The gas accretion process can fuel both star formation and black hole activity, playing a critical role in galaxy evolution. The counter-rotating structures are believed to originate from gas accretion, serving as an ideal laboratory to study its impact on galaxy evolution. Based on the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey, we built a sample of 147 galaxies with counter-rotating stellar disks (CRDs). This is the largest CRD sample to date, accounting for similar to 1.5% of the MaNGA survey. For a subset of 138 CRDs, global stellar mass (M*) and star formation rate (SFR) were measured in reference. We constructed a control sample with similar M* and SFR but lacking counter-rotating structures. The CRDs relatively exhibit more bulge-dominated morphology, lower molecular gas mass fraction, and reside in a less dense environment, supporting the hypothesis that they primarily originate from gas accretion. We classified 96 out of 138 CRDs into four types based on their stellar and gas kinematics following the criteria from M. Bao et al. There are two additional CRD types: eight CRDs show misalignment between both stellar disks and gas disk, indicating multiple gas accretion events with differing angular momentum directions; while 34 CRDs lack ionized gas emission, showing the highest M* among all the CRD types, which may represent a final stage of CRD evolution. We compared the radial gradients of gas-phase metallicity and stellar population properties between CRD types and found that the impact of gas accretion on galaxy evolution primarily depends on the abundance of pre-existing gas in progenitors.

Poststarburst galaxies (PSBs), identified by strong Balmer absorption and weak nebular emission, provide a key laboratory for studying rapid quenching. Using the final data release of the Sloan Digital Sky Survey IV MaNGA survey, we follow the traditional PSB selection criteria of Y.-M. Chen et al. and develop a new method to identify regions that simultaneously exhibit PSB features and nuclear activities (AGN-PSBs). Our final sample comprises 48 AGN-PSBs, 92 central PSBs (CPSBs), 89 ringlike PSBs (RPSBs), and 828 irregular PSBs (IPSBs). We find the global and spatially resolved properties of CPSBs and RPSBs are consistent with the results of Y.-M. Chen et al. In this work, we focus on the properties of AGN-PSBs, comparing them with CPSBs, RPSBs, and control galaxies. Similar to CPSBs and RPSBs, AGN-PSBs show positive D _n 4000 gradients relative to negative D _n 4000 gradients of their controls, which indicates younger stellar populations in the central region than in the outskirts. Among the three subtypes, high-mass CPSBs (H-CPSBs; with $\mathrm{log}({M}_{* }/{M}_{\odot })\gt 9.5$ ) display the highest incidence of merger remnants and gas–star kinematic misalignment, consistent with a merger-/interaction-dominated origin. AGN-PSBs and RPSBs, however, show lower and comparable fractions of merger remnants and gas–star kinematic misalignment, favoring less violent external mechanisms. Based on radial profiles of the mass-weighted age and V _star / σ _star , we suggest that RPSBs can evolve into AGN-PSBs, whereas H-CPSBs likely follow a distinct evolutionary pathway. The existence of RPSBs and IPSBs also indicates that AGN feedback is not a necessary condition for the formation of PSBs.

Stellar metallicity gradients (del[Z/H]) provide a fossil record of the assembly history of galaxies. We present an analysis of del[Z/H] for 90 nearby low-mass galaxies using Very Large Array (VLT)/MUSE integral field unit (IFU) spectroscopy, spanning stellar masses from 106.5 to 1010M circle dot(median similar to 108.5M circle dot) and significantly extending the mass coverage of existing IFU surveys into the classical dwarf regime. Our primary finding is a robust negative correlation between del[Z/H] and light-weighted stellar age (divided by r divided by greater than or similar to 0.7) measured out to similar to 2 & times; effective radius: older dwarf galaxies have steeper (more negative) gradients. This holds regardless of stellar mass, structural compactness, or large-scale environment (group/field) and is strongest in the intermediate-mass regime ( 8.2 less than or similar to logM star/M circle dot less than or similar to 9.0 ). The slope of the age-del[Z/H] relation is close to that in the FIRE-2 simulations, indicating that stellar radial migration driven by feedback-induced potential fluctuations may be fundamental in dwarf evolution. But this apparent consistency is likely coincidental given the simulations' overly efficient feedback and chemical mixing. On the other hand, the H i deficiency parameter, an indicator of past environmental stripping, shows a moderate yet highly significant correlation with del[Z/H], second only to stellar age in strength: galaxies with higher H i deficiency tend to have more negative gradients, strongly indicating that environment-driven outside-in quenching and the ensuing gradual truncation of metal enrichment reshape the stellar metallicity distribution. Our analysis suggests that the chemical evolution of dwarf galaxies likely arises from a synergy of feedback-driven dynamical heating and external environmental processing, though only the latter has robust observational support.

