Other
Scientific paper
May 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011aas...21823502b&link_type=abstract
American Astronomical Society, AAS Meeting #218, #235.02; Bulletin of the American Astronomical Society, Vol. 43, 2011
Other
Scientific paper
Cosmic shear, the distortion of galaxy images by weak lensing, induces correlated ellipticities in the images of galaxies that are not physically close to one another. However, correlated galaxy images may also occur by mechanisms other than lensing (e.g., the galaxy formation process, or physical interactions after galaxy formation, may induce correlations in the images of galaxies that are close to one another). Such "intrinsic" alignments occur naturally in CDM and in shallow surveys (e.g., the SDSS) correlated ellipticities due to intrinsic alignments dominate over the correlated ellipticities due to cosmic shear. Because of the challenges of detecting and interpreting correlated galaxy images, the weak lensing community is now investigating cosmic magnification as a complement to cosmic shear.
Cosmic magnification alters the clustering of galaxies. Lensing dilutes the local number density of galaxies because the area of a given patch of sky is increased. Also, since lensing conserves surface brightness, additional sources are added to the sample due to the fact that their images are magnified sufficiently that their lensed magnitudes fall within the magnitude limit of the data. The net effect is either a suppression or enhancement of the number density of galaxies, depending upon the logarithmic slope of the number counts. Here we present a preliminary measurement of cosmic magnification using SDSS galaxies. We compute the angular cross-correlation of foreground and background galaxies, using a combination of spectroscopic and photometric redshifts to define the foreground and background populations. The foreground and background are separated by a sufficient amount that they are not physically correlated. Therefore, any observed clustering of the foreground with the background is a sign of cosmic magnification. Lastly, we investigate the dependence of the lensing-induced cross-correlation on physical properties of the foreground galaxies.
This work was supported in part by the National Science Foundation.
Brainerd Tereasa G.
Wenger T. V.
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