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

Abstract

We present a high-resolution analysis of the host galaxy of fast radio burst (FRB) 190608, an SB(r)c galaxy at z = 0.11778 (hereafter HG 190608), to dissect its local environment and its contributions to the FRB properties. Our Hubble Space Telescope Wide Field Camera 3 ultraviolet and visible light image reveals that the subarcsecond localization of FRB 190608 is coincident with a knot of star formation (Σ_SFR = 1.5 × 10^-2 M _⊙ yr^-1 kpc^-2) in the northwest spiral arm of HG 190608. Using Hβ emission present in our Keck Cosmic Web Imager integral field spectrum of the galaxy with a surface brightness of ${\mu }_{{\rm{H}}\beta }=(3.36\pm 0.21)\times {10}^{-17}\,\mathrm{erg}\,{{\rm{s}}}^{-1}\,{\mathrm{cm}}^{-2}\,{\mathrm{arcsec}}^{-2}> , we infer an extinction-corrected Hα surface brightness and compute a dispersion measure (DM) from the interstellar medium of HG 190608 of DM_Host,ISM = 94 ± 38 pc cm^-3. The galaxy rotates with a circular velocity v _circ = 141 ± 8 km s^-1 at an inclination i _gas = 37° ± 3°, giving a dynamical mass ${M}_{\mathrm{halo}}^{\mathrm{dyn}}\approx {10}^{11.96\pm 0.08}\,{M}_{\odot }> . This implies a halo contribution to the DM of DM_Host,Halo = 55 ± 25 pc cm^-3 subject to assumptions on the density profile and fraction of baryons retained. From the galaxy rotation curve, we infer a bar-induced pattern speed of Ω _p = 34 ± 6 km s^-1 kpc^-1 using linear resonance theory. We then calculate the maximum time since star formation for a progenitor using the furthest distance to the arm's leading edge within the localization, and find ${t}_{\mathrm{enc}}={21}_{-6}^{+25}> Myr. Unlike previous high-resolution studies of FRB environments, we find no evidence of disturbed morphology, emission, or kinematics for FRB 190608.