Trying to figure out that a random green blob of gas is a light echo was anything but easy. In this comic book, we try and tell the story of what it was like for the people involved and how exactly astronomy – in its not exactly Indiana Jones fashion – can be an amazing adventure. The project was written largely by a team of volunteers from CONvergence, and the art is by two amazing students here at SIUE.

Here is what we wrote over on the Galaxy Zoo Blog:

line art: Elea Braasch, color: Chris Spangler

This past Monday, at about 8pm Central (GMT -4), a Voorwerpish webcomic was delivered to Sips Comics for printing. Tuesday morning we got the page proofs, and now, one by one, they are being made into full color reality.

We could say a lot of things right now: We could tell you about playing round robin with the script, digitally passing it from person to person under the guidance of Kelly, sometimes into the wee hours of the night. We could tell you about watching the art come to life; transforming from line drawings to fully rendered pages in the hand of our artists Elea and Chris. We could tell you how many pencil tips were broken, and how many digital files grew so big our computers crawled.

We could talk a lot, but instead, let us invite you to join us for the World Premier and share with you a few images.

You’re Invited to a World Premier

• Time: 3 September, 10pm Eastern (GMT -5)
• Online: via Hanny’s Voorwerp Webcomic or via direct UStream Link
• In Person: At Dragon*Con
  Crystal Ballroom
  Hilton Atlanta
  255 Courtland Street NE
  Atlanta, GA

Come meet the artists, hear a brief talk by Bill, and generally revel in the Voorwerp’s awesomeness.

And come dressed as a Voorwerp for a chance to win a prize for best costume!

See you in Atlanta?

Pamela, Hanny, Bill, Kelly, Elea and Chris

Star Stryder: An Interview with Zookeepers [Mp3 - 13.8 Mb]

As you may have periodically read in this blog, I’m currently working on a project that is going to require a lot of work with the Sloan Digital Sky Survey (SDSS – the online catalogue users of Galaxy Zoo are working with). Getting at the data I want is going to require me to get better at jumping through the web forms on SDSS than I am right now, but while I’m still learning, I want share a few of the tricks I’ve learned.

Trick 1: So, you want a pretty picture of the field around your favorite obscure star/galaxy/cluster

1. Go to this link (For navigate tool)
2. Type in the coordinates of your object (NOTE: it has RA in decimal degrees!!!!)
3. Re-center, zoom, and unzoom
4. Download the image your telescope just can’t quite pull off.

The screen capture above right is for AH Leo, my favorite little variable.

Trick 2: Get numerical Data without fighting with IRAF! You can then get quick photometry for the objects in a given field here, or do a more detailed search – and this is what I’ll be using with my student – here. When using that form to download freely available spectra of galaxies around the center of an Abell cluster, it is possible to confirm spectra and get a sense of which of the shiny galaxies are cluster members and which are foreground objects.

Cool.

I’m making a start, and might be making progress (or I might be delusional). As I tell my grad students, often it is required that you try grabbing / processing / plotting / etc your data at least 4 times before you know you have what you meant to get.

But I’m making a start. And now you know how to make your start.

And we know who the zoo keepers are when we need help.

Galaxies began to form just a few billion years after the Big Bang. As we learned yesterday, it now looks like this formation took too different paths, with giant spiral galaxies forming out of mass gas + dust collapse, that had the stars and the full fledged giant galaxy all forming at once. at the same time, in other less dense areas, smaller systems also formed dwarf and often irregular galaxies. In their earliest days, these fresh born systems shown blue, with the light of sort lived O and B giant stars dominating the total light emitted by the galaxies. Over time each of these types of systems had different evolutionary patterns, until today we find ourselves living in a universe populated by red elliptical galaxies devoid of blue O and B stars. Red and dead, these giant systems often live in large groups, clusters and super clusters of galaxies. Side by side on the sky, but not in the universe, we find blue spiral galaxies like our own. These star forming systems are often isolated, in small groups, or on the edges of galaxy clusters (where they have yet to interact with other systems).

Understanding stellar evolution requires one to separate out many variables: size of galaxy, environment of galaxy, and when in time we are observing the galaxy (objects that are farther away we see as they appeared in the past because it takes time for the light to reach us).

