Huiyuan Wang

A possible origin of disk galaxy warps is the misalignment between galactic disks and their host dark matter halos, the orientations of which are found to be statistically aligned with the large-scale tidal field. In this work, we test this scenario by examining the alignment between warped disk galaxies and the large-scale tidal field reconstructed from the ELUCID project. We find a statistically significant alignment signal between disk orientations and the t ₁ direction, with warped and nonwarped galaxies showing different alignment behaviors. Warped galaxies show an excess of intermediate angles and a preference for orientations slightly offset from perfect parallel and perpendicular alignments. In contrast, nonwarped galaxies exhibit a deficit of intermediate angles relative to random expectations, which becomes more pronounced after matching to a control sample. We also find a clear mass dependence, with high-mass warped galaxies contributing the excess of intermediate-angle signal. No significant alignment signal in warped galaxies is detected in the t ₃ direction. Taken together, these results provide statistical support for the disk–halo misalignment scenario for disk warps, in which misalignment between the disk plane and the halo minor axis may play an important role.

Warped structures are often observed in disk galaxies, yet their physical origin is still under investigation. We present a systematic study of warped edge-on disk galaxies based on imaging data from the DESI Legacy Imaging Surveys DR8, with the expectation that this large sample size, enabled by wide-area surveys, will offer new perspectives on the formation of disk warps. Using a deep learning approach, we trained an EfficientNet-B3 convolutional neural network to classify the morphology of edge-on-disk galaxies into warped and nonwarped categories. Our model was trained on a curated and visually verified set of labeled galaxy images and applied to a large dataset of 595,651 edge-on disk galaxies selected from the Galaxy Zoo DESI catalog. Our results provide the largest warp catalog to date, consisting of 23,996 warped edge-on disk galaxies, and reveal statistical trends between warp occurrence and galaxy properties. Compared to their nonwarped counterparts, these warped disk galaxies tend to have bluer colors, lower stellar masses, higher gas fractions and star formation rates, smaller Sérsic indices, and larger disk sizes. In addition, warped disk galaxies show higher projected number densities of neighboring galaxies than their nonwarped counterparts, particularly within R _proj ≲ 50 kpc, where the local number density is roughly twice as high.

Precession is a very common phenomenon for small-scale astronomical objects. However, the precession of galactic disks, occurring on scales of kiloparsecs or more, has been insufficiently studied in past works. Quantifying this precession observationally remains challenging due to the lack of high-resolution dynamical data. Cosmological simulations, in which gravitational interactions are self-consistently modeled, offer a unique avenue for investigating disk precession. Leveraging the IllustrisTNG simulations, we trace the evolution of the spin orientation in Milky Way–like galaxies over cosmic time. We find that disk precession is ubiquitous in galaxies and significantly affects galaxy evolution. It is driven by the external tidal torque originating from the anisotropic matter distribution within 30 kpc, and is violent at z > 1, becoming gentler but still significant by z  ∼ 0, when disks are considered dynamically settled. Disk precession can induce significant warping of cold gas, which is often observed in the Milky Way and nearby galaxies. We predict that the Milky Way is currently precessing at a rate of ≃3°–10° Gyr ^–1 based on its observed warp. Violent precession can heat the orbits of stars, which may eventually produce prolate elliptical galaxies. The tidal torque from central galaxies can cause the precession of nearby satellite galaxies, causing their disk planes to point toward the centrals, which explains the observed radial alignment. We also find that the precession of accreted cold gas streams, regulated by galactic torques, is crucial for the evolution of disk galaxies.

Stellar feedback, as a key process regulating the baryon cycle, is thought to greatly redistribute baryonic material inside and outside the dark matter halos (DMHs); however, the observational evidences are lacking. Through stacking analyses of ∼400,000 galaxy spectra from Dark Energy Spectroscopic Instrument (DESI), we find star formation–driven cool outflows in the Mg ii absorption line. Assuming only gravity acts on the launched gas, our calculations reveal that outflows from low-mass galaxies ( M ∗ < 10 10   M ⊙ ) are capable of escaping beyond the DMHs, which aligns well with our finding in the circumgalactic medium (CGM) absorption along the minor axes of galaxies using background quasars. This research offers indirect evidence that stellar feedback drives the low baryon retention rate in low-mass halos, implicating that baryonic processes within galaxies are connected with the diffuse matter beyond the DMHs.

