Astronomers in a Castle

From Ringberg Castle looking to the mountains. Image Credit: D. Kocevski

On a bluff in the foothills of the Bavarian Alps, overlooking the placid waters of the Tegernsee, sits a castle. Now, castles are not uncommon in Germany, but this particular one is special for astronomers and many other scientists around the world. In 1973, this castle, Schloss Ringberg, was donated to the Max Planck Society and ultimately converted into a location for scientific meetings and conferences. Here, as many as 60 scientists can get together in a picturesque location, away from the bustle of everyday academic life, and put their minds together to tackle interesting and relevant questions in their fields, in a setting that promises good food, comfortable quarters, gorgeous views, camaraderie and colorful insights into the romantic, and only a bit outlandish, inspiration of the castle's creators and architects, the Wittelsbach Duke Luitpold and the early twentieth century artist, Friedrich Attenhuber.

Chess and science in the Duke's office.Image Credit: D. Kocevski

Every room is a testament to Alpine culture and design: warm and dark wood paneling, green spectrum paint, runic filigree embellishments, enormous tiled stoves in each room, pastoral and woodland themed tapestries and murals on walls and balconies. It was to this rather unique setting that a group of astronomers and astrophysicists, including several CANDELS team members, converged on the 3rd of December, a cold and snowy Monday, for a conference to discuss the connection between Active Galactic Nuclei (AGN) and the galaxies in which they are found. This connection is of key interest to astronomers studying how galaxies form and change with time, as discussed in many older posts in this blog. The primary aim of the meeting was to bring together some of the best theoretical models of galaxy evolution and compare them with our fresh and recent understanding of AGN from various observational campaigns, many of which have gained from the superb coverage of CANDELS.

AGN, to this enamored scientist, are some of the most fantastic denizens of our astounding Universe. Our best picture of these beasts is one in which profoundly dense super-massive black holes, millions to billions of times as massive as our Sun, are growing as vast amounts of gas fall into them, in a process that is, as yet, poorly understood. Immense sources of energy, they pump radiation and powerful winds into their environments, and, through this, halt the formation of stars by blowing out or heating essentially all the gas in the galaxies they inhabit. It turns out, however, that it is genuinely very hard to pinpoint the moment in which AGN actually directly affect their 'host' galaxy, mostly because such 'feedback' happens over a very short time, a fleeting heartbeat of an instant in the long eons of cosmic time. Instead, galaxy modelers can tell observers like me what the long-term effects of feedback are and we can go out to our telescopes and vast datasets and try to search for the smoking gun, the imprint of AGN feedback on their host galaxies.

Astronomers at the Ringberg AGN meeting, deep in the middle of a discussion session.
Image Credit: D. Kocevski

At the meeting, some spectacular examples were shown of heating and winds from AGN, clearly supporting the notion that feedback from the black hole has its place in the panoply of astronomical processes. However, a number of new studies show a very weak relationship between star-formation and AGN activity -- not what is expected, either by models or if feedback is widely present. We had some interesting and fruitful discussions at the meeting about this apparent mismatch. Is feedback not as efficient at halting star-formation as we had thought? Do we understand well enough the timescales over which feedback acts on galaxies? Are we missing something in the models? A clear picture eluded us, but we moved on with a set of new experiments and concepts with which to tackle these problems.

Another interesting and relevant question that took up a lot of discussion is why AGN turn on in the first place: what triggers them? Bright AGN are rare - another poorly understood aspect of their nature. Their frequency, how common they are in galaxies, has a directly relation to how much they can affect the evolution of their galaxies, especially if their occurrence is tied to an important phase in a galaxy's life. For example, if a galaxy happens to enjoy a windfall of gas from intergalactic space which spurs the formation of stars, some of that gas may fall to the center and light up the black hole. The resultant AGN will then blow out the gas from the galaxy - the ultimate cosmic killjoy. In this case, the trigger is the process that dumps gas into the AGN's host galaxy and the processes that carry it to the center. Other popular triggers are galaxy mergers, vast collisions that roil up galaxies and spur huge bursts of stars and nuclear activity.

At the meeting, we learned about novel and interesting ways to fuel and trigger AGN in the early Universe. Back then, the Universe was a lot denser than it is now, and streams of gas would fall on to galaxies from intergalactic space. In a process similar to mergers, these flows of gas could shake up the galaxy and send a lot of gas into its center. Such a process is not expected to be important in the present-day Universe around us - a reminder of the arrow of time and the finite history of the Cosmos. In more local AGN, a clear sign of the role of galaxy mergers was shown from studies of pairs of AGNs in the Sloan Digital Sky Survey. In addition, a simple connection was shown to exist between AGN and the gas content of a galaxy, which suggested that, while mergers are a good way to trigger AGN, they are probably not the most important process in nearby galaxies. The meeting helped to underline the complex variety of ways that gas feeds the monstrous black holes in the centers of galaxies.

