Photometric evidence of an intermediate-age stellar population in the inner bulge of M31
We explore the assembly history of the M31 bulge within a projected major-axis radius of 180 arcsec (~680 pc) by studying its stellar populations in Hubble Space TelescopeWide Field Camera 3 and Advanced Camera for Surveys observations. Colours formed by comparing nearultraviolet versus optical band...
| Autores: | , , , , , , , |
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| Tipo de recurso: | artículo |
| Estado: | Versión publicada |
| Fecha de publicación: | 2015 |
| País: | España |
| Institución: | Consejo Superior de Investigaciones Científicas (CSIC) |
| Repositorio: | DIGITAL.CSIC. Repositorio Institucional del CSIC |
| OAI Identifier: | oai:digital.csic.es:10261/389768 |
| Acceso en línea: | http://hdl.handle.net/10261/389768 |
| Access Level: | acceso abierto |
| Palabra clave: | Galaxies: abundances Galaxies: bulges Galaxies: evolution Galaxies: stellar content |
| Sumario: | We explore the assembly history of the M31 bulge within a projected major-axis radius of 180 arcsec (~680 pc) by studying its stellar populations in Hubble Space TelescopeWide Field Camera 3 and Advanced Camera for Surveys observations. Colours formed by comparing nearultraviolet versus optical bands are found to become bluer with increasing major-axis radius, which is opposite to that predicted if the sole sources of near-ultraviolet light were old extreme horizontal branch stars with a negative radial gradient in metallicity. Spectral energy distribution fits require a metal-rich intermediate-age stellar population (300 Myr to 1 Gyr old, ~Z<inf>⊙</inf>) in addition to the dominant old population. The radial gradients in age and metallicity of the old stellar population are consistent with those in previous works. For the intermediate-age population, we find an increase in age with radius and a mass fraction that increases up to 2 per cent at 680 pc away from the centre. We exclude contamination from the M31 disc and/or halo as the main origin for this population. Our results thus suggest that intermediate-age stars exist beyond the central 5 arcsec (19 pc) of M31 and contribute ~1 per cent of the total stellar mass in the bulge. These stars could be related to the secular growth of the M31 bulge. © 2015 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. |
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