168 research outputs found
: a new compilation of the Milky Way rotation curve data
We present , a novel compilation of kinematic measurements
tracing the rotation curve of our Galaxy, together with a tool to treat the
data. The compilation is optimised to Galactocentric radii between 3 and 20 kpc
and includes the kinematics of gas, stars and masers in a total of 2780
measurements carefully collected from almost four decades of literature. A
simple, user-friendly tool is provided to select, treat and retrieve the data
of all source references considered. This tool is especially designed to
facilitate the use of kinematic data in dynamical studies of the Milky Way with
various applications ranging from dark matter constraints to tests of modified
gravity.Comment: Description of out-of-the-box public tool to treat data compilation
first used in Nature Physics 11, 245-248 (2015). Please cite SoftwareX and
Nature Physics papers together. Refer to https://github.com/galkintool/galkin
for source code and additional informatio
Lithium synthesis in microquasar accretion
We study the synthesis of lithium isotopes in the hot tori formed around
stellar mass black holes by accretion of the companion star. We find that
sizable amounts of both stable isotopes 6Li and 7Li can be produced, the exact
figures varying with the characteristics of the torus and reaching as much as
1e-2 Msun for each isotope. This mass output is enough to contaminate the
entire Galaxy at a level comparable with the original, pre-galactic amount of
lithium and to overcome other sources such as cosmic-ray spallation or stellar
nucleosynthesis
Mapping dark matter in the Milky Way, a synopsis
Mapping the dark matter distribution across our Galaxy represents a central
challenge for the near future as a new generation of space-borne and
ground-based astronomical surveys swiftly comes online. Here we present a
synopsis of the present status of the field, reviewing briefly the baryonic
content and the kinematics of the Milky Way and outlining the methods used to
infer the dark matter component. The discussion then proceeds with some of the
latest developments based on our own work. In particular, we present a new
compilation of kinematic measurements tracing the rotation curve of the Galaxy
and an exhaustive array of observation-based baryonic models setting the
contribution of stellar bulge, stellar disc and gas to the total gravitational
potential. The discrepancy between these two components is then quantified to
derive the latest constraints on the dark matter distribution and on modified
Newtonian dynamics. We shall end with an overview of future directions to
improve our mapping of the dark matter distribution in the Milky Way.Comment: Proceedings of highlight talk at the 34th International Cosmic Ray
Conference, 30 July-6 August, 2015, The Hague, The Netherlands, 16 pages, 2
figures, 1 tabl
Testing modified Newtonian dynamics in the Milky Way
Modified Newtonian dynamics (MOND) is an empirical theory originally proposed
to explain the rotation curves of spiral galaxies by modifying the
gravitational acceleration, rather than by invoking dark matter. Here,we set
constraints on MOND using an up-to-date compilation of kinematic tracers of the
Milky Way and a comprehensive collection of morphologies of the baryonic
component in the Galaxy. In particular, we find that the so-called "standard"
interpolating function cannot explain at the same time the rotation curve of
the Milky Way and that of external galaxies for any of the baryonic models
studied, while the so-called "simple" interpolating function can for a subset
of models. Upcoming astronomical observations will refine our knowledge on the
morphology of baryons and will ultimately confirm or rule out the validity of
MOND in the Milky Way. We also present constraints on MOND-like theories
without making any assumptions on the interpolating function.Comment: 6 pages, 3 figure
Dynamical constraints on the dark matter distribution in the Milky Way
An accurate knowledge of the dark matter distribution in the Milky Way is of
crucial importance for galaxy formation studies and current searches for
particle dark matter. In this paper we set new dynamical constraints on the
Galactic dark matter profile by comparing the observed rotation curve, updated
with a comprehensive compilation of kinematic tracers, with that inferred from
a wide range of observation-based morphologies of the bulge, disc and gas. The
generalised Navarro-Frenk-White (NFW) and Einasto dark matter profiles are
fitted to the data in order to determine the favoured ranges of local density,
slope and scale radius. For a representative baryonic model, a typical local
circular velocity of 230 km/s and a distance of the Sun to the Galactic centre
of 8 kpc, we find a local dark matter density of 0.420+0.021-0.018 (2 sigma) +-
0.025 GeV/cm^3 (0.420+0.019-0.021 (2 sigma) +- 0.026 GeV/cm^3) for NFW