In Amanda Bauer’s nice talk she discussed how mass alone effects galaxy evolution by observing a set of field galaxies – isolated galaxies that do not belong to groups (like the one we are in) or larger systems (clusters, like the Abell systems you often see in the news). She found “a clear separation between disk-dominated (sersic n > 2.5) and bulge-dominated galaxies, such that disky galaxies have higher specific star formation rates and lower stellar masses at all redshifts.” This means that galaxies like the sombreo galaxy (shown above, image credit NASA / Hubble Heritage Team) have within the past several years all tended to look and behave the same way : They are actively forming stars, but they haven’t come anywhere close to using up their gas and dust, and remain rich in materials available for future star formation. At the same time, she notes the highest mass objects in her sample have the lowest specific star formation rates.

If you want to live some where alive, live somewhere small. The fat die young in galaxy populations.

The specific star formation rate is an interesting analytical way of looking at things I hadn’t previously used. It looks at the rate of star formation as a function of a galaxies stellar mass. I’m going to have to look into this more and write more later. For now, here’s a paper.

This research used the CTIO 4-m telescope to image optical and find lyman alpha emitting blobs (that are red shifted to visual), Spitzer IR images, Magellan 6.5m telescope spectra to get distances (and thus time the light was emitted), and HST ACS to determine sizes using hi resolution images.

These objects had already formed by 2 billion years after the big bang. Through mergers they built galaxies larger and larger systems until today those once many small systems have combined into a few small systems. This is an ongoing process (that is slowing), with small galaxies continuing to form, and merge, and build new systems.

This is a previously suspected idea (there are just so many things out there that can form galaxies!), and it’s good to see the list of possible things get narrowed down to at least 1 certain culprit (it may have had accomplices).

It should be noted, this only applies to Milky Way sized systems. Elizabeth McGrath of UC Santa Cruz points out in another new discovery that the biggest galaxies actually formed via gas collapse. Rather then waiting for a bunch of little systems to form and combine, these systems just collapsed very rapidly while forming stars

In peering around the universe we tend to stumble across a lot of weird small stuff. Blobs of gas. Blobs of stars. Blobs.

Ever find some mysterious blob on your kitchen counter? You know something splattered, but the question often is “What was that?”

New Hubble images in combination with GALEX ultraviolet images, and archived Hubble data have allowed astronomers to determine that these blue blobs (example at right, dwarf galaxy Holmberg IX) are actually clusters of 20,000 stars – dwarf galaxies newly forming in today’s universe.

Located 12 million light years away, these bobs were observed in systems near M81, M82, and NGC3077. They aren’t gravitationally bound to these systems, but they are located in the neutral hydrogen clouds associated with these galaxies. (orange in image at left is hydrogen gas)

deMello and her team determined these blue blobs are forming dwarf galaxies by comparing the ultraviolet and Hydrogen Alpha light from these systems to the light coming from objects we understand. From their light profile, it was determined these objects are less than 200 million years old. As M81, M82, and NGC3077 interacted ~200 million years ago, material was stripped from each of these systems. As the stripped material coalesced, it formed these new young systems that today are polluting the intergalactic medium – the gas and dust between galaxies – with enriched material like heavy atoms that could grow into the stuff of planets and people.

From a splat comes star formation, comes supernova, comes new and interesting science that explains how the heck titanium is found between galaxies.

Got to love what happens when galaxies collide.

One of the most elusive creatures speculated to lurk within the sky are the mysterious very high-redshift Lyman alpha emission galaxies. These systems, without the metal found in their more common and larger low-redshift cousins, are rich in hydrogen and slow in producing stars. Scientists had long speculated these systems had to exist, but despite 30 years of searching beyond the Lyman Alpha Forest, none of these systems had ever before been found.

Now, astronomers using the Very Large Telescope in Chile bring us word of a serendipitous discovery of 27 of these elusive systems. They were found quite by accident in a 92 hour spectral image that was being taken to look for faint intergalactic gas. According to UK astronomer Michael Rausch, “As often happens in science, we got a surprise and found something we weren’t looking for – dozens of faint, discrete objects emitting radiation from neutral hydrogen in the so-called Lyman alpha line, a fundamental signature of protogalaxies.”

