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 ($\hat{I}{\pounds }_{\mathrm{SFR}}=1.5\times 10^{-2}{M}_{\odot }\mathrm{y}{\mathrm{r}}^{-1}\mathrm{kp}{\mathrm{c}}^{-2}$) in the northwest spiral arm of HG~190608. Using H${\hat{I}}^2$ emission present in our Keck Cosmic Web Imager integral field spectrum of the galaxy with a surface brightness of $\hat{I}{¼}_{\mathrm{H}{\hat{\mathrm{I}}}^2}=(3.36\pm 0.21)\times 10^{-17}\mathrm{erg}{\mathrm{s}}^{-1}\mathrm{c}{\mathrm{m}}^{-2}\mathrm{arcse}{\mathrm{c}}^{-2}$, we infer an extinction-corrected H$\hat{I}\pm$ surface brightness and compute a dispersion measure (DM) from the interstellar medium of HG 190608 of $\mathrm{D}{\mathrm{M}}_{\mathrm{Host},\mathrm{ISM}}=94\pm 38\mathrm{pc}\mathrm{c}{\mathrm{m}}^{-3}$. The galaxy rotates with a circular velocity $v_{\mathrm{circ}}=141\pm 8\mathrm{km}{\mathrm{s}}^{-1}$ at an inclination $i_{\mathrm{gas}}=37\pm 3^{\circ }$, 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 $\mathrm{D}{\mathrm{M}}_{\mathrm{Host},\mathrm{Halo}}=55\pm 25\mathrm{pc}\mathrm{c}{\mathrm{m}}^{-3}$ 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 $\hat{I}{\text{c◯}}_p=34\pm 6\mathrm{km}{\mathrm{s}}^{-1}\mathrm{kp}{\mathrm{c}}^{-1}$ 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.

21 pages, 11 figure files, 10 figures in paper, 3 tables. Accepted to ApJ on Sept. 16, 2021, published Nov. 29, 2021