Comment on 'a slightly oblate dark matter halo revealed by a retrograde precessing Galactic disk warp' by Huang et al

Abstract

Huang et al. (2024) measured the derivative of the phase ${\varphi }_{\mathrm{w}}$ of the Galactic warp traced by classical Cepheids with respect to their age $\tau$ and interpreted it as the warp precession rate $\omega \equiv \mathrm{d}{\varphi }_{\mathrm{w}}/\mathrm{d}t=-\mathrm{d}{\varphi }_{\mathrm{w}}/\mathrm{d}\tau$. This interpretation is unfounded: young stars follow trajectories close to those of their parental gas and trace the instantaneous gas warp, not its shape at their time of birth: ${\varphi }_{\mathrm{w}}$ should hardly depend on Cepheid age. We show that the measured $\mathrm{d}{\varphi }_{\mathrm{w}}/\mathrm{d}\tau >0$ is consistent with an omitted-variable bias from neglecting the natural twist $\mathrm{d}{\varphi }_{\mathrm{w}}/\mathrm{d}R$ of the warp and the $R$-$\tau$ correlation for Cepheids (originating from the Galactic metallicity gradient and the Cepheid metallicity-age correlation).

3 pages, 2 figures, Comment on arXiv:2407.00319