Stories exchanged over beer in the fabulous Hexenzimmer.
Image Credit: D. Kocevski

Over two and a half days of presentations and lengthy discussions, we pondered the physics of unfathomably incredible forces in the far reaches of our Universe as heavy snow piled up on the trees and coated the castle grounds. Over breaks for coffee and lunch, we huddled in smaller groups and debated over some of the finer points of theory or interpretation, skeptical inquiry that defines the method of science. Over big glasses of fresh Bavarian beer in the evenings, we traded our scientist hats for other metaphorical headgear, as we exchanged stories and banter, and got to know each other better on a personal basis. This is probably one of the lasting legacies of a meeting at Schloss Ringberg - collaborations, future plans, friendships. All because a Duke decided decades ago to build a picturesque castle that he couldn't quite afford on a hill in Germany.

See more pictures of Schloss Ringberg and the AGN meeting

A Week at the LBT

One of the most rewarding aspects of a career in astronomy is the chance to go observing at a professional observatory. I recently spent a week at the Large Binocular Telescope (LBT) in Arizona, observing for the Max Planck Institute. With me were two other observers, Hugh and Mario, members of other research teams at the Institute. In total, we had 6 full nights with which to pursue our various science programs, as well as collect astronomical data for other scientists in our research consortium.

The LBT is a marvel of engineering. It consists of two enormous primary mirrors, each 8 meters (26 ft) in diameter, mounted on the same huge superstructure, a squat but airy truss of red-painted steel, carbon fibre, cabling and glass. The mirrors are built to look up at the same region of sky and the LBT can track an object through its pair of binocular 'eyes' with incredible sub-arcsecond accuracy. The two telescopes will eventually be combined into an Interferometer - an advanced technology instrument that behaves a bit like a single telescope 12 meters in size.

Standing below one of the LBT mirrors.
Click for an album of images from my trip.

A large telescope such as the LBT is used at the forefront of astronomical research. Take for example the kinds of science that we were pursuing for those 6 nights. I was using an instrument called LUCI that is sensitive to light in the near-infrared. With LUCI, I obtained spectra of galaxies that are tens of billions of light years away, when stars were forming throughout the Universe at a furious pace. Hugh was using LUCI to precisely measure the apparent sizes of nearby stars, allowing him to look for the presence of disks of dust around them, solar systems in their youth. Intense star-forming regions in our Milky Way galaxy interested Mario: he wanted to train LUCI on some of their most massive stars.

The 2 hour drive from Tucson went up a windy mountain road rising from the desert to the pine and fir crested peak that hosts the Mount Graham International Observatory. In a large trolley, we carried up a week's worth our of groceries up to the Observer's dining area, which sported large windows overlooking the Pinaleño mountains, a row of big refrigerators, a full kitchen, comfy couches and - joy! - a pool table. This, and the attached sleeping cubicles, were to be our home for the duration of our run. We chatted with the last shift of observers, talked about science and telescope issues, settled into our rooms and got accustomed to the thin air at 11,000 ft.

The next day we started our run. Things didn't go according to plan.

In the heady days of tall ships, being caught in the Equatorial becalming zones called the Doldrums came to be a bane of sailors. The word was adopted into modern English to mean times of ennui and lack of activity. Bizarrely, at the LBT, the Doldrums happen when the wind is high, because the telescope dome cannot be opened if it's blowing so hard that the telescope structure could suffer serious stress. We waited and watched unsuccessfully for the telescope to open while howling gale-force winds buffeted the top of Mount Graham. An unusual weather system, which started before we arrived at the peak, kept up a steady barrage of dusty winds for four whole days and nights (taking a night away from the observers before us). As a result, we never actually looked at sky for half of our run, though, if one had stood on the balcony of the telescope dome and look up without being blown off, one would have seen a lovely Milky Way over the horizon and bright stars burning against a velvet black sky. This was a painful reminder of one of the misfortunes of astronomical observing - Weather. Observatories are built in far off and inaccessible places for a reason: those very places, usually deserts or high mountain tops, have the best observing conditions. Time on a big telescope comes at a premium, both monetary and in man hours, so they are designed for a maximum return.

