2021/05/31 by Zhaozhou Li, Zhao-Zhou Li, Jiaxin Han · 13 citations
Physics and Astronomy · #Astrophysics #Astrophysics and Star Formation Studies #Dark matter halo #Dwarf galaxy #Galaxies: Formation, Evolution, Phenomena #Galaxy #Halo #Milky Way #Physics #RADIUS #Stellar, planetary, and galactic studies #Virial mass #Virial theorem #astro-ph.CO #astro-ph.GA
paper · pdf · doi:10.3847/2041-8213/ac0a7f
published in The Astrophysical Journal Letters 915(1), L18 (IOP Publishing) · 9 pages, 4 figures; accepted to ApJL
openalex publication_date 2021/07/01 · arxiv created 2021/07/04 · arxiv updated 2021/07/06 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/06
Abstract We measure for the first time the outermost edges of the Milky Way (MW) halo in terms of the depletion and turnaround radii. The inner depletion radius, r id , identified at the location of maximum infall velocity, separates a growing halo from the draining environment, while the turnaround radius, r ta , marks the outermost edge of infalling material toward the halo, both of which are located well outside the virial radius. Using the motions of nearby dwarf galaxies within 3 Mpc, we obtain a marginal detection of the infall zone around the MW with a maximum velocity of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>v</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>inf</mml:mi> <mml:mo>,</mml:mo> <mml:mi>max</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mo>−</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>46</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>39</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>24</mml:mn> </mml:mrow> </mml:msubsup> <mml:mspace width="0.25em"/> <mml:mi>km</mml:mi> <mml:mspace width="0.33em"/> <mml:msup> <mml:mrow> <mml:mi mathvariant="normal">s</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:math> . This enables us to measure r id = 559 ± 107 kpc and r ta = 839 ± 121 kpc. The measured depletion radius is about 1.5 times the MW virial radius ( R 200m ) measured from internal dynamics. Compared with halos in the cosmological simulation Illustris TNG100, the factor 1.5 is consistent with that of halos with similar masses and dynamical environments to the MW but slightly smaller than typical values of Local Group analogs, potentially indicating the unique evolution history of the MW. These measurements of halo edges directly quantify the ongoing evolution of the MW outer halo and provide constraints on the current dynamical state of the MW that are independent from internal dynamics.