Speaker: Bart Wakker

Title: How Small-scale Structure Affects the Measured N(HI)

Abstract: We compared HI column densities from Lyα data toward 59 AGNs with 21-cm data using 10–36 arcmin beams. The ratio N(Lyα) / N(21-cm) on average is 0.8–0.9, with a dispersion of ~0.1. The shape of the distribution can be explained by 3D MHD simulations, but the offset in the average ratio is not understood. There is also a systematic difference in the N(GBT) / N(LAB) ratio.

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