THE RECENT STELLAR ARCHEOLOGY OF M31-THE NEAREST RED DISK GALAXY
- Herzberg Institute of Astrophysics, National Research Council of Canada, 5071 West Saanich Road, Victoria, BC V9E 2E7 (Canada)
- Department of Astronomy, University of Massachusetts, LGRT 619-E, Amherst, MA 01003-9305 (United States)
- LERMA, UMR CNRS 8112, Observatoire de Paris, 61 Avenue de l'Observatoire, 75014 Paris (France)
- Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom)
- Sydney Institute for Astronomy, School of Physics, A28, The University of Sydney, NSW 2006 (Australia)
- Division of Astronomy and Astrophysics, University of California, Los Angeles, 430 Portola Plaza, Box 951547, Los Angeles, CA 90095-1547 (United States)
We examine the star-forming history of the M31 disk during the past few hundred Myr. The luminosity functions (LFs) of main-sequence stars at distances R{sub GC} > 21 kpc (i.e., >4 disk scale lengths) are matched by models that assume a constant star formation rate (SFR). However, at smaller R{sub GC} the LFs suggest that during the past {approx}10 Myr the SFR was 2-3 times higher than during the preceding {approx}100 Myr. The rings of cool gas that harbor a significant fraction of the current star-forming activity are traced by stars with ages {approx}100 Myr, indicating that (1) these structures have ages of at least 100 Myr and (2) stars in these structures do not follow the same relation between age and random velocity as their counterparts throughout the disks of other spiral galaxies, probably due to the inherently narrow orbital angular momentum distribution of the giant molecular clouds in these structures. The distribution of evolved red stars is not azimuthally symmetric, in the sense that the projected density along the northeast segment of the major axis is roughly twice that on the opposite side of the galaxy. The northeast arm of the major axis thus appears to be a fossil star-forming area that dates to intermediate epochs. Such a structure may be the consequence of interactions with a companion galaxy.
- OSTI ID:
- 22037219
- Journal Information:
- Astrophysical Journal, Vol. 751, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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