Online Material3 and illustrated in the Appendix images.
SL2S J09013-0158 at z = 0.30 (Fig. A.1):
The luminosity distribution is elongated in the north-south direction. We report a straight arc between the two main bright central galaxies: this is a typical beak-to-beak configuration (Kassiola et al. 1992). This arc is found closer to the northern galaxy ( ) than the southern one. No HST image is available for this group. A radio source has been reported by Condon et al. (1998) between the two bright central galaxies. Given the coordinates and associated errors of this radio source, it could be associated with one of the two smaller central galaxies.
SL2S J22214-0053 at z = 0.334 (Fig. A.2):
The SDSS provides a redshift measurement for the main galaxy populating the deflector of 0.334, and a velocity dispersion of 281 45 km s-1. The strong lensing deflector is populated by a single bright galaxy.
SL2S J08544-0121 at z = 0.351 (Fig. A.3):
The strong lensing deflector is populated by a single bright galaxy whose ellipticity and position angle equals 0.3 and degrees, respectively. The luminosity contours are elongated in the east-west direction and define a position angle consistent with that of the bright galaxy. We also find the position angle of the SIE halo (21 degrees, Sect. 5) to be consistent with that of the bright galaxy.
Note (Fig. A.3) that the innermost luminosity contour at 107 kpc-2 encompass the SL system but also two bright galaxies located 54 east from the SL system, making this light distribution bimodal. This is the only group for which the luminosity distribution is not clearly dominated by the lens, making this configuration rather exceptional: the large Einstein radius ( ) points toward a massive structure associated with this lens, but the luminosity distribution is found bimodal. This suggest a dynamically young structure in the process of formation. This bright galaxy has a spectroscopic redshift measured from Keck of 0.3514. We detect two multiply imaged systems: the brightest one is perturbed by a small satellite galaxy whose redshift is equal to 0.3517 (FORS 2); and the outer one is seen on the ACS colour image (Fig. A.3). Note how the northern counter image is found much further ( ) than the main arc ( ), suggesting a strong contribution from the external shear associated with the host galaxy group. The HST data brings significant additional information on this lensing feature.
SL2S J09413-1100 at z = 0.385 (Fig. A.4):
The luminosity contours look circular. The strong lensing deflector is populated by a bright galaxy whose stellar halo is extended and presents a large ellipticity (b/a = 0.59) with a position angle of 74 degrees. Interestingly, this position angle is found compatible with the orientation of the luminosity contours. Note that this is the only group for which the central galaxy presents an extended stellar halo. We measured a spectroscopic redshift for this galaxy using FORS 2 to be 0.385. We report a blue arc composed by two merging images north of the deflector, with its counter image. We have not been able to find another counter image on the other side of the deflector, even after subtraction of the galaxy on the HST images.
SL2S J14081+5429 at z = 0.416 (Fig. A.5):The luminosity distribution is elongated in the north-south direction. The centre of this group is dominated by three bright galaxies aligned in the north-south direction. The brightest one (A, magi=18.03) is the central one, that is also closest to the arc feature. North of A is a galaxy B (magi=18.37) and south of is a galaxy C (magi=18.46). The SDSS provides a redshift measurement for A ( z=0.415979) and for B ( z=0.411022). A straight arc without any detected feature is located between bright central galaxies.
SL2S J14300+5546 at z = 0.435 (Fig. A.6):
The luminosity distribution is elongated in the east-west direction. The strong lensing deflector is populated by a single galaxy whose redshift equals 0.435 (Gemini). A tangential arc is found south-east of the deflector. The position angle of the galaxy populating the deflector (45 degrees) is consistent with the position angle defined by the luminosity distribution.
