Cosmic Evolution of Virial and Stellar Mass in Massive Early-Type Galaxies

Abstract

We measure the average mass properties of a sample of 41 strong gravitational lenses at moderate redshift (z ∼ 0.4 -0.9), and present the lens redshift for 6 of these galaxies for the first time. Using the techniques of strong and weak gravitational lensing on archival data obtained from the Hubble Space Telescope, we determine that the average mass overdensity profile of the lenses can be fit with a powerlaw profile (∆Σ ∝ R −0.86±0.16 ) that is within 1-σ of an isothermal profile (∆Σ ∝ R −1 ) with velocity dispersion σ v = 260 ± 20 km s −1 . Additionally, we use a two-component de Vaucouleurs+NFW model to disentangle the total mass profile into separate luminous and dark matter components, and determine the relative fraction of each component. We measure the average rest frame V-band stellar mass-to-light ratio (Υ V = 4.0±0.6 h M ⊙ /L ⊙ ) and virial mass-to-light ratio (τ V = 300±90 h M ⊙ /L ⊙ ) for our sample, resulting in a virial-to-stellar mass ratio of M vir /M * = 75 ± 25. Relaxing the NFW assumption, we estimate that changing the inner slope of the dark matter profile by ∼20% yields a ∼30% change in stellar mass-to-light ratio. Finally, we compare our results to a previous study using low redshift lenses, to understand how galaxy mass profiles evolve over time. We investigate the evolution of M vir /M * (z) = α(1 + z) β , and find best fit parameters of α = 51 ± 36 and β = 0.9 ± 1.8, constraining the growth of virial to stellar mass ratio over the last ∼7 Gigayears. We note that, by using a sample of strong lenses, we are able to constrain the growth of M vir /M * (z) without making any assumptions about the IMF of the stellar population.

Limits on the power-law mass and luminosity density profiles of elliptical galaxies from gravitational lensing systems

“…This simple but well-tested mass model is strongly supported by recent observations of early-type galaxies both in the inner regions i.e. within the Einstein radii (Lagattuta et al 2010;Ruff et al 2011) and at larger distances of ∼ 50 − 300 h −1 kpc (Sheldon et al 2004;Mandelbaum et al 2006).…”

Warm dark matter chills out: constraints on the halo mass function and the free-streaming length of dark matter with eight quadruple-image strong gravitational lenses

“…The stellar velocity dispersions implied by the Einstein radii of these systems is significantly lower than the stellar velocity dispersion in the sample of quads used to calibrate the halo-to-stellar mass ratio in Lagattuta et al (2010), and as such the estimate of the halo mass using the above procedure may not be accurate for these systems. For B1422, PS J1606, and WGD J0405, we therefore assume the population mean of 10 13.3±0.3 M inferred by Lagattuta et al (2010). We also assume the population mean halo mass for WFI 2026 since the lens redshift used to estimate the central velocity dispersion is very uncertain.…”

On the evolution of environmental and mass properties of strong lens galaxies in COSMOS

“…The Keck/DEIMOS observations were taken with the 830 line/mm grating and using the OG550 blocking filter, which lead to a dispersion of 0.47 Å per pixel. The Keck/LRIS targets were simultaneously observed with both blue grating (300/5000, dispersion: 2.55 Å per pixel) and red grating (600/7500, dispersion: 1.28 Å per pixel) (see Lagattuta et al 2010).…”