The structure of the outer Galactic disc as revealed by IPHAS early A stars

S.E. Sale, J.E. Drew, C. Knigge, A.A. Zijlstra, M.J. Irwin, R.A.H. Morris, S. Phillipps, J. Drake, R. Greimel, Y.C. Unruh, P. Groot, A. Mampaso, N.A. Walton

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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 Hα 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 .
Original languageEnglish
Pages (from-to)713-723
JournalMonthly Notices of the Royal Astronomical Society
Issue number2
Publication statusPublished - 2010


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