Welcome to the official website of the H2O southern Galactic Plane Survey (HOPS), hosted at Macquarie University, Australia.

The HOPS project is led by Dr Andrew Walsh (Curtin University) in collaboration with Dr Steven Longmore (LJMU) and Dr Cormac Purcell (Macquarie University & The University of Sydney). The full HOPS collaboration is composed of members from institutions in Australia and around the world.

If you make use of HOPS data please reference all of the core HOPS papers:

The H2O southern Galactic Plane Survey (HOPS): I. Techniques and H2O maser data
Walsh et al. 2011, MNRAS Vol 416, Pg 1764.

The H2O southern Galactic Plane Survey (HOPS): NH3 (1,1) and (2,2) catalogues
Purcell et al. 2012, MNRAS Vol 426, Pg 1972.

The H2O southern Galactic Plane Survey (HOPS): Paper III - Properties of Dense Molecular Gas across the Inner Milky Way
Longmore at al. 2017, submitted.

Explore the HOPS Results

A full-screen version of the viewer is available here (opens in new window).

Use the slider to fade between different transitions and MSX IR images. You can pan by clicking and dragging the image, or zoom using the '+' and '-' buttons or the scroll-wheel on your mouse. To re-arrange the order of the transitions simply drag a label up or down the slider.


HOPS is a survey of selected bands in the 12mm window with the Mopra radio-telescope. HOPS covers 100 square degrees of the sky, starting from l=290o and continuing through the Galactic centre (l=0o) and through to l=30o. The survey width is 1o in Galactic latitude (ie. | b | ≤0.5o), centred on the Galactic plane. The observations have been conducted over the summer months, when the telescope is unavailable for 3mm observations, but the conditions are still good enough for 12mm observations.

HOPS observations were completed by the end of May, 2010, with approximately 6 weeks of observations each summer, starting in 2008.

The aims of HOPS are:

To provide an untargeted survey of water masers towards the inner Galaxy

This will allow a direct comparison of the occurrence of water and methanol masers (using the results of the Methanol Multibeam Survey). We will be able to determine how much overlap there is between the two masers, which will help us understand the onset and end of the maser phase in the context of star formation. An untargeted survey will also tell us about the relative prevalence of water masers in different astrophysical objects, such as sites of low/high mass star formation or evolved stars.

To map the high density component of the inner Galaxy

Using the (1,1), (2,2) and (3,3) inversion transitions of ammonia, we will not only be able to determine where the high density gas lies, but we can also derive its temperature and column density. This work will focus on identifying new sites of high mass star formation that may not show up as infrared sources.

To search for emission from unusual lines in the Galaxy

We are able to cover 16 bands simultaneously, which allows us to search for emission from many spectral lines. See Survey Specs for more information.

Last modified 6th June 2017.