2011MNRAS.417.3000S -
Mon. Not. R. Astron. Soc., 417, 3000-3009 (2011/November-2)
The X-Shooter Lens Survey – I. Dark matter domination and a salpeter-type initial mass function in a massive early-type galaxy.
SPINIELLO C., KOOPMANS L.V.E., TRAGER S.C., CZOSKE O. and TREU T.
Abstract (from CDS):
We present the first results from the X-Shooter Lens Survey: an analysis of the massive early-type galaxy SDSS J1148+1930 at redshift z= 0.444. We combine its extended kinematic profile – derived from spectra obtained with X-Shooter on the European Southern Observatory Very Large Telescope – with strong gravitational lensing and multicolour information derived from Sloan Digital Sky Survey (SDSS) images. Our main results are as follows. (i) The luminosity-weighted stellar velocity dispersion is #963;>( ≲ Reff) = 352±10±16 km/s, extracted from a rectangular aperture of 1.8 {x} 1.6 arcsec2 centred on the galaxy, more accurate and considerably lower than a previously published value of ∼ 450 km/s. (ii) A single-component (stellar plus dark) mass model of the lens galaxy yields a logarithmic total-density slope of γ'= 1.72+0.05_- 0.06_(68 per cent confidence level, CL; ρtotαr–gamma') within a projected radius of ∼ 2.16 arcsec. (iii) The projected stellar mass fraction, derived solely from the lensing and dynamical data, is f*(<RE) = 0.19+0.04_- 0.09_(68 per cent CL) inside the Einstein radius for a Hernquist stellar profile and no anisotropy. The dark matter fraction inside the effective radius fDM(<Reff) = 0.60+0.15_- 0.06_± 0.1 (68 per cent CL), where the latter error is systematic. (iv) Based on the SDSS colours, we find f_*, Salp(<RE_) = 0.17±0.06 for a Salpeter initial mass function (IMF) and f_*, Chab(<RE_) = 0.07±0.02 for a Chabrier IMF. The lensing and dynamics constraints on the stellar mass fraction agree well with those independently derived from the SDSS colours for a Salpeter IMF, which is preferred over a Chabrier IMF at variance with standard results for lower mass galaxies. Dwarf-rich IMFs in the lower mass range of 0.1–0.7 M☉, with α ≥ 3 (with dN/dM∝M–α) – such as that recently suggested for massive early-type galaxies with α= 3 in the mass range 0.1–1 M☉– are excluded at the >90 per cent CL and in some cases violate the total lensing-derived mass limit. We conclude that this very massive early-type galaxy is dark-matter-dominated inside one effective radius, consistent with the trend recently found from massive Sloan Lens ACS (SLACS) galaxies, with a total density slope shallower than isothermal and an IMF normalization consistent with Salpeter.
Abstract Copyright:
2011 The Authors Monthly Notices of the Royal Astronomical Society2011 RAS
Journal keyword(s):
gravitational lensing: strong - galaxies: elliptical and lenticular, cD - galaxies: formation - galaxies: kinematics and dynamics - galaxies: structure - dark matter
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