We report on the detailed analysis of a gravitationally-lensed Y-band dropout, A2744 YD4, selected from deep Hubble Space Telescope imaging in the Frontier Field cluster Abell 2744. Band 7 observations with the Atacama Large Millimeter Array (ALMA) indicate the proximate detection of a significant 1mm continuum flux suggesting the presence of dust for a star-forming galaxy with a photometric redshift of z 8. Deep X-SHOOTER spectra confirms the high redshift identity of A2744 YD4 via the detection of Lyman α emission at a redshift z=8.38. The association with the ALMA detection is confirmed by the presence of [OIII] 88µm emission at the same redshift. Although both emission features are only significant at the 4 σ level, we argue their joint detection and the positional coincidence with a high redshift dropout in the HST images confirms the physical association. Analysis of the available photometric data and the modest gravitational magnification (µ 2) indicates A2744 YD4 has a stellar mass of ∼ 2×10 9 M , a star formation rate of ∼ 20 M /yr and a dust mass of ∼6×10 6 M . We discuss the implications of the formation of such a dust mass only 200 Myr after the onset of cosmic reionisation.

Peptide bonds (N-C=O) play a key role in metabolic processes since they link amino acids into peptide chains or proteins. Recently, several molecules containing peptidelike bonds have been detected across multiple environments in the interstellar medium (ISM), growing the need to fully understand their chemistry and their role in forming larger pre-biotic molecules. We present a comprehensive study of the chemistry of three molecules containing peptide-like bonds: HNCO, NH 2 CHO, and CH 3 NCO. We also included other CHNO isomers (HCNO, HOCN), and C 2 H 3 NO isomers (CH 3 OCN, CH 3 CNO) to the study. We have used the uclchem gas-grain chemical code and included in our chemical network all possible formation/destruction pathways of these peptide-like molecules recently investigated either by theoretical calculations or in laboratory experiments. Our predictions are compared to observations obtained toward the proto-star IRAS16293-2422 and the L1544 pre-stellar core. Our results show that some key reactions involving the CHNO and C 2 H 3 NO isomers need to be modified to match the observations. Consistently with recent laboratory findings, hydrogenation is unlikely to produce NH 2 CHO on grain surfaces, while a combination of radicalradical surface reactions and gas-phase reactions is a better alternative. In addition, better results are obtained for NH 2 CHO when a slightly higher activation energy of 25 K is considered for the gas-phase reaction NH 2 + H 2 CO → NH 2 CHO + H. Finally, our modelling shows that the observed correlation between NH 2 CHO and HNCO in star-forming regions may come from the fact that HNCO and NH 2 CHO react to temperature in the same manner rather than from a direct chemical link between the two species.

The L1544 pre-stellar core has been observed as part of the ASAI IRAM 30m Large Program as well as follow-up programs. These observations have revealed the chemical richness of the earliest phases of low-mass star-forming regions. In this paper we focus on the twenty-one sulphur bearing species (ions, isotopomers and deuteration) that have been detected in this spectral-survey through fifty one transitions: CS, CCS, C 3 S, SO, SO 2 , H 2 CS, OCS, HSCN, NS, HCS + , NS + and H 2 S. We also report the tentative detection (4 σ level) for methyl mercaptan (CH 3 SH). LTE and non-LTE radiative transfer modelling have been performed and we used the nautilus chemical code updated with the most recent chemical network for sulphur to explain our observations. From the chemical modelling we expect a strong radial variation for the abundances of these species, which mostly are emitted in the external layer where non thermal desorption of other species has previously been observed. We show that the chemical study cannot be compared to what has been done for the TMC-1 dark cloud, where the abundance is supposed constant along the line of sight, and conclude that a strong sulphur depletion is necessary to fully reproduce our observations of the prototypical pre-stellar core L1544.

Phosphorus (P) is one of the essential elements for life due to its central role in biochemical processes. Recent searches have shown that P-bearing molecules (in particular PN and PO) are present in star-forming regions, although their formation routes remain poorly understood. In this Letter, we report observations of PN and PO towards seven molecular clouds located in the Galactic Center, which are characterized by different types of chemistry. PN is detected in five out of seven sources, whose chemistry is thought to be shock-dominated. The two sources with PN non-detections correspond to clouds exposed to intense UV/X-rays/cosmic-ray radiation. PO is detected only towards the cloud G+0.693−0.03, with a PO/PN abundance ratio of ∼1.5. We conclude that P-bearing molecules likely form in shocked gas as a result of dust grain sputtering, while are destroyed by intense UV/X-ray/cosmic ray radiation.

For decades, the detection of phosphorus-bearing molecules in the interstellar medium was restricted to high-mass star-forming regions (e.g., SgrB2 and Orion KL) and the circumstellar envelopes of evolved stars. However, recent higher-sensitivity observations have revealed that molecules such as PN and PO are present not only toward cold massive cores and low-mass star-forming regions with PO/PN ratios 1 but also toward the giant molecular clouds in the Galactic center known to be exposed to highly energetic phenomena such as intense UV radiation fields, shock waves, and cosmic rays. In this paper, we carry out a comprehensive study of the chemistry of phosphorus-bearing molecules across different astrophysical environments that cover a range of physical conditions (cold molecular dark clouds, warm clouds, and hot cores/hot corinos) and are exposed to different physical processes and energetic phenomena (proto-stellar heating, shock waves, intense UV radiation, and cosmic rays). We show how the measured PO/PN ratio (either 1, as in, e.g., hot molecular cores, or 1, as in UV strongly illuminated environments) can provide constraints on the physical conditions and energetic processing of the source. We propose that the reaction P+OH→PO+H, not included in previous works, could be an efficient gas-phase PO formation route in shocks. Our modeling provides a template with which to study the detectability of P-bearing species not only in regions in our own Galaxy but also in extragalactic sources.