Our Blog Featured on Learning Space

Last week, Janine Pforr and I participated in a live Google Hangout on Learning Space,with Nicole Gugliucci and Georgia Bracey from CosmoQuest. We discussed the CANDELS survey, public outreach, and this blog. Take a look below!

Team Meeting Tweets

The CANDELS team meeting is complete! One way that astronomers can listen in on conferences that they cannot attend in person is to follow them on Twitter. We've tried this for a couple of our meetings and it can be really useful. Basically, anyone that is interested can write snippets about the meeting that they think are interesting and share them on Twitter with a common hash tag (in this case, #CANDELS2013). We have saved all of our team meeting tweets and shared them using Storify below.

In the coming days we will be writing a few posts about different aspects of the meeting. Until then, take a look at what we had to talk about during the meeting itself!

On Mountain Tops and Lasers

The Subaru Telescope (left) next to the two Keck Telescopes on Mauna Kea.
Image Credit: J. Pennington

Tonight I am sitting on top of a 14,000 foot mountain observing distant galaxies. This is the second of a three night run at the Subaru Telescope on Mauna Kea on the Big Island of Hawaii. In a previous post I talked about a run to obtain spectroscopy on one of the Keck Telescopes and some of the excitement, including ups and downs, that are part and parcel of an observing run. This run is no exception!

Initially, my collaborators from the University of Hawaii and I proposed to obtain near-infrared spectroscopy of distant luminous and ultraluminous infrared galaxies using an instrument called FMOS. Due to a problem with the telescope, that instrument turned out to be unavailable during this run so we had to scramble to change our science program to use a completely different instrument. I'm sure I'll talk more about FMOS in the future, but for now I'll focus on what we're doing this week!

The instrument we are using is called IRCS - the Infrared Camera and Spectrograph. We are only using the imaging mode of this camera. The exciting thing about this run is that we are also using the Laser guide star adaptive optics system on Subaru. Briefly, adaptive optics is a technique used by astronomers to obtain images at a higher resolution (and therefore allows us to study features at greater detail) than we normally can from the ground. Since we have to observe through the Earth's atmosphere, our images are blurrier than they would be from space. The reason for this is that the turbulence of the atmosphere causes the light from distant objects to shift in position on a very short timescale (this is why stars twinkle!). As you take an image with a camera on a telescope, this shifting adds up, causing the resulting image to be blurry. Ever notice how a picture on your digital camera is blurry if your subject moves while you are taking it?

Image of the nuclear region of a nearby galaxy (NGC 7469) taken with
and without adaptive optics at CFHT.
Image credit: Center for Adaptive Optics

We can counteract some of this by placing our telescopes on top of tall mountains (such as Mauna Kea) and therefore above some of the atmosphere. We can improve on this even more by using adaptive optics. Adaptive optics uses a bright star to correct for the effects of the atmosphere. Since we know what a star is supposed to look like (it should be point-like in images), the distortions introduced by the atmosphere can be calculated and a deformable mirror is re-shaped so that the light goes where it's supposed to. These corrections can result in images almost or just as sharp as those taken from space (check out the example to the left)! However, since the turbulence of the atmosphere is different at every point on the sky, in order to make these corrections you need to have a bright star that is very close to the object you are trying to observe. This isn't always possible and can be very difficult in our deep fields. This is where Laser Guide Star Adaptive Optics comes in!

Laser from the Subaru Telescope
Image credit: D. Birchall

Laser Guide Star Adaptive Optics is used to create an artificial star close to the object you are observing anywhere in the sky. A bright star is still needed, but it can be a little fainter and a little farther away. This technology has opened up a much larger area of the sky for this kind of imaging! As I am typing this, there is a laser from Subaru aimed at the target I am observing. Keck is also using their laser tonight. You can often see these lasers in images of the telescopes (such as the ones to the right and below).

