Bingxiao Xu Johns Hopkins University Outlines Science motivation Automate arcfinder Test the arcfinder by simulations Priliminary results Future prospects Why Giant Arcs The abundance of the giant arcs is sensitive to the inner structure of the clusters and cosmology ID: 213489
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Slide1
Finding and Characterizing the Giant Arcs
Bingxiao Xu
Johns Hopkins UniversitySlide2
Outlines
Science motivation
Automate arcfinder
Test the arcfinder by simulations
Priliminary results
Future prospectsSlide3
Why Giant Arcs?
The abundance of the giant arcs is sensitive to the inner structure of the clusters and cosmology
The enhanced signal-to-noise ratio allows us to resolve the substructures within the highly magnified objectsSlide4
Advantages of CLASH samples
Less biased selection
Depth: ~20 orbits per cluster
Higher limiting mag for arc detection
Higher resolution for substructure
Extensive multi-bands imaging
Redshift distribution of giant arcs
Stellar population within the highly
magnified galaxiesSlide5
Arc detection algorithm
Set intensity threshold as positive median value of the difference of Gaussian (DoG) images, to obtain the image segmentation
Use eccentricity to filter out the less elongated featuresSlide6
Gradient based algorithm
Calculate the intensity gradient of the each pixel to obtain an orientation map
quantize the orientation into 4 directions and assign a digit to each pixel (1,2,3,4)Slide7
Maximum supression
The intensity of the pixels on the arc's rigid line should be larger than that of the adjacent pixel along its gradient direction and opposite direction
Slide8
Shift the pixels to local maximaSlide9
Intensity-INDEPENDENT pixel selection
The orientation of the pixels close to the arc's rigid lines should not change much
The intensity value of the pixels close to the arc's rigid lines experience in the DoG and original image during the shifting should be positiveSlide10Slide11
Orientation Criteria
The tangential arc’s orientation should be perpendicular to the line connecting the arc and the center of cluster
Turn off the criteria at the very center (r < 100 pix ) to preserve the radial arcs Slide12
Removal of the star spikesSlide13
Test the arcfinder
(Furlanetto et al. 2013)Slide14
Detection rate testSlide15
Contamination rate testSlide16
Preliminary Results Slide17
Preliminary Results ( 176 arcs )Slide18
Future Prospects
Arc statistics
Distribution of the Einstein radius
De-lensing the giant arcs to study galaxy formation and evolution at high redshift Slide19
Arc Statistics
Order of magnitude discrepancy (Bartelmann M., et al 1998) recent works! No longer discrepancy, but tension still exists...
Possible solutions
Central BCGs and substructure (Hennawi et al. 2007; Meneghetti et al 2010)
Triaxiality of clusters (Oguri et al. 2003)
Major merger (Torri et al. 2004; Fedeli et al. 2006)
Distribution of the background sources (Wambsganss et al. 2004; Dalal et al. 2004)
…… there is still a factor of 2 discrepancy out there