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LSB Galaxies and the Tully-Fisher Relation

We present VLA HI imaging of four LSB galaxies which were thought to strongly deviate from the TF relation based on Arecibo single-dish observations. We do not detect three of the four targeted LSB galaxies in HI down to a 4-sigma limit of 0.08Jy km/s. We find that two of the four of these LSBs have bright galaxies which have contaminated the Arecibo signal. A further examination of the Arecibo sample shows that five out of the six galaxies that were found to deviate from TF have nearby bright galaxies and we conclude that possibly all but one of the non-TF galaxies are contaminated by HI from nearby galaxies. The sixth galaxy was not detected by us. A new observation by Arecibo did not confirm the earlier detection. The integrated profiles of the bright galaxies are consistent with the Arecibo results both in velocity range and amplitude, which indicates that most of the extreme deviators from the TF relation must have been affected by bright companions in this earlier HI survey. A more recent determination of the sidelobe structure of the Arecibo beam supports our conclusion and shows that the degree of sidelobe contamination was much larger than could have been initially predicted. Hence, we have corrected the results found in O'Neil et al. (2000) and have reconstructed the TF relation. These new observations then show a) a reconstructed TF relation that has relatively large scatter at all values of rotational velocity (possibly indicating the true range in disk galaxy properties) and b) the presence of at least some red, gas poor, LSB disks that indeed may be in an advanced evolutionary state as the faded remnants of their former high surface brightness actively star forming state.