The well respected Lyman Alpha line is from the esteemed hydrogen spectral series. His lazier (or at least lower energy) cousin, Balmer alpha (aka Hydrogen alpha) is known for hanging out in the “Open” signs at bars were he often glows red as his only electron jumps up to its 3rd energy level and then falls down to its second level, always losing a 1.9-eV, red photon in the process. Lyman Alpha is more energetic, and his high diving electron climbs up to level 2 and jumps 10.2 eV down while flinging an ultraviolet photon into space. Lyman alpha is perhaps most often found emitting light in hydrogen clouds being illuminated by hot young stars. More often, however, Lyman Alpha absorbs light instead of emitting it. Whole families of Lyman alpha absorbers lurk in the space between galaxies, in the form of gas clouds, and these systems create a messy forest of Lyman Alpha absorption lines in the spectra of background galaxies and quasars.

This new discover of Lyman Alpha emitters and their host extremely-distant galaxies adds one more piece to the galaxy construction puzzle. From the pieces that had already been put together, astronomers suspected the final image would show that small systems grow into large galaxies through the joining of gas unto gas and star unto star through the garivational bond of eternal mergered bliss. (This is very different from the frequently temporary bond of binary stars, which occasionally split violently. No known previously joined galaxies have been seen to come apart, although the poly-gactic joining of many systems into 1 system has been observed in many systems, including our own Milky Way galaxy).

“What makes our discovery particularly exciting is that it opens the route to find large numbers of building blocks of normal galaxies and that we will now be able to study in detail how galaxies like our Milky Way have come together,” says Martin Haehnelt.

It may be a long time before astronomers get a second glimpse at this elusive population. The 92 hours of VLT time necessary to obtain this first image of these very faint system took two years to obtain. Until another image is acquired, scientists will have to satisfy themselves with examining and re-examing these 27 systems to try and sort out what these galaxies are like and if the are the true genetic predecessors to the hydrogen rich damped Lyman alpha galaxies we find in more recent epochs.

Image Credit: ESO

There are good times. For instance, in about three months this summer and fall Fraser Cain and I, with the help of undergraduate Rebecca Bemrose-Fetter and graduate student Georgia Bracey, managed to do a quick a solid study on who listens to Astronomy Cast and responds to surveys. The paper is already published and you can find it here. That was fun, challenging to analyze in a “I need a brain but not a Nobel prize” kind of way. That’s the type of low-hanging-fruit every researcher likes to pick and munch every now and again.

The research I worked on today, however, led me to question the logical nature of my field. Along with another student (whose name I’m not publishing without permission), I’m currently working on a follow-up project to my dissertation. Back in 2002, I noticed (and I’m not the only one to notice this) that there is a trend as a function of density in how galaxy clusters evolve. Basically, small groups of galaxies, like the one we live in, don’t really evolve that much over the course of the universe. Spiral galaxies stay spiral and violence like collisions and gravitational harassment just don’t happen that often. At the same time, really rich large clusters form first and very quickly and they whip their member galaxies into a frenzy of mutual destruction. Galaxies are quickly beaten into elliptical forms, star formation is cut off, and anything new that falls in is quickly destroyed.  It is the mid-sized systems that are most interesting. They start out filled with spirals, but as the millenniums tick by the spirals collide into one another, one by one, until today these systems are devoid of star formation and rich boring elliptical galaxies.

Observationally, we have specific ways to describe cluster density and the fraction of spiral to elliptical galaxies. Unfortunately, we have more than one way to do each of these things. This is where my personal frustration comes in. My student and I wanted to cull for the astronomy literature a large collection of published values and than look for a general trend. We were even prepared to solve for ways to convert from one way of determining galaxy density to another way. What we hadn’t expected is the utter lack of relationship we are finding in some cases. Let me see if I can explain at least one aspect of this problem.

Let’s take galaxy size and density. The most well known catalogue of galaxy clusters is probably the Abell Catalogue.  In his original 1958 paper, Abell described cluster richness using the number of galaxies “counted in a cluster that are not more than 2 mag. fainter than the third brightest member.” This method requires the counter to know where the edge of the galaxy is, and doesn’t work very well for large, diffuse systems that are difficult to sort out from background and foreground systems (think, Zwicky clusters). It also doesn’t work well for systems that are rich, but only have a few extraordinarily bright galaxies and scores of fainter systems.

Since that catalogue, people have been trying over and over to find a better way. For instance, Butcher and Oemler count galaxies “with projected distances from the cluster center less than R30, and with absolute visual magnitudes Mv <= -20″ where R30 “is the radius of the circle containing [30]% of the cluster’s projected galaxy distribution.” This system consistently counts the same type of galaxies, and while R30 isn’t perfect, it is better than trying to define the whole galaxy cluster.

