The Milky Way, an Exceptionally Quiet Galaxy: Implications for the Formation of Spiral Galaxies

118

We use ∼ 100 cosmological galaxy formation 'zoom-in' simulations using the smoothed particle hydrodynamics code gasoline to study the effect of baryonic processes on the mass profiles of cold dark matter haloes. The haloes in our study range from dwarf (M 200 ∼ 10 10 M ⊙ ) to Milky Way (M 200 ∼ 10 12 M ⊙ ) masses. Our simulations exhibit a wide range of halo responses, primarily varying with mass, from expansion to contraction, with up to factor ∼ 10 changes in the enclosed dark matter mass at 1 per cent of the virial radius. Confirming previous studies, the halo response is correlated with the integrated efficiency of star formation:In addition, we report a new correlation with the compactness of the stellar system: ǫ R ≡ r 1/2 /R 200 . We provide an analytic formula depending on ǫ SF and ǫ R for the response of cold dark matter haloes to baryonic processes. An observationally testable prediction is that, at fixed mass, larger galaxies experience more halo expansion, while the smaller galaxies more halo contraction. This diversity of dark halo response is captured by a toy model consisting of cycles of adiabatic inflow (causing contraction) and impulsive gas outflow (causing expansion). For net outflow, or equal inflow and outflow fractions, f , the overall effect is expansion, with more expansion with larger f . For net inflow, contraction occurs for small f (large radii), while expansion occurs for large f (small radii), recovering the phenomenology seen in our simulations. These regularities in the galaxy formation process provide a step towards a fully predictive model for the structure of cold dark matter haloes.

Section: Discussionmentioning

confidence: 71%

NIHAO IX: the role of gas inflows and outflows in driving the contraction and expansion of cold dark matter haloes

Dutton

Macciò

Dekel³

et al. 2016

118

“…Klypin et al 1999) and whether our Galaxy is an archetypical spiral galaxy comparing to other local spiral galaxies (e.g. Hammer et al 2007). As introduced in Section 1, the RC provides the most fundamental, direct probe of the mass distribution of the Milky Way.…”

Section: Galactic Mass Models and The Fit Resultsmentioning

confidence: 96%

The Milky Way's rotation curve out to 100 kpc and its constraint on the Galactic mass distribution

Huang

Liu

Yuan

et al. 2016

160

179

The rotation curve (RC) of the Milky Way out to ∼ 100 kpc has been constructed using ∼ 16, 000 primary red clump giants (PRCGs) in the outer disk selected from the LSS-GAC and the SDSS-III/APOGEE survey, combined with ∼ 5700 halo K giants (HKGs) selected from the SDSS/SEGUE survey. To derive the RC, the PRCG sample of the warm disc population and the HKG sample of halo stellar population are respectively analyzed using a kinematical model allowing for the asymmetric drift corrections and re-analyzed using the spherical Jeans equation along with measurements of the anisotropic parameter β currently available. The typical uncertainties of RC derived from the PRCG and HKG samples are respectively 5-7 km s −1 and several tens km s −1 . We determine a circular velocity at the solar position, V c (R 0 ) = 240 ± 6 km s −1 and an azimuthal peculiar speed of the Sun, V ⊙ = 12.1 ± 7.6 km s −1 , both in good agreement with the previous determinations. The newly constructed RC has a generally flat value of 240 km s −1 within a Galactocentric distance r of 25 kpc and then decreases steadily to 150 km s −1 at r ∼ 100 kpc. On top of this overall trend, the RC exhibits two prominent localized dips, one at r ∼ 11 kpc and another at r ∼ 19 kpc. From the newly constructed RC, combined with other constraints, we have built a parametrized mass model for the Galaxy, yielding a virial mass of the Milky Way's dark matter halo of 0.90 +0.07 −0.08 × 10 12 M ⊙ and a local dark matter density, ρ ⊙,dm = 0.32 +0.02 −0.02 GeV cm −3 .

“…7 is that the stellar mass of the primary galaxies is below recent estimates for either the MW (5.2 × 10 10 M , according to Bovy & Rix 2013) or M31 (1.03 × 10 11 M , according to Hammer et al 2007). Indeed, none of our 24 primaries has masses exceeding 5 × 10 10 M , a consequence of the low virial masses of our selected LG pairs coupled with the relatively low galaxy formation efficiency of the EAGLE 'Ref' model in ∼10 12 M haloes.…”

Section: Most Massive Satellitesmentioning

confidence: 88%

The apostle project: Local Group kinematic mass constraints and simulation candidate selection

Fattahi

Navarro

Sawala

et al. 2016

214

268

We use a large sample of isolated dark matter halo pairs drawn from cosmological N-body simulations to identify candidate systems whose kinematics match that of the Local Group of Galaxies (LG). We find, in agreement with the "timing argument" and earlier work, that the separation and approach velocity of the Milky Way (MW) and Andromeda (M31) galaxies favour a total mass for the pair of ∼ 5 × 10 12 M ⊙ . A mass this large, however, is difficult to reconcile with the small relative tangential velocity of the pair, as well as with the small deceleration from the Hubble flow observed for the most distant LG members. Halo pairs that match these three criteria have average masses a factor of ∼ 2 times smaller than suggested by the timing argument, but with large dispersion, spanning more than a decade in mass. Guided by these results, we have selected 12 halo pairs with total mass in the range 1.6-3.6 × 10 12 M ⊙ for the APOSTLE project (A Project Of Simulations of The Local Environment), a suite of resimulations at various numerical resolution levels (reaching up to ∼ 10 4 M ⊙ per gas particle) that use the hydrodynamical code and subgrid physics developed for the EA-GLE project. These simulations reproduce, by construction, the main kinematics of the MW-M31 pair, and produce satellite populations whose overall number, luminosities, and kinematics are in good agreement with observations of the MW and M31 companions. These diagnostics are sensitive to the total mass assumed for the MW-M31 pair; indeed, the LG satellite population would be quite difficult to reproduce for pair masses as high as indicated by the timing argument. The APOSTLE candidate systems thus provide an excellent testbed to confront directly many of the predictions of the ΛCDM cosmology with observations of our local Universe.