The fountain of the luminous infrared galaxy Zw049.057 as traced by its OH megamaser
In one sentence
Using high-resolution radio and millimetre observations of the luminous infrared galaxy Zw049.057, we caught its hidden nucleus driving a two-component outflow: a fast collimated jet, traced by the high-velocity wings of HCN emission, sheathed in a slower wide-angle “fountain” traced by the source’s bright OH megamaser.
What’s the question?
Some galaxies host an extraordinarily compact, dust-buried engine in their core: a Compact Obscured Nucleus (CON). These are so opaque that we cannot easily tell whether they are powered by a black hole or by extreme star formation, and we struggle to see whether — and how — they push gas back out into the host galaxy. Yet feedback of this kind is central to galaxy evolution: it is what regulates the growth of the galaxy and, ultimately, of the supermassive black hole inside it. So: what is actually coming out of a CON, and how fast is it moving?
What did we do?
We obtained very high-resolution e-MERLIN and ALMA observations of Zw049.057, one of the closest CONs known. The galaxy hosts a strong OH megamaser — a natural molecular amplifier that brightens otherwise faint emission to spectacular levels — and we used it as a velocity-resolved tracer of the gas in the nuclear region. We also detected a faint formaldehyde (H₂CO) megamaser within the inner ~30 parsecs.
The maser emission spans a large velocity range, with a clear structure: a fast (> 250 km s⁻¹), collimated component, and a slow (∼50 km s⁻¹), wide-angle component. By combining the OH and H₂CO morphologies and kinematics with the millimetre dust and HCN data from ALMA, we showed that these two components naturally fit a model in which the fast outflow drives a more diffuse, slower wind around it — a molecular fountain.
Why does it matter?
The galaxy is dust-buried in the optical, so without molecular tracers we would simply not see this. The fast component carries enough momentum to leave the galaxy entirely; the slower fountain will fall back, recycling enriched gas back onto the disk. That distinction matters: feedback that escapes removes mass and quenches future star formation; feedback that recycles mostly stirs the disk and may actually feed it. Mapping both components in the same nucleus tells us how a buried engine sets the tempo of its host galaxy’s evolution — and shows that megamasers are unusually powerful tools for doing this work in obscured systems.
My role
First author. I led the observational analysis, the modelling of the OH and H₂CO maser kinematics, and the interpretation of the two-component fountain.