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Gravitational microlensing for the detection of MACHOs towards M31: data analysis with the AGAPE method

Abstract : This thesis work is dedicated to the problem of the search
and the characterisation of dark matter. From an observational
point of view, on different lenght scale, from galatic to the entire Universe,
it exists a disagreement between the dynamical and luminous
estimation of the mass of astrophysical objects (as galaxies and cluster
of galaxies). This is a sort of missing mass problem.
This makes necessary, in the framwork of the standard
cosmological model, the introduction of a dark component
of mass, dark meaning that it doesn't emit electromagnetic radiation
and whose presence can be detected through its gravitational effects.
Even if both theory and observation agree on the need of
such a component, a still unanswered question is the nature of
such mass component.

We are going to address the problem of
the dark matter component in galatic haloes, where
the observational evidences in this sense (rotation curves)
are very robust. To this end we use an original set of data
(the MDM data) collected with the aim of studying the dark componenent
in form of MACHOs (Massive Astrophysical Compact Halo Objects)
in the halo of our and of the nearby galaxy of Andromeda (M31).
This search is based on the gravitational microlensing effect,
the deflection of light due to the presence of a massive body (the MACHO)
along the line of sight between the observer and a luminous source.
This effects shows as a temporal luminosity variation of the source.
From this analysis it is possible to estimate the distribution
of the mass in form of MACHO in the halo.

This search has been caried out using the pixel lensing technique
(proposed and developped by the AGAPE collaboration), that allows one
to detect luminosity variations of unresolved sources.

In the first chapter we recall some basics points about
the cosmological model and on the problem of dark matter.
We the review the microlensing effect and the
pixel lensing tecnique. Chapter two is devoted
to the description of the experimental setup,
and to different points linked with the image analysis
(calibration, composition). In chapter three we deal
with the tecniques used to analyse the signal
with respect to the problem of the detection
of microlening event. The background noise
being given here by variable stars, in particular
we study how we can characterize the achromaticity
propertie of the signal that interest us.
We then discuss the results from two simulations:
the first one aimed at the study of the selection
criteria we use to detect interesting variations,
the second a Monte Carlo simulaton of the experience.
In chapter 4 we consider various aspects of the analysis.
Dealing with the chromatic effects, we study some
kind of variable sources. We carry out an extension
of known microlensing candidates detected by other collaborations.
Eventually, we come to the discussion of the results of our selection,
where we get five light curve compatible with a microlensing signal.
Looking at the simulation, we then draw our conclusion on the problem.

Our analysis tends to confirm that only a small fraction
of the galactic haloes is in form of MACHO, and in particular
to exclude as a major component substellar objects.
Complete list of metadata
Contributor : Sebastiano Calchi Novati <>
Submitted on : Tuesday, November 11, 2003 - 7:40:43 PM
Last modification on : Wednesday, September 23, 2020 - 4:34:25 AM
Long-term archiving on: : Friday, April 2, 2010 - 7:09:33 PM


  • HAL Id : tel-00003739, version 1




Calchi Novati Sebastiano. Gravitational microlensing for the detection of MACHOs towards M31: data analysis with the AGAPE method. Astrophysics [astro-ph]. Università degli studi di Salerno, 2001. Italian. ⟨tel-00003739⟩



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