1,721,242 research outputs found
Local dark matter searches with LISA
Full text linkThe drag-free satellites of LISA will maintain the test masses in geodesic motion over many years with residual accelerations at unprecedented small levels and time delay interferometry (TDI) will keep track of their differential positions at a level of picometers. This may allow investigations of fine details of the gravitational field in the solar system previously inaccessible. In this spirit, we present the concept of a method for measuring directly the gravitational effect of the density of diffuse local dark matter (LDM) with a constellation of a few drag-free satellites, by exploiting how peculiarly it would affect their relative motion. Using as a test-bed an idealized LISA with rigid arms, we find that the separation in time between the test masses is uniquely perturbed by the LDM, so that they acquire a differential breathing mode. Such an LDM signal is related to the LDM density within the orbits and has characteristic spectral components, with amplitudes increasing in time, at various frequencies of the dynamics of the constellation. This is the relevant result in that the LDM signal is brought to non-zero frequencies
Dark Matter distribution in the Milky Way: Microlensing and dynamical constraints
No full textWe 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, ρ0 = 0.20-0.56GeV/cm3 at 1σ, that is found to be compatible with estimates in the literature based on different techniques. © 2011 IOP Publishing Ltd and SISSA
An upgrade of the microlensing rate
No full textWe study different models of dark-matter distribution for the halo of
our galaxy. Assuming that the dark matter is in form of MACHOs, we compute the
expected number of microlensing events and their average time duration for an
experiment monitoring stars in the LMC. The main effect of considering models with
anisotropy in the velocity space is to reduce the microlensing rate by about 30% and
to increase, but only slightly, the mean event duration, as compared to the standard
spherical halo model. Consideration of different luminous models for the visible part
of the galaxy also induce variations in the microlensing results by roughly the same
amount as mentioned above
X-ray emission from dark clusters of MACHOs
No full textMACHOs (Massive Astrophysical Compact Halo Objects) - as discovered by microlensing experiments towards the LMC - provide a natural explanation for the galactic halo dark matter. A realistic possibility is that MACHOs are brown dwarfs of mass similar to 0.1 M.. Various arguments suggest that brown dwarfs should have a coronal X-ray emission of similar to 10(27) erg s(-1). As MACHOs are presumably clumped into dark clusters (DCs), each DC is expected to have a total X-ray luminosity of similar to 10(30) - 10(32) erg s(-1). We discuss the observational prospects for DCs in the X-ray band
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Colour and stellar population gradients in galaxies
No full textWe discuss the colour, age and metallicity gradients in a wide sample of local SDSS early- and late-type galaxies. From the fitting of stellar population models we find that metallicity is the main driver of colour gradients and the age in the central regions is a dominant parameter which rules the scatter in both metallicity and age gradients. We find a consistency with independent observations and a set of simulations. From the comparison with simulations and theoretical considerations we are able to depict a general picture of a formation scenario
Baryonic dark clusters in galactic halos
No full textMACHOs (Massive Astrophysical Compact Halo Objects) discovered by microlensing, cold molecular clouds (mainly of H2) may well contribute substantially to the galactic halo dark matter. We describe a model for the formation and evolution of proto globular clusters towards either globular clusters or dark clusters of MACHOs and molecular clouds, depending on the distance from the galactic centre. Moreover, we discuss various methods to test this scenario, which rely upon observations in several bands of the electromagnetic spectrum. In particular, we estimate the γ-ray flux arising from halo molecular clouds through the interaction with high-energy cosmic-ray protons. Molecular clouds can also be detected via the absorption lines they would produce in the spectrum of stars located in the Large Magellanic Cloud and via the anisotropy they would introduce in the Cosmic Background Radiation when looking at the halo of M31 galaxy. Finally, we address the possibility of discovering MACHOs by infrared searches
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