  But that's only part of the job.  What we really want is to understand what these galaxies look like, how they got there, and what they imply for the process of reionization. This is a job for the CANDELS theory crew.

So what do we want to figure out?

The biggest questions here are among the most basic:
a) What are the sources responsible for reionization? and
b) What is the topology of reionization?

While we know what galaxies look like today, there are good reasons to think that the first galaxies responsible for reionization might have looked quite different.  For one thing, like in a new house, there hasn't been much time for dust to accumulate. This is critical, because it turns out that star formation as we know it today requires dust as a catalyst. So how can stars form in the first galaxies with little or no dust?

The answer is: very slowly. But the stars that do form can be incredibly massive -- perhaps hundreds of times heavier than the Sun! These first stars, known as Population III stars, are copious emitters of ionizing radiation that can eat away at the cold fog of neutral hydrogen. On the flip side, because they form slowly, they are rare, so it's unknown whether there will be enough of them to power reionization.  Current thinking says probably not, but don't bet your first-born on it.

  This animation of a simulation from John Wise shows heavy elements (yellow) surrounding Population III stars after they have exploded.  

Moreover, these massive Population III stars have a short life, exploding in spectacular hypernovae after just a few million years. The details of these explosions are crucial:  Heavy elements like carbon, oxygen, and silicon are catalyzed in copious amounts during their short lives, and the hypernova could disperse them widely to form dust that quickly transitions star formation to the more familiar Population II (dust-catalyzed) mode. On the other hand, if the star collapses directly to a massive black hole, it would suck most of these heavy elements into oblivion, and the Population III era would continue for longer. Since Population III stars are no longer around today, it is difficult to see how they work in detail, and insights from models are often all we have to go on.

Even after the Population III epoch ends, it remains unclear whether there are enough stars to power re-ionization. CANDELS, as impressive as it is, only allows us to view the brightest of reionization-epoch galaxies -- Hubble cannot directly detect the fainter galaxies (this is what JWST will do). If there are not enough galaxies to provide the reionizing photons needed, it may indicate that there are more exotic contributors such as early black holes or an unexpected preponderance of Population III stars. Yet many models indicate that these faint galaxies are so numerous, that they actually dominate the radiation output! Clearly, tallying the total photon budget from CANDELS galaxy counts remains a poorly constrained yet critical aspect for understanding the sources of re-ionization.

This movie of a simulation from Tiziana di Matteo shows an evolving cube of the cosmos as sources begin to ionize the surrounding gas, eventually leaving a transparent Universe after about 1 billion years. Note the complex topology of filaments and sheets that houses early galaxy formation; this is known as the Cosmic Web.

As if those uncertainties aren't enough, there is the issue of topology. Topology refers to the spatial distribution, in this case of the protons and electrons.  While radiation from early galaxies can ionize hydrogen, the Universe is still sufficiently dense that the dissociated protons and electrons can quickly re-join back into hydrogen. This is a process known as recombination.

While recombinations are (cosmically) rare today, nature has perversely arranged the timescales for reionization and recombination to be annoyingly comparable during the EoR. This means one has to understand the spatial clustering or topology of protons and electrons, in order to know how often after being so cruelly separated, they will bump into each other again and re-discover their lost electrochemical bonds of love. This can be quantified by the clumping factor of protons and electrons.  If the clumping factor is high, it requires many photons to ionize a single atom, since protons and electrons remain close enough to recombine again after being ionized. If clumping is low, a single photon might be enough to keep an atom ionized. Hence we not only have to count how many photons are being emitted, but we also have to understand matter clumping in order to know how effective each photon is at reionizing the cosmic fog.

With all this uncertain physics flying around, it's not surprising that the EoR represents one of the most difficult modeling problems in astronomy today. Our most sophisticated simulations include all the complex processes we use to model galaxy formation at later epochs, plus the dispersal of heavy elements via outflows along with radiative transfer -- the emission and propagation of photons from cosmic sources. This last aspect is particularly challenging, requiring massive supercomputers to move not only mass but light around the simulated cosmos.

