The Circumgalactic H-alpha Spectrograph: First Light Observations and Data Analysis of Early Science Targets Featuring NGC 4631

We present first light data taken with the Circumgalactic Hα Spectrograph (CHαS) following its Dec 2019 - Feb 2020 commissioning at the MDM Observatory. CHαS is a wide-field integral field unit (IFU) spectrograph designed to measure exceedingly faint emission from diffuse gas in the local universe. During its brief time on-sky in March 2020, CHαS imaged a number of key galaxy/nebulae targets that will inform the instrument calibration and data pipeline development. Most notably, we have used CHαS to collect a multi-hour integration on the Whale Galaxy - NGC 4631. We present spectral imaging of NGC 4631 collected with CHαS and our preliminary analysis of velocity structures in the galactic disk. CHαS collects >60,000 spectra over a 10 sq arcmin FOV, measuring gas kinematics down to 30 km/s (R ~ 10,000) and resolving structure on the scale of ~100 pc (Δθ ~ 2.6 arcsec) in NGC 4631. These IFU observations with CHαS complement a number of existing narrowband Hα images and low-resolution long-slit spectroscopy measurements of ionized gas in NGC 4631, and our analysis benefits greatly from a long literature of multi-wavelength ancillary data available for this galaxy. As observatory operations have been halted since March, we have returned CHαS to the laboratory for additional calibration/testing. We hope to be back on-sky in Spring 2021.