Monday, August 27, 2012

How I Ended up Studying Distant Galaxies

As Janine Pforr mentioned, we've decided that from time to time we will be using blog posts to introduce ourselves and say something about how we got into astronomy. I'm writing this post on a long flight back from Arizona to Baltimore, so apologies in advance if I ramble a bit.

I am Henry C. Ferguson, known to my colleagues as Harry. I am co-Principal investigator of CANDELS along with Sandy Faber. I am an astronomer at the Space Telescope Science Institute (STScI), in Baltimore Maryland. STScI is the science operations center for the Hubble telescope, and will be operating the James Webb Space Telescope (JWST) when it launches in 2018. All the scientists at the institute divide their time between their own research and providing support for the observatories. My research interests broadly center around galaxies and cosmology, and I've been spending most of my time over the past couple decades on surveys of the distant universe.  For my support work, I have most recently been running the Webb Instrument Team as we try to work out the details of how to operate and calibrate the cameras and spectrographs on the new telescope. I've done similar work in the past for Hubble. In my spare time, I enjoy playing Irish traditional music on hammered dulcimer and accordion, most recently as a member of the Tanzania Ceili band.

I've been interested in astronomy since my early teens. I went to high school at St. Paul's, a boarding school in Concord, New Hampshire. The school had a small observatory, and a remarkable science teacher, Walter Hawley. There were no formal astronomy classes, but there was an astronomy club. Skies were reasonably dark, and a friend and I spent many nights observing and sketching the Messier objects. Walter Hawley arranged trips for the astronomy club to the Harvard College observatory, where we got to do some astrophotography with a much larger telescope (a 16-inch reflecting telescope). He had also made the connection with some folks that my parents knew, who had a ten-inch refracting telescope that was equipped with a camera and spectrograph. The telescope had been purchased in a previous generation by a vice-president of General Electric, who was also an amateur astronomer. When it was built, I suspect it was probably the most advanced telescope in the country not owned by a university. The telescope together with the mount probably weighed a couple of tons, and it was inside a big copper-clad observatory with a rotating dome. The camera was a professional device that used glass plates, mounted on a moving stage so that you could track a nearby guide star to keep the images sharp during a long time exposure. I basically had the telescope to myself for a couple of summers, and taught myself by trial and error how to take deep sky images, process them in the dark room, and make nice prints. Back in high-school, the astronomy club would have open nights for elementary school students, scout troops, and the like, and club members would give a little astronomy lecture or slide show before the telescope viewing. So I learned something about galaxies, stars and planets in putting together those shows.

Walter N. Hawley, science teacher
at St. Paul's School. In 1998 he was
awarded the Thomas Brennan award
for excellence in astronomy teaching
by the Astronomical Society of the
Pacific. He also has a main-belt asteroid
named after him. 
Before going on, I'd like to add a few more notes about Walter Hawley. In addition to having a real passion for astronomy, he has to be one of the most intrepid, energetic, and organized people I ever met. When I was a student at the school, we had two telescopes - the 5-inch Alvan Clarke refractor in the observatory, and portable Questar telescope that we could take out into a field. By the time he retired, the school had an Astronomy Center with four domes, a chart house, and a 27-inch robotically-operated reflecting telescope equipped with a CCD camera. About a quarter of the school now takes one of the astronomy courses sometime before they graduate. Walter Hawley's vision and persistence didn't stop at the edge of the school grounds. He was instrumental in building the Christa McAuliffe planetarium in Concord, in honor of the local science teacher who was to have been the first teacher in space when she perished in the space-shuttle Challenger explosion in 1986. His other passion was sailing. He was not a sailor for sport, but I think approached it as a combination of art and engineering. He supervised the building of a wooden yawl at a shipyard run by two 80-year-old boat builders in New Bedford Mass. It was launched while I was still in high school. When I was in college, he sailed it back and forth across the Atlantic, and spent several months in the Carribean on his boat, with his dog, sailing by day and observing variable stars by night. I count myself extremely fortunate to have encountered such a remarkable person during my formative years.

I majored in astronomy at Harvard. The Center for Astrophysics there has one of the largest concentrations of astronomers in the world. At the time, in the late 70's and early 80's, it was the operations center for the Einstein X-ray observatory. I worked with Rick Harnden as a research assistant. Astronomers working on Einstein at the time were not only making great advances in our knowledge of the X-ray sky, but were also inventing new ways to calibrate, analyze and interpret data. Working with Rick, I learned that solving the mystery of why an instrument behaves the way it does is often a subtle and interesting challenge in and of itself. That's part of what makes working as a support astronomer at an observatory appealing, at least to me.

After college I taught science for a year at Maret School in Washington DC, and then went to the Johns Hopkins University for graduate school. When I entered graduate school, the launch of Hubble was imminent. It was still imminent when I finished grad school eight years later. I worked for a few years on the Hopkins Ultraviolet Telescope with Arthur Davidsen and a close-knit team astronomers, students and postdocs. The telescope was scheduled to be launched in the space shuttle in 1986, coinciding with the passage of Halley's comet. On January 28 1986, we watched in horror as the Challenger exploded. Our mission had been next in line. The telescope finally flew four years later as part of the Astro-1 mission, and again in 1995 as part of the Astro-2 mission. But in the meantime, I was left searching for a new PhD thesis topic.

