263 research outputs found
A MULTIWAVELENGTH STRONG LENSING ANALYSIS OF BARYONS AND DARK MATTER IN THE DYNAMICALLY ACTIVE CLUSTER AC 114
No full textContext. Strong lensing studies can provide detailed mass maps of the inner regions even in dynamically active galaxy clusters. Aims. We illustrate the important role of a proper modelling of the intracluster medium, i.e., the main baryonic component. We demonstrate that the addition of a new contribution accounting for the gas can increase the statistical significance of the lensing model. Methods. We propose a parametric method for strong lensing analyses that exploits multiwavelength observations. The mass model accounts for cluster-sized dark matter halos, galaxies (whose stellar mass can be obtained from optical analyses), and the intracluster medium. The gas distribution is fitted to lensing data exploiting prior knowledge from X-ray observations. This gives an unbiased insight into each matter component and allows us to study the dynamical status of a cluster. The method was applied to AC 114, an irregular X-ray cluster. Results. We find positive evidence of dynamical activity, the dark matter distribution being shifted and rotated with respect to the gas. On the other hand, the dark matter follows the galaxy density in terms of both shape and orientation, illustrating the collisionless nature of dark matter. The inner region (≲ 250 kpc) is underluminous in optical bands, whereas the gas fraction (∼20 ± 5%) slightly exceeds typical values. Evidence of lensing and X-ray suggests that the cluster develops in the plane of the sky and is not affected by the lensing over-concentration bias. Despite the dynamical activity, the matter distribution seems to agree with predictions of N-body simulations. An universal cusped profile provides a good description of either the overall or the dark matter distribution, whereas theoretical scaling relations seem to be accurately fitted. © 2010 ESO
The M31 pixel lensing plan campaign : macho lensing and self-lensing signals
Get PDFA.G. was supported by NSF grant AST-1103471. M.D. is thankful to Qatar National Research Fund (QNRF), member of Qatar Foundation, for support by grant NPRP 09-476-1-078. P.J. acknowledges support by the Swiss National Science Foundation.We present the final analysis of the observational campaign carried out by the PLAN (Pixel Lensing Andromeda) collaboration to detect a dark matter signal in form of MACHOs through the microlensing effect. The campaign consists of about 1 month/year observations carried out over 4 years (2007-2010) at the 1.5 m Cassini telescope in Loiano (Astronomical Observatory of BOLOGNA, OAB) plus 10 days of data taken in 2010 at the 2 m Himalayan Chandra Telescope monitoring the central part of M31 (two fields of about 13′ × 12.′6). We establish a fully automated pipeline for the search and the characterization of microlensing flux variations. As a result, we detect three microlensing candidates. We evaluate the expected signal through a full Monte Carlo simulation of the experiment completed by an analysis of the detection efficiency of our pipeline. We consider both "self lensing" and "MACHO lensing" lens populations, given by M31 stars and dark matter halo MACHOs, in M31 and the Milky Way, respectively. The total number of events is consistent with the expected self-lensing rate. Specifically, we evaluate an expected signal of about two self-lensing events. As for MACHO lensing, for full 0.5(10-2) M☉ MACHO halos, our prediction is for about four (seven) events. The comparatively small number of expected MACHO versus self-lensing events, together with the small number statistics at our disposal, do not enable us to put strong constraints on that population. Rather, the hypothesis, suggested by a previous analysis, on the MACHO nature of OAB-07-N2, one of the microlensing candidates, translates into a sizeable lower limit for the halo mass fraction in form of the would-be MACHO population, f, of about 15% for 0.5 M☉ MACHOs.Peer reviewe
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
LMC Self-Lensing from a new perspective
Get PDFWe present a new analysis of the location of the observed microlensing events in the direction of the Large Magellanic Cloud (LMC). This is carried out starting from a recently drawn coherent picture of the geometrical structure and dynamics of the LMC disk and by considering different configurations for the LMC bar. In this framework it clearly emerges that the spatial distribution of the events observed so far shows a near-far asymmetry. This turns out to be compatible with the optical depth calculated for the LMC halo objects. Our main conclusion, supported by a statistical analysis of the outcome of an evaluation of the microlensing rate, is that self-lensing cannot account for all the observed events. Finally we propose a general inequality to calculate quickly an upper limit to the optical depth along a line of view through the LMC center
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 0.1M. Various arguments suggest that brown dwarfs should have a coronal X-ray emission of 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 10^29 − 10^32 erg s^−1. We discuss the possibility that dark clusters contribute to the diffuse X-ray background (XRB) or show up as discrete sources in very deep field X-ray satellite observations.
