Cosmology with supernova Encore in the strong lensing cluster MACS J0138$-$2155: photometry, cluster members, and lens mass model

TL;DR

This work builds a state-of-the-art strong-lensing mass model for the MACS J0138$-$2155 cluster using JWST imaging, HST data, and MUSE spectroscopy to exploit the strongly lensed SN Encore for time-delay cosmography. It identifies 84 cluster members, catalogues eight lensed-image systems across four background redshifts, and tests seven mass-model parametrizations (including multi-plane configurations and a mass-sheet component). An ultimate model formed from four well-fitting multi-plane configurations predicts the positions and magnifications of SN Encore and SN Requiem with quantified uncertainties, while also providing convergence and shear estimates for microlensing studies. The results favor cored isothermal cluster halos over NFW and establish a robust foundation for future $H_0$ constraints from lensed SNe in this system, as well as broader SN host galaxy analyses.

Abstract

The strongly lensed Supernova (SN) Encore at a redshift of $z = 1.949$, discovered behind the galaxy cluster MACS J0138$-$2155 at $z=0.336$, provides a rare opportunity for time-delay cosmography and studies of the SN host galaxy, where previously another SN, called SN Requiem, had appeared. To enable these studies, we combine new James Webb Space Telescope (JWST) imaging, archival Hubble Space Telescope (HST) imaging, and new Very Large Telescope (VLT) spectroscopic data to construct state-of-the-art lens mass models that are composed of cluster dark-matter (DM) halos and galaxies. We determine the photometric and structural parameters of the galaxies across six JWST and five HST filters. We use the color-magnitude and color-color relations of spectroscopically-confirmed cluster members to select additional cluster members, identifying a total of 84 galaxies belonging to the galaxy cluster. We construct seven different mass models using a variety of DM halo mass profiles, and explore both multi-plane and approximate single-plane lens models. As constraints, we use the observed positions of 23 multiple images from eight multiply lensed sources at four distinct spectroscopic redshifts. In addition, we use stellar velocity dispersion measurements to obtain priors on the galaxy mass distributions. We find that six of the seven models fit well to the observed image positions. Mass models with cored-isothermal DM profiles fit well to the observations, whereas the mass model with a Navarro-Frenk-White cluster DM profile has an image-position $χ^2$ value that is four times higher. We build our ultimate model by combining four multi-lens-plane mass models and predict the image positions and magnifications of SN Encore and SN Requiem. Our work lays the foundation for building state-of-the-art mass models of the cluster for future cosmological analysis and SN host galaxy studies.

Figures (9)

• Figure 1: Colour image of MACS J0138$-$2155 from combining JWST/NIRCam and HST/WFC3 data. The RGB image is constructed from the filters F105W+F115W+F125W (blue), F150W+F160W+F200W (green), and F277W+F356W+F444W (red). The observed images of SN Encore are shown in solid white circles, the expected positions of images D and possibly E are in dashed white circles. The observed and predicted images for SN Requiem are shown in blue following the same pattern. The images were drizzled to a pixel scale of 0.04/pix. (Image Credit: STScI, A. Koekemoer, T. Li)
• Figure 2: Results from modelling the BCG light with Sérsic profiles in the HST F160W filter. The left panel shows the observed image, the middle panel shows our BCG light model, and the right panel is the BCG subtracted image. The images cover the central $50\arcsec \times 50\arcsec$ around the BCG.
• Figure 3: Examples for Sérsic fits to objects in the field in the JWST F200W filter. From left to right: data image, model image, and residual image. The photometric IDs of the objects are shown in blue on the data image. Object 82 is a bright background galaxy at a redshift $z_{\rm bg} = 0.371$, and the other galaxies are cluster members close to the BCG.
• Figure 4: Colour image of MACS J0138$-$2155 built from JWST NIRCam filters (red: F277W, F356W, F444W; green: F150W, F200W; blue: F115W). Spectroscopically confirmed objects are marked with squares, coloured in cyan for cluster members, and blue and yellow for the foreground and background objects, respectively. Objects selected from the colour-magnitude fit are marked as red circles, and green triangles are the colour-colour selections.
• Figure 5: Colour-magnitude diagram in the field of MACS J0138$-$2155. Spectroscopically confirmed cluster members and non-members are indicated as blue and red points, respectively. Sources with no spectroscopic confirmation are shown in grey. The blue line and region indicate the fitted red sequence and the 1$\sigma$ scatter. Red crosses (X) mark cluster members that do not follow the red sequence and yellow plus signs indicate the photometrically selected members that are included in our lens model. Objects inside the red sequence with a red minus sign are not included as photometric cluster members due to the lack of, or unreliable, F160W photometry.