Our Galaxy and Nearby Galaxies

 

From star birth to death, from the most diffuse interstellar plasmas to the most compact stellar forms, X-rays can provide crucial information pertaining to the structure and evolution of spiral galaxies and their constituent parts. Despite this, up until the launch of Chandra and XMM-Newton (XMM), our knowledge of the X-ray properties of our own Galaxy and of other similar spiral galaxies in the local Universe remained highly constrained by the observational limitations, in terms of spatial and spectral resolution, sensitivity and bandpass coverage. Fortunately 6 years post-launch, both the XMM and Chandra archives now contain a wealth of relevant information, with the prospect of even more comprehensive datasets becoming available as both missions enter their “legacy” phases.

We are currently engaged in three inter-relating projects in this area. Two of these involve current and planned X-ray surveys of our own Galaxy with the third focusing on the study of a sample of nearby spiral galaxies. The core themes of the investigation are: (a) the characterisation and study of the discrete X-ray source population in our own Galaxy over a very broad luminosity range; (b) the study of the thermal and non-thermal processes which give rise to the copious diffuse X-ray emission emanating from active regions in normal spiral galaxies, for which our own Galactic Centre provides the most obvious test-bed; (c) the comparative study of the X-ray properties of late-type spirals as a class, with a view to identifying the range of factors influencing both the incidence of the most luminous discrete (binary) sources and the X-ray luminosity and spectral characteristics of the residual emission.

Some recent highlights from this programme are illustrated in the accompanying figures.

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First evidence in the X-ray source counts for a major low/intermediate Lx (1031-34 erg/s) source population in the Galactic Plane.

 

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