Ages and metallicities of early-type galaxies in the SDSS: new insight into the physical origin of the colour-magnitude and the Mg2-sigmaV relations

We exploit recent constraints on the ages and metallicities of early-type galaxies in the Sloan Digital Sky Survey (SDSS) to gain new insight into the physical origin of two fundamental relations obeyed by these galaxies: the colour-magnitude and the Mg2-sigmaV relations. Our sample consists of 26,003 galaxies selected from the SDSS DR2 on the basis of their concentrated light profiles, for which we have previously derived median-likelihood estimates of stellar metallicity, light-weighted age and stellar mass. Our analysis provides the most unambiguous demonstration to date of the fact that both relations are primarily sequences in stellar mass and that total stellar metallicity, alpha-elements-to-iron abundance ratio and light-weighted age all increase with mass along the two relations. For high-mass ellipticals, the dispersion in age is small and consistent with the error. At the low-mass end, there is a tail towards younger ages, which dominates the scatter in colour and index strength at fixed mass. A small, but detectable, intrinsic scatter in the mass-metallicity relation also contributes to the scatter in the two observational scaling relations, even at high masses. Our results suggest that the chemical composition of an early-type galaxy is more tightly related to its dynamical mass (including stars and dark matter) than to its stellar mass. The ratio between stellar mass and dynamical mass appears to decrease from the least massive to the most massive galaxies in our sample.Comment: 22 pages, 19 figures, accepted for publication in MNRAS, couple of references added and minor changes after proof correctio

Superconducting RF Enabling technology for modern light sources

Superconducting radio frequency SRF technology holds the promise of low beam impedance, high gradient, CW operation and thus is ideally suited for use in high power synchrotron light sources. Over 30 years of research and development has helped to bring the technology to maturity and to the point that its near turn key operation is now feasible in such facilities. Many SRF systems are in routine operation in both storage ring and LINAC based light sources and are the key to the realization of a number of novel light source concepts such as ERLs, compact sources, x ray oscillator FELs, or short pulse operation in storage rings. An overview of the principles and advantages of SRF as well as the technology s state of the art and future challenges is give