Dissecting the Local Environment of FRB 190608 in the Spiral Arm of its Host Galaxy

We present a high-resolution analysis of the host galaxy of fast radio burst FRB 190608, an SBc galaxy at $z=0.11778$ (hereafter HG 190608), to dissect its local environment and its contributions to the FRB properties. Our Hubble Space Telescope WFC3/UVIS image reveals that the sub-arcsecond localization of FRB 190608 is coincident with a knot of star-formation ($\Sigma_{SFR} = 1.2 \times 10^{-2}~ M_{\odot} \, kpc^{-2}$) in one of the prominent spiral arms of HG 190608. This is confirmed by H$\beta$ emission present in our Keck/KCWI integral field spectrum of the galaxy with a surface brightness of $\mu_{H\beta} = (3.35\pm0.18)\times10^{-17}\;erg\;s^{-1}\;cm^{-2}\;arcsec^{-2}$. We infer an extinction-corrected H$\alpha$ surface brightness and compute a dispersion measure from the interstellar medium of HG 190608 of ${DM}_{Host,ISM} = 82 \pm 35~ pc \, cm^{-3}$. The galaxy rotates with a circular velocity $v_{circ} = 141 \pm 8~ km \, s^{-1}$ at an inclination $i_{gas} = 37 \pm 3^\circ$, giving a dynamical mass $M_{halo}^{dyn} \approx 10^{11.96 \pm 0.08}~ M_{\odot}$. A surface photometric analysis of the galaxy using FORS2 imaging suggests a stellar disk inclination of $i_{stellar} = 26 \pm 3^\circ$. The dynamical mass estimate implies a halo contribution to the dispersion measure of ${DM}_{Host,Halo} = 55 \pm 25\; pc \, cm^{-3}$ subject to assumptions on the density profile and fraction of baryons retained. The relatively high temporal broadening ($\tau = 3.3 \pm 0.2 \; ms$ at 1.28 GHz) and rotation measure ($ RM = 353 \pm 2\; rad \; m^{-2}$) (Day et al. 2020) of FRB 190608 may be attributable to both turbulent gas within the spiral arm and gas local to the FRB progenitor. In contrast to previous high-resolution studies of FRB progenitor environments, we find no evidence for disturbed morphology, emission, nor kinematics for FRB 190608.