SL2S J02140-0532 at z = 0.444 (Fig. A.7):
The luminosity distribution is elongated in the north-south direction. The strong lensing deflector is populated by three galaxies. The two brightest ones have redshift measured spectroscopically from Keck (0.4422 and 0.4439) and may be bound gravitationally. We report an arc north of the deflector composed by two merging images showing substructure. The counter image is easily identified east of the deflector. Note that on the ground based image, we see a possible counter image south of the deflector which seems to have colour compatible with the other images. However, on the ACS data, it is clear that this feature cannot be associated with the proposed multiply imaged system. This is also confirmed by the modelling: no acceptable fit was able to reproduce the multiple images as one could have inferred from the ground based data. We note, however, that a recent independent study by Alard (2009) considers the southern image as part of the multiply imaged system. Spectroscopy of each feature is needed in order to remove the uncertainty. The HST data brings significant additional information on this lensing feature: not only does it help to identify the different images belonging to the same system, but it also resolves substructures within each lensed image, increasing
the number of constraints for the analysis. The halo of the deflector is oriented with a position angle well constrained at degrees. This is the same direction as the one defined by the luminosity contours.
SL2S J02254-0737 at z = 0.511 (Fig. A.8):The luminosity contours look circular. The strong lensing deflector is populated by a single galaxy whose redshift equals 0.511 (Gemini). We observe a tangential arc north of the lens galaxy, likely to be composed by two merging images, with an additional counter image a bit further east. The location of the deflector coincide with a radio emission reported by Condon et al. (1998).
SL2S J22130-0030 at z = 0.61 (Fig. A.9):
The luminosity distribution is elongated in the north-south direction. The HST image reveals that the strong lensing deflector is populated by a very compact group of at least 6 galaxies. We report a blue arc east of the deflector, and a likely counter image presenting the same colour as the arc on the other side of the deflector.
SL2S J02215-0647 at z = 0.618 (Fig. A.10):
We find a gap of 1.3 mag in the R band between the brightest and the second brightest galaxy, not enough to be considered as a fossil group. The strong lensing deflector is populated by a single galaxy whose redshift equals 0.618 (FORS 2). We report an arc south of the deflector, composed by two merging images. There is a counter image south-east of the deflector, as well as an additional counter image located on the other side of the deflector, resolved by HST data. We report a possible second multiply imaged system constituted by two images with same CFHTLS colours.
SL2S J14314+5533 at z = 0.64 (Fig. A.11):
The luminosity distribution is elongated in the south-east north-west direction. A small tangential arc is found around bright galaxies. We cannot conjugate any images that may merge to form the arc. It is possible that this blue lensed feature in fact is singly imaged.
SL2S J08591-0345 at z = 0.647 (Fig. A.12):
The lens is located close (75 = 508 kpc) to the edge of the field of view. It is very likely that we are missing a significant part of this group. Therefore, we have not been reported any values of this group luminosity, neither did we pursue any weak lensing analysis for this group. We observe a rather exotic strong lensing configuration: the deflector is populated by three bright galaxies and two smaller ones. One of the bright one has a redshift of 0.647 (FORS 2). The multiple images draw an oval contour around the deflector. It is difficult at this point to know how many multiple images we observe and if they are coming from a single or multiple background sources. An advanced modelling of this exotic lens would be very interesting and will require deep multi colour space based data with dedicated ground based spectroscopy.
SL2S J22133+0048 at z = 0.83 (Fig. A.13):
The luminosity distribution is elongated in the south-east north-west direction. The strong lensing deflector is populated by a single galaxy. A tangential arc composed by two merging images is found east of the deflector. A possible counter image on the other side of the deflector is detected on the space based images. The location of the deflector coincides with a radio emission reported by Condon et al. (1998). Our weak lensing analysis yields a velocity dispersion between 432 and 1218 km s-1. The upper limit is therefore consistent with a galaxy cluster. Since its Einstein radius is estimated to be about 3.4 , it is possible that SL2S J22133+0048 is indeed a galaxy cluster with a velocity dispersion larger than 1000 km s-1 lensing a close background source. An estimate of the redshift of the strongly lensed background source would help to alleviate the doubt. We note also that the redshift of this structure has been estimated photometrically. If this estimation is biased and if this structure is located at lower redshift, then we are currently overestimating its velocity dispersion.