2004/03/16 by Robert R. Uglesich, R. Uglesich, Arlin Crotts +7 · 5 citations
Physics and Astronomy · #Andromeda Galaxy #Astronomy #Astrophysics #Astrophysics and Star Formation Studies #Bulge #Dark matter #Dark matter halo #Galactic halo #Galaxies: Formation, Evolution, Phenomena #Galaxy #Gravitational microlensing #Halo #Large Magellanic Cloud #Milky Way #Physics #Stars #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/422131
published as Astrophys.J. 612 (2004) 877-893 · 25 pages, LaTex; 11 figures. Revised, refereed manuscript resubmitted to The Astrophysical Journal. Corrected Figure 8 and other minor points
arxiv created 2004/03/16 · openalex publication_date 2004/09/10 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
We have completed an intensive monitoring program of two fields on either side of the center of M31 and report here on the results concerning microlensing of stars in M31. These results stem from a 3 yr study (the Vatican Advanced Technology Telescope [VATT]/Columbia survey) of microlensing and variability of M31 stars, emphasizing microlensing events of 3 day to 2 month timescales and likely due to masses in M31. These observations were conducted intensively from 1997 to 1999, with baselines 1995 to present, at the VATT and the 1.3 m telescope at MDM Observatory, with additional data from the Isaac Newton Telescope, including about 200 epochs total. The two fields monitored cover 560 arcmin 2 total, positioned along the minor axis on either side of M31. Candidate microlensing events are subject to a number of tests discussed here with the purpose of distinguishing microlensing from variable star activity. A total of four probable microlensing events, when compared with carefully computed event rate and efficiency models, indicate a marginally significant microlensing activity above that expected for the stars alone in M31 (and the Galaxy) acting as lenses. A maximum likelihood analysis of the distribution of events in timescale and across the face of M31 indicates a microlensing dark matter halo fraction consistent with that seen by MACHO in our Galaxy toward the Large Magellanic Cloud. Specifically, for a nearly singular isothermal sphere model, we find a microlensing halo mass fraction f b = 0.29 of the total dark matter and a poorly constrained lensing component mass (0.02-1.5 M ☉ ; 1 σ limits). This study serves as the prototype for a larger study approaching completion; between the two there is significant evidence for an asymmetry in the distribution of microlensing events across the face of M31 and therefore a large population of halo microlensing dark matter objects.