Abstract
The observed properties of high redshift galaxies depend on the underlying foreground distribution of large scale structure, which distorts their intrinsic properties via gravitational lensing. We focus on the regime where the dominant contribution originates from a single lens and examine the statistics of gravitational lensing by a population of virialized and non-virialized structures using sub-mm galaxies at z ~ 2.6 and Lyman-break galaxies at redshifts z ~ 6 - 15 as the background sources. We quantify the effect of lensing on the luminosity function of the high redshift sources, focusing on the intermediate and small magnifications, mu < 2, which affect the majority of the background galaxies, and comparing to the case of strong lensing. We show that, depending on the intrinsic properties of the background galaxies, gravitational lensing can significantly affect the observed luminosity function even when no obvious strong lenses are present. Finally, we find that in the case of the Lyman-break galaxies it is important to account for the surface brightness profiles of both the foreground and the background galaxies when computing the lensing statistics, which introduces a selection criterion for the background galaxies that can actually be observed. Not taking this criterion into account leads to an overestimation of the number densities of very bright galaxies by nearly two orders of magnitude.
Highlights
The detection of high-redshift galaxies is a primary frontier in observational cosmology
We considered the effects of gravitational lensing on the luminosity functions of Lyman-break galaxies (LBGs) at z ~ 6-10 and sub-millimeter galaxies at z ~ 2-4 in the regime when a single lens makes a dominant contribution
The regime of intermediate lensing was not studied in the literature and may appear to be important for future precise analysis of these two populations of sources when observed by instruments such as Hubble Space Telescope (HST), James Webb Space Telescope (JWST), Atacama Large Millimeter/submillimeter Array (ALMA), and Herschel
Summary
The detection of high-redshift galaxies is a primary frontier in observational cosmology. A reliable number counts of resolved sources from this population are being provided for the first time (Karim et al 2013) by the Atacama Large Millimeter/submillimeter Array (ALMA) Another population of high-redshift sources that is not well constrained at the moment are the galaxies existing during the epoch of reionization and observed in their rest-frame UV at redshifts out to z ~ 10 by the Wide Field Camera 3 infrared channel (WFC3/IR, Kimble et al 2008) on board the Hubble Space Telescope (HST), with plans to push this frontier to even higher redshifts with the James Webb Space Telescope (JWST). Galaxies that are not strongly lensed still undergo magnification (or demagnification) by foreground structure and can be mildly magnified without being multiply imaged In this case the effect of lensing can be overlooked, leading to an overprediction (or underprediction) of the number counts of background galaxies, and to an erroneous estimation of their properties. Throughout this work, we adopt the standard set of cosmological parameters (Ade et al et al 2014)
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