Photometric evidence of an intermediate-age stellar population in the inner bulge of M31

DOI: 
10.1093/mnras/stv1256
Publication date: 
21/08/2015
Main author: 
Dong H.
IAA authors: 
Dong H.
Authors: 
Dong H., Li Z., Daniel Wang Q., Lauer T.R., Olsen K.A.G., Saha A., Dalcanton J.J., Williams B.F.
Journal: 
Monthly Notices of the Royal Astronomical Society
Publication type: 
Article
Volume: 
451
Pages: 
4126-4138
Number: 
Abstract: 
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.
Database: 
WOK
SCOPUS
ADS
URL: 
https://ui.adsabs.harvard.edu/#abs/2015MNRAS.451.4126D/abstract
ADS Bibcode: 
2015MNRAS.451.4126D
Keywords: 
Galaxies: abundances; Galaxies: bulges; Galaxies: evolution; Galaxies: stellar content