scholarly journals Evidence of a population of dark subhaloes from Gaia and Pan-STARRS observations of the GD-1 stream

2021 ◽  
Vol 502 (2) ◽  
pp. 2364-2380
Author(s):  
Nilanjan Banik ◽  
Jo Bovy ◽  
Gianfranco Bertone ◽  
Denis Erkal ◽  
T J L de Boer
Keyword(s):  
Dark Matter ◽  
Mass Fraction ◽  
Molecular Clouds ◽  
Globular Clusters ◽  
Cold Dark Matter ◽  
Joint Analysis ◽  
Giant Molecular Clouds ◽  
Total Abundance ◽  
Hydrodynamical Simulation ◽  
Stellar Density

ABSTRACT New data from the Gaia satellite, when combined with accurate photometry from the Pan-STARRS survey, allow us to accurately estimate the properties of the GD-1 stream. Here, we analyse the stellar density variations in the GD-1 stream and show that they cannot be due to known baryonic structures such as giant molecular clouds, globular clusters, or the Milky Way’s bar or spiral arms. A joint analysis of the GD-1 and Pal 5 streams instead requires a population of dark substructures with masses ≈107–$10^9 \ \rm {M}_{\odot }$. We infer a total abundance of dark subhaloes normalized to standard cold dark matter $n_{\rm sub}/n_{\rm sub, CDM} = 0.4 ^{+0.3}_{-0.2}$ (68 per cent), which corresponds to a mass fraction contained in the subhaloes $f_{\rm {sub}} = 0.14 ^{+0.11}_{-0.07} {{\ \rm per\ cent}}$, compatible with the predictions of hydrodynamical simulation of cold dark matter with baryons.

scholarly journals Effects of initial density profiles on massive star cluster formation in giant molecular clouds

2021 ◽  
Author(s):  
Yingtian Chen ◽  
Hui Li ◽  
Mark Vogelsberger
Keyword(s):  
Angular Momentum ◽  
Star Formation ◽  
Molecular Clouds ◽  
Globular Clusters ◽  
Cluster Formation ◽  
Initial Density ◽  
Giant Molecular Clouds ◽  
Density Profiles ◽  
Stellar Feedback ◽  
Gas Accretion

Abstract We perform a suite of hydrodynamic simulations to investigate how initial density profiles of giant molecular clouds (GMCs) affect their subsequent evolution. We find that the star formation duration and integrated star formation efficiency of the whole clouds are not sensitive to the choice of different profiles but are mainly controlled by the interplay between gravitational collapse and stellar feedback. Despite this similarity, GMCs with different profiles show dramatically different modes of star formation. For shallower profiles, GMCs first fragment into many self-gravitation cores and form sub-clusters that distributed throughout the entire clouds. These sub-clusters are later assembled ‘hierarchically’ to central clusters. In contrast, for steeper profiles, a massive cluster is quickly formed at the center of the cloud and then gradually grows its mass via gas accretion. Consequently, central clusters that emerged from clouds with shallower profiles are less massive and show less rotation than those with the steeper profiles. This is because 1) a significant fraction of mass and angular momentum in shallower profiles is stored in the orbital motion of the sub-clusters that are not able to merge into the central clusters 2) frequent hierarchical mergers in the shallower profiles lead to further losses of mass and angular momentum via violent relaxation and tidal disruption. Encouragingly, the degree of cluster rotations in steeper profiles is consistent with recent observations of young and intermediate-age clusters. We speculate that rotating globular clusters are likely formed via an ‘accretion’ mode from centrally-concentrated clouds in the early Universe.

scholarly journals Understanding the large inferred Einstein radii of observed low-mass galaxy clusters

2020 ◽  
Vol 494 (4) ◽  
pp. 4706-4712 ◽  
Author(s):  
Andrew Robertson ◽  
Richard Massey ◽  
Vincent Eke
Keyword(s):  
Dark Matter ◽  
Galaxy Clusters ◽  
Gravitational Lensing ◽  
Cold Dark Matter ◽  
Baryonic Matter ◽  
Analysis Method ◽  
Critical Curves ◽  
Hydrodynamical Simulation ◽  
Low Mass ◽  
Main Effects

