As Chris mentioned last Saturday, scientists from the Sloan Digital Sky Survey have gathered in Chicago to review accomplishments and look ahead to the future. The Sloan Digital Sky Survey (SDSS) is the project that provided all the images for Galaxy Zoo; but additionally, it has provided some of the most amazing results in astronomy over the past decade or so.

The final talk of the conference was given by Jim Gunn, an astronomer at Princeton who has spent most of the past 20 years guiding SDSS from its initial planning stages to today. Jim was an excellent choice to give the talk. Chris was in the audience too, and liveblogged the talk from his blog, so you can see how two people from the same audience interpret in the same talk.

Here is what I recorded during the talk yesterday:

4:22 PM

Gunn has just started speaking. “In the next 20 minutes, I will describe a large chunk of astrophysics,” he says. That’s quite a promise. He says that Sloan was first thought up in 1987. Now it’s 2008; if the project were born here in the States then, it would now be old enough to drink.

The original goal of the SDSS came from a desire to get caught up with technology. Astronomers before had always worked with photographic plates, which can be hard to use to get quantitative data. They wanted to design a project that would use digital cameras to see the sky instead. This is common today but was a new idea in 1987.

It became clear that just getting images of the sky wasn’t enough; we also needed to know what the distances to galaxies were. To do that, SDSS needed to get spectra to find redshifts. To get the number of distances they needed, they would need to get spectra for a million galaxies. The problem is that it takes 1 hour to get a spectrum, and 1 hour x 1 million galaxies = 1,000 years. So they came up with a clever solution to get 600 spectra at once.

4:25 PM

“SDSS has touched almost all the fields of astrophysics,” Gunn said. He’s reviewing some of those areas now.

The field of large-scale structure (the way galaxies are distributed into a map of the universe) was the main scientific justification for the SDSS. The survey has always billed itself as a “map of the universe.” SDSS has made key contributions to what Gunn calls “precision cosmology” - making large-scale measurements to learn something about the properties of the universe as a whole. SDSS has led to the discovery of lots of new tools for measuring these parameters.

4:31 PM

“I think the richest part of SDSS has been galaxies,” Gunn said. That is a significant statement - the original promise of SDSS was to learn about large-scale structure, but what we have learned about the nature of galaxies has been amazing too. SDSS spectra are amazingly good. For a long time, a lot of great telescopes, including Hubble, were seeing the universe, but just a few galaxies at a time. By seeing millions of galaxies at once, all over the sky, the SDSS has helped us learn more about what galaxies are like.

4:35 PM

Gunn just mentioned Steven’s Galaxy Zoo talk. “I’m glad to see that the subject of morphology [the study of galaxy shape] has come to the fore again,” he said. He described our project as the “democratic Galaxy Zoo” Galaxy Morphology - this used to be all we knew about galaxies. “I’m very glad to see that the subject has come to the fore again.” Gunn described our project as “democratic Galaxy Zoo,” which I’m pleased to hear; part of the excitement was the chance to work democratically with so many of you to learn about the universe.

4:40 PM

The SDSS has also led to exciting discoveries about our own galaxy, the Milky Way. It’s a much more complex place than we had previously thought; it’s been built up by nearly constant combinations of smaller galaxies into our own larger one. One of the talks here was about the Monoceros Stream, a long stream of stars discovered by the SDSS, which Gunn described as “still a bit of a mystery.”

4:44 PM

SDSS has also led to discoveries about stars and about our solar system. One particularly interesting result announced at this meeting was the discovery of a new “minor planet” called 2006 SQ 372, an icy ball so distant that it takes 22,000 years to orbit the Sun. There is a good possibility that it is either the first or second object from the Inner Oort Cloud. The SDSS has also produced exciting results in understanding supernovae, the exploding stars that can tell us something about the history of the universe.

4:49 PM
The future of astronomy is bright - there are lots of new surveys planned, including a 6-year extension to the SDSS called SDSS-III, PanSTARRS, and LSST. Gunn is now reviewing lessons that he thinks we learned from the SDSS. The one that stands out for me is his last one: “it really is possible for hundreds of people at tens of institutions to work together in a ‘non-cat-herded’ manner.” He adds, “it’s been fun as well.”

4:58 PM

Gunn just received a standing ovation, the longest one I’ve ever seen at a scientific conference. People here are really proud of what the SDSS has accomplished, and Galaxy Zoo is a part of that.

