Gravitational lensing and dynamics in SL2S\,J02140-0535: Probing the
  mass out to large radius
  We aim to probe the mass of SL2S\,J02140-0535, a galaxy group at $z$ = 0.44
from the Strong Lensing Legacy Survey (SL2S). We combine strong lensing
modeling and dynamical constraints. The strong lensing analysis is based on
multi-band HST/ACS observations exhibiting strong lensing features that we have
followed-up spectroscopically with VLT/FORS2. To constrain the scale radius of
an NFW mass profile that cannot be constrained by strong lensing, we propose a
new method by taking advantage of the large-scale dynamical information
provided by VLT/FORS2 and KECK/LRIS spectroscopy of group members. In constrast
to other authors, we show that the observed lensing features in
SL2S\,J02140-0535 belong to different background sources: one at $z$ = 1.7
$\pm$ 0.1 produces three images, while the other at $z$ = 1.023 $\pm$ 0.001 has
only a single image. Our unimodal NFW mass model reproduces these images very
well. It is characterized by a concentration parameter $c_{200}$ = 6.0 $\pm$
0.6, which is slightly greater than the value expected from $\Lambda$CDM
simulations for a mass of M$_{200}$ $\approx$ 1 $\times$ 10$^{14}$ M$_{\sun}$.
The spectroscopic analysis of group members also reveals a unimodal structure
that exhibits no evidence of merging. We compare our dynamic mass estimate with
an independent weak-lensing based mass estimate finding that both are
consistent. Our combined lensing and dynamical analysis of SL2S\,J02140-0535
demonstrates the importance of spectroscopic information in reliably
identifying the lensing features. Our findings argue that the system is a
relaxed, massive galaxy group where mass is traced by light. This work shows a
potentially useful method for constraining large-scale properties inaccessible
to strong lensing, such as the scale radius of the NFW profile.