ABSTRACT We assess a claim that observed galaxy clusters with mass ${\sim}10^{14} \mathrm{\, M_\odot }$ are more centrally concentrated than predicted in lambda cold dark matter (ΛCDM). We generate mock strong gravitational lensing observations, taking the lenses from a cosmological hydrodynamical simulation, and analyse them in the same way as the real Universe. The observed and simulated lensing arcs are consistent with one another, with three main effects responsible for the previously claimed inconsistency. First, galaxy clusters containing baryonic matter have higher central densities than their counterparts simulated with only dark matter. Secondly, a sample of clusters selected because of the presence of pronounced gravitational lensing arcs preferentially finds centrally concentrated clusters with large Einstein radii. Thirdly, lensed arcs are usually straighter than critical curves, and the chosen image analysis method (fitting circles through the arcs) overestimates the Einstein radii. After accounting for these three effects, ΛCDM predicts that galaxy clusters should produce giant lensing arcs that match those in the observed Universe.

scholarly journals Disruption of giant molecular clouds and formation of bound star clusters under the influence of momentum stellar feedback

2019 ◽  
Vol 487 (1) ◽  
pp. 364-380 ◽  
Author(s):  
Hui Li ◽  
Mark Vogelsberger ◽  
Federico Marinacci ◽  
Oleg Y Gnedin
Keyword(s):  
Star Formation ◽  
Molecular Clouds ◽  
Star Clusters ◽  
Giant Molecular Clouds ◽  
Density Profiles ◽  
Stellar Feedback ◽  
Wide Range ◽  
Gas Removal ◽  
Formation Efficiency ◽  
Stellar Density

Abstract Energetic feedback from star clusters plays a pivotal role in shaping the dynamical evolution of giant molecular clouds (GMCs). To study the effects of stellar feedback on the star formation efficiency of the clouds and the dynamical response of embedded star clusters, we perform a suite of isolated GMC simulations with star formation and momentum feedback subgrid models using the moving-mesh hydrodynamics code Arepo. The properties of our simulated GMCs span a wide range of initial mass, radius, and velocity configurations. We find that the ratio of the final stellar mass to the total cloud mass, ϵint, scales strongly with the initial cloud surface density and momentum feedback strength. This correlation is explained by an analytic model that considers force balancing between gravity and momentum feedback. For all simulated GMCs, the stellar density profiles are systematically steeper than that of the gas at the epochs of the peaks of star formation, suggesting a centrally concentrated stellar distribution. We also find that star clusters are always in a sub-virial state with a virial parameter ∼0.6 prior to gas expulsion. Both the sub-virial dynamical state and steeper stellar density profiles prevent clusters from dispersal during the gas removal phase of their evolution. The final cluster bound fraction is a continuously increasing function of ϵint. GMCs with star formation efficiency smaller than 0.5 are still able to form clusters with large bound fractions.

scholarly journals CO observations of spiral structure and the lifetime of giant molecular clouds

1979 ◽  
Vol 84 ◽  
pp. 277-283
Author(s):  
N. Z. Scoville ◽  
P. M. Solomon ◽  
D. B. Sanders
Keyword(s):  
Molecular Cloud ◽  
Mass Fraction ◽  
Molecular Clouds ◽  
Spiral Structure ◽  
Large Mass ◽  
Giant Molecular Clouds ◽  
Spiral Pattern ◽  
The Galaxy ◽  
Co Emission ◽  
Co Observations

Observations of CO emission at ℓ=0 to 70°, |b| ≤ 1° are analyzed to give a map of the molecular cloud distribution in the galaxy as viewed from the galactic pole. From the fact that this distribution shows no obvious spiral pattern we conclude that the giant molecular clouds sampled in the CO line are situated in both arm and interarm regions and they must last more than 108 years. A similar age estimate is deduced from the large mass fraction of H2 in the interstellar medium in the interior of the galaxy. An implication of this longevity is that the great masses of these clouds may be accumulated through cloud-cloud collisions of originally smaller clouds.

