Infrared Array Camera (IRAC) Observations of M81

Creators: Willner, S. P.; Ashby, M. L. N.; Barmby, P.; Fazio, G. G.; Pahre, M.; Smith, H. A.; Kennicutt, Robert C., Jr.; Calzetti, Daniela; Dale, Daniel A.; Draine, B. T.; Regan, Michael W.; Malhotra, S.; Thornley, Michele D.; Appleton, P. N.; Frayer, D.; Helou, G.; Stolovy, S.; Storrie-Lombardi, L.

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Abstract

Infrared Array Camera (IRAC) images of M81 show three distinct morphological constituents: a smooth distribution of evolved stars with bulge, disk, and spiral arm components; a clumpy distribution of dust emission tracing the spiral arms; and a pointlike nuclear source. The bulge stellar colors are consistent with M-type giants, and the disk colors are consistent with a slightly younger population. The dust emission generally follows the blue and ultraviolet emission, but there are large areas that have dust emission without ultraviolet and smaller areas with ultraviolet but little dust emission. The former are presumably caused by extinction, and the latter may be due to cavities in the gas and dust created by supernova explosions. The nucleus appears fainter at 8 μm than expected from ground-based 10 μm observations made 4 years ago.

Additional Information

© 2004 American Astronomical Society. Received 2004 March 26. Accepted 2004 May 27. This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under NASA contract 1407. Support for this work was provided by NASA through contract 1256790 issued by JPL/Caltech. Support for the IRAC instrument was provided by NASA through contract 960541 issued by JPL. M. A. P. acknowledges NASA/LTSA grant NAG5-10777. IRAF is distributed by the National Optical Astronomy Observatories, which are operated by the Association of Universities for Research in Astronomy, Inc., under cooperative agreement with the National Science Foundation. This research has made use of the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.

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