Intermediate-mass black holes are widely considered to be the seeds of supermassive black holes, a substantial population of which is expected to remain displaced from galactic nuclei owing to hierarchical galaxy assembly and inefficient dynamical friction. While several fueling channels can sustain central black holes, those pathways are largely inaccessible to off-nuclear black holes, leaving their fuel supply uncertain. As these wandering black holes move through the interstellar medium of their host galaxies, theory predicts that they can capture gas from the dense wake produced by gravitational focusing. However, direct observational evidence for this process has remained elusive. Here we report evidence for a wandering intermediate-mass black hole of 35,000 solar mass accreting through such a gravitational wake. Its black-hole nature is supported by broad-line emission, a compact continuum counterpart, long-term optical variability, and a power-law-like spectral energy distribution. Multi-epoch spectroscopy reveals three distinct gas components: a blueshifted, low-density upstream flow; a redshifted, dense downstream wake; and optically thick absorbers well within the capture radius that drive rapid changing-look variability in the broad-line emission. This discovery establishes a previously unobserved channel for the growth of wandering intermediate-mass black holes.

Studying active galactic nucleus (AGN) pairs and their host galaxies is essential for understanding the interplay between galaxy mergers and key internal processes such as supermassive black hole fueling and feedback. We crossmatch between the Big Multi-AGN Catalog and the public data archive of the Very Large Telescope (VLT)/MUSE, and obtain 12 AGN pair candidates in the local Universe ( z ≲ 0.1) with a projected distance of r _p ≤ 20 kpc. Using archival VLT/MUSE data, we present a spatially resolved study of the ionized gas kinematics and ionization properties of these 12 AGN pair candidates. By decomposing the optical emission lines into two Gaussian components, we try to separate gas associated with disk rotation from noncircular motions. We further identify dominant ionization mechanisms using spatially resolved Baldwin–Phillips–Terlevich diagnostics. We find that both nuclei in four of the 12 systems are classified as a Seyfert or LINER. In addition, three nuclei are classified as star-forming or composite in the optical diagnostics, but are identified as AGNs at other wavelengths. Kinematically, regularly rotating ionized gas disks are detected in 16 of 24 nuclei. Prominent tidal features traced by ionized gas are also detected in nine systems. Ionized gas outflows are widespread and are detected in 18 nuclei. Finally, for three nuclei (Mrk 739A, NGC 7592B, and J1544+0446A), we find evidence for fading AGN activity over the past several tens of thousands of years, based on optical emission-line ratios and an assumed AGN photoionization model.

Changing-look active galactic nuclei (CL-AGNs) provide a unique opportunity to probe the coupling between accretion flows and relativistic jets in supermassive black holes. We investigate the long-term radio behavior of CL-AGNs over approximately 20 years by combining FIRST and VLASS observations with quasi-simultaneous optical spectroscopy and photometry. From a parent sample of 1092 CL-AGNs, we identify 58 sources with radio detections. Radio-detected CL-AGNs exhibit systematically higher radio kinetic efficiency, quantified by P_ j/L_ bol, than both typical radio-detected AGNs and radio transients, consistent with their preference for low Eddington ratios. At the population level, the expected anti-correlation between radio emission and accretion rate is weak. However, a clear source-by-source anti-correlation emerges in a small subset of CL-AGNs with continuous multi-epoch coverage. We further identify four radio transients, including both radio turn-on and turn-off events, and one source exhibiting a multiwavelength flare that may be indicative of tidal disruption event-like activity. These results suggest that radio activity in CL-AGNs is not governed by instantaneous accretion state changes but is instead regulated by long-term accretion history and jet evolution, with additional stochastic or transient channels contributing in rare cases.

