Microlensing Search toward M33 ---A Test of Dark Matter in the Local Group---

Details Microlensing Search toward M33 ---A Test of Dark Matter in the Local Group--- Microlensing Search toward M33 ---A Test of Dark Matter in the Local Group---

Jul 2000

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000pthph.104...83a&link_type=abstract

Progress of Theoretical Physics, Vol. 104, No. 1, pp. 83-94.

Physics

Scientific paper

We propose a microlensing search toward an intermediate-inclination Local Group spiral galaxy M33. The slow rotation velocity (≅ 100 km/s) of M33 provides the possibility to distinguish MACHOs of our galaxy and those of M33 statistically. The optical depth of the MACHOs of our galaxy was calculated to be ≅ 3 × 10-7, and the average event timescale is ≅ 60 days for M = 0.5 Modot. The optical depth of the M33 MACHOs is position dependent; it was calculated along the major axis to be 0.5 - 2 × 10-7. The average event timescale of the M33 MACHOs was calculated to be 90 - 150 days for M = 0.5 Modot. An excess of long timescale events for the M33 MACHOs may be observed around the central region if we can obtain enough events. The observation of M33 has the advantage of avoiding the self-lensing problem. The calculation of the disk-disk lensing showed that the optical depth is small and does not yield a background of MACHOs for R > 3 kpc. Observation of very distant galaxies provides a unique opportunity to explore intergalactic lensing objects. Calculations for the intergalactic lensing objects were made for two types of mass distributions: (1) a single isothermal sphere, and (2) a double isothermal sphere. The optical depth for the single isothermal sphere was calculated to be >= 2 × 10-7. The average event timescale is very long (500 - 550 days for M = 0.5Modot), and separation from MACHOs can be made. The event rate was calculated to be >= 1 × 10-7 events/star . year which is detectable in the long-term (~ 5 years) observations if approximately 107 stars are observed. The optical depth and the event rate for the double isothermal sphere strongly depend on the half-mass radius. But intergalactic lensing objects can be detected by long-term observations, unless they are widely diffused (rh > 300 kpc). The average event timescale was found to be 250 - 500 days for M = 0.5 Modot, depending on the core radius and rh. Feasibility of the M33 observation is discussed. Current large aperture wide-field telescopes, such as SUBARU, are promising for the observation.

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