Statistics for Galaxy Outflows at $z\sim 6-9$ with Imaging and Spectroscopic Signatures Identified with JWST/NIRCam and NIRSpec Data

Abstract: We present statistics of $z\sim 6-9$ galaxy outflows indicated by spatially-extended gas emission and broad lines. With a total of 61 spectroscopically confirmed galaxies at $z\sim 6-9$ in the JWST CEERS, GLASS, and ERO data, we find four galaxies with [O{\sc iii}]+H$\beta$ ionized gas emission significantly extended beyond the kpc-scale stellar components on the basis of the emission line images constructed by the subtraction of NIRCam broadband (line on/off-band) images. By comparison with low-$z$ galaxies, the fraction of galaxies with the spatially extended gas, 4/18, at $z\sim 6-9$ is an order of magnitude higher than those at $z\sim 0-1$, which can be explained by events triggered by frequent major mergers at high redshift. We also investigate medium- and high-resolution NIRSpec spectra of 30 galaxies at $z\sim 6-9$, and identify five galaxies with broad ($140-800$ km s$^{-1}$) lines in the [O{\sc iii}] forbidden line emission, suggestive of galaxy outflows. One galaxy at $z=6.38$ shows both the spatially-extended gas emission and the broad lines, while none of the galaxies with the spatially-extended gas emission or broad lines present a clear signature of AGN either in the line diagnostics or Type 1 AGN line broadening ($>1000$ km s$^{-1}$), which hint outflows mainly driven by stellar feedback. The existence of galaxies with/without spatially-extended gas emission or broad lines may be explained by different viewing angles towards outflows, or that these are galaxies in the early, late, post phases of galaxy outflows at high redshift, where the relatively large fractions of such galaxies indicate the longer-duration and/or more-frequent outflows at the early cosmic epoch.