scholarly journals The Magellanic Group and the Seven Dwarfs

2008 ◽  
Vol 4 (S256) ◽  
pp. 473-478 ◽  
Author(s):  
Elena D'Onghia ◽  
George Lake
Keyword(s):  
Velocity Distribution ◽  
Galaxy Formation ◽  
Milky Way ◽  
Dwarf Galaxies ◽  
Magellanic Clouds ◽  
Tidal Disruption ◽  
Circular Velocity ◽  
Orbital Configuration

AbstractThe Magellanic Clouds were the largest members of a group of dwarf galaxies that entered the Milky Way (MW) halo at late times. This group, dominated by the LMC, contained ~4% of the mass of the Milky Way prior to its accretion and tidal disruption, but ≈70% of the known dwarfs orbiting the MW. Our theory addresses many outstanding problems in galaxy formation associated with dwarf galaxies. First, it can explain the planar orbital configuration populated by some dSphs in the MW. Second, it provides a mechanism for lighting up a subset of dwarf galaxies to reproduce the cumulative circular velocity distribution of the satellites in the MW. Finally, our model predicts that most dwarfs will be found in association with other dwarfs. The recent discovery of Leo V (Belokurov et al. 2008), a dwarf spheroidal companion of Leo IV, and the nearby dwarf associations supports our hypothesis.

scholarly journals The VMC survey

2020 ◽  
Vol 641 ◽  
pp. A134
Author(s):  
Thomas Schmidt ◽  
Maria-Rosa L. Cioni ◽  
Florian Niederhofer ◽  
Kenji Bekki ◽  
Cameron P. M. Bell ◽  
...  
Keyword(s):  
Proper Motion ◽  
Milky Way ◽  
Dwarf Galaxies ◽  
Dynamical Evolution ◽  
Large Magellanic Cloud ◽  
Small Population ◽  
Magellanic Cloud ◽  
Magellanic Clouds ◽  
Proper Motions ◽  
Flow Motion

Context. The Magellanic Clouds are a nearby pair of interacting dwarf galaxies and satellites of the Milky Way. Studying their kinematic properties is essential to understanding their origin and dynamical evolution. They have prominent tidal features and the kinematics of these features can give hints about the formation of tidal dwarfs, galaxy merging and the stripping of gas. In addition they are an example of dwarf galaxies that are in the process of merging with a massive galaxy. Aims. The goal of this study is to investigate the kinematics of the Magellanic Bridge, a tidal feature connecting the Magellanic Clouds, using stellar proper motions to understand their most recent interaction. Methods. We calculated proper motions based on multi-epoch Ks-band aperture photometry, which were obtained with the Visible and Infrared Survey Telescope for Astronomy (VISTA), spanning a time of 1−3 yr, and we compared them with Gaia Data Release 2 (DR2) proper motions. We tested two methods for removing Milky Way foreground stars using Gaia DR2 parallaxes in combination with VISTA photometry or using distances based on Bayesian inference. Results. We obtained proper motions for a total of 576 411 unique sources over an area of 23 deg2 covering the Magellanic Bridge including mainly Milky Way foreground stars, background galaxies, and a small population of possible Magellanic Bridge stars (< 15 000), which mostly consist of giant stars with 11.0 <  Ks <  19.5 mag. The first proper motion measurement of the Magellanic Bridge centre is 1.80 ± 0.25 mas yr−1 in right ascension and −0.72 ± 0.13 mas yr−1 in declination. The proper motion measurements of stars along the Magellanic Bridge from the VISTA survey of the Magellanic Cloud system (VMC) and Gaia DR2 data confirm a flow motion from the Small to the Large Magellanic Cloud. This flow can now be measured all across the entire length of the Magellanic Bridge. Conclusions. Our measurements indicate that the Magellanic Bridge is stretching. By converting the proper motions to tangential velocities, we obtain ∼110 km s−1 in the plane of the sky. Therefore it would take a star roughly 177 Myr to cross the Magellanic Bridge.

scholarly journals Subhalo destruction in the Apostle and Auriga simulations

2019 ◽  
Vol 492 (4) ◽  
pp. 5780-5793 ◽  
Author(s):  
Jack Richings ◽  
Carlos Frenk ◽  
Adrian Jenkins ◽  
Andrew Robertson ◽  
Azadeh Fattahi ◽  
...  
Keyword(s):  
Dark Matter ◽  
Velocity Distribution ◽  
Galaxy Formation ◽  
Milky Way ◽  
State Of The Art ◽  
Systematic Errors ◽  
Mass Function ◽  
New Method ◽  
The Galaxy