Hunting for Globular Clusters in the early universe

2019 ◽  
Vol 14 (S351) ◽  
pp. 212-215
Author(s):  
Frederika Phipps ◽  
Sadegh Khochfar ◽  
Anna Lisa Varri
Keyword(s):  
Dark Matter ◽  
High Resolution ◽  
Globular Clusters ◽  
Dwarf Galaxies ◽  
High Redshift ◽  
Stellar Systems ◽  
Mass Relation ◽  
Cosmological Context ◽  
Low Mass ◽  
Stellar Density

AbstractSetting the formation of globular clusters (GCs) within a cosmological context and characterising the properties of proto-GCs at high redshift is currently a major challenge. In this work, we address that challenge by exploring a suit of high-resolution cosmological simulations from the First Billion Years (FiBY) project z at ⩾6 to investigate theoretical scenarios concerning the formation of old, low-mass stellar systems with a particular focus on GCs. Two distinct groups of objects are identified in the simulations. The first group of objects, with a high baryon fraction, we associate with proto-GCs. The second group, that exhibit a high stellar fraction, could be forming ultra-faint dwarf galaxies (UFDs). The objects with high baryon fraction are promising proto-GC candidates because they have little to no dark matter (DM), have number densities consistent with predictions from the literature, are very compact and have a high stellar density. We fit and also assess the redshift-zero globular system mass - halo mass relation and find it provides a reasonable fit to our proto-GC objects, indicating that this relation is likely set at formation.

scholarly journals The ultra-diffuse dwarf galaxies NGC 1052-DF2 and 1052-DF4 are in conflict with standard cosmology

2019 ◽  
Vol 489 (2) ◽  
pp. 2634-2651 ◽  
Author(s):  
Moritz Haslbauer ◽  
Indranil Banik ◽  
Pavel Kroupa ◽  
Konstantin Grishunin
Keyword(s):  
Dark Matter ◽  
Globular Cluster ◽  
Globular Clusters ◽  
Cold Dark Matter ◽  
Dwarf Galaxy ◽  
Stellar Mass ◽  
Peculiar Velocity ◽  
Standard Cosmology ◽  
The Galaxy ◽  
Velocity Motion

ABSTRACT Recently van Dokkum et al. reported that the galaxy NGC 1052-DF2 (DF2) lacks dark matter if located at 20 Mpc from Earth. In contrast, DF2 is a dark-matter-dominated dwarf galaxy with a normal globular cluster population if it has a much shorter distance near 10 Mpc. However, DF2 then has a high peculiar velocity wrt. the cosmic microwave background of 886 $\rm {km\, s^{-1}}$, which differs from that of the Local Group (LG) velocity vector by 1298 $\rm {km\, s^{-1}}$ with an angle of $117 \, ^{\circ }$. Taking into account the dynamical M/L ratio, the stellar mass, half-light radius, peculiar velocity, motion relative to the LG, and the luminosities of the globular clusters, we show that the probability of finding DF2-like galaxies in the lambda cold dark matter (ΛCDM) TNG100-1 simulation is at most 1.0 × 10−4 at 11.5 Mpc and is 4.8 × 10−7 at 20.0 Mpc. At 11.5 Mpc, the peculiar velocity is in significant tension in the TNG100-1, TNG300-1, and Millennium simulations, but naturally in a Milgromian cosmology. At 20.0 Mpc, the unusual globular cluster population would challenge any cosmological model. Estimating that precise measurements of the internal velocity dispersion, stellar mass, and distance exist for 100 galaxies, DF2 is in 2.6σ (11.5 Mpc) and 4.1σ (20.0 Mpc) tension with standard cosmology. Adopting the former distance for DF2 and assuming that NGC 1052-DF4 is at 20.0 Mpc, the existence of both is in tension at ≥4.8σ with the ΛCDM model. If both galaxies are at 20.0 Mpc the ΛCDM cosmology has to be rejected by ≥5.8σ.

scholarly journals Galaxy Formation in a Universe Dominated by Cold Dark Matter

1987 ◽  
Vol 117 ◽  
pp. 360-360
Author(s):  
Edmund Bertschinger
Keyword(s):  
Dark Matter ◽  
Galaxy Formation ◽  
Globular Clusters ◽  
Cold Dark Matter ◽  
Mass Function ◽  
Spherical Approximation ◽  
De Sitter ◽  
Density Peaks ◽  
Lower Amplitude ◽  
Baryonic Mass