(Einasto), where the second error is an estimate of the systematic due to
baryonic modelling. Apart from the Galactic parameters, the main sources of
uncertainty inside and outside the solar circle are baryonic modelling and
rotation curve measurements, respectively. Upcoming astronomical observations
are expected to reduce all these uncertainties substantially over the coming
years.Comment: 10 pages, 5 figures, 2 tables, matches published versio
Pinpointing Cosmic Ray Propagation With The AMS-02 Experiment
The Alpha Magnetic Spectrometer (AMS-02), which is scheduled to be deployed
onboard the International Space Station later this year, will be capable of
measuring the composition and spectra of GeV-TeV cosmic rays with unprecedented
precision. In this paper, we study how the projected measurements from AMS-02
of stable secondary-to-primary and unstable ratios (such as boron-to-carbon and
beryllium-10-to-beryllium-9) can constrain the models used to describe the
propagation of cosmic rays throughout the Milky Way. We find that within the
context of fairly simple propagation models, all of the model parameters can be
determined with high precision from the projected AMS-02 data. Such
measurements are less constraining in more complex scenarios, however, which
allow for departures from a power-law form for the diffusion coefficient, for
example, or for inhomogeneity or stochasticity in the distribution and chemical
abundances of cosmic ray sources.Comment: 12 pages, 7 figures, 3 tables, matches published versio
Gamma-ray triangles: a possible signature of asymmetric dark matter in indirect searches
We introduce a new type of gamma-ray spectral feature, which we denominate
gamma-ray triangle. This spectral feature arises in scenarios where dark matter
self-annihilates via a chiral interaction into two Dirac fermions, which
subsequently decay in flight into another fermion and a photon. The resulting
photon spectrum resembles a sharp triangle and can be readily searched for in
the gamma-ray sky. Using data from the Fermi-LAT and H.E.S.S. instruments, we
find no evidence for such spectral feature and therefore set strong upper
bounds on the corresponding annihilation cross section. A concrete realization
of a scenario yielding gamma-ray triangles consists of an asymmetric dark
matter model where the dark matter particle carries lepton number. We show
explicitly that this class of models can lead to intense gamma-ray spectral
features, potentially at the reach of upcoming gamma-ray telescopes, opening a
new window to explore asymmetric dark matter through indirect searches.Comment: 11 pages, 6 figures. Published versio
Multi-messenger constraints on the annihilating dark matter interpretation of the positron excess
The rise in the energy spectrum of the positron ratio, observed by the PAMELA
satellite above 10 GeV, and other cosmic ray measurements, have been
interpreted as a possible signature of Dark Matter annihilation in the Galaxy.
However, the large number of free parameters, and the large astrophysical
uncertainties, make it difficult to do conclusive statements about the
viability of this scenario. Here, we perform a multi-wavelength,
multi-messenger analysis, that combines in a consistent way the constraints
arising from different astrophysical observations. We show that if standard
assumptions are made for the distribution of Dark Matter (we build models on
the recent Via Lactea II and Aquarius simulations) and the propagation of
cosmic rays, current DM models cannot explain the observed positron flux
without exceeding the observed fluxes of antiprotons or gamma-ray and radio
photons. To visualize the multi-messenger constraints, we introduce "star
plots", a graphical method that allows to show in the same plot theoretical
predictions and observational constraints for different messengers and
wavelengths.Comment: 15 pages, 8 figures, matches published versio
Dark Matter distribution in the Milky Way: microlensing and dynamical constraints
We show that current microlensing and dynamical observations of the Galaxy
permit to set interesting constraints on the Dark Matter local density and
profile slope towards the galactic centre. Assuming state-of-the-art models for
the distribution of baryons in the Galaxy, we find that the most commonly
discussed Dark Matter profiles (viz. Navarro-Frenk-White and Einasto) are
consistent with microlensing and dynamical observations, while extreme
adiabatically compressed profiles are robustly ruled out. When a baryonic model
that also includes a description of the gas is adopted, our analysis provides a
determination of the local Dark Matter density, \rho_0=0.20-0.56 GeV/cm^3 at
1\sigma, that is found to be compatible with estimates in the literature based
on different techniques.Comment: 12 pages, 5 figures, matches published versio
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