Tidal-torque theory predicts that galaxy angular momenta are imprinted by the primordial tidal field acting on proto-structures and that they can retain information about the early Universe through cosmic evolution. Here we test this prediction by comparing observed galaxy angular momentum vectors with those predicted from the primordial density field reconstructed by ELUCID for the nearby Universe. Among the galaxy populations considered, the gas component of central massive elliptical galaxies provides the clearest signal, exhibiting a strong direction correlation at a significance of about 7σ. These results provide robust observational evidence for tidal-torque theory and open a window for cosmological measurements of neutrino mass and other cosmological parameters. Combining galaxy kinematics with a reconstruction of the primordial density field has enabled the detection of a substantial imprint of primordial tidal torques in present-day galaxy spins. This strengthens evidence that the angular momentum of galaxies originates from large-scale tidal forces on their proto-halos at very early times.

Low-mass galaxies are the building blocks of massive galaxies in the framework of hierarchical structure formation. To enable detailed studies of galactic ecosystems in dwarf galaxies by spatially resolving different galactic components, we have carried out the Dwarf Galaxy Integral-field Survey (DGIS). This survey aims to acquire observations with spatial resolutions as high as 10–100 pc while maintaining reasonably high signal-to-noise ratios with the Very Large Telescope/MUSE and ANU-2.3 m/WiFeS. The whole sample will be composed of 63 dwarf galaxies with M _* < 10 ^9 M _⊙ , selected from the Spitzer Local Volume Legacy survey. The overall scientific goals include studying baryonic cycles in dwarf galaxies, searching for off-nuclear (intermediate)-massive black holes, and quantifying the inner density profiles of dark matter. In this work, we describe the sample selection, data reduction, and high-level data products. By integrating the spectra over the field of view for each galaxy, we obtained the integrated gas-phase metallicity and discussed its dependence on stellar mass and star formation rate (SFR). We find that the overall relation between metallicity and stellar mass of our DGIS nearly follows the extrapolation from the higher mass end. Its dispersion does not decrease by invoking the dependence on SFR.

4C+29.30 is a postmerger galaxy hosting a rejuvenated active galactic nucleus (AGN) with a complex multiscale radio morphology, making it an ideal laboratory to study the interplay between different AGN feedback modes. We present a multiwavelength analysis combining optical integral field spectroscopy (SDSS/MaNGA and CFHT/SITELLE) with radio continuum imaging (VLASS) to map the ionized-gas kinematics and ionization structure across the galaxy. We uncover a galaxy-scale biconical ionized-gas outflow whose axis is misaligned by similar to 26 degrees from the radio jet. This outflow, characterized by broad line widths and Seyfert-like ionization, is mostly consistent with a radiatively driven wind from the central supermassive black hole, which is accreting at a relatively high Eddington ratio (Lbol/LEdd greater than or similar to 0.1). In contrast, the northern radio lobe clearly drives localized gas acceleration and increased velocity dispersion, indicative of jet-driven shocks interacting with the interstellar medium, consistent with previous X-ray findings. The coexistence of a radiatively driven galactic-scale outflow and a distinct, misaligned radio jet demonstrates that multiple AGN feedback channels can operate simultaneously within the same system, providing new evidence for the concurrent action of radiative and mechanical feedback.

Post-starburst (PSB) galaxies, identified by strong Balmer absorption and weak nebular emission, provide a key laboratory for studying rapid quenching. Using the final data release of the SDSS-IV MaNGA survey, we follow the traditional PSB selection criteria of Chen et al. (2019) and develop a new method to identify regions that simultaneously exhibit PSB features and nuclear activities (AGN-PSBs). Our final sample comprises 48 AGN-PSBs, 92 central PSBs (CPSBs), 89 ring-like PSBs (RPSBs), and 828 irregular PSBs (IPSBs). We find the global and spatially resolved properties of CPSBs and RPSBs are consistent with the results of Chen et al. (2019). In this work, we focus on the properties of AGN-PSBs, comparing them with CPSBs, RPSBs, and control galaxies. Similar to CPSBs and RPSBs, AGN-PSBs show positive D_n4000 gradients relative to negative D_n4000 gradients of their controls, which indicates younger stellar populations in the central region than that in the outskirt. Among the three sub-types, high-mass CPSBs (H-CPSBs, with log(M_*/M_⊙)>9.5) display the highest incidence of merger remnants and gas–star kinematic misalignment, consistent with a merger/interaction-dominated origin. AGN-PSBs and RPSBs, however, show lower and comparable fractions of merger remnants and gas–star kinematic misalignment, favoring less violent external mechanisms. Based on radial profiles of mass-weighted age and V_ star/σ_ star, we suggest that RPSBs can evolve into AGN-PSBs, whereas H-CPSBs likely follow a distinct evolutionary pathway. The existence of RPSBs and IPSBs also indicates that AGN feedback is not a necessary condition for the formation of PSB.

