The Sheet of Giants: Unusual properties of the Milky Way’s immediate neighbourhood

Neuzil, Maria; Mansfield, Philip; Kravtsov, Andrey V.

doi:10.1093/mnras/staa898

Cited by 28 publications

(19 citation statements)

References 105 publications

(172 reference statements)

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“…Nonetheless, the potential bright-end discrepancy is reminiscent of similar tensions noted for Local Volume field (Neuzil et al 2020) and satellite (Carlsten et al 2020b) galaxies when compared with models that differ from ours in detail, hinting at a more systematic issue that may exist in various theoretical predictions, including those from hydrodynamical simulations. The flexibility of our model allows us to quantify the possible sources of the tension and to study potential solutions.…”

Section: Discussionsupporting

confidence: 65%

The SAGA Survey. II. Building a Statistical Sample of Satellite Systems around Milky Way-like Galaxies

Mao,

Geha,

Wechsler

et al. 2020

Preprint

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We present the Stage II results from the ongoing Satellites Around Galactic Analogs (SAGA) Survey. Upon completion, the SAGA Survey will spectroscopically identify satellite galaxies brighter than M r,o = −12.3 around one hundred Milky Way (MW) analogs at z ∼ 0.01. In Stage II we have more than quadrupled the sample size of Stage I, delivering results from 127 satellites around 36 MW analogs, with an improved target selection strategy and deep photometric imaging catalogs from the Dark Energy Survey and the Legacy Surveys. We have obtained 25,372 galaxy redshifts, peaking around z = 0.2. These data significantly increase spectroscopic coverage for very low-redshift objects in 17 < r o < 20.75 around SAGA hosts, creating a unique data set that places the Local Group in a wider context. The number of confirmed satellites per system ranges from 0 to 9, and correlates with host galaxy luminosity and brightest satellite luminosity. We find that the number and the luminosities of MW satellites are consistent with being drawn from the same underlying distribution as SAGA systems. The majority of confirmed SAGA satellites are star forming, and the quenching fraction increases as satellite stellar mass and projected radius from the host galaxy decrease. Overall, the satellite quenching fraction among SAGA systems is lower than that in the Local Group. We compare the luminosity functions and radial distributions of SAGA satellites with theoretical predictions based on Cold Dark Matter simulations and an empirical galaxy-halo connection model, and find that the results are broadly in agreement.

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Section: Discussionsupporting

confidence: 65%

The SAGA Survey. II. Building a Statistical Sample of Satellite Systems around Milky Way-like Galaxies

Mao,

Geha,

Wechsler

et al. 2020

Preprint

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“…In the hierarchical assembly that characterizes CDM , this is the natural result of DM haloes formed in overdense environments. Recent studies find that the MW lives in a region of 8 Mpc radius that is 2.5σ overdense with respect to the mean matter density (Neuzil, Mansfield & Kravtsov 2020). Constrained hydrodynamical simulations that reproduce the high-density large-scale environment of the Local Group indeed predict a relatively early assembly of the Galaxy (Carlesi et al 2020), which confirms this scenario.…”

Section: Discussion a N D C O N C L U S I O N Ssupporting

confidence: 55%

The kinematics of globular cluster populations in the E-MOSAICS simulations and their implications for the assembly history of the Milky Way

Trujillo-Gomez

Kruijssen

Reina-Campos

et al. 2021

Monthly Notices of the Royal Astronomical Society

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We present a detailed comparison of the Milky Way (MW) globular cluster (GC) kinematics with the 25 Milky Way-mass cosmological simulations from the E-MOSAICS project. While the MW falls within the kinematic distribution of GCs spanned by the simulations, the relative kinematics of its metal-rich ($[\rm {Fe}/\rm {H}]>-1.2$) versus metal-poor ($[\rm {Fe}/\rm {H}]<-1.2$), and inner (r < 8 kpc) versus outer (r > 8 kpc) populations are atypical for its mass. To understand the origins of these features, we perform a comprehensive statistical analysis of the simulations, and find 18 correlations describing the assembly of L* galaxies and their dark matter haloes based on their GC population kinematics. The correlations arise because the orbital distributions of accreted and in-situ GCs depend on the masses and accretion redshifts of accreted satellites, driven by the combined effects of dynamical fraction, tidal stripping, and dynamical heating. Because the kinematics of in-situ/accreted GCs are broadly traced by the metal-rich/metal-poor and inner/outer populations, the observed GC kinematics are a sensitive probe of galaxy assembly. We predict that relative to the population of L* galaxies, the MW assembled its dark matter and stellar mass rapidly through a combination of in-situ star formation, more than a dozen low-mass mergers, and 1.4 ± 1.2 early (z = 3.1 ± 1.3) major mergers. The rapid assembly period ended early, limiting the fraction of accreted stars. We conclude by providing detailed quantitative predictions for the assembly history of the MW.

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“…Connecting LG hosts to a statistical sample of similar hosts will be crucial in evaluating the significance of planar alignments and the validity of proposed formation mechanisms, demonstrating the need for large surveys with e.g., the Nancy Grace Roman Space Telescope, which promises to significantly augment the observational sample of MW analogues. LG galaxies are also aligned with large scale structure, along a local sheet, which is not captured in our simulations and may play a part in the formation of satellite planes (Neuzil et al 2020). Simulations that can accurately reproduce this large scale structure may offer new insight into satellite planes (Libeskind et al 2020).…”

Section: Discussionmentioning

confidence: 84%

Planes of satellites around Milky Way/M31-mass galaxies in the FIRE simulations and comparisons with the Local Group

Samuel

Wetzel

Chapman

et al. 2021

Monthly Notices of the Royal Astronomical Society

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We examine the prevalence, longevity, and causes of planes of satellite dwarf galaxies, as observed in the Local Group. We use 14 Milky Way/Andromeda-(MW/M31) mass host galaxies from the FIRE-2 simulations. We select the 14 most massive satellites by stellar mass within dhost ≤ 300 kpc of each host and correct for incompleteness from the foreground galactic disc when comparing to the MW. We find that MW-like planes as spatially thin and/or kinematically coherent as observed are uncommon, but they do exist in our simulations. Spatially thin planes occur in 1–2 per cent of snapshots during z = 0 − 0.2, and kinematically coherent planes occur in 5 per cent of snapshots. These planes are generally transient, surviving for <500 Myr. However, if we select hosts with an LMC-like satellite near first pericenter, the fraction of snapshots with MW-like planes increases dramatically to 7 − 16 per cent, with lifetimes of 0.7 − 3 Gyr, likely because of group accretion of satellites. We find that M31’s satellite distribution is much more common: M31’s satellites lie within ∼1σ of the simulation median for every plane metric we consider. We find no significant difference in average satellite planarity for isolated hosts versus hosts in LG-like pairs. Baryonic and dark matter-only simulations exhibit similar levels of planarity, even though baryonic subhaloes are less centrally concentrated within their host haloes. We conclude that planes of satellites are not a strong challenge to ΛCDM cosmology.

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The Sheet of Giants: Unusual properties of the Milky Way’s immediate neighbourhood

Cited by 28 publications

References 105 publications

The SAGA Survey. II. Building a Statistical Sample of Satellite Systems around Milky Way-like Galaxies

The SAGA Survey. II. Building a Statistical Sample of Satellite Systems around Milky Way-like Galaxies

The kinematics of globular cluster populations in the E-MOSAICS simulations and their implications for the assembly history of the Milky Way

Planes of satellites around Milky Way/M31-mass galaxies in the FIRE simulations and comparisons with the Local Group

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