Journal Article

On the prospect of inferring the halo structure and the masses of dark objects through parallax microlensing

D. Marković

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 299, issue 4, pages 929-941
Published in print October 1998 | ISSN: 0035-8711
Published online October 1998 | e-ISSN: 1365-2966 | DOI:
On the prospect of inferring the halo structure and the masses of dark objects through parallax microlensing

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We study the proposed use of parallax microlensing in the direction of the Large Magellanic Cloud (LMC) to separate the effects of the mass function of dark massive halo objects (MHOs or ‘machos’) on the one hand, and their spatial distribution and kinematics on the other. This disentanglement is supposed to allow a much better determination of the two than could be achieved entirely on the basis of the durations of events. We restrict our treatment to the same class of power‐law spherical models for the halo of MHOs studied in a previous paper by Marković 38 Sommer‐Larsen, and assume that one can eliminate microlensing events caused by massive objects outside the halo (e.g., the LMC halo). Whereas the duration‐based error in the average MHO mass, μ¯ ≡ M¯/M, exceeds (at N = 100 events) μ¯ by a factor of 2 or more, parallax microlensing remarkably brings it down to 15–20 per cent of μ¯, regardless of the shape of the mass function. In addition, the slope α of the mass function, dn/dμ ∝ μα, can be inferred relatively accurately (σα < 0.4) for a broader range, −3 < α < 0. The improvement in the inference of the halo structure is also significant: the index γ of the density profile ( ρ ∼ R−γ) can be obtained with the error σγ < 0.4. While in a typical situation the errors for the parameters specifying the velocity dispersion profile are of about the same magnitude as the parameters themselves, virtually all the uncertainty is ‘concentrated’ in linear combinations of the parameters that may have little influence on the profile, thus allowing its reasonably accurate inference.

Keywords: Galaxy: fundamental parameters; Galaxy: halo; Galaxy: kinematics and dynamics; dark matter; gravitational lensing

Journal Article.  0 words. 

Subjects: Astronomy and Astrophysics

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