Cool gas clues to galaxy evolution
doi:10.1038/nindia.2012.125 Published online 28 August 2012
Astrophysicists have detected four new light-absorbing phenomena in metal-rich gaseous regions of galaxies
These galaxies are between 9 and 35 billion light years away from Earth against the backdrop of quasars. The absorption of light takes place due to presence of neutral hydrogen atoms in gaseous structures known as MgII absorbers in the clouds of dust and gas floating between stars (the interstellar medium or ISM).
Given their star-forming roles, absorption by neutral hydrogen atoms — known as 21-cm absorption — in a sample of MgII absorbers is important. Although MgII absorption lines are known to arise from the gas associated with galaxies, the exact nature and underlying physical processes are not yet properly understood.
To understand such processes better, the researchers scanned distant galaxies moving away from Earth. In these red-shifted galaxies, they specifically observed 85 MgII absorbers containing 21-cm absorption. For the observation, they used three earth-bound telescopes in the US, India and the Netherlands.
The study detected four new 21-cm absorption lines in a sample of 17 strong MgII absorbers. Comparing this finding with previous results, they showed that 21-cm detection rates were higher towards compact quasars.
The cold atomic and molecular phases of ISM contribute to star formation. "Since 21-cm absorption is a good tracer of cold gas in ISM, large blind surveys of 21-cm absorption lines with the upcoming Square Kilometre Array (SKA) radio telescope will provide a complete view of the evolution of cold gas in galaxies and throw light on the nature of MgII systems," says R. Srianand, one of the researchers.
The authors of this work are from: ASTRON, the Netherlands Institute for Radio Astronomy, the Netherlands; the Inter-University Centre for Astronomy and Astrophysics, Pune, India; and UPMC-CNRS, Institut d'Astrophysique de Paris, Paris, France.