TITLE:
Ellipticity of dark matter halos with galaxy-galaxy weak lensing.
AUTHOR(S):
Rachel Mandelbaum, Christopher M. Hirata, Tamara Broderick, Uros Seljak (Princeton Univ.); Jonathan Brinkmann (APO).
DATE:
2005 Jul 05 (arXiv, v1, posted); 2005 Jul 05 (MNRAS, submitted); 2006 Apr 30 (revised); 2006 May 10 (MNRAS, accepted); 2006 May 10
(arXiv, v2, posted); 2006 Jun 22 (MNRAS, published).
AVAILABILITY:
arXiv astro-ph/0507108 (free);
Blackwell Synergy
(requires subscription).
PUBLICATION INFORMATION: MNRAS 370, 1008--1024 (2006).
ABSTRACT:
We present the results of attempts to detect the ellipticity of dark matter halos using galaxy-galaxy weak lensing with SDSS data. We
use 2,020,256 galaxies brighter than r=19 with photometric redshifts (divided into colour and luminosity subsamples) as lenses and
31,697,869 source galaxies. We search for and identify several signal contaminants, which if not removed lead to a spurious detection.
These include systematic shear that leads to a slight spurious alignment of lens and source ellipticities, intrinsic alignments (due to
contamination of the source sample by physically-associated lens source pairs), and anisotropic magnification bias. We develop methods
that allow us to remove these contaminants to the signal. We split the analysis into blue (spiral) and red (elliptical) galaxies.
Assuming Gaussian errors as in previous work and a power-law profile, we find fh=eh/eg=0.1+/-0.06 for
red galaxies and -0.8+/-0.4 for
blue galaxies using 20-300 kpc/h, averaged over luminosity. Inclusion of the more realistic non-Gaussian error distributions and of the
NFW density profile (which predicts much smaller ellipticity of the shear for scales above the scale radius) yields 0.60+/-0.38 for
ellipticals and -1.4+1.7-2.0 for spirals. While there is no concrete detection of alignment in either case, there is a suggestion in the
data of a positive alignment in the brightest lens sample of ellipticals. Our results appear to be mildly inconsistent with a previously
reported detection by Hoekstra et al. (2004), but more data and further tests are needed to clarify whether the discrepancy is real or a
consequence of differences in the lens galaxy samples used and analysis methods.
ADS BIBLIOGRAPHIC CODE: 2006MNRAS.370.1008M
COMMENTS: SDSS Publication #518. The paper by Hoekstra et al. is here.