ABSTRACT N-body simulations make unambiguous predictions for the abundance of substructures within dark matter haloes. However, the inclusion of baryons in the simulations changes the picture because processes associated with the presence of a large galaxy in the halo can destroy subhaloes and substantially alter the mass function and velocity distribution of subhaloes. We compare the effect of galaxy formation on subhalo populations in two state-of-the-art sets of hydrodynamical Λcold dark matter (ΛCDM) simulations of Milky Way mass haloes, Apostle and Auriga. We introduce a new method for tracking the orbits of subhaloes between simulation snapshots that gives accurate results down to a few kiloparsecs from the centre of the halo. Relative to a dark matter-only simulation, the abundance of subhaloes in Apostle is reduced by 50 per cent near the centre and by 10 per cent within r200. In Auriga, the corresponding numbers are 80 per cent and 40 per cent. The velocity distributions of subhaloes are also affected by the presence of the galaxy, much more so in Auriga than in Apostle. The differences on subhalo properties in the two simulations can be traced back to the mass of the central galaxies, which in Auriga are typically twice as massive as those in Apostle. We show that some of the results from previous studies are inaccurate due to systematic errors in the modelling of subhalo orbits near the centre of haloes.

scholarly journals The Milky Way’s stellar streams and globular clusters do not align in a Vast Polar Structure

2020 ◽  
Vol 494 (1) ◽  
pp. 983-1001 ◽  
Author(s):  
Alexander H Riley ◽  
Louis E Strigari
Keyword(s):  
Galaxy Formation ◽  
Globular Cluster ◽  
Globular Clusters ◽  
Milky Way ◽  
Data Sets ◽  
Open Problems ◽  
Polar Structure ◽  
Dark Energy Survey ◽  
Stellar Streams ◽  
Orbital Configuration

ABSTRACT There is increasing evidence that a substantial fraction of Milky Way satellite galaxies align in a rotationally supported plane of satellites, a rare configuration in cosmological simulations of galaxy formation. It has been suggested that other Milky Way substructures (namely young halo globular clusters and stellar/gaseous streams) similarly tend to align with this plane, accordingly dubbed the Vast Polar Structure (VPOS). Using systemic proper motions inferred from Gaia data, we find that globular cluster orbital poles are not clustered in the VPOS direction, though the population with the highest VPOS membership fraction is the young halo clusters (∼30 per cent). We additionally provide a current census of stellar streams, including new streams discovered using the Dark Energy Survey and Gaia data sets, and find that stellar stream normals are also not clustered in the direction of the VPOS normal. We also find that, based on orbit modelling, there is a likely association between NGC 3201 and the Gjöll stellar stream and that, based on its orbital pole, NGC 4147 is likely not a Sagittarius globular cluster. That the Milky Way’s accreted globular clusters and streams do not align in the same planar configuration as its satellites suggests that the plane of satellites is either a particularly stable orbital configuration or a population of recently accreted satellites. Neither of these explanations is particularly likely in light of other recent studies, leaving the plane of satellites problem as one of the more consequential open problems in galaxy formation and cosmology.

scholarly journals Tidal disruption of the Magellanic Clouds by the Milky Way

Nature ◽  
10.1038/29466 ◽  
1998 ◽  
Vol 394 (6695) ◽  
pp. 752-754 ◽  
Author(s):  
M. E. Putman ◽  
B. K. Gibson ◽  
L. Staveley-Smith ◽  
G. Banks ◽  
D. G. Barnes ◽  
...  
Keyword(s):  
Milky Way ◽  
Magellanic Clouds ◽  
Tidal Disruption

scholarly journals Extremely metal-poor stars in dwarf galaxies

2009 ◽  
Vol 5 (S265) ◽  
pp. 237-240
Author(s):  
Anna Frebel ◽  
Joshua D. Simon ◽  
Evan Kirby ◽  
Marla Geha ◽  
Beth Willman
Keyword(s):  
Galaxy Formation ◽  
Milky Way ◽  
Dwarf Galaxies ◽  
Formation Model ◽  
Abundance Pattern ◽  
Halo Stars ◽  
Abundance Patterns ◽  
Upper Limits ◽  
Stellar Halo ◽  
Metallicity Distribution

