Issue |
A&A
Volume 430, Number 3, February II 2005
|
|
---|---|---|
Page(s) | 853 - 864 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361:20041566 | |
Published online | 26 January 2005 |
Detecting cold H2 globules in the outer Galactic disc by microlensing towards the Maffei 1 elliptical
Geneva Observatory, Ch. des Maillettes 51, 1290 Sauverny, Switzerland e-mail: Roger.Fux@obs.unige.ch
Received:
30
June
2004
Accepted:
20
September
2004
A candidate source of dark matter in spiral galaxies is
cold molecular hydrogen globules with a condensed central core and a
disc-like space distribution probably similar to that of neutral
hydrogen. This paper shows that the H2 cores are sufficiently
compact and massive to be detected by microlensing in the outer
Galactic disc and that the Maffei 1 elliptical galaxy, at a distance
of 3 Mpc and Galactic latitude , offers an ideal
target for such an experiment. The microlensing optical depth of H2
cores along the line of sight to this galaxy is estimated to
if most of the dark mass in the Milky Way
resides in such cores, and the typical event timescale to
1 day. Detection rates are computed both in the classical and
pixel lensing approaches in the I- and K-bands, and for a
representative selection of existing observing facilities. In the more
efficient pixel lensing case, two 10-h observing runs, separated
in time by at least several days, should yield of the order of 10 positive
detections at the
level using ground-based 8 m-class
telescopes in the K-band or the Hubble Space Telescope ACS camera in
the I-band, and the corresponding fraction of events with timescale
measurable to an accuracy better than
amounts to about
and
respectively for these observing alternatives.
Key words: cosmology: dark matter / Galaxy: disk / ISM: molecules / gravitational lensing / methods: observational
© ESO, 2005
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