Other methods also measure the number of galaxies brighter than certain cutoff magnitudes within a specific number of megaparsecs, or the number of galaxies within a specific number of megaparsecs of the cluster’s brightest galaxy or radio galaxy.

I’ve come to the conclusion that there are as many ways of measuring cluster size as there are groups measuring cluster parameters. The radical differences in the systems means there isn’t even a direct way to convert from one system to another. This means that it just isn’t possible to look for detailed relationships using all the data that is out there without doing some serious reanalysis. What had looked like a nice easy literature review project to work on with a student grew into something that is requiring a lot of head scratching, and I’m afraid that to do the project right, we’ll need to use SDSS data, which makes this very much not a 1 semester project for an undergrad. So… we’re going to do what we can with all the published data that we can get on a mostly standard system (and it looks like we’ll be using Abell counts, as flawed as they are).

At least it’s not quite apples and oranges. I think I can safely call all our data citrus. Unfortunately, I think the clemintines got mixed in with the tangerines.

Image Credit: That ones all mine It’s a galaxy cluster I discovered as part of my dissertation research.

But I have to admit that I had to do a bit of googling first. This is because Seyfert’s Sextet doesn’t have 6 member galaxies, and Stephan’s Quintet doesn’t have 5 member galaxies. And while I didn’t remember just how many the two of them had, I knew the answer was attached to the captions of the two pretty pictures above.

So, here’s the breakdown.

Seyfert’s Sextet has 4 gravitationally bound galaxies, a tidal tail, and one background galaxy.
Stephan’s Quintet has 4 gravitationally bound galaxies, and 1 foreground galaxy.

So, both clusters have 4 members.

Moving on…

So, in this article, they postulate that Seyfert’s Sextet (SS) is 2-3 billion years more evolved than Stephan’s Quintet (SQ). Basically, once your sort out what belongs and what doesn’t, we are looking at a child and a teenager of the same cosmic species.

Both systems have 4 galaxies that are interacting, however the galaxies in SS have been more disrupted – they are more shapeless, more of their stars have been stripped into the intergalactic media, and there is that weirdo tidal tail that has been mistaken for a galaxy. These changes are the signs of a few extra galactic eons of evolution.

Detailed studies of these two systems allow astronomers to piece together the process of CGG merger. It was initially thought these systems would evolve quickly, with the unstable orbits leading to a mass infall and the formation of isolated “Fossil Elliptical” galaxies. The thing is, no one has found fossil ellipticals even though CGG are very common. This seems to imply they aren’t forming as often as we would expect. One mechanism to explain this slow-down in formation is through dark matter halos. The gravitational pull of dark matter halos can slow mergers and allow a system like SS or SQ to exist for as long as the universe has existed without fully collapsing into a single large galaxy.

Today, we believe that these systems slowly grind away on one another, gravitationally rending one another, star by star, as they first transform one another from spiral systems to lenticular (S0) and elliptical systems. Tidal tails will get teased out of the carnage, and some of the galaxies may even turn on their central supermassive blackholes, glowing as Active Galactic Nuclei during periods of intense star formation. During this process, all the gas in the galaxies will be stripped out, and once the gas is gone, the star formation ends, and we are left with deformed systems orbiting more and more tightly together. Someday, the dead galaxies will merge into a single elliptical system (after perhaps ejecting something), they may eat other galaxies in the process, or gravitationally interact with and spit out other galaxies. But, given enough time, all systems will lead to that single blob in the sky.

It’s kind of sad. My favorite objects to image are transitory, and someday, given enough galactic eons, all galaxies groups of this kind will be dead (the universe isn’t exactly still forming groups in large numbers, and what galaxies it is producing are getting more and more scarce ever year). We live in a special (admittedly possibly 10+ billion year long) time that allows us to see small groups, and to see them evolve.

But at least what we see, using science, we can understand. This brief little blog entry doesn’t even make a dent in explaining the 70 pages of text, images, tables, graphs and graphics contained in this paper (and I admit freely to only reading the abstract, intro, and discussion in their entireties). If you want to check out this solid piece of science, you can find links here.

Astronomers in Switzerland and Washington, lead by A. Eigenbrod, observed Einstein’s Cross spectroscopically using the Very Large Telescopes in Chile. In a study spanning 2 years, they systematically mapped the structure of Q2337+0305 using microlensing. Here is what is happening: The light from the quasar bends through the intervening galaxy along different paths. Over time, stars in the galaxy will pass through these paths. When a star enters the light from the quasar, it magnifies the light (this is called microlensing). As the star passes in front of different parts of the quasar, those parts get their light amplified, while the other parts stay at a constant brightness. Over time, the star will move across different parts of the quasar, systematically amplifying new areas. By measuring what is amplified over time, as a star crosses, a map can be built.

