Comment on ‘a slightly oblate dark matter halo revealed by a retrograde precessing Galactic disk warp’ by Huang et al
Walter Dehnen, Ralph Sch"onrich, Ronald Drimmel, v{Z}ofia Chrob’akov’a, Eloisa Poggio, Marcin Semczuk
arXiv:2407.06341v1 Announce Type: new
Abstract: Huang et al. (2024) measured the derivative of the phase $phi_{mathrm{w}}$ of the Galactic warp traced by classical Cepheids with respect to their age $tau$ and interpreted it as the warp precession rate $omegaequivmathrm{d}phi_{mathrm{w}}/mathrm{d}t=-mathrm{d}phi_{mathrm{w}}/mathrm{d}tau$. 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: $phi_{mathrm{w}}$ should hardly depend on Cepheid age. We show that the measured $mathrm{d}phi_{mathrm{w}}/mathrm{d}tau>0$ is consistent with an omitted-variable bias from neglecting the natural twist $mathrm{d}phi_{mathrm{w}}/mathrm{d}R$ of the warp and the $R$-$tau$ correlation for Cepheids (originating from the Galactic metallicity gradient and the Cepheid metallicity-age correlation).arXiv:2407.06341v1 Announce Type: new
Abstract: Huang et al. (2024) measured the derivative of the phase $phi_{mathrm{w}}$ of the Galactic warp traced by classical Cepheids with respect to their age $tau$ and interpreted it as the warp precession rate $omegaequivmathrm{d}phi_{mathrm{w}}/mathrm{d}t=-mathrm{d}phi_{mathrm{w}}/mathrm{d}tau$. 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: $phi_{mathrm{w}}$ should hardly depend on Cepheid age. We show that the measured $mathrm{d}phi_{mathrm{w}}/mathrm{d}tau>0$ is consistent with an omitted-variable bias from neglecting the natural twist $mathrm{d}phi_{mathrm{w}}/mathrm{d}R$ of the warp and the $R$-$tau$ correlation for Cepheids (originating from the Galactic metallicity gradient and the Cepheid metallicity-age correlation).