CANDELS theorists have developed a remarkable simulation code, called MARCH, capable of handling all these physical effects with essentially no simplifying approximations. Using MARCH, we have been able to show that the clumping factor is around 3, in contrast to earlier estimates of 10-30, and that CANDELS is directly detecting the sources that provide about one-quarter of the photons needed for reionization. While these results are encouraging, there remain many uncertainties in such calculations, particularly the escape fraction, i.e. the number of ionizing photons that escape from within galaxies. There is a long way to go before we can confidently model all the processes going on during the EoR.

Nonetheless, the EoR remains one of the most vibrant and revolutionary areas of study in the CANDELS team. CANDELS data provides the boundary conditions for theorists' models, while the models inform the interpretation of the observations. The recent CANDELS team meeting in Santa Cruz enabled the High-Redshift Working Group to assess where we stand now in both observations and theory, and how to best proceed in concert. Together, we are shining a new light on the Cosmic Dark Ages by peering boldly into the dawn of galaxies.

Monday, September 17, 2012

The 3rd CANDELS team meeting in a nutshell

Last week about 90 of the CANDELS team members came together at the University of California in Santa Cruz for the third annual team meeting. Throughout the week we provided some snippets of the meeting but let me wrap up the meeting with a summary.

As is typical for collaboration meetings, the week consisted of break out or splinter sessions and plenary sessions. Plenary sessions are attended by everyone and meant to update the team on the activities of the several working groups and the status of the survey itself. Splinter sessions on the other hand provide the working groups with an opportunity to get into more detail of on-going projects and plan future work. Most surveys undertaken by a large collaboration have different working groups. The working groups offer a communication platform to team members with a specific science interest to discuss their work among a smaller group and focus on their specific issues. Within CANDELS we have several working groups such as Multi-wavelength cataloging, structure and morphology, high redshift science, AGN science, Theory, Supernova science, UV science, SED-fitting and photometric redshifts, Education and Public Outreach, Junior Scientists and many more. Many of these groups had splinter sessions during this year's team meeting. 

The CANDELS team at the 3rd annual meeting in Santa Cruz, California. Image credit & copyright: Dale Kocevski

The team meeting started off with a splinter session for the SED-fitting and photometric redshift working group. Bahram Mobasher and Tomas Dahlen who are leading this working group gave us an overview of the recent photometric redshift and stellar mass estimations. Several working group members, myself included, presented their current work in this area in the morning. Most of the afternoon was then spent discussing these results and making plans on how to proceed and turn these works into publications. 

Tuesday was the first day of plenary sessions. As we told you in last Wednesday's post, on this day we mainly heard progress reports from the working group leaders on the achievements and goals of the working groups. We heard that the collaboration as a whole has already published 13 papers and 9 have been submitted and are in the refereeing process (scientific papers for publication are submitted to a journal and then evaluated by a referee who provides suggestions for improvement and clarification before the paper is published). Sandy Faber, one of the principal investigators for CANDELS, summarized the most interesting science that has come out of the survey so far. In Karina Caputi's paper a new population of very red, and dust obscured galaxies has been discovered of which you will hear more about in a future post. Another science highlight was the very heavily star-forming dwarf galaxies Arjen van der Wel told you about in his previous post. Of course there were many other interesting results discussed!

As leader of the education and public outreach working group I summarized details on this blog and provided some statistics on the number of viewers and readers we have already! I also listed some ideas for the future which we later discussed in our own splinter session on Thursday. We will tell you about these soon here, too!

As is tradition during conferences and team meetings, we also had a team dinner. Ours happened Tuesday evening during which some team members were honored for their special contributions to the team. And now we also finally have a team logo! You can read more about it in this post from last week. 

