Galaxy-scale lens search in the PEARLS NEP TDF and CEERS JWST fields

TL;DR

This study leverages deep, high-resolution JWST NIRCam imaging of two blank fields (NEP TDF and CEERS) to conduct a galaxy-scale strong lens search. A visual inspection identifies candidates, which are then vetted via photometric redshifts and parametric lens modelling (SIE with external shear) and enhanced with a multi-Gaussian expansion light decomposition as an alternative approach. The authors present 5 high-confidence lenses with redshifts $0.38<z_{lens}<1.25$ and $1<z_{source}<3.6$, Einstein radii $0.7''<\theta_E<1.3''$, and velocity dispersions $200<\sigma<250$ km s$^{-1}$, corresponding to a density of $125\pm37$ deg$^{-2}$. They show that JWST can yield extremely high numbers of secure lenses per unit area, particularly at high redshift and small angular scales, and forecast that a pure-parallel JWST survey of comparable depth could yield ~80 galaxy-scale lenses, with about one-third having $z_{lens}>1$ and $z_{source}>3$.

Abstract

We present four galaxy scale lenses discovered in two JWST blank-fields: the ~ 54 arcmin^2 of the PEARLS North-Ecliptic-Pole Time-Domain Field (NEP TDF) and in the ~ 90 arcmin^2 of CEERS. We perform the search by visual inspection of NIRCam photometric data, obtaining an initial list of 16 lens candidates. We down-select this list to 5 high-confidence lens candidates, based on lens modelling of the image configuration and photometric redshift measurements for both the source and the deflector. We compare our results to samples of lenses obtained in ground-based and space-based lens searches and theoretical expectations. We expect that JWST observations of field galaxies will yield approximately 1 galaxy scale lens every three to four NIRCam pointings of comparable depth to these observations (~ 9 arcmin^2 each). This shows that JWST, compared to other lens searches, can yield an extremely high number of secure lenses per unit area, with redshift and size distributions complementary to lens samples obtained from ground-based and wide-area surveys. We estimate that a single JWST pure-parallel survey of comparable depth could yield $\sim 80$ galaxy scale lenses, with a third of them having z_lens>1 and z_source>3.

Figures (7)

• Figure 1: Lens candidates in PEARLS NEP field and CEERS fields. The cutouts are 10"$\times$10", and the magenta contours highlight the potential lensing features noticed in the visual inspection process. We note that the main arc in CEERS J142031.8+525822 lies in the region where there is no blue NIRCam data.
• Figure 2: The four lenses fit with a SIE mass distribution plus external shear. From left to right, the panels show the single-band image data (F444W) for each lens, the data where a Sérsic model subtracts the foreground lens emission, the image–plane lensed source model, the residual difference between the image, and the reconstructed source plane with the tangential caustic highlighted in yellow.
• Figure 3: Example of three systems modelled using the pipeline similar to the one employed in COWLS (COWLS_I). From left to right, the panels show the single-band image data (F444W), a foreground-subtracted image using a Multi-Gaussian Expansion (note that the centre of the cutout is not masked), the model lensed source in the image plane, and source-plane reconstructions.
• Figure 4: Properties of our lens sample (arrows) compared with the lenses in SL2S (red, Sonnenfeld_SL2S_2013) and COWLS (orange dashed, COWLS_I). The left and middle panels show the deflector and source redshift distributions, respectively. The right panel shows the Einstein radius distribution.
• Figure 5: Comparison between the Einstein radius vs lens redshift distribution in our sample of lenses (left panel, orange and purple points), in COWLS (central panel, markers are mapped to the confidence score of each lens, S06 being the lowest and M25 the highest) and SL2S (right panel, red crosses). On top of each panel is reported the telescope used to conduct the relative lens search. The contours represent the iso-probability levels predicted using the galess analytical model (Ferrami_lensstat), including a cut in velocity dispersion ($\sigma_{\rm{SIE}}<210$ km/s) in the central panel. The shaded dashed contours in the right panel represent the expected distribution in SL2S if we assume the cut in velocity dispersion required to reproduce the distribution of COWLS.