  Collisionless low Mach number shocks are abundant in astrophysical and space
plasma environments, exhibiting complex wave activity and wave-particle
interactions. In this paper, we present 2D Particle-in-Cell (PIC) simulations
of quasi-perpendicular nonrelativistic ($\vsh \approx (5500-22000)$ km/s) low
Mach number shocks, with a specific focus on studying electrostatic waves in
the shock ramp and the precursor regions. In these shocks, an ion-scale oblique
whistler wave creates a configuration with two hot counter-streaming electron
beams, which drive unstable electron acoustic waves (EAWs) that can turn into
electrostatic solitary waves (ESWs) at the late stage of their evolution. By
conducting simulations with periodic boundaries, we show that EAW properties
agree with linear dispersion analysis. The characteristics of ESWs in shock
simulations, including their wavelength and amplitude, depend on the shock
velocity. When extrapolated to shocks with realistic velocities ($\vsh \approx
300$ km/s), the ESW wavelength is reduced to one tenth of the electron skin
depth and the ESW amplitude is anticipated to surpass that of the quasi-static
electric field by more than a factor of 100. These theoretical predictions may
explain a discrepancy, between PIC and satellite measurements, in the relative
amplitude of high- and low-frequency electric field fluctuations.