Speed brainstorming breakout session, image credit: Dale Kocevski
Wednesday was the second day of plenary sessions. We heard about the HST mosaics for the CANDELS fields and observation scheduling from Anton Koekemoer and Norman Grogin and about other catalogues for galaxy properties that have been produced by other team members. But it's not all about science with CANDELS data alone! Part of the morning was dedicated to observing proposals to use facilities other than the Hubble Space Telescope that are planned within the team. But all the good science needs some organising, too! So some of Wednesday was spent on planning out the telecon schedule, announcing up-coming meetings of some of the working groups, and suggesting a time plan for papers in progress. After all there is still a lot more science to do with CANDELS!

While the senior members of the team had their own executive council dinner, the Junior Scientists (i.e., students and postdocs) finished off the day with their own social event including wine and cheese.  This gave us a chance to get to know each other better and bring up any issues without senior members present. We also got some job-finding and application advice from some members of the team that just recently obtained permanent jobs and made the jump from a postdoctoral position to a faculty job. We could ask questions and got some real insights, and all of that while munching cheese, nibbling on some fruit and sipping wine!

Two happy principal investigators at the end of the meeting!
Harry Ferguson and Sandy Faber, Image credit: Dale Kocevski
Thursday and Friday were completely devoted to splinter sessions for different working groups. During the splinter sessions most time was spent on short talks and lots and lots of discussion on future projects. I attended the session for Structure and Morphology and led the session for the Education and Public Outreach working group. You already read a good summary of both of these last Friday. In parallel, the working groups for Star formation rates, AGN, UV science and spectroscopy met. Unfortunately, one cannot be in several places at the same time! Dale Kocevski will give you a summary of the AGN working group in a few days time. During the session for the newly formed star formation rate working group a lot of different star formation rate estimators were discussed. Since this working group is not very old yet, a lot of the session time was dedicated to discussion on possible projects and science that needs to be done. The UV working group discussed how to use the remaining observation time and planned the observation scheduling. They also addressed the data reduction for the UV data. In the high-redshift session team members presented their results on some of the most distant galaxies and how to decode their properties while during the spectroscopy session we got an overview over what spectral data is available in the CANDELS fields from other surveys. 

As another tradition, during the lunch break on Thursday, a team photo was taken. We already showed you the team photo from last year's meeting in Edinburgh, I won't tell you in which post, but can you find it? This year's photo is shown as the first photo above. This time, almost everyone looked into the camera smiling! That's quite hard to achieve with nearly 100 people.

Finally, the meeting was finished off with a few drinks after the last sessions before everybody got on their way back to their institutes to do all that amazing science that has been discussed and planned during the meeting. We are curious to hear about the results and to meet everyone again next year

Friday, September 14, 2012

Splinter Session Science

CANDELS astronomers listening to talks. Image credit: Janine Pforr
With the plenary sessions of Tuesday and Wednesday behind us, Thursday was a busy day of working group splinter sessions. Several of the different working groups got together in smaller numbers to discuss specific topics. This morning started off with the Structure and Morphology Working Group Session that I organized. To kick off the session I gave an overview talk about the status of the group, the papers we have been working on, and the catalogs we have produced. After this, we had a fun series of quick talks (ten minutes total for each, including discussion!). The purpose of these talks was to give the entire group a flavor of what everyone else is working on and the status of various projects. They also allowed us a chance to ask questions and discuss some interesting scientific topics. There were 17 of these talks in total, spanning a wide range of topics.

Our group will meet again this morning, this time to discuss future research topics. In particular, we want to decide upon the most important scientific questions that we should be answering in the next year with our rich set of data. The science that can be done is unlimited, so a discussion like this really helps us to focus on what would be the most interesting and the most useful to the scientific community.

During the afternoon, there were three concurrent sessions. It was tough to decide which one to go to! I chose to go to the session on Education and Public Outreach, lead by Janine Pforr. During this session, we mapped out strategies for how to proceed with this blog in the future. We brainstormed about possible post topics that would be interesting to our readers as well as ways to increase our readership. We also discussed some other project ideas and started to get organized about what information is needed and who could be appointed to coordinate. We think we came up with a lot of great ideas and you'll be hearing more about them in the future!