4C+29.30 is a post-merger galaxy hosting a rejuvenated active galactic nucleus (AGN) with a complex multi-scale radio morphology, making it an ideal laboratory to study the interplay between different AGN feedback modes. We present a multi-wavelength analysis combining optical integral field spectroscopy (SDSS/MaNGA and CFHT/SITELLE) with radio continuum imaging (VLASS) to map the ionized gas kinematics and ionization structure across the galaxy. We uncover a galaxy-scale, biconical ionized gas outflow whose axis is misaligned by ∼26^∘ from the radio jet. This outflow, characterized by broad line widths and Seyfert-like ionization, is mostly consistent with a radiatively driven wind from the central supermassive black hole, which is accreting at a relatively high Eddington ratio (L_bol/L_Edd≳ 0.1). In contrast, the northern radio lobe clearly drives localized gas acceleration and increased velocity dispersion, indicative of jet-driven shocks interacting with the interstellar medium, consistent with previous X-ray findings. The coexistence of a radiatively driven galactic-scale outflow and a distinct, misaligned radio jet demonstrates that multiple AGN feedback channels can operate simultaneously within the same system, providing new evidence for the concurrent action of radiative and mechanical feedback.

Studying AGN pairs and their host galaxies is essential for understanding the interplay between galaxy mergers and key internal processes such as supermassive black hole fueling and feedback. We cross-match between the Big Multi-AGN Catalog (The Big MAC) and the public data archive of the VLT/MUSE, and obtain 12 AGN pair candidates in the local universe (z≲0.1) with a projected distance r_ p≤ 20 kpc. Using the archival VLT/MUSE data, we present a spatially resolved study of the ionized gas kinematics and ionization properties of these 12 AGN pair candidates. By decomposing the optical emission lines into two Gaussian components, we try to separate gas associated with disk rotation from non-circular motions. We further identify dominant ionization mechanisms using spatially resolved BPT diagnostics. We find that both nuclei in 4 of the 12 systems are classified as Seyfert or LINER. In addition, three nuclei are classified as star-forming or composite in the optical diagnostics, but are identified as AGNs at other wavelengths. Kinematically, regularly rotating ionized gas disks are detected in 16 of 24 nuclei. Prominent tidal features traced by ionized gas are also detected in 9 systems. Ionized gas outflows are widespread and are detected in 18 nuclei. Finally, for three nuclei (Mrk 739A, NGC 7592B, and J1544+0446A), we find evidence for fading AGN activity over the past several 10^4 yr, based on optical emission-line ratios and an assumed AGN photoionization model.

One important question in active galactic nuclei (AGN) is how gas is brought down to the galaxy center. Both internal secular evolution (torque induced by nonaxisymmetric galactic structures such as bars) and external processes (e.g., mergers or interactions) are expected to redistribute the angular momentum (AM) and transport gas inward. However, it is still under debate whether these processes can significantly affect AGN activities. Here we for the first time report that AGN fraction increases with the difference of kinematic position angles (ΔPA ≡ ∣PA _gas − PA _star ∣) between ionized gas (PA _gas ) and stellar disks (PA _star ) in blue and green galaxies, meanwhile this fraction remains roughly constant for red galaxies. Also, the high luminosity AGN fraction increases with ΔPA, while the low luminosity AGN fraction is independent of ΔPA. These observational results support a scenario in which the interaction between accreted and preexisting gas provides the AM loss mechanism, thereby the gas inflow fuels the central BH activities, and the AM loss efficiency is positively correlated with the ΔPA.