This process can’t usually be used because different parts of the quasar naturally vary in brightness. Under normal circumstances it isn’t possible to determine if there is microlensing or if the quasar is fluctuating just because it can. In the unique case of Einstein’s Cross, observers will see the quasar’s natural variations in all four images while microlensing events will only appear in one image.

In looking at Einstein’s cross, Eigenbrod and his team specifically studied how different atomic lines, which come from regions of different densities and temperatures, varied over time. This allows detailed density maps to be built.

In their initial study, they saw significant variations in 2 of the 4 images in Einstein’s cross, and as they watch they expect to eventually see variations in the other images as well. The differences in microlensing in the four images is related to the distributions of orbits in the intervening galaxy, and its willingness to provide stars to orbit through each of the images of Q2337+0305. Over time, as more orbits have a chance to send stars across the images, more and more details maps can be built.

This is one of those really great cases of the universe providing some really neat built in tools, like Easter Eggs hidden among the stars.

That aside, this episode did a good job high lighting all the different types of galaxies that are our there. What it didn’t discuss (let’s face it, you can only do so much in 50 minutes), is how this zoo of galaxies represents a continuum of evolution.

A paper published by Searle and Zinn in 1978 and substantiated by countless papers since then, states one of the possible explanations for galaxy formation is hierarchical clustering. In this model, small clumps form and merge to form larger clumps, which merge to form even larger clumps. We can see this happening today as we look around our own local group of galaxies. Small dwarf galaxies, like the Sagittarius dwarf spheroidal galaxy, are constantly getting consumed by the Milky Way galaxy. These smaller systems are adding their mass to the Milky Way, and both bringing in new material and shaking things up a bit. Past interactions have caused the disk of our galaxy to bloat up, forming the thick disk. They have brought metal poor stars to the local neighborhood of stars, and they have even placed globular clusters – gravitationally bound clusters of thousands of stars – in orbit the wrong way around the galaxy.

It is hard to know exactly what the original population of galaxies looked like. From extremely deep images of the sky we know that young galaxies in the early universe were distorted and blue with star formation (only very young stars can be blue. While a red star could be any age, only systems with on going or just completed star formation have blue stars). The image above left (credit: Y. Izotov (Main Astronomical Obs., Ukraine), T. Thuan (Univ. Virginia), ESA, NASA) shows an image of a diminutive, 500 million year old galaxy (for reference, the Sun is ~4.5 billion years old). We assume that galaxies formed in a variety of different sizes, with the largest areas of extra mass – the largest over densities – forming larger galaxies while areas with less mass formed smaller galaxies or just clouds of gas.

These early collections of material tended to clump up, with galaxies forming groups and clusters, and these groups and clusters forming super clusters. In the process of clumping up, somehow spiral and elliptical galaxies were formed. How you go from blob of gas and stars to spiral galaxy is a bit of a mystery. Hopefully, the next generation space telescope, James Webb, will allow us to peer at younger galaxies and catch snap shots of galaxies in the process of forming.

At one stage during the universe’s construction process, these larger spiral and sometimes elliptical galaxies began to actively consume gas rich small galaxies in large numbers. While not all active galaxies are spiral galaxies, many of them are, and these spectacular systems have amazingly illuminated cores that contain supermassive black holes. Depending on how much material is being consumed and what angle we are looking at the galaxy from, we classify these busily eating systems as quasars, Seyfert galaxies or just active galaxies. In reality, these systems are all just a continuum of the same object. This different names come from not being able to, well, watch a galaxy grow up. Imagine you stumbled across 3 random humans: a 4 day old baby, a pregnant woman, and a 90 year old crone. Would you recognize them as all belonging to the same species? It takes us time to sort out the evolution of a form, especially when that evolution can take billions of years and humans have only had telescopes pointed at the stars for 400 years. We’re getting there however.

And as out understanding grows, we’re realizing that we are living in a nice calm age. The active galaxies are dieing out as gas rich food becomes scarce. The number of collisions is decreasing, and the amount of local fireworks is minimal.

When talking about galaxies, the dead are red. Without dust, without star formation, the universe grows monochrome.

