Barbara Šiljeg, Elizabeth A. K. Adams, Tom A. Oosterloo, Filippo Fraternali, Kelley M. Hess, Jin-Long Xu, Ming Zhu
Published 2026-01-18, 8 pages, 8 figures, accepted for publication in Astronomy & Astrophysics
Dark galaxies - systems rich in neutral hydrogen (HI) gas but with no stars - are a common prediction of numerous theoretical models and cosmological simulations. However, the unequivocal identification of such sources in current HI surveys has proven challenging. In this work, we present interferometric follow-up observations with the VLA of a former dark galaxy candidate J0139+4328, originally detected with the single-dish FAST telescope. The improved spatial resolution of the VLA data allow us to identify a faint optical counterpart and characterize the galaxy. Located at a distance of about 31 Mpc, J0139+4328 has a stellar mass of 3 x 10^6 M_Sun and a relatively high gas richness of M_HI/M_star = 18. Despite its high ratio, the galaxy is consistent, within the scatter, with the stellar-to-HI mass relation of HI-selected samples in the literature and with the baryonic Tully-Fisher relation (BTFR), although its kinematic measurement is subject to large uncertainties. This case highlights the potential of modern high-sensitivity HI surveys for detecting low surface brightness, gas-rich galaxies, but underscores the need for careful interpretation of low-resolution HI data, with potentially large centroid errors, and for sufficiently deep optical imaging to ensure robust identification.
Ruisong Xia, Chen Qin, Huynh Anh N. Le, Yongquan Xue, Shifu Zhu, Mengqiu Huang, Hao Liu, Xiaozhi Lin
Published 2026-02-07, 21 pages, 14 figures, accepted for publication in ApJ
Active galactic nucleus (AGN)-driven gas outflows are one of the best tracers of AGN feedback in action, as these powerful outflows expel/heat or compress the surrounding interstellar medium (ISM), thus quenching or enhancing star-forming activity in their hosts. Studying the kinematics of outflows in different gas phases is crucial for comprehending how AGNs impact the ISM within their host galaxies. However, the differences in the physical natures of ionized and warm molecular gas outflows remain largely unexplored. To obtain a complete picture of AGN outflows and their feedback effects, we present a study of both ionized and warm molecular gas outflows in six type-2 AGNs ($z<0.1$) that exhibit strong ionized outflows in previous optical observations. Utilizing the Triple Spectrograph and Double Spectrograph instruments on the Palomar 200-inch Hale Telescope, we conduct spatially resolved measurements in the slit direction of strong emission lines from both ionized and warm molecular gas, such as $\rm [O\ III]$, $\rm Paα$, $\rm H_{2}$ 1-0 S(1), etc., allowing for a direct comparison of their outflow properties. One out of six AGNs shows significant ionized and warm molecular outflows in near-infrared bands, exhibiting the most powerful kinematics and highest luminosity. A positive correlation between the kinematics and AGN luminosity is shown, suggesting that more luminous AGNs, which reflect higher levels of AGN activity, tend to have a greater impact on the gases, probably driving the outflows.