It is crucial to understand the star-forming activity in the host galaxies of high-redshift quasars for the connection between supermassive black hole activity and galaxy evolution. While most studies so far were biased toward luminous quasars, we conducted carbon monoxide (CO) observations of 17 gravitationally lensed quasars that have four images using the IRAM 30m telescope to investigate the molecular gas content of moderate- to low-luminosity quasars. CO emission is detected in 5 out of 17 quasars, which corresponds to a detection rate of about 30%. The analysis of their star formation activity revealed that these quasars live in gas-rich environments, but exhibit weaker starbursts and lower star formation efficiencies than other luminous high-redshift quasars. In addition, the CO spectral line energy distributions of two quasars (SDSS J0924+0219 and SDSS J1330+1810) are also consistent with mild star formation instead of extreme starbursts. These results suggest that these lensed quasars reside in weaker starburst environments.

Massive protoclusters at z similar to 1.5 - 4, the peak of the cosmic star formation history, are key to understanding the formation mechanisms of massive galaxies in today's clusters. However, studies of protoclusters at these high redshifts remain limited, primarily due to small sample sizes and heterogeneous selection criteria. For this work, we conducted a systematic investigation of the star formation and cold gas properties of member galaxies of eight massive protoclusters in the COSMOS field, using the statistical and homogeneously selected sample from the Noema formIng Cluster survEy (NICE). Our analysis reveals a steep increase in the star formation rates per halo mass (Sigma(SFR)/M-halo) with redshifts in these intensively star-forming protoclusters, reaching values one to two orders of magnitude higher than those observed in the field at z > 2. We further show that instead of an enhancement of starbursts, this increase is largely driven by the concentration of massive and gas-rich star-forming galaxies in the protocluster cores. The member galaxies still generally follow the same star-forming main sequence as in the field, with a moderate enhancement at the low-mass end. Notably, the most massive protocluster galaxies (M-star > 8x10(10) M-circle dot) exhibit higher mu(gas) and tau(gas) than their field counterparts, while remaining on the star-forming main sequence. These gas-rich, massive, and star-forming galaxies are predominantly concentrated in the protocluster cores and are likely progenitors of massive ellipticals in the center of today's clusters. These results suggest that the formation of massive galaxies in such environments is sustained by substantial gas reservoirs, which in turn support persistent star formation and drive early mass assembly in forming cluster cores.

The morphology of ionized gas velocity maps provides a direct probe of the internal gas kinematics of galaxies. Using integral field spectroscopy from SDSS-IV MaNGA, we analyze a sample of 528 low-inclination, regular disk galaxies to investigate the correlations between velocity map morphology, star formation rate, and gas-phase metallicity. We quantify velocity map morphology using harmonic expansion and adopt two complementary diagnostics: the global kinematic asymmetry, which traces nonaxisymmetric perturbations, and the first-order term ratio, which captures axisymmetric radial motions. We find that galaxies with higher kinematic asymmetry are more likely to deviate from the scaling relations, typically lying either above or below the star formation main sequence and systematically below the mass-metallicity relation. In contrast, the first-order term ratio shows only a correlation with gas-phase metallicity in the low-mass range and no significant dependence on star formation rate. Moreover, galaxies below the mass-metallicity relation generally exhibit higher H I gas fractions. These results suggest that external gas accretion is the primary driver of the observed phenomena: inflowing metal-poor gas increases velocity map asymmetry in disk galaxies, dilutes the metallicity, and triggers enhanced star formation. Feedback-driven outflows, bar- and spiral-driven inflows, and galaxy mergers may also contribute but likely play a secondary role.

