Abridged: We present analysis of Spitzer Space Telescope observations of the
three low surface brightness (LSB) optical giant galaxies Malin 1, UGC 6614 and
UGC 9024. Mid- and far-infrared morphology, spectral energy distributions, and
integrated colors are used to derive the dust mass, dust-to-gas mass ratio,
total infrared luminosity, and star formation rate (SFR). The 8 micron images
indicate that polycyclic aromatic hydrocarbon molecules are present in the
central regions of all three metal-poor LSB galaxies. The diffuse optical disks
of Malin 1 and UGC 9024 remain undetected at mid- and far-infrared wavelengths.
The dustiest of the three LSB galaxies, UGC 6614, has infrared morphology that
varies significantly with wavelength. The 8 and 24 micron emission is
co-spatial with H\alpha emission previously observed in the outer ring of UGC
6614. The estimated dust-to-gas ratios, from less than 10^{-3} to 10^{-2},
support previous indications that the LSB galaxies are relatively dust poor
compared to the HSB galaxies. The total infrared luminosities are approximately
1/3 to 1/2 the blue band luminosities, suggesting that old stellar populations
are the primary source of dust heating in these LSB objects. The SFR estimated
from the infrared data ranges ~0.01-0.88 M_sun yr^{-1}, consistent with results
from optical studies.Comment: Accepted in ApJ (2007, July 20 issue), 34 pages, 10 postscript
figures, 2 table
