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Paper: Observational Constraints to the Initial Mass Function in Normal Late-Type Galaxies
Volume: 440, UP2010: Have Observations Revealed a Variable Upper End of the Initial Mass Function?
Page: 199
Authors: Boselli, A.; Boissier, S.; Cortese, L.; Buat, V.; Hughes, T.; Gavazzi, G.
Abstract: We use GALEX far-ultraviolet (FUV, 1539 Å) and Hα data for a large sample of nearby objects to study the shape of the initial mass function (IMF) of normal late-type galaxies in the high mass (m ≥ 2 M☉) stellar range. The data are corrected for dust attenuation using the most accurate techniques at present available, namely the Balmer decrement for Hα data and the total far-infrared to FUV flux ratio for GALEX data. The Hα to FUV flux ratio of the observed galaxies increases with their total stellar mass by a factor of ∼ 1.4 dex in the stellar mass range 107 ≤ Mstar ≤ 1011 M☉ but reduces to ∼ 0.2 dex when AGN, highly inclined or starburst galaxies are excluded, becoming a weak trend whose statistical significance needs still to be confirmed. We show however that this weak trend might be totally removed using different extinction correction recipes and is thus not robust evidence of an intrinsically varying Hα over FUV flux ratio in late-type galaxies. If real, this trend can be explained by variations of the slope of the IMF from γ = 2.35 for massive galaxies to γ = 2.60 in low luminosity systems. We show however that this observed trend can also be due to the different micro history of star formation in massive galaxies with respect to dwarf systems.
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