Tonight we are targeting galaxies within COSMOS and EGS that fall outside of the CANDELS WFC3 HST coverage. In this way, we can obtain high resolution near-infrared images of select interesting targets in order to study their morphology in detail. These galaxies are all sources with extreme infrared luminosities and with this data we will be able to search for signatures of galaxy mergers and study the properties of any star-forming clumps we detect. Our first night was lost due to some problems with the dome shutter but those problems have been fixed and tonight we making our way through our list of targets! 

Using the laser always makes for a particularly busy night of observing because there are many things to consider when shining a bright laser into the sky. First of all, all of our targets must be submitted to Space Command for approval ahead of time to insure that the laser does not interfere with any passing satellites. Because of this, there are certain times of the nights where we must pause our observations or switch targets. We also have to be careful about any planes that might be passing overhead. While the laser is shining, there are always a couple of people standing outside watching, ready to turn off the laser just in case. So far, tonight is going pretty well and the forecast looks great for tomorrow as well!

Panoramic image showing lasers from Subaru and both Keck Telescopes. Image Credit: D. Birchall

Our First Google Hangout

Last week, members of the CANDELS team participated in a Google hangout hosted  by Tony Darnell and Alberto Conti at the Space Telescope Science Institute. You can follow their regular Google Hangouts at #SpaceFan on Twitter or through their YouTube channel at the above link. Several team members, including Steven Finkelstein, Romeel Dave', and Darren Croton, a few of our regular bloggers, Joel Primack, and Cathy Caviglia discussed CANDELS and their own research using CANDELS data. 

Check out the video below and let us know what you think! We will try to do more of these in the future covering a range of science topics.

Astronomy in the Alps

View of the Alps from the conference location in Italy
Image Credit: Janine Pforr

This week, about forty astronomers from all over the world are gathered in Sesto, Italy, a small town in the Alps to discuss the process of star formation in galaxies and how it has evolved over the history of the Universe. A great many of these astronomers are CANDELS team members who are presenting their own research based on CANDELS data. The meeting is being hosted by the Sexten Center for Astrophysics. The location is idyllic this time of year (see pictures) and is a premier hot spot for skiing. This remote location is perfect for a workshop like this because astronomers can really focus on the topic being discussed and can also socialize and have fun together.

The goal of the meeting is to understand star formation at high redshift, from z~2 galaxies all the way out to galaxies in the z~8 Universe. Astronomers from both CANDELS and many of the Herschel deep surveys are attending since all of these surveys are crucial for studying this topic. We are discussing various approaches to studying high redshift star formation, so in a few posts over the next couple of weeks, we will write about some of the interesting talks being presented.

The NASA Hyperwall at AAS

The NASA Hyperwall at the 2012 AAS meeting in Austin.
Image Credit

At this year's AAS meeting, the CANDELS team was given the opportunity to present the survey to the wider astronomical community by giving a presentation on the NASA Hyperwall. The NASA Hyperwall (shown to the right) is a set of nine high resolution screens put together to form a large display wall. It is taken to meetings like the AAS and set up in the exhibit hall. The high resolution (4104 x 2304 pixels) is fantastic for showing HD movies and animations and large astronomical images.

Janine Pforr, David Jones, and I gave the CANDELS presentation on the Wednesday of the meeting. The exhibit hall was full of people viewing posters at the time, so many people stopped by to watch our presentation. Janine kicked it off with a description of the CANDELS survey, our goals, and some of the science objectives that we have been discussing in various blog posts here. She showed the large color mosaic of GOODS-S and zoomed in to just a portion of the field so the audience could see the richness of the data set and many of the galaxies in detail. These images look fantastic on such a large screen and it was our first opportunity to see our data displayed this way. Janine also showed a couple of galaxy simulations (such as the one below).

Bolshoi Simulation: Bolshoi Fly-Through, by Anatoly Klypin and Joel Primack, visualized by Chris Henze, NASA Ames Research Center.

