So here is the paper. On a quick read, this is just another paper on what happens to gas when and star formation when an AGN gets involved. If you’ve listened to many episodes of Astronomy Cast, you might have heard me explain this before. AGN (short for Active Galactic Nuclei) are actively feeding black holes in the centers of galaxies. These giant monsters are capable of calmly devouring vast quantities of gas and dust with accretion rates (the rate they take stuff in) of anywhere from 1 to 100 Solar Masses a year. AGN can occur in all sorts of different galaxies, and once upon a time, our own Milky Way galaxy might have had one in its core. Spiral galaxies with lots of gas and dust can recover from their AGN phase to go on to billions of years of happy go lucky star formation. Elliptical galaxies aren’t so lucky.

If you look out at the sky with a reasonably large telescope and you explore the distribution of colors and shapes of galaxies, you’ll find that spirals are generally (but not always) blue, and elliptical galaxies are generally (but not always) red. Any of you who have played with Galaxy Zoo have probably seen this too, and cursed your fair share of boring red blobs. The only way to get a blue galaxy is to look at a system that contains lots of hot stars, and hot stars don’t live that long, so either you are looking at something with ongoing star formation or something that produced stars until very recently. This tells us that in general, spiral galaxies are actively forming stars, and ellipticals are not. As we look at these systems across other wavelengths, looking for gas and dust using Infrared and radio and all the colors of light in between, we also find that elliptical galaxies are poor in gas and dust and spirals are rich in those exact same things. This means ellipticals generally just don’t even have the stuff in them necessary to form stars.

The question is, how did they get that way?

The standard answer has always been that there is a burst of star formation (often triggered during the formation of the elliptical, or the merger of a spiral galaxy into an elliptical), and the gas and dust not involved in this sudden burst is driven into the super massive black hole in the center of the system (and when I say super, I mean something 10,000,000,000 solar masses or so in size!) This process causes the galaxy to first light up with star formation, then the AGN turns on, and in the end the AGN is all that is left signaling the recent event. The timescale for this process was originally thought to be determined largely by the rate of star formation, but star formation is a slow thing, with many billion years being required to eat away the gas and dust. But… with timescales that long we should see more blue(r) ellipticals. The longer something lives, the more likely we are to see it. (Think of being in a room with a variety of lights that randomly turn on and off that are on all sides of you. Those that turn on for the longest period of time are the ones that you are most likely to see, while those that flick on the smallest fraction of a second are very unlikely to be something you see well enough to learn anything about them.)

So here we were with a model and a universe that weren’t in perfect alignment.

But then came this paper, to tell us we had underestimated the effects of an AGN. In this paper, they look at a series of 24 galaxies (10 Star Forming, 10 AGN+Star Forming, and 4 AGN). What they found was about 200 Million years after the Star Forming turns on, the AGN kicks into full swing, and the Star Formation dies quickly – it dies in a fraction of the time predicted from models that use star formation to devour the dust. This indicates that the AGN is having more of an effect on the dust than previously thought.

They put forward in this paper that AGN feedback is responsible for destroying the gas that would have otherwise gone into star formation. This process was already thought to exist, but the magnitude of the role it plays hadn’t been assumed to be this big! It appears that the actively feeding AGN is able to heat and expel the gas very quickly. We knew this happened in GIANT galaxies, with GIANT AGN (think M87), the type of systems that often sport massive jets and other rather radical high energy phenomenas. What we didn’t know was that low luminosity AGN do the exact same thing. And that is just cool. (Or actually “That’s Hot”).

This paper gives us a cleaner insight into how effectively black holes can kill things. That is a very flippant remark, but to put it more scientifically – we now have new insights into how actively feeding black holes can disrupt the surrounding gas so effectively that they shut down star formation essentially instantly (on cosmic timescales at least). From alive to AGN to dead and red in a billion years flat, that may be the life of even the most mundane elliptical galaxy.

While this paper does use a lot of technical language, it explains itself well and is well referenced. If you feel like chewing through something that will hopefully change how we look at ellipticals, give it a read.

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On a completely unrelated note: There is a remarkably ugly huricane on its way to Texas. One of the worst nights of my life involved a tropical storm parked over Houston that caused flooding and tornadoes as far north as Austin (the barn I used to keep horses at flooded and several hundred horses had to be evacuated in the middle of the night with water rising faster then a human could run). Just looking at the satillite imagery is making quesy with anxiety. My heart goes out to everyone on the Gulf coast. Stay safe everyone.

This is scientifically a wonderful thing: Being able to understand what a black hole that is actively feeding looks like as a function of feeding rate and angle of view allows us to say something based on the physics of the system, where as having a bunch of names associated with a bunch of different images is more like leaf collecting without taking DNA samples. Being able to understand how an icy object looks in the solar system both when it is out near Pluto, and when it is making a plunge past the Sun allows us to see how materials get distributed through the solar system. The more we learn, the more we see everything can be broken down into a series of fewer and fewer large boxes.