Moreover, from the observed diffuse XRB we infer
that the amount of virialized diffuse gas present in the galactic halo can at most make up 5% of the halo dark matter
Effective-one-body Hamiltonian with next-to-leading order spin-spin coupling
Get PDFWe propose a way of including the next-to-leading (NLO) order spin-spin coupling in an effective-one-body (EOB) Hamiltonian. This work extends by S. Balmelli and P. Jetzer, [Phys. Rev. D 87, 124036 (2013)], which is restricted to the case of equatorial orbits and aligned spins, to general orbits with arbitrary spin orientations. This is done by applying appropriate canonical phase-space transformations to the NLO spin-spin Hamiltonian in Arnowitt-Deser-Misner (ADM) coordinates, and systematically adding effective quantities at NLO to all spin-squared terms appearing in the EOB Hamiltonian. As required by consistency, the introduced quantities reduce to zero in the test-mass limit. We expose the result both in a general gauge and in a gauge-fixed form. The last is chosen such as to minimize the number of new coefficients that have to be inserted into the effective spin squared. As a result, the 25 parameters that describe the ADM NLO spin-spin dynamics get condensed into only 12 EOB terms
Microlensing towards the SMC: a new analysis of OGLE and EROS results
Get PDFWe present a new analysis of the results of the EROS-2, OGLE-II, and OGLE-III microlensing campaigns towards the Small Magellanic Cloud (SMC). Through a statistical analysis we address the issue of the \emph{nature} of the reported microlensing candidate events, whether to be attributed to lenses belonging to known population (the SMC luminous components or the Milky Way disc, to which we broadly refer to as "self lensing") or to the would be population of dark matter compact halo objects (MACHOs). To this purpose, we present profiles of the optical depth and, comparing to the observed quantities, we carry out analyses of the events position and duration. Finally, we evaluate and study the microlensing rate. Overall, we consider five reported microlensing events towards the SMC (one by EROS and four by OGLE). The analysis shows that in terms of number of events the expected self lensing signal may indeed explain the observed rate. However, the characteristics of the events, spatial distribution and duration (and for one event, the projected velocity) rather suggest a non-self lensing origin for a few of them. In particular we evaluate, through a likelihood analysis, the resulting upper limit for the halo mass fraction in form of MACHOs given the expected self-lensing and MACHO lensing signal. At 95% CL, the tighter upper limit, about 10%, is found for MACHO mass of 10−2M⊙, upper limit that reduces to above 20% for 0.5M⊙ MACHOs
Monte Carlo analysis of MEGA microlensing events towards M 31
No full textWe perform an analytical study and a Monte Carlo (MC) analysis of the main features for microlensing events in pixel lensing observations towards M 31. Our main aim is to investigate the lens nature and location of the 14 candidate events found by the MEGA collaboration. Assuming a reference model for the mass distribution in M 31 and the standard model for our galaxy, we estimate the MACHO-to-self lensing probability and the event time duration towards M 31. Reproducing the MEGA observing conditions, as a result we get the MC event number density distribution as a function of the event full-width half-maximum duration t1/2 and the magnitude at maximum R_max. For a MACHO mass of 0.5~Msun we find typical values of t1/2 ≃ 20 day and Rmax ≃ 22, for both MACHO-lensing and self-lensing events occurring beyond about 10 arcmin from the M 31 center. A comparison of the observed features (t1/2 and Rmax) with our MC results shows that for a MACHO mass > 0.1~Msun the four innermost MEGA events are most likely self-lensing events, whereas the six outermost events must be genuine MACHO-lensing events
Dark matter in the dwarf galaxy NGC 247
No full textDwarf galaxies are dominated by dark matter even in the innermost regions and, therefore, provide excellent probes for the investigation of dark halos. To that purpose, we analyse ROSAT PSPC-data of the dwarf galaxy NGC 247. We focus in particular on the diffuse X-ray emission in the 1/4 keV band. Assuming an isothermal density profile, we find that the mass of the hot emitting gas is about 10(8 ) Msun, corresponding to ≲ 0.5% of the total dynamical mass of the galaxy. The total mass of NGC 247, as derived from the X-ray data agrees quite well with the value obtained from the measured rotation curve (Burlak \cite{burlak}). The X-ray profile in the 3/4 keV and 1.5 keV band shows an excess at a radial distance of about 15 arcmin from the center. Such a ``hump'' in the radial X-ray profile can be explained by the presence of a cluster of young low mass stars or brown dwarfs. Therefore, NGC 247 offers the possibility to observe the formation of a halo of MACHOs
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