Next, I took that portion of the mosaic and zoomed into a handful of interesting objects to highlight some of our science goals and some of our papers. I showed the power of deep near-infrared imaging with a comparison of galaxies with very different morphology in the optical. I discussed the work that our group has been doing with galaxy morphology at high redshift and also highlighted the papers of Arjen van der Wel and Stijn Wuyts. Finally, David Jones wrapped up the presentation by discussing the results of the the supernovae part of the project.

In addition to CANDELS, both of the other multicycle treasury projects gave presentations. Julianne Dalcanton presented PHAT -- the Panchromatic Hubble Andromeda Treasury Survey. PHAT is imaging a large portion of the Andromeda Galaxy with Hubble in several different filters. With HST resolution, millions of individual stars can be identified and studied in great detail. The images that Julianne showed on the Hyperwall were stunning!

There was also a presentation on CLASH -- the Cluster Lensing And Supernova survey with Hubble -- PI: Marc Postman. CLASH is imaging 25 massive galaxy clusters with Hubble in order to map out the distribution of dark matter in great detail and study even more distant galaxies that have been gravitationally lensed by the mass of the cluster.

During the meeting there were many other amazing presentations on the Hyperwall. I particularly enjoyed the talk by Frank Summers from the Space Telescope Science Institute on astronomical visualizations. He showed many HST images as well as some fascinating movies that combine simulation data and real images in incredible ways. My personal favorite was the one shown below, which illustrates the entire merger sequence of galaxies by combining a merger simulation with HST images of galaxy mergers at various stages. This video looked great on such a large screen!

Galaxy Merger visualization of a supercomputer simulation illustrating the entire merger sequence. Credit: NASA, ESA, and F. Summers (STScI). Simulation Data: Chris Mihos (Case Western Reserve University) and Lars Hernquist (Harvard University)

We had a good time preparing our Hyperwall presentation and getting to see all of the other things people presented on the big screen. Part of the fun was that all of these talks were quite different from normal astronomical talks. These talks were really focused on the visuals with very little, if any, text on the screen. They were also aimed at a level that everyone, even non experts, could enjoy. I am looking forward to the creative things presented on the Hyperwall next year! 

Life as an Observer

The Keck Telescopes on Mauna Kea
Courtesy W. M. Keck Observatory

One of the best aspects of being an astronomer is actually using a telescope and collecting data. Tonight, I have the opportunity to use one of the best telescopes in the world along with an exciting new instrument. Fellow CANDELS team member Mark Dickinson and I are observing on one of the Keck telescopes atop Mauna Kea on the Big Island of Hawaii. Mauna Kea is one of the best observing sites on the planet because the peak of the mountain where the telescopes are located sits above a substantial portion of the atmosphere. Because of this, the atmosphere has less of an effect on the images of astronomical objects than it would from an observatory at sea level. While the Keck telescopes themselves are at the summit of the 14,000 foot mountain, observers work from a remote observing facility located in Waimea. Being at this lower altitude makes it much easier to work and all of the instruments can be controlled remotely. 

The instrument that we are using is called MOSFIRE (Multi-Object Spectrometer for InfraRed Exploration) and is very new. It is a top of the line instrument that allows us to obtain sensitive, high resolution near-infrared spectroscopy of many objects at the same time. Most spectrographs in the near-infrared observe one object at a time. There are now several available that can observe many objects at once but they are often difficult to use for very faint galaxies. MOSFIRE is still brand new but so far has been working well. CANDELS team member Jonathan Trump recently published a paper on some first results! 

Mark Dickinson and I observing in the Keck I Remote Observing
Control Room

We spent the last several days carefully selecting targets to observe in two of the CANDELS fields, GOODS-S and COSMOS. Our primary targets of interest are distant luminous infrared galaxies detected by the Herschel Space Observatory at z~2. At this redshift, many of the interesting optical emission lines (such as the Hydrogen line known as H-alpha) are shifted into the near infrared. We can use these various lines to measure precisely how far away the galaxies are, whether or not an AGN might be present, how important that AGN is to the energy output of the galaxy, how much star formation is taking place in the galaxy, as well as many other things.

