Much of our knowledge of galaxies comes from analysing the radiation emitted by their stars, which depends on the present number of each type of star in the galaxy. The present number depends on the stellar initial mass function (IMF), which describes the distribution of stellar masses when the population formed, and knowledge of it is critical to almost every aspect of galaxy evolution. More than 50 years after the first IMF determination1, no consensus has emerged on whether it is universal among different types of galaxies2. Previous studies indicated that the IMF and the dark matter fraction in galaxy centres cannot both be universal3,4,5,6,7, but they could not convincingly discriminate between the two possibilities. Only recently were indications found that massive elliptical galaxies may not have the same IMF as the Milky Way8. Here we report a study of the two-dimensional stellar kinematics for the large representative ATLAS3D sample9 of nearby early-type galaxies spanning two orders of magnitude in stellar mass, using detailed dynamical models. We find a strong systematic variation in IMF in early-type galaxies as a function of their stellar mass-to-light ratios, producing differences of a factor of up to three in galactic stellar mass. This implies that a galaxy’s IMF depends intimately on the galaxy's formation history.
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Salpeter, E. E. The luminosity function and stellar evolution. Astrophys. J. 121, 161–167 (1955)
Bastian, N. Covey, K. R. & Meyer, M. R. A universal stellar initial mass function? A critical look at variations. Annu. Rev. Astron. Astrophys. 48, 339–389 (2010)
Cappellari, M. et al. The SAURON project – IV. The mass-to-light ratio, the virial mass estimator and the fundamental plane of elliptical and lenticular galaxies. Mon. Not. R. Astron. Soc. 366, 1126–1150 (2006)
Tortora, C., Napolitano, N. R., Romanowsky, A. J., Capaccioli, M. & Covone, G. Central mass-to-light ratios and dark matter fractions in early-type galaxies. Mon. Not. R. Astron. Soc. 396, 1132–1150 (2009)
Treu, T. et al. The initial mass function of early-type galaxies. Astrophys. J. 709, 1195–1202 (2010)
Thomas, J. et al. Dynamical masses of early-type galaxies: a comparison to lensing results and implications for the stellar initial mass function and the distribution of dark matter. Mon. Not. R. Astron. Soc. 415, 545–562 (2011)
Dutton, A. A. et al. Dark halo response and the stellar initial mass function in early-type and late-type galaxies. Mon. Not. R. Astron. Soc. 416, 322–345 (2011)
van Dokkum, P. G. & Conroy, C. A substantial population of low-mass stars in luminous elliptical galaxies. Nature 468, 940–942 (2010)
Cappellari, M. et al. The ATLAS3D project – I. A volume-limited sample of 260 nearby early-type galaxies: science goals and selection criteria. Mon. Not. R. Astron. Soc. 413, 813–836 (2011)
Cappellari, M. Measuring the inclination and mass-to-light ratio of axisymmetric galaxies via anisotropic Jeans models of stellar kinematics. Mon. Not. R. Astron. Soc. 390, 71–86 (2008)
Emsellem, E., Monnet, G. & Bacon, R. The multi-gaussian expansion method: a tool for building realistic photometric and kinematical models of stellar systems I. The formalism. Astron. Astrophys. 285, 723–738 (1994)
Navarro, J. F., Frenk, C. S. & White, S. D. M. The structure of cold dark matter halos. Astrophys. J. 462, 563–575 (1996)
Klypin, A. A., Trujillo-Gomez, S. & Primack, J. Dark matter halos in the standard cosmological model: results from the Bolshoi simulation. Astrophys. J. 740, 102 (2011)
Gnedin, O. Y. et al. Halo contraction effect in hydrodynamic simulations of galaxy formation. Preprint at 〈http://arxiv.org/abs/1108.5736〉 (2011)
Cappellari, M. & Emsellem, E. Parametric recovery of line-of-sight velocity distributions from absorption-line spectra of galaxies via penalized likelihood. Publ. Astron. Soc. Pacif. 116, 138–147 (2004)
Vazdekis, A. et al. Evolutionary stellar population synthesis with MILES - I. The base models and a new line index system. Mon. Not. R. Astron. Soc. 404, 1639–1671 (2010)
Maraston, C. Evolutionary population synthesis: models, analysis of the ingredients and application to high-z galaxies. Mon. Not. R. Astron. Soc. 362, 799–825 (2005)
Bruzual, G. & Charlot, S. Stellar population synthesis at the resolution of 2003. Mon. Not. R. Astron. Soc. 344, 1000–1028 (2003)
Kroupa, P. On the variation of the initial mass function. Mon. Not. R. Astron. Soc. 322, 231–246 (2001)
Chabrier, G. Galactic stellar and substellar initial mass function. Publ. Astron. Soc. Pacif. 115, 763–795 (2003)
Duffy, A. R. et al. Impact of baryon physics on dark matter structures: a detailed simulation study of halo density profiles. Mon. Not. R. Astron. Soc. 405, 2161–2178 (2010)
Bell, E. F. & de Jong, R. S. Stellar mass-to-light ratios and the Tully-Fisher relation. Astrophys. J. 550, 212–229 (2001)
Cappellari, M. et al. The ATLAS3D project – VII. A new look at the morphology of nearby galaxies: the kinematic morphology-density relation. Mon. Not. R. Astron. Soc. 416, 1680–1696 (2011)
Renzini, A. in The Initial Mass Function 50 Years Later (ed. Corbelli, E., Palla, F. and Zinnecker, H. ) 221 (Springer, 2005)
Ferreras, I., Saha, P. & Burles, S. Unveiling dark haloes in lensing galaxies. Mon. Not. R. Astron. Soc. 383, 857–863 (2008)
Hoversten, E. A. & Glazebrook, K. Evidence for a nonuniversal stellar initial mass function from the integrated properties of SDSS galaxies. Astrophys. J. 675, 163–187 (2008)
Gunawardhana, M. L. P. et al. Galaxy and mass assembly (GAMA): the star formation rate dependence of the stellar initial mass function. Mon. Not. R. Astron. Soc. 415, 1647–1662 (2011)
Kroupa, P. & Weidner, C. Galactic-field initial mass functions of massive stars. Astrophys. J. 598, 1076–1078 (2003)
Deason, A. J., Belokurov, V., Evans, N. W. & McCarthy, I. G. Elliptical galaxy masses out to five effective radii: the realm of dark matter. Astrophys. J. 748, 2 (2012)
Moster, B. P. et al. Constraints on the relationship between stellar mass and halo mass at low and high redshift. Astrophys. J. 710, 903–923 (2010)
M.C. acknowledges support from a Royal Society University Research Fellowship. This work was supported by the rolling grants ‘Astrophysics at Oxford’ from the UK Research Councils. R.L.D. acknowledges support from Christ Church College, Oxford University, and from the Royal Society in the form of a Wolfson Merit Award. S.K. acknowledges support from the Royal Society Joint Projects Grant. R.M.M. is supported by the Gemini Observatory. T.N. and M. Bois acknowledge support from the DFG Cluster of Excellence ‘Origin and Structure of the Universe’. M.S. acknowledges support from a STFC Advanced Fellowship. N.S. and T.A.D. acknowledge support from an STFC studentship.
The authors declare no competing financial interests.
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Cappellari, M., McDermid, R., Alatalo, K. et al. Systematic variation of the stellar initial mass function in early-type galaxies. Nature 484, 485–488 (2012). https://doi.org/10.1038/nature10972
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