Lilan Yang

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 a reconstruction of the large-scale structure, using the James Webb Space Telescope (JWST) COSMOS-Web program to trace environmentally driven galaxy evolution up to z ∼ 7. We apply a weighted kernel density estimation method to 164,000 galaxies with robust photometric redshifts. We find that stellar mass has a positive correlation with density at all redshifts, which is stronger for quiescent galaxies (QGs) at z ≲ 2.5, while at higher redshifts (2.5 ≲ z ≲ 5.5) this trend is confined to extreme overdense environments, consistent with early mass assembly in protoclusters. The star formation rate (SFR) shows a negative trend with density for QGs at z ≲ 1.2, reversing at z ≳ 1.8, while star-forming galaxies (SFGs) show a mild positive correlation up to z ∼ 5.5. The specific SFR remains nearly flat for SFGs and declines with density for QGs at z ≲ 1.2. Moreover, mass and environmental quenching efficiencies show that mass-driven processes dominate at z ≳ 2.5, that the two processes act with comparable strength between 0.8 ≲ z ≲ 2.5, and that environmental quenching becomes stronger for low-mass galaxies ( M _⋆ ≲ 10 ¹⁰ M _⊙ ) at z ≲ 0.8. These findings reveal that large-scale structure drives galaxy evolution by enhancing early mass assembly in dense regions and increasingly suppressing star formation in low-mass systems at later times, establishing the environmental role of the cosmic web across cosmic history. COSMOS-Web, the largest JWST survey, provides accurate and deep photometric redshifts, reaching 80% mass completeness at log M ⋆ / M ⊙ ∼ 8.7 at z ∼ 7, enabling the first view of how environments shaped galaxy evolution from the Epoch of Reionization to the present day.

We analyzed the 25 richest galaxy groups in COSMOS-Web across the redshift range z = 0.18–3.65, identified using the Adaptive Matched Identifier of Clustered Objects (AMICO) algorithm. The groups have about 20–30 galaxies with a high (> 75%) membership probability. Our study reveals both passive-density and active-density relations, with late-type galaxies (LTGs) preferring both higher central overdensities than early-type galaxies (ETGs) across all groups, and secondly many massive LTGs have colors typical for quiescent galaxies. We identify red sequences (RS) in five out of 25 galaxy groups, prominently established at z < 1, with early emergence in the RS locus up to z ∼ 2.2. Although LTGs outnumber ETGs, ETGs are quenched much more efficiently than LTGs up to z ∼ 3.5. This finding suggests that group environments represent a transitional phase where star formation quenching precedes morphological transformation, contrasting with the classical morphology–density relation observed in rich clusters. In the central regions of the identified groups, within a radius of ∼33″ (100 kpc) from the group centers, we identified 86 galaxies. Among them, 23 (∼27%) were classified as ETGs and 63 (∼73%) as LTGs. High-mass galaxies ( M _★ > 10 ^10.5 M _⊙ ) undergo rapid, transformative quenching over ∼1 Gyr, becoming predominantly spheroidal ETGs, indicating that morphological transformation accelerates dramatically in the most massive systems during the epoch of peak cosmic star formation. Intermediate-mass galaxies (10 ⁹ < M _★ /M _⊙ < 10 ^10.5 ) show mild quenching, while low-mass galaxies ( M _★ < 10 ⁹ M _⊙ ) remain largely star-forming, with environmental processes gradually suppressing star formation without destroying disk structures, suggesting that environmental quenching in groups operates on longer timescales than mass quenching. Overall, mass-dependent quenching dominates at the high-mass end, while environment-driven quenching shapes lower-mass systems, highlighting the dual nature of galaxy evolution across cosmic time. The fraction of high−luminosity active galactic nuclei (HLAGN) for both group and field galaxies increases with redshift, peaking at z ∼ 2, with groups consistently showing a higher AGN fraction than field. We suggest that AGN feedback plays a partial role in the rapid cessation of star formation in high-mass galaxies, while mergers may contribute to triggering AGN activity.

