SCALE-LENGTH DETERMINATIONS OF EXPONENTIAL DISKS OF SPIRAL GALAXIES - A COMPARISON

Values for the scale lengths h of the exponential discs of spiral galaxies, as found by different authors, have been compared. For a given galaxy, two published values for h may show a discrepancy of almost a factor two. The average value of the discrepancy for more than 120 galaxies is 23%, with a standard deviation of 20%. We see no systematic trends, nor correlations of the discrepancies with obvious galaxy parameters, such as morphological type, arm class or inclination. We do observe that semi-automated ways of determining the scale length introduce relatively large discrepancies.

These results show the difficulty of determining reliable scale length values, and further emphasize that one should be careful when interpreting physically the exponential nature of discs of spiral galaxies.