Laboratory tests of hypotheses for the super-solar Fe abundance problem in black hole accretion disks

We will present data of the first ever Fe L-shell x-ray emission spectra from laboratory photoionized plasmas on the Z facility. Such data have been a laboratory astrophysics goal for two decades but are even more critical now because of the "Super-Solar" Fe abundance problem. Fe abundances in accretion disks inferred from x-ray spectra emitted by photoionized plasma surrounding about a dozen black holes appear to contain 5-20 times more iron than the Sun. This contradicts the widely held expectation that most objects in the universe have the Sun's composition. One prevailing theory is that effects of high electron density are not properly accounted for in the models. Reinterpreting the x-ray spectra with updated high density models resolved much of the discrepancy partly because of differences predicted in the Fe L-shell emission features. However, laboratory benchmarks for photoionized plasma models have not been available until now. The platform mimics the photon flux, density, and temperature conditions in black hole accretion disks, and we control the composition, uniformity, and spectral resolution. We also measured photoionized calcium K-shell spectra as a surrogate for Fe K-shell spectra from black holes. The relativistically broadened iron K emission features also have the potential to strongly influence black hole fundamental parameters. We will describe our progress using the data to evaluate model accuracy and its potential to inform the Super-Solar Fe abundance problem.