EDP Sciences
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Volume 373, Number 3, July III 2001
Page(s) 886 - 894
Section Galactic structure and dynamics
DOI http://dx.doi.org/10.1051/0004-6361:20010680

A&A 373, 886-894 (2001)
DOI: 10.1051/0004-6361:20010680

Early galaxy evolution from deep wide field star counts

II. First estimate of the thick disc mass function
C. Reylé and A. C. Robin

CNRS UMR 6091, Observatoire de Besançon, BP 1615, 25010 Besançon Cedex, France
    e-mail: annie.robin@obs-besancon.fr

(Received 11 April 2001 / Accepted 23 April 2001 )

Star counts at high and intermediate galactic latitudes, in the visible and the near infrared, are used to determine the density law and the initial mass function of the thick disc population. The combination of shallow fields dominated by stars at the turnoff with deep fields allows the determination of the thick disc mass function in the mass range 0.2-0.8 $M_{\odot}$. Star counts are compared with simulations of a synthesis population model. The fit is based on a maximum likelihood criterion. The best fit model gives a scale height of 800 pc, a scale length of 2500 pc and a local density of 10-3 stars pc-3 or $7.1 \times 10^{-4}$ $M_{\odot}$ pc-3 for $M_v \leq 8$. The IMF is found to follow a power law dN/d $m \propto m^{-0.5}$. This is the first determination of the thick disc mass function.

Key words: Galaxy: structure -- Galaxy: stellar content -- Galaxy: general

Offprint request: C. Reylé, celine.reyle@obs-besancon.fr

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