Resolving the age bimodality of galaxy stellar populations on kpc scales

DOI: 
10.1093/mnras/stx251
Publication date: 
01/01/2017
Main author: 
Zibetti, Stefano
IAA authors: 
García Benito, R.;Kehrig, C.;Márquez, I.
Authors: 
Zibetti, Stefano;Gallazzi, Anna R.;Ascasibar, Y.;Charlot, S.;Galbany, L.;García Benito, R.;Kehrig, C.;de Lorenzo-Cáceres, A.;Lyubenova, M.;Marino, R. A.;Márquez, I.;Sánchez, S. F.;van de Ven, G.;Walcher, C. J.;Wisotzki, L.
Journal: 
Monthly Notices of the Royal Astronomical Society
Refereed: 
Yes
Publication type: 
Article
Pages: 
1902-1916
Abstract: 
Galaxies in the local Universe are known to follow bimodal distributions in the global stellar populations properties. We analyze the distribution of the local average stellar-population ages of 654 053 sub-galactic regions resolved on ̃1-kpc scales in a volume-corrected sample of 394 galaxies, drawn from the CALIFA-DR3 integral-field-spectroscopy survey and complemented by SDSS imaging. We find a bimodal local-age distribution, with an old and a young peak primarily due to regions in early-type galaxies and star-forming regions of spirals, respectively. Within spiral galaxies, the older ages of bulges and inter-arm regions relative to spiral arms support an internal age bimodality. Although regions of higher stellar-mass surface-density, μ<SUB>★</SUB>, are typically older, μ<SUB>★</SUB> alone does not determine the stellar population age and a bimodal distribution is found at any fixed μ<SUB>★</SUB>. We identify an 'old ridge' of regions of age ̃9 Gyr, independent of μ<SUB>★</SUB>, and a 'young sequence' of regions with age increasing with μ<SUB>★</SUB> from 1-1.5 Gyr to 4-5 Gyr. We interpret the former as regions containing only old stars, and the latter as regions where the relative contamination of old stellar populations by young stars decreases as μ<SUB>★</SUB> increases. The reason why this bimodal age distribution is not inconsistent with the unimodal shape of the cosmic-averaged star-formation history is that i) the dominating contribution by young stars biases the age low with respect to the average epoch of star formation, and ii) the use of a single average age per region is unable to represent the full time-extent of the star-formation history of 'young-sequence' regions.
Database: 
ADS
SCOPUS
URL: 
https://www.scopus.com/inward/record.uri?eid=2-s2.0-85021082134&doi=10.1093%2fmnras%2fstx251&partnerID=40&md5=24e2baba5c2c0b391b66f7ead4f8ddbf
ADS Bibcode: 
2017MNRAS.468.1902Z
Keywords: 
galaxies:stellar content;galaxies: structure;galaxies:statistics;Astrophysics - Astrophysics of Galaxies