Resolved DENIS and UKIRT Infrared Stellar Observations Towards the Galactic Centre

Abstract

IJK _s DENIS images, in a crowded region towards the centre of the Galaxy, covering 17.4 deg² in |l| < 5°, |b| < 1.5°, result in ∼ 750000 sources per colour. An investigation of the completeness and systematic effects present in these crowded images suggests that the standard DENIS magnitude limits of ∼18, 16 and 14 in I,J and K _s were not achieved due to crowding — 80% completeness falls about 2 magnitudes brighter than these limits

We convolve a detailed model of the systematic and random errors in the photometry with a simple model of the Galactic disk and dust distribution, to simulate expected colour-magnitude diagrams. These are in good agreement with the observed diagrams, allowing us to isolate those stars from the inner disk and bulge. After correcting for local dust-induced asymmetries, we find evidence for longitude-dependent asymmetries in the distant J and K _s sources, consistent with the general predictions of some Galactic bar models. Complementary nbL-band (3.6µm) observations taken at UKIRT at b= -0.1° and l=±4.3° and l=±2.3° are also presented. The magnitude limit (∼12) and low coefficient for interstellar extinction at this wavelength (A _nbL =0.047A _V ), allows us to observe bulge giants. We successfully match 95% of nbL sources with DENIS K _s sources. Dereddened number counts show an excess of ∼15% and N5% in source counts at l = -4.3° and l = -2.3° compared to l = +4.3° and l = +2.3° respectively. This is in the same sense as predicted by many bar models, with our results favouring gas dynamical models and the recent deconvolution of surface photometry data (e.g. Binney et al. 1991; Binney et al. 1997), over earlier treatments of photometric data (e.g. Dwek et al., 1995).