Allan Sandage in front of the 100-inch Hooker telescope
on mount Wilson (Image from Carnegie Observatories/
Carnegie Institution of Washington)
Fortunately for me, another remarkable person arrived as at Johns Hopkins as a visiting professor at just about the same time. Allan Sandage had been Edwin Hubble's assistant when he was right out of graduate school, and was probably one of the most famous astronomers alive. As a graduate student, he had been instrumental in figuring out how to connect the observations of the colors and brightnesses of stars in globular clusters to the emerging knowledge of stellar structure and nuclear fusion, and was able to use that knowledge to estimate the ages of the oldest stars in our galaxy. As Hubble's assistant and for a good portion of his career thereafter, he built much of the foundation of modern observational cosmology. He is well-known for his measurements of the Hubble constant, the expansion rate of the universe, and for his battles with other astronomers over the various systematic uncertainties in these measurements. But he also laid the foundations for studies of very distant galaxies, in a classic paper in 1961 outlining what the great Mount Palomar Telescope could do, and later in a review article on observational tests of world models that grew out of a course he gave while I was at Hopkins. I believe he has told some people that I was the only student able to do the problem sets. That's not true. I was a senior graduate student and mostly was auditing the course. I don't recall even doing the problem sets. I do recall several amazing 3-4 hour sessions in his office, talking about my thesis, but then free-associating on many questions about galaxies and cosmology and how to use galaxies as measuring rods or chronometers to help explore the evolution of the universe. I also recall that when I handed him a draft of a chapter of my thesis, it would come back to me practically the next day with voluminous comments on all aspects of the work from organization to writing style to the technical minutiae of the analysis. I have never met anyone before or since who paid so much attention to the words on a page.

Sandage had arrived at Hopkins with a stack of enormous glass photographic plates with deep images of the Fornax Cluster of galaxies and a few other nearby groups of galaxies. I spent a couple years inspecting, measuring and classifying galaxies on these plates, and then trying to make sense of the correlations that we found in these measurements. Most of the galaxies in nearby clusters are dwarf-elliptical galaxies. I became very good at identifying these amidst thousands of more distant galaxies. It turns out that these galaxies follow a pretty tight correlation between size and brightness. I helped quantify that with my thesis measurements, but to this day we don't really understand what causes this correlation.

Deep-sky image obtained by Tom Shanks
with the William Herschel Telescope.
The color-stretch on this image shows the faint-blue
quite prominently. If you look closely you will notice that
most of the space between the bright reddish and greenish
galaxies is filled with very faint blue galaxies.
After grad school, I spent three years as a postdoc at the Institute of Astronomy in Cambridge. One of the most talked-about topics in astronomy at the time was the problem of "faint blue galaxies:" there were too many of them. A factor of ten more than expected from the favored cosmological model. Most cosmologists were unwilling to accept that the problem might be in the geometry of the universe itself, rather than in our understanding of galaxies. I spent several years working on the problem from the galaxy perspective, thinking that whatever these faint, blue galaxies were, they might be related to the dwarf galaxies I had been studying in nearby clusters. Together with another postdoc, Arif Babul, I explored a somewhat radical model, which postulated that gas in dwarf galaxies collected there early in the universe, but didn't didn't become cool enought to form stars for billions of years. When the gas finally cooled, it formed stars in a rapid burst, making the galaxies briefly shine brightly enough to be seen at great distance. The theory was at least plausible, and matched a lot of the observations.

A small portion of the Hubble Deep Field.

This was just one of several competing models that were being published when I arrived back in Baltimore as a Hubble Fellow at STScI. One of the ways to try to figure out what was going on would be to take a really long time exposure with Hubble, counting up the number of galaxies to even fainter limits. Ideas like this were floating around when the first images from the refurbished Hubble telescope came back to earth in mid 1993, and showed that it would now be capable of obtaining the sharp images that had been promised. Bob Williams, the STScI director at the time, decided to pour most of his "director's discretionary time" into a very long time exposure -- the Hubble Deep Field (HDF). I became deeply involved in planning and executing these observations, calibrating the data, and trying to interpret the results. The observations immediately ruled out our theory, and many of the others. In fact, within a couple years, observations of distant supernovae, along with other lines of evidence, made it clear that the cosmologists had been wrong: the faint-blue-galaxy problem was due primarily to an incorrect assumption about the geometry of the universe.

The Hubble Deep Field became one of the most studied patches of sky and demonstrated the value of bringing combining observations not just from Hubble but from many different observatories. It also demonstrated the value of making the data immediately public to the astronomical community, without the usual proprietary period to a small group of investigators.  It paved the way for the CANDELS survey and many others.

It has been a long couple of flights, with a delay on the connecting flight. So I fear I have gone on too long. I'm returning to Baltimore from a planning meeting for the Large Synoptic Survey Telescope (LSST), a telescope to be built in Chile to survey the entire southern sky, roughly once every four nights. Albeit without quite the clarity of the Hubble images, this telescope will reach the depths of the original Hubble Deep Field over an area 25 million times larger. As a project, it has much of the attraction of the HDF and CANDELS -- it is aimed at gathering a representative sample of the universe (in this case a very large representative sample!), to enable a huge variety of scientific investigations. And all the data will be public. With that and JWST operating at the same time, there is a lot to look forward to.


  1. Interestingly, I went searching for a picture of the observatory I used during the summers as a teenager and found that the house is for sale , for anyone with a cool $3.5M to spare You can take a virtual tour of the observatory. The telescope looks a bit rusty, but I can attest from personal experience that with some steel wool and elbow grease and a few cans of marine gray it will clean up well. If the setting circles are stuck, try judicious application of cocoa cola and leverage :)

  2. What's in a name...

    First I noticed your mention of a Hawley, then here comes along a mention of a Babul.

    Reminiscent of the moniker in astrophysics for magneto-rotational instability in accretion disks --- a.k.a. the "Balbus-Hawley" instability.

    Amusing coincidence, or more to it?
    I wonder if your Walter N. Hawley is related to the John F. Hawley who wrote the 1991 paper with Balbus (not Babul, alas).