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Hi Pea Hunters,  

Kevin and I wanted to give you an update with where we are in our Peas investigation.  We haven’t answered all of our questions, but from detailed inspections of their spectra, it appears that the Peas are a mixed bag.  A large portion of them appears to be powered by star formation, and perhaps an equal number show evidence of an active central black hole.  The details of what I’ve done so far are below.  Feel free to chime in with any questions or suggestions you all might have! The first thing I did was look at all of the peas that were highly rated as Green in our Pea Picker hunt.  When I plotted them against a sample of randomly selected galaxies of at similar redshifts, they do stand out.  This first plot is a color-magnitude diagram.  In my opinion its one of the most widely used of all plots astronomers can make.  Practically, this is probably because only 2 images are necessary to make this plot, but also historically because we’ve found out plots like these can tell us so much (eg. the HR diagram). 

 In the Pea color-magnitude diagram, you can see that the sample of typical galaxies lie at a U-R color near 3, while all of the peas identified here on this thread are much bluer.  I know it might be confusing because we selected the peas to appear ‘Green’ in the SDSS images, but all that Green means there is that they are very bright in the ‘R’ band.     The next step up in complexity from a color magnitude diagram is a color - color plot.  I made several of these for the Peas, but if you look at the one I’ve posted here, you can see that the Peas jump out as very distinct from the galaxy sample.  If we restrict our query to compact objects at the pea’s redshifts, ask for an [OIII] line to be detected in the Spectrum, and throw out luminous Quasars (QSOs) we find a sample of 439 Peas.  I’ve plotted this sample of pea’s on both the color-magnitude diagram and the color-color diagram in Purple.  (This Pea-search also returns all of Peas found by eye as well).

  

Now came the exciting part, figuring out what powers the peas.  We downloaded all of their spectra from Sloan and used Gandalf to analyze their Spectral lines.  Unfortunately, quite a few of our spectra had bright spectral lines we could see by eye, but did not have a high enough Signal-to-Noise ratio to make a precise measurement of the line flux.  I also closely examined the fit of each spectrum and noticed that Gandalf had trouble with many of the Active Galaxies (AGN) in our sample.  We’ve contacted the author of Gandalf and he is going to help us go back and fit these galaxies better so we can add them back in our sample of Peas.  For now we’ve accurate spectral fits for 36 of the Peas.  I’ve plotted them on a typical BPT diagram below.  The BPT diagram was introduced by Baldwin, Philllips and Terlevich in 1981 and is a diagnostic, which can indicate if the gas in a galaxy is being heated by star formation (as in a starburst galaxy) or by very hot gas near a central black hole (as in an Active Galactic Nucleus).  You can see most of them end up on the Starburst portion of the plot.  However, this is simply because most of the fits to the AGN spectra were poor and so they were thrown out of our sample.  Looking at the spectra by eye, it looks as though they are fairly evenly split between AGN and Starburst, but we’ll get a better handle on this when we can accurately fit the AGN spectra.

  

For the Peas powered by star formation, we can look at how many stars are forming each year.   For comparison, Milky way’s star formation rate is around 1-2 solar masses per year.  The typical Pea from our sample seems to have a star formation rate nearly 5 times higher than this, and for many Peas the rate at which they form stars is up to 40 times larger.  Because the Peas are so much smaller then the Milky Way, these are incredibly large star formation rates.

Right now we’re working on improving our spectral analysis and searching the data archives for evidence of X-ray emission from the Peas.  With X-ray emission we will be able to measure the AGN activity and where Star Formation dominates, we can get a second estimate of the star formation rate in the Peas.  We are also looking for infrared emission from the peas.  This will be an additional measure of their star formation rates & their stellar masses.  Finally, we plan to apply for time on a larger telescope to get better spectra.  These higher Signal-to-Noise spectra will allow us to measure the BPT line diagnostics better for a larger number of our Peas, and most importantly it will let us look at other spectral features that can inform us on the Peas stellar masses. 

Carie & Kevin 

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I’m sitting in the back of the third day of the conference here in Chicago, and a fairly animated question has just been asked of Changbom Park, who has been working with a set of galaxies classified by an automatic routine. (You can find some of their results in this paper). I’ll need more thinking time to properly blog the debate (and the responses we’re getting to Galaxy Zoo) there’s one quote which sums it up : 

We don’t classify zebras as horses because they look the same - we use the colours.

The equivalent galaxy argument is whether we should classify according to shape (which we call morphology to confuse people) and then look at colour, as Steven does or whether a ‘true classification’ would take into account all the available information. The consensus seemed to be the former, but then I’m biased…

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Greeting from a very sunny Chicago! Several members of the Galaxy Zoo team are here this week (Steven, Chris and Bob, along with various new additions) for the Sloan Digital Sky Survey Symposium: “From Asteroids to Cosmology”.

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