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Age and Abundance Discrimination in Old Stellar Populations Using Mid-Ultraviolet Colors | | Ben Dorman
; Robert W. O’Connell
; Robert T. Rood
; | | Date: |
20 Mar 2003 | | Journal: | Astrophys.J. 591 (2003) 878-890 | | Subject: | astro-ph | | Affiliation: | 1,2), Robert W. O’Connell , and Robert T. Rood ( University of Virginia, NASA/GSFC-LHEA | | Abstract: | The restframe mid-ultraviolet spectral region (2000-3200 A) is important in analyzing the stellar populations of the "red envelope" systems observed at high redshifts. Here, we explore the usefulness of the mid-UV for determining ages and abundances of old populations. A mid-UV to optical/IR wavelength baseline provides good separation of population components because the main sequence turnoff dominates the integrated light between 2500 and 4000 A. We find a six magnitude difference in the mid-UV continuum level over the metallicity range -1.5 < log Z/Z_o < +0.5 and a comparable difference (per unit log t) for ages in the range 4-16 Gyr. Logarithmic derivatives of mid-UV colors with respect to age or metal abundance are 3-10 times larger than for the UBV region. Most of the spectral information on old populations therefore resides below 4000 A. We investigate the capability of UBV and mid-UV broad-band colors to separately determine age and abundance, taking into account precision in the color measurements. We find that the mid-UV improves resolution in (log t,log Z) space by about a factor of 3 for a given observational precision. Contamination by hot horizontal branch phases can seriously affect mid-UV spectra, reaching over 80% in some cases. However, this is straightforward to remove as long as far-UV measurements are available. Finally, we show that a 4 Gyr, solar abundance model based on empirical spectra provides an excellent fit to the mid-UV spectrum of the E galaxy M32. This indicates that the poorer results obtained from theoretical spectra arise from limitations of the synthesis models for individual stars. [Condensed] | | Source: | arXiv, astro-ph/0303477 | | Services: | Forum | Review | PDF | Favorites | |
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