The First Detections of the Key Prebiotic Molecule Po in Star-Forming Regions

Abstract

Phosphorus is a crucial element in biochemistry, in particular the P−O bond, which is key in the formation of the backbone of deoxyribonucleic acid. So far, PO has only been detected toward the envelope of evolved stars, but never toward star-forming regions. We report the first detection of PO toward two massive star-forming regions, W51 e1/e2 and W3(OH), using data from the IRAM 30 m telescope. PN has also been detected toward the two regions. The abundance ratio PO/PN is 1.8 and 3 for W51 and W3(OH), respectively. Our chemical model indicates that the two molecules are chemically related and are formed via gas-phase ion-molecule and neutralneutral reactions during cold collapse. The molecules freeze out onto grains at the end of the collapse and desorb during the warm-up phase once the temperature reaches ∼35 K. Similar abundances of the two species are expected during a period of ∼5 × 10 4 yr at the early stages of the warm-up phase, when the temperature is in the range 35-90 K. The observed molecular abundances of 10 −10 are predicted by the model if a relatively high initial abundance of 5 × 10 −9 of depleted phosphorus is assumed.

The Chemistry of Phosphorus-bearing Molecules under Energetic Phenomena

“…More recently, higher-sensitivity observations have revealed the presence of P-bearing molecules such as PN and PO in regions with active low-mass and high-mass star formation (Caux et al 2011;Yamaguchi et al 2011;Lefloch et al 2016;Rivilla et al 2016). Also, PN has been reported toward massive starless cores , which suggests that this molecule could form in relatively quiescent and cold gas (Mininni et al 2018).…”

“…In this section, we compare our modeling results to the abundances of PN and PO measured toward low-mass/ high-mass starless/pre-stellar cores (Turner et al 1990;Mininni et al 2018), massive hot cores (Turner et al 1990;Rivilla et al 2016), GMCs in the Galactic center (Rivilla et al 2018), and molecular outflows (Yamaguchi et al 2011;Lefloch et al 2016). …”

“…Also, PN has been reported toward massive starless cores , which suggests that this molecule could form in relatively quiescent and cold gas (Mininni et al 2018). In all cases, PO seems to be slightly more abundant than PN (by factors of 2-3; see, e.g., Rivilla et al 2016), 3 and the PO/PN ratio can potentially be used as a length indicator of the pre-stellar collapse phase (see Aota & Aikawa 2012;Lefloch et al 2016). The analysis of the P-bearing content of the giant molecular clouds (GMCs) in the Galactic center shows that PN and PO can also be detected in molecular clouds subject to extreme conditions, such as those found in galactic nuclei (Rivilla et al 2018).…”

“…The recent detections of PN and PO in star-forming regions has triggered a new interest in the chemistry of phosphorus in the ISM. While Yamaguchi et al (2011) and Lefloch et al (2016) proposed that P-bearing species are produced in shocked gas after the sputtering of dust grains, Rivilla et al (2016) suggested that P-bearing molecules are formed during the cold collapse phase and subsequently frozen onto dust grains (Caux et al 2011;Fontani et al 2016;Rivilla et al 2016). The detection of PN and PO in the Galactic center poses even more unknowns to the chemistry of phosphorus (Rivilla et al 2018).…”

Gas versus solid-phase deuterated chemistry: HDCO and D2CO in massive star-forming regions

“…To estimate the molecular column densities of H 2 CO, HDCO, and D 2 CO, we used the MADCUBAIJ software that assumes LTE conditions (Martín et al 2011;Rivilla et al 2016). We adopted a source size of 6 .…”