Rafael Bachiller

Context. The L1157 outflow is a prototype of chemically active outflows in which to look for molecular species linked to complex chemistry. Aims. With the aim of imaging the large (parsec) scale structure of key prebiotic molecules, we aim to map the whole blue lobe of the L1157 outflow with the Large Millimeter Telescope (LMT), proving the potential of this facility to detect weak and extended molecular emission. Methods. Isocyanic acid (HNCO), an important precursor of complex chemistry, was chosen to be observed in its (4 _0,4 –3 _0,3 ) transition at 87.925 GHz with the SEQUOIA focal-plane array, covering an area of 3×3 arcmin ² centered at the position of the main shock L1157-B1, which included a large portion of the vicinity of the protostellar region. Results. The HNCO emission was detected not only from the outflow, it was also found tracing a structure of about 0.3 pc in length, corresponding to the filament from which the protostellar system was born. Conclusions. The HNCO molecule was found to be a tracer of the densest part of filaments in molecular clouds, and given its importance in the formation of more complex molecules, its presence in the cold, quiescent filamentary gas indicates that the building blocks of complex chemistry are already well established in stages prior to protostellar warming or shocks. By allowing the detection of structures related to the filament, these observations proved the LMT’s potential to map weak and extended components in molecular clouds.

Erratum: “A Detailed Temperature Map of the Archetypal Protostellar Shocks in L1157” (2022, ApJL, 933, L35), Feng, S., Liu, H. B., Caselli, P., Burkhardt, A., Du, F., Bachiller, R., Codella, C., Ceccarelli, C. Erratum: “A Detailed Temperature Map of the Archetypal Protostellar Shocks in L1157” (2022, ApJL, 933, L35), Feng, S., Liu, H. B., Caselli, P., Burkhardt, A., Du, F., Bachiller, R., Codella, C., Ceccarelli, C.

Context. Compact jets from active galactic nuclei (AGN) are commonly assumed to be in equipartition between particle and magnetic-field energy densities at the regions where the radio emission dominates at centimetre wavelengths. This assumption has significant implications for both jet physics and the accuracy of VLBI-based astrometry and geodesy. Aims. We tested the validity of the energy equipartition hypothesis in AGN cores at centimetre wavelengths by analysing the blazar 1803+784 using simultaneous broadband full-polarization observations with the VLBI Global Observing System (VGOS). Methods. We present VGOS observations of the blazar 1803+784 covering the 3–11 GHz frequency range. The data were processed using a dedicated calibration pipeline, followed by model fitting and multi-frequency imaging analysis. We measured the frequency-dependent core shift and mapped the spectral index and rotation measure (RM) across the source. Results. We find a core-shift power-law index of k_r = 0.73_−0.19^+0.12, significantly deviating from the expected equipartition value of k_r = 1. This indicates that either the equipartition condition or the conical jet geometry, or both, are not fulfilled in the centimetre-wavelength core region. The wide frequency coverage of VGOS also allows us to decouple the Faraday rotation of the core into an internal component (RM_I = 121 ± 8 rad m⁻², produced in the core region) and an external component (RM_E = −44 ± 9 rad m⁻², associated with a distant, extended medium that may also affect the polarization in downstream regions of the jet at larger scales). Conlcusions. These results demonstrate the power of VGOS for high-fidelity simultaneous multi-frequency polarimetric studies of compact AGN jets, and underline the need to account for non-equipartition effects in both jet astrophysics and geodetic VLBI.

The Cepheus A East high-mass star-forming region has been mapped at 1.4 mm using the OCS(17–16) and (18–17) lines observed with the IRAM 30 m antenna. Contour maps and high-resolution line profiles reveal the association of OCS with both (i) the hot-core region, and (ii) with the NE, SE, and S outflows driven by the young stellar objects. This confirms that OCS is among the main S-molecules observed in the gas-phase after thermal evaporation due to protostellar heating or shocks due to propagation of protostellar jets. Adopting Local Thermodynamic Equilibrium conditions, optically thin emission, and a temperature of 100 K, the total OCS column density (after correction for beam dilution) of the hot-core component is ∼10¹⁶ cm⁻². For the outflow component, assuming a temperature range of 20–100 K, and extended emission, the OCS column density is ≤ 5 ×10¹⁴ cm⁻² for a temperature ≥ 20 K.

We analyse deuterated water (HDO) and sulfur dioxide (SO ₂ ) at high-angular resolution in the binary system SVS13-A. We propose that molecular emission is produced by an accretion shock at the interface between the accretion streamer and the disk.

