We examine a well resolved 8″ lensed image that is symmetrically bent in the middle by an edge-on lenticular galaxy , in the Hubble Frontier Field ( HFF ) data of MACSJ0416.1-20403 .
The lengthy image is generated primarily by the large tangential shear of the cluster with a local secondary deflection by the member galaxy out to a limiting radius of \simeq 18 kpc .
The lensing lenticular galaxy is also well resolved and evidently lies nearly edge-on in projection .
This fortuitous combination of a long arc intersecting an edge on galaxy provides us with an opportunity to place relatively strong constraints on the lensing effect of this galaxy .
We can model the stellar lensing contribution using the observed pixels belonging to the galaxy , in 2D , and we add to this a standard parameterised dark halo component .
Irrespective of the detailed choice of parameters we obtain a combined total mass of \approx 3 \times 10 ^ { 11 } M _ { \odot } .
Depending on the dark halo parameters , the stellar contribution to this is limited to the range 5 - 15 \times 10 ^ { 10 } M _ { \odot } , or 20-50 % of the total mass , in good agreement with the independent stellar mass computed from the photometry of 5 \times 10 ^ { 10 } M _ { \odot } for a Chabrier IMF , or 8 \times 10 ^ { 10 } M _ { \odot } for a Salpeter IMF .
The major axis of the DM halo is constrained to be nearly orthogonal to the plane of the galaxy , within a range of \sim 15 ^ { \circ } , and with an ellipticity e \approx 0.15 corresponding to an axis ratio a / c = 0.54 .
We show that these conclusions are very weakly dependent on the model of the cluster , or the additional influence of neighbouring galaxies or the properties of the lensed source .
Alternative theories of gravity where the radial dependence is modified to avoid the need for DM are challenged by this finding since generically these must be tied to the baryonic component which here is a stellar disk oriented nearly orthogonally to the lensed image deflection .
Other such fortuitously useful lenses can be examined this way as they become uncovered with more HFF data to help provide a more statistical distribution of galaxy halo properties .