1 We use the standard notation, [X/Y]=log(X/Y)-log(X⊙/Y⊙), where X and Y are the masses of either individual, or groups of, elements. The term abundance is used to refer to the mass of a specific element divided by that of H [X/H], while abundance ratios are specified with respect to Fe [X/Fe]. Overall metallicity is represented by [Z/H].
A comparison of stellar populations in galaxy spheroids across a wide range of Hubble types
Version of Record online: 25 JUN 2002
Monthly Notices of the Royal Astronomical Society
Volume 333, Issue 3, pages 517–543, July 2002
How to Cite
Proctor, R. N. and Sansom, A. E. (2002), A comparison of stellar populations in galaxy spheroids across a wide range of Hubble types. Monthly Notices of the Royal Astronomical Society, 333: 517–543. doi: 10.1046/j.1365-8711.2002.05391.x
- Issue online: 25 JUN 2002
- Version of Record online: 25 JUN 2002
- Accepted 2002 February 5. Received 2002 February 5; in original form 2001 July 16
- galaxies: abundances;
- galaxies: evolution;
- galaxies: formation;
- galaxies: stellar content
We present line-strengths and kinematics from the central regions of 32 galaxies with Hubble types ranging from E to Sbc. Spectral indices, based on the Lick system, are measured in the optical and near-infrared (NIR). The 24 indices measured, in conjunction with models of the effects of varying abundance ratios, permit the breaking of age/metallicity degeneracy, and allow estimation of enhancements in specific light elements (particularly C and Mg). The large range of Hubble types observed allows direct comparison of line-strengths in the centres of early-type galaxies (E and S0) with those in spiral bulges, free from systematic differences that have plagued comparisons of results from different studies. Our sample includes field and Virgo cluster galaxies. For early-type galaxies our data are consistent with previously reported trends of Mg2 and Mgb with velocity dispersion. In spiral bulges we find trends in all indices with velocity dispersion. We estimate luminosity-weighted ages, metallicities and heavy-element abundance ratios (enhancements) from optical indices. These show that bulges are less enhanced in light (α-capture) elements and have lower average age than early-type galaxies. Trends involving age and metallicity also differ sharply between early and late types. An anticorrelation exists between age and metallicity in early types, while, in bulges, metallicity is correlated with velocity dispersion. We consider the implications of these findings for models of the formation of these galaxies. We find that primordial collapse models of galaxy formation are ruled out by our observations, while several predictions of hierarchical clustering (merger) models are confirmed.