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Context. We have studied the dense gas morphology and kinematics towards the infrared dark cloud (IRDC) G034.77-00.55, shock-interacting with the SNR W44, to identify evidence of early-stage star formation induced by the shock. Aims. We used high angular resolution N₂H⁺(1−0) images across G034.77-00.55, obtained with the Atacama Large Millimeter/sub-Millimeter Array. N₂H⁺is a well-known tracer of dense and cold material, optimal for identifying gas that has the highest potential to harbour star formation. Methods. The N₂H⁺emission is distributed in two elongated structures, one towards the dense ridge at the edge of the source and one towards the inner cloud. Both elongations are spatially associated with well-defined mass-surface density features. The velocities of the gas in the two structures (i.e. 38–41 km s⁻¹and 41–43 km s⁻¹) are consistent with the lowest velocities of the J- and C-type parts, respectively, of the SNR-driven shock. A third velocity component is present at 43–45.5 km s^–1. The dense gas shows a fragmented morphology with core-like fragments at scales consistent with the Jeans lengths, masses of ~1–20 M_⊙, densities of (n(H₂)≥10⁵cm^–3) sufficient to host star formation in free-fall timescales (a few 10⁴yr), and with virial parameters that suggest a possible collapse. Results. The W44 driven shock may have swept up the encountered material, which is now seen as a dense ridge, almost detached from the main cloud, and an elongation within the inner cloud, well constrained in both N₂H⁺emission and mass surface density. This shock compressed material may have then fragmented into cores that are either in a starless or pre-stellar stage. Additional observations are needed to confirm this scenario and the nature of the cores. 

The Milky Way’s Central Molecular Zone (CMZ) differs dramatically from our local solar neighbourhood, both in the extreme interstellar medium conditions it exhibits (e.g. high gas, stellar, and feedback density) and in the strong dynamics at play (e.g. due to shear and gas influx along the bar). Consequently, it is likely that there are large-scale physical structures within the CMZ that cannot form elsewhere in the Milky Way. In this paper, we present new results from the Atacama Large Millimeter/submillimeter Array (ALMA) large programme ACES (ALMA CMZ Exploration Survey) and conduct a multi-wavelength and kinematic analysis to determine the origin of the M0.8–0.2 ring, a molecular cloud with a distinct ring-like morphology. We estimate the projected inner and outer radii of the M0.8–0.2 ring to be 79″ and 154″, respectively (3.1 pc and 6.1 pc at an assumed Galactic Centre distance of 8.2 kpc) and calculate a mean gas density >10⁴cm⁻³, a mass of ~10⁶M_⊙, and an expansion speed of ~20 km s⁻¹, resulting in a high estimated kinetic energy (>10⁵¹erg) and momentum (>10⁷M_⊙km s⁻¹). We discuss several possible causes for the existence and expansion of the structure, including stellar feedback and large-scale dynamics. We propose that the most likely cause of the M0.8–0.2 ring is a single high-energy hypernova explosion. To viably explain the observed morphology and kinematics, such an explosion would need to have taken place inside a dense, very massive molecular cloud, the remnants of which we now see as the M0.8–0.2 ring. In this case, the structure provides an extreme example of how supernovae can affect molecular clouds. 

Context.Supernova remnants (SNRs) may regulate star formation in galaxies. For example, SNR-driven shocks may form new molecular gas or compress pre-existing clouds and trigger the formation of new stars. Aims.To test this scenario, we measured the deuteration of N₂H⁺, D_frac^N₂H+– a well-studied tracer of pre-stellar cores – across the infrared-dark cloud (IRDC) G034.77-00.55, which is known to be experiencing a shock interaction with the SNR W44. Methods.We use N₂H⁺and N₂D⁺J= 1−0 single pointing observations obtained with the 30m antenna at the Instituto de Radioas-tronomia Millimetrica to infer D_frac^N₂H+towards five positions across the cloud, namely a massive core, different regions across the shock front, a dense clump, an₊d ambient gas. Results.We find D_frac^N₂H+in the range 0.03−0.1, which is several orders of magnitude larger than the cosmic D/H ratio (~10⁻⁵). The D_frac^N₂H+across the shock front is enhanced by more than a factor of 2 (D_frac^N₂H+~ 0.05 - 0.07) with respect to the ambient gas (≤0.03) and simila₊r to that measured generally in pre-stellar cores. Indeed, in the massive core and dense clump regions of this IRDC we measure D_frac^N₂H+~ 0.01. Conclusions.We find enhanced deuteration of N₂H⁺across the region of the shock, that is, at a level that is enhanced with respect to regions of unperturbed gas. It is possible that this has been induced by shock compression, which would then be indirect evidence that the shock is triggering conditions for future star formation. However, since unperturbed dense regions also show elevated levels of deuteration, further, higher-resolution studies are needed to better understand the structure and kinematics of the deuterated material in the shock region; for example, to decipher whether it is still in a relatively diffuse form or is already organised in a population of low-mass pre-stellar cores. 

