C. Lu, K. Schlaufman, and S. Cheng. (2020)cite arxiv:2009.06638Comment: 13 pages, 6 figures, and 6 Tables in aastex63 format; accepted for publication in AJ.
F. Vogt, E. Pérez, M. Dopita, L. Verdes-Montenegro, and S. Borthakur. (2017)cite arxiv:1701.01728Comment: 12 pages, 11 figures, accepted for publication in A&A. Supplementary movie assocociated with Fig. 8 is available (until publication) at: http://www.sc.eso.org/~fvogt/supp_mat/HCG91c/O_gradient.mp4.