Phase spirals in cosmological simulations of Milky Way-sized galaxies

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We study the vertical perturbations in the galactic disc of the Milky Way-size high-resolution hydrodynamical cosmological simulation named GARROTXA. We detect phase spirals in the vertical projection Z - V-Z of disc's stellar particles for the first time in this type of simulations. Qualitatively similar structures were detected in the recent Gaia data, and their origin is still under study. In our model, the spiral-like structures in the phase space are present in a wide range of times and locations across the disc. By accounting for an evolving mix of stellar populations, we observe that, as seen in the data, the phase spirals are better observed in the range of younger-intermediate star particles. We measure the intensity of the spiral with a Fourier decomposition and find that these structures appear stronger near satellite pericentres. Current dynamical models of the phase spiral considering a single perturber required a mass at least of the order of 10(10) M-circle dot, but all three of our satellites have masses of the order of similar to 10(8) M-circle dot. We suggest that there are other mechanisms at play which appear naturally in our model such as the physics of gas, collective effect of multiple perturbers, and a dynamically cold population that is continuously renovated by the star formation. Complementing collisionless isolated N-body models with the use of fully cosmological simulations with enough resolution can provide new insights into the nature/origin of the phase spiral.
The authors wish to thank the anonymous Referee for her/his comments and suggestions that improved this work. BGC and SRF work has been supported by the Madrid Government (Comunidad de Madrid-Spain) under the Multiannual Agreement with Complutense University in the line Program to Stimulate Research for Young Doctors in the context of the V PRICIT. They also acknowledge financial support from the Spanish Ministry of Economy and Competitiveness (MINECO) under grant number AYA2016-75808-R, AYA2017-90589-REDT, and S2018/NMT-429, and from the CAMUCM under grant number PR65/19-22462. SRF acknowledges support from a Spanish postdoctoral fellowship, under grant number 2017-T2/TIC-5592. TA acknowledges the grant RYC2018-025968I funded by MCIN/AEI/10.13039/501100011033 and by `ESF Investing in your future'. This work was (partially) funded by the Spanish MICIN/AEI/10.13039/501100011033 and by `ERDF A way of making Europe' by the `European Union' through grant RTI2018095076-B-C21, and the Institute of Cosmos Sciences University of Barcelona (ICCUB, Unidad de Excelencia 'María de Maeztu') through grant CEX2019-000918-M. PR acknowledges support by the Agence Nationale de la Recherche (ANR project SEGAL ANR19-CE31-0017 and project ANR-18-CE31-0006) as well as from the European Research Council (ERC grant agreement No. 834148). Simulations were performed on the MIZTLI supercomputer at the DGTIC, UNAM, within the research project LANCAD-UNAMDGTIC-151.
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