The Maser Monitoring Organisation is a collection of researchers exploring the use of time-variable maser emission in the investigation of astrophysical phenomena. The forward directed aspects of research primarily involve using maser emission as a tool to investigate star formation. Simultaneously, these activities have deepened knowledge of maser emission itself in addition to uncovering previously unknown maser transitions. Thus a feedback loop is created where both the knowledge of astrophysical phenomena and the utilised tools of investigation themselves are iteratively sharpened. The project goals are open-ended and constantly evolving, however, the reliance on radio observatory maser monitoring campaigns persists as the fundamental enabler of research activities within the group.

Recently, remarkable progress has been made in understanding the formation of high mass stars. Observations provided direct evidence that massive young stellar objects (MYSOs), analogously to low-mass ones, form via disk-mediated accretion accompanied by episodic accretion bursts, possibly caused by disk fragmentation. In the case of MYSOs, the mechanism theoretically provides a means to overcome radiation pressure, but in practice it is poorly studied - only three accretion bursts in MYSOs have been caught in action to date. A significant contribution to the development of the theory has been made with the study of masers, which have proven to be a powerful tool for locating “bursting” MYSOs. This overview focuses on the exceptional role that masers play in the search and study of accretion bursts in massive protostars.

The RadioAstron space-VLBI mission has successfully detected extragalactic H2O MegaMaser emission regions at very long Earth to space baselines ranging between 1.4 and 26.7 Earth Diameters (ED). The preliminary results for two galaxies, NGC 3079 and NGC 4258, at baselines longer than one ED indicate masering environments and excitation conditions in these galaxies that are distinctly different. Further observations of NGC 4258 at even longer baselines are expected to reveal more of the physics of individual emission regions.

Line emissions of high- and low-density molecular tracers serve as powerful diagnostic tools for the ISM in both Galactic and extragalactic star formation environments. The emission line strengths and line ratios may be interpreted using detailed modeling of both the dominant physics and the chemistry of the molecular constituents. Observed molecular line ratios will thus reveal the signatures of dominant UV, X-ray, and CR radiation fields and of mechanical heating and feedback from the star formation process. In addition, certain line ratios reflect the physical and chemical changes resulting from the time-evolution of a star formation region. In this paper, we present results of Galactic sources and extragalactic starbursts covering a large range of FIR luminosities and illustrate the similarities between the diagnostics of these environments.

The IAU Working Group on Radio Frequency Interference (RFI) Mitigation was setup in the 2000 IAU GA in Manchester and its mandate was renewed at subsequent IAU GAs in 2003 and 2006. It was noted that that there are important issues related to RFI mitigation that extend beyond the regulatory function of IUCAF, and hence a more extended working group, which may include IUCAF members, was established.

A report on studies using the observed line ratios of high-density molecular tracers to diagnose the physics and chemistry of the ISM in star-formation environments.

The Square Kilometre Array (SKA) is the radio telescope of the next generation, providing an increase in sensitivity and angular resolution of two orders of magnitude over existing telescopes. Currently, the SKA is expected to span the frequency range 0.1-25 GHz with capabilities including a wide field-of-view and measurement of polarised emission. Such a telescope has enormous potential for testing fundamental physical laws and producing transformational discoveries. Important science goals include using H2O megamasers to make precise estimates of H0, which will anchor the extragalactic distance scale, and to probe the central structures of accretion disks around supermassive black holes in AGNs, to study OH megamasers associated with extreme starburst activity in distant galaxies and to study with unprecedented precision molecular gas and star formation in our Galaxy.

We present EVN observations of hydroxyl (OH) main-line emission in two megamaser sources Mrk 231 and IC 694. The observations indicate that the broad maser emission lines originate within the nuclear regions. A single 1667 MHz main-line feature is seen at the nucleus of IC 694. In Mrk 231 both main-lines were observed in an extended “half-circular” region of 150 pc by 50 pc surrounding the radio nucleus.

The variety of molecular megamasers trace different classes of galaxies and provide information on their various nuclear components. H2O megamaser regions may trace the inner parsec-scale regions with keplerian disks of the LINER and Seyfert 2 nuclei, which are relatively naked and not dominated by dust or starforming regions. The OH and H2CO megamaser emissions exhibit the physics and dynamics of the inner few hundred parsecs of ultra-luminous FIR galaxies, which are dusty, compact, and whose perturbed nuclei are powered by compact starbursts.

Megamaser emission provides an unprecedented view of the inner nuclear regions of active galaxies. The characteristics of OH, H2CO, and H2O sources identify different physical environments in the nuclei of megamaser host galaxies. Various classification schemes suggest a dominant starburst nature for the OH and H2CO sources providing the NIR/FIR radiation field as a pump. The molecular emission originates in a 50–100 parsec disk/torus, which is not yet completely observed. For H2O masers in relatively dust-free LINER/Seyfert 2 sources, the AGN provides the X-ray radiation field for pumping in a compact sub-parsec thin disk.

Megamaser emission provides new insights into the physics of active galactic nuclei. The megamaser phenomenon is consistent with a low-gain amplification model, where inverted foreground molecules amplify the radio continuum from the nucleus. The molecular gas seen in emission in the megamaser galaxies is located between 50 and 300 parsecs from the nucleus covering part of a possible NLR. Megamasers have been found for the molecules OH, H2CO and H2O. However, only OH megamasers form a clearly identifiable group of galaxies. They occur in prominent FIR galaxies and the FIR radiation field serves as a pumping agent for the OH molecules (Baan 1988). As a result only the ground state lines of OH are in emission, while the lines from excited states are in absorption (see Henkel, Güsten and Baan 1987).

On 1984 October 6 we conducted a 3-station intercontinental Mark II VLBI experiment in order to study the very luminous water vapor maser source in the nucleus of the galaxy NGC 3079, which was detected first by Haschick and Baan (1985) using the Haystack Observatory 36.6 m antenna. The cross correlation spectrum for the longest Owens Valley to MPI baseline is presented in Figure 1 and shows the phase variation across the width of the brightest feature at 955.7 km s−1 to be less than 10 degrees of phase.