91̽��

Abstract:

We present 8-13 μm multi-colour maps of the central 25” x 25” of the Galaxy, obtained with beam diameter \ge2” and spectral resolution of λ/Δλ\ge40. Also presented are pointed spectra with high signal-to-noise (\gt 100) obtained using 2” beams in the region of the east-west bar between IRS 1 and IRS 2. Model fits to the spectra, from both pointed observations and the map, yield information on the temperature and opacity structure of the region and indicate that the compact 10 μm sources display enhancements in the dust temperature, in some cases slightly displaced from the intensity peaks, and that the temperature decreases towards the lateral edges of the northern arm and east-west bar. The northern arm, and particularly the region around IRS 1, are regions where emission from silicate dust is significantly enhanced. We find no evidence for temperature gradients or rim heating centred on the region of IRS 16/SgrA$^*$. Comparison with radio continuum studies of the region leads to the conclusion that nebular heating supplies only a small fraction of the infrared luminosity of the ionized filaments. IRS 1 and 10 must therefore contain internal heating sources, and in the absence of an externally centred temperature gradient, a substantial part of the infrared luminosity of the filaments must also come from internal heating.

Abstract:

THE dynamics of nearby galaxies 91̽�� the existence of a large concentration of mass (the 'Great Attractor') in the Centaurus region at a redshift (z) between 0.012 and 0.015 (refs 1, 2). Scaramella et al3 have suggested that a concentration of rich clusters of galaxies at z≈0.05 in the Centaurus region may also have a significant role in perturbing the local Hubble flow. The existence of such overdense regions in the Universe would have a profound effect on ideas about the formation of large-scale structure4. At present the reality of such regions is 91̽��ed by some, but not by all, studies of the streaming of distant galaxies1,2,5-9. We demonstrate here that redshifts of galaxies that are in the Infrared Astronomical Satellite (IRAS) survey show the existence of an extended supercluster at z ≈0.05 surrounding the concentration of clusters described by Scaramella et al. Its contribution to the Local Group peculiar (non-Hubble) velocity is probably minor, although it may dominate motions on the far side of the Great Attractor. © 1990 Nature Publishing Group.