A census of metals and baryons in stars in the local Universe - AstrophysicsReport as inadecuate

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Abstract: We combine stellar metallicity and stellar mass estimates for a large sampleof galaxies drawn from the SDSS DR2 spanning wide ranges in physicalproperties, in order to derive an inventory of the total mass of metals andbaryons locked up in stars today. Physical parameter estimates are derived fromgalaxy spectra with high S-N >20. Coadded spectra of galaxies with similarvelocity dispersions, absolute r-band magnitudes and 4000\AA-break values areused for those regions of parameter space where individual spectra have lowerS-N. We estimate the total density of metals and of baryons in stars and, fromthese two quantities, we obtain a mass- and volume-averaged stellar metallicityof =1.04+-0.14 Z sun, i.e. consistent with solar. We also study howmetals are distributed in galaxies according to their mass, morphology and age,and we then compare these distributions with the corresponding distributions ofstellar mass. We find that the bulk of metals locked up in stars in the localUniverse reside in massive, bulge-dominated galaxies, with red colours and high4000\AA-break values corresponding to old stellar populations. Bulge-dominatedand disc-dominated galaxies contribute similar amounts to the total stellarmass density, but have different fractional contributions to the mass densityof metals in stars, in agreement with the mass-metallicity relation.Bulge-dominated galaxies contain roughly 40% of the total amount of metals instars, while disc-dominated galaxies less than 25%. Finally, at a given galaxystellar mass, we define two characteristic ages as the median of thedistributions of mass and metals as a function of age. These characteristicages decrease progressively from high-mass to low-mass galaxies, consistentwith the high formation epochs of stars in massive galaxies.

Author: Anna Gallazzi 1,2, Jarle Brinchmann 3, Stephane Charlot 4,2, Simon D.M. White 2 1MPIA, Heidelberg, 2MPA, Garching, 3CAUP, Porto,

Source: https://arxiv.org/


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