Context. In the past few years, there has been a rise in the detection of streamers, asymmetric flows of material directed toward the protostellar disk with material from outside a star’s natal core. It is unclear how they affect the process of mass accretion, in particular beyond the Class 0 phase. Aims. We investigate the gas kinematics around Per-emb-50, a Class I source in the crowded star-forming region NGC 1333. Our goal is to study how the mass infall proceeds from envelope to disk scales in this source. Methods. We use new NOEMA 1.3 mm observations, including C 18 O, H 2 CO, and SO, in the context of the PRODIGE MPG – IRAM program, to probe the core and envelope structures toward Per-emb-50. Results. We discover a streamer delivering material toward Per-emb-50 in H 2 CO and C 18 O emission. The streamer’s emission can be well described by the analytic solutions for an infalling parcel of gas along a streamline with conserved angular momentum, both in the image plane and along the line-of-sight velocities. The streamer has a mean infall rate of 1.3 × 10 −6 M ⊙ yr− 1 , five to ten times higher than the current accretion rate of the protostar. SO and SO 2 emission reveal asymmetric infall motions in the inner envelope, additional to the streamer around Per-emb-50. Furthermore, the presence of SO 2 could mark the impact zone of the infalling material. Conclusions. The streamer delivers sufficient mass to sustain the protostellar accretion rate and might produce an accretion burst, which would explain the protostar’s high luminosity with respect to other Class I sources. Our results highlight the importance of late infall for protostellar evolution: streamers might provide a significant amount of mass for stellar accretion after the Class 0 phase. 

Context. Protostellar jets are an important agent of star formation feedback, tightly connected with the mass-accretion process. The history of jet formation and mass ejection provides constraints on the mass accretion history and on the nature of the driving source. Aims. We characterize the time-variability of the mass-ejection phenomena at work in the class 0 protostellar phase in order to better understand the dynamics of the outflowing gas and bring more constraints on the origin of the jet chemical composition and the mass-accretion history. Methods. Using the NOrthern Extended Millimeter Array (NOEMA) interferometer, we have observed the emission of the CO 2–1 and SO N J = 5 4 –4 3 rotational transitions at an angular resolution of 1.0″ (820 au) and 0.4″ (330 au), respectively, toward the intermediate-mass class 0 protostellar system Cep E. Results. The CO high-velocity jet emission reveals a central component of ≤400 au diameter associated with high-velocity molecular knots that is also detected in SO, surrounded by a collimated layer of entrained gas. The gas layer appears to be accelerated along the main axis over a length scale δ 0 ~ 700 au, while its diameter gradually increases up to several 1000 au at 2000 au from the protostar. The jet is fragmented into 18 knots of mass ~10 −3 M ⊙ , unevenly distributed between the northern and southern lobes, with velocity variations up to 15 km s −1 close to the protostar. This is well below the jet terminal velocities in the northern (+ 65 km s −1 ) and southern (−125 km s −1 ) lobes. The knot interval distribution is approximately bimodal on a timescale of ~50–80 yr, which is close to the jet-driving protostar Cep E-A and ~150–20 yr at larger distances >12″. The mass-loss rates derived from knot masses are steady overall, with values of 2.7 × 10 −5 M ⊙ yr −1 and 8.9 × 10 −6 M ⊙ yr −1 in the northern and southern lobe, respectively. Conclusions. The interaction of the ambient protostellar material with high-velocity knots drives the formation of a molecular layer around the jet. This accounts for the higher mass-loss rate in the northern lobe. The jet dynamics are well accounted for by a simple precession model with a period of 2000 yr and a mass-ejection period of 55 yr.