scholarly journals Globular cluster ejection, infall, and the host dark matter halo of the Pegasus dwarf galaxy

2020 ◽  
Vol 492 (4) ◽  
pp. 5102-5120
Author(s):  
Ryan Leaman ◽  
Tomás Ruiz-Lara ◽  
Andrew A Cole ◽  
Michael A Beasley ◽  
Alina Boecker ◽  
...  
Keyword(s):  
Dark Matter ◽  
Relaxation Time ◽  
Density Profile ◽  
Globular Cluster ◽  
Dwarf Galaxy ◽  
Orbital Evolution ◽  
Dark Matter Halo ◽  
Host Galaxy ◽  
Structural Constraints ◽  
The Galaxy

ABSTRACT Recent photometric observations revealed a massive, extended (MGC ≳ 105 M⊙; Rh ∼ 14 pc) globular cluster (GC) in the central region (D3D ≲ 100 pc) of the low-mass (M* ∼ 5 × 106 M⊙) dwarf irregular galaxy Pegasus. This massive GC offers a unique opportunity to study star cluster inspiral as a mechanism for building up nuclear star clusters, and the dark matter (DM) density profile of the host galaxy. Here, we present spectroscopic observations indicating that the GC has a systemic velocity of ΔV = 3 ± 8 km s−1 relative to the host galaxy, and an old, metal-poor stellar population. We run a suite of orbital evolution models for a variety of host potentials (cored to cusped) and find that the GC’s observed tidal radius (which is ∼3 times larger than the local Jacobi radius), relaxation time, and relative velocity are consistent with it surviving inspiral from a distance of Dgal ≳ 700 pc (up to the maximum tested value of Dgal = 2000 pc). In successful trials, the GC arrives to the galaxy centre only within the last ∼1.4 ± 1 Gyr. Orbits that arrive in the centre and survive are possible in DM haloes of nearly all shapes, however to satisfy the GC’s structural constraints a galaxy DM halo with mass MDM ≃ 6 ± 2 × 109 M⊙, concentration c ≃ 13.7 ± 0.6, and an inner slope to the DM density profile of −0.9 ≤ γ ≤ −0.5 is preferred. The gas densities necessary for its creation and survival suggest the GC could have formed initially near the dwarf’s centre, but then was quickly relocated to the outskirts where the weaker tidal field permitted an increased size and relaxation time – with the latter preserving the former during subsequent orbital decay.

scholarly journals The Dark Blue Compact Dwarf Galaxy NGC 2915

1997 ◽  
Vol 14 (1) ◽  
pp. 77-80 ◽  
Author(s):  
Gerhardt R. Meurer
Keyword(s):  
Dark Matter ◽  
Mass Distribution ◽  
Dwarf Galaxy ◽  
Dark Matter Halo ◽  
High Mass ◽  
Mass Star ◽  
Normal Galaxies ◽  
The Galaxy ◽  
Dark Blue ◽  
Blue Compact Dwarf Galaxy

AbstractRecent results on NGC 2915, the first blue compact dwarf galaxy to have its mass distribution modelled, are summarised. NGC 2915 is shown to have HI well beyond its detected optical extent. Its rotation curve is well determined and fit with maximum disk mass models. The dark matter halo dominates the mass distribution at nearly all radii, and has a very dense core compared to those of normal galaxies. High-mass star formation energises the HI in the centre of the galaxy, but appears to be maintained in viriai equilibrium with the dark matter halo. The implications of these results are briefly discussed.

scholarly journals Mass and shape of the Milky Way’s dark matter halo with globular clusters from Gaia and Hubble

2019 ◽  
Vol 621 ◽  
pp. A56 ◽  
Author(s):  
Lorenzo Posti ◽  
Amina Helmi
Keyword(s):  
Dark Matter ◽  
Phase Space ◽  
Globular Cluster ◽  
Globular Clusters ◽  
Cluster System ◽  
Dark Matter Halo ◽  
Proper Motions ◽  
Axis Ratio ◽  
The Galaxy ◽  
Globular Cluster System

