Documentation

The Southern Parkes Large-Area Survey in Hydroxyl (SPLASH; Dawson et al. 2014, 2022), is a sensitive, unbiased single-dish survey of the Southern Galactic Plane in all four ground-state transitions of the OH radical at 1612, 1665, 1667 and 1720 MHz.

The 18-cm OH lines are well-known for their maser emission, which traces a diverse range of astrophysical phenomena, from star-formation, to SNRs, to evolved stellar envelopes. However, 18-cm OH can also be used to study the extended molecular ISM, including diffuse, CO-dark H2 (e.g. Li et al. 2018, Busch et al. 2021), and the interaction zones around HII regions (Petzler, Dawson & Wardle 2020).

The SPLASH survey covers the inner Galactic Plane, Central Molecular Zone and Galactic Centre over the range |b| < 2◦, 332◦ < l < 10◦, with a small extension between 2◦ < b < 6◦, 358◦ < l < 4◦. It is the most sensitive large-scale survey of OH to-date, reaching a characteristic root-mean-square sensitivity of ∼15 mK for an effective velocity resolution of ∼0.9 km/s, and an effective spatial resolution of ~15'. Detailed survey specs can be found here.

The spectral line datacubes are optimised for the analysis of extended, quasi-thermal OH, but also contain numerous maser sources, which have been confirmed interferometrically and published separately (Qiao et al. 2016, 2018, 2020).

Image descriptions: Left: Top-down survey coverage map. Right: Combined peak emission/absorption maps for all four transitions, showing the most extreme value of the brightness temperature at each spatial position. The sense of the emission and absorption encodes information about the physical state of the gas.