It is unfortunate, however, that our understanding didn’t come before we had a chance to come up with 40 million names for what we now know are related objects. For instance, all of the following objects are active galactic nuclei: QSOs, Qausars, Seyfert 1s, Seyfert 2s, BL Lac objects, Blazers, and LINERs. Similarly, novae, dwarf novae, classic novae, recurrent novae, Z Cam objects, U Gem objects, and SU Urs objects are all types of cataclysmic variables. The journey to our understanding was a long one, and it came by bringing together many small groups of objects, one at a time, and seeing that at their core they are all the same.

What we are realizing there is a taxonomy of the sky. Just as I am a [mammal, primate, hominid, homo sapiens], a star system might be [binary, cataclysmic variable, U Gem object].

But while we have a clear and agreed upon language for discussing the names of biologicals, such a precise language doesn’t yet exist in astronomy. If I want to find all the latest papers on galaxies with actively feeding supermassive black holes that have observable broad and narrow line absorption regions and tiny little radio jets, I need to search on the terms active galaxy, radio galaxy, Seyfert 1, and active supermassive black hole. This lack of precision in language slows the progress of research. One team may make huge strides, developing their own methods and vocabulary and publishing in one set of journals with one set of keywords, while another group makes parallel and complementary progress, developing different methods and vocabulary while publishing in a different set of journals with another set of keywords. If the teams don’t happen to meet at a conference or have someone point out one another’s work, it could be a couple years into the research before they realize they are doing something that would greatly benefit from collaboration.

As our ideas are unifying we need to take care to unify our language as well. We need to take care to use all appropriate keywords and not be lazy as we check boxes, and we need to take the time to do literature searches on every possible archaic turn of language as well. Even though we now know Andromeda is a galaxy (really, it is), there are those that still call it the Andromeda Nebula. It won’t be easy to change our language habits, but it will be good for the soul (or at least good for those of us doing literature searches) if we can find a way to manage it.

So, why should any one care? Well, quasars are giant black holes in the process of feeding on gas and dust (and maybe even stars and planets) that just happen to get too close). By giant black holes, I mean black holes that are hundreds of thousands to tens of billions of times larger than the Sun. And, by feeding, I mean they are chowing on solar system masses worth of gas and dust with each bite, and sometimes spraying jets off high-energy particles while giving off light in ways that make these things the brightest shining actors in the entire universe. One quasar is just cool, and getting three cool things together all at once is, well, something that naturally attracts the observational astronomy paparazzi (or atleast grad students seeking projets).

More scientifically, we have a lot of theories on how galaxies form and grow from the start of time to today. These theories indicate that galaxy mergers and quasar activity were both more prevalent in the past, with the epoch of quasars peaking around a redshift of z = 2, when the universe was just 2 billion years old. While we’re still working to understand the physics of quasars, it seems that quasar activity is related to galaxy-galaxy interactions, and galaxy interactions should occur in large numbers at similar times. Thus, theoretically, if you are going to find interacting systems of QSOs, it makes sense that you find them somewhere near z = 2. This triple system was found at z = 2.076, matching that theory.

This system, QQQ 1432-0106, was initially identified as a potential double quasar gravitational lens. This means, it was identified as a system where a single distant quasar had its light bent by an intervening massive object such that it appeared as two objects rather than one. This is a common effect, with quasars being found split into as many as 5 different apparent objects (You can read more aboutthis effect here. Additional observations of these two objects, however, turned up a third object, and gravitational lensing models cannot replicate these observed pattern of three objects and their luminosities. The luminosity ratios of the quasars are 1: 25 : 200. This, in non-straight forward ways, reflects differences in mass, with the brightest system being approximately billions of solar masses and the second brightest being hundreds of millions of solar masses.

Spectroscopic observations of these systems give additional evidence that these are three physically related objects instead of a gravitational lensed single object. While all three systems have similar emission lines and appear at the exact same redshift, there are minor differences in the spectra that indicate slightly different distributions of material are present in the three systems.

Our current understanding describes this as a system consisting of three physically related interacting quasars that will eventually merge together. A possibly disturbed galaxy is visible around the brightest of these three quasars. The supermassive black holes in their cores – the angry monsters that power the quasar light – will interact in ways that may result in one or more of the supermassive black holes. This theory-based result has interesting implications. It is possible that there are free-roaming supermassive black holes wandering the universe, periodically consuming intra-galactic dust and gas. It also raises questions on how today’s galaxies end up with central supermassive black holes that have sizes directly related to the characteristics of the parent galaxies. This time, theory leaves us in a place without a lot of observational evidence to support us. To verify our concepts, astronomers need to identify galaxies lacking supermassive black holes, galaxies with supermassive black holes of unusual size (too small, rather than too large like ROUS*), or catch a system in the process of ejecting central black holes during merger. (for neat animations, see This Site.)

So, at the end of the day, some theories have added evidence, and some theories leave us asking questions, but no matter what, the quasars are spectactular and the science in this bit of observing is solid. This is a case of good science, done right, going through the scientific process to correct false starts and firmly establish this as the first gravitational interacting three quasar system. Kudos to George Djorgovski (CalTech) and his team for a job well done.

*Rodents of Unusual Size, from the Princess Bride