Can we use weak lensing to measure total mass profiles of galaxies on 20 kpc scales?
Current constraints on dark matter density profiles from weak lensing are typically limited to radial scales greater than 50–100 kpc. In this paper, we explore the possibility of probing the very inner regions of galaxy/halo density profiles by measuring stacked weak lensing on scales of only a few tens of kpc. Our forecasts focus on scales smaller than the 'equality radius' (R_eq), where the stellar component and the dark matter component contribute equally to the lensing signal. We compute the evolution of R_eq as a function of lens stellar mass and redshift and show that R_eq = 7–34 kpc for galaxies with M* = 10^(9.5)–10^11.5 M_⊙. Unbiased shear measurements will be challenging on these scales. We introduce a simple metric to quantify how many source galaxies overlap with their neighbours and for which shear measurements will be challenging. Rejecting source galaxies with close-by companions results in an ∼20 per cent decrease in the overall source density. Despite this decrease, we show that Euclid and Wide Field Infrared Survey Telescope will be able to constrain galaxy/halo density profiles at Req with S/N >20 for M_* > 10^10 M_⊙. Weak lensing measurements at Req, in combination with stellar kinematics on smaller scales, will be a powerful means by which to constrain both the inner slope of the dark matter density profile as well as the mass and redshift dependence of the stellar initial mass function.
© 2015 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2015 February 24. Received 2015 February 19; in original form 2014 December 3. First published online March 30, 2015. We are grateful to the referee for a careful reading of the manuscript and for providing thoughtful comments. We thank Robert Lupton for useful discussions during the preparation of this paper and Naoshi Sugiyama for practical advice during the data analysis. This work, AL, and SM are supported by World Premier International Research Center Initiative (WPI Initiative), MEXT, Japan. MINK acknowledges the financial support from N. Sugiyama (25287057) by Grants-in-Aid from the Ministry of Education, Culture, Sports, Science, and Technology of Japan. NO (26800097) is supported by Grants-in-Aid from the Ministry of Education, Culture, Sports, Science, and Technology of Japan. CL is supported by the ILP LABEX (under reference ANR-10-LABX-63 and ANR-11-IDEX-0004-02). JR was supported by JPL, run under a contract for NASA by Caltech. TTT has been supported by the Grant-in-Aid for the Scientific Research Fund (23340046), for the Global COE Program Request for Fundamental Principles in the Universe: from Particles to the Solar system and the Cosmos, and for the JSPS Strategic Young Researcher Overseas Visits Program for Accelerating Brain Circulation, commissioned by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan.
Submitted - 1502.06604v1.pdf
Published - MNRAS-2015-Kobayashi-2128-43.pdf