Confirmation of interstellar phosphine towards asymptotic giant branch star IRC\(+\)10216

Abstract

Phosphorus (P) is an important element for the chemical evolution of galaxies and many biochemical reactions. Phosphorus is one of the crucial chemical compounds in the formation of life on our planet. In an interstellar medium, phosphine (\(\hbox {PH}_{3}\)) is a crucial biomolecule that plays a major role in understanding the chemistry of phosphorus-bearing molecules, particularly phosphorus nitride (PN) and phosphorus monoxide (PO), in the gas phase or interstellar grains. We present the first confirmed detection of phosphine (\(\hbox {PH}_{3}\)) in the asymptotic giant branch (AGB) carbon-rich star IRC\(+\)10216 using the Atacama Large Millimeter/Submillimeter Array (ALMA) band 6. We detect the \(J = 1_{0}-0_{0}\) rotational transition line of \(\hbox {PH}_{3}\) with a signal-to-noise ratio (SNR) of \(\ge \)3.5\(\sigma \). This is the first confirmed detection of phosphine (\(\hbox {PH}_{3}\)) in the ISM. Based on LTE spectral modeling, the column density of \(\hbox {PH}_{3}\) is \((3.15\pm 0.20)\times 10^{15}\) \(\hbox {cm}^{-2}\) at an excitation temperature of \(52\pm 5\) K. The fractional abundance of \(\hbox {PH}_{3}\) with respect to \(\hbox {H}_{2}\) is \((8.29\pm 1.37)\times 10^{-8}\). We also discuss the possible formation pathways of \(\hbox {PH}_{3}\), and we claim that \(\hbox {PH}_{3}\) may be created via the hydrogenation of \(\hbox {PH}_{2}\) on the grain surface of IRC\(+\)10216.