Understanding the origin of galactic angular momentum and its connection to the cosmic web remains a pivotal issue in galaxy formation. Using kinematic data from the MaNGA survey, we investigate the alignment between the spin directions of spiral galaxies and their host cosmic filaments. By incorporating filament spin measurements derived from redshift asymmetry across filament spines, we reveal a mass-dependent anti-parallel correlation: low-mass spiral galaxies (log_10(M_*/M_⊙) ≲ 10) exhibit a statistically significant anti-parallel alignment between their stellar/gas spins and filament spins, while high-mass spirals show no such trend. Spatial analysis further indicates that high-mass spirals preferentially reside near filament spines, whereas low-mass spirals occupy filament outskirts. These findings extend previous alignment studies that neglected directional spin correlations and provide new insights into how cosmic environments shape galactic angular momentum. The observed anti-parallel trend suggests a critical role for filament spin in regulating the angular momentum acquisition of low-mass spirals. This anti-parallel alignment is significantly enhanced for low-mass spirals residing in dynamically cold filaments, highlighting the importance of filament properties in shaping galaxy spin.

Using the data from Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) and H i -MaNGA surveys, we build a sample of 37 gas–star misaligned galaxies with robust H i detections, which are believed to have undergone external gas accretion processes. Both star-forming (SF) and quiescent (QS) misaligned galaxies exhibit narrower H i line widths compared to their gas–star aligned controls. The H i profiles of SF misaligned galaxies tend to be single-peaked, displaying a slightly higher fraction of single-peaked shape compared to their aligned controls. The QS misaligned galaxies exhibit prominently single-peaked H i profiles, while their aligned controls show distinct double-horned profiles. The shape of H i profiles is expected to change with the H i surface density radial gradients through external gas accretion—the interaction between the accreted gas and the pre-existing gas leads to the redistribution of angular momentum and induces gas inflow. This suggests that the progenitors of SF misaligned galaxies are central H i enriched; in this case, the shapes of the H i profiles are insensitive to further increases in central H i surface density. The progenitors of QS misaligned galaxies are central H i deficient, hence the transition from central H i deficient to H i enriched surface density leads to significantly more single-peaked H i profiles.

We select 36 double-peaked narrow emission-line galaxies (DPGs) from 10 010 unique galaxies in MaNGA survey. These DPGs show double-peaked Balmer lines and forbidden lines in the spectra. We use a double Gaussian model to separate the double-peaked profiles of each emission line into blue and red components (lambda(blue) < lambda(red)), and analyse the spatially resolved kinematics and ionization mechanisms of each component. We find that in 35 out of 36 DPGs, the flux ratio between the blue and red components varies systematically along the major axes, while it keeps roughly a constant along the minor axes. The blue and red components of these DPGs exhibit similar distributions in both the value of line-of-sight velocity and the velocity dispersion. Additionally, 83.3 per cent DPGs have both blue and red components located in the same ionization region in the [S-II]-BPT diagram. Combining all these observational results, we suggest that the double-peaked emission line profiles in these 35 DPGs primarily originate from rotating discs. The remaining one galaxy shows clear outflow features. 8 out of 35 DPGs show symmetric line profiles that indicate undisturbed rotating discs, and the other 27 DPGs exhibit asymmetric profiles, suggesting dynamic disturbances in the rotating discs. Furthermore, we find that 58.3 per cent DPGs experienced external processes, characterized by tidal features, companion galaxies, as well as gas-star misalignments. This fraction is about twice as much as that of the control sample, suggesting the origin of double-peaked emission line profiles is associated with external processes.

Using the integral field unit data from the Mapping Nearby Galaxies at Apache Point Observatory survey, we build a sample of gas-star misaligned galaxies. The large-scale environment of misaligned galaxies is dominated by filaments and clusters, while it is less dense relative to the gas-star aligned control galaxies. The direction of the large-scale structure (LSS) is defined by its minor axis ( e 3 ), which indicates the slowest collapsing direction. For the aligned controls, the gas and stellar spins are preferentially perpendicular to e 3 , since these galaxies reside in high-mass host halos. For the misaligned galaxies, the gas spins also tend to be perpendicular to e 3 , suggesting that misaligned gas is recently accreted from the LSS. Meanwhile, there is no correlation between their stellar spins and e 3 . There are two possible explanations for this observational phenomenon: (1) the large-scale environments of misaligned galaxies evolve as they grow, with stellar angular momenta acquired in different environments having different orientations; (2) the correlation between stellar spins and the LSS is smeared out since a relatively higher portion of misaligned galaxies in sheet environments are statistically analyzed together with those in filament environments.