Faint Extended OH Emission from the Local Interstellar Medium in the Direction l \approx 108\circ, b \approx 5\circ

TL;DR

This study maps faint 1667 MHz OH emission in the local interstellar medium, revealing widespread OH correlated with HI but with distinct brightness behavior, and providing new insights into the molecular composition of the local Galaxy.

Contribution

First detailed mapping of faint OH emission in the local interstellar medium, showing its widespread presence and relationship with HI, with implications for understanding molecular gas.

Findings

OH emission is widespread and correlates with HI in the local Galaxy.

OH brightness continues to increase even when HI saturates.

Less than 10% of OH features are associated with CO emission.

Abstract

We have mapped faint 1667 OH line emission (TA \approx 20 - 40 mK in our \approx 30' beam) along many lines of sight in the Galaxy covering an area of \approx 4\circ \times 4\circ in the general direction of l \approx 108\circ, b \approx 5\circ. The OH emission is widespread, similar in extent to the local HI (r </= 2 kpc) both in space and in velocity. The OH profile amplitudes show a good general correlation with those of HI in spectral channels of \approx 1 km/s; this relation is described by TA(OH) \approx 1.50 \times 10^{-4} TB(HI) for values of TB(HI) </\approx 60 - 70 K. Beyond this the HI line appears to "saturate", and few values are recorded above \approx 90 K. However, the OH brightness continues to rise, by a further factor \approx 3. The OH velocity profiles show multiple features with widths typically 2 - 3 km/s, but less than 10% of these features are associated with CO(1-0) emission in existing surveys of the area smoothed to comparable resolution.