Broadest ever absorption line shows cold HI speeding towards AGN

Feb 13, 2013

Observations of the compact radio source PMN J2054-4242 with the 6-dish Australian Telescope Compact Array (ATCA) and its Broadband Backend (CABB) have now revealed the broadest and weakest absorption line of cold neutral hydrogen gas at 21cm yet detected. Observations of such lines have been rare, but this might change now with a new Bayesian spectral-line finding and fitting technique that is a promising tool for upcoming large-scale blind surveys on next generation radio telescopes such as ASKAP and the SKA.

In their new publication (Monthly Notices of the Royal Astronomical Society, 22 January 2013), the team of four Sydney-based CAASTRO researchers present their extended observations and analyses – building on a previous paper (MNRAS 2012) – and confirm the existence of this broad HI absorption line, using their new technique.

From the spectral-line and optical spectroscopic redshifts, the researchers also concluded that the detection relates to cold gas either rotating or infalling towards the central radio source (or Active Galactic Nucleus, AGN) at high speed, either in one single gas cloud or in a blended sequence of clouds. High velocity gas flows can provide insights into feedback between the radio source and star formation in the host galaxy.

Publication details:

J. R. Allison, S. J. Curran, E. M. Sadler and S. N. Reeves in MNRAS 2013

Broad, weak 21 cm absorption in an early type galaxy: spectral-line finding and parameterisation for future surveys