In addition to these targets, we are also observing AGN selected in other ways, such as through X-ray detections or from the shape of their SED in the near-infrared. If there is any space left we are also looking at other types of galaxies at these high redshifts to see if we can detect lines. 

Once our target selection was complete, we waited anxiously to see what the weather would do. The forecast called for clear skies but starting last night the summit of Mauna Kea became foggy. We awoke this morning (morning for an observing astronomer is really about 2 PM) to find that the fog had not cleared and some clouds had rolled in. We were really starting to get nervous! However, we proceeded as planned and began our afternoon setup. Around sunset, things were really looking dicey and it started to snow! Luckily for us that didn't last too long and the road to the summit remained clear for the night crew to head up and check things out. After a couple of hours, the fog cleared and the humidity dropped to a level low enough to open. We had a good time learning how to operate this new instrument and at 9:30 PM we started our first exposure on a set of galaxies in GOODS-S!

 

Video from a webcam at CFHT (the Canada-France-Hawaii Telescope) on Mauna Kea showing the clouds roll in Wednesday night and ice starting to form on the camera itself. Video courtesy of CFHT Observatory

Over the course of the night clouds have come and gone but the weather has steadily been improving. Right now we are observing galaxies in COSMOS and things are looking good. We are anxious to analyze our data and see how many of our galaxies have been detected. With any luck, we will soon be writing a blog post about our results! 

This is our last blog post before the holidays but we look forward to discussing more CANDELS science in January. Happy Holidays! 

Follow the Keck Observatory on Twitter!  

Binary Black Hole Workshop

Illustration of binary black holes. Image credit: P. Marenfield (NOAO)

Last week, I attended a workshop on Binary Black Holes and Dual AGN sponsored by NOAO in Tucson, Arizona. This workshop was held in memory of David de Young, an NOAO astronomer who passed away last December. Dave received his PhD in 1967 from Cornell University and joined the NOAO staff in 1980. Dave's own research focused on Active Galactic Nuclei (AGN) and he had over 120 scientific publications over the course of his career. The focus of last week's workshop was on a topic that Dave's research related to in many ways.

In previous posts, we introduced super massive black holes and AGN. This meeting focused on the search for pairs of black holes in galaxies. Why are these interesting? There is evidence to suggest that all massive galaxies contain a supermassive black hole in their centers. When two galaxies merge together, each of the two likely had their own black hole. Eventually, the two black holes will merge together at the center of the coalesced galaxy, but before this happens there should be a time when the two black holes are observable separately. In some cases, both may be active, in which case a dual AGN might be observable. Finding and studying these systems can tell us a lot about what happens in the final stages of a merger and we can learn a lot about black hole physics.

The goal of the workshop was to discuss many aspects of binary black holes, including how to identify them and how they affect their host galaxy. One of the methods used to identify binary black holes is to simply look for pairs of AGN on the sky at the same redshift. This is usually done by selecting AGN identified in the X-ray, but can also be done using a variety of other AGN selection techniques. This method is straight-forward, but it requires that both black holes be active and detectable, and thus finding such systems is very rare. Another common method is to look for spectroscopic signatures of two black holes. Due to the motions of two black holes in orbit around each other, spectra of such systems often have emission lines with two peaks, one for each black hole. However, since other processes can cause these types of emission lines, detailed follow-up observations and analysis is required for these candidates.

We also heard a lot about adaptive optics (AO) observations of binary black holes. Since the two black holes in a merging system are so close together on the sky, it can be very difficult to separate them from each other in images. One technique for obtaining very high resolution images from the ground is called adaptive optics (or AO for short). With AO, images are corrected for the distortions that are caused by atmospheric turbulence so that the final image is much sharper than would have been obtained otherwise. With AO, astronomers are able to peer into the very center of nearby merging galaxies and separate double nuclei and identify the two black holes. In many cases, the surrounding area can be studied in great detail in order to determine how the black holes have affected their surroundings.

