The bolocam galactic plane survey. X. A complete spectroscopic catalog of dense molecular gas observed toward 1.1 mm dust continuum sources with 7.°5 ≤ l ≤ 194°

The Bolocam Galactic Plane Survey (BGPS) is a 1.1 mm continuum survey of dense clumps of dust throughout the Galaxy covering 170 deg². We present spectroscopic observations using the Heinrich Hertz Submillimeter Telescope of the dense gas tracers, HCO⁺ and N₂H ⁺ 3-2, for all 6194 sources in the BGPS v1.0.1 catalog between 7.°5 ≤ l ≤ 194°. This is the largest targeted spectroscopic survey of dense molecular gas in the Milky Way to date. We find unique velocities for 3126 (50.5%) of the BGPS v1.0.1 sources observed. Strong N₂H ⁺ 3-2 emission (T _mb > 0.5 K) without HCO⁺ 3-2 emission does not occur in this catalog. We characterize the properties of the dense molecular gas emission toward the entire sample. HCO⁺ is very sub-thermally populated and the 3-2 transitions are optically thick toward most BGPS clumps. The median observed line width is 3.3 km s^-1 consistent with supersonic turbulence within BGPS clumps. We find strong correlations between dense molecular gas integrated intensities and 1.1 mm peak flux and the gas kinetic temperature derived from previously published NH ₃ observations. These intensity correlations are driven by the sensitivity of the 3-2 transitions to excitation conditions rather than by variations in molecular column density or abundance. We identify a subset of 113 sources with stronger N₂H⁺ than HCO⁺ integrated intensity, but we find no correlations between the N ₂H⁺/HCO⁺ ratio and 1.1 mm continuum flux density, gas kinetic temperature, or line width. Self-absorbed profiles are rare (1.3%).