Tuesday, January 10, 2012

1201.1677 (Brendon J. Brewer et al.)

The SWELLS survey. III. Disfavouring "heavy" initial mass functions for spiral lens galaxies    [PDF]

Brendon J. Brewer, Aaron A. Dutton, Tommaso Treu, Matthew W. Auger, Philip J. Marshall, Matteo Barnabè, Adam S. Bolton, David C. Koo, Léon V. E. Koopmans
We present gravitational lens models for 20 strong gravitational lens systems observed as part of the Sloan WFC Edge-on Late-type Lens Survey (SWELLS) project. Fifteen of the lenses are taken from paper I while five are newly discovered systems. The systems are galaxy-galaxy lenses where the foreground deflector has an inclined disc, with a wide range of morphological types, from late-type spiral to lenticular. For each system, we compare the total mass inside the critical curve inferred from gravitational lens modelling to the stellar mass inferred from stellar population synthesis (SPS) models, computing the stellar mass fraction within the critical curve. We find that, for the lower mass SWELLS systems, adoption of a Salpeter stellar initial mass function (IMF) leads to estimates of the stellar mass fraction that exceed 1. This is unphysical, and provides strong evidence against the Salpeter IMF being valid for these systems. Taking the lower mass end of the SWELLS sample (lensing velocity dispersion less than 230 km/s), we find that the IMF is lighter (in terms of stellar mass-to-light ratio) than Salpeter with 98% probability, and consistent with the Chabrier IMF. This result is consistent with previous studies of spiral galaxies based on independent techniques. In combination with the heavier IMF inferred from the lensing and dynamical analysis of more massive early-type lens galaxies from the SLACS sample, this result provides strong evidence against a universal stellar IMF.
View original: http://arxiv.org/abs/1201.1677

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