New DLS website launched

Posted by dwittman on July 19, 2013  • 

Our new website has been launched. We hope you like it!

Photometric redshift innovations

Posted by dwittman on February 26, 2013  • 

A paper describing the DLS photometric redshifts (Schmidt & Thorman) has been accepted. An innovative feature is that Schmidt & Thorman used the data itself to measure the z-band throughput curve. Anyone with z band data from the Mosaic cameras on Kitt Peak or Cerro Tololo should be aware of this improved z-band throughput curve.

The full abstract is:

Wide, deep photometric surveys require robust photometric redshift estimates (photo-zs) for studies of large-scale structure. These estimates depend critically on accurate photometry. We describe the improvements to the photometric calibration and the photo-z estimates in the Deep Lens Survey (DLS) from correcting three of the inputs to the photo-z calculation: the system response as a function of wavelength, the spectral energy distribution templates and template prior probabilities as a function of magnitude. We model the system response with a physical model of the MOSAIC camera's CCD, which corrects a 0.1 mag discrepancy in the colours of type M2 and later stars relative to the Sloan Digital Sky Survey z photometry. We provide our estimated z response function for the use of other surveys that used MOSAIC before its recent detector upgrade. The improved throughput curve, template set and Bayesian prior lead to general improvement in the predicted photometric redshifts, including a 20 per cent reduction in photo-z scatter at low redshift and a reduction of the bias by a factor of more than 2 at high redshift. This paper serves as both a photo-z data release description for DLS and a guide for testing the quality of photometry and resulting photo-zs generally.

Cosmic shear results

Posted by dwittman on January 18, 2013  • 

The DLS cosmic shear paper (Jee et al) has been accepted. This paper provides a joint constraint on the cosmological parameters Ωm ( 0.262 ± 0.051 ) and σ8 (0.868 ± 0.071). Combining the current results with the Wilkinson Microwave Anisotropy Probe 7 year (WMAP7) likelihood data, we obtain Ωm = 0.278 ± 0.018 and σ8 = 0.815 ± 0.020. This paper also includes a section demonstrating the power of a deep survey vs a shallower CFHTLS-like survey for constraining cosmic shear. A second paper in preparation uses tomography (the redshift dependence of cosmic shear) to constrain dark energy.

DLS cluster hints at nature of dark matter

Posted by dwittman on January 9, 2013  • 

The Musket Ball cluster, discovered by the DLS, is in the news again, as DLS team member Will Dawson has used it to provide evidence that dark matter may be self-interacting. If you want to learn more about how we model these merging clusters, you can read a detailed paper describing the modeling, or a summary for nonphysicists.

Cosmic magnification first

Posted by dwittman on October 15, 2012  • 

MNRAS has published our cosmic magnification paper (Morrison et al). This paper demonstrates, for the first time, cosmic magnification tomography. Non-experts are encouraged to read this explanation of the paper for laypeople.

Cluster collision separates dark matter from gas

Posted by dwittman on April 12, 2012  • 

The Musket Ball cluster, discovered by the DLS, is in the news. The Musket Ball is actually a collision between two clusters of galaxies, and the collision has stripped the gas away from the dark matter. Read more at the Chandra press release, the journal article, or team member Will Dawson's website.

Successful DEIMOS run

Posted by dwittman on March 3, 2011  • 

The DLS team completed a successful run with the DEIMOS multi-object spectrograph on the Keck II telescope, obtaining hundreds of high-quality spectra.

HST imaging acquired

Posted by dwittman on January 26, 2011  • 

Hubble Space Telescope imaging of a merging cluster in the DLS has been acquired, and it's beautiful!

Chandra X-ray data acquired

Posted by dwittman on January 4, 2011  • 

Chandra X-ray spectro-imaging of a merging cluster in the DLS has been acquired.