A&A 421, 969-976 (2004)
DOI: 10.1051/0004-6361:20035957

A possible age-metallicity relation in the Galactic thick disk?

T. Bensby, S. Feltzing and I. Lundström

Lund Observatory, Box 43, 221 00 Lund, Sweden
    e-mail: [sofia;ingemar]@astro.lu.se

( Received 30 December 2003 / Accepted 21 March 2004 )

Abstract
A sample of 229 nearby thick disk stars has been used to investigate the existence of an age-metallicity relation (AMR) in the Galactic thick disk. The results indicate that that there is indeed an age-metallicity relation present in the thick disk. By dividing the stellar sample into sub-groups, separated by 0.1 dex in metallicity, we show that the median age decreases by about 5-7 Gyr when going from [Fe/H] to [Fe/H] . Combining our results with our newly published -element trends for a local sample of thick disk stars that show signatures from supernovae type Ia (SN Ia), we draw the conclusion that the time-scale for the peak of the SN Ia rate is of the order of 3-4 Gyr in the thick disk. The tentative evidence for a thick disk AMR that we present here also has implications for the thick disk formation scenario; star-formation must have been an ongoing process for several billion years. This appears to strengthen the hypothesis that the thick disk originated from a merger event with a companion galaxy that puffed up a pre-existing thin disk.

Key words: stars: Hertzsprung-Russell (HR) and C-M diagrams -- stars: kinematics -- Galaxy: disk -- Galaxy: kinematics and dynamics -- Galaxy: solar neighbourhood -- Galaxy: formation

Offprint request: T. Bensby, thomas@astro.lu.se

© ESO 2004