But we’re not to that stage yet. Things are just slowing.

It’s a middle aged universe out there.

In a recent survey, lead by Igor Karachentsev of the Special Astrophysical Observatory in Russia*, a team of astronomers looked for the signature of dark galaxies in the light of isolated luminous galaxies. Here’s how it works: When two galaxies interact gravitationally the become extremely distorted. A quick look a few nearby colliding galaxies, such as “The Mice,”(1, top left) “The Tadpole,”(2, right) and the “The Antenna”(3, bottom left) all show signs of violent, shape altering, interactions. In each of these situations, we are looking at two visible galaxies interacting. If dark galaxies are out there, we should at some point find a lone luminous galaxy that looks like it has been tele-ported out of one of these train-wrecked galaxies and deposited in the middle of empty space. The distortions will be caused by the effects of the dark galaxy. (Images at left: 1&2. NASA, H. Ford (JHU), G. Illingworth (UCSC/LO), M.Clampin (STScI), G. Hartig (STScI), the ACS Science Team, and ESA, 3. Bob and Bill Twardy/Adam Block/NOAO/AURA/NSF)

Karachentsev and his team observed 1500 isolated galaxies and only found 8 systems that appeared significantly disturbed. Using the old 6-meter telescope in the Northern Caucuses, they carefully verify none of the small faint galaxies that appeared in the same field as the disturbed galaxy were located at the same distance. It appears that these systems are legitimate candidates for visible galaxy – dark galaxy collisions. This is both good and sad.

It is good because we can say that it is likely that dark matter galaxies are likely out there, living their non-luminous lives in the midst of their more illuminated brethren. That is just really cool. It is sad because when you look at 1500 places to potentially discover an interaction and only find 8 interactions, it implies these things just aren’t that common. So, as always seems to be the case, the really cool stuff is really hard to find and rare.

But, would the cool and interesting stuff be so cool and interesting if it was common?

Additional Random Notes:

* The Special Astrophysical Observatory in Russia is the first professional observatory I ever worked at. It was really cool to see some one from there publish a paper I wanted to write about

1) Neither of my computer’s keyboards have the old fashioned division symbol. You know, the one with the line and a dot above and below it that appears on every calculator keyboard. I remember this key being on my old type writer in high school. I’m not sure when it disappeared, and I’m very confused.

2) A quick look over my reading history shows that if a journal article contains the word “Ammonia” in the title, I’m pretty much guaranteed to never read it. I don’t know why.

Kepley’s team looked at 231 stars within 25,000 2,500 parsecs of the Sun that are less than 1/10th the metal content of the Sun. This sample includes stars with accurate distances, velocities, and metallicities. They find 5% of these stars appear to be streaming into the disk, raining down around the solar system from a system the Milky Way consumed 6-9 billion years ago. This stream was originally noted by Amina Helmi (University of Groingen) and collaborators in 1999. In Kepley’s work, they find these stars are formed out of gas and dust that was enriched primarily by type II supernovae.

Other stars in Kepley’s sample appear to also come from the normal (and random) distribution of halo stars, as well as from tidal debris of systems destroyed in the past. Six stars in the sample are moving in retrograde compared to the bulk motions of the stars. These stars could come from a side impact collision with a small galaxy.

On the surface, Kepley’s work is a detailed study of how a lot of stars are moving, and it boils down to many remarkably boring tables. Looked at broadly, this paper shows that our galaxy, even locally, is a dynamic place that shows evidence everywhere of past collisions with small systems of stars (systems like dwarf galaxies). As more and more studies like this one are completed, probing larger and larger distances into the galaxy, we will be able to build a detailed picture of our galaxy’s history that includes information on which stars may have been stolen from other galaxies, and what the stars in those shredded systems were made out of.

Just 15 years ago, we didn’t know if the galaxy formed out of a lot of small systems combining into a larger galaxy, or if our large Milky Way galaxy formed in situ from a large cloud of gas that fractured into us and the smaller systems. Today, thanks to all the observations of tidal streams and stellar populations that are being done, we can say with certainty that our galaxy was build out of the pieces of smaller systems.

Boring tables lead to exciting understanding, one data point at a time.

It’s name is Andromeda XII, and its speed indicates it is an evader that came from beyond (beyond the local group that is), and represents our first chance to get a good look at an unperturbed dwarf galaxy.

