This may partly reflect the larger errors associated with stellar metallicity determinations. This is expected since the nebular metallicity traces the metallicity of the last generations of stars to form, whereas the stellar metallicity represents an average over the entire star formation history of the galaxy. Radial gradients in the properties of stellar populations are known to exist for both bulge-dominated (Henry & Worthey 1999; Saglia et al. For more massive galaxies, the median age continues to increase, but only by about 0.2 dex (∼1.6 Gyr) over one order of magnitude in stellar mass. We note that some galaxies exhibit a steeper metallicity profile in the outer disc than in the inner disc. is the mass of galaxies, and Mtot is the total mass in that region. Also, the ages are constrained within 0.2 dex for almost all the galaxies, the typical uncertainty being ∼0.12 dex. The main weakness of the original calibration of Lick indices is that it relies on spectra which were not calibrated in flux, and for which the resolution [∼9-Å full width at half-maximum (FWHM)] is three times lower than achieved by modern spectroscopic galaxy surveys, such as the Sloan Digital Sky Survey (SDSS; York et al. Our sample, drawn from the SDSS DR2, includes unique spectra of 196 673 galaxies with Petrosian r-band magnitudes in the range 14.5 < r < 17.77 (after correction for foreground Galactic extinction using the extinction maps of Schlegel, Finkbeiner & Davis 1998). the relative abundance of elements other than hydrogen and helium) of a galaxy requires some words of caution because in a given galaxy, depending where one looks, this quantity may vary substantially. To purchase short term access, please sign in to your Oxford Academic account above. The flux- and wavelength-calibrated spectra cover the range from 3800 to 9200 Å with a resolution of ∼1800. In the left-hand panels of Fig. We note that gas-phase metallicity is best determined for star-forming galaxies, whereas stellar metallicity is best determined for early-type galaxies. The strength of each line is fitted independently. This cut reduces the original sample by about 75 per cent and biases our analysis towards high surface brightness, high concentration galaxies. For early-type galaxies of different masses, the largest change in median metallicity from one edge of the survey to the other is about 0.2 dex. High-concentration galaxies do not exhibit any significant trend in age, but the typical age of low-concentration galaxies decreases by about 0.2 dex over the same redshift range. For reference, the rms scatter is typically comparable to (or smaller than) the average uncertainty for stellar metallicity and age, but always larger than the average uncertainty for stellar mass. We explore the relationships between metallicity, age and stellar mass and the dependence of these relationships on galaxy structure. when accreted onto a galaxy, can lower the metallicity. This naive conclusion is not consistent with that of Tremonti et al. 1 are the analogous distributions in resolving power for a subsample of galaxies with mean S/N per pixel greater than 20. 9. The orientation of the age–metallicity degeneracy in Figs 11 and 12 indicates that it cannot be responsible for the trends in age and metallicity as a function of stellar mass identified above. Faber 1973; Worthey et al. The solid line indicates the median of the final conditional distribution, and the dashed lines the 16th and 84th percentiles. High stellar masses, and the dependence of this sample ) in plots metallicity of galaxies D4000, which are likely be... However, we describe our approach for deriving metallicities, ages and metallicities from the SDSS samples should substantially our... 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