ABSTRACT The mass spectrum of bound baryonic systems (galaxies and globular clusters) is computed as a function of redshift in an Einstein-de Sitter (Ω=1) universe dominated by weakly interacting, cold dark matter. Baryons are assumed to fall into primordial density peaks in the cold particle distribution when the mass in the peaks exceeds the baryon Jeans mass. The distribution of peaks is computed using Gaussian statistics. As the universe expands the baryonic mass attached to a given peak increases because of infall (treated in a spherical approximation), and new peaks of lower amplitude become nonlinear. Globular clusters form first (by z∼40 if the galaxies represent a biased mass distribution). The remaining gas may be reheated to ∼10000 K if a few percent of globular cluster (or Pop. III) stars are very massive. Reheating increases the baryon Jeans mass and delays galaxy formation until z≲10. The present method reproduces the shape (but not the amplitude) of the Schechter galaxy mass function when merging of substructure is included in an approximate fashion.

scholarly journals Cusp-to-core transition in low-mass dwarf galaxies induced by dynamical heating of cold dark matter by primordial black holes

2020 ◽  
Vol 492 (4) ◽  
pp. 5218-5225
Author(s):  
Pierre Boldrini ◽  
Yohei Miki ◽  
Alexander Y Wagner ◽  
Roya Mohayaee ◽  
Joseph Silk ◽  
...  
Keyword(s):  
Black Holes ◽  
Dark Matter ◽  
Time Scale ◽  
Mass Fraction ◽  
Cold Dark Matter ◽  
Dwarf Galaxies ◽  
Dwarf Galaxy ◽  
Initial Density ◽  
Primordial Black Holes ◽  
Low Mass

ABSTRACT We performed a series of high-resolution N-body simulations to examine whether dark matter candidates in the form of primordial black holes (PBHs) can solve the cusp–core problem in low-mass dwarf galaxies. If some fraction of the dark matter in low-mass dwarf galaxies consists of PBHs and the rest is cold dark matter, dynamical heating of the cold dark matter by the PBHs induces a cusp-to-core transition in the total dark matter profile. The mechanism works for PBHs in the 25–100 M⊙ mass window, consistent with the Laser Interferometer Gravitational-Wave Observatory (LIGO) detections, but requires a lower limit on the PBH mass fraction of 1 ${{\rm per\ cent}}$ of the total dwarf galaxy dark matter content. The cusp-to-core transition time-scale is between 1 and 8 Gyr. This time-scale is also a constant multiple of the relaxation time between cold dark matter particles and PBHs, which depends on the mass, the mass fraction, and the scale radius of the initial density profile of PBHs. We conclude that dark matter cores occur naturally in haloes composed of cold dark matter and PBHs, without the need to invoke baryonic processes.

Pregalactic formation of globular clusters in cold dark matter

1988 ◽  
Vol 330 ◽  
pp. 191 ◽  
Author(s):  
Edward I. Rosenblatt ◽  
S. M. Faber ◽  
George R. Blumenthal
Keyword(s):  
Dark Matter ◽  
Globular Clusters ◽  
Cold Dark Matter

scholarly journals The APOSTLE simulations: Rotation curves derived from synthetic 21-cm observations

2017 ◽  
Vol 13 (S334) ◽  
pp. 213-218
Author(s):  
Kyle A. Oman
Keyword(s):  
Dark Matter ◽  
Galaxy Formation ◽  
Cold Dark Matter ◽  
Local Group ◽  
Synthetic Data ◽  
Formation Model ◽  
Rotation Curves ◽  
Hydrodynamical Simulation ◽  
The Galaxy ◽  
Spectrally Resolved

AbstractThe apostle cosmological hydrodynamical simulation suite is a collection of twelve regions ~5 Mpc in diameter, selected to resemble the Local Group of galaxies in terms of kinematics and environment, and re-simulated at high resolution (minimum gas particle mass of 104 M⊙) using the galaxy formation model and calibration developed for the eagle project. I select a sample of dwarf galaxies (60 < Vmax/km s−1 < 120) from these simulations and construct synthetic spatially- and spectrally-resolved observations of their 21-cm emission. Using the 3Dbarolo tilted-ring modelling tool, I extract rotation curves from the synthetic data cubes. In many cases, non-circular motions present in the gas disc hinder the recovery of a rotation curve which accurately traces the underlying mass distribution; a large central deficit of dark matter, relative to the predictions of cold dark matter N-body simulations, may then be erroneously inferred.

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