scholarly journals MeerKAT-16 H i observation of the dIrr galaxy WLM

2020 ◽  
Vol 497 (4) ◽  
pp. 4795-4813
Author(s):  
Roger Ianjamasimanana ◽  
Brenda Namumba ◽  
Athanaseus J T Ramaila ◽  
Anna S Saburova ◽  
Gyula I G Józsa ◽  
...  
Keyword(s):  
Dark Matter ◽  
Mass Distribution ◽  
Neutral Hydrogen ◽  
Major Axis ◽  
Dark Matter Halo ◽  
Chi Square ◽  
Best Fitting ◽  
The One ◽  
A Minor ◽  
Harmonic Distortions

ABSTRACT We present observations and models of the kinematics and the distribution of the neutral hydrogen (H i) in the isolated dwarf irregular galaxy, Wolf-Lundmark-Melotte (WLM). We observed WLM with the Green Bank Telescope (GBT) and as part of the MeerKAT Early Science Programme, where 16 dishes were available. The H i disc of WLM extends out to a major axis diameter of 30 arcmin (8.5 kpc), and a minor axis diameter of 20 arcmin (5.6 kpc) as measured by the GBT. We use the MeerKAT data to model WLM using the tirific software suite, allowing us to fit different tilted-ring models and select the one that best matches the observation. Our final best-fitting model is a flat disc with a vertical thickness, a constant inclination and dispersion, and a radially varying surface brightness with harmonic distortions. To simulate bar-like motions, we include second-order harmonic distortions in velocity in the tangential and vertical directions. We present a model with only circular motions included and a model with non-circular motions. The latter describes the data better. Overall, the models reproduce the global distribution and the kinematics of the gas, except for some faint emission at the 2σ level. We model the mass distribution of WLM with pseudo-isothermal (ISO) and Navarro–Frenk–White (NFW) dark matter halo models. The NFW and the ISO models fit the derived rotation curves within the formal errors, but with the ISO model giving better reduced chi-square values. The mass distribution in WLM is dominated by dark matter at all radii.

scholarly journals Brightest cluster galaxies: the centre can(not?) hold

2020 ◽  
Vol 500 (1) ◽  
pp. 310-318
Author(s):  
Roberto De Propris ◽  
Michael J West ◽  
Felipe Andrade-Santos ◽  
Cinthia Ragone-Figueroa ◽  
Elena Rasia ◽  
...  
Keyword(s):  
Dark Matter ◽  
Local Environment ◽  
Major Axis ◽  
Theoretical Models ◽  
Dark Matter Halo ◽  
Gas Distribution ◽  
X Ray ◽  
Cluster Galaxies ◽  
Peculiar Velocities ◽  
Brightest Cluster Galaxies

ABSTRACT We explore the persistence of the alignment of brightest cluster galaxies (BCGs) with their local environment. We find that a significant fraction of BCGs do not coincide with the centroid of the X-ray gas distribution and/or show peculiar velocities (they are not at rest with respect to the cluster mean). Despite this, we find that BCGs are generally aligned with the cluster mass distribution even when they have significant offsets from the X-ray centre and significant peculiar velocities. The large offsets are not consistent with simple theoretical models. To account for these observations BCGs must undergo mergers preferentially along their major axis, the main infall direction. Such BCGs may be oscillating within the cluster potential after having been displaced by mergers or collisions, or the dark matter halo itself may not yet be relaxed.

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 Cold Dark Matter Substructure and the Heating of Galactic Disks

2003 ◽  
Vol 208 ◽  
pp. 391-392
Author(s):  
Andreea S. Font ◽  
Julio F. Navarro
Keyword(s):  
Dark Matter ◽  
Cold Dark Matter ◽  
Milky Way ◽  
Dark Matter Halo ◽  
Stellar Disk ◽  
Minor Role ◽  
Galactic Disks ◽  
Cosmological Simulations ◽  
A Minor

We investigate recent suggestions that substructure in cold dark matter (CDM) halos has potentially destructive effects on galactic disks. N-body simulations of disk/bulge models of the Milky Way, embedded in a dark matter halo with substructure similar to that found in cosmological simulations, show that tides from substructure halos play only a minor role in the dynamical heating of the stellar disk. This suggests that substructure might not preclude CDM halos from being acceptable hosts of thin stellar disks.

scholarly journals Determining the Properties of Galaxy 2237+0305 using Gravitational Lensing

2004 ◽  
Vol 220 ◽  
pp. 109-114
Author(s):  
Cathryn Trott ◽  
Rachel Webster
Keyword(s):  
Dark Matter ◽  
Mass Distribution ◽  
Gravitational Lensing ◽  
Dark Matter Halo ◽  
Spectroscopic Observations ◽  
Photometric And Spectroscopic Observations ◽  
Dynamical Information

