Correcting the z ̃ 8 Galaxy Luminosity Function for Gravitational Lensing Magnification Bias
Abstract
We present a Bayesian framework to account for the magnification bias from both strong and weak gravitational lensing in estimates of highredshift galaxy luminosity functions (LFs). We illustrate our method by estimating the z ̃ 8 UV LF using a sample of 97 Yband dropouts (Lyman break galaxies) found in the Brightest of Reionizing Galaxies (BoRG) survey and from the literature. We find the LF is well described by a Schechter function with characteristic magnitude of {{M}^{\star }}=19.85_{0.35}^{+0.30}, faintend slope of α =1.72_{0.29}^{+0.30}, and number density of {{log }_{10}}{{{\Psi }}^{\star }}(Mp{{c}^{3}})=3.00_{0.31}^{+0.23}. These parameters are consistent within the uncertainties with those inferred from the same sample without accounting for the magnification bias, demonstrating that the effect is small for current surveys at z ̃ 8, and cannot account for the apparent overdensity of bright galaxies compared to a Schechter function found recently by Bowler et al. and Finkelstein et al. We estimate that the probability of finding a strongly lensed z ̃ 8 source in our sample is in the range ̃315% depending on limiting magnitude. We identify one strongly lensed candidate and three cases of intermediate lensing in BoRG (estimated magnification μ > 1.4) in addition to the previously known candidate groupscale strong lens. 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. Magnification bias will need to be accounted for in order to derive accurate estimates of highredshift LFs in these surveys and to distinguish between galaxy formation models.
 Publication:

The Astrophysical Journal
 Pub Date:
 May 2015
 DOI:
 10.1088/0004637X/805/1/79
 arXiv:
 arXiv:1502.03795
 Bibcode:
 2015ApJ...805...79M
 Keywords:

 galaxies: highredshift;
 galaxies: luminosity function;
 mass function;
 gravitational lensing: strong;
 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 Accepted for publication in ApJ. 20 pages, 13 figures