The Mass of the Milky Way from the H3 Survey

Shen, Jeff; Eadie, Gwendolyn; Murray, Norman; Zaritsky, Dennis; Speagle, Joshua S.; Ting, Yuan-Sen; Conroy, Charlie; Cargile, Phillip A.; Johnson, Benjamin D.; Naidu, Rohan P.; Han, Jiwon Jesse

doi:10.3847/1538-4357/ac3a7a

“…At z = 0, the mass of the MW host halo in both our CDM and SIDM simulation is 1.6 × 10 12 M e . This mass is consistent with many recent MW mass measurements (e.g., see Shen et al 2022 for a recent compilation). Furthermore, the virial concentration of both our CDM and SIDM host halos is c NFW = 11.4, which is also broadly consistent with the inferred concentration of the MW halo (e.g., Callingham et al 2019).…”

Section: Cosmological Zoom-in Simulationssupporting

confidence: 91%

Strong Dark Matter Self-interactions Diversify Halo Populations within and surrounding the Milky Way

Yang

¹

,

Nadler

²

,

Yu

³

2023

ApJ

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We perform a high-resolution cosmological zoom-in simulation of a Milky Way (MW)–like system, which includes a realistic Large Magellanic Cloud analog, using a large differential elastic dark matter self-interaction cross section that reaches ≈100 cm2 g−1 at relative velocities of ≈10 km s−1, motivated by the diverse and orbitally dependent central densities of dwarf galaxies within and surrounding the MW. We explore the effects of dark matter self-interactions on satellite, splashback, and isolated halos through their abundance, central densities, maximum circular velocities, orbital parameters, and correlations between these variables. We use an effective constant cross section model to analytically predict the stages of our simulated halos’ gravothermal evolution, demonstrating that deviations from the collisionless R max – V max relation can be used to select deeply core-collapsed halos, where V max is a halo’s maximum circular velocity, and R max is the radius at which it occurs. We predict that a sizable fraction (≈20%) of subhalos with masses down to ≈108 M ⊙ is deeply core collapsed in our SIDM model. Core-collapsed systems form ≈10% of the isolated halo population down to the same mass; these isolated, core-collapsed halos would host faint dwarf field galaxies with extremely steep central density profiles. Finally, most halos with masses above ≈109 M ⊙ are core-forming in our simulation. Our study thus demonstrates how self-interactions diversify halo populations in an environmentally dependent fashion within and surrounding MW-mass hosts, providing a compelling avenue to address the diverse dark matter distributions of observed dwarf galaxies.

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“…The Milky Way's outer halo contains significant substructure, and is in fact dominated by it. Due to the prominence of these disequilibrium structures, any efforts to measure the Milky Way's properties in the outer halo-from its mass to the perturbative response of its dark matter halo (e.g., Garavito-Camargo et al 2019Shen et al 2022)-will require more sophisticated and timedependent modeling (e.g., Vasiliev et al 2021;Koposov et al 2023;Lilleengen et al 2023).…”

Section: An Outer Halo In Disequilibriummentioning

confidence: 99%

Distant Echoes of the Milky Way’s Last Major Merger

Chandra

¹

,

Naidu

²

,

Conroy

³

et al. 2023

ApJ

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The majority of the Milky Way’s stellar halo consists of debris from our galaxy’s last major merger, the Gaia-Sausage-Enceladus (GSE). In the past few years, stars from the GSE have been kinematically and chemically studied in the inner 30 kpc of our galaxy. However, simulations predict that accreted debris could lie at greater distances, forming substructures in the outer halo. Here we derive metallicities and distances using Gaia DR3 XP spectra for an all-sky sample of luminous red giant stars, and map the outer halo with kinematics and metallicities out to 100 kpc. We obtain follow-up spectra of stars in two strong overdensities—including the previously identified outer Virgo Overdensity—and find them to be relatively metal rich and on predominantly retrograde orbits, matching predictions from simulations of the GSE merger. We argue that these are apocentric shells of GSE debris, forming 60–90 kpc counterparts to the 15–20 kpc shells that are known to dominate the inner stellar halo. Extending our search across the sky with literature radial velocities, we find evidence for a coherent stream of retrograde stars encircling the Milky Way from 50 to 100 kpc, in the same plane as the Sagittarius Stream but moving in the opposite direction. These are the first discoveries of distant and structured imprints from the GSE merger, cementing the picture of an inclined and retrograde collision that built up our galaxy’s stellar halo.

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“…Another constraint on the mass and extent of the plasma in the MW halo comes from radio observations of pulsars in the Large and Small Magellanic Clouds (LMC and SMC; e.g., Ridley et al 2013). The LMC and SMC are located ∼50 and 60 kpc away, respectively (Pietrzyński et al 2019;Graczyk et al 2020), but this distance is only a small fraction of the virial radius of the MW (using the definition of Bryan & Norman 1998, current estimates of the latter are typically between 180 and 250 kpc; Bovy 2015;Cautun et al 2020;Shen et al 2022).…”

Section: Introductionmentioning

confidence: 99%

An FRB Sent Me a DM: Constraining the Electron Column of the Milky Way Halo with Fast Radio Burst Dispersion Measures from CHIME/FRB

Cook

¹

,

Bhardwaj

²

,

Gaensler

³

et al. 2023

ApJ

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The CHIME/FRB project has detected hundreds of fast radio bursts (FRBs), providing an unparalleled population to statistically probe the foreground media that they illuminate. One such foreground medium is the ionized halo of the Milky Way (MW). We estimate the total Galactic electron column density from FRB dispersion measures (DMs) as a function of Galactic latitude using four different estimators, including ones that assume spherical symmetry of the ionized MW halo and ones that imply more latitudinal variation in density. Our observation-based constraints of the total Galactic DM contribution for ∣b∣ ≥ 30°, depending on the Galactic latitude and selected model, span 87.8–141 pc cm−3. This constraint implies upper limits on the MW halo DM contribution that range over 52–111 pc cm−3. We discuss the viability of various gas density profiles for the MW halo that have been used to estimate the halo’s contribution to DMs of extragalactic sources. Several models overestimate the DM contribution, especially when assuming higher halo gas masses (∼3.5 × 1012 M ⊙). Some halo models predict a higher MW halo DM contribution than can be supported by our observations unless the effect of feedback is increased within them, highlighting the impact of feedback processes in galaxy formation.

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The Mass of the Milky Way from the H3 Survey

Cited by 23 publications

References 90 publications

Strong Dark Matter Self-interactions Diversify Halo Populations within and surrounding the Milky Way

Strong Dark Matter Self-interactions Diversify Halo Populations within and surrounding the Milky Way

Distant Echoes of the Milky Way’s Last Major Merger

An FRB Sent Me a DM: Constraining the Electron Column of the Milky Way Halo with Fast Radio Burst Dispersion Measures from CHIME/FRB

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