SPLASH: the Southern Parkes Large-Area Survey in Hydroxyl - data description and release

J. R. Dawson*, P. A. Jones, C. Purcell, A. J. Walsh, S. L. Breen, C. Brown, E. Carretti, M. R. Cunningham, J. M. Dickey, S. P. Ellingsen, S. J. Gibson, J. F. Gómez, J. A. Green, H. Imai, V. Krishnan, N. Lo, V. Lowe, M. Marquarding, N. M. McClure-Griffiths

*Corresponding author for this work

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    Abstract

    We present the full data release for the Southern Parkes Large-Area Survey in Hydroxyl (SPLASH), 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 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°. SPLASH 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-1. The spectral line datacubes are optimized for the analysis of extended, quasi-thermal OH, but also contain numerous maser sources, which have been confirmed interferometrically and published elsewhere. We also present radio continuum images at 1612, 1666, and 1720 MHz. Based on initial comparisons with 12CO(J = 1-0), we find that OH rarely extends outside CO cloud boundaries in our data, but suggest that large variations in CO-to-OH brightness temperature ratios may reflect differences in the total gas column density traced by each. Column density estimation in the complex, continuum-bright Inner Galaxy is a challenge, and we demonstrate how failure to appropriately model sub-beam structure and the line-of-sight source distribution can lead to order-of-magnitude errors. Anomalous excitation of the 1612 and 1720 MHz satellite lines is ubiquitous in the inner Galaxy, but is disabled by line overlap in and around the Central Molecular Zone.

    Original languageEnglish
    Pages (from-to)3345-3364
    Number of pages20
    JournalMonthly Notices of the Royal Astronomical Society
    Volume512
    Issue number3
    DOIs
    Publication statusPublished - 1 May 2022

    Bibliographical note

    This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society, Volume 512, Issue 3, May 2022, Pages 3345–3364, https://doi.org/10.1093/mnras/stac636. Copyright 2022 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.

    Keywords

    • Galaxy: disc
    • ISM: molecules
    • radio lines: ISM
    • surveys

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