We study the stellar mass function (SMF) of quiescent and star-forming galaxies and its dependence on morphology in ten redshift bins at 0.2 < z < 5.5. We used the COSMOS2025 catalog, built from the 0.54 deg ² JWST imaging from the COSMOS-Web survey, to select galaxies by type using the NUVrJ rest-frame color diagram and to classify them morphologically based on their bulge-to-total light ratio ( B / T ). The SMF of quiescent galaxies shows a rapid early build-up, with the most massive, log( M _★ /M _⊙ )≳11, being assembled by z ∼ 1 and evolving little since. The star-forming SMF evolves more slowly with redshift, following a mass-evolution scenario where galaxies grow in mass via star formation and quench once they reach the characteristic log( M ^∗ /M _⊙ ) ∼ 10.6. Bulge systems ( B / T > 0.6) dominate the quiescent SMF at log( M _★ /M _⊙ ) > 10 at all redshifts, while disk systems ( B / T < 0.2) dominate at log( M _★ /M _⊙ ) < 9. However, most bulge-dominated galaxies in the Universe are star forming, with their fraction increasing with redshift and decreasing mass, consistent with them being progenitors of quiescent bulges. We find evidence for the onset of environmental quenching as early as z ∼ 3 from the upturn in the quiescent SMF at log( M _★ /M _⊙ ) < 9.5. This upturn is contributed by disk-dominated galaxies, consistent with environmental quenching scenarios in which satellites are quenched, but retain their disk morphologies. The number densities of log( M _★ /M _⊙ ) > 10 quiescent galaxies are lower than in the recent literature by 0.1 − 0.7 dex, but agree well with cosmological galaxy formation simulations at 2 < z < 3. However, at z > 3, simulations increasingly underpredict the observations. Finally, we built a simple empirical model to describe the redshift evolution of galaxy number densities by parameterizing the quenching rate of all and bulge-dominated galaxies, stellar fraction, and bulge formation function. Our model is consistent with an evolutionary scenario where star-forming galaxies grow a central bulge before permanently quenching in massive halos.

We present the data reduction methodology used for the COSMOS-Web survey JWST NIRCam data. Covering 0.54 deg ² with four broadband filters (F115W, F150W, F277W, F444W) and a total exposure time of approximately 270 hr, COSMOS-Web represents the largest contiguous field surveyed during JWST Cycle 1, posing unique data reduction challenges due to its extensive scale. By combining the official JWST Calibration Pipeline with custom improvements for noise removal, background subtraction, and astrometric alignment, we achieve high-fidelity science-ready mosaics. We detail the systematic approach employed in the three stages of the JWST Calibration Pipeline. The data, collected in three epochs from 2023 January to 2024 January, encompass 152 visits and have been processed into 20 mosaic tiles to optimize computational efficiency and data processing. The final data products achieve 5 σ depths of 26.7–28.3 AB mag in 0 . ″ 15 apertures. The processed and calibrated datasets are made available to the public.

To investigate the formation and evolution of vertical structures in disk galaxies, we measure global sech ² scale heights, averaging thin and thick components when present, for 2631 edge-on disk galaxies with M _* > 10 ¹⁰ M _⊙ at 0 < z < 3.5 from the JWST COSMOS-Web survey. We show that dust extinction systematically overestimates scale heights at shorter rest-frame wavelengths and therefore adopt a fixed rest-frame wavelength of 1 μ m. After further correcting for projection-induced bias using a new accurate method, we find that the median disk scale height increases from 0.56 ± 0.03 kpc at z = 3.25 to 0.84 ± 0.04 kpc at z = 1.25, and subsequently decreases to 0.67 ± 0.06 kpc at z = 0.25. The bias-corrected disk scale length-to-height ratio remains constant at 2.7 ± 0.2 for z > 1.5 but rises to 4.0 ± 0.4 at z = 0.25. These results imply that the high-redshift progenitors of present-day thick disks were of intermediate thickness, neither thin nor thick, yet dynamically hot and dense. The observed radial variation of scale height is consistent with the artificial flaring expected from observational effects, disfavoring minor mergers as the primary mechanism of disk thickening. Instead, we suggest that the high-redshift intermediate-thickness disks were single-component systems that increased their vertical scale height through decreasing surface mass density and/or violent gravitational instabilities, eventually producing thick disks. Thin-disk growth begins at z ≈ 2 and dominates at z ≲ 1, yielding a vertically more compact system with decreasing scale heights from z ≈ 1 to 0. The inferred thin-disk mass fraction increases from 0.1 ± 0.03 at z = 1 to 0.6 ± 0.1 at z = 0. Together, these findings reveal a continuous evolutionary link between high-redshift single-component disks and present-day disks comprising thick and thin components.

