We estimated the galactic model parameters for a set of 20
intermediate-latitude fields with galactic longitudes 0<l<100 and 160<l<240,
included in the currently available Data Release 6 (DR6) of SDSS, to explore
their possible variation with galactic longitude. The local space densities of
the thick disc and halo are almost the same for all fields,
=6.52% and =0.35%, respectively, a result
different than the one cited for high-latitude fields. The thin disc's
scaleheight is 325 pc in the galactic centre changes to 369 pc in the third
quadrant, which confirms the existence of disc flare, whereas the thick disc
scaleheight is as large as 952 pc at galactic longitude l=20 and 10% lower at
l=160, which confirms the existence of the disc long bar in the direction l=27.
Finally, the variation of the axis ratio of the halo with galactic longitude is
almost flat, =0.56, except a slight minimum and a small maximum in the
second and third quadrants, respectively, indicating an effect of the long bar
which seems plausible for a shallow halo. We estimated the metallicities of
unevolved G-type stars and discussed the metallicity gradient for different
vertical distances. The metallicity gradient is d[M/H]/dz=-0.30 dex kpc−1
for short distances, confirming the formation of this region of the Galaxy by
dissipational collapse. However, its change is steeper in the transition
regions of different galactic components. The metallicity gradient is almost
zero for inner halo (5<z<10 kpc), indicating a formation of merger or accretion
of numerous fragments such as dwarf galaxies.Comment: 31 pages, 18 figures and 4 tables, accepted for publication in New
Astronom
