The NGC 6334I star formation region studied at the highest possible frequencies for the ALMA radio telescope

An article published in the journal “Astrophysical Journal Letters” presents the first results of a pilot program to investigate at the highest possible frequencies for the ALMA radio telescope. A team of researchers used the NGC 6334I star formation region within the Cat’s Paw Nebula as a target for observations in what is called band 10 detecting glycolaldehyde and a compact bipolar outflow containing heavy water and carbon monosulfide from the protostar MM1B.

The ALMA (Atacama Large Millimeter/submillimeter Array) radio telescope was inaugurated in March 2012 but already begun earlier to provide results that were important from a scientific point of view. It can detect frequencies in a series of 10 bands and for example over the years observations in the bands 3-7 (84-373 GHz) allowed to discover many molecules in interstellar space and to study their chemical history and their interaction with their physical environment.

The bands at the highest frequencies have been used very little to conduct molecular investigations so here the team led by the chemist Brett McGuire of the National Radio Astronomy Observatory (NRAO) exploited band 10 (787-950 GHz, 0.3-0.4 millimeters) to detect large and small molecules. The target of the observations was the NGC 6334I star formation region, already known for other studies conducted with ALMA such as the one of the protostar NGC 6334I-MM1, described in an article published again in the journal “Astrophysical Journal Letters” in March 2017.

On April 5, 2018 the atomospheric conditions were ideal to conduct these observations of the NGC 6334I region, about 4,300 light years from Earth, also chosen based on interesting results obtained with other space and ground-based telescopes. One of the problems in the observations carried out from the ground is that the Earth’s atmosphere contains a certain amount of water vapor even in the most arid conditions, such as those of the Atacama desert, and this telescopes the signals coming from extraterrestrial sources. That day, however, the conditions were so good that ALMA was able to detect that signal from the protostar MM1B or from a small protostar cluster, in the form of heavy water in the version with a deuterium atom and one of common hydrogen (HDO).

The top image (ALMA (ESO/NAOJ/NRAO): NRAO/AUI/NSF, B. Saxton) shows a composite image of NGC 6334I in which heavy water, indicated in blue, is moving away from a protostar or from a small protostars cluster. Heavy water that collides with the surrounding gas is a crucial molecule to generate natural low-frequency masers, analogous to lasers with microwaves emission instead of visible light. The masers were detected using another radio telescope, VLA (Very Large Array), in observations complementary to ALMA’s.

In the same outflow caused by the processes that are leading to the birth of a star and at the same time are ejecting jets of materials, carbon monosulfide (CS) was also detected. In the region the complex organic molecule glycolaldehyde (HC(O)CH2OH) was also detected, the simplest of the molecules linked to sugar. This molecule was already identified in other bands but, together with others, confirms the value of the detections in band 10. The bottom image (NRAO/AUI/NSF, S. Dagnello) contains an artistic illustration of the NGC 6334I region and some molecules found in this research.

There’s excitement for new telescopes and radio telescopes already inaugurated or still under construction and rightly so but ALMA confirms that it’s still at the forefront of scientific research. The years of experience accumulated are leading to an even more sophisticated use of ALMA to make the most of its power and sensitivity.

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