Stellar Populations and the Star Formation Histories of LSB Galaxies: IV
  Spitzer Surface Photometry of LSB Galaxies
  Surface photometry at 3.6$\mu$m is presented for 61 low surface brightness
(LSB) galaxies ($\mu_o < 19$ 3.6$\mu$m mag arcsecs$^{-2}$). The sample covers a
range of luminosity from $-$11 to $-$22 in $M_{3.6}$ and size from 1 to 25 kpc.
The morphologies in the mid-IR are comparable to those in the optical with
3.6$\mu$m imaging reaches similar surface brightness depth as ground-based
optical imaging. A majority of the resulting surface brightness profiles are
single exponential in shape with very few displaying upward or downward breaks.
The mean $V-3.6$ color of LSB is 2.3 with a standard deviation of 0.5.
Color-magnitude and two color diagrams are well matched to models of constant
star formation, where the spread in color is due to small changes in the star
formation rate (SFR) over the last 0.5 Gyrs as also suggested by the specific
star formation rate measured by H$\alpha$.
