Chronicling the Host Galaxy Properties of the Remarkable Repeating FRB 20201124A

We present the Australian Square Kilometre Array Pathfinder (ASKAP) localization and follow-up observations of the host galaxy of the repeating FRB 20201124A, the fifth such extragalactic repeating fast radio burst (FRB) with an identified host. From spectroscopy using the 6.5-m MMT Observatory, we derive a redshift of $z=0.0979 \pm 0.0001$, SFR(H$\alpha$) $\approx 2.1 M_{\odot}$ yr$^{-1}$, and global metallicity of 12+log(O/H)$\approx 9.0$. By jointly modeling the 12-filter optical-MIR photometry and spectroscopy of the host, we infer a median stellar mass of $\approx 2 \times 10^{10} M_{\odot}$, internal dust extinction of $A_V\approx 1-1.5$ mag, and a mass-weighted stellar population age of $\approx 5-6$ Gyr. Connecting these data to the radio and X-ray observations, we cannot reconcile the broad-band behavior with strong AGN activity and instead attribute the dominant source of persistent radio emission to star formation, likely originating from the circumnuclear region of the host. The modeling also indicates a hot dust component contributing to the mid-IR luminosity at a level of $\approx 10-30\%$. We construct the host galaxy's star formation and mass assembly histories, finding that the host assembled $>90\%$ of its mass by 1 Gyr ago and exhibited a fairly constant rate of star formation for most of its existence, with no clear evidence of any star-burst activity.