While we were discussing EPO, the star formation rate indicators group was also meeting. Unfortunately, I had to miss it but I got to hear a lot about it from my collaborators and it seems that they had some very interesting discussions on how to best measure the rates at which galaxies form stars. The stars that influence star formation rates the most are massive stars. Massive stars are very bright in ultraviolet light. You might guess that if we could measure the total ultraviolet light from a galaxy, then we would be able to measure the total star formation rate. This is only half true. It turns out that galaxies are not that simple. A lot of them also have dust, and that dust hides the ultraviolet light from galaxies -- just like a hazy day when light from the Sun is blocked. So if we only use ultraviolet light, we will underestimate the star formation rate. Fortunately, the hidden ultraviolet light isn't lost. It goes toward heating the dust and then that dust emits light in the infrared. Because of this, astronomers try to gather both ultraviolet and infrared light from galaxies to recover the true star formation rate of galaxies. This method is just an example. There are many other ways that have been proposed to measure star formation rates. Yesterday's discussion certainly helped us to get one step closer to obtaining the real number of newly born stars in distant galaxies. New data sets in the CANDELS fields, including far-infrared imaging from the Herschel Space Observatory and near-infrared spectroscopy from the WFC3 grism, will be immensely useful for addressing this question.

The third group that met was the theory working group. The group discussed some of their own data products, including catalogs based on simulations. These simulations are very useful for observers, so one of the main goals of this session was to discuss the best way to combine theoretical models with observations from CANDELS. 

Today, the last day of our meeting, several other groups will be meeting (AGN, UV, high redshift galaxies) to have similar discussions about their science results so far and their plans for the future. It's hard to believe that the meeting is almost over!

Wednesday, September 12, 2012

Day 2 of the CANDELS Team Meeting: Working Groups and the Social Side of Meetings

Yesterday's agenda at the team meeting was packed with a lot of interesting science! It was the first of two days of plenary sessions, meaning that for these two days everyone will be here and meet in one room. For the other days, we are meeting in smaller groups to discuss specific topics in detail. The bulk of today's agenda included summary talks from each of the working group leaders discussing what the different groups have accomplished so far and what their goals are for the future. As mentioned in our last post, CANDELS has several working groups on different science topics that work together to produce necessary data sets and write papers. For example, I lead the morphology working group and so gave a talk about the papers we have published so far and the data products we produced. It was quite useful to hear what all of the individual groups have been up to and what each is planning for the next year. CANDELS has published a lot of papers so far, but there is so much more we would like to do. The plans are ambitious, and there is a delicate balance between the important tasks we must each undertake (such as producing catalogs for the team to use) and writing papers.

We also had a very fruitful discussion at the end of the day about how various aspects of the team organization works, for example, how each of the groups communicates about their results to the rest of the team. We got to hear what works and what doesn't, and brainstorm ideas for ways to improve how the team interacts with each other.

After all of the talks were over, the team gathered together at a nice restaurant by the water in Santa Cruz for our team dinner. It is typical at a meeting like this to plan a group dinner on one of the evenings so that everyone has a chance to socialize and get to know each other a little better while talking about the meeting in an informal setting. This is often a lot of fun! The evening was made even more interesting by some announcements from Sandy Faber and Harry Ferguson, the principal investigators of the project.

The new CANDELS logo, designed by
Dale Kocevski and Nina McCurdy
Since the formation of the team back in 2009, various ideas have been tossed around for a team logo. Having a logo for a collaboration such as this is great because it gives the team a visual representation of what they do and can be used in various places. For example, logos are often used in presentations or included on posters. In order to come up with a good one, and have a little bit of fun in the process, Harry and Sandy suggested having a logo contest. So, everyone was free to submit their ideas for logos and encouraged to be creative. Many ideas were submitted and we all voted. Tonight, the winning logo was announced. The designers of our new logo are Dale Kocevski and Nina McCurdy. The logo itself is shown to the right. It depicts the Hubble Space Telescope overlayed on an HST image with the CANDELS team name written around in a circle. We are all quite excited to have a new logo to start using! What do you think?

