Dust-induced reversal of the optical wavelength dependence of spiral-arm pitch angles
- 1Secretaría de Ciencia, Humanidades, Tecnología e Innovación (SECIHTI), Av. Insurgentes Sur 1582 Colonia Crédito Constructor , Benito Juárez, Ciudad de México , , C.P. 03940
- 2Instituto Nacional de Astrofísica, Óptica y Electrónica , Luis E. Erro 1, Tonantzintla, Puebla , , C.P. 72840
- 3Instituto de Radioastronomía y Astrofísica , UNAM, Campus Morelia, Michoacán , , C.P. 58089
Abstract
The classical density-wave scenario predicts a blue-to-red age–colour gradient across the spiral arms of disc galaxies as a consequence of shock-induced star formation. However, observations of spiral-arm pitch angles at different wavelengths sometimes suggest the opposite trend, namely a red-to-blue “colour jump”. The origin of this apparent contradiction remains unclear. In this work, we investigate the effects of dust attenuation on post-shock stellar emission, together with the streamline motions of gas and stellar populations. We find that dust attenuation in regions with relatively high optical depths, τ ̂V ≳ 0.2, can produce an apparent red-to-blue spatial sequence, with respect to the shock location, by reversing the relative positions of the flux maxima of stellar populations observed in different bands. Moreover, streamline motions confine post-shock stellar populations near the spiral arms for longer than in a circular-orbit model, thereby modifying the spatial distribution of the emitted light. We conclude that the apparent red-to-blue colour jump does not necessarily contradict the classical density-wave scenario. Instead, it can arise from the same post-shock stellar populations that intrinsically produce a blue-to-red age–colour gradient if their emission is modified by dust attenuation.
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BibTeX
@article{martinezgarcia2026dustinduced,
title = {{Dust-induced reversal of the optical wavelength dependence of spiral-arm pitch angles}},
author = {Eric E Martínez-García and Rosa A González-Lópezlira and Ivânio Puerari and A I Gómez-Ruiz},
journal = {Monthly Notices of the Royal Astronomical Society},
year = {2026},
month = nov,
doi = {10.1093/mnras/stag2099},
url = {https://academic.oup.com/mnras/advance-article/doi/10.1093/mnras/stag2099/9011269},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Dust-induced reversal of the optical wavelength dependence of spiral-arm pitch angles
AU - Eric E Martínez-García
AU - Rosa A González-Lópezlira
AU - Ivânio Puerari
AU - A I Gómez-Ruiz
PY - 2026
DA - 2026/11/03
JO - Monthly Notices of the Royal Astronomical Society
DO - 10.1093/mnras/stag2099
UR - https://academic.oup.com/mnras/advance-article/doi/10.1093/mnras/stag2099/9011269
AB - The classical density-wave scenario predicts a blue-to-red age–colour gradient across the spiral arms of disc galaxies as a consequence of shock-induced star formation. However, observations of spiral-arm pitch angles at different wavelengths sometimes suggest the opposite trend, namely a red-to-blue “colour jump”. The origin of this apparent contradiction remains unclear. In this work, we investigate the effects of dust attenuation on post-shock stellar emission, together with the streamline motions of gas and stellar populations. We find that dust attenuation in regions with relatively high optical depths, τ ̂_V ≳ 0.2, can produce an apparent red-to-blue spatial sequence, with respect to the shock location, by reversing the relative positions of the flux maxima of stellar populations observed in different bands. Moreover, streamline motions confine post-shock stellar populations near the spiral arms for longer than in a circular-orbit model, thereby modifying the spatial distribution of the emitted light. We conclude that the apparent red-to-blue colour jump does not necessarily contradict the classical density-wave scenario. Instead, it can arise from the same post-shock stellar populations that intrinsically produce a blue-to-red age–colour gradient if their emission is modified by dust attenuation.
SN - 0035-8711
SN - 1365-2966
ER -