Program: GS-2023A-FT-201

Strong gaseous outflows in galaxies are a known quenching mechanism and can be driven by star-formation processes (e.g., stellar winds, SNe) or from AGN activity. Measuring the strong outflows, ISM conditions, and recent star-formation activity using nebular emission lines is crucial for us to understand what drives strong outflows, especially around cosmic noon (z ~ 2) when such quenching mechanisms start to dominate. In a recent search of the Gemini Science Archive, we came across COSMOS-506868 which we have determined via archival GMOS-N/B600 observations is a massive 10^10.35 Msol galaxy that has strong Lya and CIV emission and shows signatures of outflows > 1000 km/s (consistent with outliers in star-forming galaxy samples). HST/ACS F814W imaging shows an elongated structure north of the galaxy which may be evidence of mass outflows. We have determined via SED fitting this galaxy may have gone through a recent burst of star-formation with SFR(10Myr) ~ 200 Msol/yr where the strong outflows may be SF-driven and is in the process of quenching. We propose for GMOS-S/Flamingos-2 HK spectroscopic follow-up of COSMOS-506868 to investigate its star-forming nature and look for evidence of what is driving the strong outflows using strong nebular emission lines (e.g., Halpha, Hbeta, [OIII], [OII]). We will use Balmer lines to trace recent star-formation, BPT and Mex diagnostics to test for an AGN component, and look for strong, broadline Halpha emission (evidence for outflows). The ionization parameter and gas-phase metallicities will also be measured to assess the ionizing photon reservoir which, if high, may imply the outflows are forming channels of HII allowing for LyC escape. This would have implications on how first-generation galaxies reionized the Universe.