FAST discovery of a fast neutral hydrogen outflow

• Main Authors: Su, Renzhi, Gu, Minfeng, Curran, S. J, Mahony, Elizabeth K, Tang, Ningyu, Allison, James R, Li, Di, Zhu, Ming, Aditya, J. N. H. S, Yoon, Hyein, Zheng, Zheng, Wu, Zhongzu
• Format: Journal Article
• Language: English
• Published: 04-09-2023
• Subjects: Physics - Astrophysics of Galaxies
• DOI: 10.48550/arxiv.2309.01890

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 nuclei (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 $\sim-1000\,\rm km\,s^{-1}$ with respect to the systemic velocity
of the host galaxy with an absorption strength of $\sim -0.6\,\rm
mJy\,beam^{-1}$ corresponding to an optical depth of 0.002 at $v=-500\,\rm
km\,s^{-1}$. The mass outflow rate ranges between $2.8\times10^{-2}$ and $3.6\,
\rm M_\odot \, yr^{-1}$, implying an energy outflow rate ranging between
$4.2\times10^{39}$ and $9.7\times10^{40}\rm\,erg\,s^{-1}$, assuming 100 K
$<T_{\rm s}<$ 1000 K. Plausible drivers of the outflow include the star bursts,
the AGN radiation, and the radio jet, the last of which is considered the most
likely culprit according to the kinematics. By analysing the properties of the
outflow, the AGN, and the jet, we find that if the HI outflow is driven by the
AGN radiation, the AGN radiation seems not 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, as well as demonstrate the capability of FAST in
detecting such outflows.