Other
Scientific paper
May 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007sptz.prop40175f&link_type=abstract
Spitzer Proposal ID #40175
Other
Scientific paper
The late type galaxy NGC 309 is one of the largest and most luminous spiral galaxies known. At a redshift distance of 83 Mpc (H=70 km/s/Mpc; Spergel et al. 2003), the absolute blue magnitude is -22.52 and the diameter is ~ 70 kpc (1 arcsec = 0.40 kpc). NGC 309 belongs to the multiple arm class 9 of Elmegreen & Elmegreen (1984). Combined with an almost face-on orientation, NGC 309 offers unique prospects for addressing important issues associated with spiral structure and star formation, including radically different morphology in optical compared with infrared wavelengths, star formation and PAH distribution. We propose to investigate the color gradients across the arms of NGC 309, and to study the distribution of macromolecules and PAHS in regimes along spiral arms where the associated shock front strengths rank amongst the highest ever encountered in a spiral galaxy. NGC 309 also provides an excellent test for the origin of exponential disks. For this giant galaxy, the outer parts should be dynamically young. At the outer radius of 35 kpc, the orbit time for 250 km/s rotation speed is only 0.88 Gyr; there have not been many rotations in the outer domains. We wish to explore whether the exponential disk continues smoothly at large radii, and whether the exponential scale length is different along different directions (asymmetric). If the exponential disk takes time to settle down, then with only a few rotations in the outer parts, it could have a different scale length in different directions, as it has not yet stabilized. On the other hand, if we find that there is a smooth, uniform exponential disk in all directions (even in the outer parts), the implication would be that the exponential disk forms at birth. Our modest program includes just one AOR, to carry out IRAC imaging of NGC 309 in all four IRAC bands.
Ashby Matthew
Block David
Elmegreen Bruce
Elmegreen Debra
Fazio Giovanni
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