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Constraining Dark Matter with the Musket Ball Cluster

Musket Ball Cluster
I have been leading the effort to study in detail a newly discovered dissociative galaxy cluster merger (DLSCL J0916.2+2951 a.k.a the Musket Ball Cluster), were the collisionless dark matter (blue, in the figure) and galaxies have become separated from the collisional cluster gas (red, in the figure). To date only ten dissociative mergers have been confirmed, the most famous being the Bullet Cluster. These dissections of the cosmos are proving to be some of the best laboratories for studying dark matter.

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For a more detailed account see our journal article "Discovery of a Dissociative Galaxy Cluster Merger with Large Physical Separation".   



Merging Cluster Collaboration

Merging Cluster Collaboration
Dark Matter is one of the great outstanding mysteries. Although still in its infancy, the study of merging galaxy clusters has been shown to be one of the best means of determining the nature of dark matter. However to realize this potential requires a concerted effort on the part of astronomers and computational theorist, due to necessity to compare simulations and observations of real systems.  UC Davis is a leading center on the observation of merging clusters, having led the investigation of four of the ten confirmed dissociative mergers.  UC Irvine is a leading center on computation/theory of simulating self interacting dark matter physics on astrophysical scales. We established a UC Davis-Irvine workgroup devoted the observation and subsequent simulation of merging galaxy clusters with the directive of determining the nature of dark matter. 

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This collaboration is supported in part by a grant from the University of California High-Performance Astrocomputing Center, STScI, and NSF.

Research Interests

  • Dark Matter
  • (Merging) Galaxy Clusters
  • Weak Lensing
  • X-ray astronomy
  • Optical astronomy
  • The Universe

Collaborators

(Apologies for the incomplete list; fortunately this has grown more rapidly than I can keep up with.)
  • Begoña Ascaso (IAA)
  • Debbie Bard (KIPAC)
  • Marusa Bradac (UC Davis)
  • Marcus Bruggen (Jacobs)
  • James Bullock (UC Irvine)
  • John Carlstrom (Chicago)
  • DLS Collaboration
  • Perry Gee (UC Davis)
  • Jack Hughes (Rutgers)
  • James Jee (UC Davis)
  • Manoj Kaplinghat (UC Irvine)
  • Brian Lemaux (LAM)
  • Alison Mansheim (UC Davis)
  • Vera Margoniner (CSU)
  • Dan Marrone (Arizona)
  • Satoshi Miyazaki (GUAS)
  • Tony Mroczkowski (JPL)
  • Annika Peter (UC Irvine)
  • Miguel Rocha (UC Irvine)
  • Sam Schmidt (UC Davis)
  • Paul Thorman (UC Davis)
  • Tony Tyson (UC Davis)
  • Yousuke Utsumi (GUAS)
  • Reinout van Weeren (Leiden)
  • Dave Wittman (UC Davis, Ph.D. Advisor)

​​Studying the First Galaxies

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I am part of the Reionization Lensing Cluster Survey (RELICS), a Hubble Space Telescope Treasury program to obtain the first HST infrared imaging of 41 massive galaxy clusters which magnify the high redshift universe and enable us to efficiently search for the first galaxies in the universe. We use a modified version of our faint satellite detection algorithm to enable detection of ultra-faint background galaxies that highly magnified and sheared through gravitational lensing by the massive foreground clusters. Our algorithms enable us to detect ultra-faint sources in two-orbit deep HST observations that with other methods were only detected in much deeper 42-orbit deep HST observations.
In the figure on the left, the background image shows the scalar magnification field (blue to red) and vector shear field (lines) for Frontier Fields cluster MACS J1149.5+2223 produced by our team (Johnson, Sharon+16), based on a lens model from bright multiply lensed background galaxies. Left: A 4''x8'' region from the 2-orbit HST-ACS F814W CLASH image in the high magnification/shear region of MACS J1149.5+2223; log scale. Middle: Segmentation image of detected sources after running our cluster lens model informed maximum likelihood detection method. The CLASH catalog shows only two detections in this region (yellow and orange, both zphot=3). We however, detect 3 additional sources with greater than 5 significance. Right: The same region and scale but from the 42-orbit HST-ACS F814W Frontier Fields survey. All of the maximum likelihood detected images from the 2-orbit image are verified in the much deeper 42-orbit image. Note that some sources within the green region are apparent but were not detected, such as the source to the upper-right of the orange source, however none of these show significant signs of shear (i.e.~they are consistent with the PSF), thus they did not have significant likelihood of being lensed background galaxies, which are the focus of our effort. Regardless, it might be possible to detect such faint PSF-like sources in the shallow CLASH survey images with our method if we had used more than one band for detection and a PSF-like model.


MACHO 2

LLNL led a microlensing survey in the 1990’s to detect Massive Compact Halo Objects (MACHOs). The optical telescope observing campaign measured the changes in the flux of stars over time to find the distinctive orders-of-magnitude flux magnification of a massive object passing across the line-of-sight. We are now pursuing a similar survey that covers longer time baselines – and thus is sensitive to more massive objects – with modern wide-field imaging instruments.
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Characteristic time scale for microlensing events as a function of the IM MACHO mass and distance between us and the MW bulge.
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Existing microlensing constraints on the fraction of the mass in the MW halo that can be composed of IM MACHO dark matter. We seek to extend the existing MACHO microlensing constraint to higher masses. The mass of the LIGO (2015) black holes are indicated in orange.
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We have experience with dense stellar fields. This is a raw and reduced images from MC2 low galactic latitude Subaru observations. Instrument rotation between exposures enables elimination of image systematics associated with bright stellar fields (e.g. bleeding). This enabled the first weak lensing measurement at low galactic latitudes.

Blind Detection of Ultra-faint Streaks with a Maximum Likelihood Method

Check out the paper.
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Synthesis of Disparate Optical Imaging Data for Space Domain Awareness

Check out the paper.
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Copyright © 2012 William Dawson