Aims. We estimate the mass of the inner (< 20 kpc) Milky Way and the axis ratio of its inner dark matter halo using globular clusters as tracers. At the same time, we constrain the distribution in phase-space of the globular cluster system around the Galaxy. Methods. We use the Gaia Data Release 2 catalogue of 75 globular clusters’ proper motions and recent measurements of the proper motions of another 20 distant clusters obtained with the Hubble Space Telescope. We describe the globular cluster system with a distribution function (DF) with two components: a flat, rotating disc-like one and a rounder, more extended halo-like one. While fixing the Milky Way’s disc and bulge, we let the mass and shape of the dark matter halo and we fit these two parameters, together with six others describing the DF, with a Bayesian method. Results. We find the mass of the Galaxy within 20 kpc to be M(<20 kpc) = 1.91−0.17+0.18×1011 M⊙, of which MDM(<20 kpc) = 1.37−0.17+0.18×1011 M⊙ is in dark matter, and the density axis ratio of the dark matter halo to be q = 1.30 ± 0.25. Assuming a concentration-mass relation, this implies a virial mass Mvir = 1.3±0.3×1012 M⊙. Our analysis rules out oblate (q <  0.8) and strongly prolate halos (q >  1.9) with 99% probability. Our preferred model reproduces well the observed phase-space distribution of globular clusters and has a disc component that closely resembles that of the Galactic thick disc. The halo component follows a power-law density profile ρ ∝ r−3.3, has a mean rotational velocity of Vrot ≃ −14km s−1 at 20 kpc, and has a mildly radially biased velocity distribution (β ≃ 0.2 ± 0.07, which varies significantly with radius only within the inner 15 kpc). We also find that our distinction between disc and halo clusters resembles, although not fully, the observed distinction in metal-rich ([Fe/H] > −0.8) and metal-poor ([Fe/H] ≤ −0.8) cluster populations.

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 A new class of galaxy models with a central BH – I. The spherical case

2019 ◽  
Vol 490 (2) ◽  
pp. 2656-2667 ◽  
Author(s):  
Luca Ciotti ◽  
Antonio Mancino ◽  
Silvia Pellegrini
Keyword(s):  
Dark Matter ◽  
Density Profile ◽  
Mass Density ◽  
Dark Matter Halo ◽  
New Class ◽  
Stellar Component ◽  
Starting Point ◽  
The Galaxy ◽  
Radial Orbit ◽  
Analytical Expressions

ABSTRACTThe dynamical properties of spherically symmetric galaxy models, where a Jaffe stellar density profile is embedded in a total mass density decreasing as r−3 at large radii, are presented. The orbital structure of the stellar component is described by the Osipkov–Merritt anisotropy; the dark matter halo is isotropic, and a black hole is added at the centre of the galaxy. First, the conditions for a nowhere negative and monotonically decreasing dark matter halo density profile are derived; this profile can be made asymptotically coincident with an NFW profile at the centre and large radii. Then, the minimum value of the anisotropy radius for phase-space consistency is derived as a function of the galaxy parameters. The Jeans equations for the stellar component are solved analytically; the projected velocity dispersion at the centre and large radii is also obtained, for generic values of the anisotropy radius. Finally, analytical expressions for the terms entering the Virial Theorem are derived, and the fiducial anisotropy limit required to prevent the onset of Radial Orbit Instability is determined as a function of the galaxy parameters. The presented models, built following an approach already adopted in our previous works, can be a useful starting point for a more advanced modelling of the dynamics of elliptical galaxies, and can be easily implemented in numerical simulations requiring a realistic dynamical model of a galaxy.

scholarly journals A 5° × 5° deep H i survey of the M81 group − II. H i distribution and kinematics of IC 2574 and HIJASS J1021+68

2020 ◽  
Vol 493 (2) ◽  
pp. 2618-2631
Author(s):  
A Sorgho ◽  
L Chemin ◽  
Z S Kam ◽  
T Foster ◽  
C Carignan
Keyword(s):  
Dark Matter ◽  
Velocity Distribution ◽  
Rotation Curve ◽  
Dwarf Galaxy ◽  
Dark Matter Halo ◽  
Eastern Region ◽  
Ring Model ◽  
The Galaxy ◽  
Group Ii

