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In Hunter et al. (2012) we presented the data for LITTLE THINGS (Local Irregulars That Trace Luminosity Extremes, The H i Nearby Galaxy Survey). This is a multi-wavelength survey on a sample of 37 nearby (<10.3 Mpc) gas-rich dwarf irregular galaxies and 4 Blue Compact Dwarfs. The data include H i-line data from the Very Large Array in B, C, and D configurations, as well as GALEX FUV and NUV, UBV JHK, Hα, and Spitzer MIR images, and together they trace the galaxy's stellar populations, gas content, gas dynamics, and star formation indicators.
In Hunter et al. (2012) we characterized the VLA data with comparisons to single-dish H i masses and velocity profiles, channel maps, H i moment 0, 1, and 2 maps, and false-color images combining H i, V-band, and FUV images. Figure 5 was a collection of azimuthally-averaged H i surface density radial profiles.
To construct these surface density profiles, we measured the flux in annuli on the velocity-integrated H i maps using ellint in the Groningen Image Processing System (GIPSY; Vogelaar & Terlouw 2001). ellint offers three different ways of constructing the average signal in annuli, and we used option number 2. Option 2 produces a simple average of the counts in an annulus (sum of the values divided by the number of values). However, we did not realize that in this option the average signal in the annuli was also divided by the area of the pixel in arcseconds-squared. We needed to remove this division by multiplying by the area of the pixel. Thus, the profiles shown in Figure 5 of Hunter et al. (2012) are low by the area of the pixel in arcseconds-squared. This effect only changes the scaling and not the shape of the profiles.
For all but two of the galaxies, the pixel scale is 1
5, and the H i column density NH i should be multiplied by 2.25 arcseconds-squared or increased in the log by 0.35. For DDO 216 and SagDIG, the pixel scale is 35, so the NH i should be multiplied by 12.25 arcseconds-squared or increased in the log by 1.09. In producing the revised version of Figure 5 here, we have also chosen to count only non-blanked pixels in the annuli, rather than averaging by the total number of pixels in each annulus regardless of the number of blank pixels. This has a minor affect on the outer most annuli. The corrected Figure 5 is shown here in Figure 1.
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Figure 1. Azimuthally-averaged H i surface density as a function of distance from the center of the galaxy. These are measured from the robust-weighted velocity-integrated H i maps, using parameters—center position, position angle of the major axis, and inclination of the galaxy—determined from the optical V-band morphology. The width of the annuli and step size for the radius of each annulus was chosen to be approximately that of the FWHM of the VLA beam. The profiles have now been corrected for a division by the area of the pixel.
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We thank Rob Kennicutt for bringing this error to our attention.