Dale Kocevski, smiling at the team dinner after
receiving his awards
In addition to the announcement of the logo contest winners, Sandy and Harry gave out several unexpected awards to various team members. Dale Kocevski received an award for the most popular CANDELS paper on Vox Charta (a website used by astronomy departments for discussing new papers as they come out). Congratulations Dale! Two different awards were given for important contributions that have benefited the entire team: Audrey Galametz for the huge effort that has gone toward creating multiwavelength catalogs, and Tomas Dahlen and Bahram Mobasher for their work on comparing photometric redshifts produced by many different groups. Karen Pena was awarded for her incredible efforts in organizing this great meeting and Adriano Fontana for the greatest contribution to CANDELS team resources. And finally, this very blog received an award for its contribution to Education and Public Outreach.

In many ways, our meeting has just begun! Today we will have a discussion about our big picture science goals for the future and the papers that only a project like CANDELS can write.

Astronomers deep in scientific discussion over lunch
Photos taken by Janine Pforr

Monday, September 10, 2012

Kicking off the CANDELS 2012 Team Meeting in Santa Cruz

As I type this, CANDELS team members from all over the world are arriving in Santa Cruz, California for the third annual team meeting. Over 85 astronomers have registered and will be meeting for the entire week at the University of California, Santa Cruz campus starting this morning. And what a week we have planned! The schedule is packed full of talks about CANDELS science and discussion of plans for the future. In addition, we will have social events throughout the week, such as a team dinner on Tuesday evening and a special event for the Junior scientists on the team on Wednesday.

The week will be broken up into plenary talk sessions that everyone is attending and breakout sessions where smaller groups of us can discuss particular topics in detail. For example, I will be leading sessions for the Morphology working group on Thursday and Friday mornings. We will be discussing the papers we have written so far and then we will discuss those we are currently working on and plan to write in the future. There will be other sessions on AGN, high-redshift galaxies, theory, and various other topics.

All this week, and probably into next week, we will be sharing various aspects of this meeting here. Not only will we tell you about some of the science we are discussing, we will also describe some of our future plans and social events. For a real-time look at our meeting, search for #CANDELS2012 on Twitter. @CANDELS_team will be posting, as well as myself and other team members.

Friday, September 7, 2012

Astronomer of the Month: Boris Häußler

Each month we will highlight a member of the CANDELS team by presenting an interview introducing them and what it's like to be an astronomer. This month's Astronomer is Boris Häußler.

Tell us a little about yourself!

My name is Boris Häußler (Haeussler) and I'm a Postdoc (research assistant) at the University of Nottingham. I was born in Karlsruhe, Germany, a long time ago and lived there until I had finished school and had studied physics at the university for 2 years. I then changed over to the University of Heidelberg to be able to take on astronomy as a side topic in my studies (Karlsruhe is only really famous for solid state physics and although that's what my dad does, I don't get it). In Germany, physics studies end with a 12 months thesis, which I carried out at MPIA with Klaus Meisenheimer and Hans-Walter Rix. I got a bit lucky there because the satellite mission that I wanted to work on was cancelled on my third day, so, looking for a new project for me to work on, Hands-Walter mentioned this new HST project that he had started and so I slipped into GEMS.  Best thing that ever happened to me, I guess. After my Diploma, I continued working on GEMS during my PhD and I managed to get involved into STAGES, a sister project of GEMS, which basically gave me my first postdoc in 2007 in Nottingham with Meghan Gray, where I continued to work on STAGES for 3 years. I also met Steven Bamford who, close to the end of my project, started a project (MegaMorph) that was basically trying to enhance exactly what I had done for years, so that gave me my second postdoc. I am now starting to look for a new position and I will see where the wind blows me.

What is your specific area of research? What is your role within the CANDELS team? 

