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We present an investigation about the shape of the initial mass function (IMF) of early-type galaxies (ETGs), based on a joint lensing and dynamical analysis, and on stellar population synthesis models, for a sample of 55 lens ETGs identified by the Sloan Lens ACS (SLACS) Survey. We construct axisymmetric dynamical models based on the Jeans equations which allow for orbital anisotropy and include a dark matter halo. The models reproduce in detail the observed textit{HST} photometry and are constrained by the total projected mass within the Einstein radius and the stellar velocity dispersion ($sigma$) within the SDSS fibers. Comparing the dynamically-derived stellar mass-to-light ratios $(M_*/L)_{rm dyn}$, obtained for an assumed halo slope $rho_{rm h}propto r^{-1}$, to the stellar population ones $(M_*/L)_{rm pop}$, derived from full-spectrum fitting and assuming a Salpeter IMF, we infer the mass normalization of the IMF. Our results confirm the previous analysis by the SLACS team that the mass normalization of the IMF of high $sigma$ galaxies is consistent on average with a Salpeter slope. Our study allows for a fully consistent study of the trend between IMF and $sigma$ for both the SLACS and ATLAS samples, which explore quite different $sigma$ ranges. The two samples are highly complementary, the first being essentially $sigma$ selected, and the latter volume-limited and nearly mass selected. We find that the two samples merge smoothly into a single trend of the form $logalpha =(0.38pm0.04)timeslog(sigma_{rm e}/200,mathrm{km~s}^{-1})+(-0.06pm0.01)$, where $alpha=(M_*/L)_{rm dyn}/(M_*/L)_{rm pop}$ and $sigma_{rm e}$ is the luminosity averaged $sigma$ within one effective radius $R_{rm e}$. This is consistent with a systematic variation of the IMF normalization from Kroupa to Salpeter in the interval $sigma_{rm e}approx90-270,mathrm{km~s}^{-1}$.
We use stellar masses, photometry, lensing, and velocity dispersions to investigate empirical correlations for the final sample of 73 early-type lens galaxies (ETGs) from the SLACS survey. The traditional correlations (Fundamental Plane [FP] and its
We present the current photometric dataset for the Sloan Lens ACS (SLACS) Survey, including HST photometry from ACS, WFPC2, and NICMOS. These data have enabled the confirmation of an additional 15 grade `A (certain) lens systems, bringing the number
In this paper we investigate whether the stellar initial mass function of early-type galaxies depends on their host environment. To this purpose, we have selected a sample of early-type galaxies from the SPIDER catalogue, characterized their environm
The stellar initial mass function (IMF) seems to be variable and not universal, as argued in the literature in the last three decades. Several relations among the low-mass end of the IMF slope and other stellar population, photometric or kinematic pa
We extend our initial study of the connection between the UV colour of galaxies and both the inferred stellar mass-to-light ratio, $Upsilon_*$, and a mass-to-light ratio referenced to Salpeter initial mass function (IMF) models of the same age and me