Hi-C 2.1 Observations of Small-scale Miniature-filament-eruption-like Cool Ejections in an Active Region Plage

We examine 172 angstrom ultra-high-resolution images of a solar plage region from the High-Resolution Coronal Imager, version 2.1 (Hi-C 2.1, or Hi-C) rocket flight of 2018 May 29. Over its five minute flight, Hi-C resolved a plethora of small-scale dynamic features that appear near noise level in concurrent Solar Dynamics Observatory (SDO) Atmospheric Imaging Assembly (AIA) 171 angstrom images. For 10 selected events, comparisons with AIA images at other wavelengths and with Interface Region Imaging Spectrograph (IRIS) images indicate that these features are cool (compared to the corona) ejections. Combining Hi-C 172 angstrom, AIA 171 angstrom, IRIS 1400 angstrom, and H alpha, we see that these 10 cool ejections are similar to the H alpha dynamic fibrils and Ca II anemone jets found in earlier studies. The front of some of our cool ejections are likely heated, showing emission in IRIS 1400 A. On average, these cool ejections have approximate widths 3.'' 2 +/- 2.'' 1, (projected) maximum heights and velocities 4.'' 3 +/- 2.'' 5 and 23 +/- 6 km s(-1), and lifetimes 6.5 +/- 2.4 min. We consider whether these Hi-C features might result from eruptions of sub-minifilaments (smaller than the minifilaments that erupt to produce coronal jets). Comparisons with SDO's Helioseismic and Magnetic Imager (HMI) magnetograms do not show magnetic mixed-polarity neutral lines at these events' bases, as would be expected for true scaled-down versions of solar filaments/minifilaments. But the features' bases are all close to single-polarity strong-flux-edge locations, suggesting possible local oppositepolarity flux unresolved by HMI. Or it may be that our Hi-C ejections instead operate via the shock-wave mechanism that is suggested to drive dynamic fibrils and the so-called type I spicules.