Progressively More Prolate Dark Matter Halo in the Outer Galaxy as Traced by Flaring H I Gas

Banerjee, Arunima; Jog, Chanda J.

doi:10.1088/2041-8205/732/1/l8

Cited by 37 publications

(47 citation statements)

References 27 publications

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“…If we believe the halo is well represented by an axisymetric logarithmic potential with velocity normalisation v0 between 210 and 250 kms −1 , then the flattening equation implies that the axis ratio of the equipotentials q satisfies 1.5 q 2. This result is consistent with the claim of Banerjee & Jog (2011), who argued for prolateness based on an analysis of the HI flaring gas layer from 8 to 24 kpc.…”

Section: Discussionsupporting

confidence: 92%

Is the dark halo of the Milky Way prolate?

Bowden

Evans

Williams

2016

Mon. Not. R. Astron. Soc.

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We introduce the flattening equation, which relates the shape of the dark halo to the angular velocity dispersions and the density of a tracer population of stars. It assumes spherical alignment of the velocity dispersion tensor, as seen in the data on stellar halo stars in the Milky Way. The angular anisotropy and gradients in the angular velocity dispersions drive the solutions towards prolateness, whilst the gradient in the stellar density is a competing effect favouring oblateness. We provide an efficient numerical algorithm to integrate the flattening equation. Using tests on mock data, we show that the there is a strong degeneracy between circular speed and flattening, which can be circumvented with informative priors. Therefore, we advocate the use of the flattening equation to test for oblateness or prolateness, though the precise value of q can only be measured with the addition of the radial Jeans equation. We apply the flattening equation to a sample extracted from the Sloan Digital Sky Survey of ∼ 15000 halo stars with full phase space information and errors. We find that between Galactocentric radii of 5 and 10 kpc, the shape of the dark halo is prolate, whilst even mildly oblate models are disfavoured. Strongly oblate models are ruled out. Specifically, for a logarithmic halo model, if the asymptotic circular speed v 0 lies between 210 and 250 kms −1 , then we find the axis ratio of the equipotentials q satisfies 1.5 q 2.

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Section: Discussionsupporting

confidence: 92%

Is the dark halo of the Milky Way prolate?

Bowden

Evans

Williams

2016

Mon. Not. R. Astron. Soc.

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“…Several studies have shown that it is difficult to reproduce the flaring within the context of spherical halo models (Narayan et al, 2005;Kalberla et al, 2007). Banerjee and Jog (2011) find that the flaring can be reproduced by a prolate dark matter halo that becomes the most prolate at ∼ 25 kpc, q 2.…”

Section: The Tilt Angles In Equation 33mentioning

confidence: 81%

Galactic searches for dark matter

2013

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For nearly a century, more mass has been measured in galaxies than is contained in the luminous stars and gas. Through continual advances in observations and theory, it has become clear that the dark matter in galaxies is not comprised of known astronomical objects or baryonic matter, and that identification of it is certain to reveal a profound connection between astrophysics, cosmology, and fundamental physics. The best explanation for dark matter is that it is in the form of a yet undiscovered particle of nature, with experiments now gaining sensitivity to the most well-motivated particle dark matter candidates. In this article, I review measurements of dark matter in the Milky Way and its satellite galaxies and the status of Galactic searches for particle dark matter using a combination of terrestrial and space-based astroparticle detectors, and large scale astronomical surveys. I review the limits on the dark matter annihilation and scattering cross sections that can be extracted from both astroparticle experiments and astronomical observations, and explore the theoretical implications of these limits. I discuss methods to measure the properties of particle dark matter using future experiments, and conclude by highlighting the exciting potential for dark matter searches during the next decade, and beyond.

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“…In such a situation it is however difficult to measure the gas velocity dispersion σg, which is a critical parameter for the model. Banerjee & Jog (2011) show that the uncertainty in σg is an important contributor to the uncertainty in the scale-height computed from the model. The calculated HI scale-height is highly sensitive to the assumed value of σg; a 10% change in σg can lead to ∼ 15% change in the calculated HI scale-height.…”

Section: Introductionmentioning

confidence: 92%

“…Further, since the HI disc generally extends to galacto-centric radii where the gravity due to stars is negligible, both the flaring of the HI disc as well as its rotational velocity can be used as diagnostic probes of the underlying potential of the dark matter halo (see e.g. Olling 1995;Becquaert & Combes 1997;Narayan, Saha, & Jog 2005;Banerjee & Jog 2008;Banerjee, Matthews, & Jog 10;Banerjee & Jog 2011). While modelling of the vertical distribution of the gas can be used to infer the properties of the dark matter distribution, comparison of models with observations is complicated by the following problem.…”

Section: Introductionmentioning

confidence: 99%

Modelling H i distribution and kinematics in the edge-on dwarf irregular galaxy KK250

Patra

Banerjee

Chengalur

et al. 2014

Monthly Notices of the Royal Astronomical Society

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We model the observed vertical distribution of the neutral hydrogen (HI) in the faint (M B ∼ −13.7 mag) edge-on dwarf irregular galaxy KK250. Our model assumes that the galaxy consists of axi-symmetric, co-planar gas and stellar discs in the external force-field of a spherical dark matter halo, and in vertical hydrostatic equilibrium. The velocity dispersion of the gas is left as a free parameter in the model. Our best fit model is able to reproduce the observed vertical distribution of the HI gas, as well as the observed velocity profiles. The best fit model has a large velocity dispersion (∼ 22 kms −1 ) at the centre of the galaxy, which falls to a value of ∼ 8 kms −1 by a galacto-centric radius of 1 kpc, which is similar to both the scale-length of the stellar disc, as well as the angular resolution of the data along the radial direction. Similarly we find that the thickness of the HI disc is also minimum at ∼ 1kpc, and increases by about a factor of ∼ 2 as one goes to the centre of the galaxy or out to ∼ 3kpc. The minimum intrinsic HWHM of the HI vertical distribution in KK250 is ∼ 350pc. For comparison the HWHM of the vertical distribution of the HI in the solar neighbourhood is ∼ 70 − 140 pc. Our results are hence consistent with other observations which indicate that dwarf galaxies have significantly puffier gas discs than spirals.

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Progressively More Prolate Dark Matter Halo in the Outer Galaxy as Traced by Flaring H I Gas

Cited by 37 publications

References 27 publications

Is the dark halo of the Milky Way prolate?

Is the dark halo of the Milky Way prolate?

Galactic searches for dark matter

Modelling H i distribution and kinematics in the edge-on dwarf irregular galaxy KK250

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