Since mergers are important for producing binary black holes, one of the topics of the meeting was trying to understand the connection between mergers and AGN activity. In this context, the recent CANDELS paper by Dale Kocevski came up as an example of the many studies that have tried to investigate this question at high redshift. There is currently a lot of debate about the role that galaxy mergers play in forming AGN in general. The relationship between AGN and their host galaxies is the topic of a meeting taking place right now in Germany and will be discussed more in a future post!

What is an Observing Proposal?

Have you ever wondered what astronomers have to do to get to go on observing runs to telescopes? You might think that there are a lot of telescopes and thus astronomers can go observing whenever they want to or you might think that they observe every night. Actually, time on telescopes is in very high demand and astronomers have to compete with each other for every night of telescope time they get. In order to enter this process, astronomers must write a document called an observing proposal. This is the typical process for almost all telescopes, including big and small facilities, facilities run by a single University, those run by groups of Universities, and national facilities. Space-based telescopes (like Hubble!) also follow this procedure.

Image of Kitt Peak National Observatory, managed by NOAO. Image credit: Michael L. Weasner

In order to apply for telescope time, the first step is to come up with a good idea. Astronomers often have multiple projects going on at once and we are always thinking of new ideas and questions and ways to improve upon what we know. Once we have an idea we have to decide what telescope (and instrument) would be the most suited to accomplishing the science goals we have in mind. The instrument needed can often be more important than the telescope itself. Is the goal imaging or spectroscopy? Is there a particular wavelength range or filter needed? Do we need to target a single object or small patch of sky or are we surveying a large area? All of these factors go into selecting the best telescope-instrument pair. This selection can also depend on the University or country that the astronomer is at. Different Universities have access to different Observatories depending on funding, instrument development, and various other partnerships. There are also various facilities run on a national level -- for example NOAO in the US or ESO in Europe.

The next step is the bulk of the work: writing the actual proposal. A typical observing proposal has several components. The main one is called the Scientific Justification -- basically, describe why the science project you want to do is interesting. This is the place where an astronomer has to really sell their idea and convince others that answering this particular question is very important and must be done. Often, those reviewing proposals do not work in the particular specialty of the proposer so a good proposal is one that can be understood by any astronomer, not just experts on that particular topic. We must also clearly lay out the strategy of the science project here: how will the observations that we are proposing for answer this important question? What kind of data will be taken and how will this data be used to solve the problem presented? Often astronomers are limited to only a couple of pages of text so it can take a lot of work to say everything you want to say succinctly.

Another typical component of an observing proposal is a technical section. This is where an astronomer must go into detail about the instrument and telescope they are proposing to use and say why this particular combination is well suited. They must clearly demonstrate how much data they need and how much time this will take overall. Since observing time is a precious commodity, any time request must be clearly justified - if you say you will need two nights to accomplish your goals then you must show that two nights are really needed and one night would not be enough. Often, this portion is reviewed by people who are experts with the given instrument and who understand how well the instrument will perform.

It is important that a proposal be very well written! In fact, the ability to write well is a very important job skill for astronomers in general. An astronomer must be clear and concise in their proposal. If there is confusion about the goals or how they are going to address a particular problem, this could negatively impact the proposal's chance of success. It is also very useful to include informative graphics that illustrate the science goals and method presented. As they say, a picture is worth a thousand words, and a clear well-thought out figure can really strengthen a proposal. Finally, this might seem obvious but it is very important that all of the rules be followed! A proposal cannot be longer than the given limit and cannot be written in too small of a font or with tiny margins. This might seem picky, but when a person has to review a lot of proposals they all need to be easy to read. At last, the proposal is complete and can be submitted (and must be on time!). At this stage, the astronomer can sit back, relax, and start thinking about their next big idea.

