Reality or Mirage? Observational Test and Implications for the Claimed Extremely Magnified Quasar at z = 6.3

Abstract

Abstract In the last two decades, approximately 200 quasars have been discovered at , hosting active supermassive black holes with masses . While these sources reflect only the tip of the iceberg of the black hole mass distribution, their detection challenges standard growth models. The most massive black hole that was inferred thus far (J0100+2802, ) was recently claimed to be lensed, with a magnification factor . Here, we perform a consistency check of this claim, finding that the detection of such a source requires a bright-end slope for the intrinsic quasar luminosity function (LF), . Commonly used values of are rejected at . If the claim is confirmed, it is very unlikely that all the remaining 51 sources in the Sloan Digital Sky Survey sample are not magnified. Furthermore, it suffices that of the remaining sources are lensed for the intrinsic LF to differ significantly (i.e., ) from the observed one. The presence of additional extremely magnified sources in the sample would lower the requirement to . Our results urge the community to perform more extended multiwavelength searches targeting lensed quasars, also among known samples. This effort could vitally contribute to solving the open problem of the growth of the brightest quasars.