AbstractWe present Keck/HIRES spectra of six metal-poor stars in two of the ultra-faint dwarf galaxies orbiting the Milky Way, Ursa Major II and Coma Berenices, and a Magellan/MIKE spectrum of a star in the classical dwarf spheroidal galaxy (dSph) Sculptor. Our data include the first high-resolution spectroscopic observations of extremely metal-poor stars ([Fe/H] < −3.0) not belonging to the Milky Way (MW) stellar halo field population. We obtain abundance measurements and upper limits for up to 26 elements between carbon and europium. The stars span a range of −3.8 < [Fe/H] < −2.3, with the ultra-faints having large spreads in Fe. A comparison with MW halo stars of similar metallicity reveals substantial agreement between the abundance patterns of the ultra-faint dwarf galaxies and Sculptor and the MW halo for the light, α and iron-peak elements (C to Zn). This agreement contrasts with the results of earlier studies of more metal-rich stars (−2.5 ≲[Fe/H]≲ −1.0) in more luminous dwarfs, which found significant abundance discrepancies with respect to the MW halo data. The abundances of neutron-capture elements (Sr to Eu) in all three galaxies are extremely low, consistent with the most metal-poor halo stars, but not with the typical halo abundance pattern at [Fe/H]≳ −3.0. Our results are broadly consistent with a galaxy formation model which predicts that massive dwarf galaxies are the source of the metal-rich component ([Fe/H]≳ −2.5) of the MW inner halo, but we propose that dwarf galaxies similar to the dSphs are the primary contributors to the metal-poor end of the metallicity distribution of the MW outer halo.

scholarly journals Are Disks of Satellites Comprised of Tidal Dwarf Galaxies?

Galaxies ◽  
2021 ◽  
Vol 9 (4) ◽  
pp. 100
Author(s):  
Michal Bílek ◽  
Ingo Thies ◽  
Pavel Kroupa ◽  
Benoit Famaey
Keyword(s):  
Galaxy Formation ◽  
Milky Way ◽  
Dwarf Galaxies ◽  
Initial Conditions ◽  
Proper Motions ◽  
Promising Alternative ◽  
Open Questions ◽  
Nearby Galaxies ◽  
First Time ◽  
Tidal Tails

It was found that satellites of nearby galaxies can form flattened co-rotating structures called disks of satellites or planes of satellites. Their existence is not expected by the current galaxy formation simulations in the standard dark matter-based cosmology. On the contrary, modified gravity offers a promising alternative: the objects in the disks of satellites are tidal dwarf galaxies, that is, small galaxies that form from tidal tails of interacting galaxies. After introducing the topic, we review here our work on simulating the formation of the disks of satellites of the Milky Way and Andromeda galaxies. The initial conditions of the simulation were tuned to reproduce the observed positions, velocities and disk orientations of the galaxies. The simulation showed that the galaxies had a close flyby 6.8 Gyr ago. One of the tidal tails produced by the Milky Way was captured by Andromeda. It formed a cloud of particles resembling the disk of satellites at Andromeda by its size, orientation, rotation and mass. A hint of a disk of satellites was formed at the Milky Way too. In addition, the encounter induced a warp in the disk of the simulated Milky Way that resembles the real warp by its magnitude and orientation. We present here, for the first time, the proper motions of the members of the disk of satellites of Andromeda predicted by our simulation. Finally, we point out some of the remaining open questions which this hypothesis, for the formation of disks of satellites, brings up.

Structure of dark matter haloes of Milky Way satellite galaxies in SIDM universes

2018 ◽  
Vol 14 (S344) ◽  
pp. 498-501
Author(s):  
Takashi Okamoto
Keyword(s):  
Dark Matter ◽  
Cross Section ◽  
Galaxy Formation ◽  
Luminosity Function ◽  
Milky Way ◽  
Dwarf Galaxies ◽  
Interaction Cross Section ◽  
Large Cross Section ◽  
Stellar Feedback ◽  
Satellite Galaxies

AbstractSelf-interacting dark matter (SIDM) can create sufficiently large cores in dark matter haloes of dwarf galaxies if the self-interaction cross-section is sufficiently large on scales of dwarf galaxies. Such a large cross-section can be realized without changing the densities and shapes of cluster-size haloes by introducing a velocity dependent cross-section. Lowering the central densities of dwarf-size haloes, however, may change the strength of stellar feedback required to reproduce observed properties of dwarf galaxies such as the luminosity function of the Milky Way’s satellite galaxies. We perform simulations of galaxy formation by employing such a velocity dependent self-interaction cross-section to investigate the coupled effect of SIDM and feedback.

