Faint extended oh emission from the local interstellar medium in the direction l ≈ 108°, b ≈ 5°

Abstract

We have mapped faint 1667 OH line emission (T A 20-40mK in our 30′ beam) along many lines of sight in the Galaxy covering an area of ≈ 4°× 4°in the general direction of l ≈ 108°, b ≈ 5°. The OH emission is widespread, similar in extent to the local H I (r ≲ 2 kpc) both in space and in velocity. The OH profile amplitudes show a good general correlation with those of H I in spectral channels of ≈ 1 km s -1; this relation is described by T A (OH) 1.50 × 10 -4 T B (H I) for values of T B (H I) ≲ 60-70 K. Beyond this the H I line appears to "saturate," and few values are recorded above ≈ 0 K. However, the OH brightness continues to rise, by a further factor ≈ 3. The OH velocity profiles show multiple features with widths typically 2-3 km s -1, but less than 10% of these features are associated with CO(1-0) emission in existing surveys of the area smoothed to comparable resolution. © 2012. The American Astronomical Society. All rights reserved.