But the process has only just started on the receiving end. Most observing proposals are then evaluated by a committee of peers (other astronomers, either from the specific institute that runs that particular telescope, or selected from all over). Every proposal is read by the entire committee and the committee gets together to discuss each one over the course of a few days. It's not always easy to pick out the best proposals to award time to. Often there are more excellent proposals than there are nights to be awarded. Intense discussions about the merits of each proposal results in a ranked list and time is given to those proposals at the very top. Every one that does not get their proposal accepted must try again next time.

This may sound like a lot of work, and it is, but whenever a proposal is accepted and we get the opportunity to observe and collect new data, it is all worth it. It is a great feeling to know that your peers have found your ideas worthy of supporting! This is a process that we go through once or twice a year for each telescope we would like to collect data with. One of the major observing seasons of the year just finished this past September. Luckily there is a little bit of a break before the next major deadline in February (for HST). This break is needed so that we can work on analyzing all of the data from the previous year!

Galaxy Zoo meets CANDELS

As we discussed in this previous post, classifying a galaxy into morphological categories can tell us a lot about its structure. We often want to have classifications of large numbers of galaxies in order to  compare various properties (such as color, mass, star formation rates, etc.) with morphology. However, visual classifications can be very time consuming and classifying large samples (thousands of galaxies or more) can be a daunting prospect for any individual. In 2007 two astronomers, Kevin Schawinski and Chris Lintott, had a unique idea for how to deal with this problem - involve the general public in classifying galaxies - and Galaxy Zoo was born.

For the original Galaxy Zoo project, over one hundred thousand volunteers signed up to classify nearly one million galaxies from the Sloan Digital Sky Survey (SDSS). These volunteers determined whether each of the galaxies was a spiral or an elliptical and if it was a spiral whether it was rotating clockwise, counter-clockwise, or viewed edge on. Galaxy mergers and image artifacts were also options that the classifiers could select. Not only did these citizen scientists quickly take to classifying galaxies, they had fun and learned a lot about galaxies in the process. The Galaxy Zoo webpage hosts a forum where volunteers can post about interesting objects they find and discuss their classifications. One of the exciting aspects of having all of these galaxies looked at individually was the ability to identify rare and unique objects that had not been seen before, such as Hanny's Voowerp. These classifications have provided an incredible data set for Galaxy Zoo scientists and a number of publications have resulted from this tremendous effort.

The Galaxy Zoo project was further expanded with the start of Galaxy Zoo 2, which included a much more detailed look at a subset of galaxies, and Galaxy Zoo Hubble, which asks volunteers to classify galaxies imaged with the Hubble Space Telescope in a number of deep fields. Last month, Galaxy Zoo relaunched in its latest incarnation and now includes reprocessed SDSS images along with HST images from CANDELS. These new images have been discussed in great detail on the Galaxy Zoo blog. This is a unique and exciting project for CANDELS because now galaxies at high redshift with near-infrared data will be classified alongside SDSS galaxies by many people to produce a fantastic data set of classifications.

A sampling of colorized CANDELS galaxies that are in the newly relaunched Galaxy Zoo

We worked together closely with the Galaxy Zoo team to produce images for the website. Astronomers are used to analyzing images taken with a specific filter, or one very narrow portion of the spectrum. As such, these images are scientifically very useful, but we must look at images taken in different filters in order to study various galaxy properties. The beautiful color astronomical images that you are probably used to seeing combine several of these filters together. Since CANDELS images are taken in the near-infrared, which is not visible to the human eye, visible colors are assigned to the different near-infrared filters. These images are thus false-colored, but these colors represent real physical properties. The pictures above highlight what some of these CANDELS galaxies look like in color as they are being classified by volunteers.

Since the success of Galaxy Zoo, a number of other Citizen Science projects have begun. Collectively, these projects are a part of the Zooniverse and include things such as finding planets around other stars, studying the surface of the moon, and investigating the history of the Earth's climate. There are a number of interesting projects that anyone out there can contribute to. We hope you explore some of these while you are exploring Galaxy Zoo and looking at CANDELS galaxies!

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!