Orientations of Dark Matter Halos in FIRE-2 Milky Way–mass Galaxies

Creators: Baptista, Jay^{1, 2, 3}; Sanderson, Robyn^{4, 5}; Huber, Dan²; Wetzel, Andrew⁶; Sameie, Omid⁷; Boylan-Kolchin, Michael⁷; Bailin, Jeremy⁸; Hopkins, Philip F.⁹; Faucher-Giguere, Claude-André¹⁰; Chakrabarti, Sukanya^{8, 11}; Vargya, Drona⁴; Panithanpaisal, Nondh⁴; Arora, Arpit⁴; Cunningham, Emily⁵

1. Yale University
2. University of Hawaii at Manoa
3. Stanford University
4. University of Pennsylvania
5. Flatiron Institute
6. University of California, Davis
7. The University of Texas at Austin
8. University of Alabama
9. California Institute of Technology
10. Northwestern University
11. Institute for Advanced Study

Abstract

The shape and orientation of dark matter (DM) halos are sensitive to the microphysics of the DM particles, yet in many mass models, the symmetry axes of the Milky Way's DM halo are often assumed to be aligned with the symmetry axes of the stellar disk. This is well motivated for the inner DM halo, but not for the outer halo. We use zoomed-in cosmological baryonic simulations from the Latte suite of FIRE-2 Milky Way–mass galaxies to explore the evolution of the DM halo's orientation with radius and time, with or without a major merger with a Large Magellanic Cloud analog, and when varying the DM model. In three of the four cold DM halos we examine, the orientation of the halo minor axis diverges from the stellar disk vector by more than 20° beyond about 30 galactocentric kpc, reaching a maximum of 30°–90°, depending on the individual halo's formation history. In identical simulations using a model of self-interacting DM with σ = 1 cm² g⁻¹, the halo remains aligned with the stellar disk out to ∼200–400 kpc. Interactions with massive satellites (M ≳ 4 × 10¹⁰M_⊙ at pericenter; M ≳ 3.3 × 10¹⁰M_⊙ at infall) affect the orientation of the halo significantly, aligning the halo's major axis with the satellite galaxy from the disk to the virial radius. The relative orientation of the halo and disk beyond 30 kpc is a potential diagnostic of self-interacting DM, if the effects of massive satellites can be accounted for.

Copyright and License

Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

Acknowledgement

J.B. acknowledges support from the Research Experience for Undergraduates program at the Institute for Astronomy, the University of Hawaii-Mānoa, funded through NSF grant #2050710. J.B. thanks the Institute for Astronomy for their hospitality during the development of this project. J.B. also acknowledges support from the Yale Science, Technology and Research Scholars (STARS) Fellowship program, funded by the Yale College Dean's Office.

J.B., R.E.S., S.C., and D.H. gratefully acknowledge support from NSF grant AST-2007232.

R.E.S. additionally acknowledges support from NASA grant 19-ATP19-0068, from the Research Corporation through the Scialog Fellows program on Time Domain Astronomy, and from HST-AR-15809 from the Space Telescope Science Institute (STScI), which is operated by AURA, Inc., under NASA contract NAS5-26555.

M.B.K. acknowledges support from NSF CAREER award AST-1752913, NSF grants AST-1910346 and AST-2108962, NASA grant 80NSSC22K0827, and HST-AR-15809, HST-GO-15658, HST-GO-15901, HST-GO-15902, HST-AR-16159, and HST-GO-16226 from STScI.

C.A.F.G. was supported by the NSF through grants AST-1715216, AST-2108230, and CAREER award AST-1652522; by NASA through grants 17-ATP17-0067 and 21-ATP21-0036; by STScI through grants HST-AR-16124.001-A and HST-GO-16730.016-A; by CXO through grant TM2-23005X; and by the Research Corporation for Science Advancement through a Cottrell Scholar Award.

A.W. received support from: the NSF, via CAREER award AST-2045928 and grant AST-2107772; NASA ATP grant 80NSSC20K0513; and HST grants AR-15809, GO-15902, and GO-16273 from STScI.

Support for P.F.H. was provided by NSF Research Grants 1911233, 20009234, and 2108318; NSF CAREER grant 1455342; and NASA grants 80NSSC18K0562 and HST-AR-15800. The numerical calculations were run on the Caltech compute cluster "Wheeler," allocations AST21010 and AST20016, supported by the NSF and TACC, and NASA HEC SMD-16-7592.

This project was made possible by the computing cluster resources provided by the Flatiron Institute Center for Computational Astrophysics.

Data Availability

The FIRE-2 simulations (Wetzel et al. 2023) are publicly available at http://flathub.flatironinstitute.org/fire. Additional FIRE simulation data are available at https://fire.northwestern.edu/data. A public version of the Gizmo code is available at http://www.tapir.caltech.edu/~phopkins/Site/GIZMO.html.

Latte snapshots for m12i, m12f, and m12m are also available at ananke.hub.yt and binder.flatironinstitute.org/~rsanderson/ananke.

The code and the associated data files generated as part of this analysis are available on Zenodo at doi:10.5281/zenodo.8174926 (Baptista 2023).

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Resource type: Journal Article
Publisher: American Astronomical Society
Published in: Astrophysical Journal, 958(1), 44, ISSN: 0004-637X.
Languages: English