2012A&A...543L...6G

An anomaly in the distribution of quasar magnitudes based on the Sloan Digital Sky survey, was reported by Longo. The angular size of this quasar anomaly is on the order of ±15° on the sky. A smooth low surface brightness structure detected in γ-rays and at 408MHz, coincides with the sky location and extent of the anomaly, and is close to the northern component of a pair of γ-ray bubbles discovered in the Fermi Gamma-ray Space Telescope survey. Molecular clouds are thought to be illuminated by cosmic rays. Molecular gas in the Galaxy, in the form of cold H₂, may be a significant component of dark matter as suggested by Pfenniger et al. I test the hypothesis that the magnitude anomaly in the quasar distribution, is due to lensing by a hypothetical supergiant molecular cloud (SGMC) either in or falling into the Galactic halo. A series of grid lens models are built by assuming that a SGMC is a fractal structure constructed with clumps of 10^–3M_☉, 10AU in size, and considering various fractal dimensions. Local amplifications are computed by using the single-plane approximation. A complex network of caustics due to the clumpy structure is present. Our best single plane lens model capable of explaining Longo's effect, at least in sparse regions, requires a mass (1.5-4.1)x10¹⁰M_☉ within 8.7x8.7x(5-8.6)kpc³ at a lens plane distance of 20kpc, and is constructed from a molecular-cloud building-block of 5x10⁵M_☉ within a scale of 30pc expanded by fractal scaling with dimension D=1.8-2 out to 5-8.6kpc for the SGMC. The mass budget depends on the cloud depth and on the fractal dimension. If such a SGMC were found to exist, it may provide at least part of a lensing explanation for the luminous anomaly discovered in quasars and red galaxies.