scholarly journals The missing dwarf galaxies of the Local Group

2020 ◽  
Vol 493 (2) ◽  
pp. 2596-2605 ◽  
Author(s):  
Azadeh Fattahi ◽  
Julio F Navarro ◽  
Carlos S Frenk
Keyword(s):  
Galaxy Formation ◽  
Milky Way ◽  
Local Group ◽  
Dwarf Galaxies ◽  
Dwarf Galaxy ◽  
Wide Field ◽  
Mass Relation ◽  
Galaxy Masses ◽  
Galaxy Population ◽  
Formation Efficiency

ABSTRACT We study the Local Group (LG) dwarf galaxy population predicted by the APOSTLE ΛCDM cosmological hydrodynamics simulations. These indicate that: (i) the total mass within 3 Mpc of the Milky Way–Andromeda mid-point (M3Mpc) typically exceeds ∼3 times the sum of the virial masses (M200crit) of the two primaries and (ii) the dwarf galaxy formation efficiency per unit mass is uniform throughout the volume. This suggests that the satellite population within the virial radii of the Milky Way and Andromeda should make up fewer than one third of all LG dwarfs within 3 Mpc. This is consistent with the fraction of observed LG galaxies with stellar mass $M_*\gt 10^7\, {\rm M}_\odot$ that are satellites (12 out of 42; i.e. 28 per cent). For the APOSTLE galaxy mass–halo mass relation, the total number of such galaxies further suggests an LG mass of $M_{\rm 3 Mpc}\sim 10^{13}\, {\rm M}_\odot$. At lower galaxy masses, however, the observed satellite fraction is substantially higher (42 per cent for $M_*\gt 10^5\, { \mathrm{ M}}_\odot$). If this is due to incompleteness in the field sample, then ∼50 dwarf galaxies at least as massive as the Draco dwarf spheroidal must be missing from the current LG field dwarf inventory. The incompleteness interpretation is supported by the pronounced flattening of the LG luminosity function below $M_*\sim 10^7\, {\rm M}_\odot$, and by the scarcity of low surface brightness LG field galaxies compared to satellites. The simulations indicate that most missing dwarfs should lie near the virial boundaries of the two LG primaries, and predict a trove of nearby dwarfs that await discovery by upcoming wide-field imaging surveys.

scholarly journals Orbital pericentres and the inferred dark matter halo structure of satellite galaxies

2021 ◽  
Vol 503 (4) ◽  
pp. 5232-5237
Author(s):  
Victor H Robles ◽  
James S Bullock
Keyword(s):  
Dark Matter ◽  
Galaxy Formation ◽  
Milky Way ◽  
Dark Matter Halo ◽  
Halo Structure ◽  
Circular Velocity ◽  
Ursa Minor ◽  
Motion Measurements ◽  
High Level ◽  
Stellar Masses

ABSTRACT Using the phat-ELVIS suite of Milky Way-sized halo simulations, we show that subhalo orbital pericentres, rperi, correlate with their dark matter halo structural properties. Specifically, at fixed maximum circular velocity, Vmax, subhaloes with smaller rperi are more concentrated (have smaller rmax values) and have lost more mass, with larger peak circular velocities, Vpeak, prior to infall. These trends provide information that can tighten constraints on the inferred Vmax and Vpeak values for known Milky Way satellites. We illustrate this using published pericentre estimates enabled by Gaia for the nine classical Milky Way dwarf spheroidal satellites. The two densest dSph satellites (Draco and Ursa Minor) have relatively small pericentres, and this pushes their inferred rmax and Vmax values lower than they would have been without pericentre information. For Draco, we infer $V_{\rm max} = 23.5 \, \pm 3.3$ km s−1 (compared to $27.3 \, \pm 7.1$ km s−1 without pericentre information). Such a shift exacerbates the traditional Too Big to Fail problem. Draco’s peak circular velocity range prior to infall narrows from Vpeak = 21–51 km s−1 without pericentre information to Vpeak = 25–37 km s−1 with the constraint. Over the full population of classical dwarf spheroidals, we find no correlation between Vpeak and stellar mass today, indicative of a high level of stochasticity in galaxy formation at stellar masses below ∼107 M⊙. As proper motion measurements for dwarf satellites become more precise, they should enable useful priors on the expected structure and evolution of their host dark matter subhaloes.

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