ABSTRACT We analyse the eastern region of a 5° × 5° deep H i survey of the M81 group containing the dwarf galaxy IC 2574 and the H i complex HIJASS J1021+68, located between the dwarf and the M81 system. The data show that IC 2574 has an extended H i envelope that connects to HIJASS J1021+68 in the form of a collection of small clouds, but no evident connection has been found between IC 2574 and the central members of the M81 group. We argue, based on the morphology of the clouds forming HIJASS J1021+68 and its velocity distribution, that the complex is not a dark galaxy as previously suggested, but is instead a complex of clouds either stripped from, or falling on to the primordial H i envelope of IC 2574. We also use the deep H i observations to map the extended H i envelope around IC 2574 and, using a 3D tilted-ring model, we derive the rotation curve of the galaxy to a larger extent than has been done before. Combining the obtained rotation curve to higher resolution curves from the literature, we constrain the galaxy’s dark matter halo parameters.

scholarly journals H i observations of IC 10 with the DRAO synthesis telescope

2019 ◽  
Vol 490 (3) ◽  
pp. 3365-3377 ◽  
Author(s):  
B Namumba ◽  
C Carignan ◽  
T Foster ◽  
N Deg
Keyword(s):  
Dark Matter ◽  
Dwarf Galaxy ◽  
Maximum Velocity ◽  
Lower Surface ◽  
Emission Feature ◽  
Dark Matter Halo ◽  
Ic 10 ◽  
The Galaxy ◽  
Total Integration ◽  
Green Bank Telescope

ABSTRACT H i observations of the nearby blue compact dwarf galaxy IC 10 obtained with the Dominion Radio Astrophysical Observatory synthesis telescope, for a total integration of ∼1000 h, are presented. We confirm the NW faint 21 cm H i emission feature discovered in Green Bank Telescope (GBT) observations. The H i feature has an H i mass of 4.7 × 105 M⊙, which is only ∼0.6 ${{\ \rm per\ cent}}$ of the total H i mass of the galaxy (7.8 × 107 M⊙). In the inner disc, the rotation curve of IC 10 rises steeply, then flattens until the last point where it rises again, with a maximum velocity of 30 km s−1. Based on our mass models, the kinematics of the inner disc of IC 10 can be described without the need of a dark matter halo. However, this does not exclude the possible presence of dark matter on a larger scale. It is unlikely that the disturbed features seen in the outer H i disc of IC 10 are caused by an interaction with M 31. Features seen from our simulations are larger and at lower surface density than can be reached by current observations. The higher velocity dispersions seen in regions where several distinct H i features meet with the main core of IC 10 suggest that there is ongoing accretion.

scholarly journals The accreted nuclear clusters of the Milky Way

2020 ◽  
Vol 500 (2) ◽  
pp. 2514-2524
Author(s):  
Joel Pfeffer ◽  
Carmela Lardo ◽  
Nate Bastian ◽  
Sara Saracino ◽  
Sebastian Kamann
Keyword(s):  
Globular Clusters ◽  
Milky Way ◽  
Dwarf Galaxy ◽  
Star Clusters ◽  
Host Galaxy ◽  
The Galaxy ◽  
Nuclear Clusters ◽  
The Common ◽  
Massive Clusters ◽  
Peculiar Case

ABSTRACT A number of the massive clusters in the halo, bulge, and disc of the Galaxy are not genuine globular clusters (GCs) but instead are different beasts altogether. They are the remnant nuclear star clusters (NSCs) of ancient galaxies since accreted by the Milky Way. While some clusters are readily identifiable as NSCs and can be readily traced back to their host galaxy (e.g. M54 and the Sagittarius Dwarf galaxy), others have proven more elusive. Here, we combine a number of independent constraints, focusing on their internal abundances and overall kinematics, to find NSCs accreted by the Galaxy and trace them to their accretion event. We find that the true NSCs accreted by the Galaxy are: M54 from the Sagittarius Dwarf, ω Centari from Gaia-Enceladus/Sausage, NGC 6273 from Kraken, and (potentially) NGC 6934 from the Helmi Streams. These NSCs are prime candidates for searches of intermediate-mass black holes (BHs) within star clusters, given the common occurrence of galaxies hosting both NSCs and central massive BHs. No NSC appears to be associated with Sequoia or other minor accretion events. Other claimed NSCs are shown not to be such. We also discuss the peculiar case of Terzan 5, which may represent a unique case of a cluster–cluster merger.

scholarly journals The Dark Matter Halo Density Profile, Spiral Arm Morphology, and Supermassive Black Hole Mass of M33

