Xuheng Ding

We present results from imaging observations of three quadruply lensed quasars by the Hubble Space Telescope and the James Webb Space Telescope at redshifts z = 2.550, 2.975, and 1.500. We model our targets assuming a singular isothermal ellipsoid mass profile and an elliptical Sérsic profile for the lensing galaxies, and reconstruct the geometric configuration of each system with measured Einstein radii of 0 . ″ 44, 0 . ″ 58, and 0 . ″ 49. While no spectroscopic measurements are available for the lenses, we constrain the redshift of each lens to 0.5 < z < 1.2, 1.0 < z < 1.5, and 0.4 < z < 0.9. For all three lenses, the best-fit light models yield a typical de Vaucouleurs n _Sérsic ∼ 4 profile and an effective radius R _e around ∼1.5–3.5 kpc. We accordingly classify the three lenses as early-type galaxies at an intermediate to high redshift, a common type for strong lensing galaxies. Compared to other known quadruple lenses, the lensing galaxies in this work are at the lower end of the distribution of Einstein radii and the upper end of the distribution of the lens redshifts. They represent an interesting quadrant of subarcsecond-separation lenses in the population of single-galaxy strong lensing, which have been largely unexplored yet and will be great targets of interest in upcoming high-resolution lensing surveys.

As plans for the construction of third-generation gravitational-wave (GW) detectors advance, research into strongly lensed GWs has become increasingly critical. It is anticipated that hundreds of multi-image lensed GWs will be detected annually. We present a comprehensive suite of lensed GW mock catalogs derived from a composite lens mass model incorporating dark matter halos, galaxies, and subhalos. We analyze three source populations with four detector network configurations considering Earth’s rotation. Our simulations encompass not only conventional doublets and quadruplets but also subhalo-lensed events, highly magnified systems, and complete three- or five-image systems with a detectable central image, a feature distinct from optical lensing. For the joint Einstein Telescope (ET) + Cosmic Explorer (CE) network, we forecast an annual detection rate of approximately 400 doublets and 36 quadruplets. Notably, this population includes roughly 107 events lensed by subhalos and 20 complete systems with detectable central images. Furthermore, we analyze high-magnification events ( μ > 3), predicting approximately 360 such cases. Under a more relaxed selection criterion that requires only at least one lensed signal to exceed the detection threshold, we estimate a total of approximately 617 lensed events. We also investigate the impact of variations in lens mass models and stellar evolution models on the event rates, as well as the distribution of signal-to-noise ratio and time-delay pairs. These results establish a more physically grounded statistical prior for the future identification and authentication of lensed GW signals. The GW lensing mock catalog has been made publicly available.

We present an analysis of the rest-frame optical JWST NIRSpec Fixed Slit spectra of extended host galaxy emission in 12 moderate luminosity quasars from the Subaru High- z Exploration of Low-Luminosity Quasars sample at redshifts 6.0 < z < 6.4. We fit and subtract a point-spread model based on observations of a calibration star and use it to remove the quasar from the 2D spectra, leaving only extended emission, which we analyze. Ten of 12 systems show spatially extended line emission, and six of 12 systems show an extended stellar continuum. From the extended [O III ] λ 5008 emission line, we measure a 132 ± 22 km s ⁻¹ ionized outflow in one system and 52 ± 12 km s ⁻¹ rotation, suggesting a coherent disk, in another. From the extended narrow H α emission, which we hypothesize is ionized by star-forming regions rather than the quasar, we measure star formation rates ranging from ∼7 to 111 M _⊙ yr ⁻¹ , the majority of which are consistent with the star-forming main sequence (SFMS) at z ≈ 6. The positions of our host galaxies on the log 10 [ O III ] λ 5008 / H β versus log 10 [ NII ] 6584 / H α (R3N2) Baldwin–Phillips–Terlevich diagram indicate ionization rates typical of active galactic nucleus (AGN) activity in the low-redshift Universe, but are consistent with the placement of other z ≈ 6 quasar host galaxies, suggesting that the R3N2 line ratios cannot distinguish AGN- and star-formation-powered line emission at high redshifts. We conclude from the consistency between our quasar host sample with z ∼ 6 galaxies that the presence of a low-luminosity AGN causes little significant change in the properties of galaxies at z ≈ 6 on 10 Myr timescales.

We investigate the rest-frame optical size–stellar mass relation of galaxies at 0.5 < z < 6.0 using deep JWST/NIRCam and MIRI imaging from the PRIMER survey. We find that star-forming galaxies (SFGs) exhibit a broken power-law relation at all redshifts, with a nearly constant pivot mass ( M _p ) of ∼10 ¹⁰ M _⊙ and a slope flattening above M _p . This highlights the prevalence of a population of compact, massive SFGs that was underrepresented in previous studies. The size distribution of quiescent galaxies (QGs) is well described by a mixture power-law model, with a pivot mass that increases from M _p ∼ 10 ^10.0 M _⊙ at z = 0.75 to M _p ∼ 10 ^10.5 M _⊙ at z = 2.6, suggesting that the minimum halo mass required to quench high-mass galaxies increases with redshift. The bending in the size–mass relation of SFGs supports two distinct size growth modes. At M _⋆ < M _p , size growth is closely coupled to halo growth, while at M _⋆ > M _p , an increasing fraction of SFGs decouple from halo growth and become compact, likely associated with rapid bulge (and black hole) growth in M _h ≳ 10 ¹² M _⊙ halos. These compact SFGs are promising progenitors of massive QGs, as evidenced by their similar masses, surface brightness profiles, and morphologies. Their high number densities can account for the observed buildup of massive QGs at z > 2, suggesting that the compaction pathway, rather than major mergers of extended SFGs, dominates the formation of high- z massive QGs.

We present an analysis of spectral energy distributions (SEDs), galaxy light profiles, and visual morphological classifications for 194 X-ray luminous active galactic nuclei (AGN) (intrinsic absorption-corrected log ( L X , 0.5 − 7 keV ) > 42.5 ( maximum 45.2 ) erg s − 1 ) with z < 1.5 in the Great Observatories Origins Deep Survey (GOODS) fields. We generate X-ray to far-infrared SEDs normalized at 1 μ m for all AGN and sort them according to their emission slopes in the ultraviolet (UV) and infrared (IR). We visually classify their host galaxies’ morphologies and compute their bulge/total light ratios using the Galaxy Shapes of Light ( galight ) software. Most (94%) GOODS AGN exhibit obscured (i.e., diminished UV and/or mid-IR emission) SEDs. Only 6% show unobscured, quasar-like SEDs. Secular processes appear to play a large role in stimulating AGN emission, since only ∼1/3 of galaxies are undergoing interactions. We also describe the morphological identification of a population of suspected postmerger spheroid galaxies with obscured UV/IR SEDs and distinguish them from the host galaxies of AGN with less obscuration in the UV or IR.