In contrast, the next three nights were fantastic! As the winds died away, the front of calm weather beyond brought superb, twinkle-less skies (heavy twinkling is a sign of turbulent air, something we call "bad seeing") and a thin young moon. With the help of our fantastic Support Astronomer, Olga, who helped deal with a niggle that kept putting the telescope an arcsecond away from where it should have been, I managed to get 7 hours of great data with which we mapped the movement of star-forming regions in twelve galaxies at a redshift of 1.5, seeing them as they were in a 5 billion year old Universe. Hugh, with a twinkle in his eye, showed us the subtle blooming of his stellar spectra that revealed a thin disk of young planetesimals in a star light years away. Mario fussed about excitedly with his spectra, judging quality and applying numerous calibrations. Things proceeded without a hitch and we even had time, while the telescope was kept busy running automated scripts on a long exposure, to play the odd game of pool in the observer's dining room.

For a century, since the rise of large institutional observatories, astronomers have packed their cases - once full of photographic plates, chemicals, and cold weather gear; now with laptops, manuals, and comfortable shoes - and climbed mountains to expand our view of the Universe. Observatories, whether on the ground or up in space, continue to enrich our knowledge and serve as test-beds for cutting edge technology, and we hope that we, as astronomers and as humans, will always be able to find that lone narrow and windy road that takes us up to the stars.

Galaxies with growing Black Holes: What makes them special?

Active Galaxies in the CANDELS survey with bright blue nuclear emission
from a growing Supermassive Black Hole (courtesy: David Rosario)

Supermassive Black Holes (we like to call them SMBHs for short) lie lurking in the heart of every large galaxy in the Universe, and possibly in many little galaxies too. A popular misconception is that black holes like these are continuously devouring stuff: stars, planets, the thin plasma that fills up most of space. In actual fact, one of the big mysteries in galaxy physics is why such monstrous black holes - some as massive as a billion suns - remain, for most of their existence, on a severe diet, not growing at all. In the area of space within a few hundred million light years of our own Milky Way galaxy, a region known as the Local Universe, there are hundreds of thousands of large galaxies like our own. Remarkably, only a few percent of them show the tell-tale signs of SMBH growth, manifested as Active Galactic Nuclei (or AGNs - see the blog post by Dale Kocevski for an introduction to these rare and remarkable objects). Nineteen out of any twenty SMBHs, while entirely capable of huge outbursts of energy as they feed on in-falling gas and stars, seem instead to be quietly biding their time in the nucleus of their 'host' galaxy. These black holes are being starved - not enough fuel comes their way to keep them active. Why exactly these black holes remain this way is not understood, but may have to do with the way that gas settles down into the centers of galaxies, and how black holes themselves influence these flows of gas.

One interesting clue to this conundrum is the observation that in the distant cosmos, far beyond the Local Universe, AGNs are both brighter and more common. In fact, much of the mass in Local SMBHs fell in many billions of years ago, during a period in the history of the Universe that we can only probe by looking deep into space (and, by extension, far back into time). Something about galaxies in the early Universe allowed black holes in their centers to grow faster than they do today. By comparing these distant galaxies to the ones we see today, we can figure out what affects black hole growth and shed some light on the question of why nearby SMBHs stay anorexic.

This is where CANDELS comes in. With the superb new capabilities of our survey, we can actually get a good look at the very galaxies that contain growing SMBHs across a vast swath of cosmic history and compare them to galaxies that don't host AGNs, to see if these galaxies are special in some way. Since CANDELS provides pictures of galaxies across a wide range of wavelengths (or colors), we can separate out the light that comes from the powerful shining active nucleus and home in on the galaxy itself.

In a recent paper from the CANDELS collaboration, we carefully looked at galaxies that shine powerfully in the X-rays, a sure sign of gas heated to millions of degrees as it falls into a growing black hole. We found that such 'active galaxies' only really distinguish themselves in one way - they contain a lot of stars. This is not too surprising; we know that such massive galaxies harbor massive black holes, and massive black holes are exactly what is needed to produce AGNs. After accounting for this difference between AGNs and other galaxies, AGN hosts have the same basic range in shape and color as normal galaxies of similar mass. Another thing we can do with the superb CANDELS images is place good constraints on the past history of star-formation in these distant galaxies. We found that active galaxies form stars in much the same way as normal galaxies, both at the time we observe them and in their past history.

What does this mean? From our study, we can tell that galaxies that host growing black holes are not remarkable in any way. In other words, the mechanisms that carry gas into the black hole mostly work on small scales, probably within a few tens of light years of the nucleus itself, and don't immediately affect the rest of the host galaxy. As the project progresses, we will be able to build on this early work by looking at more and brighter AGNs. In time, CANDELS will be a powerful tool as we uncover the complete story of how black holes and galaxies evolve in the early Universe. Stay tuned to this blog as the picture develops.