Archive for Dark Energy Survey

Eight Papers from the Dark Energy Survey

Posted in The Universe and Stuff with tags , , , , on November 9, 2018 by telescoper

Just a quick post to point out the exciting news that this week a clutch of papers on cosmology using Type 1a Supernovae have been released by the Dark Energy Survey team. Naturally, all of them are on the arXiv. You can also read them here. For convenience I’ve provided links below to arXiv versions through their titles:

  1. Steve: A hierarchical Bayesian model for Supernova Cosmology
  2. First Cosmology Results Using Type Ia Supernovae from the Dark Energy Survey: Effects of Chromatic Corrections to Supernova Photometry on Measurements of Cosmological Parameters
  3. First Cosmology Results using Type Ia Supernova from the Dark Energy Survey: Simulations to Correct Supernova Distance Biases
  4. First Cosmology Results Using Type Ia Supernovae From the Dark Energy Survey: Photometric Pipeline and Light Curve Data Release
  5. First Cosmology Results Using Type Ia Supernovae From the Dark Energy Survey: Analysis, Systematic Uncertainties, and Validation
  6. First Cosmological Results using Type Ia Supernovae from the Dark Energy Survey: Measurement of the Hubble Constant
  7. Cosmological Constraints from Multiple Probes in the Dark Energy Survey
  8. First Cosmology Results using Type Ia Supernovae from the Dark Energy Survey: Constraints on Cosmological Parameters

Here’s a plot showing some of the cosmological constraints:

The parameter plotted on the vertical axis is the dark energy equation of state parameter, w, and w=-1 corresponds to a cosmological constant.

For those of youparticularly interested in the Hubble constant, the headline value from Paper 6 is H0 = 67.77 +/- 1.30 km s-1 Mpc-1. This closer to the value obtained from Planck and in tension with other values as I’ve blogged about before, and gives me an excuse to continue my online poll:

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Mapping the Universe

Posted in The Universe and Stuff with tags , , on August 5, 2017 by telescoper

Following yesterday’s post, here’s a nice visualisation of how much (and indeed how little) of the Universe the latest galaxy surveys have mapped.

In this animation the Earth is at the centre, and the dots represent observed galaxies, with distances are estimated using redshifts Every blue dot in the animation is a galaxy measured by the Dark Energy Survey. Gold dots are galaxies in the DES supernova fields (measured by OzDES) and red dots are from the Sloan Digital Sky Survey. The dark space in between the surveys is yet to be mapped….

Cosmological Results from the Dark Energy Survey

Posted in The Universe and Stuff with tags , , , , , on August 4, 2017 by telescoper

At last the Dark Energy Survey has produced its first cosmological results. The actual papers have not yet hit the arXiv but they have been announced at a meeting in the USA and are linked to from this page.

I’ll jump straight to this one, which shows the joint constraints on S8 which is related to σ8 (a measure of the level of fluctuations in the cosmological mass distribution) via S8= σ8m/0.3)0.5 against the cosmological density parameter, Ωm.

These constraints, derived using DES Y1 measurements of galaxy clustering, galaxy-galaxy lensing, and weak lensing cosmic shear are compared with those obtained from the cosmic microwave background using Planck data, and also combined with them to produce a joint constraint. Following usual practice, the contours are 68% and 95%  posterior probability regions.

The central values of DES and Planck values are different, but the discrepancy is only marginal. Compare this with a an equivalent diagram from a paper I discussed last year.

The KIDS analysis used to produce this plot uses only weak lensing tomography, so you can see that using additional measures reduces the viable region in this parameter space.

It’s great to see new data coming in, but at first sight it seems it is tending to confirm the predictions of the standard cosmological model, rather than providing evidence of departures from it.

Incidentally, this little video shows the extent to which the Dark Energy Survey is a global project, including some of my former colleagues at the University of Sussex!

 

Dark Matter from the Dark Energy Survey

Posted in The Universe and Stuff with tags , , , on April 14, 2015 by telescoper

I’m a bit late onto this story which has already been quite active in the media today, and has generated an associated flurry of activity on social media, but I thought it was still worth passing it on via the medium of this blog. The Dark Energy Survey has just released a number of papers onto the arXiv, the most interesting of which (to me) is entitled Wide-Field Lensing Mass Maps from DES Science Verification Data. The abstract reads as follows (the link was added by me):