Context.Gas phase Elemental abundances in molecular CloudS (GEMS) is an IRAM 30-m Large Program aimed at determining the elemental abundances of carbon (C), oxygen (O), nitrogen (N), and sulfur (S) in a selected set of prototypical star-forming filaments. In particular, the elemental abundance of S remains uncertain by several orders of magnitude, and its determination is one of the most challenging goals of this program.Aims.This paper aims to constrain the sulfur elemental abundance in Taurus, Perseus, and Orion A based on the GEMS molecular database. The selected regions are prototypes of low-mass, intermediate-mass, and high-mass star-forming regions, respectively, providing useful templates for the study of interstellar chemistry.Methods.We have carried out an extensive chemical modeling of the fractional abundances of CO, HCO⁺, HCN, HNC, CS, SO, H₂S, OCS, and HCS⁺to determine the sulfur depletion toward the 244 positions in the GEMS database. These positions sample visual extinctions fromA_V~ 3 mag to >50 mag, molecular hydrogen densities ranging from a few × 10³cm⁻³to 3 × 10⁶cm⁻³, andT_k~ 10–35 K. We investigate the possible relationship between sulfur depletion and the grain charge distribution in different environments.Results.Most of the positions in Taurus and Perseus are best fitted assuming early-time chemistry,t= 0.1 Myr, ζH₂~ (0.5−1) × 10⁻¹⁶s⁻¹, and [S/H] ~ 1.5 × 10⁻⁶. On the contrary, most of the positions in Orion are fitted witht= 1 Myr and ζH₂~ 10⁻¹⁷s⁻¹. Moreover, ~40% of the positions in Orion are best fitted assuming the undepleted sulfur abundance, [S/H] ~ 1.5 × 10⁻⁵. We find a tentative trend of sulfur depletion increasing with density.Conclusions.Our results suggest that sulfur depletion depends on the environment. While the abundances of sulfur-bearing species are consistent with undepleted sulfur in Orion, a depletion factor of ~20 is required to explain those observed in Taurus and Perseus. We propose that differences in the grain charge distribution might explain these variations. Grains become negatively charged at a visual extinction ofA_V~ 3.5 mag in Taurus and Perseus. At this low visual extinction, the S⁺abundance is high,X(S⁺) > 10⁻⁶, and the electrostatic attraction between S⁺and negatively charged grains could contribute to enhance sulfur depletion. In Orion, the net charge of grains remains approximately zero until higher visual extinctions (A_V~ 5.5 mag), where the abundance of S⁺is already low because of the higher densities, thus reducing sulfur accretion. The shocks associated with past and ongoing star formation could also contribute to enhance [S/H].

We present sensitive NH₃ (1,1)–(7,7) line images from the Karl G. Jansky Very Large Array toward successive shocks, which are associated with the blueshifted outflow lobe driven by the compact protobinary system L1157. Within a projection distance of 0.1 pc, our observations not only trace the quiescent and cold gas in the flattened envelope, but also illustrate the complex physical and chemical processes that take place where the high-velocity jet impinges on its surrounding medium. Specifically, the NH₃ ortho-to-para ratio is enhanced by a factor of 2–2.5 along the jet path, where the velocity offset between the line peak and the blueshifted wing reaches values as high as 10 km s⁻¹; it also shows a strong spatial correlation with the NH₃ column density, which is enhanced to >10¹⁶ cm⁻² toward the shock cavities. At a linear resolution of 1500 au, our refined temperature map from the seven NH₃ lines shows a gradient from the warm B0 eastern cavity wall (>120 K) to the cool cavity B1 and the earlier shock B2 (<80 K), indicating shock heating.

We present observations of SO and SO₂ lines toward the shocked regions along the L1157 chemically rich outflow, taken in the context of the Seeds of Life in Space IRAM Northern Extended Millimeter Array Large Program, and supported by data from the Submillimeter Array and IRAM-30 m telescope at 1.1–3.6 mm wavelengths. We simultaneously analyze, for the first time, all of the brightest shocks in the blueshifted lobe, namely, B0, B1, and B2. We found the following. (1) SO and SO₂ may trace different gas, given that the large(-scale) velocity gradient analysis indicates for SO₂ a volume density ( ) denser than that of the gas emitting in SO by a factor up to an order of magnitude. (2) Investigating the 0.1 pc scale field of view, we note a tentative gradient along the path of the precessing jet. More specifically, decreases from the B0–B1 shocks to the older B2. (3) At a linear resolution of 500–1400 au, a tentative spatial displacement between the two emitting molecules is detected, with the SO peak closer (with respect to SO₂) to the position where the recent jet is impinging on the B1 cavity wall. Our astrochemical modeling shows that the SO and SO₂ abundances evolve on timescales less than about 1000 years. Furthermore, the modeling requires high abundances (2 × 10⁻⁶) of both and S/H injected in the gas phase due to the shock occurrence, so prefrozen OCS only is not enough to reproduce our new observations.

Context. Low-mass protostars drive powerful molecular outflows that can be observed with millimetre and submillimetre telescopes. Various sulfuretted species are known to be bright in shocks and could be used to infer the physical and chemical conditions throughout the observed outflows. Aims. The evolution of sulfur chemistry is studied along the outflows driven by the NGC 1333-IRAS4A protobinary system located in the Perseus cloud to constrain the physical and chemical processes at work in shocks. Methods. We observed various transitions from OCS, CS, SO, and SO₂ towards NGC 1333-IRAS4A in the 1.3, 2, and 3 mm bands using the IRAM NOrthern Extended Millimeter Array and we interpreted the observations through the use of the Paris-Durham shock model. Results. The targeted species clearly show different spatial emission along the two outflows driven by IRAS4A. OCS is brighter on small and large scales along the south outflow driven by IRAS4A1, whereas SO₂ is detected rather along the outflow driven by IRAS4A2 that is extended along the north east–south west direction. SO is detected at extremely high radial velocity up to + 25 km s⁻¹ relative to the source velocity, clearly allowing us to distinguish the two outflows on small scales. Column density ratio maps estimated from a rotational diagram analysis allowed us to confirm a clear gradient of the OCS/SO₂ column density ratio between the IRAS4A1 and IRAS4A2 outflows. Analysis assuming non Local Thermodynamic Equilibrium of four SO₂ transitions towards several SiO emission peaks suggests that the observed gas should be associated with densities higher than 10⁵ cm⁻³ and relatively warm (T > 100 K) temperatures in most cases. Conclusions. The observed chemical differentiation between the two outflows of the IRAS4A system could be explained by a different chemical history. The outflow driven by IRAS4A1 is likely younger and more enriched in species initially formed in interstellar ices, such as OCS, and recently sputtered into the shock gas. In contrast, the longer and likely older outflow triggered by IRAS4A2 is more enriched in species that have a gas phase origin, such as SO₂.