Outflow Interaction in Cep-E: Numerical Simulation and Observational Manifestation

Abstract

There is clear observational evidence that the main Class 0/I stages of the star formation process are associated with powerful collimated outflows (jets), which sometimes propagate up to distances as large as $10^{4-5}$ au scales in molecular clouds. Additionally, intermediate high-mass and low-mass protostars have often been observed to form in crowded clusters, where the typical separation distance between any two cluster members is of the same order or smaller than the scale of the outflow length. Therefore, there must be an interaction between the molecular outflows of different protostars within the protostellar association. A good example of this is the case of Cepheus E-mm, which is a protostellar outflow extending over a few dozen au. At its core is a binary system consisting of two protostars, Cep E-A and Cep E-B, separated by about 1000 au. Both protostars eject molecular jets at velocities of ~100 km/s. The interaction between these molecular outflows provides an opportunity to study the effects of jet collisions in a clustered star-forming environment, as they may leave detectable imprints on the morphology of the main envelope of the system. Our work aims to study the effects of the collision of molecular jets associated with the components of the binary system Cep-A and Cep-E, analyzing the disruption or reduction of molecular emission in the main envelope of the system, which the molecular outflow { launched} by Cep-A presumably pushes. If we characterize the collision in this system, we can provide insights into the expected morphology and molecular emissions in collisions of molecular outflows { associated to star forming process.

Figures (11)

• Figure 1: (Left) CO $J$= 2--1 emission detected in the Cep E protostellar core with the IRAM interferometer at 1 (820 au) resolution. The black contours trace the emission from the low-velocity gas ($|V-V_{lsr}|$ < $8\hbox{km s$^{-1}$}$), and the blue/red contours trace the high-velocity jet ($V-V_{lsr}$ > $50\hbox{km s$^{-1}$}$, powered by component A of the Cep E protostellar core. The data are from Lefloch2015 and Schutzer2022. (Right) SiO $J$= 5--4 emissions detected in the Cep E protostellar core with the IRAM interferometer at $1.4\arcsec$ (1150 au) resolution in the jets powered by protostars A (red and white contours) and B (blue and red contours). The velocity intervals of integrated flux are reported (in km s$^{-1}$) next to the lobes of the jets from A and B. The first contour and contour interval are $10\%$ and $20\%$ of the maximum peak intensity. The data are from Ospina-Zamudio2018.
• Figure 2: Interaction between the southern low-velocity outflow lobe of A, at $[-8;-6]\hbox{km s$^{-1}$}$ (black contours) and the Eastern lobe of the jet from B (red contours), as observed with the IRAM interferometer in the molecular lines of CO $J$=2-1 and CS $J$=2-1 (left), and SiO $J$=2-1 and H$_2$CO (right).
• Figure 3: Probability of two outflows overlapping for: two wide cavities (in black continuous line) and for two collimated jets (blue line). The dashed line represents the observed separation of Cep E-A and Cep E-B, which could be larger because of projection effects.
• Figure 4: Two protostellar sources inject high velocity material. The gas density around each source is stratified with a power law. In our simulations the jets injections are not meant to collide if they preserve their width, but, since they expand thermically and by entrainment, the evolved jets, that is, high velocity material, could collide.
• Figure 5: (Upper panel) Snapshot of the gas density of a single jet (model M1) at $t=1875$ yr. One can see the work surface structure can be seen due to the consideration of the variable jet. The envelope shows a higher density at the "base" of the jet and a lower one towards the front. (Lower panels). Snapshots of the gas density of the jet interaction model (model M2) at 3 evolutionary times, t=1375, 1625 and 1875 yr (top, middle and bottom panels). Considering the estimated age of the Cep E protostellar outflow, $\sim$1500 yr Schutzer2022, it shows different stages of evolution around this age. All the snapshots are present on the $xy$ plane.