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Date and Time of the Query: 2019-05-21 T02:30:54 PDT
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For refcode 2007AJ....134..321P:
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Copyright by American Astronomical Society. Reproduced by permission
2007AJ....134..321P H{delta} In The Integrated Light Of Galaxies: What Are We Actually Measuring? L. C. Prochaska, James A. Rose, Nelson Caldwell, Bruno V. Castilho, Kristi Concannon, Paul Harding, Heather Morrison, Ricardo P. Schiavon Abstract. We present a cautionary study exploring the reliability of the H{delta} line in the integrated spectra of galaxies for determining galaxy ages. Our database consists of the observed integrated spectra of ~120 early-type galaxies, 7 metal-rich globular clusters in M31 and the Galactic globular cluster 47 Tuc, and the open cluster M67. We have measured H{delta} using index definitions designed to assess 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}. We find systematic differences in the ages derived from H{delta} measurements among the various definitions when extracting ages from H{delta} in old stellar populations with enhanced CN bands due to nonsolar abundance ratios. We propose that neighboring CN lines have a strong effect on pseudocontinuum and central bandpass levels. For stellar populations that have nonsolar abundance ratios in C and/or N, population synthesis models that do not account for abundance ratio variations cannot accurately reproduce the CN 4216 Angstrom 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 nonsolar abundance ratios. Key words: galaxies: abundances-galaxies: evolution-galaxies: stellar content
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