SDSS astronomers at Ohio State have made a new, more robust measurement of the relationship between stellar mass and the abundance of elements heavier than helium and hydrogen. The measurement of elements is called the “gas-phase metallicity” and is based on measuring weak auroral lines that are typically undetected in galaxy spectra (dubbed the “direct method”). The relationship between these two is called the mass-metallicity relationship. To enhance the signal-to-noise ratio of these lines, the astronomers stacked ~200,000 galaxy spectra from the SDSS-II Data Release 7.

(Figure) The new mass-metallicity relation is shown by the points and black line. The colored lines indicate previous mass-metallicity relations based on less certain strong line methods. This new measurement of the mass-metallicity relation provides important constraints for galaxy evolution models, especially for the efficiency of galactic winds.

Lead author Brett Andrews has prepared a brief video describing the main results for a general audience:

For more details please see the published paper:
“The Mass-Metallicity Relation with the Direct Method on Stacked Spectra of SDSS Galaxies”
Andrews & Martini (2013)
The Astrophysical Journal, 765, 140.
http://arxiv.org/abs/1211.3418
http://adsabs.harvard.edu/abs/2013ApJ…765..140A