71 research outputs found
Effects of BBN on Population III stars
The presence (or absence) of CNO elements in the primordial gas determines
different behaviours in population III stars formation and evolution: we
therefore present an analysis of the main channels for the synthesis of these
elements in BBN in order to understand, within a reliable interval, their
abundance in the primordial material.Comment: 2 pages, Proceedings of the conference "Observing, Thinking and
Mining the Universe" held in Sorrento (Italy), sept. 200
The lithium problem, a phenomenologist's perspective
Thirty years after the first observation of the 7Li isotope in the atmosphere
of metal-poor halo stars, the puzzle about its origin persists. Do current
observations still support the existence of a "plateau": a single value of
lithium abundance, constant over several orders of magnitude in the metallicity
of the target star? If this plateau exists, is it universal in terms of
observational loci of target stars? Is it possible to explain such observations
with known astrophysical processes? Can yet poorly explored astrophysical
mechanisms explain the observations or do we need to invoke physics beyond the
standard model of Cosmology and/or the standard model of Particle Physics to
explain them? Is there a 6Li problem, and is it connected to the 7Li one? These
questions have been discussed at the Paris workshop Lithium in the Cosmos, and
I summarize here its contents, providing an overview from the perspective of a
phenomenologist.Comment: Proceedings of the workshop "Lithium in the Cosmos"; held at Institut
d'Astrophysique de Paris in February 27-29, 2012. To appear in Mem.S.A.It.
Suppl., Vol 2
WIMP Dark Matter and the First Stars: a critical overview
If Dark Matter (DM) is composed by Weakly Interacting Massive Particles, its
annihilation in the halos harboring the earliest star formation episode may
strongly influence the first generation of stars (Population III). Whereas DM
annihilation at early stages of gas collapse does not dramatically affect the
properties of the cloud, the formation of a hydrostatic object (protostar) and
its evolution toward the main sequence may be delayed. This process involves DM
concentrated in the center of the halo by gravitational drag, and no consensus
is yet reached over whether this can push the initial mass of Population III to
higher masses. DM can also be captured through scattering over the baryons in a
dense object, onto or very close to the Main Sequence. This mechanism can
affect formed stars and in principle prolonge their lifetimes. The strength of
both mechanisms depends upon several environmental conditions and on DM
parameters; such spread in the parameter space leads to very different
scenarios for the observables in the Population. Here I summarize the state of
the art in modelling and observational expectations, eventually highlighting
the most critical assumptions and sources of uncertainty.Comment: Proceedings of Cosmic Radiation Fields: Sources in the early
Universe; DESY Hamburg, November 9-12, 2010. A note adde
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
: 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
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
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
Constraints on Dark Matter annihilations from reionization and heating of the intergalactic gas
Dark Matter annihilations after recombination and during the epoch of
structure formation deposit energy in the primordial intergalactic medium,
producing reionization and heating. We investigate the constraints that are
imposed by the observed optical depth of the Universe and the measured
temperature of the intergalactic gas. We find that the bounds are significant,
and have the power to rule out large portions of the `DM mass/cross section'
parameter space. The optical depth bound is generally stronger and does not
depend significantly on the history of structure formation. The temperature
bound can be competitive in some cases for small masses or the hadronic
annihilation channels (and is affected somewhat by the details of structure
formation). We find in particular that DM particles with a large annihilation
cross section into leptons and a few TeV mass, such as those needed to explain
the PAMELA and FERMI+HESS cosmic ray excesses in terms of Dark Matter, are
ruled out as they produce too many free electrons. We also find that low mass
particles (<~ 10 GeV) tend to heat too much the gas and are therefore
disfavored.Comment: 22 pages, 5 figures; v2: minor comments added, matches version
published on JCA
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