Washington, Nov 1 : Astronomers have probed the physical conditions in the active inner regions of a number of Ultraluminous Infrared Galaxies (ULIRGs), with the help of the James Clerk Maxwell Telescope (JCMT).
ULIRGs are characterized by an enormous energy output, which is totally hidden from view for optical telescopes by massive gas and dust clouds inside these galaxies.
When the universe was much younger, such galaxies were much more common than now, and scientists believe that galaxies of this type have played a key role in shaping the present-day universe.
Their enormous energy output is attributed to extremely rapid conversion of the available gas into young, luminous stars, and to energetic processes associated with supermassive black holes.
Astronomers Kate Isaak (Cardiff University, United Kingdom), Paul van der Werf (Leiden University, The Netherlands) and Padeli Papadopoulos (Bonn University, Germany) have recently used the JCMT to probe the physical conditions in the active inner regions of a number of ULIRGs directly.
According to Dr Papadopoulos, "The submillimetre radiation observed by the JCMT can penetrate the dust shroud obscuring the nuclear regions of the ULIRGs, but the spectral lines emitted from these regions are still very faint."
"Therefore, we had to use the JCMT and its sensitive HARP receiver for up to 12 hours under very good atmospheric conditions, to detect just a single line in a single galaxy," he added.
"These spectra are among the deepest ever obtained with the JCMT", said Professor Gary Davis, the Director of the James Clerk Maxwell Telescope.
"They demonstrate the extraordinary sensitivity of HARP, our new, state-of-the-art receiver. It is rewarding to see new science discoveries emerging which would previously have been impossible," he added.
Among the molecular fingerprints that the team has observed are spectral lines of warm and dense carbon monoxide and of the formyl ion.
However, the most prized spectral line observed by the team is hydrogen cyanide. This line originates from warm, dense, and toxic hydrogen cyanide gas in the most active regions of the ULIRGs.
When interpreted together with the rest of the data, it becomes obvious that this spectral line probes the most extremely dense gas, the very immediate fuel of the massive star formation in these objects.
According to Dr van der Werf, "Unlike other spectral lines which probe more remote gaseous regions in these galaxies which may not be actively forming stars, the hydrogen cyanide intensity changes dramatically from galaxy to galaxy."
"This depends on, and reveals, the intense gravitational tides and their effects on the densest of the gas phases in the centres of the ULIRGs," he added.