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We present high spatial resolution, integral field spectrograph (IFS)observations of the nearby LINER (low ionization nuclear emission line region)galaxy NGC 404 at 1.25 $\mu$m (J band) and 2.2 $\mu$m (K band) near-infraredwavelengths. Although NGC 404 is thought to host an intermediate mass blackhole at its center, it has been unclear whether accretion onto the black holeor another mechanism such as shock excitation drives its LINER emission atoptical/near-infrared wavelengths. We use the OSIRIS IFS at Keck Observatorybehind laser guide star adaptive optics to map the strength and kinematics of[FeII], H$_2$, and hydrogen recombination lines at spatial resolutions of 1 pcacross the central 30 pc of the galaxy. The H$_2$ gas is in a central rotatingdisk and ratios of multiple H$_2$ lines indicate that the molecular gas isthermally excited, with some contribution from UV fluorescence. The [FeII]emission is more extended and diffuse than the molecular gas and has adifferent kinematic structure that reaches higher velocities/dispersions. Wealso map the strength of the CO stellar absorption feature and constrain thedominant age of the nuclear stellar population to $\sim$1 Gyr. Finally, we findregions across the nucleus of NGC 404 with [FeII]/Pa$\beta$ line ratios up to6.5, $\sim$2.5 times higher than the ratio measured from spatially-integratedspectra. From these high line ratios, we conclude that shocks are the dominatephysical mechanism exciting NGC 404's LINER emission and argue that a possiblesource of this shock excitation is a supernova remnant.

Widespread Shocks in the Nucleus of NGC 404 Revealed by Near-infrared Integral Field Spectroscopy