We have studied the mass distribution in the lensing galaxy 2237+0305 using constraints from both gravitational lensing and photometric and spectroscopic observations. We find that with sufficient dynamical information we can constrain the mass-to-light ratio of the luminous components and determine the dynamical contribution of the disk. in addition, future observations should allow us to place constraints on the shape of the dark matter halo and its inner slope.

scholarly journals The effect of warm gas on the buckling instability in galactic bars

2020 ◽  
Vol 634 ◽  
pp. A122
Author(s):  
Ewa L. Łokas
Keyword(s):  
Dark Matter ◽  
Milky Way ◽  
Gas Content ◽  
Dark Matter Halo ◽  
Buckling Instability ◽  
Radial Profiles ◽  
Formation And Evolution ◽  
The One ◽  
Gas Fractions ◽  
Gas Component

By using N-body and hydro simulations, we study the formation and evolution of bars in galaxies with significant gas content focusing on the phenomenon of the buckling instability. The galaxies are initially composed of a spherical dark matter halo and only stellar, or stellar and gaseous, disks with parameters that are similar to the Milky Way and are evolved for 10 Gyr. We consider different values of the gas fraction f = 0−0.3 and in order to isolate the effect of the gas, we kept the fraction constant during the evolution by not allowing the gas to cool and form stars. The stellar bars that form in simulations with higher gas fractions are weaker and shorter, and they do not form at all for gas fractions that are higher than 0.3. The bar with a gas fraction of 0.1 forms sooner due to initial perturbations in the gas, but despite the longer evolution, it does not become stronger than the one in the collisionless case at the end of evolution. The bars in the gas component are weaker; they reach their maximum strength around 4 Gyr and later decline to transform into spheroidal shapes. The distortion of the stellar bar during the buckling instability is weaker for higher gas fractions and weakens the bar less significantly, but it has a similar structure both in terms of radial profiles and in face-on projections. For f = 0.2, the first buckling lasts significantly longer and the bar does not undergo the secondary buckling event, while for f = 0.3, the buckling does not occur. Despite these differences, all bars develop boxy/peanut shapes in the stellar and gas component by the end of the evolution, although their thickness is smaller for higher gas fractions.

scholarly journals Grape-SPH Simulations of the Chemodynamical Evolution of Dwarf Galaxies

1996 ◽  
Vol 174 ◽  
pp. 395-396 ◽  
Author(s):  
Masao Mori ◽  
Yuzuru Yoshii ◽  
Takuji Tsujimoto ◽  
Ken'ichi Nomoto
Keyword(s):  
Dark Matter ◽  
Three Dimensional ◽  
Elliptical Galaxies ◽  
Dark Matter Halo ◽  
Chemical Abundances ◽  
Simulation Code ◽  
Element Abundances ◽  
Dwarf Elliptical Galaxies ◽  
Dimensional Simulation ◽  
The One

The central concentration of the luminosity distribution in dwarf elliptical galaxies (dEs) is weaker than that of giant elliptical galaxies (Es). In other words, the luminosity profiles in Es follow the de Vaucouleurs' law whereas dEs have exponential luminosity profiles. Athanassoula(1994) describes the one dimensional simulations of the formation of dEs that include the feedback effects from supernovae. The model with no dark matter halo is shown to be much better agreements with the observations than with dark matter halo. However no attempt has yet been made to reproduce much lower heavy element abundances in dEs than in Es. We calculate the chemodynamical evolution of a less massive gas cloud with an SPH+N-body three dimensional simulation code to explore the luminosity profile and chemical abundances in dEs.

scholarly journals Beyond ΛCDM with H i intensity mapping: robustness of cosmological constraints in the presence of astrophysics

2020 ◽  
Vol 496 (4) ◽  
pp. 4115-4126 ◽  
Author(s):  
Stefano Camera ◽  
Hamsa Padmanabhan
Keyword(s):  
Dark Matter ◽  
Modified Gravity ◽  
Cosmological Parameters ◽  
Neutral Hydrogen ◽  
Temperature Fluctuations ◽  
Dark Matter Halo ◽  
Cosmological Constraints ◽  
Intensity Mapping ◽  
Standard Cosmological Model ◽  
First Time

