Abstract
Aims. This work investigates the properties (metallicity and kinematics) and interfaces of the Galactic thick disc as a function of height above the Galactic plane. The main aim is to study the thick disc in a place where it is the main component of the sample. Methods. We take advantage of former astrometric work in two fields of several square degrees in which accurate proper motions were measured down to V-magnitudes of 18.5 in two directions, one near the north galactic pole and the other at a galactic latitude of 46 ◦ and galactic longitude near 0 ◦ . Spectroscopic observations have been acquired in these two fields for a total of about 400 stars down to magnitude 18.0, at spectral resolutions of 3.5 to 6.25 A. The spectra have been analysed with the code ETOILE, comparing the target stellar spectra with a grid of 1400 reference stellar spectra. This comparison allowed us to derive the parameters effective temperature, gravity, [Fe/H] and absolute magnitude for each target star. Results. The Metallicity Distribution Function (MDF) of the thin-thick-disc-halo system is derived for several height intervals between 0 and 5 kpc above the Galactic plane. The MDFs show a decrease of the ratio of the thin to thick disc stars between the first and second kilo-parsec. This is consistent with the classical modelling of the vertical density profile of the disc with 2 populations with different scale heights. A vertical metallicity gradient, ∂[Fe/H]/∂z = −0.068 ± 0.009 dex kpc −1 , is observed in the thick disc. It is discussed in terms of scenarios of formation of the thick disc.
Highlights
The determination of the properties of the thick disc of the Milky Way has been a longstanding issue since its detection nearly three decades ago (Gilmore & Reid 1983)
In this article we investigate the properties of the thick disc as a function of the height above the Galactic plane and we examine the interfaces between the thin disc, thick disc and halo
421 spectra of field stars, spanning the magnitude range 12.5 < V < 18, were selected, with no kinematical or chemical bias, in the proper motion catalogues of Soubiran (1992) and Ojha et al (1994). These stars were observed with the low resolution spectrographs CARELEC (Δλ = 3.5 Å) and MOS-SIS (Δλ = 6.25 Å), respectively installed at the HauteProvence observatory and on the Canada-France-Hawaii telescope
Summary
The determination of the properties of the thick disc of the Milky Way has been a longstanding issue since its detection nearly three decades ago (Gilmore & Reid 1983). 2008; Bond et al 2010; Carollo et al 2010), synthesis of photometric observations (Reylé & Robin 2001), photometry in Kapteyn Selected Areas (Siegel et al 2002, 2009), the Radial Velocity Experiment, RAVE (Steinmetz et al 2006; Zwitter et al 2008; Veltz et al 2008), the Sloan Extension for Galactic Understanding and Exploration, SEGUE (Yanny et al 2009) Some results of these studies are discussed in Sect.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
