2010/07/31 by Adrienne L. Erickcek, Nicholas M. Law · 3 citations
Physics and Astronomy · #Astronomy and Astrophysical Research #Baryonic dark matter #Dark matter #Galaxies: Formation, Evolution, Phenomena #Gravitational lens #Gravitational microlensing #Halo #Solar mass #Stellar, planetary, and galactic studies #astro-ph.CO #astro-ph.GA
paper · pdf · doi:10.1088/0004-637x/729/1/49
published as Astrophys.J.729:49,2011 · 18 pages, 8 figures, minor revisions made to match version to appear in ApJ
arxiv created 2011/01/23 · openalex publication_date 2011/02/08 · arxiv updated 2015/05/19 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
High-resolution N -body simulations of dark matter halos indicate that the Milky Way contains numerous subhalos. When a dark matter subhalo passes in front of a star, the light from that star will be deflected by gravitational lensing, leading to a small change in the star's apparent position. This astrometric microlensing signal depends on the inner density profile of the subhalo and can be greater than a few microarcseconds for an intermediate-mass subhalo ( M vir ≳ 10 4 M ☉ ) passing within arcseconds of a star. Current and near-future instruments could detect this signal, and we evaluate the Space Interferometry Mission 's ( SIM 's), Gaia 's, and ground-based telescopes' potential as subhalo detectors. We develop a general formalism to calculate a subhalo's astrometric lensing cross section over a wide range of masses and density profiles, and we calculate the lensing event rate by extrapolating the subhalo mass function predicted by simulations down to the subhalo masses potentially detectable with this technique. We find that, although the detectable event rates are predicted to be low on the basis of current simulations, lensing events may be observed if the central regions of dark matter subhalos are more dense than current models predict (≳1 M ☉ within 0.1 pc of the subhalo center). Furthermore, targeted astrometric observations can be used to confirm the presence of a nearby subhalo detected by gamma-ray emission. We show that, for sufficiently steep density profiles, ground-based adaptive optics astrometric techniques could be capable of detecting intermediate-mass subhalos at distances of hundreds of parsecs, while SIM could detect smaller and more distant subhalos.