Weak gravitational lensing allows one to reconstruct the spatial distribution of the projected mass density across the sky. These “mass maps” provide a powerful tool for studying cosmology as they probe both luminous and dark matter. In this paper, we present a weak lensing mass map reconstructed from shear measurements in a 139 deg^2 area from the Dark Energy Survey (DES) Science Verification (SV) data overlapping with the South Pole Telescope survey. We compare the distribution of mass with that of the foreground distribution of galaxies and clusters. The overdensities in the reconstructed map correlate well with the distribution of optically detected clusters. Cross-correlating the mass map with the foreground galaxies from the same DES SV data gives results consistent with mock catalogs that include the primary sources of statistical uncertainties in the galaxy, lensing, and photo-z catalogs. The statistical significance of the cross-correlation is at the 6.8 sigma level with 20 arcminute smoothing. A major goal of this study is to investigate systematic effects arising from a variety of sources, including PSF and photo-z uncertainties. We make maps derived from twenty variables that may characterize systematics and find the principal components. We find that the contribution of systematics to the lensing mass maps is generally within measurement uncertainties. We test and validate our results with mock catalogs from N-body simulations. In this work, we analyze less than 3% of the final area that will be mapped by the DES; the tools and analysis techniques developed in this paper can be applied to forthcoming larger datasets from the survey.

This is by no means a final result from the Dark Energy Survey, as it was basically put together in order to test the telescope, but it is interesting from the point of view that it represents a kind of proof of concept. Here is one of the key figures from the paper which shows a reconstruction of the mass distribution of the Universe (dominated by dark matter) obtained indirectly by the Dark Energy Survey using distortions of galaxy images produced by gravitational lensing by foreground objects, onto which the positions of large galaxy clusters seen in direct observations have been plotted. Although this is just a small part of the planned DES study (it covers only 0.4% of the sky) it does seem to indicate that the strong concentrations of dark matter (red) do corrrelate with the positions of concentrations of galaxy clusters.

DES_MAP

It all seems to work, so hopefully we can look forward to lots of interesting science results in future!

P.S. When I first saw the map it looked like a map of the North of England Midlands and I was surprised to see that the survey showed such strong support for the Greens…

Why Cosmology Isn’t Boring

Posted in Brighton, The Universe and Stuff with tags , , , on October 23, 2014 by telescoper

As promised yesterday, here’s a copy of the slides I used for my talk to the ~150 participants of the collaboration meeting of the Dark Energy Survey that’s going on here this week at Sussex. The title is a reaction to a statement I heard that recent developments in cosmology, especially from Planck, have established that we live in a “Maximally Boring Universe”. I the talk I tried to explain why I don’t think the standard cosmology is at all boring. In fact, I think it’s only now that we can start to ask the really interesting questions.

At various points along the way I stopped to sample opinions…

IMG-20141022-00439

I did however notice that Josh Frieman (front left) seemed to vote in favour of all the possible options on all the questions.  I think that’s taking the multiverse idea a bit too far..

 

Cosmology, to be precise…

Posted in The Universe and Stuff with tags , on October 22, 2014 by telescoper

After an extremely busy morning I had the pleasant task this afternoon of talking to the participants of a collaboration meeting of the Dark Energy Survey that’s going on here at Sussex. Now there’s the even more pleasant task in front of me of having drinks and dinner with the crowd. At some point I’ll post the slides of my talk on here, but for the mean time here’s a pretty accurate summary..

Summary

Cosmology Webcasts Coming Up…

Posted in The Universe and Stuff with tags , , , , on September 29, 2012 by telescoper

Courtesy of freelance science writer Bruce Lieberman, whom I met briefly at the recent “Origin of the Expansion of the Universe” meeting in Flagstaff, AZ,  here’s a plug for two live webcasts on topical topics that are coming up in the next couple of weeks. On behalf of the Kavli Foundation, Bruce will be interviewing astronomers about the new Hubble XDF image (Oct. 4) and the new Dark Energy Survey camera, which just saw First Light (Oct. 11).

Live Q&A and Webcast: What Does Hubble’s Deepest Image of the Universe Reveal?

Click on the above heading for  direct link to webcast.

October 4, 11-11:30 am PDT (18-18:30 GMT; 19-19:30 BST)

Using data from the Hubble Space Telescope, a multi-national team of astronomers recently released our deepest-ever image of the
universe. Pascal Oesch, a Hubble Fellow at the University of California at Santa Cruz, and Michele Trenti, a researcher at the Kavli Institute for Cosmology, Cambridge at the University of Cambridge in the U.K., answer your questions about how the image was created and what it reveals about the early universe.

Viewers may submit questions to the two Hubble researchers via Twitter using #KavliAstro or email to info@kavlifoundation.org.

Live Q&A and Webcast: Can a New Camera Unravel the Nature of Dark Energy?

Click on the above heading for  direct link to webcast.

October 11, 9-9:30 am PDT (16-16:30 GMT; 17-17:30 BST)

Scientists have great expectations for the newly operational Dark Energy Camera, which may significantly advance our understanding of the mysterious force expanding the universe at an ever accelerating rate. Fermilab scientists Brenna Flaugher, project manager for the Dark Energy Camera, and Joshua Frieman, director of the Dark Energy Survey, answer your questions about the camera and what it’s expected to reveal.

Viewers may submit questions via Twitter using #KavliAstro or email to info@kavlifoundation.org.