2011 ◽  
Vol 2011 ◽  
pp. 1-8 ◽  
Author(s):  
Marc S. Seigar
Keyword(s):  
Black Hole ◽  
Dark Matter ◽  
Density Profile ◽  
Pitch Angle ◽  
Rotation Curve ◽  
Dark Matter Halo ◽  
Black Hole Mass ◽  
Supermassive Black Hole ◽  
Virial Mass ◽  
Spiral Arm

We investigate the dark matter halo density profile of M33. We find that the HI rotation curve of M33 is best described by an NFW dark matter halo density profile model, with a halo concentration of and a virial mass of . We go on to use the NFW concentration of M33, along with the values derived for other galaxies (as found in the literature), to show that correlates with both spiral arm pitch angle and supermassive black hole mass.

scholarly journals Central Dynamics of Globular Clusters: the Case for a Black Hole in ω Centauri

2007 ◽  
Vol 3 (S246) ◽  
pp. 341-345
Author(s):  
Eva Noyola ◽  
Karl Gebhardt ◽  
Marcel Bergmann
Keyword(s):  
Black Hole ◽  
Relaxation Time ◽  
Globular Cluster ◽  
Globular Clusters ◽  
Dwarf Galaxy ◽  
Kinematic Data ◽  
The Core ◽  
Galactic System ◽  
Interesting Candidate ◽  
Radial Anisotropy

AbstractThe globular cluster ω Centauri is one of the largest and most massive members of the Galactic system. Its classification as a globular cluster has been challenged making it a candidate for being the stripped core of an accreted dwarf galaxy; this and the fact that it has one of the largest velocity dispersions for star clusters in our galaxy makes it an interesting candidate for harboring an intermediate mass black hole. We measure the surface brightness profile from integrated light on an HST/ACS image, and find a central power-law cusp of logarithmic slope -0.08. We also analyze Gemini GMOS-IFU kinematic data for a 5”x5” field centered on the nucleus of the cluster, as well as for a field 14″ away. We detect a clear rise in the velocity dispersion from 18.6 kms−1 at 14″ to 23 kms−1 in the center. Given the very large core in ω Cen (2.58'), an increase in the dispersion in the central 10″ is difficult to attribute to stellar remnants, since it requires too many dark remnants and the implied configuration would dissolve quickly given the relaxation time in the core. However, the increase could be consistent with the existence of a central black hole. Assuming a constant M/L for the stars within the core, the dispersion profile from these data and data at larger radii implies a black hole mass of 4.0+0.75−1.0×104M⊙. We have also run flattened, orbit-based models and find a similar mass. In addition, the no black hole case for the orbit model requires an extreme amount of radial anisotropy, which is difficult to preserve given the short relaxation time of the cluster.

scholarly journals Refracting into ultra-diffuse galaxy NGC 1052-DF2 by passing near the centre of NGC 1052

2020 ◽  
Vol 495 (1) ◽  
pp. L144-L148 ◽  
Author(s):  
Ran Huo
Keyword(s):  
Dark Matter ◽  
Physical Mechanism ◽  
Dwarf Galaxy ◽  
Recent Observation ◽  
Tidal Effect ◽  
Natural Consequence ◽  
Formation Theory ◽  
The Galaxy ◽  
Standard Structure ◽  
Flat Distribution

ABSTRACT The recent observation of the ultra-diffuse galaxy NGC 1052-DF2 shows a galaxy may lack dark matter, which becomes a challenge to the standard structure formation theory. Here, we show that such phenomena can be a natural consequence if the NGC 1052-DF2 had experienced a single passage within a few kpc to the centre of the galaxy NGC 1052. The tidal effect of NGC 1052 in the encounter will heat the NGC 1052-DF2, and stretch the previous dwarf galaxy significantly into its current size. The relative lack of dark matter in the observed region is a natural consequence of the dark matter limited total amount in the corresponding small central region before the encounter, together with a systematic underestimation of the trace mass estimator method during revirialization after the encounter. The observed flat distribution of the ultra-diffuse galaxy can be reproduced with a cored initial star profile, which is a major improvement compared with the previous work. Our results show no need for introducing any new physical mechanism, as well as an alternative origin of an ultra-diffuse galaxy without repeated pericentre passage.

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