Voigt, L. M. and Bridle, S. L. and Amara, A. and Cropper, M. and Kitching, T. D. and Massey, R. and Rhodes, J. and Schrabback, T. (2012) The impact of galaxy colour gradients on cosmic shear measurement. Monthly Notices of the Royal Astronomical Society, 421 (2). pp. 1385-1398. ISSN 0035-8711 http://resolver.caltech.edu/CaltechAUTHORS:20120508-155304331
Full text not available from this repository.
Use this Persistent URL to link to this item: http://resolver.caltech.edu/CaltechAUTHORS:20120508-155304331
Cosmic shear has been identified as the method with the most potential to constrain dark energy. To capitalize on this potential, it is necessary to measure galaxy shapes with great accuracy, which in turn requires a detailed model for the image blurring by the telescope and atmosphere, the point spread function (PSF). In general, the PSF varies with wavelength and therefore the PSF integrated over an observing filter depends on the spectrum of the object. For a typical galaxy the spectrum varies across the galaxy image, thus the PSF depends on the position within the image. We estimate the bias on the shear due to such colour gradients by modelling galaxies using two co-centred, co-elliptical Sérsic profiles, each with a different spectrum. We estimate the effect of ignoring colour gradients and find the shear bias from a single galaxy can be very large depending on the properties of the galaxy. We find that halving the filter width reduces the shear bias by a factor of about 5. We show that, to the first order, tomographic cosmic shear two point statistics depend on the mean shear bias over the galaxy population at a given redshift. For a single broad filter, and averaging over a small galaxy catalogue from Simard et al., we find a mean shear bias which is subdominant to the predicted statistical errors for future cosmic shear surveys. However, the true mean shear bias may exceed the statistical errors, depending on how accurately the catalogue represents the observed distribution of galaxies in the cosmic shear survey. We then investigate the bias on the shear for two-filter imaging and find that the bias is reduced by at least an order of magnitude. Lastly, we find that it is possible to calibrate galaxies for which colour gradients were ignored using two-filter imaging of a fair sample of noisy galaxies, if the galaxy model is known. For a signal-to-noise ratio of 25 the number of galaxies required in each tomographic redshift bin is of the order of 10^4.
|Additional Information:||© 2012 The Authors. Monthly Notices of the Royal Astronomical Society © 2012 RAS. Accepted 2011 December 15. Received 2011 December 14; in original form 2011 May 29. Article first published online: 1 Feb 2012. We are grateful to Lance Miller, Gary Bernstein, Catherine Heymans, Henk Hoekstra, Stefano Andreon, Eduardo Cypriano, Marcella Carollo, Ignacio Ferreras, Ewan Cameron, Alexandre Refregier, Michael Seiffert, Kevin Bundy, Stephane Paulin- Henrikkson, Anais Rassat, Donnacha Kirk, Ole Host, Filipe Abdalla, Ofer Lahav, Chris Hirata and Sam Thompson for helpful discussions. LMV acknowledges support from the STFC. SLB thanks the Royal Society for support in the form of a University Research Fellowship and the European Research Council for support in the form of a Starting Grant. TDK is supported by a RAS 2010 Fellowship. RJM thanks STFC for support in the form of an Advanced Fellowship. JR was supported by the Jet Propulsion Laboratory, operated by the California Institute of Technology under a contract for NASA. TS acknowledges support from NSF through grant AST-0444059-001, and the Smithsonian Astrophysics Observatory through grant GO0-11147A.|
|Subject Keywords:||gravitational lensing: weak; cosmology: observations; large scale structure of Universe|
|Official Citation:||Voigt, L. M., Bridle, S. L., Amara, A., Cropper, M., Kitching, T. D., Massey, R., Rhodes, J. and Schrabback, T. (2012), The impact of galaxy colour gradients on cosmic shear measurement. Monthly Notices of the Royal Astronomical Society, 421: 1385–1398. doi: 10.1111/j.1365-2966.2011.20395.x|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Ruth Sustaita|
|Deposited On:||09 May 2012 17:26|
|Last Modified:||09 May 2012 17:26|
Repository Staff Only: item control page