Yougang Wang

We investigate the relative importance of active galactic nucleus (AGN) feedback and environmental processes using a large sample of H i galaxies from the Arecibo Legacy Fast ALFA Survey (ALFALFA) and FAST All Sky H i Survey (FASHI) surveys. By applying the optical spectroscopy from Sloan Digital Sky Survey DR7/DR8 and the Dark Energy Spectroscopic Instrument survey, we analyse the gas content and physical properties of AGN-hosting galaxies in group environments. Our results show that AGN-hosting galaxies exhibit significantly suppressed star formation rates and H i gas fraction, approximately one order of magnitude lower than star-forming counterparts, regardless of their group-centric position. AGN-hosting satellites exhibit a significant and persistent deficit in both gas fraction and star formation rate relative to normal satellites without an AGN, even at the halo virial radius ( R / R ₁₈₀ ≈ 1). This suggests that cold gas depletion is primarily driven by internal AGN feedback before these galaxies experience intense environmental interactions. The relatively flat radial profiles of gas fraction and specific star formation rate further indicate that the evolution of AGN-hosting satellites is governed by internal physical processes rather than environmental interactions. Moreover, the apparent increase in H i gas at R / R ₁₈₀ < 0.3 is identified as an artifact of beam confusion. We conclude that for the AGN-hosting population, internal feedback is likely the prior quenching mechanism, while environmental effects act as a secondary, subsequent process.

We present the first blind search for OH 18 cm absorption with the Five-hundred-meter Aperture Spherical Telescope (FAST), conducted alongside the H i 21 cm absorption search. Our previous FAST blind H i absorption search identified 34 systems. In this work, we extend the search using 2024 and part of the 2025 CRAFTS and FAST All Sky H i Survey data (394.4 hr and 1622.1 deg ² ) together with FATHOMER observations, yielding four known and three new H i absorbers, for a total of 41 H i absorption systems. We search for OH absorption in 19 H i absorption systems whose OH redshifted frequencies fall within the FAST band. The known OH absorber toward PKS 1413+135 was redetected, making our survey the first blind survey to detect OH absorption. No new OH absorbers were identified. We examine the relationship between N _OH and N _HI , applying survival analysis to account for upper limits. The analysis does not provide statistically significant evidence for either an N _OH – N _HI correlation or redshift evolution of N _OH / N _HI . Finally, spectral stacking sets 3 σ OH column density upper limits of 4.93, 1.64, and 1.72 T _ex / c _f,OH × 10 ¹² cm ⁻² K ⁻¹ for associated, intervening, and combined samples, corresponding to [OH]/[H i ] ratios of −8 , −8 , and −8 , assuming T _ex = 10 K for OH and T _s = 100 K for H i . These results place the strongest constraints to date on the OH content in radio-selected H i absorbers and establish a blind-survey benchmark for future studies of molecular gas in H i -selected systems. They also demonstrate that known H i 21 cm absorbers provide an effective parent sample for systematic OH absorption searches, paving the way for future larger surveys.

We present the beam pattern measurement of the Tianlai Cylinder Pathfinder Array. As it is a pure drift-scan instrument, we exploit the North-South motion of the Sun to demonstrate that the primary beam is factorizable. Leveraging this property, we decompose the primary beam into independent East-West (E-W) and North-South (N-S) components. Using the Sun as a calibration source, we obtain the E-W beam profiles at various elevations, applying normalization to eliminate the effects of solar activity. Subsequently, we simulate the observed signals using a sky map model to derive the best-fit N-S beam. The results of this work are consistent with previous expectations.

