HCN emission from the H ii regions G75.78+0.34 and G75.77+0.34

Abstract

We present images for the 3.5 mm continuum and HCN (J=1-0) hyperfine line emission from the surroundings of the H ii regions G75.78+0.34 and G75.77+0.34 obtained with the Berkeley Illinois Maryland Association (BIMA) interferometer using the D configuration at a spatial resolution of ∼18 arcsec and spectral sampling of 0.34 km s-1. The continuum emission of both objects is dominated by free-free emission from the ionized gas surrounding the exciting stars. Dust emission may contribute only a small fraction of the 3.5 mm continuum from G75.78+0.34 and is negligible for G75.77+0.34. The high spectral resolution reached by BIMA allowed us to separate the emission from each hyperfine transition (F=1-1, 2-1 and 0-1), as well as to construct velocity channel maps along each emission-line profile. The HCN flux distributions are similar to those observed for the CO emission but with some knots of high intensities indicating that the HCN traces high-density clouds not seen in CO. The HCN hyperfine line ratios for both H ii regions differ from those predicted theoretically for local thermodynamic equilibrium, probably due to scattering of radiation processes. The velocity channels show that the HCN emission of G75.78+0.34 follows the bipolar molecular outflows previously observed in CO. For G75.77+0.34, the outflowing gas contributes only a small fraction of the HCN emission. © 2010 The Authors. Journal compilation © 2010 RAS.