Stellar halos are the only major stellar component of disk galaxies that lack systematic observational characterization, yet they encode critical information about galaxy merger histories. We present the first systematic census of stellar halos in a large, flux-limited sample of 169 high-inclination central galaxies with stellar masses 7.3 ≤ log M ⋆ / M ⊙ ≤ 11.0 and redshift z < 0.1, using Hyper Suprime-Cam Subaru Strategic Survey Deep optical images. Stellar halos are detected in 93 galaxies, primarily through their low isophotal ellipticities in the outskirts, improving upon conventional methods of stellar halo identification. The halo detection rate reaches ∼50% at log M ⋆ / M ⊙ > 9.9 and ≳70% for Milky Way (MW)-mass galaxies. We derive halo surface brightness profiles, colors, and masses, finding that stellar halos generally follow power-law radial profiles. Higher-mass galaxies, on average, exhibit smaller power-law indices and larger halo mass fractions, indicating more extended halos and more active merger histories. A significant stellar halo color–mass correlation, driven mainly by the mass–metallicity relation, suggests dominance by a few massive accretion events. MW-mass galaxies have a median stellar halo fraction of 10% ± 5%. Among nearby galaxies with halo measurements within 25 Mpc, two-thirds (including the MW) lie below the mean stellar halo fraction–galaxy mass relation. Overall, the nearby galaxies show a median halo deficit of ∼0.3 dex, implying unusually quiescent merger histories. We show that this deficit follows a broader trend in which typical halo fractions increase with heliocentric distance, tracking the gradual rise in matter density toward the cosmic average by z ≲ 0.07.

We present the Two Deep Fields Imaging Survey (2DFIS), a wide-field imaging program conducted with the Canada-France-Hawaii Telescope (CFHT) targeting two astrophysically distinct regions: one containing a repeating fast radio burst (FRB) source and another hosting a candidate of a rotating galaxy cluster. Achieving a depth of r~26mag, the survey enables a search for faint optical counterparts and environmental signatures associated with the FRB, while high-quality photometric and galaxy shape measurements in the cluster field support a weak-lensing analysis of its mass distribution. This paper describes the observing strategy and data processing methodology adopted for 2DFIS, including the use of the LSST Science Pipelines with survey-specific adaptations for CFHT/MegaCam data. We outline a complete workflow for transforming raw CFHT exposures into science-ready data products, including calibrated single-epoch images, multi-band coadded mosaics, and extensive source catalogs. These data products provide the foundation for ongoing and future studies of FRB host environments, cluster mass reconstruction, and related cosmological applications.

Protoclusters, galaxy clusters’ high-redshift progenitors, hold the key to understanding the formation and evolution of clusters and their member galaxies. However, their cosmological distances and spatial extensions (tens of Mpc) have inhibited complete mapping of their structure and constituent galaxies, which is key to robustly linking protoclusters to their descendants. Here we report the discovery of the Bigfoot, a tridimensional structure at z = 3.98 including 11 subgroups traced by 55 (700) spectroscopic (photometric) redshifts with JWST, extending over 15 × 37 × 49 cMpc ³ in the PRIMER-UDS field. Bigfoot’s large-scale and mass function of member galaxies closely match constrained simulations’ predictions for the progenitors of today’s most massive clusters ( M ₀ > 10 ¹⁵ M _⊙ ). All subgroups with M _h > 10 ^12.5 M _⊙ exhibit enhanced fractions of massive galaxies (>10 ^10.0 M _⊙ ) compared to lower-mass halos and fields, demonstrating the accelerated formation of massive galaxies in massive halos. The presence of this massive protocluster with a large central halo (10 ^13.0 M _⊙ ) in a JWST deep field bears important cosmological implication that favors high σ ₈ of PLANCK cosmology over low-redshift probes.