COSMOS Reveals the Cosmos

By Sean Carroll | January 8, 2007 1:20 pm

The internet works so that we don’t have to! This week is the big annual meeting of the American Astronomical Society in Seattle, so expect to see a series of astro-news stories pop up all through the week. The first one concerns a new result from the Cosmological Evolution Survey (COSMOS) — they’ve used weak lensing to reconstruct a three-dimensional image of where the dark matter is. Here is an image from the Nature paper by Richard Massey et al. (subscription required).

COSMOS dark matter map

It is, needless to say, really cool. The image itself is not where the real science lies, of course; it’s spatially distorted, and very hard to show error bars in a 3-d plot. But there is definitely important science lurking in the details; for example, they seem to find dark-matter concentrations with little or no ordinary matter in the same place. It’ll take some work to figure out whether this is easily compatible with the theoretical models (one could imagine dissipative effects clearing baryons out of a region, leaving dark matter behind, in a mini-version of the Bullet Cluster), or whether we’re going to be challenged. Fun either way!

Fortunately, I don’t have to go into details about the result, as others already have. Phil, Clifford, Rob, Angela, and Steinn have all blogged about the finding. (We’re all on a first-name basis around here.) Steinn’s post is, admittedly, pretty consise, but he wins points for breaking an even better story — Google is joining the Large Synoptic Survey Telescope consortium! Rob is even live-blogging the entire meeting, which is an heroic undertaking. (Yes, it’s true that he did bump into me up in Seattle, but I’m not there for the meeting! In fact I’m already back in LA. There are reasons to visit Seattle other than the AAS.)

Ah, I remember the good old days of ’04, when there wasn’t any competition out there in the cosmo-blogging world. Our internet is all grown up now. Sadly, Michael Bérubé is retiring from the game, which will leave the blogosphere a much poorer place. Read Sunday’s Credo for an example. Without his inspiration, I certainly wouldn’t be doing this myself.

Anyway — the COSMOS project is well worth being wowed by in its own right. It’s an ambitious undertaking; they take a two-square-degree field of the sky and beat on it with every telescope they can find — in optical, infrared, ultraviolet, X-rays, and radio waves. More than half a dozen ground-based telescopes, as well as five satellites (the Hubble Space Telescope, Spitzer infrared observatory, XMM and Chandra for X-rays, and GALEX for the ultraviolet), are joined in the effort. Here’s the abstract from one of their recent summary papers:

The Cosmic Evolution Survey (COSMOS) is designed to probe the correlated evolution of galaxies, star formation, active galactic nuclei (AGN) and dark matter (DM) with large-scale structure (LSS) over the redshift range z < 0.5 to 6. The survey includes multi-wavelength imaging and spectroscopy from X-ray to radio wavelengths covering a 2 square deg area, including HST imaging. Given the very high sensitivity and resolution of these datasets, COSMOS also provides unprecedented samples of objects at high redshift with greatly reduced cosmic variance, compared to earlier surveys. Here we provide a brief overview of the survey strategy, the characteristics of the major COSMOS datasets, and summarize the science goals.

This new dark matter map is just the beginning of fun stuff to emerge from this collaboration — stay tuned!

Update: There I go again.

“I like to think of visible matter as the olive in the martini of dark matter,” said Sean Carroll, a theoretical physicist at Caltech.

I love my job.

CATEGORIZED UNDER: Science
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Cosmic Variance

Random samplings from a universe of ideas.

About Sean Carroll

Sean Carroll is a Senior Research Associate in the Department of Physics at the California Institute of Technology. His research interests include theoretical aspects of cosmology, field theory, and gravitation. His most recent book is The Particle at the End of the Universe, about the Large Hadron Collider and the search for the Higgs boson. Here are some of his favorite blog posts, home page, and email: carroll [at] cosmicvariance.com .

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