Spitzer Observations of the Andromeda Spiral Galaxy

(released 13 Oct 2005)

Spitzer Press Release
Podcast with Robert Hurt interviewing Karl Gordon and George Rieke.
Univ. of Arizona Press Release
Space.com article on the new MIPS images.

Observations of the Andromeda galaxy (M31) were taken with the Spitzer Space Telescope (Spitzer) on 25 Aug 2004, exactly one year after the launch of Spitzer. The observations were done with the Multiband Imaging Photometer for Spitzer (MIPS) which observes at 24, 70, and 160 microns. These observations took nearly the whole day and were composed of approximately 11,000 individual snapshots at each wavelength which were combined to produce mosiacs of M31 in the three MIPS bands. For more information, see the the official Spitzer site.

The MIPS images were used to investigate the global morphology of our neighbor spiral galaxy at a level of detail and depth not possible with previous infrared images. For the first time, it is possible to roughly trace the spiral arms in M31 from the nuclear region, where the arms seem to originate from a bar, to well beyond the approximately 10 kpc radius ring of of star formation. This ring of star formation does not seem to be part of the spiral structure as it is very circular and offset from the nucleus when the disk of M31 is deprojected using M31's known inclination. In addition, the ring is split near the location of M32, a satellite galaxy of M31. Detailed numerical simulations of the interaction between M31 and M32 were used to show that M32 may have recently punched through M31's disk creating the split in the ring as well as pulling the ring off center. The results of this investigation have been submitted to the Astrophysical Journal Letters (ApJ) for publication.

A movie showing the simulation of the M31-M32 interaction is available (MPEG, MOV). M32 is shown as the blue ball. The red balls represent the gas disk, while the old stellar component is in white. The large white balls represent star formation events, leaving behind young stars (small white balls). The end of the movie shows the face-on projection of the resulting gas surface density at the present day, with M32 projected onto the middle of a hole in the ISM.

The MIPS images were taken by a team composed Karl D. Gordon, Jeremy Bailin, Charles W. Engelbracht, George H. Rieke, Karl A. Misselt, William B. Latter, Erick T. Young, Matthew L. N. Ashby, Pauline Barmby, B. K. Gibson, Dean C. Hines, Joannah Hinz, Oliver Krause, Deborah A. Levine, Francine R. Marleau, Alberto Noriega-Crespo, Susan Stolovy, David A. Thilker, and Mike W. Werner.

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