The Circumgalactic Medium

Image: T. Müller / J. Stern

J. Stern: "The video shows a reconstruction of the distribution of gas around low-redshift, Milky-Way-sized galaxies. The reconstruction is based on a new photoionization modeling method for CGM absorption lines surveys, which I developed in Stern et al. (2016) and applied to the COS-Halos survey. The new method relaxes the assumption used by almost all previous studies that the absorbing gas has a single density and physical scale, instead allowing the gas to span a range of densities and scales. Our analysis suggests an absorbing gas mass which is < 20% of gas mass estimates based on standard modeling methods. The new method can be applied to additional surveys of CGM absorption lines. The realization shown in the video is described in section 4.4 of the paper."

The hierarchical cloud data is structured as follows: the main cloud (R = 280kpc) encompasses 57 clouds (level 0, L0, 35kpc). Each of these L0-clouds encompasses 45 clouds (level 1, L1, 3.9kpc) and each of these L1-clouds again encompasses 45 clouds (level 2, L2, 440pc). This continues until level 4 (5.5pc) where we have 233'735'625 clouds. The density of each level increases by a factor of 10 compared to the previous level.

Sampling all clouds in one large volume for later ray casting is unfeasible. Hence, a hierarchical rendering was developed based on view frustum culling, hierarchical loading of cloud data, sphere intersection calculation, sorting of intersections for correct blending, and early ray termination.

The video was produced in cooperation with  Jonathan Stern (MPIA) and Joe Hennawi (MPIA).

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