ABSTRACT Mapping the unresolved intensity of the 21-cm emission of neutral hydrogen (H i) is now regarded as one the most promising tools for cosmological investigation in the coming decades. Here, we investigate, for the first time, extensions of the standard cosmological model, such as modified gravity and primordial non-Gaussianity, taking self-consistently into account. The present constraints on the astrophysics of H i clustering in the treatment of the brightness temperature fluctuations. To understand the boundaries within which results thus obtained can be considered reliable, we examine the robustness of cosmological parameter estimation performed via studies of 21-cm intensity mapping, against our knowledge of the astrophysical processes leading to H i clustering. Modelling of astrophysical effects affects cosmological observables through the relation linking the overall H i mass in a bound object, to the mass of the underlying dark matter halo that hosts it. We quantify the biases in estimates of standard cosmological parameters and those describing modified gravity and primordial non-Gaussianity that are obtained if one misconceives the slope of the relation between H i mass and halo mass, or the lower virial velocity cut-off for a dark matter halo to be able to host H i. Remarkably, we find that astrophysical uncertainties will not affect searches for primordial non-Gaussianity – one of the strongest science cases for H i intensity mapping – despite the signal being deeply linked to the H i bias.

scholarly journals Thin Planes of Satellites in ΛCDM are not kinematically coherent

2016 ◽  
Vol 11 (S321) ◽  
pp. 40-41
Author(s):  
Tobias Buck ◽  
Aaron A. Dutton ◽  
Andrea V. Macciò
Keyword(s):  
Dark Matter ◽  
High Resolution ◽  
Cold Dark Matter ◽  
High Redshift ◽  
Large Fraction ◽  
Dark Matter Halo ◽  
Kinematic Structure ◽  
Andromeda Galaxy ◽  
High Incidence ◽  
The One

Recently it has been shown by Ibata et al. (2013) that a large fraction of the dwarf satellite galaxies found in the PAndAS survey (McConnachie et al. 2009) and orbiting the Andromeda galaxy are surprisingly aligned in a thin, extended, and kinematically coherent planar structure. The presence of such a structure seems to challenge the current Cold Dark Matter paradigm of structure formation (Ibata et al. 2014, Pawlowski et al. 2014), which predicts a more uniform distribution of satellites around central objects. We show that it is possible to obtain a thin, extended, rotating plane of satellites resembling the one in Andromeda in cosmological collisionless simulations based on this model. Our new 21 high-resolution simulations (see Buck et al. 2015) show a correlation between the formation time of the dark matter halo and the thickness of the plane of satellites. Our simulations have a high incidence of satellite planes as thin, extended, and as rich as the one in Andromeda and with a very coherent kinematic structure when we select early forming haloes. By tracking the formation of the satellites in the plane we show that they have mainly been accreted onto the main object along thin dark matter filaments at high redshift (Dekel et al. 2009, Libeskind et al. 2009, 2011). Our results show that the presence of a thin, extended, rotating plane of satellites is not a challenge for the Cold Dark Matter paradigm, but actually supports one of the predictions of this paradigm related to the presence of filaments of dark matter around galaxies at high redshift.

scholarly journals Origins of Stellar Halos

2015 ◽  
Vol 11 (S317) ◽  
pp. 1-8
Author(s):  
Kathryn V. Johnston
Keyword(s):  
Dark Matter ◽  
Milky Way ◽  
Stellar Populations ◽  
Observational Evidence ◽  
Dark Matter Halo ◽  
Theoretical Understanding ◽  
Stellar Halo ◽  
The One ◽  
Halo Population

AbstractThis contribution reviews ideas about the origins of stellar halos. It includes discussion of the theoretical understanding of and observational evidence for stellar populations formed “in situ” (meaning formed in orbits close to their current ones), “kicked-out” (meaning formed in the inner galaxy in orbits unlike their current ones) and “accreted” (meaning formed in a dark matter halo other than the one they currently occupy). At this point there is general agreement that a significant fraction of any stellar halo population is likely “accreted”. There is modest evidence for the presence of a “kicked-out” population around both the Milky Way and M31. Our theoretical understanding of and the observational evidence for an “in situ” population are less clear.

HI in the Dusty Elliptical Galaxy NGC 5266

1995 ◽  
Vol 12 (2) ◽  
pp. 143-145 ◽  
Author(s):  
R. Morganti ◽  
A. Pizzella ◽  
E. M. Sadler ◽  
F. Bertola
Keyword(s):  
Mass Distribution ◽  
Elliptical Galaxy ◽  
Neutral Hydrogen ◽  
Major Axis ◽  
Minor Axis ◽  
Dust Lane ◽  
Central Regions ◽  
Intrinsic Shape ◽  
Geometry And Kinematics ◽  
Compact Array

AbstractRecent observations with the Australia Telescope Compact Array show that the elliptical galaxy NGC 5266 has a disk of neutral hydrogen extending to almost 10Re. This HI disk lies along the galaxy’s major axis, at right angles to the inner minor-axis dust lane. The geometry and kinematics of the gas will allow us to determine both the intrinsic shape of the stellar galaxy and the mass distribution. The mass-to-light ratio M/LB rises from about 2 in the central regions to ~12 at 9Re (H0 = 50km s−1 Mpc−1).

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