Sale, S. E., Drew, J. E., Knigge, C., Zijlstra, A. A., Irwin, M. J., Morris, R. A. H., Phillipps, S., Drake, J. J., Greimel, R., Unruh, Y. C., Groot, P. J., Mampaso, A. and Walton, N. A.
The structure of the outer galactic disc as revealed by IPHAS early A stars.
Monthly Notices of the Royal Astronomical Society, 402, (2), . (doi:10.1111/j.1365-2966.2009.15746.x).
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This study is an investigation of the stellar density profile of the Galactic disc in the anticentre direction. We select over 40?000 early A stars from INT/WFC Photometric H? Survey of the Northern Galactic Plane (IPHAS) photometry in the Galactic longitude range 160° < l < 200° close to the equatorial plane (?1° < b < +1°) .
We then compare their observed reddening-corrected apparent magnitude distribution with simulated photometry obtained from parametrized models in order to set constraints on the anticentre stellar density profile. By selecting A stars, we are appraising the properties of a population only ?100 Myr old.
We find that the stellar density profile of young stars is well fit to an exponential with length-scale of (3020 ± 120statistical± 180systematic) pc , which is comparable to that obtained in earlier studies, out to a Galactocentric radius of RT= (13.0 ± 0.5statistical± 0.6systematic) kpc . At larger radii, the rate of decline appears to increase with the scalelength dropping to (1200 ± 300statistical± 70systematic) pc.
This result amounts to a refinement of the conclusions reached in previous studies that the stellar density profile is abruptly truncated. The IPHAS A star data are not compatible with models that propose a sudden change in metallicity at RG= 10 kpc .
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