This system was first discovered October 2006 using the the Mega Cam on Canada-France Telescope during a wide-field survey that was searching for dwarf galaxies associated the nearby Andromeda galaxy. This system was originally seen as nothing more than a blip of stars that had colors and magnitudes (brightnesses) in a color-magnitude plot that indicated that they belonged to the same population. This system is so small and so diffuse that it doesn’t standout against the background stars and galaxies.

Followup observations taken with the DEIMOS spectrograph at Keck II telescope show that this small family of stars is physically related, and are all moving together at a speed of 281 km/sec toward the Andromeda Galaxy (M31). This speed is so fast that it can’t be orbiting M31, but rather must have formed somewhere else and then been gravitationally pulled into M31.

According to Zezas, And. XII likely formed 3.3-4.5 million light years (1.0-1.4 Mpc) away from Andromeda, and is now on its first pass through the local group. This is particularly exciting because dwarf galaxies are considered to be the building blocks of larger galaxies like our Milky Way. These systems formed first, and in a bottom up view of galaxy formation, they coalesced into larger structures. Previous to this discovery, all the known dwarf galaxies were bedraggled systems that had been knocked about, stripped of materials, and in some case torn into tidal streams through gravitational interactions with other systems. This means we haven’t been able to get a clear understanding of what the building blocks off our galaxy looked like originally.

This system, gives us our first chance to see the raw materials of a galaxy. While hard to study due to small size, faint nature, and large distance, it is a start. (And if you want to look toward it without actually seeing it, the stars are in the same binocular field as M31).

M81 in detail: M81 is a well known spiral galaxy that can be seen from dark locations with binoculars, and from less dark locations with small telescopes. The Hubble Space Telescope recently turned its ACS camera at this little system, and for 2.5 days worth of exposure time, captured the system in detail. Clearly visible in a zoomable version of the image are large stars, star forming regions, and globular clusters. Also apparent are background galaxies the before had simply melted into the light of M81. This spectacular image will be used to study the star formation history and action in this nearby galaxy.

Void Not Pulling: In the final announcement of the morning, Dr. Brent Tully (University of Hawaii, and famed for the Tully-Fisher relationship) laid out a nice bit of vector addition that shows that while our local group is getting pulled toward the Virgo Super Cluster, Great Attractor, and Shapley Concentrations (all large groups of galaxies and collections of galaxy clusters), it is also not moving toward the local void. At the edge of the local group of galaxies, there is a giant void containing 120 million lightyears of just about nothing. The normal, random distribution of galaxies that forms a clumpy sphere around us generally pulls gravitationally on the local group at very levels. They void, by not pulling on us, lets us drift away from it. This effectively causes the void to grow (as things get pulled away from it, leaving emptiness behind). This is just part of the standard evolution of the cosmology from swiss cheese with small holes to swiss cheese with giant holes and really dense cheese between the bubbles.

The lack of gravitational pull from the void, actually allows our galaxy to move at roughly 260 km/s away from. Its always neat when the lack of something can cause a motion.
The next press conference is in 20 minutes and it is predicted to be the big one of the day. More to come. After that, I’ll be off to the poster room and conference center to see what NASA has to give away.

At the two ends of the scale, the continuity isn’t surprising. Planets and asteroids are formed out of a fragmenting proto-planetary disk, and stars in open clusters are forming out of fragmenting molecular clouds. These are related, top-down, physical processes. On the other end, small galaxies are falling together to form large galaxies, and small groups are falling together to form large clusters. These are related, bottom-up, gravitational clustering processes. What is odd, is that these two very different ways of building structures bridge together reasonably well.

Their functions aren’t a perfect fit, but they are good. (Please see the copyrighted figures 9 and 10 in the paper). The function for planets is a bit shallow on one end and too steep on the other, the section for stars is a bit variable, and there may be a break between the mass of brown dwarf stars and giant planets. The mass function does match well at the boundary between fragmented molecular clouds, star clusters, and galaxies however, at the location where the physics likely flips from top-down fragmentaion to bottom-up formation.

This is a nice example of astronomers looking for trends in the big picture and seeing an unexplained trend spanning space. We don’t know why this is, but like so many of the inexplicable just-so relations in astronomy, it points to a universal bit of truth. In this case, the little guy always has the upper hand when you look at the numbers. The microbes outnumber the mammals, the m-dwarfs out number the O stars, and the dwarf spheroidals outnumber the giant ellipticals; that’s just the way it is.

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