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We estimate the Einstein-radius-enclosed total mass for 177 cluster-scale strong gravitational lenses identified by the ChicagO Optically selected Lenses Located At the Margins of Public Surveys (COOL-LAMPS) collaboration with lens redshifts ranging from 0.2 ⪅ z ⪅ 1.0 using the brightest-cluster-galaxy (BCG) redshift and an observable proxy for the Einstein radius. We constrain the Einstein-radius-enclosed luminosity and stellar mass by fitting parametric spectral energy distributions to aperture photometry from the Dark Energy Camera Legacy Survey (DECaLS) in the g -, r -, and z -band Dark Energy Camera filters. We find that the BCG redshift, enclosed total mass, and enclosed luminosity are strongly correlated and well described by a planar relationship in 3D space. We find that the enclosed total mass and stellar mass are correlated with a logarithmic slope of $0.50{0}_{-0.031}^{+0.029}$ , and the enclosed total mass and stellar-to-total mass fraction are correlated with a logarithmic slope of $-0.49{5}_{-0.033}^{+0.032}$ . In tandem with the small radii within which these slopes are constrained, this may suggest invariance in baryon conversion efficiency and feedback strength as a function of cluster-centric radii in galaxy clusters. Additionally, the correlations described here should have utility in ranking strong-lensing candidates in upcoming imaging surveys—such as Rubin/Legacy Survey of Space and Time—in which an algorithmic treatment of strong lenses will be needed due to the sheer volume of data these surveys will produce.

Radio observations of strongly lensed objects are valuable as cosmological probes. Lensed radio sources have proven difficult to identify, in large part due to the limited depth and angular resolution of the previous generation of radio sky surveys, and, as such, only a few dozen lensed radio sources are known. In this work, we present the results of a pilot study, using the Very Large Array Sky Survey (VLASS) in combination with optical data to more efficiently identify lensed radio sources. We obtain high-resolution (0 $\mathop{.}\limits^{\unicode{x02033}}$ 2) VLA follow-up observations for 11 targets that we identify using three different techniques: (i) a search for compact radio sources offset from galaxies with high lensing potential, (ii) VLASS detections of known lensed galaxies, and (iii) VLASS detections of known lensed quasars. Five of our targets show radio emission from the lensed images, including 100% of the lensed optical quasar systems. This work demonstrates the efficacy of combining deep- and high-resolution wide-area radio and optical survey data to efficiently find lensed radio sources, and we discuss the potential impact of such an approach using next-generation surveys with the Vera C. Rubin Observatory, Euclid, and Nancy Grace Roman Space Telescope.

We present a strong lensing analysis of COOL J1241+2219, the brightest known gravitationally lensed galaxy at z ≥ 5, based on new multiband Hubble Space Telescope (HST) imaging data. The lensed galaxy has a redshift of z = 5.043, placing it shortly after the end of the “Epoch of Reionization,” and an AB magnitude z _AB = 20.47 mag (Khullar et al.). As such, it serves as a touchstone for future research of that epoch. The high spatial resolution of HST reveals internal structure in the giant arc, from which we identify 15 constraints and construct a robust lens model. We use the lens model to extract the cluster mass and lensing magnification. We find that the mass enclosed within the Einstein radius of the z = 1.001 cluster lens is $M(\lt 5\buildrel{\prime\prime}\over{.} \,77)={1.079}_{-0.007}^{+0.023}\times {10}^{13}{M}_{\odot }$ , significantly lower than other known strong lensing clusters at its redshift. The average magnification of the giant arc is 〈 μ _arc 〉 = ${76}_{-20}^{+40}$ , a factor of ${2.4}_{-0.7}^{+1.4}$ greater than previously estimated from ground-based data; the flux-weighted average magnification is 〈 μ _arc 〉 = ${92}_{-31}^{+37}$ . We update the current measurements of the stellar mass and star formation rate (SFR) of the source for the revised magnification to $\mathrm{log}({M}_{\star }/{M}_{\odot })\,=$ 9.7 ± 0.3 and SFR = ${10.3}_{-4.4}^{+7.0}$ M _⊙ yr ^−1 , respectively. The powerful lensing magnification acting upon COOL J1241+2219 resolves the source and enables future studies of the properties of its star formation on a clump-by-clump basis. The lensing analysis presented here will support upcoming multiwavelength characterization with HST and JWST data of the stellar mass assembly and physical properties of this high-redshift lensed galaxy.

We report the discovery of five bright, strong gravitationally lensed galaxies at 3 < z < 4: COOL J0101+2055 ( z = 3.459), COOL J0104−0757 ( z = 3.480), COOL J0145+1018 ( z = 3.310), COOL J0516−2208 ( z = 3.549), and COOL J1356+0339 ( z = 3.753). These galaxies have magnitudes of r _AB , z _AB < 21.81 mag and are lensed by galaxy clusters at 0.26 < z < 1. This sample nearly doubles the number of known bright lensed galaxies with extended arcs at 3 < z < 4. We characterize the lensed galaxies using ground-based grz / giy imaging and optical spectroscopy. We report model-based magnitudes and derive stellar masses, dust content, and star formation rates via stellar population synthesis modeling. Building lens models based on ground-based imaging, we estimate source magnifications ranging from ∼29 to ∼180. Combining these analyses, we derive demagnified stellar masses in the range ${\mathrm{log}}_{10}({M}_{* }/{M}_{\odot })\sim 9.69-10.75$ and star formation rates in the youngest age bin in the range ${\mathrm{log}}_{10}(\mathrm{SFR}/({M}_{\odot }\,{\mathrm{yr}}^{-1}))\sim 0.39-1.46$ , placing the sample galaxies on the massive end of the star-forming main sequence in this redshift interval. In addition, three of the five galaxies have strong Ly α emissions, offering unique opportunities to study Ly α emitters at high redshift in future work.

In the third paper from the COOL–LAMPS Collaboration, we report the discovery of COOL J0542-2125, a gravitationally lensed quasar at z = 1.84, observed as three images due to an intervening massive galaxy cluster at z = 0.61. The lensed quasar images were identified in a search for lens systems in recent public optical imaging data and have separations on the sky up to 25.″9, wider than any previously known lensed quasar. The galaxy cluster acting as a strong lens appears to be in the process of merging, with two subclusters separated by ∼1 Mpc in the plane of the sky, and their central galaxies showing a radial velocity difference of ∼1000 km s ^−1 . Both cluster cores show strongly lensed images of an assortment of background sources, as does the region between them. A preliminary strong lens model implies masses of ${M}_{\lt 250{\rm{k}}{\rm{p}}{\rm{c}}}={1.79}_{-0.01}^{+0.16}\times {10}^{14}\,{M}_{\odot }$ and ${M}_{\lt 250{\rm{k}}{\rm{p}}{\rm{c}}}={1.48}_{-0.10}^{+0.04}\times {10}^{14}\,{M}_{\odot }$ for the east and west subclusters, respectively. This line of sight is also coincident with an ROSAT ALL-sky Survey source, centered between the two confirmed cluster halos reminiscent of other major cluster-scale mergers. Archival and new follow-up imaging show flux variability in the quasar images of up to 0.4 mag within ∼1 yr, and new multicolor imaging data reveal a 2 σ detection of the underlying quasar host. A lens system with this configuration offers rare opportunities for a range of future studies of both the lensed quasar and its host and the foreground cluster merger causing the lensing.