The primary building material for the emerging young stars, which are created during the process of gravitational gas collapse, is the so-called neutral hydrogen contained inside gaseous space clouds. The abundance of this element is directly related to the star formation rates in all galaxies and certainly is one of most important factors deciding the galactic evolutionary processes.

As the new stars form, the resources of neutral hydrogen are gradually depleted, meaning that a galaxy enters its ‘adult’ phase of life. However, the formation of stars isn’t the only way for a galaxy to lose the gas reserves: sometimes this happens due to a massive… theft.

Well, who or what is capable to do that? Certainly, we have to look at the same heavyweight category, or, simply put, other galaxies. The rules are simple enough: the object with the strongest gravity attracts the gas towards itself via a process called tidal stripping. And, although the ‘forced’ loss of neutral hydrogen occurs on a cosmic scale, it is not always easy to notice, especially when it happens in smaller groups of galaxies exhibiting lower-density environments, rather than in tightly-packed galactic clusters.

A new study published at arXiv.org claims that the main clues pointing to the interstellar ‘gas robbery’ may be found by detecting galaxies with an unusual quantities of neutral hydrogen. Scientists from Swinburne University of Technology in Australia and CSIRO Astronomy and Space Science division describe the identification and analysis of gas-deficient galaxies, their groups and ongoing environmental processes, like the previously mentioned gravitational gas stripping.

The astronomers used the data from HI Parkes All Sky Survey (HIPASS) to determine the neutral hydrogen content of galaxies and its relations to their diameter and luminosity, in different optical and infrared wavebands. Different measurement wavebands were selected due to their sensitivity to different stellar populations of a galaxy. Relations between the hydrogen content and physical parameters of the galaxies were later used to pick out the objects with abnormal content of neutral hydrogen.

The scientists performed more observations of the sample galaxies using Australia Telescope Compact Array (ATCA) and noticed clearly visible deformations of the neutral hydrogen disc in galaxies, which have at least 4 times less neutral hydrogen compared with the late-type galaxies with the same luminosity. The deformations of the gaseous disc were also extending towards the center of the galaxy group these objects belong to.

The authors suggest that the main gas stripping mechanism may the tidal interactions of these observed galaxies with the other group member galaxies. However, the authors also point that these are only the preliminary results, which could be refined with further higher resolution observations of the neutral hydrogen content in the same and, possibly, additional galaxies with similar properties.

By Alius Noreika, Source: www.technology.org