Evidence for a Non-Uniform Initial Mass Function in the Local Universe - Astrophysics > Astrophysics of GalaxiesReport as inadecuate

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Abstract: Many results in modern astrophysics rest on the notion that the Initial MassFunction IMF is universal. Our observations of HI selected galaxies in thelight of H-alpha and the far-ultraviolet FUV challenge this notion. The fluxratio H-alpha-FUV from these two star formation tracers shows strongcorrelations with the surface-brightness in H-alpha and the R band: Low SurfaceBrightness LSB galaxies have lower ratios compared to High Surface Brightnessgalaxies and to expectations from equilibrium star formation models usingcommonly favored IMF parameters. Weaker but significant correlations ofH-alpha-FUV with luminosity, rotational velocity and dynamical mass are foundas well as a systematic trend with morphology. The correlated variations ofH-alpha-FUV with other global parameters are thus part of the larger family ofgalaxy scaling relations. The H-alpha-FUV correlations can not be due to dustcorrection errors, while systematic variations in the star formation historycan not explain the trends with both H-alpha and R surface brightness. LSBgalaxies are unlikely to have a higher escape fraction of ionizing photonsconsidering their high gas fraction, and color-magnitude diagrams. The mostplausible explanation for the correlations are systematic variations of theupper mass limit and-or slope of the IMF at the upper end. We outline ascenario of pressure driving the correlations by setting the efficiency of theformation of the dense star clusters where the highest mass stars form. Ourresults imply that the star formation rate measured in a galaxy is highlysensitive to the tracer used in the measurement. A non-universal IMF also callsinto question the interpretation of metal abundance patterns in dwarf galaxiesand star formation histories derived from color magnitude diagrams. Abridged.

Author: Gerhardt R. Meurer, O.I. Wong, J.H. Kim, D.J. Hanish, T.M. Heckman, J. Werk, J. Bland-Hawthorn, M.A. Dopita, M.A. Zwaan, B. Korib

Source: https://arxiv.org/

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