We measure galaxy sizes from 2 < z < 10 using COSMOS-Web, the largest-area JWST imaging survey to date, covering ∼0.54 deg ² . We analyze the rest-frame optical (∼5000 Å) size evolution and its scaling relation with stellar mass ( R e ∝ M * α ) for star-forming and quiescent galaxies. For star-forming galaxies, the slope α remains approximately 0.20 at 2 < z < 8, showing no significant evolution over this redshift range. At higher redshifts, the slopes are −0.13 ± 0.15 and 0.37 ± 0.36 for 8 < z < 9 and 9 < z < 10, respectively. At fixed galaxy mass, the size evolution for star-forming galaxies follows R _e ∝ (1 + z ) ^{−1.21±0.05} . For quiescent galaxies, the size–mass relation is steeper with α ∼ 0.5–0.8 at 2 < z < 5, and size evolves as R _e ∝ (1 + z ) ^{−0.81±0.26} . We find that the size−mass relation is consistent between UV and optical at z < 8 for star-forming galaxies. However, we observe a decrease in the slope from UV to optical at z > 8, with a tentative negative slope in the optical at 8 < z < 9, suggesting a complex interplay between intrinsic galaxy properties and observational effects such as dust attenuation. We discuss the ratio between galaxies’ half-light radius and underlying halos’ virial radius, R _vir , and find the median value of R _e / R _vir = 2.7%. The star formation rate surface density evolves as log ( Σ SFR / ( M ⊙ / yr / kpc 2 ) ) = (0.20 ± 0.08) z + (−0.65 ± 0.51), and the Σ _SFR – M _* relation remains flat at 2 < z < 10. Lastly, we identify a threshold in stellar mass surface density log ( Σ e / ( M ⊙ / kpc 2 ) ) ∼ 9.5 − 10 marking the transition to compact, quenched galaxies from extended, star-forming progenitors. In summary, our findings show that the extensive COSMOS-Web dataset at z > 3 provides new insights into galaxy size and related properties in the rest-frame optical.

Recent JWST observations have revealed a population of red, compact, high-redshift objects called “Little Red Dots” (LRD), whose host components have remained largely unconstrained, possibly due to their extreme compactness. Current morphological studies have been limited by small samples, as well as by insufficient imaging depth, which may not allow reliable separation between point-like and extended components, leaving the existence and properties of extended components in LRD largely unconstrained. Here, we perform the image stacking analysis of 217 LRDs in four NIRCam bands, representing the largest and homogeneous sample observed from COSMOS-Web survey to date. Our results reveal an unambiguous detection of faint extended emission in the F444W band, with a typical size of ~200 parsecs and magnitude of ~27.7 AB at z~6.5. We perform four-band photometric SED fitting based on galaxy templates and derive a stellar mass of 8.91+-~0.1 logM_sun. Given this stellar mass, the host galaxy is compact, i.e., ~2.5 times smaller than star-forming populations at similar mass, and the typical black hole mass of LRDs is elevated by ~1.5 dex above the local MBH-M* relation. This work provides direct observational evidence for the existence of LRD host galaxies and offers crucial insights into the growth of the host galaxy and the co-evolution of galaxies and their black holes within the first billion years after the Big Bang.