Isolated dwarf galaxies are intrinsically faint and difficult to detect. The limited sample size makes it challenging to observationally constrain the physical mechanisms that quench their star formation. To disentangle the quenching mechanisms of isolated dwarfs, we identify a non-negligible population of such galaxies in the TNG50 simulation. In addition to the previously discovered ``backsplash" galaxies that were quenched by environmental effects when they were once satellites in more massive halos, we find another primary quenching channel in a population of galaxies whose star formation is suppressed by excessively strong gas outflows that prevent the gas from cooling and collapsing to form stars. We further demonstrate that these outflows are highly likely driven by stellar feedback and predominantly occur in high-gas-fraction dwarfs, which within our studied stellar mass range ($10^7$--$10^{9.5},M_\odot$) are always located toward the low-mass end.

We present the H i galaxy observation results of FATHOMER, a pilot drift scan survey by the Five-hundred-meter Aperture Spherical radio Telescope (FAST). The survey comprises 28 hr of observations over seven nights in 2021, covering a 60 deg ² sky area in the frequency range 1.05–1.45 GHz. The H i galaxies are identified using both a matched-filtering algorithm and the SoFiA source-finding pipeline, which yield consistent detections. We derive the velocity width ( W ₅₀ ), flux density, and Hi mass for detected galaxies. A total of 702 galaxies are identified with H i mass above 10 ^6.2 M _⊙ , signal-to-noise ratio greater than 5, and redshift z < 0.09. Among these, 331 are previously known from the ALFALFA survey. Of the newly detected sources, 9 have spectroscopic confirmation from the Sloan Digital Sky Survey (SDSS), 285 are matched to SDSS or DESI photometric data, and 77 lack optical counterparts–possible candidates for dark or faint galaxies. Comparison with ALFALFA shows that FAST enables the detection of galaxies at higher redshifts and with lower Hi fluxes, despite the radio frequency interference (RFI) and partial data masking. A preliminary Hi mass function analysis reveals a higher characteristic mass and steeper low-mass slope than ALFALFA, indicating FAST’s enhanced sensitivity to massive and distant H i systems. These results demonstrate FAST’s strong potential for future deep H i surveys and highlight the importance of improved RFI mitigation and completeness correction.

The Tremaine-Weinberg (TW) method and its variations provide the most direct means to measure the pattern speeds of galactic bars. We establish a unifying framework by deriving an integral form of the continuity equation over an arbitrary closed loop. This naturally defines a local pattern speed for any chosen region in a galactic disk (including bars and spirals). We demonstrate that this intuitive formalism recovers all standard variants of the TW method as special cases corresponding to specific choices of the integration loop. In this paper, we validate this framework and demonstrate its diagnostic power. By applying it to a diverse set of test cases from the TNG50 simulation, including face-on prototype barred galaxies and highly constrained Mock Milky Way standard configurations, we show that this formalism accurately recovers both constant global pattern speeds and radially varying profiles. Rather than relying on rigid geometric approximations, our method naturally differentiates coherent solid-body rotators (bars) from spirals. Our results validate that this unified integral framework provides a robust, geometrically flexible, and practically extensible tool for decoding complex dynamics of galactic structures.

The Tianlai Cylinder Pathfinder Array consists of three adjacent cylindrical reflectors fixed on the ground, each 40 m long and 15 m wide, with the cylinder axis oriented along the North–South (N–S) direction. Dual linear polarization feeds are distributed along the focus line, parallel to the cylinder axis. Measurement of the primary beam profile of these cylindrical reflectors is difficult, as they are too large to be placed in an anechoic chamber. While the beam profile along the East–West (E–W) direction can be measured with the transit observations of bright astronomical radio sources, the beam profile along the N–S direction remains very uncertain. We present a preliminary measurement of the beam profile of the Tianlai cylindrical antenna along both the N–S direction and E–W direction in the frequency range of 700–800 MHz, using a calibrator source carried by an unmanned aerial vehicle (UAV) flying in the far field. The beam profile of the Tianlai cylindrical antenna is determined from the analysis of the auto-correlation signals from the cylinder array correlator, taking into account the emitter antenna beam profile, itself measured with a dipole antenna on the ground. The accuracy of the UAV-based determination of the cylinder beam profiles is validated by comparing the results with the one derived from bright astronomical source transits, and with simulated beams.