FAST Discovery of a Fast Neutral Hydrogen Outflow

In this letter, we report the discovery of a fast neutral hydrogen outflow in SDSS J145239.38+062738.0, a merging radio galaxy containing an optical type I active galactic nucleus (AGN). This discovery was made through observations conducted by the Five-hundred-meter Aperture Spherical radio Telescope (FAST) using redshifted 21 cm absorption. The outflow exhibits a blueshifted velocity likely up to ∼−1000 km s ^−1 with respect to the systemic velocity of the host galaxy with an absorption strength of ∼−0.6 mJy beam ^−1 corresponding to an optical depth of 0.002 at v = −500 km s ^−1 . The mass outflow rate ranges between 2.8 × 10 ^−2 and 3.6 M _⊙ yr ^−1 , implying an energy outflow rate ranging between 4.2 × 10 ^39 and 9.7 × 10 ^40 erg s ^−1 , assuming 100 K < T _s < 1000 K. Plausible drivers of the outflow include the starbursts, AGN radiation, and radio jet, the last of which is considered the most likely culprit according to the kinematics. By analyzing the properties of the outflow, AGN, and jet, we find that if the H i outflow is driven by the AGN radiation, the AGN radiation does not seem powerful enough to provide negative feedback, whereas the radio jet shows the potential to provide negative feedback. Our observations contribute another example of a fast outflow detected in neutral hydrogen and demonstrate the capability of FAST in detecting such outflows.