Understanding the baryon cycle and chemical enrichment in the Universe requires access to galaxy populations invisible in conventional optical surveys. In this talk, I will present recent progress in uncovering such hidden components of galaxy evolution by combining radio and sub/millimeter observations.

First, I will discuss new constraints on the cosmic origin of fluorine using hydrogen fluoride (HF). Recent observations toward a gravitationally lensed dusty star-forming galaxy at z=6.02 place stringent upper limits on the HF abundance, indicating that fluorine enrichment was still inefficient only ~1 Gyr after the Big Bang.

Second, I will introduce a large-area survey of radio-detected AGNs based on Subaru-HSC in combination with VLASS and LOFAR. This approach enables a systematic census of accretion activity across cosmic time, including heavily obscured systems that are often missed in optical and X-ray surveys. The synergy between optical and radio data enables studies of galaxy-black hole co-evolution.

Third, I will highlight the emerging population of near-infrared dark galaxies identified using ALMA and JWST. These systems, faint or undetected in deep near-infrared imaging, likely represent a key phase of rapid, dust-obscured star formation. I will present results from recent surveys such as ALCS and VENUS, including [C II] 158 um observations of an H-band dropout galaxy in a gravitationally lensed galaxy group at z=4.3.

Finally, I will argue that a comprehensive understanding of these obscured populations requires wide-band, multiplexed sub/mm spectroscopy, enabled by integrated superconducting spectrograph (ISS) technology for wide-band imaging spectrographs and IFUs. In combination with next-generation large-aperture submm facilities such as AtLAST/LST, this approach will enable transformative large-scale spectroscopic surveys including [O III] 88 um line intensity mapping during cosmic reionization.