Abstract details

We have explored the reliability of the H-delta line in the integrated spectra of galaxies for determining galaxy ages. We have measured H-delta using index definitions designed to evaluate contamination from the CN molecule in and around H-delta by choosing combinations of bandpasses that both avoid and include a region of CN molecular lines redward of H-delta. When extracting ages from H-delta in old stellar populations with enhanced CN bands due to non-solar abundance ratios, we find systematic differences in the ages derived from the various definitions. We propose that neighboring CN lines have a strong effect on continuum and central bandpass levels. For stellar populations which have non-solar abundance ratios in C and/or N, population synthesis models do not accurately reproduce the CN 4216 A band, which leads to a corresponding inaccuracy in reproducing the various H-delta indices. Hence, caution must be used when extracting galaxy ages from the H-delta line in old stellar populations with significant non-solar abundance ratios.