Shuanghao Shu

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 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.

Axions are one of the leading dark matter candidates. If we are embedded in a Milky Way dark matter halo comprised of axions, their stimulated decay would enable us to observe a counterimage (“axion gegenschein”) with a frequency equal to half the axion mass in the opposite direction of a bright radio source. This spectral line emission will be broadened to Δν/ν ∼ σ _d /c ∼ 10⁻³ due to the velocity dispersion of dark matter, σ _d . In this pilot study, we perform the first search for the expected axion gegenschein image of Vela supernova remnant with 26.4 hr of effective ON–OFF data from the Five-hundred-meter Aperture Spherical radio Telescope (FAST) L-band (1.0–1.5 GHz) 19 beam receiver. Our null detection limits the axion–photon coupling strength to be g _aγγ ≲ 2 × 10⁻¹⁰ GeV⁻¹ in the mass ranges of 8.7 μeV ≤ m _a ≤ 9.44 μeV and 10.85 μeV ≤ m _a ≤ 12.01 μeV. These results provide a stronger constraint on g _aγγ in this axion mass range than the current limits obtained by the direct search of an axion decay signal from a dwarf galaxy that uses FAST observations, but are a factor of ∼3 times weaker than the current CERN Axion Solar Telescope limit. Based on our observation strategy, data processing methods, and results, the expected sensitivity will reach ∼10⁻¹¹ GeV⁻¹ with ∼2000 hr of observation in the future.

We present the calibration procedures and validation of source measurement with the data of the Commensal Radio Astronomy FAST Survey for H i intensity mapping by the Five-hundred-meter Aperture Spherical Radio Telescope. Using a 70 hr drift-scan observation with the L-band (1.05–1.45 GHz) 19 beam receiver, we obtain the data covering a 270 deg² sky area. We employ both the pulsar backend and the spectrum backend to calibrate the spectral time-ordered data (TOD) before projecting them onto HEALPix maps. We produce calibrated TOD with a frequency resolution of 30 kHz and time resolution of 1 s and the map data cube with a frequency resolution of 30 kHz and spatial resolution of 2.95 arcmin². We examine the pointing errors, noise overflow, radio-frequency interference (RFI) contamination, and their effect on the data quality. The resulting noise level is ∼5.7 mJy for the calibrated TOD and 1.6 mJy for the map, consistent with the theoretical predictions within 5% at RFI-free channels. We also validate the data by principal component analysis and find that the residual map looks thermal noise dominated after removing 30 modes. We identify 447 isolated bright continuum sources in our data matching the NRAO VLA Sky Survey catalog, with relative flux error of 8.3% for TOD and 6.6% for the map level. We also measure the H i emission of 90 galaxies with redshift z < 0.07 and compare them with H i-MaNGA spectra, yielding an overall relative H i integral flux error of 16.7%. These results provide an important first step in assessing the feasibility of conducting cosmological H i detection with CRAFTS.

This work presents the initial results of the drift-scan observation for the neutral hydrogen (Hi) intensity mapping survey with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). The data analyzed in this work were collected in night observations from 2019 through 2021. The primary findings are based on 28 hr of drift-scan observation carried out over 7 nights in 2021, which covers 60 deg² sky area. Our main findings are, first, our calibration strategy can successfully correct both the temporal and bandpass gain variation over the 4 hr drift-scan observation. Second, the continuum maps of the surveyed region are made with frequency resolution of 28 kHz and pixel area of 2.95 arcmin 2 . The pixel noise levels of the continuum maps are slightly higher than the forecast assuming T _sys = 20 K, which are 36.0 mK (for 10.0 s integration time) at the 1050–1150 MHz band, and 25.9 mK (for 16.7 s integration time) at the 1323–1450 MHz band, respectively. Third, the flux-weighted differential number count is consistent with the NRAO-VLA Sky Survey (NVSS) catalog down to the confusion limit ∼7 mJy beam⁻¹. Finally, the continuum flux measurements of the sources are consistent with those found in the literature. The difference in the flux measurement of 81 isolated NVSS sources is about 6.3%. Our research offers a systematic analysis for the FAST Hi intensity mapping drift-scan survey and serves as a helpful resource for further cosmology and associated galaxies sciences with the FAST drift-scan survey.