S319p.75 — Correcting High-Redshift Galaxy Luminosity Functions for Gravitational Lensing Magnification Bias

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Aug 10th at 6:00 PM until 6:00 PM

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Author(s): Charlotte Mason5, Tommaso Treu4, Kasper Borello Schmidt4, Thomas Collett1, Michele Trenti6, Philip Marshall2, Robert Barone-Nugent6, Larry Bradley3, Massimo Stiavelli3, Stuart Wyithe6

Institution(s): 1. Institute for Cosmology and Gravitation, University of Portsmouth, 2. Kavli Institute for Particle Astrophysics and Cosmology, Stanford University, 3. Space Telescope Science Institute, 4. University of California, Los Angeles, 5. University of California, Santa Barbara, 6. University of Melbourne

We present a Bayesian framework to account for the magnification bias from strong, intermediate and weak gravitational lensing in estimates of high-redshift galaxy UV luminosity functions (LFs), which is expected to significantly modify the bright-end of the LF. We illustrate our method by estimating the z ~ 8 UV LF using a sample of 97 Y-band dropouts (Lyman-break galaxies) found in the Brightest of Reionizing Galaxies (BoRG) survey and from the HUDF. We find the LF is well described by a Schechter function with parameters consistent within the uncertainties of those inferred from the same sample without accounting for the magnification bias (Schmidt et al. 2014), demonstrating that the effect is small for current surveys at z ~ 8. Hence we find that magnification bias alone cannot account for the apparent overdensity of z ~ 7 bright galaxies compared to a Schechter function found recently by Bowler et al. (2014a,b) and Finkelstein et al. (2014). Using a range of theoretical LFs we conclude that magnification bias will dominate wide-field surveys – such as those planned for the Euclid and WFIRST missions – especially at z > 10. In order to derive accurate estimates of high-redshift LFs in these surveys and to distinguish between galaxy formation models it will be vital to account for the magnification bias. We show that magnification bias can be an additional tool to probe the high-redshift universe and demonstrate this via a physical model for the UV LF at z > 8.