Generally, I work on galaxy evolution. More specifically, I have worked on blue spheroidal galaxies (which we think are an intermediate step between galaxy mergers, which turn galaxies into ellipticals, but still recent enough to contain young, blue stars) and the dependence (basically none) of galaxy boxyness/diskiness on galaxy environment. Technically, I have worked on simulating galaxy/survey images to then test galaxy profile fitting codes. I am currently developing a new technique that allows GALFIT (the actual fitting software) to use multi-band data simultaneously, thus down-weighting image noise and returning good values for many more galaxies as previously possible.
This technique enables us to do research in many areas of galaxy evolution that were previously not possible due to lack of a good code and good fitting values. I won't tell which ones, though, I want to do that work myself. As I am 100% occupied with the development of this new code, I have not actually done much work with CANDELS. I have created some images for people to test their codes on and helped to figure out some biases seen in the fitting data. Other than that, my main contribution is that I got the CANDELS and the GALAXY ZOO teams together (as I am a member of both), so we will have CANDELS galaxies classified by the public. Together with Jennifer Donley, I am also the junior scientists representative in the CANDELS team. 

What made you want to become an astronomer? At what age did you know you were interested in astronomy? 

I was always good at physics at school, it came naturally that I did something in that direction. At university I noticed that solid state physics wasn't quite my thing. I had a subscription to a physics magazine and I noticed that I only ever read the astronomy articles and then stored it away. I had also always enjoyed star gazing and astronomy pictures, so the decision to do astronomy at least as a side topic was an easy one. After my change to the University of Heidelberg, I did this and then decided to do my diploma thesis on an astronomical topic. Once I was in research, there was no way back for me because I thoroughly enjoyed it.

What obstacles have you encountered on your path to becoming an astronomer and how did you overcome them? 

I haven't encountered many obstacles yet. My career so far has been pretty straight forward and lucky. The job market is a bit of an annoyance, especially for longer-term jobs, which I have not gotten yet, but I stay optimistic about it. If a scientific career does not work out, I am very keen on outreach jobs as well. Ideally, I'd like to do a bit of both.

Who has been your biggest scientific role model and why? 

I don't really have a role model. I have more than a few people that I do NOT want to be like, but of course I am not going to mention anyone here. If I HAD to pick one, I could mention Carl Sagan. Although, being German, I didn't known of him when I was a kid, I found him very inspiring once I discovered him. He had a very easy but still accurate way of explaining things to non-specialists and I think this is an invaluable skill. Richard Feynman was the same way.

What is it like to be an astronomer? What is your favorite aspect? 

Being an astronomer is the coolest job in the world! It's fun to simply 'find out stuff' and look at things that no one has seen before. My favourite aspect would possibly be that I largely have freedom in what (and when!) I am doing. Also, traveling to nice places for conferences is fantastic. 

What motivates you in your research? 

As I said, 'finding out new things' is pretty cool. I currently run an outreach project here at Nottingham where we go to schools and the pupils reactions to astronomy and the shining eyes (at least for some kids) are a real motivation.

What is your favorite astronomical facility? (This could include telescopes or super computers, for example) 

Gosh! That's tough! I haven't visited many. Of the ones I have used, I would say UKIRT, mainly because of its location on Hawaii. Gemini next door is pretty cool, LBT is a great project, and VLT simply amazes me every time. I think in the future, the E-ELT will blow us away!

Where do you see yourself in the future? What are your career aspirations? 

That's a difficult question. Ideally, I would stay in a scientific research career, but with time for outreach activities on the side. If I had to choose between the two, my decision usually jumps from one to the other over a timescale of a year or so. Both are fun and I want to continue doing both. Certainly, in 5 years time, I see myself in a longer-term position, but I am open to where that would be. 

If you could have any astronomy related wish, what would it be? 

I would wish that telescopes of all kinds are built within their forecasted timeline and budget, because it would make the whole experience a LOT cheaper and faster. More telescopes mean more data to work with. 

What is your favorite, most mind-boggling astronomy fact? 

The emptiness of space. Once you have seen how empty space is even in a crowded place like the solar system, you cannot forget that. The universe is VAST and we're only a tiny living being on a tiny speck of dust.

Is there anything else you would like for the public to know about you or astronomy in general? 

Not really, I have to get back to work, I have a paper to write!