Strong Lensing Model and Dust Extinction Maps of the Host Galaxy of Type Ia Supernova H0pe

TL;DR

This study shows that including the extended surface brightness of a lensed SN host arc significantly enhances the precision of cluster-scale mass models, reducing uncertainties by about an order of magnitude and enabling spatially resolved dust extinction maps in the host galaxy of SN H0pe. Using JWST/NIRCam data and the Glee lens modeling framework, the authors compare a point-like, position-only model to an extended-image model, finding a mass-parameter precision gain of roughly $\approx 12$. They reconstruct the SN host surface brightness across six JWST bands, derive an image-plane dust extinction of $A_V^{\mathrm{H0pe}} = 0.94 \pm 0.25$ (in agreement with independent analyses), and map dust in the source plane, placing SN H0pe on the edge of a high-extinction region. The results underscore the value of extended-image modeling for time-delay cosmography with strongly lensed SNe and lay the groundwork for more flexible models and foreground-light treatments in future work.

Abstract

Strong gravitational lensing by massive galaxy clusters offers particularly rare opportunities to observe multiple images of distant ($z\gtrsim2$) Type Ia supernovae (SNe) and resolve the properties of their host galaxies. A recent outstanding example is the Type Ia SN "H0pe" ($z=1.78$), discovered in James Webb Space Telescope (JWST) NIRCam images when it was still triply imaged by the galaxy cluster PLCK G165.7+67.0 (G165, $z=0.35$). In this work we build a new strong lensing model of G165, first by using only the position of multiple images of background galaxies. We then increase significantly the number of constraints around the position of SN H0pe by modeling the extended surface brightness of the SN host galaxy. The average uncertainty on mass model parameters is reduced by more than an order of magnitude. We also study the spatial distribution of dust in the arc to estimate the dust extinction at the position of SN H0pe. We find good statistical agreement of the extinction estimate at $\lesssim1σ$ with three fully independent methods based on spectral energy distribution fitting. Moreover, our extended-image lens model of G165 allows us to map the dust distribution of the host galaxy from the image plane to the source plane. Supernova H0pe exploded in a region with a relatively high extinction of $A_V \approx 0.9\ {\rm mag}$ at around $\sim 1\ {\rm kpc}$ from its host center. This work shows that extended image modeling in lensing clusters simultaneously reduces the uncertainty on lens model parameters and enables spatially resolved analyses of lensed transients host galaxies. Such modeling advances are expected to play an important role in future cosmological analyses using strongly lensed SNe.

Figures (7)

• Figure 1: JWST color composite image of G165 (where the combination for blue is $\rm F090W + F115W + F150W$; green is $\rm F200W + F277W$ and red is $\rm F356W + F410M + F444W$). White crosses indicate the position of point-like multiple images used as model constraints 2024ApJ...961..171F. The magenta contour outlines the mask used to model the surface brightness of the SN H0pe host (Arc 2, composed of the SN host images 2a, 2b and 2c). Cyan circles show a subset of the cluster members included in our lens models. Our lens models also include two cluster-scale mass components, each located around the main concentrations of cluster members. The figure also indicates Arc 1 and Arc 7 which we mention in the text.
• Figure 2: Joint posterior distribution of the mass parameters for the two cluster-scale components. Contours are the 68% and 95% confidence levels for the model using only the point-like images as constraints (red) and the one including the full surface brightness of SN H0pe host galaxy (blue).
• Figure 3: Color composite of the reconstructed source-plane image of the SN H0pe host galaxy ($z=1.78$). The filters F090W, F150W and F200W correspond to the blue, green and red channels, respectively. The white star indicates the position of SN H0pe. The pixel scale is $0\farcs048$.
• Figure 4: Image-plane dust extinction map of SN H0pe host galaxy. Left panel: dust extinction map within the arc mask and at the resolution of the F444W data, which is also shown in grayscale (see Sect. \ref{['ssec:dust:image_plane']} for more details). The dashed line rectangles indicate the zoom-in regions of the middle and right panels. These panels show the F200W data in grayscale and corresponding isophotes (logarithmically spaced), showing consistency between the dust extinction and dimmer regions of the arc. In all panels, North is at the top and east is to the left..
• Figure 5: Top panel: Dust extinction map of SN H0pe host galaxy, reconstructed in the source plane based on our extended-image lens model. The green star shows the position of the SN with respect to its host, whose (logarithmically spaced) isophotes are indicated with thin black contours. We note the consistency between the perturbed isophotes and the dust extinction map. The bottommost high-extinction feature ($\sim 3$ bottom rows of the source-plane grid) is mainly due to low data S/N and image-plane flux contamination at the edge of the arc mask. North is at the top and east is to the left. Bottom panel: $A_V$ uncertainty due to the posterior uncertainty of our strong lensing model. In both panels, the pixel scale is $0\farcs048$.